Quantitative Analysis of Valve Contribution to the Failure Probability of Carbon Dioxide Suppression System

Abstract

Carbon dioxide suppression systems are used in nuclear power plants to extinguish oil fires and ensure integrity of critical equipment. In this study, the contributions of the valves in the carbon dioxide suppression system to the failure probability of suppression were quantitatively analyzed, and the failure probability of the fire suppression system applied to the fire Probabilistic Safety Assessment (PSA) was evaluated for appropriateness. Then, a reliability evaluation model was developed in the form of a fault tree, and the reliability data were analyzed for the major component. The failure probability of the carbon dioxide suppression system with early air-release equipment was assessed as 6.22 × 10<sup>-3</sup>/demand, which is 2.67 times that of the system without such equipment. The results were attributed to the addition of the diverted line isolation valves and quick exhaust valve to release residual air into the atmosphere before supplying carbon dioxide to the fire area. It was also confirmed that the failure probability of the carbon dioxide suppression system with the early air-release equipment was 15.6% that of the suppression provided by the fire PSA and that the failure probability of suppression by the fire PSA was conservative. There are no reported guidelines in literature for analyzing the reliabilities of carbon dioxide fire suppression systems, and the fire PSA currently use the failure probability of suppression recommended by the NSAC-179L.