NOBLE METAL CHEMICAL ADDITION FOR IGSCC MITIGATION OF BWRs - FIELD SUCCESSES

摘要

Noble metal chemical addition (NMCA) technology has been successfully used to improve the efficacy of hydrogen water chemistry (HWC) in mitigating intergranular stress corrosion cracking (IGSCC) of BWR internals. The use of NMCA technology in combination with low levels of feedwater hydrogen enables to achieve the IGSCC mitigation potential of-230 mV(SHE) of boiling water reactor (BWR) internals without the undesirable operating dose rate increases due to partitioning o f N 16 into the steam phase. NMCA is a simpler method of applying noble metal on to BWR internals surfaces using reactor water as the transport medium which causes the deposition of noble metal from solution onto all wetted surfaces. This approach has successfully decreased the electrochemical corrosion potential (ECP) of surfaces below -230 mV(SHE), prevented crack initiation and mitigated crack growth rates in stoichiometric excess hydrogen in simulated boiling water reactor (BWR) environments. The technology is being currently used in eight operating BWRs in the United States. One BWR has completed two cycles (36 months) of plant operation after NMCAwhile a second BWR has completed more than one year of operation with no identified side effects. This paper describes the field successes from NMCA treated BWRs in achieving the HWC specification potential under low HWC conditions with no long-term increase in operating dose rates.