Improved electrodes for BWR in-plant ECP monitoring

In January 1978, NWT Corporation was contracted to obtain electrochemical potential (ECP) measurements of 304 stainless steel during exposure to reactor water at the Vermont Yankee boiling water reactor (BWR). Since existing electrode technology was inadequate for long term BWR ECP monitoring, NWT developed designs of measuring and reference electrodes to facilitate such measurements. The reference electrode is basically a silver/silver chloride electrode enclosed in a solid Teflon chamber filled with saturated silver chloride aqueous solution, and connected to the solution of interest through a liquid junction. The electrodes were qualified in a laboratory test facility to 2880C (5500F). Subsequent evaluation at Vermont Yankee demonstrated that the reference electrode was stable, resistant to thermal cycling, reproducible, interchangeable, and durable. One reference electrode performed satisfactorily for over 21 months (19 months at 2700C) in the Vermont Yankee reactor water cleanup system. Routine long-term ECP monitoring in BWR reactor water systems is now achievable with the new electrodes