Since the initial function of a spaceship power source
is to blow the ship into orbit, making that completely safe
I saw experiments on TV of repeatedly shooting a laser
at the underside of a flying disc. This caused air under
the disc to expand and push it upwards. But that was
some time ago and obviously it hasn't caught on.
As for a nuclear explosion, I think that's a matter of
ordinary physics: if gas or liquid or air is heated or
evaporated, either it expands, or if it can't then
pressure increases and eventually it breaks out
of whatever it's contained in. Nuclear reactors usually
are built not to let anything out, but maybe under
pressure it's better to leak than to explode. Like a
good pressure cooker with a safety valve.