Controls on the solution chemistry are in place to prevent the initiation and propagation of pitting and stress corrosion cracking in high level waste (HLW) 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 reducing the minimum molar nitrite concentration required to confidently inhibit pitting. The experimental results and conclusions provided herein will support a statistical basis to quantify the probability of pitting for the tank wall, when exposed to various solutions containing dilute concentrations of nitrate and nitrite. Coupon testing was performed within the framework of the statistical test matrix to determine the pitting propensity associated with inhibitor concentrations. The visual observation results indicate a potential for inhibitor reductions without consequence in the solution space. The majority of corrosion occurred at the interface of the solution and vapor space. Only one sample with the dilute concentration of both nitrate and nitrite exhibited visible pitting in the solution space.
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