235U properties

The other major springboard for the fluorocarbon chemical industry was the "Manhattan Project to develop the atomic bomb. This required the large-scale production of highly corrosive elemental fluorine and uranium(VI) fluoride for the separation of the radioactive 235U isotope. Oils capable of resisting these materials were needed to lubricate pumps and compressors, and polymers were needed to provide seals. Peril uorinated alkanes and polymers such as PTFE and poly(chlorotrifluoroethylene) (PCTFE) proved to have the appropriate properties so practical processes had to be developed for production in the quantities required. In 1947 much of this work was declassified and was published in an extensive series of papers3 which described the fundamental chemistry on which the commercial development of various fluoro-organic products, especially fine chemicals, was subsequently based. 

This isotope, 239Pu, was shown to have a cross section for thermal neutron-induced fission that exceeded that of 235U, a property that made it important for nuclear weapons, considering that it could be prepared by chemical separation as compared to isotopic separation that was necessary for 235U. 

Uranium-plutonium mixed oxides Uranium-plutonium mixed oxides (MOX) are becoming increasingly important, since plutonium is produced during the reprocessing of spent fuel elements. In these mixed oxide fuel elements a mixture of uranium(IV) and plutonium(IV) oxides with a plutonium content of 3 to 4% is utilized instead of ca. 4% 235u-enriched uranium(IV) oxide. Such fuel elements have similar nuclear physical properties to the standard elements with and can therefore be used in their place. 

The first transuranium elements, neptunium and plutonium, were obtained in tracer amounts from bombardments of uranium by McMillan and Abelson and by Seaborg, McMillan, Kennedy, and Wahl, respectively, in 1940. Both elements are obtained in substantial quantities from the uranium fuel elements of nuclear reactors. Only plutonium is normally recovered and is used as a nuclear fuel since, like 235U, it undergoes fission its nuclear properties apparently preclude its use in hydrogen bombs. Certain isotopes of the heavier elements are made by successive neutron capture in 239Pu in high-flux nuclear reactors (> 1015 neutrons cm-2 sec- ). Others are made by the action of accelerated heavy ions of B, C, N, O or Ne on Pu, Am or Cm. 

The practical importance of the actinide elements derives mainly from their nuclear properties. The principal application is in the production of nuclear energy. Controlled fission of fissile nuclides in nuclear reactors is used to provide heat to generate electricity. The fissile nuclides 233u 235u and Pu constitute an enormous, practically inexhaustible, energy source. 

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