Accelerated optimization of chromium coating microstructures for nuclear fuel applications through electrochemical corrosion testing

Abstract

Corrosion of zirconium alloy fuel cladding in nuclear reactors is one of the main limiting factors to component lifespan. Protective coatings may be applied to reduce the corrosion rate during regular operation and can have the added benefit of mitigating follow-on risks associated with loss-of-coolant accidents. This study considers the use of electrochemical testing to rapidly evaluate the corrosion protection of chromium coatings on zirconium alloys. By correlating these electrochemical testing results with the microstructural characteristics and mechanical properties of the coating, it is possible to qualitatively predict the performance of these coatings during long-term autoclave testing and eventual in-reactor use. A series of chromium coatings were deposited using cathodic arc physical vapor deposition (CA-PVD) with varying substrate bias. Electrochemical testing showed that the coatings provided improvements in corrosion protection over the uncoated baseline zirconium alloys, with further improvements observed for substrates to which voltage bias was applied. This is attributed to the increased adatom mobility during the deposition process, allowing for the development of a dense, uniform microstructure of the chromium coating. These results were compared to autoclave exposure data over a 56-day period to show the effectiveness of electrochemical testing towards predicting significant differences in corrosion resistance under regular operating conditions. This approach provided limited qualitative insight on long-term performance in its present state, but shows promise for further development.