Processing of nuclear materials for either military or civilian purposes generates waste products. The nuclear wastes are generally stored in plain carbon or stainless steel underground tanks. Corrosive wastes are inhibited to minimize the corrosion of these tanks and maintain tank structural integrity under normal and off-normal conditions. Storage tanks have fairly static conditions, although processing of the waste in these tanks to more stable forms will produce dynamic conditions, which may lead to localized corrosion. Corrosion monitoring under either condition, therefore, would ensure that inhibitive conditions are maintained.

A preliminary investigation was conducted to evaluate electrochemical noise measurements for corrosion monitoring of waste tanks. The initial results indicated that current and potential noise correlate to the solution corrosivity. Further development is necessary to differentiate among the various forms of corrosion.

Electrochemical noise measurements were made in the laboratory with plain carbon steel electrodes under simulated conditions for storage and processing of nuclear waste. Coupons were also exposed in the laboratory test vessels. The primary aggressive species of the waste was the nitrate anion, which induces pitting. The simulated waste was initially inhibited with sodium nitrite and sodium hydroxide. The nitrate concentration was increased over the test period to increase the corrosivity of the solution. The temperature was held constant at 40°C.

The current and potential noise showed an increasing trend with nitrate concentrations. Under inhibited storage conditions, the noise data were fairly stable. Inspection of the electrodes revealed little general corrosion with minimal pitting. The coupons, however, had a significant amount of pitting. This difference was attributed to the microstructure of the electrodes and coupons.