Natural uranium

Natural uranium (NU or Unat) is <a href="/facts/Uranium/n2sGWBzU">uranium</a> with the same <a href="/facts/Isotopic_ratio/dGjaAwc9">isotopic ratio</a> as found in nature. It contains 0.711% <a href="/facts/Uranium-235/pe0RznDM">uranium-235</a>, 99.284% <a href="/facts/Uranium-238/QhcHm6q8">uranium-238</a>, and a trace of <a href="/facts/Uranium-234/nKrs059u">uranium-234</a> by weight (0.0055%). Approximately 2.2% of its <a href="/facts/Radioactive_decay/Ya6FVjt4">radioactivity</a> comes from uranium-235, 48.6% from uranium-238, and 49.2% from uranium-234.
Natural uranium can be used to fuel both low- and high-power <a href="/facts/Nuclear_reactor/8xqjIbge">nuclear reactors</a>. Historically, <a href="/facts/Graphite-moderated_reactor/d10WE8fv">graphite-moderated reactors</a> and <a href="/facts/Heavy_water/3dbSrTw5">heavy water</a>-moderated reactors have been fueled with natural uranium in the pure metal (U) or <a href="/facts/Uranium_dioxide/BqI7GJDq">uranium dioxide</a> (UO2) <a href="/facts/Ceramic/9JKudpqX">ceramic</a> forms. However, experimental fuelings with <a href="/facts/Uranium_trioxide/RRK8J8A3">uranium trioxide</a> (UO3) and <a href="/facts/Triuranium_octaoxide/NfF0nDEA">triuranium octaoxide</a> (U3O8) have shown promise.
The 0.72% uranium-235 is not sufficient to produce a self-sustaining critical <a href="/facts/Chain_reaction/5UwHTKXS">chain reaction</a> in <a href="/facts/Light_water_reactor/c330w1Wt">light water reactors</a> or <a href="/facts/Nuclear_weapon/QVdBcMdm">nuclear weapons</a>; these applications must use <a href="/facts/Enriched_uranium/vSb2Tcsb">enriched uranium</a>. Nuclear weapons take a concentration of 90% uranium-235, and light water reactors require a concentration of roughly 3% uranium-235. Unenriched natural uranium is appropriate fuel for a <a href="/facts/Heavy-water_reactor/YfjI0tqR">heavy-water reactor</a>, like a <a href="/facts/CANDU_reactor/fAKl2X0L">CANDU reactor</a>.
On rare occasions, earlier in geologic history when uranium-235 was more abundant, uranium ore was found to have naturally engaged in fission, forming <a href="/facts/Natural_nuclear_fission_reactor/G7FIGsEV">natural nuclear fission reactors</a>. Uranium-235 decays at a faster rate (<a href="/facts/Half-life/kGVH8BAB">half-life</a> of 700 million years) compared to uranium-238, which decays extremely slowly (half-life of 4.5 billion years). Therefore, a billion years ago, there was more than double the uranium-235 compared to now.
During the <a href="/facts/Manhattan_Project/gtg8yRK2">Manhattan Project</a>, the name Tuballoy was used to refer to natural uranium in the refined condition; this term is still in occasional use. Uranium was also codenamed "X-Metal" during World War II. Similarly, enriched uranium was referred to as Oralloy (<a href="/facts/Oak_Ridge_National_Laboratory/Elq84HKF">Oak Ridge</a> alloy), and <a href="/facts/Depleted_uranium/oKGvpUlW">depleted uranium</a> was referred to as Depletalloy (depleted alloy).

Natural uranium open-in-new

Natural uranium