Natural uranium (NU) refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7% uranium-235, 99.3% uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2% comes from uranium-235, 48.6% uranium-238, and 49.2% uranium-234.
Natural uranium can be used to fuel both low- and high-power reactors. Historically, graphite moderated reactors and heavy water moderated reactors have been fueled with natural uranium in the pure metal (U) or uranium dioxide (UO2) ceramic forms, however experimental fuelings with uranium trioxide (UO3) and triuranium octaoxide, (U3O8) have shown promise.
The 0.72% U-235 is not sufficient to produce a self-sustaining critical chain reaction in light water reactors or nuclear weapons; these applications must use enriched uranium. In rare occasions, earlier in geologic history when U-235 was more abundant, uranium ore was found to have naturally engaged in fission, forming natural nuclear fission reactors.
During the Manhattan Project, the name Tuballoy was used to refer to natural uranium in the refined condition; this term is still in occasional use at present.
Famous quotes containing the word natural:
“The whole of natural theology ... resolves itself into one simple, though somewhat ambiguous proposition, That the cause or causes of order in the universe probably bear some remote analogy to human intelligence.”
—David Hume (1711–1776)