THE ROLE OF FPGA-BASED ARCHITECTURES IN THE CONTROL ROOM MODERNIZATION PROCESS: PRELIMINARY RESULTS OF A CASE-STUDY

摘要

In the context of a plant modernization, developing digital I&C technology is a crucial challenge to improve nuclear plants safety and reliability. Digital technology is usually oriented to achieve functions such as plant control, monitoring, simulation and protection in a user-friendly way. On the other hand, the analogue instrumentation implemented in the so-called "old generation consoles" is often essential and not immediately or completely replaceable. As a consequence, the interaction between the analogue and digital data seems to be a necessary step before starting the digital I&C licensing process. The fundamental difference between analogue and digital technologies relies on the fact that digital logic is based on processors, hence it can be customized by programming its software. However, introducing new code can result in a new set of potential failure modes to be accounted for. As a consequence, original analogue systems mostly assure a higher level of protection with respect to digital systems. In this scenario, a benefit could arise from the use of Field-Programmable Gate Arrays (FPGAs), based on a hardware architecture whose routing is made via software, thus resulting in a variety of possible tasks. FPGAs' employment ranges from automotive and industrial applications, ASIC prototyping, software defined radios, radar, image and DSP. In this work a critical analysis of FPGA fundamental features and potentialities in nuclear plant I&C design is achieved in conjunction with some practical applications. Troubles arising from coping with processor-based system are presented and compared to benefits and potentialities offered by FPGA real-time architectures: in- deed, FPGAs comprise a higher number of logic blocks and functions able to manage parallel processes with self triggering, and provided into a "non-frozen " structure but easily reconfigurable. This characteristics of being in-system programmable (ISP), i.e. a device capable of being programmed while remaining resident in a high-level system, can be considered as the main advantage of using FPGA. The employment on a large scale is also justified by its high determinism and testability, leading to high performance in terms of reliability. As a case-study, we propose a supervisory full-digital system that has been designed, realized, tested and validated implementing a FPGA architecture to be used in parallel to the TRIG A nuclear reactor RC-1 analogue console at the ENEA Casaccia Research Centre in Rome. We report on the design choices, and on pros and cons of using FPGA instead of the classical processor-based architectures. This preliminary apparatus has been developed using the LABVIEW environment and FPGA-based technology, an appropriate tool to get across simulation to Hardware-in-the-Loop (HIL) technique allowing to move on production from prototyping.