ADMIRALTY BRASS MAIN CONDENSER TUBE DEGRADATION AT FITZPATRICK

摘要

The James A. FitzPatrick Nuclear Power Plant is a General Electric Boiling Water Reactor (BWR 4 design) located on the southeast shore of Lake Ontario. The main condenser was re-tubed in 1994, with all admiralty brass condenser tubes replaced in-kind (the titanium impingement tubes were not replaced). The station operates with low feedwater hydrogen injection and Online NobleChem™ (OLNC) for mitigation of intergranular stress corrosion cracking (IGSCC) of reactor internals. Feedwater zinc injection is implemented for primary system (i.e., reactor recirculation system) shutdown radiation field control. The main condenser circulating water system is chlorinated to minimize microbiological fouling of the main condenser tubes. Operating Cycle 21 ended in August 2014. During Cycle 21, the station experienced a number of large condenser tube leaks. Over 60 power reductions were performed since 2011 to isolate and plug leaking condenser tubes. Visual examinations showed that a number of the leaks were associated with longitudinal tube splits, some up to two feet in length. Some tubes were severed where the ends of the severed tube were flared outward. Significant wall thinning was also identified. Increasing impurity levels in the condenser hotwell from condenser leaks challenges a BWR in maintaining low levels of detrimental anions (e.g., sulfate and chloride). These impurities enter the reactor vessel directly from the feedwater system and can initiate or accelerate intergranular stress corrosion cracking (IGSCC) of reactor internals. Further, other impurities from condenser leaks, such as silica, can impact BWR fuel performance. This paper provides a summary discussion of the probable failure mechanism leading to the admiralty brass condenser tube splits, actions taken by the station to minimize impurity levels in the reactor coolant during Cycle 21, the effectiveness of these actions, and results of inspections in the fall 2014 refueling outage to assess fuel reliability and IGSCC of reactor vessel components from the unusual Cycle 21 chemistry conditions. The main condenser was completely re-tubed in the fall of 2014 with titanium.