원자력발전소 2차계통 슬러지 부착 저감방법 연구

Abstract

The purpose of this study is to present the method to reduce the sludge attachment of the secondary system through the cases of reduction in electric power by the sludge of the main feed water system of Younggwang(YGN) #5 and #6 Nuclear Power Plant. In the event of YGN #5 and #6, the clogging phenomenon in the Feed Water Control Valve Cage has continued to have severe changes in the Feed Water Flow, as a result, it has experienced several problems in reduction of electric power at the end of the cycle, loss of power from the increase of speed in Main Feed Water Pump, replacement of the Feed Water Control Valve Cage for each cycle and others. The Main Feed Water Pump & the Feed Water Booster Pump impeller had the foreign substance deposited and an increasing phenomenon of the Main Feed Water Pump speed and discharge pressure. As a result, there was loss of power due to the increase of the pump rotation speed. EFCV (Economizer Flow Control Valve) & DFCV (Downcomer Flow Control Valve) Cage had the foreign substance deposited which reduces the DFCV flow and EFCV opening by the increase of flow resistance. In addition, At approximately 80% opening of the EFCV, it is the zone that enlarges the diameter of the Valve Cage Hole which enlarges the width of change for the Feed Water Flow that is used as an input variable of the plant power to enable the power of the Nuclear Power Plant to approach the licensed power limit, resulting in maintaining the electric power lower than it can. As a result of increasing the concentration of hydrazine and ammonia step-by-step to heighten the pH of steam and Feed Water, the iron concentration within the system was reduced to improve the feed water flow and opening of the DFCV and EFCV. As a result of this study focusing on the plan to reduce the generation of iron oxidation substance through the hydro-chemical environment adjustment, the time of clogging up the cage of the Feed Water Control Valve which increases the main feed water pressure and reduces the flow of the DFCV was considered as accelerated after October 2004 when the water treatment method was changed from ammonia to ethanolamine in the secondary system. As a result, it is resolved by optimizing the concentration of the chemical substances(Ethanolamine/NH3OH/N2H4) as used in the water treatment. Through this study, optimal hydro-chemical conditions and operation method for minimizing the corrosion in the secondary system of the Pressurized Water Reactor have been prepared, and as a result, it enhances the production efficiency of the electric power and contributes to safe operation and extension in the life cycle of the steam generator.