I would say "none" but just containment failing is not equivalent of meltdown. If left to own devices, fusion would stop. You can get some kind of explosion/fir

I would say "none" but just containment failing is not equivalent of meltdown. If left to own devices, fusion would stop. You can get some kind of explosion/fire, since you know, high energies are involved, but it would be simple thermal explosion. There are still issues, like most fusion reactions produce neutrons, which are not great by themselves, and basically most dangerous type of radiation. They can make regular matter radioactive. But we are far from that stage when this is a problem.