The Nuclear Fuel Cycle

Uranium is mined using in situ leach, open pit, underground and by-product methods. Mining operations worldwide produce a U3O8 concentrate, referred to as yellowcake.

Nuclear fission is primarily the result of the splitting of the fissionable uranium-235 (U-235) isotope. U-235, found in naturally-occurring uranium minerals, makes up 0.711% of uranium naturally, while uranium-234 and uranium-238 make up 0.006% and 99.283%, respectively.

While some reactors are designed to operate with natural 0.711% U-235, most are designed for higher concentrations of the U-235 isotope. Through chemical and physical processes, the concentration of U-235 can be increased, a process called enrichment. Commercial nuclear power plants require enrichments of 3-5% to operate efficiently.

The “typical” enrichment process requires about 10 pounds of natural U3O8 to produce 1 pound of EUP for fuel fabrication. The enrichment process results in fuel-grade uranium, and left-over depleted uranium – uranium that has less than 0.711% U-235 concentrations – called enrichment “tails.”

The enriched UF6, referred to as low enriched uranium (LEU) or enriched uranium product (EUP), is delivered to fabrication facilities around the world where it is converted to UO2, and manufactured into fuel assemblies ready for loading into nuclear reactors. An average reload for a 1,000 MW light water reactor would use nearly 800,000 pounds U3O8.

Fission results in the buildup of “fission products” in the fuel that inhibit the chain reaction. Eventually, the spent fuel must be removed and replaced with fresh fuel (every 12-24 months). Spent fuel still contains some fissionable U-235. That remaining U-235 can be recovered through chemical and physical “reprocessing”. Because reprocessing results in the isolation of plutonium, many countries have taken the position that reprocessing increases nuclear weapon proliferation risks, and do not allow reprocessing. However, plutonium is a fissionable element and can be burned in reactors.

Spent fuel is highly radioactive when removed from a reactor, and quite hot. When unloaded from the reactor, fuel assemblies are placed into storage ponds on site where the water shields the radiation and absorbs the heat. Spent fuel can remain in the storage pond for several years. When sufficiently cooled, the spent fuel assemblies are sent for reprocessing or are prepared for final disposal.