Document: NUREG-0800
Document ID: fe8ec6c2-e960-404c-854f-55c77bde1672
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2400/ML24005A077.pdf
Revision Date: 2024-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
ount for potential spurious operation. b. The different portions of the DI&C system are sufficiently diverse to perform the safety function without relying on the performance of common components, and the SSCs and software of the different portions are not vulnerable to the same CCFs. c. The diverse portions of the DI&C system do not have common or shared resources, such as power supplies, memory, bus, or communications modules, whose failure could result in a failure to perform safety functions or in adverse plant conditions that cannot be reasonably mitigated. Also, the diverse portions of the DI&C system do not share engineering or maintenance tools whose failure could affect both or all portions. d. Each diverse portion used to perform the credited safety functions is shown to be reliable and available in the plant conditions during which the associated event needs to be prevented or mitigated. e. Periodic surveillance criteria are used to verify the continuing functionality of each diverse portion. 3.1.2 Use of Testing to Eliminate the Potential for Common-Cause Failures from Further Consideration CCF vulnerabilities in DI&C systems have two general causes: (1) errors introduced by the system hardware or software design, and (2) errors or defects introduced during the development of the software, hardware, or software-based logic. When designing a DI&C system, the applicant might use a robust (high-quality) development process, in conjunction with thorough system analysis (e.g., failure modes and effects analysis, system-theoretic process analysis), to correct many potential design errors in the requirements or specifications for both analog and digital equipment. Thorough testing can help to identify latent design defects in DI&C systems, provided the design is simple enough to allow such testing. Testing can be used to uncover latent design defects for correction in the design process and to demonstrate that any identified latent design defects have been