[1] http://scholarship.law.georgetown.edu/cgi/viewcontent.cgi?ar... [2] https://books.google.com/ngrams/graph?content=NMRI%2CMRI%2C+... [3] https://books.google.com/ngrams/graph?content=nuclear+magnet...
(See the decomissioning section on the 1964-1969 Oak Ridge thorium reactor if you think they are problem free https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment...)
The problem with most of that 'waste' (at least the non-byproducts kind) is that it's exactly that, actual waste instead of burnt fuel.