Performance Enhancement of Reactor Building Containment Isolation System by Use of Direct-Acting Solenoid Valves

Abstract

Containment isolation system is an important safety system of nuclear reactors, designed to reduce the radiological consequences and risk to the public from various postulated design basis accident conditions. Reliability and performance of containment isolation system to assure containment integrity during power operation and other stated activities are ascertained by routine functional checks on system components. The work presented here focuses on performance and reliability enhancement of containment isolation system of Dhruva Research Reactor, BARC, Mumbai. The enhancement was achieved by replacing pilot-operated solenoid valves (SVs) with direct-acting SVs in the logic circuit. On several occasions, during routine functional checks of the logic circuit of isolation damper actuators, isolation dampers were observed to be partial/incompletely closed, leading to uncertainty of containment integrity on actual demand conditions. Faults in the logic circuit of isolation damper actuators were analyzed, and the root cause was identified to be lack of minimum operating differential pressure (MOPD) available across the pilot-operated SVs during routine checks. Based on manufacturer’s product literature [1], direct-acting SVs were found to be most suitable for use in the concerned application. The direct-acting SVs were qualified for use in the logic circuit of isolation damper actuators, after a series of performance and environmental tests. The performance of the logic circuit of isolation damper actuators with direct-acting SVs was improved along with no reported failure occurrence. A fault tree analysis [2] was carried out based on the failure data of pilot-operated and direct-acting SVs for a period of 5 years, to compare the failure probability of the logic circuit of isolation damper actuators. The failure probability of the logic circuit of isolation damper actuators after installation of direct-acting SVs was found to be improved by a decade.