Temperature-dependent oxidation behavior of Cr-coated zry in steam at 1100-1350C

Pham, V. H.  ; 北垣 徹  ; 岡田 裕史*; 佐藤 大樹*

Pham, V. H.; Kitagaki, Toru; Okada, Yuji*; Sato, Daiki*

Chromium coated zirconium alloys (Cr-coated Zry) have been widely developed to improve the oxidation resistance of fuel cladding under both normal operation and accident conditions. While the Cr coating provides effective protection at elevated temperatures through the formation of a CrO layer, its performance at high temperatures remains a subject of ongoing investigation due to the potential transition in oxidation mechanisms. In this study, zirconium alloy substrates fully coated with chromium were used. Oxidation tests were conducted at 1100-1350C for 1 h in a steam/Ar atmosphere using a thermogravimetric system equipped with a steam generator. In addition, a volatilization test of CrO powder was performed at 1300C for 3 h under identical conditions to evaluate its stability in high temperature steam. The results show a clear temperature dependent evolution in oxidation behavior. At 1100 C, oxidation followed parabolic kinetics consistent with CrO scale formation. In the temperature range of 1200-1275C, a linear oxidation behavior was observed, associated with the concurrent formation of ZrO beneath the coating and reduction of CrO. At temperatures above 1300C, parabolic kinetics reappeared, with behavior comparable to that of uncoated Zry.