Document: NUREG-0800
Document ID: d52a97d0-a519-4817-9ad6-64d94c9518af
Document Type: srp
Title: DATA COMMUNICATION SYSTEMS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159B177.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.9
CFR Part: 
CFR Title: 

Content:
o support self- testing and surveillance testing (refer to SRP BTP 7-17). • Time coherency of data - Methods to ensure the correct sequence of data packets at receiving DCS nodes should be reviewed. • Control of access - The review should confirm that the DCS does not present an electronic path by which unauthorized personnel can change plant software or display erroneous plant status information to the operators. Computers or equipment outside the control of the plant staff may be connected to nonsafety DCS (e.g., connections to remote data displays off site). In such cases, the connections should be through gateways that prevent unauthorized transactions originating from off site. Remote access to safety systems should not be implemented. 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) 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