Ah, thanks for pointing that out! I stand corrected. I was thinking about what happened at Chernobyl with the explosion, and yes… at worst, it could be considered a dirty bomb. There was an explosion, and enough fissile material ejected to be considered radioactive fallout, but it wasn’t an A-bomb. It was a steam explosion from all the coolant overheating.

Both fission and fusion are both “nuclear” reactions… but that’s where the commonalities end.

In fission, a radioactive isotope (such as uranium or plutonium) is constantly shedding particles and melting down. And the reactor uses graphite rods and heavy water cooling to moderate and manage how much of a chain reaction can take place. Without the rods and water, you could have a runaway chain reaction which could lead to reactor core meltdown… and if there’s more than critical mass of nuclear fuel… an A-bomb explosion to go with the meltdown. (Edit: As u/dewafelbakkers pointed out, this isn't really a concern as reactors don't use anywhere close to the critical mass required for an atomic explosion, nor do they do they enrich the fuel enough to reach such a critical point.)

Not to mention, radioactive decay of spent fuel and remaining uranium/plutonium goes on for aeons.

In Fusion, there is no natural radioactive decay. The natural state doesn’t lead to a meltdown, and there’s not really a need to actively moderate the reactor. In fusion, a lot of energy is needed to get the reaction going as well as to sustain and confine it. If the Torus breaks down for some reason, the magnetic confinement will fail, and plasma pressure will drop and the reaction will stop. And you are left with hydrogen/deuterium gas or heavy water.

It takes a lot of energy to get atoms to collide. Even in an H-bomb, the reaction trigger is provided by an A-bomb. So the energy from the first fission explosion collides the hydrogen atoms together to release the much larger output of the fusion reaction. And, in the fusion reactors, most of the energy spent is trying to get the hydrogen atoms in a hot plasma to collide inside a confined magnetic donut. If the magnets fail, the plasma disappears… sure it might do some damage due to hot gas, but that’s about it.