Fusion accidents are much less likely - they need to be constantly supplied with new fuel for the reaction to continue. If they get hit by an earthquake / terrorist attack / other emergency, the natural tendency of the system is to stop moving things, including the fuel, which means that the source of energy is immediately removed, and the danger with it. At worst the reactor itself may get destroyed, but containment techniques should guarantee minimal radiation escaping to the environment.
Fission on the other hand requires a large quantity of fuel just to get the chain reaction started, so if things go wrong, you'd better have a robust cooling system, because nothing is going to stop that fuel from producing lots of waste heat. The fuel melts and escapes containment, radiating surrounding groundwater and the general environment. Even without catastrophes, fission results in lots of irradiated coolants and 'spent' fuel that is still hot enough that it needs to be stored in water for years after it leaves the reactor.
Fission on the other hand requires a large quantity of fuel just to get the chain reaction started, so if things go wrong, you'd better have a robust cooling system, because nothing is going to stop that fuel from producing lots of waste heat. The fuel melts and escapes containment, radiating surrounding groundwater and the general environment. Even without catastrophes, fission results in lots of irradiated coolants and 'spent' fuel that is still hot enough that it needs to be stored in water for years after it leaves the reactor.