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Deuterium — An isotope of hydrogen whose nucleus contains one neutron and 

 one proton, and is therefore about twice as heavy as the nucleus of 

 normal hydrogen, which is only a single proton. It occurs in nature as 

 1 atom to 6500 atoms of normal hydrogen and is not radioactive. 

 Energy — The capability of doing work. 



Enriched uranium — Uranium in which the amount of uranium-235 present has 

 been artificially increased above that found in nature. Enriched uranium 

 for civil nuclear power is generally enriched to about 3 to 6 percent ; 

 enriched uranium for weapons is above 00 percent. 



Fast breeder reactor — A nuclear reactor that operates with neutrons at the 

 fast speed of their initial emission from the fission process, and that 

 produces more fissionable material than it consumes. 



Fast reactor — A nuclear reactor in which the fission chain reaction is sustained 

 primarily by fast neutrons rather than by thermal or intermediate 

 neutrons. 



Feed materials — Refined uranium or thorium metal or their pure compounds 

 in a form suitable for use in nuclear reactor fuel elements or as feed for 

 uranium enrichment processes. 



Fertile material — A material, not itself fissionable by thermal neutrons, which 

 can be converted into a fissionable material by irradiation in a nuclear 

 reactor. The two basic fertile materials are uranium-238 and thorium- 

 232. When these fertile materials capture neutrons, they become fission- 

 able plutonium-230 and uranium-233. respectively. 



Fission — The splitting of a heavy nucleus into two approximately equal parts 

 (which are radioactive nuclei of lighter elements), accompanied by the 

 release of a relatively large amount of energy and generally one or more 

 neutrons. Fission can occur spontaneously, but usually is caused by 

 nuclear absorption of neutrons or other particles. 



Fissile material — "While sometimes used as a synonym for fissionable material, 

 this term has also acquired a more restricted meaning, namely, any 

 material fissionable by neutrons of all energies. 



Fission produces — The nuclei formed by the fission of heavy elements, plus 

 nuclides formed by the fission fragments' radioactive decay. 



Fissionable material — Any material fissionable by slow neutrons. The three basic 

 ones are uranium-235. plutonium-239 and uranium-233. 



Fuel cycle — The series of steps involved in supplying fuel for nuclear power 

 reactors. It includes mining, refining, fabrication of fuel elements, their 

 use in a nuclear reactor, chemical processing to recover remaining 

 fissionable material, reenrichment of the fuel, and refabrication into new 

 fuel elements. 



Fuel element — A rod. tube, plate or other shape or form into which nuclear 

 fuel is fabricated for use in a reactor. 



Fuel reprocessing — The processing of reactor fuel to recover the unused, residual 

 fissionable materials. 



Fusion — The formation of a heavier nucleus from two lighter ones, such as 

 hydrogen isotopes, with the attendant release of energy. 



Gas centrifuge process — A method of enrichment in which heavier uranium 

 adorns are partially separated from lighter ones by centrifugal force. 



Gaseous diffusion process — A method of uranium enrichment based on the fact 

 that gas atoms or mo^cules with different masses will diffuse through 

 a porous barrier, or membrane, at different rates. 



Isotope — One of two or more atoms with the same atomic number but with 

 different atomic weights. Isotopes usually have very nearly the same 

 chemical properties, but somewhat different physical properties. 



Licensed material — Source material, special nuclear material, or byproduct 

 material received, possessed, used or transferred under a general or 

 special license issued by the Atomic Energy Commission. 



Magnetohydrodymmics (MHD) — A process for converting energy of very hot. 

 electrically conducting gases into electricity by the movement of streams 

 of such gases in a magnetic field. The process in theory offers a sub- 

 stantial improvement in thermal efficiency over conventional steam- 

 turbine-generator systems. 



Maximum credible accident — The most serious reactor accident that can reason- 

 ably be imagined from any adverse combination of equipment malfunc- 

 tion, operating errors, and other foreseeable causes. 



Megawatt — One million watts, one thousand kilowatts. 



