Extension of CFD codes - application to two-phase flow safety problems, phase 2

This document is an extension of the NEA/SEN/SIN/AMA(2006)2 report produced by the Writing Group 3 on the extension of CFD to two-phase flow safety problems, which was formed following the recommendations made at the “Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems” held in Aix-en-Provence, in May 2002. Extension of CFD codes to two-phase flow is a chance for safety investigations, by giving some access to smaller scale flow processes which were not seen by present tools. Using such tools as part of a safety demonstration may bring a better understanding of physical situations, more confidence in the results, and an estimation of safety margins. The increasing computer performance allows a more extensive use of 3D modelling of two-phase Thermalhydraulics with finer nodalization. However, models are not as mature as in single phase flows and a lot of work has still to be done on the physical modelling and numerical schemes in such two-phase CFD tools. The Writing Group listed and classified the NRS problems where extension of CFD to two-phase flow may bring real benefit and also classified different modelling approaches. First ideas were reported about the specification and analysis of needs in terms of validation and verification.