Document: NUREG-0800
Document ID: 965060de-8238-4868-a4c8-9a07c3e8cf13
Document Type: srp
Title: Diversity and
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A199.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.9
CFR Part: 
CFR Title: 

Content:
at runs on the computers linked together by the data communications system. They may support protection systems, other safety systems, diverse I&C systems, control systems, or any combination thereof. A design may provide separate safety and nonsafety data communications systems. The review topics applicable to any data communications system are the combination of topics applicable to the I&C systems supported by that data communications system. Computer internal data communication is at present accomplished by high-speed databuses that are usually designed by the makers of the computer system package itself. There are a number of standardized computer internal buses, and, unlike data communications systems, no software is involved (other than operating system software). Operation of computer internal buses is usually under the control of hardware. Unless this situation changes, computer internal data communication should be reviewed by confirming critical hardware characteristics. If software is involved in computer internal data communication, the review should proceed as described above under data communications systems. 3.3 Review of Diversity and Defense in Depth I&C safety systems incorporating digital computer technology in the reactor protection system or ESFAS should comply with the NRC position on diversity and defense-in-depth described in the Staff Requirements Memorandum (SRM) on SECY-93-087, “Policy, Technical, and Licensing Issues Pertaining to Evolutionary and Advanced Light-Water Reactor (ALWR) Designs.” Figure 7.0-A-4 of this appendix illustrates the process for review of the system-level diversity and defense in depth features to determine compliance with the position. SRP BTP 7-19 describes in detail the regulatory bases, material to be reviewed, acceptance criteria, and review process. For simple modifications, such as incorporating a single digital function into an otherwise analog I&C system, the diversity and defense in depth analysis may