STEPWISE INTEGRAL SCALING METHOD FOR SEVERE ACCIDENT ANALYSIS AND ITSAPPLICATION TO CORIUM DISPERSION IN DIRECT CONTAINMENT HEATING

Accident sequences which lead to severe core damage and to possible ra dioactive fission products into the environment have a very low probab ility. However, the interest in this area increased significantly due to the occurrence of the small break loss-of-coolant accident at TMI-2 which led to partial core damage, and of the Chernobyl accident in th e former USSR which led to extensive core disassembly and significant release of fission products over several countries. In particular, the latter accident raised the international concern over the potential c onsequences of severe accidents in nuclear reactor systems. One of the significant shortcomings in the analyses of severe accidents is the l ack of well-established and reliable scaling criteria for various mult iphase flow phenomena. However, the scaling criteria are essential to the severe accident, because the full scale tests are basically imposs ible to perform. They are required for (1) designing scaled down or si mulation experiments, (2) evaluating data and extrapolating the data t o prototypic conditions, and (3) developing correctly scaled physical models and correlations. In view of this, a new scaling method is deve loped for the analysis of severe accidents. Its approach is quite diff erent from the conventional methods. In order to demonstrate its appli cability, this new stepwise integral scaling method has been applied t o the analysis of the cerium dispersion problem in the direct containm ent heating.