Localized Corrosion Risk of 316L Stainless Steel in Deep Geological Repository Environment

Abstract The concept of the Czech deep geological repository (DGR) design of the waste disposal package for spent nuclear fuel includes a stainless-steel inner case. This study investigated the localized corrosion resistance of austenitic stainless steel 316L under simulated DGR conditions, focusing on the synergistic effects of sulfate-reducing bacteria (SRB) and radiolysis. These factors are difficult to predict and may pose risks to long-term material integrity. Exposure tests were conducted in bentonite suspensions with or without SRB promotion, and control samples were tested without bentonite. Samples were incubated under anaerobic conditions (6% H 2 /94% Ar) and subjected to various stressors, such as temperature (up to 60 °C), irradiation, and the presence of oxidizing agents generated by bacterial metabolism and radiolysis of water. At elevated temperatures and in the presence of thiosulfates, metastable pits were initiated that could either repassivate or evolve into stable defects. SRB appeared to promote pit propagation, while thiosulfates compromise the integrity of the passive layer integrity. Over time, biofilm formation likely reduced corrosion propagation by limiting metal exposure. Localized corrosion was especially evident above 40 °C, indicating temperature as a critical factor. These findings emphasize the need to maintain repository temperatures below this threshold to ensure long-term canister durability.