Another thing I've always wondered - what would have happen if everyone in the room freaked out and just ran away, leaving the two reflector halves completed cl

Another thing I've always wondered - what would have happen if everyone in the room freaked out and just ran away, leaving the two reflector halves completed closed? Would it have actually gone bang like a bomb, or more like just get insanely hot and give off an insane amount of radiation, but over the span of many seconds?