Document: NUREG-0800
Document ID: 96afb1d6-6ce9-41e4-b4ec-1fc7747bc0b2
Document Type: srp
Title: Revision 8 – January 2021
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2033/ML20339A647.pdf
Revision Date: 2023-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
n that contributes significantly to plant safety. BTP 7-19-15 Revision 8 – January 2021 • They are capable of directly changing the reactivity or power level of the reactor and their failure could initiate an accident sequence or could adversely affect the integrity of a safety barrier (i.e., fuel cladding, reactor vessel, or containment). • Applicable GDCs may require diversity for SSCs in this category, or the FSAR may credit them for meeting diversity requirements. c. lowest safety significance: NSR SSCs that do not perform safety-significant functions SSCs in this category have one or more of the following characteristics: • They perform functions that are not considered significant contributors to plant safety. • They have no direct effect on the reactivity or power level of the reactor and do not affect the integrity of a safety barrier (i.e., fuel cladding, reactor vessel, or containment). 2.2 Using Safety Significance to Determine Whether a Diversity and Defense in Depth Assessment Is Necessary A D3 assessment is necessary for all systems determined to be of high safety significance. As stated in SECY-18-0090, a D3 assessment demonstrates “that failures due to software or failures propagated through connectivity cannot result in a failure to perform safety functions or adverse plant conditions that cannot be reasonably mitigated.” Therefore, in accordance with Principle 3 in SECY-18-0090, a D3 assessment “may not be necessary for some low-safety-significance l&C systems” if the application demonstrates that the failure of the SSC “would not adversely affect a safety function or place a plant in a condition that cannot be reasonably mitigated.” To accept a failure analysis in lieu of a D3 assessment, the reviewer should determine whether the proposed system is of low safety significance. Section 4 of the attachment to RIS 2002-22, Supplement 1, provides guidance on factors to consider for review of failure analyses of DI&C SSCs.