Our Industry > The Nuclear Fuel Cycle
The Nuclear Fuel Cycle
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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