Use of field-programmable gate arrays in nuclear I&C safety systems : Case stepwise shutdown system

Software-based safety systems have become increasingly common in nuclear power plants. Due to their complexity, software applications can almost never be exhaustively tested and proved error-free. FPGA technology could alleviate these problems with the less complex hardware and flexible capabilities of software. As FPGA technology is rather new in the nuclear industry, there are currently no commonly accepted regulations or guidance directly addressing the use of FPGAs in NPPs. This paper presents how we implement two variants of an I&C safety system called Stepwise Shutdown System using FPGA technology. One of the variants contains a design error, and the other is free of errors. We demonstrate how the nuclear domain I&C systems can be designed using this technology, and show how the design error in the I&C design was found using simulation and hardware tests.