The Transition of protective coating to no-longer protective coating of Cr-coated Zry cladding in high temperature steam oxidation

高温水蒸気雰囲気におけるCrコーテッドZry被覆管の保護被膜破損への移行

Mohamad, A. B. ; 根本 義之  ; 古本 健一郎*; 岡田 裕史*; 佐藤 大樹*

Mohamad, A. B.; Nemoto, Yoshiyuki; Furumoto, Kenichiro*; Okada, Yuji*; Sato, Daiki*

The development of Accident Tolerant Fuel (ATF) started with the investigation of new concepts to improve the safety of Light Water Reactors (LWR). It is well known that the Cr coating on Zry cladding has shown improved behaviour under accident conditions and in normal operation. However, many questions remain about the oxidation behaviour of Cr-coated Zry cladding as it approaches the Cr-Zr eutectic temperature. In the present study, the steam oxidation tests were carried out under different oxidation conditions in order to understand the oxidation behaviour of the Cr-coated material mainly above the eutectic temperature. The results obtained showed that the Cr coating can protect the Zry substrate at 1100C to 1200C/5min. However, at 1200C/30min, the Cr coating no longer protected the Zry substrate. This is due to the formation of Zr at the Cr grain boundary where it becomes a short path for O diffusion and reacts with the Zry substrate.