Severe Accident Phenomenology… Milestones of Nuclear Safety: 2011 Fukushima Accident

Dr. Ing. Mazzini, Ph.D. Nuclear & Industrial Safety (pdf): Severe Accident Phenomenology… Milestones of Nuclear Safety: 2011 Fukushima Accident (1st for an External Event)

• Ex-Vessel Accident Phenomena:
  -> The molten debris falls into the reactor cavity. This produces boiling off of whatever water is there. If sufficient water is present, the core would be cooled and solidify, and would subsequently re-melt.
  -> Steam explosions may also occur at this time as the molten fuel falls onto water in the reactor cavity. This can disperse fuel, create radioactive aerosols, and increase the rate of heat transfer to the containment atmosphere.
  -> Molten corium attacks the concrete basement, which proceeds to penetrate, and creates a cauldron that releases aerosols and gases [and] containment pressure rises.

http://download.cvrez.cz/cvrez_mazzini_severe_accident_phenomenology.pdf