The Emergency Power Supply (EPS) DG system is one of the most critical components in CANDU plant since it supplies power to operate the seismically qualified systems such as Emergency Water Supply (EWS), Emergency Core Coolant System (ECCS), control power for MSSVs, etc., in the case of loss of Class III and Class IV electric power including the failure of standby diesel generators. The EPS DG system comprises two fully independent and seismically qualified supply trains. Each train consists of a 4.16 kV medium voltage Diesel Generator (DG) set. The EPS DG set includes diesel generator, battery, battery charger, and fuel day tank. As part of the seismic risk analysis, the seismic capability of the EPS DG set is assessed.A seismic walkdown was conducted to evaluate the seismic capacities of the equipment in a CANDU 6 plant. The following components of the EPS DG set were identified for further seismic capability evaluation after the seismic walkdown.1. EPS Diesel Generator2. EPS DG Batteries3. Battery Charger for EPS DG Starting Batteries4. EPS DG Control Panel5. EPS DG Fuel Day TankThe Seismic capacity of the EPS DG set is calculated as High Confidence of Low Probability of Failure (HCLPF) capacity. The HCLPF capacity could be calculated using either the Fragility Analysis (FA) method [1] or the Conservative Deterministic Failure Margin (CDFM) method [2]. The FA method is used in this paper to calculate the HCLPF capacity of the EPS DG set. Background for the FA methodology is given in this paper.The possible failure modes of the EPS components were identified and investigated. Fragility analyses for the as-installed conditions were performed. The HCLPF values obtained for the EPS DG set indicate robustness of the Emergency Power Supply System in a CANDU 6 for earthquakes.
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