Analysis of in-vessel corium pool behaviour using CFD tools

In-vessel retention (IVR) is a severe accident mitigation strategy that is considered for several reactor designs, as well as a backfitting option for some operating plants. However, due to significant uncertainties, demonstrating its feasibility for high power reactors remains a complex issue. The European H2020 IVMR project has been launched in 2015 to harmonize and improve the analysis methodology for IVR. In particular, activities have been launched to assess the potential of CFD codes for the study of corium pool thermalhydraulics. Two core topics are addressed in this paper: thin layer thermalhydraulics, and behaviour of homogeneous oxide pools. The experimental data base and current modelling practices in integral codes is discussed. Due to the challenge presented by in-vessel phenomena, a code assessment on relevant simulant-based experimental data was chosen as the first step. Good results have been obtained on full-scale water-based tests, and are presented in this paper; various approaches to turbulence modelling are compared. While further validation is needed, these results have also been used to set up first exploratory computations under prototypical conditions: hypothesis and first trends are discussed in this paper.