Investigating applications of ICARE/CATHARE code to air ingress issues

Experimental results demonstrate that in the presence of oxygen the UO2 fuel and its fission products undergo oxidation reactions, especially under high temperature conditions as those encountered in a severe accident. It is generally accepted that the circumstances in which air can come in contact with irradiated fuel, after a core fusion accident, are related to the reactor lower head failure. Studies indicate that a natural circulation loop can be established between the containment and the reactor pressure vessel through the breaks of the later. In these conditions, the geometry of the core, the fuel and cladding state and the temperatures inside core can be significant for the source term evaluation. In ICARE/CATHARE v2, there is a model for zirconium oxidation by air, taking into account the presence of noncondensable gases, the differences from steam oxidation with respect to the kinetics and energy of reaction and also zirconium nitriding. The paper illustrates the application of ICARE/CATHARE v2 to the post-test analysis of QUENCH-10 air oxidation experiment and to PWR reactor scenarios with air ingression. (authors)