Document: NUREG-0800
Document ID: fe8ec6c2-e960-404c-854f-55c77bde1672
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2400/ML24005A077.pdf
Revision Date: 2024-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
-significant functions SSCs in this category have one or more of the following characteristics:  They provide an auxiliary or indirect function in the achievement or maintenance of a safety-related function.  They perform a design function that is not safety related but that contributes significantly to plant safety.  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).  They are credited in the FSAR for meeting diversity requirements. c. Lowest safety significance: SSCs that are not safety related 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 When a Detailed Defense-in-Depth and Diversity Assessment Is Necessary A detailed 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 BTP 7-19-16 Revision 9 — May 2024 SSC “would not adversely affect a safety function or place a plant in a condition that cannot be reasonably mitigated.” Acceptance Criteria for Elimination of Further