Verification for flow analysis capability in the model of three-dimensional natural convection with simultaneous spreading, melting and solidification for the debris coolability analysis module in the severe accident analysis code 'SAMPSON', (I)

The debris coolability analysis module in the severe accident analysis code 'SAMPSON' has been enhanced to predict more mechanistically the safety mar gin of present reactor pressure vessels in a severe accident. The module ca lculates debris three-dimensional natural convection with simultaneous spre ading, melting and solidification using the 'debris spreading-cooling model ' in combination with the temperature distribution of the vessel wall and i t evaluates the wall failure. Debris spreading is solved by the free surfac e calculation method in which the height function is applied, The model mak es possible a multiplex heat and mass transfer analysis with flow spearhead and melt front transportation for a single-phase flow analysis code throug h the resetting of two types of mesh attributions and re-arrangement of the pressure matrix at each time step. The results calculated with the present model are compared with the results from a water spreading experiment. The comparisons verify the model capability for predictions of debris flow in the spreading process. The module provides a good tool for prediction of th e reactor safety margin in a severe accident through the three-dimensional natural convection analysis of debris with simultaneous spreading, melting and solidification.