Document: NUREG-0800
Document ID: 7a278d84-5310-4198-b914-fa3af5a0a0ef
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500553.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
e prone to different kinds of failures than are traditional analog systems. Self-testing and watchdog timers may reduce the time to detect and identify failures, but are not a guarantee of hardware or software error detection. Computer self-testing is most effective at detecting random hardware failures. Surveillance testing taken together with automatic self-testing should provide a mechanism for detecting all detectable failures. The characteristics of digital systems must be considered in the review of technical specification surveillance features. Architectural differences between digital and analog systems warrant careful consideration during the review of surveillance test provisions. Furthermore, the concepts used to determine test intervals for hardware-based systems do not directly apply to the software used in digital computer-based instrumentation and control systems. Therefore, previous reliability analysis used to establish test intervals may not apply. Similar reviews are performed as necessary to verify the self-test and periodic test provisions for non-safety systems. 2. Information to be Reviewed Applicant/licensee's technical description of surveillance and self-test features, single-failure analyses, failure mode and effect analyses, and plant technical specifications should be considered in the review. 3. Acceptance Criteria Surveillance test and self-test features for digital computer-based protection systems should conform to the guidance of Reg. Guide 1.22, Reg. Guide 1.118, and Reg. Guide 1.153, "Criteria for Power, Instrumentation, Rev. 4 — June 1997 Appendix 7-A BTP HICB-17-4 and Control Portions of Safety Systems." Bypasses necessary to enable testing should conform with the guidance of Reg. Guide 1.47. Failure Detection Failures detected by hardware, software, and surveillance testing should be consistent with the failure detectability assumptions of the single-failure analysis and the failure modes and effects analysis. Self-Test