Zirconium oxide coatings on P91 and zircaloy (Zr-2.5%Nb) substrates for use in SCWRs

The CANDU-SCWR presents difficult operating conditions for materials of construction and innovative methods, such as corrosion-resistant coatings, are being developed for reactor materials. In this study, Zircaloy (Zr-2.5%Nb) and P91 were coated with tightly adhering layers of zirconium-based oxides (ZrO2 or Zr-NbO2) through a plasma spray deposition (PSD) process. The coupons were exposed to deoxygenated supercritical water at 500oC and 25 MPa for increasing durations, up to 900 hours. Coated coupons showed a reduced weight gain at all exposure times when compared to uncoated samples however SEM work reveals that poor coating adhesion resulted in degradation of the coating through oxide loss by spallation or dissolution processes. (author)