With mainstream present-day fission technology, it takes about 200 tonnes of natural mined uranium to fuel a 1000 MWe reactor for a year: http://www.world-nucl

With mainstream present-day fission technology, it takes about 200 tonnes of natural mined uranium to fuel a 1000 MWe reactor for a year: http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/introduction/nuclear-fuel-cycle-overview.aspx http://www.world-nuclear.org/information-library/nuclear-fue... The same 300 kWh would then require about (300 / (1000 * 24 * 365 * 1000)) * (200000000) = 6.85 grams of natural uranium. Note that this is well below the theoretical energy density available from the fission of uranium. The main loss is because the naturally fissile isotope of uranium, U-235, is less than 1% of naturally occurring uranium. The much more common U-238 can be used completely in a breeder reactor, but there are currently only two operating breeder reactors in the world that generate electricity: https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-800_reactor https://en.wikipedia.org/wiki/BN-800_reactor