Document: NUREG-0800
Document ID: dd687b37-3f26-4512-91d8-633ddb655821
Document Type: srp
Title: DATA COMMUNICATION SYSTEMS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1602/ML16020A097.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.9
CFR Part: 
CFR Title: 

Content:
safety systems should not be implemented. 7.9-8 Revision 6 - August 2016 Additional major design considerations that should be emphasized in the review of DCS safety systems are identified below: • Single-failure criterion - See SRP Appendix 7.1-B, Subsection 4.2, or SRP Appendix 7.1-C, Subsection 5.1. The use of DCSs as single paths for multiple signals or data raises particular concerns regarding extensive consequential failures as the result of a single failure. This review should confirm that channel assignments to individual communication subsystems are appropriate to ensure that both redundancy and diversity requirements (refer to SRP BTP 7-19, “Guidance for Evaluation of Diversity and Defense-in-Depth in Digital Computer- Based Instrumentation and Control Systems”) within the supported systems are met. NUREG/CR-6082 provides additional discussion of independence and failure modes. • Independence - See SRP Appendix 7.1-B, Subsections 4.6 and 4.7, or SRP Appendix 7.1-C, Subsections 5.6 and 6.3, and SRP Appendix 7.1-D, Subsection 5.6. Redundant communications networks may lose a degree of their independence and therefore their redundancy if interconnected. If the redundant communications networks are not interconnected, or if safety and nonsafety communications networks are not interconnected, the determination of communications independence is self-evident. If, however, there is such an interconnection, the determination of independence is significantly more complex and will take more effort and time. The review will need to ensure that the interconnection is such that each safety system will perform its safety function with no input or influence from the interconnected system, and that any failure of the interconnected system, failure of communications from that system or faulty data transmitted by that system will not prevent or influence that independent safety determination. The review should confirm that a physical, electrical, logical or software