Analysis on Spurious Turbine Runback of the Unit 2 at Qinshan Ⅱ NPP

This paper described the turbine runback transient resulted by spurious signal of low-selected reactor coolant average temperature,which happened at Unit 2 of Qinshan Ⅱ NPP.Changes of key parameter during the transient were provided,and responds of the unit control systems（especially Rod Control System and Steam Bypass Dumping System） were analyzed.Since high-selected reactor coolant average temperature was adopted as the input variable for Rod Control System and Steam Bypass Dumping System,during the overall transient,the control systems could cooperate well according to the difference value between average temperature and reference temperature,meanwhile the other main control systems such as the steam generator level,the pressurizer level and pressure could respond correctly and timely,finally the unit was stabilized at lower power state.The data from the transient will be used as a base for the plant modification.