Development of phenomenological degradation models for Cr-Coated Zr alloy cladding under high-temperature oxidation conditions

谷口 良徳 ; Luu, V. N. ; 田崎 雄大 ; 宇田川 豊  ; 勝山 仁哉  

Taniguchi, Yoshinori; Luu, V. N.; Tasaki, Yudai; Udagawa, Yutaka; Katsuyama, Jinya

Advanced technology fuels (ATF) with improved oxidation resistance are under development to enhance the safety of light water reactors. Cr-coated Zr alloy cladding, a promising near-term ATF, exhibits excellent oxidation resistance below the Cr-Zr eutectic temperature. However, its gradual loss of protective effect over time, even without mechanical damage, indicates the need to understand its degradation mechanisms. This article presents a phenomenological model describing degradation due to high-temperature oxidation, focusing on Zr ingress into the Cr coating and the formation of oxygen pathways that accelerate oxygen uptake into the Zr matrix. The model was validated against experimental data at 1200C and 1300C, reproducing key trends such as oxide growth, weight gain, and oxygen concentration profiles. Applying the same parameters to a different PVD-coated cladding test gave reasonable agreement at 1200C, while discrepancies at 1300C suggest Cr-Zr eutectic reactions from local temperature variations, highlighting the model's sensitivity near the eutectic point.