text: Extensive work was done from 1970 to 1990 on the possibility of a steam explosion or FCI when molten corium contacted water. Many experiments suggested quite low conversion of thermal to mechanical energy, whereas the theoretical models available appeared to suggest that much higher efficiencies were possible. A NEA/OECD report was written on the subject in 2000 which states that a steam explosion caused by contact of corium with water has four stages.
  * Premixing
  **As the jet of corium enters the water, it breaks up into droplets. During this stage the thermal contact between the corium and the water is not good because a vapor film surrounds the droplets of corium and this insulates the two from each other. It is possible for this meta-stable state to quench without an explosion or it can trigger in the next step
  * Triggering
  **A externally or internally generated trigger (such as a pressure wave) causes a collapse of the vapor film between the corium and the water.
  * Propagation
  **The local increase in pressure due to the increased heating of the water can generate enhanced heat transfer (usually due to rapid fragmentation of the hot fluid within the colder more volatile one) and a greater pressure wave, this process can be self-sustained. (The mechanics of this stage would then be similar to those in a classical ZND detonation wave).
  * Expansion
  **This process leads to the whole of the water being suddenly heated to boiling. This causes an increase in pressure (in layman's terms, an explosion), which can result in damage to the plant.