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:
002-22, Supplement 1, describes a methodology, called “qualitative assessment,” to assess the likelihood of failure due to CCF in DI&C systems and components. RIS 2002-22, Supplement 1, identifies acceptance criteria to determine whether a DI&C system’s likelihood of failure due to CCF is low enough so that current licensing assumptions will continue to be met, because the likelihood of CCF is much lower than that of other kinds of failures considered in the FSAR. This level of likelihood of CCF is referred to as “sufficiently low,” and its definition compares the likelihood of failure of a proposed DI&C system to that of other failures documented in the FSAR. The qualitative assessment is a less technically rigorous type of D3 assessment, and, as such, is sufficient to eliminate CCF vulnerabilities from further consideration only for systems of lower or lowest safety significance. As described in RIS 2002-22, Supplement 1, the qualitative assessment is a technical basis for demonstrating that a proposed DI&C system will exhibit a low likelihood of failure (i.e., a low likelihood of CCF). The technical basis includes (1) three factors used to demonstrate that the proposed system will exhibit a low likelihood of failure, and (2) failure analyses (e.g., failure modes and effects analyses (FMEA), fault tree analyses (FTA)) to support the qualitative assessment. First, the reviewer should consider the factors used in the qualitative assessment to demonstrate that the DI&C system will exhibit a low likelihood of failure (i.e., a low likelihood of CCF). The reviewer should confirm that the likelihood of failure of the proposed DI&C system remains consistent with the assumptions in the licensing basis. A qualitative assessment should consider the following factors: BTP 7-19-23 Revision 9 — May 2024  the design attributes and features of the DI&C system  the quality of the design process for the DI&C system  any applicable operating experience for the