A nuclear disaster could take several forms. The most obvious would be a meltdown at a nuclear reactor plant. Though the plant could not explode, the results of such a disaster would very likely be the release of massive amounts of radiation and radioactive material into the environment. And it would take hundreds of years to decay to anything near "safe" levels. Cleaning it up is out of the question, as exemplified by the Chernobyl disaster. In the Ukraine event, the reactor actually caught fire and burned. Prypiat is a ghost town. In the case of Three Mile Island, the meltdown was contained within the reactor vessel and the containment building, but there were some large releases of steam that was heavily laced with the radioactive debris of spent fuel fission fragments. These radioactive materials, which would normally be contained inside fuel elements, were released into the primary coolant when a loss-of-coolant accident overcame the plant.