Verification, validation and uncertainty quantification in multi-physics modeling for nuclear reactor design and safety analysis

Abstract

The qualification procedure of coupled multi-physics code systems is based on the qualification framework (verification and validation) of separate physics models/codes, and includes in addition Verification and Validation (V&V) of the coupling methodologies of the different physics models. The extended verification procedure involves testing the functionality, the data exchange between different physics models, and their coupling, which is designed to model combined effects determined by the interaction of models. The extended validation procedure compares the predictions from coupled multi-physics code systems to available measured data and reference results. It is important to emphasize that such validation should be based on a multi-level approach similar to the one utilized in validating coupled neutronics/thermal–hydraulics codes in international standard problems. Appropriate benchmarks have been developed in international co-operation led by the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development (OECD) that permits testing the neutronics/thermal–hydraulics coupling, and verifying the capability of the coupled codes to analyze complex transients with coupled core/plant interactions. This paper describes the above-mentioned multi-level V&V approach along with examples of the OECD benchmarks. In recent years there has been an increasing demand from nuclear research, industry, safety, and regulation for best estimate predictions to be provided with their confidence bounds. The ongoing OECD Light Water Reactor (LWR) Uncertainty Analysis in Modeling (UAM) benchmark activities contribute to establishing an unified framework to estimate safety margins supplemented by Uncertainty Quantification (UQ), which would provide more realistic, complete and logical measure of reactor safety. The paper describes the progress of the OECD LWR UAM benchmark. This activity is designed to address current regulation needs and issues related to practical implementation of risk informed regulation. Establishing such internationally accepted LWR UAM benchmark framework offers the possibility to accelerate the licensing process when using best estimate methods.