Our group have supposed that a corrosion rate of an overpack made of carbon steel is controlled with a diffusion rate of water in iron-oxide film formed on the overpack during the long-term storage in the deep-underground.  Therefore, it was tried to estimate a diffusion coefficient of water in iron-oxide films of Fe₃O₄ or Fe₂O₃.  The oxide films were formed on the iron plate specimens by being heated in air at various temperatures.  D2O solution was contacted to the film on the specimen in the sealed container for a given time.  The amount of D₂O penetrating in the film was determined  by a quadrupole mass spectrometer with heating system.  As a result, it was found that an amount of D₂O increased with an increase in a root of a contacting time, and was finally a constant.  The finding suggested that D₂O penetrated on the diffusion process, and then the data were analyzed on the basis of Fick's law to estimate a diffusion coefficient of D₂O in the oxide film.  The estimated values were 9.5 x 10^-13 cm² s^-1 for the Fe₃O₄ film and 5.4 x 10^-13 to 2.1 x 10^-12 cm² s^-1 for the Fe₂O₃ film.

overpack, corrosion, diffusion coefficient, heavy water, magnetite(EFC Members) 7th International Workshop on Long-term Prediction of Corrosion Damage in Nuclear Waste Systems (LTC 2019)