LOMIR: Long-Term Monitoring of C-14 Compounds Released During Corrosion of Irradiated Metal

Project Dates: 1/01/2022 – 31/12/2024

Project Status: Ongoing

Project Website: N/A

Carbon-14 is a dose-determining radionuclide released during the corrosion of irradiated steel in a repository environment. Knowledge of the chemical forms of the ¹⁴C-bearing carbon compounds released during corrosion in highly alkaline anoxic conditions and the relation between the ¹⁴C release and steel corrosion rates is required to support safety assessments for a cement-based repository.

The CAST project addressed the release mechanisms of carbon-14 from radioactive waste materials under geological disposal facility conditions.  The LOMIR project continues the steel corrosion experiment initiated in May 2016 by the Laboratory for Waste Management (LES) at the Paul Scherrer Institute (PSI) in the framework of the CAST project.

The corrosion experiment in question focuses on two activated ~1 g steel nut specimens provided by Gösgen nuclear power plant (KKG). The specimens are mounted in a gas-tight reactor and immersed in artificial cement porewater (pH = 12.5) and have a well characterised ¹⁴C inventory. The LOMIR project supports a continuation of the sampling campaign for this experiment over the three years of the project.

The overall objective of the LOMIR project is to extend the duration of the PSI irradiated steel corrosion experiment for a further three years to provide essential information on ¹⁴C speciation in support of safety assessments for deep geological repositories. The specific objectives of the project are:

• to test the hypothesis of an increase in the concentrations of ¹⁴C-bearing gaseous compounds driven by progressing corrosion of irradiated steel;
• to quantify the ratio between ¹⁴C carried by gaseous species and ¹⁴C carried by water-soluble organic and inorganic carbon compounds with time;
• to relate the release of ¹⁴C-containing carbon compounds to the corrosion process (production of H₂), allowing in a longer term to determine the ¹⁴C production in the repository based on the corrosion rate of steels; and,
• to quantify the retention of ⁶⁰Co during the corrosion of steel.