The objective of this study is to find out the impact of instrumentation and control (I&C) components on the availability of I&C systems in terms of sensitivity analysis using Bayesian network. The analysis has been performed on I&C architecture of reactor protection system. The analysis results would be applied to develop I&C architecture which will meet the desire reliability features and save cost. RPS architecture unavailability and availability were estimated to and for failure (0) and perfect (1) states, respectively. The impact of I&C components on overall system risk has been studied in terms of risk achievement worth (RAW) and risk reduction worth (RRW). It is found that circuit breaker failure (TCB), bi-stable processor (BP), sensor transmitter (TR), and pressure transmitter (PT) have high impact on risk. The study concludes and recommends that circuit breaker bi-stable processor should be given more consideration while designing I&C architecture. 1. Introduction The last two decades are the witnesses of rapid development of digital technology in the nuclear industry. Though instrumentation and control (I&C) architecture of nuclear power plants has been established to a certain level, yet it is design dependent and not standardized for all the industry. Holbert and Lin highlighted the need of improved methods for monitoring, control, and diagnostics due to economic constraints and applied fuzzy logic to enhance plant availability by assessing equipment condition [1]. I&C architecture of safety and protection systems in case of research reactors is also not standardized and research on the reliability is needed to demonstrate an optimized architecture for business as well as standardization. Moreover it is essential to find which architecture will perform better among digital, analog, or hybrid designs. Digital I&C still has to win confidence because advent of digital I&C systems in nuclear power plants has created new challenges for safety analysis and it is necessary to quantify the risk impact of digital systems specially related to software, processing unit (CPU), and common cause failures [2]. Therefore suitable architecture should be identified. In spite of technical basis, research on I&C architecture of research reactor is also based on social demand. The steadily increasing demand of research reactors by educational and research institutes nationwide as well as international is basis for this research. At present, there are 232 operating research reactors worldwide which differ in design based on objective. There are many types of
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