Fuzzy methodology applied to Probabilistic Safety Assessment for digital system in nuclear power plants

A fuzzy inference system (FIS) modeling technique to treat a nuclear reliability engineering problem is presented. Recently, many nuclear power plants (NPPs) have performed a shift in technology to digital systems due to analog obsolescence and digital advantages. The fuzzy inference engine uses these fuzzy IF-THEN rules to determine a mapping of the input universe of discourse over the output universe of discourse based on fuzzy logic principles. The risk priority number (RPN) (typical of a traditional failure mode and effects analysis – FMEA) is calculated and compared to fuzzy risk priority number (FRPN), obtained by the use of the scores from expert opinions. It was adopted the digital feedwater control system as a practical example in the case study. The results demonstrated the potential of the inference system to this class of problem.