Operating temperature windows for fusion reactor structural materials

A critical analysis is presented of the operating temperature windows for n ine candidate fusion reactor structural materials: four reduced-activation structural materials (oxide-dispersion-strengthened and ferritic/martensiti c steels containing 8-12%Cr, V-4Cr-4Ti, and SiC/SiC composites), copper-bas e alloys (CuNiBe), tantalum-base alloys (e.g. Ta-8W-2Hf), niobium alloys (N b-1Zr), and molybdenum and tungsten alloys. The results are compared with t he operating temperature limits for Type 316 austenitic stainless steel. Se veral factors define the allowable operating temperature window for structu ral alloys in a fusion reactor. The lower operating temperature limit in al l body-centered cubic (BCC) and most face-centered cubic (FCC) alloys is de termined by radiation embrittlement (decrease in fracture toughness), which is generally most pronounced for irradiation temperatures below similar to 0.3 T-M where T-M is the melting temperature. The lower operating temperat ure limit for SiC/SiC composites will likely be determined by radiation-ind uced thermal conductivity degradation, which becomes more pronounced in cer amics with decreasing temperature. The upper operating temperature limit of structural materials is determined by one of four factors, all of which be come more pronounced with increasing exposure time: (1) thermal creep (grai n boundary sliding or matrix diffusional creep); (2) high temperature He em brittlement of grain boundaries; (3) cavity swelling (particularly importan t for SiC and Cu alloys); or (4) coolant compatibility/corrosion issues. In many cases, the upper temperature limit will be determined by coolant corr osion/compatibility rather than by thermal creep or radiation effects. The compatibility of the structural materials with Li, Pb-Li, Sn-Li, He and Fli be (Li2BeF4) coolants is summarized. (C) 2000 Elsevier Science B.V. All rig hts reserved.