I'm trying to write a paper arguing for why we should spend more money on nuclear fusion research. I keep reading that "nuclear fusion produces no long lived radioactive waste", but when I looked up why this is the only good source I could find was Quora, clearly not something I can really cite. So, I was hoping someone here could explain it to me, and hopefully also leave their sources so I could use them as well.
Fusion does create highly radioactive waste, in the following way.
The main power output of a fusion reactor comes in the form of high-speed neutrons. These then give up their kinetic energy in collisions with the so-called first wall inside the reactor, which heats up. Heat exchange piping then carries away this heat, which is used to boil water and spin a turbogenerator set.
That piping is made from stainless steel superalloys, which are exposed to an intense flux of neutrons while the reactor is running. When the chrome, nickel and iron in the stainless happen to capture any of those neutrons, they can get transmuted into unstable isotopes which then undergo radioactive decay. Some of these decay products are violently radioactive and remain so for years.
(As for the first wall "blanket" itself, refractory ceramics are favored, but their exact compositions have not been completely worked out so the amount of radioactivity they will produce by getting activated by neutron capture isn't well-known yet.)