Screening of Six Different Potential HLRW Canister Materials Surrounded by Bentonite

Most countries seeking strategies for the disposal of high-level nuclear (HLW) waste envisage the use of metallic
containers. In some deep geological repositories, the canister will be in contact with bentonite. Different types of metals
were tested so far with ambiguous results. Consistent data are available for copper and carbon steel. Different performances, however, were reported for stainless steel. In the present study six different alloys were tested: three iron-matrix alloys with different carbon contents and grain sizes, a copper-nickel alloy, zirconium, and stainless steel. They were immersed with water saturated bentonite for 10 months at 23°C under anaerobic conditions. Corrosion was assessed gravimetrically and using electron- and X-ray microscopy. Stainless steel did not show any reaction with the bentonite despite its widespread classification as disadvantageous because of its susceptibility for local corrosion at low pH and high Cl- concentrations. Many studies using stainless steel, however, were conducted with simulating bentonite pore waters but without contact with bentonite which meanwhile is known to buffer both pH and redox potential (Eh).
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The promising results of the stainless-steel corrosion tests in the present study encourage further systematic investigations to improve the predictability of stainless-steel performance as HLW canister material surrounded by bentonite.