In-Reactor Creep Behavior of Zircaloy-2

A BWR pre-irradiated re-crystallized (RXA) Zircaloy-2 tube was creep tested in the Halden Reactor in a dedicated creep rig connected to a light water supply and connected to a variable pressure gas supply allowing the magnitude and direction of the applied stress to be changed during the test. A three-point contact diameter gauge was used for making in-reactor outside diameter measurements on the sample. The sample was tested for 14,410 hours. A total of eight hoop stress changes were applied in series to the sample during different irradiation periods. The data and two different evaluations of the data were previously reported. This paper updates the data and evaluation of the data taking into account new oxide thickness measurements and observations of the morphology of the oxide on the sample and on the diameter gauge calibration steps. The sample creep strains were re-calculated, correcting for the time dependent oxide thickness increases over the region of the sample that exhibited intact oxide. The oxide thickness correction decreased the irradiation creep strains. That is, for positive strains, the correction decreased the strain to lower values. In the case of negative strains, the correction resulted in larger negative numbers. The oxide thickness correction changedmore » the creep rates. The oxide thickness did not affect the saturated transient strains. The transient irradiation creep component was dependent on the magnitude of the stress change. The re-occurrence was associated with a threshold stress change of about 41 MPa. The irradiation creep rates in tension are higher than those in compression. Comparison of the irradiation creep rates with other investigations suggests that the creep rate data are in transient irradiation creep and not in steady state irradiation creep. Alternatively, the differences may be due to differences between RXA Zircaloy-2 and RXA Zircaloy-4, which was used in the other investigations. (authors)« less