...
For postulated BDBEs, the fuel rods severely degrade resulting in a substantial amount of hydrogen generation and molten material (or corium). In this case, the objective is to eliminate any combustible gas hazards and allow the degraded core materials to attain a long-term coolable state. The floating plant strategy is to retain the corium inside the RPV, which is achieved by flooding the RPV cavity with containment water. This in-vessel retention strategy ensures that the thermo-mechanical loads on the containment remain low; moreover, given that the containment is initially under near-vacuum conditions, it would not be possible for hydrogen combustion to occur in a steam-inerted environment. As such, we expect to effectively eliminate the need for containment venting even in case of severe accidents.
...