FORMATION AND DISSOLUTION OF OXIDE FILM ON ZIRCONIUM ALLOYS IN 288-DEGREES-C PURE WATER UNDER GAMMA-RAY IRRADIATION

Laboratory corrosion tests for zirconium alloys which were based on Zi rcaloy-2 were performed in 288 degrees C oxygenated pure water for 100 days both with and without Co-60 gamma-ray irradiation. No nodular ox ide was observed. Corrosion weight gains of the alloy which had the lo west nodular corrosion resistance were lower for the irradiated condit ion than the non-irradiated condition. On the other hand, the alloys w hich had higher nodular corrosion resistances showed almost the same w eight gains for both conditions. Differences of weight gain with and w ithout irradiation were attributed to dissolution of the oxide film in the high temperature water. Dissolution tests of single crystal yttri a-doped ZrO2 indicated that 30-40% larger amounts dissolved into water under the gamma-ray irradiation. Low angle incident X-ray diffraction analysis showed that the tetragonal-ZrO2 fraction in the oxide film w as lower with irradiation than without it, especially for the near sur face area. The water radiolysis species accelerated the dissolution of the oxide film, especially film on the alloy with lower nodular corro sion resistance. This dissolution led to the lower tetragonal-ZrO2 fra ction and was considered to be one of the factors causing a localized breakdown of the barrier oxide film to make the nodular oxide. (C) 199 7 Elsevier Science B.V.