Corrosion behaviour of container candidate materials for HLW disposal in granite-bentonite media

An extensive laboratory program is being carried out in order to evaluate the corrosion behavior of candidate container materials for the deep geological disposal of High Level Waste (HLW)^(1-5). According to the Spanish multi-barrier concept for granite site, in which canisters are surrounded by compacted bentonite blocks, the corrosion behavior of various proposed container materials in saturated bentonite with granite water has been assessed. The studied materials have been S355 carbon steel, AISI 316L stainless steel, electrolytic copper and Cu30Ni alloy. Specimens from these alloys have been placed in saturated bentonite and tested at different temperatures and times. General corrosion rates and penetration data based on metallographic examinations have been obtained together with the analysis of the corrosion products generated during the test. S355 carbon steel shows the higher general corrosion attack, with average corrosion rates of 10 μm per year when tested at 100 °C. The main corrosion product for carbon steel has been siderite, FeCO₃. At 25 and 50 °C, corrosion products with a high sulfur content are observed, thus indicating a microbiologically corrosion phenomena due to bacteria present in the bentonite. No corrosion attack has been observed in AISI 316L stainless steel samples. Good corrosion resistance have been shown by cooper and Cu30Ni, with general corrosion rates below 1 μm/year after being tested at 100 °C for 18 months.