In a broad sense, natural uranium refers to natural uranium resources (including uranium ore and uranium contained in seawater) and those that have the same isotopic composition as natural uranium. In a strict sense, it refers to metallic uranium and its compounds (oxides, fluorides, carbides, nitrides). When used in comparison to enriched uranium and depleted uranium, it is used in this limited sense.
Natural uranium extracted from uranium contains an approximate proportion of 99.3% of isotope 238, and 0.7% of isotope 235. Of these, uranium 235 radioisotopes can be used as nuclear fuel in a nuclear reactor.
At the beginning of the 21st century, the type of reactor most used to generate electricity in the world is the light water nuclear reactor. The extracted natural uranium is converted to enriched uranium by increasing the proportion of uranium 235 in uranium enrichment plants for use in light water reactors. Uranium that is not concentrated is called natural uranium with respect to concentrated uranium.
Origin and formation of natural uranium
Like other elements with an atomic number higher than iron, uranium formed in supernovae. The main uranium isotopes were 235-U, 238-U and 236-U, which, due to the short half-life, had completely transformed into Thorium.
When planet Earth formed, the concentration of the 235-U isotope was approximately 3% compared to the current 0.711%. Therefore, a higher initial concentration of 235 U was able to trigger a fission chain reaction under appropriate conditions. In this way, one of the few natural nuclear reactors, which was located in Gabon, Africa, was created in the Oklo uranium deposit.
Uranium is widely distributed in the earth's crust and seawater, and is estimated to be 40 times more than silver and tin. Among them, proven recoverable reserves are estimated at 5.47 million tons.
The main nations with uranium resources are Australia, Kazakhstan, Canada, South Africa and the United States, in descending order of reserves. It is possible that the Democratic People's Republic of Korea (Republic of Korea, Japan Atomic Energy Industry Council) with an estimated 4 million tons of mineable reserves may exceed Australia's proven number one reserve.