Assessing microbially influenced corrosion of titanium as novel canister material for geological disposal facilities

Abstract

In response to the growing global inventory of nuclear waste and the urgent need for secure long-term disposal solutions, geological disposal facilities (GDFs), also known as deep geological repositories, are being pursued worldwide. Several national programmes, including those in the UK, Japan, and Canada, are evaluating corrosion-resistant alloys for waste canisters. Among these, novel materials such as titanium alloys have emerged as promising candidates due to their protective TiO2 films. However, the threat of microbial corrosion under repository-relevant conditions remains highly unexplored. To address this, titanium discs (grade 2, ASTM B348) were incubated in bentonite slurries with synthetic pore-water at 30 °C and 60 °C under strictly anoxic, dark conditions, mimicking deep underground GDF environments. Electron donors (acetate, lactate) and an electron acceptor (sulphate) were added to stimulate microbial activity and assess long-term canister performance. All titanium samples retained an intact TiO2 layer with no detectable pitting or localised damage. Microscopic (SEM) and spectroscopic (XPS) analyses showed slight thinning of titanium oxide films and microbial presence co-located with bentonite, but no evidence of corrosion products or metal loss. Micro-FTIR showed functional groups associated with microbial presence (proteins, lipids, and polysaccharides) in the bentonite, but not on titanium surfaces. The experimental design aimed to promote bacterial activity by simulating worst-case GDF biotic conditions. These findings demonstrate titanium’s exceptional stability against microbially influenced corrosion (MIC) in stimulated GDF-like environments. This study supports the structural viability of titanium canisters for nuclear waste disposal and underscores the importance of considering microbial factors in long-term corrosion assessments.