Document: NUREG-0800
Document ID: 743c65f7-fe56-43cc-8658-f69bb64672dc
Document Type: srp
Title: Final Revision 0 – April 2014
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1311/ML13115A156.pdf
Revision Date: 2023-06
Chapter: 18
Section ID: 18
CFR Part: 
CFR Title: 

Content:
tory Commission (NRC) staff issued DI&C ISG-02, “Diversity and Defense-in-Depth Issues,” Revision 1 in September 2007. DI&C-ISG-02, Revision 1, specifically discussed adequate diversity and manual operator actions as follows: Manual operator actions may be credited for responding to events in which the protective action subject to a CCF is not required for at least the first 30 minutes and the plant response is bounded by BTP 7-19 recommended acceptance criteria. DI&C-ISG-02, Revision 1, further stated the following: The licensee or applicant should demonstrate through a suitable human factors engineering (HFE) analysis that manual operator actions that can be performed inside the control room are acceptable in lieu of automated backup functions. Subsequent to issuing DI&C-ISG-02, the NRC staff determined that further guidance was necessary for crediting manual operator action during an AOO/PA concurrent with a software CCF. As a result, on November 3, 2008, the NRC staff issued DI&C-ISG-05, Revision 1. The guidance, provided as Section 3 of DI&C-ISG-05, Revision 1, described a general methodology applicable to crediting operator action in lieu of automated back-up functions, regardless of whether the protective action was required in more or less than 30 minutes. In April 2009, the Advisory Committee on Reactor Safeguards (ACRS) reviewed DI&C-ISG-05, Revision 1. The ACRS noted that Phase 1 of the guidance for crediting of operator actions included a list of methods acceptable to the NRC staff for deriving estimates of time required for task components and concluded that the time estimates using these methods can be biased and the associated uncertainties can be difficult to assess. Furthermore, as the difference between the time available and time required decreases, confidence in the analysis decreases. In an April 21, 2009, letter to then Chairman Dale E. Klein, the ACRS provided these observations with associated recommendations to revise the guidance in