Humid-air and aqueous general and pitting corrosion models (including their uncertainties) for the carbon steel outer containment barrier were developed using the corrosion data from literature for a suite of cast irons and carbon steels which have similar corrosion behaviors to the outer barrier material. The corrosion data include the potential effects of various chemical species present in the testing environments. The atmospheric corrosion data also embed any effects of cyclic wetting and drying and salts that may form on the corroding specimen ' surface. The humid-air and aqueous general corrosion models are consistent in that the predicted humid-air general corrosion rates at relative humidities between 85 and 100% RH are close to the predicted aqueous general corrosion rates. Using the expected values of the model parameters, the model predicts that aqueous pitting corrosion is the most likely failure mode for the carbon steel outer banier, and an earliest failure (or initial pit penetration) of the 100-mm thick barrier may occur as early as about 500 years if it is exposed continuously to an aqueous condition at between 60 and 70°C.The current design concept of a multi-barrier waste container for the disposal of the nation's high-level nuclear waste in the potential repository at Yucca Mountain, Nevada, calls for a thick layer (about 100 mm) of carbon steel corrosion-allowance material (CAM) as the outer barrier, and a thin layer (about 20 mm) of Alloy 825 corrosion-resistant material (0 as the inner barrier. The initial post-closure near-field environment of the potential repository will be hot and dry, and following the peak temperature period, the near-field environment would cool down gradually. Thus, the waste containers are expected to undergo humid-air corrosion initially at elevated temperatures, and their corrosion mode w i l l gradually shift to aqueous corrosion as the near-field environment continues to cool down to lower temperatures and more humid conditions. This paper discusses the general and pitting corrosion models for CAM in humid-air and aqueous conditions, which were developed for the total system performance assessment-1995 (TSPA-1995) [l]. The models will be improved (or refined) as more site-relevant corrosion data become available. HUMID-AIR CORROSION MODELS. . ata C w A total, of 166 atmospheric corrosion data (up to 16 years) of cast irons and carbon steels which have similar corrosion behaviors to the candidate CAM were collected from literature.
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