Normal radioactive decay. Check out RTGs, which generate electricity without any criticality whatsoever: http://en.wikipedia.org/wiki/Radioisotope_thermoelectri

Normal radioactive decay. Check out RTGs, which generate electricity without any criticality whatsoever: http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen...