GRS Method for Uncertainty and Sensitivity Evaluation of Code Results and Applications

TLDR

Computational reactor safety analysis is shifting from conservative models to best‑estimate calculations that include uncertainty analysis to enable meaningful comparisons with regulatory limits. The study aims to evaluate the margin to acceptance criteria, such as maximum fuel rod clad temperature, using the upper bound of the calculated uncertainty range. GRS proposes basic techniques applied to a large‑break loss‑of‑coolant accident on a reference reactor and to an experiment simulating containment behavior. The authors present methods that quantify the uncertainty of computer code results.

Abstract

During the recent years, an increasing interest in computational reactor safety analysis is to replace the conservative evaluation model calculations by best estimate calculations supplemented by uncertainty analysis of the code results. The evaluation of the margin to acceptance criteria, for example, the maximum fuel rod clad temperature, should be based on the upper limit of the calculated uncertainty range. Uncertainty analysis is needed if useful conclusions are to be obtained from “best estimate” thermal-hydraulic code calculations, otherwise single values of unknown accuracy would be presented for comparison with regulatory acceptance limits. Methods have been developed and presented to quantify the uncertainty of computer code results. The basic techniques proposed by GRS are presented together with applications to a large break loss of coolant accident on a reference reactor as well as on an experiment simulating containment behaviour.