The influence of irradiation temperature on the extent of change in Charpy-V (C^v) notch ductility and tension test properties of low alloy structural steels and welds was explored for reactor vessel applications. Specimens were irradiated at 288°C and 316°C in temperature-controlled assemblies in the Ford Nuclear Reactor (FNR) at the University of Michigan. Irradiation at 316°C to 7.9 × 10¹⁸ n/cm², E > 1 MeV, produced 41-J temperature elevations that were on average 51% of those produced by 260°C irradiation. Thermal aging at 316°C for 5000 h had little effect on C^v and tension test properties. NRC Regulatory Guide 1.99 Rev. 2 projections for irradiation-induced embrittlement at 288°C are compared to the experiment measurements.