Could you create robust, modular storage vats that double as interlocking elements of a sea-wall to hold back future tsunamis? I imagine it'd be expensive but you're killing a few birds with one stone. If containment in a single vat fails then the radioactive water is dispersed in a vast sea as opposed to a small land area.
I also wonder if you could blast pellets of radioactive waste with a very big laser like the one at the NIF [0]. I don't know much about physics so I accept this could be a disastrous or futile idea but if anyone can comment that would be great.