The environmental impact of nuclear power results from the nuclear fuel cycle, operation, and the effects of nuclear accidents. The greenhouse gas emissions from nuclear fission power are much smaller than those associated with coal, oil and gas, and the routine health risks are much smaller than those associated with coal. However, there is a "catastrophic risk" potential if containment fails, which in nuclear reactors can be brought about by over-heated fuels melting and releasing large quantities of fission products into the environment. This potential risk could wipe out the benefits. The most long-lived radioactive wastes, including spent nuclear fuel, must be contained and isolated from the environment for a long period of time. On the other side, spent nuclear fuel could be reused,