Corrosion Behavior of Magnesium Alloys in Alkaline Solutions Simulating a Low‐Level Radioactive Waste Repository

Magnesium alloys have excellent oxidation resistance and have been used as fuel cladding materials of gas‐cooled reactors. In Japan, some parts of fuel cladding are stored as low‐level radioactive waste. To investigate the feasibility of disposing of magnesium alloys as solid radioactive waste embedded in cementitious matrices, the corrosion behavior of two types of magnesium alloy was evaluated in an alkaline solution at temperatures ranging from 15°C to 40°C. It was clarified that the corrosion rate decreased with increasing immersion time because brucite with low solubility or hydrotalcite was formed on the specimen surface as a protective film. This protective film maintains the corrosion resistance even when environmental changes (drying and liquid level fluctuations) occur. The estimated corrosion depth of the two magnesium alloys in cement equilibrium water at pHs 12.7–12.8°C and 15°C over 10 000 years ranged from 0.1 to 11 mm. The corrosion behavior is affected by pH and temperature. Over the ranges of test conditions, the corrosion rate decreases with decreasing temperature or increasing pH. In cement equilibrium water at 15°C, brucite or hydrotalcite is formed.