I remember about 15-20 years ago, a mate of mine was contracted out to 'Maralinga' for the
'clean-up' after the nuclear tests performed by the British in the 1950's. (Outback Australia).
What they did, was to dig a series of gigantic holes, and bulldozed tons of radioactive top-
soil & general remaining junk. Then they filled it on top with tons of Silicon. (Fine sand). There
must have been some 'conductive' compound too, because they then inserted Giant probes,
and using massive generators, heated it until it formed a gigantic 'glass' slug on top, to seal
it in 'permanently', before finally burying all that. Sounds like it's out of some Science Fiction
movie, but that's what they did!! They tried to get the British to foot the bill. (??)