Dryout heat flux in debris beds with different size particles

In the event of a severe LWR accident, degraded core materials would form a debris bed which would continue to release decay heat. In order to mitigate such an accident within the reactor vessel, it is important to estimate the coolability of the debris bed. This can be determined from the dryout heat flux and depends on many parameters such as the configuration of the debris bed and the coolant flow conditions. In the present study, the pressure drop and dryout heat flux in a debris bed with mixed particles were measured and empirical correlations for permeabilities for laminar and turbulent flow were developed. The correlations were applied to an analytical model to predict dryout heat flux. The following conclusions were drawn: (1) the dryout heat flux decreases when smaller particles are mixed with larger particles; and (2) the analytical model gives reasonable agreement with the measured dryout heat flux when the mass fraction of small diameter particles is less than 0.3. (author). Poster presentation. 6 refs, 5 figs