Regulatory review of computer based systems: Indian perspectives

The use of state of art digital instrumentation and control (I&C) in safety and safety related systems in nuclear power plants has become prevalent due to the performance in terms of accuracy, computational capabilities and data archiving capability for future diagnosis. Added advantages in computer based systems are fault tolerance, self-testing, signal validation capability and process system diagnostics. But, uncertainty exists about the quality, reliability and performance of such software based nuclear instrumentation which poses new challenges for the industry and regulators in using them for safety and safety related systems. To obtain adequate confidence in licensing them for use in NPPs, CBS were deployed gradually from monitoring system to control system (i.e, non-safety, safety related & lastly safety systems). Based upon the experience over a decade, AERB safety guide AERB/SGID-25 was prepared to prescribe the criteria and requirements to assess the qualitative reliability of such software based nuclear instrumentation. This paper describes the regulatory review and audit process as required by the above guide. Further, Software Configuration Management (SCM) is an important item during life cycle of CBS, whether it is design phase or operating phase. Configuration control becomes necessary due to operation feedback, introduction of additional features and due to obsolescence. Therefore configuration control during operating phase for CBS becomes all the more important. This paper elaborates on the regulatory approach adopted by AERB for regulatory review and control of design modifications in operating phase of NPPs. This paper also covers a case study of AERB audit on verification & validation activities for software based safety and safety related systems used in an Indian plant.