某压水堆核电厂热停期间GCT-a阀门频繁动作原因及解决方案探究

Study on the Cause and Solution of Frequent Action of GCT-a Valve during Hot Shutdown Station in a PWR Plant

摘要: 某压水堆核电厂在热停堆平台期间，现场发现汽轮机旁路排大气系统(GCT-a)阀门(GCT133VV)开关频繁动作，估计频率为10 s一次，现场可以明显听到主阀落座的声音，阀门出口消音器也可观察到明显的排汽变化，即GCT-a阀门出现了较频繁的振荡现象。本文对该现象进行了原因分析，并针对性的给出了解决方案。研究表明，GCT-a阀门采用比例积分微分(PID)控制系统进行动作控制，其中比例系数P参数的大小表征的是阀门开启的速率，该参数设置越大，阀门开启越快。由于该阀门的功能是限制瞬变过程中二回路超压，因此该参数需要保证II类瞬态中不发生二回路超压现象，即需要找到一组P参数既能满足安全要求，又能降低阀门振荡频率。通过P参数敏感性分析及二类瞬态超压最恶劣工况(丧失厂外电源LOOP)的安全评价，本文给出了不同P参数的分析结果，电厂通过优化P参数设置后，解决了现场阀门频繁动作的问题。本文研究结果可供电厂运行参考。

Abstract: During the hot shutdown station of a certain PWR nuclear power plant, it was found that the GCT133VV valve was frequently switched on and off, and the estimated frequency was once switched on and off at 10 s. The sound of the main valve seated could be obviously heard on the site, and the obvious steam change could also be observed in the muffler at the valve outlet, that is, the GCT-a valve was frequently oscillated. In this paper, the causes of this phenomenon are analyzed, and targeted solutions are given. The research shows that the GCT-a valve is controlled by PID control system, and the value of the proportional coefficient P parameter represents the opening rate of the valve. The larger the parameter setting, the faster the valve opening. Because the function of the valve is to limit the overpressure in the secondary circuit during transient process, this parameter is needed to avoid the overpressure phenomenon in the secondary circuit during DBC II transient. So it is necessary to find a set of P parameters that can not only meet the safety requirements, but also reduce the oscillation frequency of the valve. Through P parameter sensitivity analysis and transient overpressure (LOOP) safety evaluation, this paper gives the analysis results of different P parameters. After optimizing P parameter setting, the plant solved the problem of frequent valve action on site. The research results of this paper can also be used as a reference for plant operation and new reactor design.