II.11 – Interpretation of complex thermochemical phenomena in severe nuclear accidents using a thermodynamic approach

Publisher Summary This chapter discusses the interpretation of complex thermochemical phenomena in severe nuclear accidents using a thermodynamic approach. In the framework of the nuclear reactor safety, the analysis of all possible scenarios of hypothetical accidents is needed. In the first step of an accident of loss of coolant in a Pressurized-Water Reactor (PWR), control rods may melt and interact with the steel structures. As the temperature increases in the core, the Zircaloy cladding might be oxidized and liquefied. Then, core degradation occurs, with the interaction of the fuel with the Zircaloy cladding. The partially melted complex mixture of all these materials, including the lower internal structures of the vessel, is called the corium. In the ultimate steps of a severe accident, the corium might melt through the vessel and slump into the concrete reactor cavity; the phenomenon is called Molten Corium–Concrete Interaction (MCCI). This chapter provides useful information on the key corium interactions and thermochemical or thermophysical properties that affects significantly the corium behavior progression during a variety of severe PWR scenarios. Simultaneously, new experiments were proposed in the areas characterized by poor knowledge or the lack of knowledge.