Vapor explosion phenomena with respect to nuclear reactor safety assessment

An important concern in the analysis of a hypothetical nuclear power reactor accident is an understanding of the consequences of reactor core overheating, leading to fuel melting and subsequent interaction of hot molten fuel with coolant. If such molten fuel-coolant interaction (MFCI) is of limited extent, the resultant work potential is relatively benign. However, as illustrated in Figure 1, it can be envisioned that under certain conditions, core overheating may lead to a sequence of events resulting in the formation of an extensive amount of hot molten fuel in a liquid coolant environment, where such molten fuel may interact with the colder liquid coolant, causing it to vaporize as a result of local heat transfer. If the local heat transfer process is rapid enough (for example, due to fine-scale fuel fragmentation and intermixing with the coolant), the vapor generation process may be extremely fast, such that shock pressurization of the system occurs. If the pressure pulse generated is of sufficient strength, then severe damage to or failure of the reactor vessel may occur. Such a process is often referred to as a “vapor explosion”.