Summary and status of OECD/NEA UAM-LWR Benchmark

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. Consequently OECD/NEA has initiated an international Uncertainty Analysis in Modeling (UAM) benchmark focused on uncertainty analysis in best-estimate coupled code calculations for design, operation, and safety analysis of LWRs. The title of this benchmark is: "Benchmarks for uncertainty analysis in modelling (UAM) for the design, operation and safety analysis of LWRs", or often referred to as "OECD/NEA UAM-LWR Benchmark". Reference systems and scenarios for coupled code analysis are defined to study the uncertainty effects for all stages of the system calculations. Measured data from plant operation are available for the chosen scenarios. The general frame of the OECD/NEA UAM LWR benchmark consists of three phases with different exercises for each phase. This paper summarizes the benchmark activity and discusses the status of each phase and exercise. Selected results are shown to illustrate the technical approach in defining different exercises and findings from benchmark analysis. For the first time this benchmarks aims to determine the uncertainty in LWR system calculations at all stages of a coupled reactor physics/thermal-hydraulics/fuel performance calculation. The full chain of uncertainty propagation from basic data, engineering uncertainties, across different scales (multi-scale), and physics phenomena (multi-physics) are tested on a number of benchmark exercises for which experimental data are available and for which the power plant details have been released. As part of this effort, the development and assessment of different methods or techniques to account for the uncertainties in the calculations are investigated and reported, which contributes to the state-of-the-art in this area. (author)