Six capsules, each containing 240 subsized tension specimens, were irradiated to fluences up to 9 × 1020 neutrons (n)/cm² (E > 1 MeV) to determine the effect of irradiation at 130, 650, and 775°F on the tensile properties of Zircaloy-4. Other specimens were tested to determine the effects of thermal aging at 650 and 750°F on the properties of Zircaloy-4.

Irradiation at 775°F had no effect on the properties of the cold-worked Zircaloy-4 but did reduce the ductility of the annealed material. The uniform elongation of the annealed material was reduced to 2 percent by irradiation; but, no further decrease in ductility occurred at fluences above 5 × 10²⁰ n/cm².

Irradiation at 130 and 650°F resulted in an increase in strength and a decrease in ductility of all materials. The uniform elongation was generally less than 0.5 percent at all test temperatures for the specimens receiving an exposure of 5 × 10²⁰ n/cm² or greater. The change in yield strength after irradiation at 650°F can be approximated by the equation Δσys=A(1−e−BΦt)1/2