IN-PROCESS ELECTROCHEMICAL CORROSION POTENTIAL MONITORING EXPERIENCE AT BOILING WATER REACTORS UTILIZING ON-LINE NOBLECHEM™ FOR MITIGATION OF INTERGRANULAR STRESS CORROSION CRACKING

摘要

Reduction of electrochemical corrosion potential (ECP) of Boiling Water Reactor (BWR) vessel and internals is essential for mitigating intergranular stress corrosion cracking (IGSCC). Hydrogen water chemistry in moderate concentrations (HWC-M) or at reduced injection rates with noble metals are IGSCC mitigation strategies employed by BWRs. In-vessel lower plenum ECP measurements have been obtained during operating conditions for BWRs utilizing normal water chemistry, HWC-M and NMCA. ECP monitoring for BWRs with OLNC has mainly been performed using probes mounted in external piping in contact with reactor coolant sample streams. The chemistry conditions and radiolysis effects at these locations are typically not as aggressive as in the lower vessel head region, where no direct in-vessel ECP measurements have previously been made during an OLNC injection. Brunswick 1 has utilized HWC-M as a mitigation strategy for protection of IGSCC since 1989. Two platinum ECP electrodes and a pre-oxidized stainless steel billet were installed in a modified local power range monitor (LPRM) during the 2014 refueling outage, and a HWC benchmark test was performed while operating under HWC-M. In August 2014, the station transitioned to On-Line NobleChem™ (OLNC). This paper will present the industry-first lower plenum in-vessel ECP measurements prior to and during the transition from HWC-M to OLNC. It will also summarize BWR experiences at plants utilizing OLNC with in-process ECP monitoring at reactor recirculation piping and bottom head drain line locations.