Formation and dissolution of oxide film on zirconium alloys in 288 C pure water under γ-ray irradiation

Laboratory corrosion tests for zirconium alloys which were based on Zircaloy-2 were performed in 288 C oxygenated pure water for 100 days both with and without 60Co γ-ray irradiation. No nodular oxide was observed. Corrosion weight gains of the alloy which had the lowest nodular corrosion resistance were lower for the irradiated condition than the non-irradiated condition. On the other hand, the alloys which had higher nodular corrosion resistances showed almost the same weight gains for both conditions. Differences of weight gain with and without irradiation were attributed to dissolution of the oxide film in the high temperature water. Dissolution tests of single crystal yttria-doped ZrO2 indicated that 30-40% larger amounts dissolved into water under the γ-ray irradiation. Low angle incident X-ray diffraction analysis showed that the tetragonal-ZrO2 fraction in the oxide film was lower with irradiation than without it, especially for the near surface area. The water radiolysis species accelerated the dissolution of the oxide film, especially film on the alloy with lower nodular corrosion resistance. This dissolution led to the lower tetragonal-ZrO2 fraction and was considered to be one of the factors causing a localized breakdown of the barrier oxide film to make the nodular oxide. (orig.)