BEPU methods using CFD codes -Progress made within OECD-WGAMA CFD activities

Abstract

International audienceOECD-NEA-CSNI Working Group for Analysis and Management of Accidents (WGAMA) initiated activities in 2003 in order to promote the use of CFD for nuclear safety. Best Practice Guidelines (BPG) for Use of CFD on Nuclear Reactor Safety Application were established. A document was written on the Assessment of CFD Codes for Nuclear Reactor Safety Problems with a compendium of current application areas and a catalogue of experimental validation data relevant to these applications. The Extension of CFD Codes to Two-Phase Flow Safety Problems was also treated in a separate document, including some first Best Practice Guidelines for two-phase CFD application to some selected NRS problems. Then a review of uncertainty methods for CFD applications was written. International benchmarks were also organized to test CFD capabilities to address reactor issues. A first benchmark was based on a mixing Tee experiment for investigating thermal fatigue. The second benchmark addressed flow in a rod bundle with specific influence of spacer grids. The third benchmark addressed physical processes occurring in a containment following a postulated severe accident in which there is a significant build-up of hydrogen in the containment atmosphere. The last benchmark was the first Uncertainty Quantification exercise on a rather simple mixing problem in presence of buoyancy effects.This paper will summarize the main outcome of these 14 years activities with particular attention to uncertainty methods and results of the last benchmark. Both uncertainty propagations methods and accuracy extrapolation methods were used with some success to the GEMIX benchmark. The degree of maturity of all the methods is still rather low but results obtained so far are encouraging. The paper will conclude on a detailed state of the art of BEPU methodologies applied with CFD simulations with an identification of the main difficulties and limitations of current approaches. Further activities are recommended to go beyond the present limitations and on-going WGAMA activities are mentioned