Development of debris coolability analysis module in severe accident analysis code SAMPSON for IMPACT project

Debris coolability in the lower plenum of the reactor pressure vessel is an important factor for the evaluation of in-vessel debris retention. The deb ris coolability analysis module has been developed to predict more mechanis tically the safety margin of the present reactor vessels in a severe accide nt. The module calculates del,ris spreading and cooling through melting and solidification in combination with the temperature distribution of the ves sel wall and it evaluates the wall failure. Debris spreading is solved by t he esl,licit method on a quasi-three-dimensional scheme and debris coolabil ity is solved oil the basis of natural convection analysis with melting and solidification. The calculated results for spreading were compared with th e results from a water spreading experiment on the floor and the results fo r coolability were compared with those from an n-octadecane melting experim ent in the rectangular vessel. The comparisons showed the capability for pr edictions of the spearhead transportation in the debris spreading process a nd of the melting front transportation and time evolution of the fluid temp erature in the melting process. The module provides a good tool for the pre diction of the reactor pressure vessel safety margin in a severe accident t hrough the analysis of debris spreading and coolability.