>>11326964For toxic compounds, oxidize until non toxic. For inherently toxic elements, bind stable oxides/fluorides of those elements together with tough ceramics as nonporous pellets, and store them.
For radionuclides, put everything into a nonporous ceramic pellet form. Mix pellets with hydrated clay, and pack into plastic drums. Place plastic drums into stainless steel drums. Place steel drums upright with some space between them in a pit in the desert, and fill gaps with concrete. Continue filling pit with drums embedded in concrete until reaching two meters below ground level, then cap off with a slab of steel-scrap-embedded concrete several feet thick, and finally back-fill remaining depression in the ground with soil.
Pellets are first line of defense and will hold all gaseous decay products until they decay into solid elements once again, without leaking. If a pellet fails and leaks, the percolation of contamination through the clay in the drum will be extremely slow. Anything that gets through the clay will still be enclosed by the plastic drum layer, which in the dark underground would take millions of years to decompose, and can handle flexing in the event of a serious seismic event. The steel drum acts as a final barrier, both making release less likely and protecting the contents from the outside world. The concrete fill between drums prevents anything getting close and impinging on the drums hard enough to cause damage. The cap layer of concrete full of cheap steel is meant to act as a barrier between the drums and the surface to both prevent accidental contact and hinder targeted attack or tampering.
This solution would work best for the almost pure fission product waste of a high efficiency breeder reactor, where there are no more fuel isotopes contained within that could be valuable to retrieve in the future. For anything less than pure waste, keeping it stored as nonporous ceramic pellets is plenty.
