This is an issue I have been interested in for a long time. The safe disposal of nuclear waste is within our grasp by developing space elevators, which will be able to safely lift containers into low earth orbit, from where they can be sent cheaply into the sun, where strong force reactions belong. The sun is the biggest gravitational source, of course, and a cheap boost from low earth orbit, even in the general direction of the sun, will get it there. The wastes should be 500 year containerized for safety, as it is likely that a century will be needed before space elevators are operating well and used routinely. Fission energy may not be all that long-term a solution, though, because the supply of enrichable uranium on earth is very limited, even if all the nuclear weapons are dismantled and used for peaceful fission plants. But, yes, it could be the main solution for reducing CO2 emissions during this century, and the safety issue can be addressed by a robust program for the development of space elevators. The idea of using the moon or an asteroid is a non-starter. Keep it simple.