I didn't mean dumping it all in a heap together, but putting it in e.g. high-density polyethylene should do the trick. It has the density of 930 to 970kg/m^3. Very good tensile strength and longevity.

There's more than enough space and geologically stable locations to put this stuff. Politically speaking and in terms of getting nuclear back in the game, I wouldn't worry too much about waste with the modern solutions within storage.