GLOSSARY 



Atomic energy — The energy released by a nuclear reaction or by radioactive 

 decay*. (See radioactive, fission, fusion, nuclear reactors, i 



Atomic number— The number of protons in the nucleus of an atom, and also its 

 positive charge. Each chemical element has its characteristic atomic 

 number, and the atomic numbers of the known elements form a complete 

 series from 1 for hydrogen to 103 for the man-made element lawrencium. 



Atomic reactor — See nuclear reactor. 



Atomic weapon — An explosive weapon in which the energy is produced by nuclear 

 fission or fusion. 



Atomic weight — The mass of an element relative to other elements. The atomic 

 weight of an element is approximately equal to the total number of 

 protons and neutrons in its nucleus. 



Boiling water reactor — A nuclear reactor in which water, used as both coolant 

 and moderator, is allowed to boil in the reactor core. The resulting steam 

 can be used directly to drive a turbine. 



Breeder reactor — A nuclear reactor so designed that it converts more uranium- 

 238 or thorium into useful nuclear fuel than the uraniumr-235 or Plu- 

 tonium which it uses. The new fissionable materials are created by 

 capture in the fertile materials of neutrons from the fission process. 

 There are three types of breeder reactors : the liquid metal, fast breeder 

 (LMFBR) : the gas cooled fast breeder (GCBR) ; and the molten-salt 

 breeder i MSBR). 



Breeder ratio — The ratio of the number of fissionable atoms produced in a 

 breeder reactor to the number of fissionable atoms consumed in the 

 reactor. 



Byproduct material — Any artificial radioactive material obtained during the 

 production or use of source material or fissionable material. It includes 

 fission products and radioisotopes produced in nuclear reactors, but not 

 radioactive materials occuring in nature or those made with accelerators 

 such as cyclotrons. 



Chain reaction — A nuclear reaction that stimulates its own repetition. In a fission 

 chain reaction, a fissionable nucleus absorbs a neutron and fissions, 

 releasing additional neutrons. These in turn can be absorbed by other 

 fissionable nuclei, releasing still more neutrons. A fission chain reaction is 

 self-sustaining when the number of neutrons released equals or exceeds 

 the number of neutrons lost by absorption in nonfissionable material or 

 by escape from the system. 



Containment The provision of a gastight shell or other enclosure around a 

 nuclear reactor to confine fission products tli.it otherwise might be 

 released to the atmosphere in the event of an accident. 



Conversion ratio The ratio of the number of atoms of new fissionable material 

 produced in a converter reactor to the original number of atoms of 

 fussionable fuel consumed. 



Converter reactor -A nuclear reactor that produces some fissionable material, 

 but less than it consumes. 



Coolant A substance circulated through a nuclear reactor to remove or transfer 

 heat. Common coolants are water, air. carbon dioxide, liquid sodium, 

 and helium. 



Core- The central portion of a nuclear reactor containing the fuel elements 

 and usually t lie moderator. 



Decay hea< The heat produced by the decay of radioactive nuclides. 



Decay, radioactive The spontaneous transformation of one nuclide into a 

 different nuclide, or into a different energy state of the same nuclide. 



Depleted uranium— Uranium having less uranium-235 than the 0.71 percent 

 found in natural uranium. 



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