Uncertainty Analysis in Modelling for Light Water ReactorsConsistent Approach for Multi-scale Modelling
Résumé
Compared to previous benchmarks and international activities, the Uncertainty Analysis in Modeling (UAM) is the most comprehensive initiative regarding uncertainty analysis in nuclear engineering. Light Water Reactor (LWR)-UAM is organized in three main Phases (I to III), with three exercises for each phase, and several test cases for each exercise. This approach let the participants focus on their own situation target, as VVER Steam Line Break or Boiling Water Reactor (BWR) stability analysis for instance. The test cases are based on real plant data for the three main types of LWR (i.e. BWR, Pressurized Water Reactor (PWR) and VVER) and relevant experimental conditions for validation. UAM Phase I, devoted to multi-scale static neutronics, is almost completed. This first Phase already provides recommendations regarding sensitivity and uncertainty analysis methods, and results to be used in the next Phases, when considering time effects (depletion and kinetics) and feedbacks (fuel and moderator). The paper focuses on the link between UAM Phase II to Phase III i.e. on the link between uncertainty propagation in single physics on local scale and multi-physics uncertainty propagation on the core scale. Particularly we present the consistency in uncertainty assessment between higher-fidelity models implemented in fuel performance codes (in Exercise II-1, dedicated to fuel physics in steady state and transient conditions), and the rather simplified models implemented in thermal-hydraulics codes, to be used for coupling with neutronics in Phase III. Similarly, the uncertainty quantification on thermal-hydraulic models is established on a relatively small scale, i.e. rod bundles, in Exercise II-3, while these results will be used in Phase III at the core scale, sometimes with different codes or models (e.g. one-fluid versus two-fluid).
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