Document: NUREG-0800
Document ID: dc63e8aa-2a74-4078-9e19-9a26ed1b4d8c
Document Type: srp
Title: Revision 6 – July 2012
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1105/ML110550791.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
ted where applicable: ● The justification for equipment diversity, or for the diversity of related system logic such as a real-time operating system, should extend to the equipment’s components to assure that actual diversity exists. For example, different manufacturers might use the same processor or license the same operating system, thereby incorporating common failure causes. Claims for diversity on the basis of the difference in manufacturer name are insufficient without consideration of the above. ● With respect to computer software and software-based logic diversity, experience indicates that independence of failure causes may not be achieved in cases where multiple versions of software, for example, are developed using the same set of software, system, and logic development tools. Other considerations, such as technology, functional and signal Revision 6 – July 2012 BTP 7-19-19 diversity that lead to different software, system, and logic requirements form a stronger basis for diversity. 3.9 System Testability If a portion or component of a system can be fully tested, then it can be considered not to have a potential for software-based CCF. Fully tested or 100% testing means that every possible combination of inputs and every possible sequence of device states are tested, and all outputs are verified for every case. Further, in assessing the system states, the guidance provided in IEEE Std. 7-4.3.2-2003, Clause 5.4.1, “Computer system [equipment qualification] testing,” should be addressed: Computer system [equipment] qualification testing (see 3.1.36) shall be performed with the computer functioning with software and diagnostics that are representative of those used in actual operation. All portions of the computer necessary to accomplish safety functions, or those portions whose operation or failure could impair safety functions, shall be exercised during testing. This includes, as appropriate, exercising and monitoring the memory, the CPU,