An Enthalpy Method to Predict Core-Melt Propagation During Severe Accident in a Fast Reactor

ABSTRACT

Heat transfer problems involving phase change are nonlinear and are not amenable to analytical solutions except in very simple cases. In the field of nuclear reactor safety, solution for such problems is often needed when analysing hypothetical accident scenarios. During a core melt down accident in a fast reactor, a significant fraction of the hot molten fuel is expected to move downwards under gravitational force, melting the underlying structures. In such a situation, the lower plate of the grid plate will be one of the solid obstacles for the molten corium to melt through, before interacting with the cold sodium pool contained beneath and eventually settling on the in-vessel core-catcher. Towards modeling heat conduction in the grid plate with phase change, a mathematical model is formulated using the explicit enthalpy method and a one dimensional code HEATRAN1 is developed. The ability of the stainless steel grid plate to resist or delay the molten material relocation further in the downward direction is investigated in this study. Detailed parametric studies have been carried out by prescribing convective or adiabatic boundary conditions at the bottom of the plate. The predictive capability of the code to track the melt-front has been established. The code is validated against the BN - 800 reactor benchmark data. When heat sink at the bottom is taken into account, complete melt-through of the plate does not occur if the heat transfer coefficient is more than a critical value. The paper provides details of the formulation and the results of the parametric studies.

---

Full Text (PDF)

© 2010 Research Publishing Services