Zirconium alloys have been successfully used as fuel cladding and structural materials in fission reactors for decades, but the industry’s desire to employ high burnup fuels requires an improvement of resistance to in-reactor corrosion. It is therefore essential to understand the mechanisms of radiation-enhanced corrosion of zirconium alloys, and especially why Zr-Nb alloys show improved properties compared to Zircaloys. In order to achieve this goal, the MUZIC-3 (Mechanistic Understanding of Zirconium Corrosion) program was established; a wide collaboration between universities and industrial partners. As part of this program, this project used advanced electron microscopy techniques to investigate in-reactor corroded samples from the Canada Nuclear Laboratory and autoclave corroded samples from Westinghouse.