Modeling of ex-vessel corium coolability with the Corquench code

The results of Melt Attack and Coolability Experiment (MACE) tests have identified several heat transfer mechanisms which could potentially lead to long term corium coolability. Based on physical observations from these tests, an integrated model of Corium Quenching (CORQUENCH) behavior is being developed. Aside from modeling of the primary physical processes observed in the tests, considerable effort has been devoted to modeling of test occurrences which deviate from the behavior expected at reactor scale. In this manner, extrapolation of the models validated against the test data to the reactor case can be done with increased confidence. The integrated model currently addresses early bulk cooling and incipient crust formation heat transfer phases, as well as follow-on crust water ingression and melt eruption heat transfer mechanisms. The latter two mechanisms lead to development of a sustained quench front progressing downwards through the debris. In terms of experiment distortions, the model is also able to mechanistically calculate crust anchoring to the test section sidewalls, as well as the subsequent melt/crust separation phase which arises due to concrete densification upon melting. In this paper, the status of model development and validation activities are described. In addition, representative calculations for PWR plant conditions are provided in order to illustrate the potential benefits of overlying water on mitigation of the accident sequence. (author)