Corrosion of Studsvik R2 AlMg3.5 Alloy Under Simulated Cementitious Repository Conditions in Fly Ash Concrete Compared to Ordinary Portland Cement Concrete

Decommissioning of research reactors leads to significant amounts of low- and intermediate-level radioactive waste that is planned to be stored under cementitious conditions in Swedish repositories. These materials contain important amounts of aluminum and its alloys which are reactive under alkaline conditions found in concrete pore water. The corrosion produces hydrogen that can lead to cracks in the concrete which can be pathways for radioactive ions. As an attempt to optimize repository conditions for aluminum-based reactor waste, parts of the ordinary Portland cement I in the concrete were replaced by fly ash. This addition may reduce pH and alkali–carbonate reactions increase the durability of the concrete. Testing of fly ash concretes is also of interest from a future availability perspective given the potential phase out of ordinary Portland cement in favor of formulations such as fly ash variants with lower CO2 emissions. Decreased corrosion rates, more uniform corrosion accompanied by ATR-FTIR (Attenuated Total Reflectance—Fourier Transform Infrared Spectroscopy) spectra and µCT (Micro computed tomography) as well as SEM-EDX (Scanning Electron Microscopy with Energy Dispersive X-ray analysis) images suggest less aggressive corrosion of the Al alloy from the decommissioned Studsvik R2 reactor in concrete with varying amount of fly ash replacement.