Document: NUREG-0800
Document ID: 1b840382-003a-4162-a666-f8ba076b669c
Document Type: srp
Title: Revision 6 – August 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A316.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
include self-test features to confirm computer system operation on system initialization. Digital computer-based I&C 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, and correctness verification of transferred parameters. SRP BTP 7-14 discusses a number of functional characteristics for software design, such as robustness and timing, which could give rise to self-testing features. Self-tests may also include automatic calibration tests such as the use of fundamental physical principles in Johnson noise thermometry to calibrate resistance temperature detectors (RTDs). The design of automatic self-test features 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 self-test should be designed to minimize the complexity of the software logic and data structures. The safety classification of the hardware and software used to perform automatic self-testing should be equivalent to that of the tested system unless physical, electrical, and communications independence are maintained such that no failure of the test function can inhibit the performance of the safety function. The positive aspects