Development, Dedication and Application of an Automatic Seismic Trip System for Nuclear Power Plants of Taiwan Power Company

This paper describes the setups of Automatic Seismic Trip System (ASTS), including development, dedication and implementation, for Nuclear Power Plants (NPPs) of Taiwan Power Company (TPC). The purposed ASTS was designed to trip the reactor when big earthquake occurs. These ASTS were classified as class 1E equipment. They were developed and dedicated for safety applications in accordance with IEEE 323-1983, IEEE 344-1987, IEEE 383-1974 and Reg. Guide 1.180 R1. In order to meet the technical specification required by TPC, three sub-units in the ASTS were developed: Earthquake sensors: Kinemetrices FBA-23 triaxial accelerometers are selected since they were successfully used in Taiwan for seismic monitoring for more than 10 years. Signal conditioning module: It is designed to reduce noise from motion accelerometer (FBA-23) and then transmit seismic signal to the set-point and trip unit via instrument amplify circuit, 0.1 to 10Hz band pass filter circuit, absolute-value converter and voltage to current converter. Trip control module: after comparing the seismic signal level and set-point, the result will decide whether to drive the output relay or not. The output relay is used as the interface between ASTS and the reactor protection system in NPP. For the commercial grade item dedication for safety application, five processes were conducted. Those processes are Seismic test: to use plant specific required response spectrum (RRS), the test required spectrum should envelop RRS: Seismic auto-trip accuracy test: must not trip when filtered PA below set point minus 0.05g, and must trip when filtered PA exceeds set point over 0.05g. Trip signals occurred within 10 second interval are considered as same events: NEMA4 water proof test for sensor box: Anti-radiation test: 8.76x100 rads over 40 years: EMI/EMC test: follow RG 1.180 requirement. The ASTS were installed in three NPPs, six units in total, without connection to RPS in 2006. After one year reliable operation, the ASTS were connected to RPS in 2007. The trip logic implemented in each NPPs are discussed based on different concerns of safety and reliability. Till now, these ASTS have been operating and periodically tested satisfactorily in NPPs