Application of archaeological analogues for a repository safety case: arguments supporting the waste container lifetime

In the Japanese HLW safety case, a carbon-steel container (overpack) was designed to have a 1 000 year lifetime, based on a corrosion allowance of 40 mm derived from laboratory data obtained under anaerobic conditions. Analogue studies have been conducted to increase confidence in the robustness of this design basis. Using X-ray computer tomography (X-CT) to measure corrosion rate, around 40 samples of archaeological iron artifacts were analysed; these were found at ancient Japanese monuments and had been buried underground for periods of several hundred to one thousand years. The corrosion rates are more than one order of magnitude less than the design allowance of 40 mm/ka, which supports the argument that the designed corrosion allowance is conservative. (authors)