Reliability assessment of instrumentation and control systems (I&Cs) is always one of the most important design and operation activities, especially for critical domains like nuclear power plants (NPPs). Intensive use of relatively new technologies like field programmable gate arrays (FPGAs) in I&C which appear in upgrades and in newly built NPPs makes task to develop and validate advanced 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&C. Moreover, FPGAs differ in some significant ways from other integrated circuits: they are shipped as blanks and are very dependent on design configured into them. Therefore, special approaches should be used for comprehensive analysis of FPGAs. This paper summarizes our experience on reliability analysis of FPGA based NPP I&C produced by Research and production corporation Radiy (RPC Radiy). Both analytical and operational reliability analyses are covered.