THE EFFECTS OF DISSOLVED OXYGEN DEPLETION ON BWR EXTERNAL SAMPLE LINE ECP MEASUREMENTS AND THE NEED FOR DISSOLVED OXYGEN ADDITION

摘要

Electrochemical corrosion potential (ECP) measurements in a Mitigation Monitoring System (MMS) ECP manifold have historically been a primary indicator of the effectiveness of an On-Line NobleChem (OLNC) application, with the MMS ECP intended to measure the catalytic effect of platinum deposited on the ECP manifold surface. In some plants ECP measurements made on untreated surfaces prior to an OLNC application were significantly lower than what would be expected for stainless steel under reactor bulk chemistry conditions. In certain cases the ECP measurements were so low that no discernible change was observed during and following the OLNC application. It has been concluded through analysis that the likely cause of the low ECP prior to the OLNC application was the absence of dissolved oxygen (DO) in the bulk liquid at the ECP measurement location, affecting the ability to confirm noble metal deposition. The depletion of oxygen along the supply line is controlled by the same recombination mechanisms for the suppression of oxidizing species via hydrogen addition. Recent proof-of-concept studies demonstrate how the injection of an oxygen-rich stream to the MMS sample water (DO Addition) can be used to reestablish the capability of external ECP measurements to monitor the catalytic behavior of platinum deposited during an OLNC injection.