BIOFOULING AND BIOCORROSION IMPACTS ON TITANIUM CANISTER DURABILITY IN DEEP GELOGICAL REPOSITIORIES

Abstract

Nuclear waste is a byproduct of nuclear power generation. It consists of materials that have become radioactive or have been contaminated by radiation, and it is categorised, based on its level of radioactivity, as: low-level waste (LLW), intermediate-level waste (ILW), and high-level waste (HLW). Deep Geological Repositories (DGR) are a possible solution for the safe disposal of radioactive waste. Several materials including titanium could be used for the canisters that will contain the nuclear waste in the DGR. It is then important to understand the biofouling and biocorrosion of titanium canisters. The following research aims to evaluate the impact of microbial activity on titanium’s corrosion resistance, focusing on the role of sulphate- reducing bacteria (SRB) and their effect on the integrity of titanium in anaerobic environments. To investigate all the possible environmental conditions three distinct microcosms were created for the experiment that reflects the possible environmental conditions in the DGR. This included BeD microcosm (bentonite only), BeDaC microcosm (bentonite with aerobic bacterial consortia), and BeDanC microcosm (bentonite with anaerobic bacterial consortia) with electron donors (acetate and lactate) and an electron acceptor (sulphate) infused in all three microcosms. Following this, several analytical techniques were used to assess changes in the chemical composition of the titanium discs and surrounding liquids. IC results indicated higher sulphide production in the BeDanC microcosms, correlating with the activity of SRB. Whereas the BeDaC and BeD microcosms exhibited less sulphate reduction, showing that the respective microcosm conditions limit the sulphide production and therefore the threat of MIC. XPS analysis confirmed significant degradation of the protective titanium oxide layer (TiO2) in BeDanC samples, particularly at 30°C, where the SRB was most active. Visual inspections further supported these findings, with BeDanC samples showing darker supernatant colours after two months. In addition, the visual observation of the titanium discs showed the highest visible degradation effect on the discs collected from the BeDanC microcosms. In presence of aerobic microorganisms, titanium was more resistant to corrosion than in the presence of anaerobic consortia subjected to microbial influenced corrosion (MIC).