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:
“I pity the men whose natural pleasures are burthens, and who fly from joy ... as if it was really an evil in itself.... Poor unfortunate creature that he is! as if the causes of anguish in the heart were not enow—but he must fill up the measure, with those of caprice; and not only walk in a vain shadow,—but disquiet himself in vain too.”
—Laurence Sterne (1713–1768)