A Practical Methodology for Checking the Status of I and C Systems in NPPS
Chanho Sung, Hee-Taeg Chung · Pacific Basin Nuclear Conference 2006 · 2006
There are several major factors to cause nuclear power plant (NPP) to shut down. The failures of the I and C(Instrumentation and Control) systems are included in the major factors and have come to over 25% in total failures of NPPs in Korea for last 15 years. Accordingly, to reduce such failures and heavy losses caused by the failures, proper transactions such as system replacements or system upgrades should be performed in a timely method. To grasp the status of systems, first of all, it is necessary to evaluate periodically I and C systems in operating power plants since they may have some problems with aging, obsolescence, high failure rates, etc. These problems may affect plant trip as well as increasing O and M (Operation and Maintenance) costs considerably. Most existing I and C systems in nuclear power plants throughout the world were based on the analog equipment and relays that were designed 30 to 50 years ago. To increase availability and to enhance the safety, many utilities are considering the modernization of some or all of their IandC systems. Due to extended use of the digital technology in industrial process and accumulated reliability in digital equipment, many nuclear power plants have replaced their old analog systems with some proven digital components. But, to adapt digital equipment to plants effectively and systemically, there is an essential prerequisite. That is to evaluate current I and C equipment. Generally, there are several methods to evaluate the status (such as health, reliability, performance, aging, etc.) of I and C system but it is not easy to apply to nuclear power plant. Because nuclear power plant has lots of I and C equipment, the equipment consists of a large number of components and the each equipment affects the others. Accordingly it requires much effort and time to evaluate lots of systems or equipment in NPP, besides it is difficult to totally assure the result evaluated by such a complicated method. This paper shows a practical methodology to evaluate the current status of I and C system of nuclear power plants before performing an upgrade or a replacement for a system. To assess the status of each I and C system, evaluation factors are required such as system importance, performance, maintenance, aging, economic efficiency, and the continuance of equipment supply. These factors are used to check up the current status of each system through the proper questionnaire corresponding to each evaluation factor. The proposed method was applied to Kori unit(KRN) 3 and 4, and Ulchin unit(UCN) 1 and 2 to support making an upgrade plan or a maintenance plan. Also we have developed an evaluation system which embarks the proposed evaluation methodology and works on internet for user's convenience.