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:
ted 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 Features Digital computer-based instrumentation and control systems should include self-test features to confirm computer system operation upon system initialization. Digital computer-based instrumentation and control systems should generally include continuous self-testing. Some small, stand-alone, embedded digital computers may not need self-testing. Typical self-tests include monitoring memory and memory reference integrity, using watch-dog timers or processors, monitoring communication channels, monitoring central processing unit status, and checking data integrity. Other self-testing features that are candidates for incorporation into digital computer-based I&C systems include: plausibility checks for intermediate results, evaluation using different methods, ranges of variables, array bound checking, well-defined outputs for detected failures, reporting of errors for which error recovery techniques are used, use of counters and reasonableness traps, correctness verification of transferred parameters, and the use of assertions (see IEC Std 880). BTP HICB-14 discusses a number of functional characteristics for software design outputs, such as robustness and timing, which could give rise to self- testing features. Hardware and software used to perform automatic self-testing should be of equivalent safety classification, quality, and reliability as the tested system. The design should maintain channel independence, maintain system integrity, and meet the single-failure criterion during testing. The scope and extent of interfaces between software that performs protection functions and software for other functions such as testing should be designed to minimize the complexity of the software logic and data structures. The hardware and software used to perform automatic