Study on Water Chemistry and Temperature Adaptability of CZ Zirconium Alloy

Abstract

The corrosion behavior of zirconium alloys is closely related to the water chemistry and operating temperature of the primary circuit. The increase of operating temperature, Li concentration and pH value will have a significant negative impact on the corrosion behavior of zirconium alloy. Autoclave corrosion tests of CZ and Zr-4 alloys were carried out under different water chemistry conditions (Li concentration and pH300 were 3.5ppm/7.2, 4.5ppm/7.2, 4.5ppm/7.5, 7ppm/7.5 respectively) and temperature conditions (360 °C, 400 °C, 430 °C, 450 °C, 500 °C). The effects of different temperature and water chemistry conditions on the corrosion rate of different zirconium alloys were obtained and the information of oxide film thickness and hydrogen content of different samples in different corrosion stages were obtained to study the temperature and water chemistry adaptability of zirconium alloys. The experimental results show that breakaway corrosion and nodule corrosion occur in Zr-4 alloy above 430 °C, and the thickness of oxide film and hydrogen absorption increase significantly. However, the corrosion law of CZ alloys keep the same from 360 °C to 500 °C, and there is no breakaway corrosion or nodule corrosion. The relationships between corrosion rate and temperature accord with Arrhenius formula, showing good temperature adaptability. Under relatively severe water chemistry conditions (Li concentration and pH300 are 4.5 ppm and 7.5 respectively), the corrosion rate of various zirconium alloys does not increase obviously, and there is no nodule corrosion phenomenon. The increase of oxide film thickness and hydrogen absorption capacity is not obvious, showing good water chemistry adaptability.