Strategic Research: In-Tank Generation of Corrosion Inhibitors

Prevention of stress corrosion cracking and pitting corrosion in high-level waste (HLW) tanks requires the periodic addition of corrosion inhibitors, sodium hydroxide and sodium nitrite. These inhibitor ions can be generated electrochemically from the nitrate present in the waste. Thus, a continuously operated electrochemical reactor placed in the top of the tank could generate nitrite and hydroxide. In-tank generation would eliminate the need to continually add process chemicals resulting in cost savings associated with the procurement, pretreatment and disposal of these chemicals. Experiments examined whether both nitrite and hydroxide could be generated simultaneously from a simple waste simulant in a single electrolytic cell. Results indicated that hydroxide, but not nitrite, formed at a rate that would be effective for in-tank generation. Nitrate reduction proceeded beyond the production of nitrite to produce other nitrogen-containing products. We recommend additional testing to identify an optimum cathode material for nitrite production. Alternatively, the in-tank generator may feature a divided cell configuration or dual electrochemical cells in which one cell generates hydroxide and the second cell generates nitrite