冬季SEC泵备用状态下积气形成机理的理论与模拟实验研究

Theoretical and Simulation Experiment Research on the Formation Mechanism of Gas Accumulation Under the Standby State of Seawater Pump in Winter

某北方核电厂重要海水系统的海水泵(SEC泵),在冬季备用状态下发生积气而无法启动,针对该现象,开展了静态条件下低温海水受环境加热析气特性的理论研究;建立了模拟实验系统,研究SEC泵的泵腔积气形成过程、海潮涨落下泵腔积气的演化特征、不同排气管倾角下气液两相流特征;在此基础上,分析了现场条件、排气系统缺陷等导致泵腔积气的机理,提出了SEC泵排气系统改造方案。研究结果表明,环境温度、海水的初始温度对海水中溶解氧总析出速率和氧气析出总量影响较大、盐度对海水中溶解氧总析出速率影响较小;SEC泵的泵腔积气形成过程具有明显的阶段性特征;在某核电厂重要厂用海水系统的布置方式下,SEC泵区域海水的赋存量、SEC泵运行状态切换周期及运行环境等因素,均有利于冬季SEC泵备用期间海水溶解气体的大量析出;海潮的涨落,均有助于积气的排放;排气管倾角对气液两相流动特征有显著影响,该排气系统存在的设计缺陷,导致海水析出气体在泵腔区域的积聚而形成体积可观的气腔。基于上述研究结论,提出的排气系统改造方案并在4台机组上应用,成功解决了该核电厂冬季备用期间SEC泵积气无法启动而可能丧失核岛热阱的风险。

The sea water pump(SEC pump)of an important seawater system in a North nuclear power plant failed to start up due to gas accumulation in winter.In view of this phenomenon,the theoretical research on the gas evolution characteristics of low-temperature seawater heated by the environment under static conditions is carried out;a simulation experimental system is established to study the formation process of gas accumulation in the pump chamber of SEC pump,the evolution characteristics of gas accumulation in pump chamber under sea tide fluctuation,and the characteristics of gas-liquid two-phase flow under different exhaust pipe inclina⁃tion angles;on this basis,the causes of gas accumulation in pump cavity caused by field conditions and exhaust system defects are analyzed.The results show that the environmental temperature and the initial temperature of seawater have great influence on the total dissolved oxygen release rate and total oxygen release rate,while the salinity has little effect on the total dissolved oxygen release rate;the formation process of gas accumulation in the pump chamber of SEC pump has obvious stage characteristics;under the layout of the important plant seawa⁃ter system of a nuclear power plant,the storage capacity of seawater in SEC pump,the standby period of SEC pump in winter and operating environment are conducive to the large amount of dissolved gas in seawater during the standby period of SEC pump in winter;the fluctuation of sea tide is conducive to the discharge of accumulat⁃ed gas;the inclination angle of exhaust pipe has a significant impact on the gas-liquid two-phase flow character⁃istics,and the design defects of the exhaust system lead to the accumulation of seawater precipitated gas in the pump cavity area and form considerable gas volume Cavity.Based on the above research conclusions,the ex⁃haust system retrofit scheme was put forward and applied to four units,which successfully solved the risk of loss of heat sink of nuclear island due to failure to start sec pump accumulated gas during winter standby.