BWR Shutdown and Startup Chemistry Experience and Application Sourcebook (BWRVIP-225, Rev. 1)

摘要

BWR water chemistry has changed significantly over the years with the adoption of hydrogen water chemistry (HWC), noble metal chemical application (NMCA), and most recently, Online NobleChem (OLNC). Some plants have experienced large increases in activated corrosion products during shutdown evolutions, when the chemistry environment at primary system surfaces transitions from reducing to oxidizing conditions. Higher activity releases may be in part related to the more reducing conditions brought about by the above mentioned processes during the operating cycle. With shorter outages decreasing the available cleanup time, some plants are experiencing increased outage radiation exposure. A significant portion of fuel cycle intergranular stress corrosion cracking (IGSCC) propagation of reactor internals and primary system piping is indicated to occur during startup and early power ascension, when dissolved oxygen and hydrogen peroxide concentrations in the reactor coolant are high and hydrogen injection is unavailable. The majority of lost hydrogen availability hours typically occurs during early startup. Startup periods following refueling outages are also when reactor coolant chemistry transients may occur due to system flow changes and residual chemical impurities from outage related work activities. Test results show that IGSCC is accelerated particularly during early startup periods of elevated reactor coolant oxidant concentrations (dissolved oxygen and hydrogen peroxide), particularly when operating at an intermediate temperature range (300 - 400 °F, 148-204 °C). Based on extensive data collection and evaluation, BWRVIP-225 Revision 1 provides good practices and conditions to avoid during plant refueling outages, including recommendations to minimize activity transport during shutdown conditions to reduce radiation exposure. In addition, good practices and conditions to avoid are provided for startup and power ascension to minimize IGSCC. This paper provides highlights from the Sourcebook on shutdown and startup industry experience, shutdown data correlations and chemistry control recommendations during shutdown and startup.