Relay Chatter Analysis With Practical Application in Seismic PSA in Nuclear Power Station

Abstract

In the seismic PSA analysis of a nuclear power plant, the relay chatter analysis is a unique and important research content. An earthquake may cause inadvertent vibration of the relay contacts with an undesired output due to the low seismic ruggedness, and if the chatter time sustained more than 2 milliseconds, it will give an error signal. The error signal may lead to a refusing action or a mis-operation of relevant equipment, which will cause trouble to the mitigation of the earthquake accident of the nuclear power plant. Relay chatter could also actuate the lockout devices or seal-in devices associated with the supply breaker for essential buses, thus operator manual recovery is needed to re-close these breakers. Considering the accessibility of these equipment locations after an earthquake, it is difficult for operators to manually restore them if the number of these equipment is large. So relay chatter may cause an adverse impact on the accident mitigation functions by rendering selected accident mitigation equipment unavailable. This paper briefly introduces the method and procedure of Relay Chatter Analysis for the nuclear power plant PSA or SMA, then, illustrate it with an example of 380 VAC contactor control circuit. Finally, the modeling and quantification process for relay chatter analysis results in seismic PSA is briefly introduced, and a reference for solving similar problems is given.