Factors Affecting the Stress Corrosion Cracking Susceptibility of Zirconium in 90% Nitric Acid

U-bend, C-ring, and slow strain rate tests were performed to evaluate the effects of texture, stress, surface condition, heat treatment, electrochemical potential, and strain rate on stress corrosion cracking (SCC) of zirconium in 90% nitric acid at room temperature. Careful control of texture, surface condition (scratching, cleaning, and oxide coating), and/or applied stress was shown to effectively lead to the prevention of SCC of zirconium in 90% HNO3. Heat treating at 760, 880, or 1000 C does not seem to improve the SCC resistance. However, if the potential of zirconium is maintained at 500 mVSCE or lower, or 200 ppm of HF is added, zirconium's SCC susceptibility in 90% HNO3 is eliminated. When adding HF, zirconium sponge must also be added to avoid high corrosion rates. The mechanism for SCC of zirconium in 90% HNO3 is apparently stress-assisted local anodic dissolution, based on the fractography, strain rate, and electrochemical potential dependence of the cracking.