Feasibility study on the relaxation of the secondary side safety injection setpoint lead-lag ratio for Maanshan Nuclear Power Plant

Since 1979, Taipower has performed its own safety analysis to effectively support plant operation, reload applications, design changes, technical specification amendments and to build up our inhouse licensing capability. One of the activities is to acquire the RELAP5/MOD2 computer code from Idaho National Engineering Laboratory (INEL) for Pressurized Water Reactor (PWR) Application. The RELAP5/MOD2 is a computer program developed for analyzing the dynamic behavior of thermal-hydraulic systems. This program has been developed primarily for analyzing postulated accidents and transients in PWR system. Maanshan is a Westinghouse 3-loop-PWR plant. The design of the secondary side low pressure Safety Injection (SI) signal is to protect the plant from main steam line break. The normal operating pressure for the secondary side is about 1000 psia and the low steam pressure SI setpoint is 600 psia. During an abnormal transient, a sudden big load change would have a chance to drop the secondary side pressure up to 40 psi, and through the amplification of the current Lead-Lag ratio (10 times), this pressure drop would initiate the SI system. In order to avoid this inadvertent SI initiation, Taipower performs a feasibility study to search the best Lead-Lag ratio for the secondary side low pressure SI signal by using RELAP5/MOD2. It concludes that this Lead-Lag ratio can be relaxed or can be removed. (author)