Scientific American notes that the world's uranium supply, the element used to create nuclear energy, can operate nuclear reactors for 200 years or more at stable consumption levels. Each nuclear reactor requires the use of low-enriched uranium fuel to create electricity. It is estimated that nuclear plants worldwide use approximately 70,000 metric tons of uranium to produce 2.8 trillion kilowatt-hours of electricity each year.
According to Scientific American, the Nuclear Energy Agency notes that as of 2009, approximately 5.5 million metric tons of uranium have been identified, and an estimated 10.5 million metric tons remain undiscovered. These combined amounts provide an estimated 230 years of nuclear energy. Uranium can be extracted from seawater in the future, but it is not currently financially feasible. This could yield an additional 4.5 billion metric tons of uranium that would supply world-wide nuclear power for an estimated additional 60,000 years at a stable consumption level, based on 2009 uranium usage amounts.
Scientific American also notes that though the world's nuclear reactors were initially expected to last no more than 40 years, many of them have been given licenses that extend use to 60 years. It is believed that the reactors are safe to operate for up to 80 years or more.