The Accelerator Production of Tritium (APT) project proposes to use a 1.0 GeV, 100 mA proton beam to produce neutrons by spallation from a tungsten target clad with Alloy 718. The neutrons are multiplied and moderated and then captured in ³He to form tritium. In this process, the materials in the target and blanket (T/B) region are exposed to a wide range of irradiation conditions. To test the effects of spallation neutrons on APT candidate materials, ASTM subsize samples were irradiated in a spallation neutron spectrum created from the interaction of an 800 MeV, 1 mA proton beam on a tungsten target at the Los Alamos Neutron Science Center (LANSCE). Specimens were located in controlled-temperature furnaces that were placed in proximity to the proton beam, but in locations where spallation neutrons would form the bulk of the exposure. The materials irradiated were the candidate APT materials 316L and 304L annealed stainless steels (SS), modified 9Cr-1Mo steel, and Alloy 718 (precipitation hardened). Irradiation temperatures varied from 100 to 280 °C and the approximate proton fluences were 4 × 10¹⁸ p/cm². The neutron fluences were ∼5 × 10¹⁹ n/cm² for energies < 0.1 MeV and 6×10¹⁹ n/cm² for energies > 0.1 MeV with the spectra including a high-energy tail up to the proton beam energy (800 MeV). The samples experienced an exposure range of 0.023 to 0.051 dpa.

The tensile tests were conducted in air at ambient temperatures (∼20° C). The results indicated that even for low exposures (> 0.05 dpa), there was a decrease in ductility for the all of the alloys. Increases in yield and ultimate strength were observed in the austenitic stainless steels and the 9Cr-1Mo alloy. The Alloy 718 showed no change in yield strength but a marked decrease in the ultimate strength. The results are discussed and compared with results of the in-beam irradiated materials where smaller S-1 type tensile samples were used. Comparison also is made with irradiations of materials in fission environments in a similar dose and temperature environment.