Document: NUREG-0800
Document ID: c90016c6-e03f-4224-8ff3-87a6f7d3ca42
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500547.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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commit to documentation of life cycle activities that permit the NRC staff to evaluate the quality of the design features upon which the safety determination is based.  To verify that implementation of the software life cycle process meets the criteria expected for high-quality software.  To assess the adequacy of the design outputs. B. Branch Technical Position Rev. 4 — June 1997 Appendix 7-A BTP HICB-14-6 1. Introduction Digital I&C safety systems must be designed, fabricated, installed, and tested to quality standards commensurate with the importance of the safety functions to be performed. Implementation of an acceptable software life cycle provides the necessary software quality. Digital I&C systems may share code, data transmission, data, and process equipment to a greater degree than analog systems. Although this sharing is the basis for many of the advantages of digital systems, it also raises a key concern: a design using shared data or code has the potential to propagate a common-cause or common-mode failure via software errors, thus defeating the redundancy achieved by the hardware architectural structure. Greater sharing of process equipment among functions within a channel increases the consequences of the failure of a single hardware module and reduces the amount of diversity available within a single safety channel. Because of these concerns, the Staff review of digital I&C systems emphasizes quality, defense-in-depth, and diversity as protection against common-mode failures within and between channels. Software quality is an important element in preventing the propagation of common-mode failures. Commercial-off-the-shelf software and software embedded in commercial-off-the-shelf components, such as meters, circuit breakers, or alarm modules should be appropriately evaluated to confirm that required characteristics are met. EPRI Topical Report TR-106439, "Guideline on Evaluation and Acceptance of Commercial Grade Digital Equipment for Nuclear