Sulphate Issues and Learning for Secondary Loop System at Dayabay Nuclear Power Plant

摘要

Dayabay NPP started up from 1994. There is no condensate polishing system(CPP) with initial design. Unfortunately there happened few times serious issues with sea water leakage into condensate. It was reconstructed and be added CPP from 1997. But we found sulphate concentration in SG will increased after ATE was put into operating, when CPP was out of service, then sulphate concentration decreased. Through the study and research for a few years, we found the root cause and we took these following improvements at site step by step, steam generation blow down water quality was significantly improved: 1. Optimize feed water distribution condition in resin bed since the shortcomings of resin bed design, resin is moving up and down during operating. To prevent resin re-separation and broken issue, we improved the structure of feed distribution and better the resin condition in resin bed; 2. Optimize regeneration process Optimize mixed bed resin transferring, separation, regeneration process, re-separation and re-mixing process during regeneration; 3. Optimize operating process Regular clean resin beads under the water chamber and resin trap to prevent resin leak into SG system; 4. Other actions Check nozzles one by one in resin bed and change these nozzles with shortcomings to prevent resin leakage into resin chamber. Upgrade cation resin type from 12% DVB to 16% DVB. According to Dayabay nuclear power plant steam generator sulphate issue experience, now in China we have improved a lot for the secondary loop condensate polishing system design, equipment manufacturing, operation process, etc. We have achieved good results in our new projects such as LingAo Phase II nuclear power plant.