Corrosion behavior of aluminum alloy 5754 in cement‐based matrix‐simulating nuclear waste disposal conditions

Abstract

Depending on the lifetime and level of radioactivity of radioactive wastes, different disposal facilities are considered. Though low‐ and intermediate‐level short‐lived waste can be disposed in surface disposal facilities, deep geological disposal is considered for high‐ and intermediate‐level long‐lived waste. In France and Belgium, long‐term disposal is studied in clay host rock media. For aluminum, the disposal concept is based on encapsulation of the waste in a cement‐based matrix. It is also well‐known that aluminum is prone to severe corrosion in sufficiently alkaline environments leading to possible hydrogen production. To ensure the safety of the disposal facilities and the integrity of the cement capsules, the amount of aluminum that is disposed in each waste package must be specified and is limited to mitigate the level of hydrogen production by aluminum corrosion. In the present study, the corrosion resistance of an aluminum alloy (grade EN‐AW‐5754/H111) in two different cement matrices was studied in different configurations at room temperature. In each case, the evolution of hydrogen production was monitored to address the corrosion rate variation versus time.

Corrosion of aluminium in ordinary Portland cement paste: Influence of matrix porosity and the presence of LiNO3 corrosion inhibitor

“…Figure 5 shows the evolution of the corrosion rate in function of time for the different samples studied in this study. As already mentioned elsewhere, [9,11,35,36] the corrosion rate decreases with time for all studied systems and reaches a steady state after ~20 days. This also confirms the trend obtained from the evaluation of the EIS measurements.…”

“…Those holes could be due to the formation of the CPL taking up a much larger volume (because of its lower mass density) than metallic aluminium, leading to stresses in the cement matrix. Hydrogen generation during the corrosion process of aluminium contributed also to the creation of internal stresses, [ 9,10 ] such as the cracks observed in the inset of Figure 4. Needle‐like phases are also observed in the cement paste of all samples (only shown for OPC‐0.36Li, Figure 6b).…”

“…The natural oxide layer formed on the aluminium surface is amphoteric and, therefore, not resistant to corrosion when brought in contact with the highly alkaline cement pore water because the protected oxide film dissolves to form, for example, aluminium oxides and hydroxides, with the liberation of hydrogen gas. [4][5][6][7][8][9] As a consequence of this phenomenon, the corrosion products will take up a larger volume compared to the original metal, leading to an increase of the internal stresses and damage of the matrix. [9,10] To decrease these problems, different methods can be used.…”

“…[4][5][6][7][8][9] As a consequence of this phenomenon, the corrosion products will take up a larger volume compared to the original metal, leading to an increase of the internal stresses and damage of the matrix. [9,10] To decrease these problems, different methods can be used. First, lowering the pH of the cement pore water and/or reducing available free water reduces the reaction of aluminium in the cement matrix.…”

Design of the third-generation neutron spallation target for the CERN’s n_TOF facility

“…In view of the final target disposal, the use of aluminum over steel for the target vessel would offer reduced activation and residual dose rate, but lead to additional constraints that would cancel these benefits. Chemical reactions may happen between aluminum and the concretebased mortar used to prepare the waste, producing hydrogen gas that may damage the package in the longterm [43,44]. For this reason, it was decided to limit the amount of aluminum in the new target and to build the new vessel in stainless steel.…”