ICONE11-36553 BWR SCC Mitigation Strategies and their Effectiveness

Abstract

Intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) internals materials is a well understood phenomenon. The degree of stress corrosion cracking (SCC) varies from plant to plant depending on weld heat affected zone residual stresses and the operating water chemistry history of each plant. Since late 80's plants have paid significant attention to reactor water chemistry control and have seen the beneficial effect of reduced incidents of SCC as a result of good water chemistry control. In addition to water chemistry control plants have also attempted to lower the electrochemical corrosion potential (ECP) of internal surfaces by employing hydrogen water chemistry (HWC) to reduce the propensity of materials to undergo SCC. Majority of the BWRs worldwide have employed HWC to mitigate IGSCC of reactor internals. Recently, 70% of US BWRs and four International BWRs have employed NobleChem TM technology to improve the effectiveness of hydrogen to lower the ECP. This paper highlights some of the shortcomings of the SCC mitigation practices that need further attention to derive the full benefit of HWC and other mitigative actions against IGSCC.