The mechanical properties of 316L/304L stainless steels, Alloy 718 and Mod9Cr-1Mo after irradiation in a spallation environment

The Accelerator Production of Tritium (APT) project proposes to use a 1.0 G eV, 100 mA proton beam to produce neutrons via spallation reactions in a tu ngsten target. The neutrons are multiplied and moderated in a lead/aluminum /water blanket and then captured in He-3 to form tritium. The materials in the target and blanket region are exposed to protons and neutrons with ener gies into the GeV range. The effect of irradiation on the tensile and fract ure toughness properties of candidate APT materials, 316L and 304L stainles s steel (annealed), modified (Mod) 9Cr-1Mo steel, and Alloy 718 (precipitat ion hardened), was measured on tensile and fracture toughness specimens irr adiated at the Los Alamos Neutron Science Center accelerator, which operate s at an energy of 800 MeV and a current of I mA. The irradiation temperatur es ranged from 50 degreesC to 164 degreesC, prototypic of those expected in the APT target/blanket. The maximum achieved proton fluence was 4.5 x 10(2 1) p/cm(2) for the materials in the center of the beam. This maximum exposu re translates to a dpa of 12 and the generation of 10000 appm H and 1000 ap pm He for the Type 304L stainless steel tensile specimens. Specimens were t ested at the irradiation temperature of 50-164 degreesC. Less than I dpa of exposure reduced the uniform elongation of the Alloy 718 (precipitation ha rdened) and Mod 9Cr-1Mo to less than 2%. This same dose reduced the fractur e toughness by 50%. Approximately 4 dpa of exposure was required to reduce the uniform elongation of the austenitic stainless steels (304L and 316L) t o less than 2%. The yield stress of the austenitic steels increased to more than twice its non-irradiated value after less than I dpa. The fracture to ughness reduced significantly by 4 dpa to similar to 100 MPa m(1/2). These results are discussed and compared with results of similar materials irradi ated in fission reactor environments. (C) 2001 Elsevier Science B.V. All ri ghts reserved.