A Sampling Method and Data Evaluation of Archaeological Samples to Support Long-Term Corrosion Prediction

Natural analogs for the long-term corrosion behavior of overpack materials, such as carbon steel data concerning the extent of corrosion from archaeological iron artifacts buried in soil, provide useful information as supporting evidence for the safety assessment of nuclear waste disposal. Although a lot of corrosion data are necessary to guarantee the validity of the long-term behavior, archaeological samples are invaluable but difficult to analyze. The purpose of this study was to investigate the corrosion behavior of an iron plow surrounded by soil excavated from Oda Castle in Japan. Usually, archaeological samples are excavated and removed carefully from the soil using a small brush and shovel; therefore, the environment around the sample, e.g., redox condition, changes during sampling. We non-destructively measured the thickness of rust of the iron sample in the soil itself using x-ray-computed tomography (x-ray CT) without contact with the atmosphere and analyzed various chemical components and microorganisms. The results show the corrosion environment of the sample was slightly oxidizing. The data were compared with other data from archaeological samples from 19 remains examined by Japan Atomic Energy Agency (JAEA, Ibaraki, Japan).