Natural analogue; Learning long-term phenomena from nature

Mitsui, Seiichiro  ; Kawakita, Ryohei  ; Ishidera, Takamitsu 

Evaluation of geological disposal deals with long-term time scales of hundreds to tens of thousands of years. On the other hand, our experiments are limited to about 20 years at the longest, and it is possible that the long-term phenomena assumed in geological disposal have not been sufficiently simulated. Regarding the corrosion behavior of carbon steel overpacks, the corrosion depths over time in immersion tests for several to ten years can be approximated by a power law. From the fact that a protective corrosion product film, such as siderite, was observed on the surface of the test piece, it is believed that this can be explained by the passive effect of the corrosion product film on the corrosion reaction. However, the effect cannot be applied to the long-term corrosion behavior based solely on the results of immersion tests. Through natural analogue studies, we concluded that the passive effect of the corrosion product film can explain long-term corrosion behavior exceeding hundreds of years.