ABSTRACT

During severe accidents in PWR, the formation and behaviour of a pool of molten materials ("corium") are important phenomena which may modify the accident scenario. We propose here a simplified transient model of a liquid molten pool, which can be integrated into scenario codes. This model yields the pool temperature distribution and the wall fluxes, for a homogeneous corium in any axisymetrical geometry varying with time. Two natural convection flow regimes are studied: laminar and turbulent. The model uses a space discretization grid, adapted at each time-step to represent the flow in the pool. The heat transfer coefficients between pool and walls are issued from correlations. The energy equation is discretized by the Finite Volume Method, implicitly with respect to time. This model was first programmed in an independent module, which calculates the pool transient behaviour until the steady-state regime. It was validated on two experiments: in water, then in UO₂. Finally, the coupling of this independent module with the ICARE2 code was performed. This coupling showed the model is satisfactorily running when integrated in a core degradation code.