These are actually far, far safer than any pure fission plant. The nice thing about these fusion-fission plants is they can be designed to be completely and utterly meltdown proof. Regular fission plants have a self-sustaining fission reaction; the plant is designed to slow the reaction down and keep it under control. With a fusion-fission plant, you can design it the opposite way. You design the fission part to be sub-critical. You use a fission fuel that cannot maintain a self-sustaining fission reaction. You design it so that the fission part is only able to maintain a reaction if it has a giant neutron beam pointed at it. And that neutron flux is provided by the fusion part of the reactor.
If anything at all goes wrong in the plant, all you have to do is cut off power to the fusion reactor. The fusion component of the reactor cannot itself make net power; it consumes electricity to keep running. So you just it off, the neutron flux collapses, and the fission portion is unable to keep its reaction going.
One advantage of these reactors is they're completely meltdown proof. You design the fission component to be sub-critical - the fission core can only maintain a reaction as long as the neutron flux from the fusion reactor is maintained. The neutron flux doesn't just enhance fission, it's a necessary component for the fission to keep going at all. And the fusion portion doesn't make net energy, it's just a glorified way of turning electricity into neutrons.
If anything goes wrong, you just flip a switch and shut down the fusion part of the reactor. Temp starts increasing too much? A sensor flips a switch and the fusion reactor shuts off automatically.