Estimation of integrity of shear key and reactor vessel during a severe accident

In this work we estimated the integrity of the shear key and the reactor vessel around the key solving three-dimensional, steady-state heat conduction equations. The reactor shear key is of a rectangular fin (60.48cm x 25.2cm x 16.25cm) attached to the plate of 15.12cm thickness. The problem domain covers the area 15 times the cross-sectional area for the fin. The constant heat flux boundary condition is applied to the inner wall. The heat flux is obtained by considering the natural convection of the molten debris pool within the lower head. Several boundary conditions are applied to the outer wall to simulate the external cooling. Results indicate that the film boiling at the bottom of the shear key raises the temperature of the region close to the melting point. Even though nucleate boiling may be maintained in the region, the heat flux at the outer wall is larger around the shear key and the Critical Heat Flux (CHF) will be lower than the without the shear key. It is thus necessary to maintain nucleate boiling at the bottom of the shear key and ensure that the vapor be not stagnant underneath the key. Results also show that the partial exposure of the fin to the air has little effect on the temperature field of the shear key and the reactor vessel