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Material Science_ Vol 1 of 2 - US DOE (1993) WW Part 13

Tham khảo tài liệu 'material science_ vol 1 of 2 - us doe (1993) ww part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Properties of Metals DOE-HDBK-1017 1-93 APPENDIX A For example if LiD salt is placed in contact with the surface of a stainless steel specimen the oxide is reduced allowing increased permeation. If a metal undergoes surface oxidation in the presence of steam permeability decreases as oxidation proceeds. Nonhvdriding Metals The mechanical integrity of nonhydriding metals in the presence of tritium is excellent because the electron bands carry away the energy of colliding beta particles without disrupting the metal structure or bonding. These metals form the most common class of tritium containment structural materials. They generally include 304L 316L 321 21-6-9 and Nitronic stainless steels as well as copper and aluminum. Inconel Ni-Cr alloys and 400-series stainless steels are generally not chosen because of corrosion or hydrogen embrittlement sensitivity. At high pressures of tritium gas however classical hydrogen embrittlement as well as helium-3 embrittlement can occur in accepted materials. For example for 304L stainless steel samples exposed to 9 kpsi of tritium at 423 K for 6 months and then aged 1.5 years fracture toughness decreased by a factor of 6. Of this a factor of two could be attributed to helium-3 alone. Substantially different fracture modes are observed between aged tritium-loaded and unloaded steel specimens. Helium-3 is vastly less soluble in metals than is hydrogen tritium helium pockets bubbles form with high internal pressures. Hydrogen embrittlement also contributes to this effect. Permeative escape rates of tritium through nonhydriding metals are generally acceptable at temperatures below 100 C to 300 C and for thicknesses of 0.1 cm or more. For 304 stainless steel 0.3 cm thick with a 1000-cm2 surface area exposed on one side to tritium gas of 1 atm pressure at 300 K the permeability is 1.6 x 10-4 Ci day t0.9 7 hours . The temperature dependence of permeation is often astounding. Cross-contamination between nonhydriding metals and tritium