[pfdietz]

What you wrote there is 100% absurd. The waste from fission power plants lacks the material properties necessary to form the walls of a fusion plant, and would be nightmarishly difficult to fabricate into anything even if it did.

There has been repeated talk of putting transuranic waste into fusion reactor blankets for destruction or breeding (so called fission-fusion hybrids) but these inherit all the negatives of fission and fusion reactors (the worst of both worlds) without any big advantages to compensate. And this would just be materially passively loaded in blankets, not essential structural elements (that, for one thing, cannot spring any significant leaks without ruining the plasma by allowing coolant into the vacuum vessel.)