Reply #34: Quite a lot of the zircalloy has gone poof already.

[AtheistCrusader]

That's the smoking gun in the presence of hydrogen that shredded the outer buildings. High heat oxidizes the zircalloy, ripping oxygen out of the water molecules, and freeing up two hydrogen atoms.

I don't see any reason why the reactors would suddenly go prompt critical now (or again, depending on what the hell happened to Reactor 2). Something monumentally wierd would have to happen. The only mechanism I can think of is the continued geological instability of the region.

I am a little concerned with the plan to fill the containment itself with water. If somethin goes really wrong, I don't think anyone has done much modeling on what those old containments will do with significant hydrostatic pressure inside. Plus, we don't know how much damage the containments may have sustained, from the earthquake itself, in which ground accelerations exceeded the rated design limits of the reactors.