Influence of the air/steam mixing ratio in atmosphere on zirconium cladding oxidation in spent fuel pool accident condition

Nemoto, Yoshiyuki  ; Kaji, Yoshiyuki  ; Ogawa, Chihiro*; Nakashima, Kazuo*; Tojo, Masayuki*

To cope with the hypothetical severe accident in spent fuel pools (SFPs), it is important to understand the high temperature oxidation behavior of the Zirconium claddings exposed in the air or in the atmosphere of air/steam mixture. In this study, oxidation tests on Zircaloy-2 (Zry2) and Zircaloy-4 (Zry4) short samples were conducted in the atmosphere of air - steam mixture, and mixing ratio was varied to evaluate its influence on the oxidation kinetics in the temperature range from 600 to 1100C. From 900 to 1000C for Zry2, and from 800 to 1000C for Zry4, oxidation rates appeared higher in air - steam mixture than in dry air or in steam without air. This tendency was appeared more evident in post-breakaway transition phase after fracture of dense oxide layer on the surface of specimens. These results suggest importance of the oxidation model development in consideration of the air - steam mixture environment for the SFP accident analysis.