| Budget Amount *help |
¥7,500,000 (Direct Cost: ¥7,500,000)
Fiscal Year 2001: ¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 2000: ¥4,800,000 (Direct Cost: ¥4,800,000)
|
|---|
| Research Abstract |
High-level radioactive waste is planned to be buried deep underground, i.e. geological isolation. Carbon steel is one of the candidate materials for an overpack, which is metallic container to prevent the high level radioactive waste from contact with groundwater for long period. Although the overpack material is supposed to be exposed to oxygen free and very week corrosive environment, corrosion monitoring is necessary for very long term safe keeping. In this work, the effect of various ionic species, which may exist in the geological isolation environment, on the corrosion rate of carbon steel, and possibility of the assessment of the very low corrosion using electrochemical noise analysis are investigated in order to establish reliable and simple corrosion monitoring system in the environment.
The corrosion behavior of SM400B carbon steel was analyzed in terms of the effect of sulfate, carbonate and bi-carbonate ions. SM400B exhibited two anodic peaks the height of which were roughly
… More
proportional to the equivalent bi-carbonate ions concentration. On the other hand sulfate did not affect the general corrosion rate. Sulfate ions, however, promoted pitting corrosion, whereas carbonate and bi-carbonate ions suppressed. Sulfate ions were also observed to be reduced at the corrosion potential of carbon steel. Therefore, sulfate ions were proved to act as oxidant for corrosion of carbon steel in the oxygen free environment.
Three coupons of SM400B were immersed in de-aerated bi-carbonate aqueous solution. The current and potential between these coupons were measured, fluctuation of them were converted into power spectrum in frequency domain. Power density at lower frequency of current, potential, and the apparent corrosion resistance, which was obtained as the division of fluctuation of potential and current, exhibited good correlation with corrosion rate which was also measured by polarization curve. The correlation coefficient between corrosion rate and power density of current fluctuation at 3 mHz attained to 0.8〜0.9, which is sufficient reliability for corrosion rate monitoring. Therefore, it is concluded that noise power density of current fluctuation between two coupons is possible to be adopted for corrosion monitoring of carbon steel in the geological isolation environment. Less
|
