As the United States reconsiders old policies on nuclear power, the problem of storing nuclear waste still looms large. And, because nuclear waste still remains radioactive long after its original users have left the scene, it's imperative to store it in containers that are not only secure but which also can be monitored reliably. Since even the most resilient waste storage containers corrode over time, deterioration rates must be monitored. Engineers have found a way to accurately monitor the corrosion of nuclear waste storage tanks: measuring their electrochemical noise.

Nuclear waste is stored at various sites in the U.S., including the Hanford nuclear waste site in Washington State. At Hanford, 177 storage tanks constructed out of welded steel contain a staggering 253 million liters of nuclear waste. To determine the corrosion rates of these tanks, engineers first tried dipping steel coupons into them. Unfortunately, these coupons did not provide good readings because of the difficulty duplicating conditions to establish accurate corrosion rates. Taking actual samples of the waste for laboratory analysis proved just as unreliable a measure.

It was not until engineers developed a probe to measure the current and voltage generated by electrochemical reactions inside the tank that they could get an accurate handle on the corrosion rate. This electrochemical noise - as the phenomenon is called - provides the most accurate means yet of determining storage tanks' rates of corrosion. According to the Hanford site's engineers, "Time-dependent fluctuations in corrosion current and corrosion potential between the electrodes are analyzed and accurately correlated to the rates of corrosion."

In addition to measuring the actual corrosion, the noise-reading probe indicates how much of a corrosion inhibitor, such as sodium hydroxide, the site's engineers should add to the tanks. The accuracy of this information is of great importance. Knowing the optimum amount of an inhibitor can save a lot of money. Since adding an improper quantity of sodium hydroxide can result in sodium addition, avoiding a misapplication is a high priority. To call sodium addition costly would be an understatement. If this situation were to occur rectifying it could cost from $750,000 to $1.2 million per ton of sodium in the waste. The use of the electrochemical probe for the purpose of indicating a proper inhibitor level alone makes it worthwhile.

Source: Electrochemical Noise Tells the Story
InTech, Nov. 15, 2001
http://www.isa.org/journals/intech/1,1110,0,00.html