Step-by-step integral scaling method

A new scaling method called step-by-step integral scaling approach is proposed and applied to scaling analysis of BWR MARK-1 corium-shell interactions. Two group mechanisms are identified : the spreading group mechanism and water-corium-concrete interactions. In the first step the former is treated considering the mass and momentum transfer of the molten corium. Two spreading mechanisms are identified : gravitational force-dominant spreading and surface tension-dominant spreading. Governing equations for the analysis of gravitational force-dominant spreading is derived using the concept of open channel flow. The second step is divided into two substeps : interactions before and after solidification starts. In the first substep thermal convection is considered and an analytical solution for a variation of the corium temperature is obtained using the characteristic method. In the second substep governing equations for crust formation at the top and the bottom of the corium are analytically solved. In the real conditions of the prototype the time constant and relative importance of each phenomenon are examed. It is found out that time constants related to water-corium-concrete interactions are much shorter than those related to spreading. Initial superheat, thermal convection rates, water and concrete cooling, and latent heat of corium solidification turn out to have high relative importance