Dynamic safety assessment of FPGA-based safety critical systems with applications in nuclear power generation
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Field Programmable Gate Arrays (FPGAS) are a type on integrated circuit that is configured by the end user to perform desired digital logic functions. FPGAs do not run any software or operating system, as the logic functions are configured as a hardware implementation on the FPGA chip. Documentation from the International Atomic Energy Agency (IAEA) states that FPGA implementations of I&C systems in Nuclear Power Plants (NPPs) is expected to increase significantly in the future. One issue facing FPGAs in the nuclear field is a lack of technical standards and design/review documentation. Therefore, the research program undertaken during this thesis considered the application of a new safety analysis methodology for the modelling and analysis of FPGA-based systems. The methodology chosen is a modern, dynamic (time-dependant) methodology known as the Dynamic Flowgraph Methodology (DFM), which is intended to be applied to digital I&C systems. Initially, a Failure Modes and Effects Analysis (FMEA) was performed to ascertain the potential failure modes that could affect FPGA-based systems, and that FMEA data was used to create and FPGA failure modes taxonomy. Using that FMEA data to provide information for fault injection, DFM was applied to analyze several FPGA-based test systems, and the results of the DFM analyses were compared and contrasted with results from Fault Tree Analysis (FTA), to determine the potential advantages and disadvantages of DFM. It was seen that DFM had several advantages when modelling clock delays, oscillating clock signals, and Multiple-Valued Logic, however for large systems DFM continues to experience the “state explosion” problem, limiting its effectiveness to small-medium sized systems. Potential avenues of future work are also presented.