It lacks the key advantage of fusion reactors over fission: not contaminating its working fluid with radioactive isotopes. For something like PACER, you have to

It lacks the key advantage of fusion reactors over fission: not contaminating its working fluid with radioactive isotopes. For something like PACER, you have to extract the heat by running the hot fluoride through heat exchangers to run steam turbines. This is difficult and expensive to make safe. Like with conventional fission reactors, you have to be extremely sure your heat exchangers will last 50 years with zero leaks, because you can't touch them once the system has been running. And leaks are extremely dangerous. So every weld has to be triple-inspected and so on. A second disadvantage is that the parts would undergo constant thermal cycling. Conventional reactors are run at a very steady output level to handle base load, because turning them up and down regularly would cause the moving parts to fatigue and crack over time.