Hmm...yeah, you apear to be correct here. Perhaps we could help funnel it through into the mantle, though I suppose we would have no way to assure it would not then circulate and come right back out under even more unfavorable circumstances through a volcano.
The current idea is to flash freeze the entire area and keeping it frozen indeffinitly.
Fission is simply a terrible idea as Fukashima proves. THe problem is that it brings to the fore the fact that we do not have control. We can manage the plant under normal circumstances, but can't assure that there wont be a tornado, or an earthquake, or a volcano, or an astroid and suddenly all the gains we made from the nuclear energy are a huge liability. The corporations involved will quickly go bankrupt once the profit evaporates leaving the clean up to the people.