One of the beautiful things about nuclear fusion reactors is that they are inherently unstable at STP. In the event of a catastrophic failure, they will simply

One of the beautiful things about nuclear fusion reactors is that they are inherently unstable at STP. In the event of a catastrophic failure, they will simply stop working (potentially after some large bangs). Nuclear fission reactions can continue on their own for quite a while. This is one of the reasons they can be so dangerous.