Document: NUREG-0800
Document ID: debf22b1-f3aa-4c75-a43c-f162d22de1c8
Document Type: srp
Title: of the plant safety analysis report (SAR).  Although the NRC did not endorse the annexes of
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A491.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.6
CFR Part: 
CFR Title: 

Content:
tegrity criteria provided by IEEE Std 603-1991, and the guidance in Subsection 5.5 of SRP Appendix 7.1-C, IEEE Std 7-4.3.2 includes criteria in Sub-Clauses 5.5.1 through 5.5.3 for designs for computer integrity, test and calibration, and fault detection and self-diagnostics activities. The following are necessary to achieve system integrity in digital equipment for use in safety systems: • Design for computer integrity • Design for test and calibration • Fault detection and self-diagnostics 5.6 Independence (IEEE Std 7-4.3.2, Clause 5.6) Consistent with the requirements of IEEE Std 603-1991, data communications between safety channels or between safety and nonsafety systems should not inhibit the performance of the safety function. Additional guidance on physical, electrical, and communication independence is provided in SRP Appendix 7.1-C Subsection 5.6. IEEE Std 603-1991 requires that safety functions be separated from nonsafety functions such that the nonsafety functions cannot prevent the safety system from performing its intended functions. In digital systems, software performing both safety and nonsafety functions may reside on the same computer and use the same computer resources. However, IEEE Std 603-1991, Sub-Clause 5.6.3.1 also requires that equipment that is used for both safety and nonsafety functions shall be classified as part of the safety system. The term “equipment” includes both software and hardware of the digital systems. For this reason, any software providing nonsafety functions that resides on a computer providing a safety function must be classified as a part of the safety system. If an applicant or licensee desires that a nonsafety function be performed by a safety computer, the software to perform that function must be classified as safety-related, with all the attendant regulatory requirements for safety software, including communications isolation from other nonsafety software. In some instances, vendors or applicants or