Nuclear bombs are not like conventional bombs. It is very difficult to make them explode. They aren’t volatile. The way the ones dropped on Japan detonated was something like two halves of a core hit each other super super hard and were propelled by a bunch of shot gun shells. Compare that to things like black powder where it’s just fire.

I don’t think fires or bombs on nuclear sites are good, nor do I necessarily believe there were nuclear weapons, but I don’t think they’d detonate like what you’re thinking. Like how a fire at a fireworks factory causes a horrible chain reaction where everything blows up. Nothing like that.