The "cleaner than" argument is largely wishful thinking.

Flux densities necessary in the containment materials and operating machinery for a fusion reactor will almost certainly be sufficiently high to produce isotope changes in the structural parts of any fusion reactor, and the radioactive isotopes of structurally useful materials generally have decay rates as long as - or longer than - the depleted fuels that most people assume are the only "waste" from fission reactors. Some materials, rendered radioactive by exposure, also produce spontaneous radiation about as "hard" as that from fission fuels.

The expected safe disposal requirements for radioactive waste from fusion reactors is not really much different than for fission reactors, since in both cases a large part of the "waste" is ordinary materials and parts made radioactive simply by being inside high flux areas within the reactor.

Of course, "we" really won't know how big the problem is until someone actually builds one that works efficiently enough to be used for a while. We just hope the experts who build it have made fairly accurate analyses before they start construction.

John