Effect of zinc on corrosion product release behavior under PWR primary system conditions

Testing has been performed by various organizations over time to measure corrosion product release rates in the presence of ppb-levels of dissolved zinc under different PWR primary system chemistry conditions. These conditions include variations in zinc concentration and other coolant chemistry parameters, and testing on oxidized and non-oxidized specimens of various base metals. This paper reports the results of a project to compile and evaluate available data to determine whether sufficient data exist to elucidate the fundamental behavior of zinc with respect to oxide formation, oxide modification and concentration of corrosion products in the coolant as a function of zinc exposure levels and time. This evaluation included laboratory data generated by EDF (e.g., Boreal loop testing), EPRI, Nuclear Steam Supply System vendors and other researchers world-wide (e.g., KHNP/KAERI, Bettis and KAPL laboratories, etc.). Assessments of plant responses to zinc injection were also considered. These included both detailed case studies of the first few plants to inject zinc as well as more global reviews using data collected by EPRI in the PWR Chemistry and Monitoring Assessment (CMA) Database and the Standard Radiation Monitoring Program (SRMP) Database. The outcome of this project included a database and recommendations for further testing needs to more fully elucidate the effect of zinc on corrosion product release behavior. The results are expected to contribute to the development of optimized zinc concentration limits in light of the two main expected benefits of zinc addition (PWSCC mitigation and radiation field mitigation) and the main perceived risk of zinc injection (an increase in corrosion product accumulation on fuel surfaces and thus increased risks of crud induced localized corrosion, CILC, and crud induced power shifts, CIPS). (author)