With a complete combustion or fission, approx. 8 kWh of heat can be generated from 1 kg of coal, approx. 12 kWh from 1 kg of mineral oil and around 24,000,000 kWh from 1 kg of uranium-235. Related to one kilogram, uranium-235 contains two to three million times the energy equivalent of oil or coal. The illustration shows how much coal, oil or natural uranium is required for a certain quantity of electricity. Thus, 1 kg natural uranium - following a corresponding enrichment and used for power generation in light water reactors - corresponds to nearly 10,000 kg of mineral oil or 14,000 kg of coal and enables the generation of 45,000 kWh of electricity.
1kg natural uranium -> 45,000 kWh
1 kg U235 -> 24,000,000 kWh
Weapons-grade uranium and plutonium surplus to military requirements in the USA and Russia is being made available for use as civil fuel. Weapons-grade uranium is highly enriched, to over 90% U-235 (the fissile isotope). Weapons-grade plutonium has over 93% Pu-239 and can be used, like reactor-grade plutonium, in fuel for electricity production. Highly-enriched uranium from weapons stockpiles has been displacing some 8850 tonnes of U3O8 production from mines each year, and met about 13% to 19% of world reactor requirements through to 2013.
In nature, uranium is found as uranium-238 (99.2739–99.2752%), uranium-235 (0.7198–0.7202%), and a very small amount of uranium-234 (0.0050–0.0059%).
Highly enriched uranium (HEU) has a 20% or higher concentration of 235U. The fissile uranium in nuclear weapon primaries usually contains 85% or more of 235U known as weapons-grade, though theoretically for an implosion design, a minimum of 20% could be sufficient (called weapon(s)-usable) although it would require hundreds of kilograms of material and “would not be practical to design”
Highly-enriched uranium in US and Russian weapons and other military stockpiles amounts to about 1500 tonnes
1500 tonnes -> 300 .. 1275 tonnes U235 -> 300000 .. 1275000 kg
24000000 kilowatt hours = 0.0240000000000 terawatt hours
7200 .. 30600 TWh
Primary energy use in the United States was 25,155 TWh or about 81,800 kWh per person in 2009. Primary energy use was 1,100 TWh less in the US than in China in 2009.
US energy consumption per year: 25,155 TWh 
China energy consumption per year: 1,100 TWh 
US: 0.28 .. 1.21 year
China 6.54 .. 27.81 year
If the Nuclear Energy Agency (NEA) has accurately estimated the planet’s economically accessible uranium resources, reactors could run more than 200 years at current rates of consumption.