Unavailability analysis of a digital hybrid platform for reactor protection systems

Transition from conventional analog technology to advanced digital technology is a global trend, and commercial and research reactors are increasingly using digital instrumentation and control (I&C) systems. However, common cause failures (CCFs) of the digital platform are significant issues. In this paper, we proposed a potential solution for such CCFs by implementing a digital hybrid model that combines two different platforms, programmable logic controller (PLC) and field programmable gate array (FPGA). PLCs have been used for decades, while FPGAs are comparatively new in nuclear safety-grade I&C systems. The digital hybrid model was compared with an analog model and individual digital models for each platform in terms of the results using fault tree analysis and generic failure rate database. The quantitative improvements of the proposed digital hybrid model were demonstrated for a reactor protection system.