Which is safer, nuclear fission, or nuclear fusion?
Depends on how you are using it. For power supply fusion is safer although it is not in commercial use at the moment. It has always been ‘just around the corner’ but there are plans to have it up and running commercially soon I have heard recently. Fission has a lot of nasty waste and the reaction is more likely to ‘run away’ than a fusion one. But in terms of weaponry, fusion bombs are far more powerful than fission ones. So in that respect fusion is more ‘dangerous’ although it is a fairly moot point as ANY nuclear weapon is fairly terrifying.
In principle, controlled fusion should be safer, because it’s so much harder to make happen and sustain. It has a strong natural tendency to stop occurring when things malfunction. With fission, uncontrolled reactions can occur, and if all of the reactor’s failure recovery mechanisms fail, you can end up with a melt-down. However, with newer reactor designs, this is incredibly unlikely. Neutronic fusion still has problems with radioactive waste, but they are much less than fission because far more energy is extracted from each fusion event than each fission event. Which means that that you need less material to fuse to get the same amount of energy, producing a lower neutron flux and less destruction of the containment shielding, which is the source of the waste in fusion reactors.
