Volume 8, Issue 3 (March 2011)
Experimental Investigation of Irradiation Creep and Growth of Recrystallized Zircaloy-4 Guide Tubes Pre-Irradiated in PWR
Re-crystallized Zircaloy-4 guide tubes were irradiated in commercial pressurized water reactors (PWRs) at three different temperatures to fluences near 1×1022 n/cm2 E>1 MeV (15 displacements per atom), resulting in moderate corrosion and three different hydrogen contents (approximately 135, 240, and 700 parts per million). Sections of the guide tubes were re-irradiated in the Halden reactor to assess the irradiation creep and growth behaviors. Three conditions were applied: Bellows-loaded axial compression creep; zero stress growth; and zero stress, zero flux (control specimens). The guide tube sections were re-irradiated under simulated PWR conditions by utilizing a pressurized light water loop operating with normal PWR water chemistry at approximately 320°C. Axial length changes were measured in-reactor by linear variable differential transformers (LVDTs), and post-irradiation hot cell measurements were done to confirm the LVDT elongation measurements. After minor corrections were made to account for reactor testing variables, it was shown that the LVDT measurements were accurate, thus creep and growth or free growth rates were established for each guide tube section. Hot cell examinations were also performed to establish the state of corrosion of each specimen, including hydrogen content, both before and after the re-irradiation in the Halden reactor. The results showed that stress free irradiation growth was different for each specimen and correlated qualitatively with the hydrogen content and commercial irradiation temperatures of the guide tubes. The higher hydrogen content, or higher commercial irradiation temperature, gave rise to higher subsequent growth rates. After subtracting the growth strain from the measured creep and growth strain values, the magnitude of creep and creep rates were essentially the same for all specimens: No effect of commercial reactor irradiation temperature or hydrogen content was observed. The results give important new data on irradiation creep and growth and on the correlation between hydrogen content and irradiation temperature on growth rates.