Plant Materials DOE-HDBK-1017/2-93 FUEL MATERIALS FUEL MATERIALS Nuclear plants require radioactive material to operate.   Certain metals that are radioactive can be used to produce and sustain the nuclear reaction.  This chapter discusses  the  materials  used  in  the  various  nuclear  applications.    The  student should refer to the Nuclear Physics and Reactor Theory Fundamentals Handbook prior to continuing to better understand the material in this chapter. EO  1.3 LIST the four radioactive materials that fission by thermal neutrons and  are  used  as reactor  fuels. EO  1.4 STATE the four considerations in selecting fuel material and the desired  effect  on   the  nuclear   properties  of  the   selected  fuel material. Overview  of  Material  Types The  reactor  core  is  the  heart  of  any  nuclear  reactor  and  consists  of  fuel  elements  made  of  a suitable fissile material.  There are presently four radioactive materials that are suitable for fission by thermal neutrons.   They are uranium-233 (²³³U), uranium-235 (²³⁵U), plutonium-239 (²³⁹Pu), and  plutonium-241  (²⁴¹Pu).     The  isotopes  uranium-238  (²³⁸U)  and  thorium-232  (²³²Th)  are fissionable by fast neutrons.   The following text discusses plutonium, uranium, and thorium as used for nuclear fuel. Plutonium Plutonium is an artificial element produced by the transmutation of ²³⁸U.   It does exist in small amounts  (5  parts  per  trillion)  in  uranium  ore,  but  this  concentration  is  not  high  enough  to  be mined commercially. Plutonium is produced by the conversion of ²³⁸U into ²³⁹Pu according to the following reaction. 23 9 8 2 U + ¹_o  n ® ²³₉ 9 2 U 23 9 9 3 Np 23 9 9 4 Pu b ® b ® This reaction occurs in reactors designed specifically to produce fissionable fuel.  These reactors are frequently called breeder reactors because they produce more fissionable fuel than is used in the reaction.   Plutonium is also produced in thermal ²³⁵U reactors that contain ²³⁸U.   Plutonium can be obtained through the processing of spent fuel elements.  To be useful as a fuel, plutonium must be alloyed to be in a stable phase as a metal or a ceramic. Rev. 0 Page 5 MS-05