Corrosion Rate of Carbon Steel in Compacted Bentonite Environment with Low-Oxygen Concentration: Round Robin Test for Standardization of Measurement Method

Abstract

A subcommittee of the Japan Society of Corrosion Engineering works to establish the test methods for evaluating the corrosion behavior of the metals potentially used for the canisters of high-level radioactive waste. As a part of this work, a standard test method was developed to measure the corrosion rate of carbon steel in the compacted bentonite with low oxygen concentrations, which corresponds to an environment long after the closure of the disposal site. In order to clarify the reproducibility and accuracy of the developed test method, round robin tests were carried out at three laboratories. A total of 15 specimens were immersed for 6 months in the compacted bentonite infiltrated with artificial seawater, and their corrosion rates were measured from the mass loss. All the measured corrosion rates followed a normal distribution, and the variation was within ±2σ; these results suggest that tests according to this standard method could give highly reproducible results without significant systematic errors. The absolute value of 3σ of the measured corrosion rate was less than 10％ of the mean; this result means the accuracy of the measured rates was up to 10％ with 99.7％ probability, suggesting that tests using this standard method could give reasonably accurate results.