Residual tensile strength of neutron irradiated Inconel 718 bolts

In the frame of the ITER task BL 14.1, the residual strength of precipitation hardened Inconel 718 bolts, preloaded to stresses up to 90% of the yield strength, after neutron irradiation has been investigated. In the ITER design, the Inconel 718 bolts are used to attach the backplate to the radial supports and may experience large shocks from off-normal events during operation. Three irradiation rigs, containing 9 bolts each, were irradiated at the HFR at dose levels of 0.2, 0.7 and 1.1 dpa, respectively, at a temperature of 573 K. The bolts were designed to resemble a scaled-down version of the actual design and the irradiation conditions were chosen to resemble the actual operation conditions. Our results show that two competitive processes occur during neutron irradiation. At low dose, dissolution of precipitates is dominant, which causes a softening of the material. At higher doses, irradiation hardening takes place. The combined effect of the two processes is that the irradiation hardening is relatively small compared to other materials.