The Study Of Secondary Water Chemistry Problem For Qinshan Ⅱ NPP

Both two units of Qinshanâ…¡experienced bad water chemistry in secondary system at beginning of commercial operation. Some water chemistry parameters could not satisfy the requirement of chemistry control. Comparing with PWR industries, there is much need to improve. Long-term bad chemistry will harm to the secondary equipments, especially to the steam generator, and will affect long-term, safety, and economic operation of the unit. According to the plant operation technical specification, the reactor will have to decrease power even shut down due to the unqualified water chemistry. It is important to find the cause of the secondary water chemistry problem. The paper adopts the method of fishbone diagram to find the causes in every part of secondary system. As to the actual secondary chemistry and its trending analysis, many causes can be excluded. When the main causes are determined, the countermeasures are established and carried out. The water chemistry is greatly improved. The main causes and countermeasures are as following.1) The impurity of chloride in sodium hydroxide used for resin regeneration of condensate polisher system is too much, which results in the chloride ion out of the mix bed can not reach the criterion and high chloride concentration in steam generator blowdown.It is settled by strengthening the chemicals surveillance and supplier management.2) The resin cross-contamination happened in mix bed resin system results the sodium ion release when the mix bed is put into operation. So the sodium ion concentration in blowdown is high. It is resolved by technical modification for the system and equipment. The regeneration process is improved and the resin cross-contamination rate is decreased. The ammonia rinse technology is adopted for the anion resin after its regeneration. These measures decreased the sodium ion greatly.3) The resin leakage problem is settled by checking the resin captures every outage.4) By increasing the pH of the secondary system, adding magnetic grid in condenser and changing part of pipe material, the corrosion product is much reduced.5) The water chemistry during startup is bad. By adjusting the condensate polisher flowrate, improving flushing process and blowdown system operation and delaying the drainage return to the deaerator.6) The makeup water quality is improved by adding reverse osmosis deviceAfter two years efforts, the condition of secondary water chemistry of Qinshanâ…¡is greatly improved. The plant WANO CPI is much closed to the WANO median value. The paper summarizes the process of dealing with the problem. Now the nuclear power is developing fast in China. The experience established in Qinshanâ…¡will be useful for the nuclear power plant both in operation and under construction.