Towards the accurate numerical prediction of thermal hydraulic phenomena in corium pools

The knowledge of heat transfer in corium pools is one of the important issues for corium retention, as it defines the safety margin for vessel integrity. In this regard, in the 90’s the BALI experimental program was performed at the CEA, France. The principal idea was to create a database regarding the heat transfer distribution at corium pool boundaries for in-vessel and ex-vessel configurations at high internal Rayleigh number (10¹⁵ to 10¹⁷). One of the tasks within the ongoing IVMR project, part of the HORIZON 2020 program, is to assess the up-to-date CFD turbulence models over a wide range of Rayleigh number for the homogenous pool tests of the BALI experiments. In the present study, the assessment of three different turbulence models is performed for two BALI test cases. These turbulence models include a linear k-ε model, a non-linear Reynolds stress model and an advanced turbulent heat flux model known as the AHFM-NRG. After an extensive and careful assessment it has been found that none of the previous models is able to correctly predict the complex heat transfer phenomena appearing in natural convection flow regimes at such high Rayleigh numbers. Hence, a new model is proposed to deal with a wide range of Rayleigh number flow regimes. Accordingly, the results obtained using this new approach are found to be in a very good agreement with the available experimental data.