Risk-Informed Design of Hybrid I&C Architectures for Research Reactors
The risk-informed probabilistic design approach toward the hybridized instrumentation and control (I&C) systems of research reactors based on sensitivity and availability criteria has been applied in this paper. An optimized hybrid I&C architecture is worthwhile and emphasized because of low budget for I&C and simple functionality of research reactors. Hybridization in input/output modules using analog and digital components has been introduced to enhance diversity and provide resistance to common mode failures. Based on the approach, two hybrid (named I and II) architecture configurations of reactor protection systems have been formulated from a reference architecture with an analysis performed on their reliability features; availability and sensitivity assessments were performed using Bayesian network models. International Electrotechnical Commission and American Society of Mechanical Engineers criteria have been applied for an evaluation of the architecture reliability features. A novel concept for assessing the sensitivity and risk impact of components based on single and multiple component risk reduction indices have been introduced and used for sensitivity evaluations. It was determined that hybrid-II architectures yielded good reliability features compared to hybrid-I and the reference architecture because the unavailability of hybrid-II architecture decreases by one or two orders of magnitude by just adding one more bi-stable processor based on the risk feedback of hybrid-I architecture. It was concluded that architecture designs based on hybrid and risk-informed design approaches have the ability to maintain high levels of safety and availability through cost-savings.