Probability-Based Corrosion Control for High Level Waste Tanks

Controls on solution chemistry are in place to prevent the initiation and propagation of pitting and stress corrosion cracking in high level waste tanks.  These controls are based upon a series of experiments performed using simulated solutions on materials used for construction of the tanks, namely ASTM A537 carbon steel.  An experimental program was undertaken to investigate the risk associated with reducing the minium molar nitraite concentration required to confidently inhyibit pitting in dilute solutions.  Electrochemical and coupon testing were performed within the framework of the statistical test matrix to determine the pitting propensity associated with inhibitor concentrations.  The experimental results and conclusions provide a statistical basis to quantify the concentrations of nitrate and nitrite.  Understanding the probability for pitting will allow the facility to make tank-specific risk-based decisions for chemistry control.