Tension specimens of Nimonic PE16 in the solution-treated and aged condition were irradiated in the experimental breeder reactor II to a maximum fluence of ∼7 × 10²² neutrons/cm² (E > 0.1 MeV) over a temperature range of 450 to 735°C. Tension tests were conducted at 232°C (fuel handling temperature), at the irradiation temperature, and at 110°C above the irradiation temperature to simulate transient reactor events. The alloy exhibited high strength and adequate ductility at 232°C. At the irradiation temperature, the strength remained high; however, a loss in ductility occurred with a trough in ductility occurring over a temperature range of 500 to 650°C. In tests simulating reactor transients, failures occurred with very low elongations (0 to 0.3 percent) over a test temperature range of 650 to 750°C.

No significant loss in grain boundary fracture stress was observed in the tests showing low ductility values. The loss in ductility can be explained by reduced differential between ultimate tensile strength and the yield stress.