PRACTICAL ASPECTS OF OPERATING AND ANALYTICAL RELIABILITY ASSESSMENT OF FPGA-BASED I&C SYSTEMS

Abstract

Operating reliability assessment of instrumentation and control systems (I&Cs) is always one of the most important activities, especially for critical domains such as nuclear power plants (NPPs). It is an important source of I&C reliability information preferable to lab testing data because it provides information on I&C reliability under real use conditions. That is the reason that now it is a common practice for companies to have an established process of collecting operating reliability data on a large variety of used components on regular basis, maintaining a database with failure information, total operation time, typical failure modes, etc. The intensive use of complicated components like field-programmable gate arrays (FPGAs) in I&C which appear in upgrades and newly-built nuclear power plants makes the task to develop and validate advanced operating reliability assessment methods that consider specific technology features very topical. Increased integration densities make the reliability of integrated circuits the most crucial point in modern NPP I&Cs. Moreover, FPGAs differ in some significant ways from other integrated circuits: they are shipped as blanks and are very dependent on the design configured into them. Furthermore, FPGA design could be changed during planned NPP outage for different reasons. Considering all possible failure modes of FPGA-based NPP instrumentation and control systems at the design stage is a quite challenging task. Therefore, operating reliability assessment is one of the most preferable ways to perform a comprehensive analysis of FPGA-based NPP I&Cs. Based on information in the literature and own experience, operational vs analytical reliability could be pretty far apart. For that reason, analytical reliability assessment using reliability block diagrams (RBD), failure modes, effects and diagnostics analysis (FMEDA), fault tree analysis (FTA), fault insertion testing (FIT), and other techniques and their combinations are important to meet requirements for such systems. The paper summarizes our experience in operating and analytical reliability assessment of FPGA based NPP I&Cs.