tailieunhanh - Material Science_ Vol 2 of 2 - US DOE (1993) WW part 9

Tham khảo tài liệu 'material science_ vol 2 of 2 - us doe (1993) ww part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 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 LIST the four radioactive materials that fission by thermal neutrons and are used as reactor fuels. EO 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-23 3 233U uranium-23 5 235U plutonium-239 239Pu and plutonium-241 241Pu . The isotopes uranium-23 8 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. 238U 1n y 239U p 239Nn p 239Pu 92U on y 92U y 93Np y 94Pu 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