Reliability analysis of microcomputer circuit modules and computer based control systems important to safety of nuclear power plants

Computer based safety related control and instrumentation (C&I) systems are being employed in Indian Nuclear Power Plants (NPPs). These systems are designed around standardized family of microcomputer based circuit modules, which are qualified to the stringent requirements of the nuclear industry. Reliability analysis of standardized microcomputer circuit modules, used in the safety related C&I systems, were carried out using the analysis package based on the methodology and database of MIL-STD-217-F1. The circuit modules are the main building blocks of the safety related C&I systems in the forthcoming Indian NPPs. The article presents reliability analysis results of microcomputer and related circuit modules and a representative safety C&I system-Programmable Digital Comparator System (PDCS). Comparison of reliability values for prototype PDCS using commercial grade components, and for upgraded version PDCS using MIL grade or equivalent screened components was made. The estimated failure rate values of standardized microcomputer circuit modules will be useful, for reliability assessment of various other safety related C&I systems developed around these modules, for ongoing and future Indian NPPs.