Radiation Effects in Metals: Hardening, Embrittlement, and Fracture 18.1 STRUCTURAL N!ETALS FOR FAST REACTORS
نویسنده
چکیده
The neutron eccmomy of a fast reactor is not so significantly affected by neutron capture in the structural materials in the core as is that of a thermal reactor. First, most neutron-capture cross sections increase with de creasing neutron energy, and the neutron population of the liquid-metal fast breeder reactor (Lhl FI~R) contains a far lower percentage of thermal neutrons than does that (If a light-water reactor (LWR). Second. the ratio of the mass of structural metal to the mass of fissile materials is much smaller in a fast reactor than in a thermal reactor. Consequently, metals that in a thermal reactor would severely impair neutron economy are acceptable in a fast reactor, and the selection of core structural materials for the I,hl FBR can be based primarily on cost and mechanical and chemical properties. The downgrading of rleutron absorption characteristics from tile selection criteria for core structural metals means that the costly zirconium alloys used in thermal reactors need not be employed in fast reactors. However, parasitic neutron absorption by nonfuel components is important enough to cause LNIFBR core designers to be quite sparing in using certain structural metals. The irradiation properties of high-nickel alloys, for example, are generally superior to those of con\, entional stainless steel, but nickel has a seriously large cross section for absorption of fast neutrons.
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