Document: NUREG-0800
Document ID: 012eaab8-824c-49d3-b5d8-7cb652f166f0
Document Type: srp
Title: B-5
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550087.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.1
CFR Part: 
CFR Title: 

Content:
o achieve functional reliability commensurate with the safety functions to be performed. 4.2. Single-Failure Criterion (IEEE Std. 279-1971 Clause 4.2) Clause 4.2 of IEEE Std. 279-1971 requires in part that any single failure within the protection system shall not prevent proper protective action at the system level when required. The applicant/licensee's analysis should confirm that the requirements of the single-failure criterion are satisfied. Guidance in the application of the single-failure criterion is provided in Regulatory Guide 1.53, "Application of the Single-Failure Criterion to Safety Systems," which endorses IEEE Std. 379-2000, "IEEE Standard Application of the Single-Failure Criterion to Nuclear Power Generating Station Safety Systems." Where it is determined that the spatial dependence of a parameter requires several sensor channels to ensure plant protection, the redundancy requirements are determined for the individual case. In certain designs, for example, adequate monitoring of core power requires a minimum number of sensors arranged in a given configuration to provide adequate protection. This aspect of redundancy is dealt with in coordination with the organization responsible for the review of reactor systems to establish redundancy requirements. Components and systems not qualified for seismic events or accident environments and non-safety-grade components and systems are assumed to fail to function if failure adversely affects protection system performance. Conversely, these components and systems are assumed to function if functioning adversely affects protection system performance. All failures in the protection system that can be predicted as a result of an event for which the protection