The FPGA utilization for signal processing and control logic execution has been approved to be feasible and cost-effective in many industries. When the demands for
more reliable performance and higher obsolescence resistance arise in nuclear industries, FPGA platform becomes a focus of advanced I&C systems. FPGAs are taken as an ideal option for the replacement of existing obsolescent systems due to its unique configurable hardware characteristics and application experience in other industries. However, challenges do exist for applying FPGA technology to NPP I&C systems since the nuclear industry has its own specific circumstances and unique life cycle requirements. Furthermore, during the FPGA design and implementation process, extra attention is needed to maximally utilize and realize its excellence in enhancing system performance. 2.4.1 Why FPGA
FPGA is not the only option for the update of NPP I&C systems but it does have attractive features to compete with other technologies. The superiority derived from the comparison against others highlights the feasibility of applying FPGAs for the purpose of updating NPP I&C system.
When comparing to old analog systems, an FPGA, as a digital system, shows its outstanding capabilities of better energy resolution, higher signal throughput, stronger obsolescence resistance, and smaller physical size. Less analog components are used in an FPGA since the propagating electrical signals are digitized, which improves the noise immunity and temperature stability. At a very high sampling rate, the incoming signals could encounter pulse overlap, i.e. the pileup. The system performance is then downgraded with a decreased system throughput. Within an FPGA-based system, the digital processing manner has more efficient pileup rejection, which leads to higher throughput. As for the obsolescence resistance feature, the standard development process of an FPGA-based system reserves the effectiveness of the verified and validated FPGA
design and guarantees the functionality of a new FPGA-based system when transplanting the design from the obsolete hardware platform. Finally, due to the higher density and lower supply voltage, FPGA-based systems reduce the size and improve the portability. Cables and cabinets used in the old analog systems can be greatly reduced.
Being a digital hardware platform, an FPGA-based system reveals its merits against software-based digital systems. With no operating system involved, the task distribution is realized directly by distributing signals into pre-configured integrated circuits. The waiting time consumed in a task queue is eliminated. The hardware components that execute the task in a software-based system, e.g. the microprocessor, data bus, and the memory, have to wait for the instructions from the operating system before moving to the next processing stage. In FPGA-based systems, task processing is arranged by building specific circuits for specific processing stages, which increases the processing speed by converting the task processing into signal propagation from input ports to output ports. Due to inherent failure modes, the V&V process of software-based systems cannot cover all the possible cases that could trigger system failure. It is then hard to categorize which inputs, of the ones that have not been executed yet, would produce a failure at execution [57]. Hence, software-based systems could lose its functionality at the appearance of unpredictable system collapse. While for an FPGA-based system, the failure modes only exist in the components of the hardware structure, which are relatively few and can be dependably predicted. Thus, as long as both the design and hardware platforms have been verified and validated, the FPGA platform configured with the design maintains its desired functionality.
FPGAs are competitive even against other modern state-of-the-art digital hardware technologies. Application specific integrated circuit (ASIC), which is most widely utilized for hardware implementation [64], has the potential of being considered as an option for NPP I&C systems. However, it requires large production volume of one ASIC design to make it profitable. On the other hand, only a few chips are needed for a specific I&C application in an NPP even with the consideration of backup and redundancy. Moreover, ASICs are not as flexible as FPGAs. In the case of system specification modification, FPGAs can be reconfigured with a revised design while the only way for an ASIC-based system is to redo the design and manufacture procedure.
In general, FPGAs have demonstrated advantages and superiorities over analog systems, software-based digital systems, and other hardware-based digital system for NPP I&C applications. These potential advantages for NPP performance improvement have attracted great interest of nuclear industry all around the world. Scientists and engineers in nuclear industry have paid a lot attention to this technology and made extraordinary progress, which will be discussed later in the review section.
2.4.2 Performance enhancement through FPGA applications
With the truth that most existing NPPs are using antiquated technologies for I&C systems, FPGAs are optimistically anticipated to enhance plant performance in NPPs. Since FPGAs have strengths in logic processing and signal processing, performance enhancement is mostly expected where signal sampling and algorithm execution are required.
Detectors and sensors are pivotal NPP instruments that provide the measurements of system variables. Accuracy and timeliness are of importance for achieving reliable performance. High throughput and resolution that can be achieved by FPGAs make the performance enhancement possible for processing of the sensor signals. As a matter of fact, most FPGA vendors now provide digital signal processing (DSP) modules within the FPGA chip such that users can realize demanded signal processing by simply specifying the configuration of these modules [65].
I&C systems that are responsible for logic/algorithm execution act as central brain of an NPP. The accuracy and timing of their performance directly affect the productivity and safety of the entire plant. For those safety-related I&C systems, enhanced performance can realize faster and stronger protection for the plant and the environment. Safety systems based on FPGA technology can utilize the fast processing feature to realize such an objective, which is the major investigation of current work and make it one of the major contributions.
Applying FPGA technology to NPP I&C system also enhances the system reliability and availability with fewer inherent failure modes. As an example, considerable progress has been made in reliability and availability by FPGA-based safety-related control and communication functions in accordance with the experience gained in Ukraine NPPs [66]. The deployed FPGA-based systems in Ukraine NPPs are qualified for complex solutions for nuclear installations of different types. They are proved to be a useful tool for retrofit and modernization of existing NPPs. Meanwhile the financial expenses in these NPPs are reduced without affecting the licensing processes.