Interest continues to be high in the effects of irradiation on the microstructure and microchemistry of Zircaloy and on the resultant effects on performance of Zircaloy components in-reactor. In this study, we have investigated the behavior of material prepared to have excellent resistance to nodular corrosion in a BWR. Coupon specimens of Zircaloy-2 were prepared having a range of critical microstructural parameters (precipitate size and distribution) by varying the thermomechanical processing history (quench rate and cumulative annealing parameter). Irradiation was conducted in a BWR at 561 K to fluences between 1.3 and 8.5 × 1025 n/m2 (E > 1 MeV).
As expected, nodular corrosion was absent in these materials, and, at low fluence, corrosion and hydriding of all materials was very low. At the highest fluences, patch-type uniform corrosion developed, with oxide thickness increasing with decreasing initial precipitate size. Detailed STEM investigation revealed that precipitates dissolved and decreased in size continuously until at the highest fluence no precipitates remained for material having the smallest initial precipitate size. Post-irradiation mechanical property tests showed strength somewhat higher than expected.
The results indicate that corrosion resistance and mechanical properties change as the microstructure evolves during irradiation. However, at the highest fluence tested, strength, ductility, and corrosion resistance ensure excellent performance of BWR components.