that idea is not as far fetched as you might imagine, the us doe, your tax $'s at work, attempted such a stunt in western colorado. an attempt to fracture the rock with a "small" blast to stimulate gas production. and they were succesful in fracturing the rock but as you have guessed, the produced gas was radioactive.

http://en.wikipedia.org/wiki/Operation_Plowshare

Now there's a justification for CO2 sequestration if I ever saw one.