NUCLEAR FISSIONDOE-HDBK-1019/1-93Atomic and Nuclear PhysicsFertileMaterialAll of the neutron absorption reactions that do not result in fission lead to the production of newnuclides through the process known as transmutation. These nuclides can, in turn, be transmutedagain or may undergo radioactive decay to produce still different nuclides. The nuclides that areproduced by this process are referred to as transmutation products. Because several of the fissilenuclides do not exist in nature, they can only be produced by nuclear reactions (transmutation).The target nuclei for such reactions are said to be fertile. Fertile materials are materials that canundergo transmutation to become fissile materials. Figure 19 traces the transmutation mechanismby which two fertile nuclides, thorium-232 and uranium-238, produce uranium-233 andplutonium-239, respectively.Figure 19 Conversion of Fertile Nuclides to Fissile NuclidesIf a reactor contains fertile material in addition to its fissile fuel, some new fuel will be producedas the original fuel is burned up. This is called conversion. Reactors that are specificallydesigned to produce fissionable fuel are called "breeder" reactors. In such reactors, the amountof fissionable fuel produced is greater than the amount of fuel burnup. If less fuel is producedthan used, the process is called conversion, and the reactor is termed a "converter."NP-01Page 52Rev. 0
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