Seismic Risk Analysis of the 380VAC Emergency Electrical Power Distribution Cabinets of a Nuclear Power Plant in China

According to the research of the operating principle, installation position and running environment of the 380VAC emergency electrical power distribution cabinets (Hereinafter referred to as electrical cabinets) of a nuclear power plant in China, there are three aspects caused by earthquake that seriously affect the safety of the electrical cabinets, including relay chatter, failure of electrical cabinet structure and spatial interactions. Relay chatter refers to contacts of the relay being changed during the period of strong shaking. It may lead to associated circuits malfunction and the equipment failure of the relay control unless it can be effectively reset. The purpose of relay chatter is to find out these relays whose consequences are unacceptable after earthquake and calculate failure probability. Failure of electrical cabinet structure in the earthquake is to carry out seismic fragility evaluation. The goal of seismic fragility evaluation is to assess a given value which describes the ground acceleration capacity and the corresponding uncertainties, and then, the conditional probability of failure as a function of peak ground acceleration [PGA] and a family of fragility curves can be obtained. In this paper, finite element model of the electrical cabinet is established using ANSYS Workbench software. According to the electric cabinets seismic failure mode, we take some of the parameters including the parameters of the floor response spectrum, material strength parameters and so on as the input to calculate the median ground acceleration capacity and the corresponding uncertain parameters. The seismic spatial interactions are defined as the electrical cabinet destroyed due to the surrounding objects failure by falling, collapse, etc. Therefore, if necessary, it is needed to evaluate the seismic fragility of the surrounding objects. Usually through walking down, checking the design drawings or the combination of the above methods, we can find out the surrounding objects for an electric cabinet. So we analyze the seismic risk of the electrical cabinet from the above three aspects. When the results of the above three aspects obtained, we convolute of the electrical cabinet fragility with the seismic hazard curve which represents the frequency of occurrence of earthquake motions at various levels of intensity at the site. Then Monte Carlo sampling is adopted to analyze the uncertainty distribution. In this article, Risk Spectrum Professional software (reference 8) and Risk Spectrum Hazard lite software (reference 9) are used to complete the calculation and get some quantitative seismic risk insights. The above seismic risk insights can support the establishment of seismic probabilistic safety analysis model (Hereinafter referred to as SPSA) for a nuclear power plant, which helps to formulate seismic improvement strategies.