The creep properties of 20 per cent cold-worked Zircaloy-2 during neutron irradiation have been determined in the temperature range 275 to 465 C and stress range 20,000 to 35,000 psi. In general, the effects of neutron irradiation on creep are small; however, some differences between in-reactor and ex-reactor tests exist. The activation energy for creep during irradiation is around 90,000 cal/mole. In the absence of irradiation, the activation energy is about equal to the self-difiusion value of 60,000 cal/mole. During reactor outages, a small increase in creep rate occurs. The time required to initiate the increase after a shutdown decreases with increasing temperature.
During irradiation, steady-state creep rates can be expressed as
In addition, total creep strain prior to the first reactor outage can be expressed in terms of Dorn's parameter