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
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Content:
determine their adequacy on a case-by-case basis. 3.1.4 Use of a Qualitative Assessment and Failure Analysis to Eliminate the Potential for Common-Cause Failure from Further Consideration RIS 2002-22, 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 system has a low likelihood of failure such that current licensing assumptions continue to be met because the likelihood of CCF is much lower than other kinds of failures considered in the FSAR. This is referred to as “sufficiently low,” and its definition compares the likelihood of failure of a proposed DI&C system or component to 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 low-safety-significance systems. The qualitative assessment, as described in RIS 2002-22, Supplement 1, is a technical basis for demonstrating that a 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 systems will exhibit a low likelihood of failure and (2) failure analyses (e.g., failure modes and effects analysis (FMEA), fault tree analysis (FTA)) to support the qualitative assessment. First, the reviewer should consider the factors used in the qualitative assessment to demonstrate that a DI&C system or component will exhibit a low likelihood of failure (i.e., low likelihood of CCF). The reviewer should confirm that the likelihood of failure of the proposed DI&C system or component remains consistent with assumptions in the licensing basis. A qualitative assessment should consider the following factors: • the design attributes and features of the DI&C system or component • the