Technical Review Guidance and Acceptance for Digital Communications in Highly Integrated Control Rooms

Abstract

This report presents review guidance and associated acceptance criteria for use by regulatory staff in confirming that highly integrated control room (HICR) designs are in conformance with Nuclear Regulatory Commission (NRC) requirements. The principal features of the HICR are extensive use of digital network communications and digital operator workstations. The purpose of this report is to document the technical basis for guidance that specifically addresses issues related to communication among safety divisions and between safety-related equipment and equipment that is not safety-related. This guidance is intended to provide clarification in recognition of the inherent differences between digital-communication-based systems and point-to-point systems that have been used in the past. Current industry and NRC guidance documents such as IEEE 7-4.3.2, Regulatory Guide 1.152, and IEEE 603 do not sufficiently define a level of detail for evaluating interdivisional communica�tions independence. The NRC seeks to establish criteria for safety systems communications that can be uniformly applied in evaluation of a variety of safety system designs. The report examines (1) accepted networking consensus practices adopted by various standards organizations in the United States and internationally, (2) operating experience of international power reactors utilizing digital network communications in safety systems, and (3) failure mechanisms arising from several possible network architectures and message types. A structured approach for evaluation of safety-to-safety and nonsafety-to-safety communications systems has emerged from this study. Two general failure categories can be considered: (1) information and (2) communication. Information failure encompasses any situation in which a message or data to a safety system appears valid but is wrong (e.g., incorrect, misguided). A communication failure refers to the loss of messages or data because of transmission. Review guidance has been developed that pertains to interdivisional communications and nonsafety-to-safety communications. Finally, an evaluation methodology has been developed that applies the report's findings to the regulatory review process.