[higgmeister]

GA Pwr reported they were in the process of shutting down for maintenance when the event occurred.

[Steely Tom]

Even a flat-out boiler explosion would dissipate much of it’s energy against the walls of the plant.

I'm obviously wrong about that one. I forgot that in the big plants the boiler is basically outside the plant, at least parts of it are (the steam drum at the top). The rest of it is inside the furnace; I think those are designed to handle a burned-through tube without blowing up.