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:
s, that is, the initial plant conditions corresponding to the onset of the event being analyzed. Point 2 also includes acceptance criteria for best-estimate methods that are less conservative than the acceptance criteria defined in the updated final safety analysis report (FSAR) for the applicable limiting events within the design basis. Initial plant event conditions include, but are not limited to, the following:  power levels  temperatures  pressures  flows  alignment of equipment  availability of plant equipment not affected by the postulated CCF SECY-18-0090 clarifies that, in addition to the best-estimate methods using realistic assumptions identified in Point 2, the best-estimate D3 assessment can be performed using a design-basis analysis. The key distinction is that a design-basis analysis uses conservative assumptions. Reviewers should consider whether each event analyzed in the accident analysis is evaluated in the best-estimate D3 assessment independently. For example, if the initiating event is a loss of offsite power, the assessment does not need to assume another concurrent design-basis event (DBE). Point 3 refers to the risk significance of CCFs, whereas Point 1 refers to the risk significance of the proposed DI&C system. Section B.3.4 discusses these concepts. Point 3 calls for an applicant to demonstrate that a postulated CCF will be reasonably prevented or mitigated or that the CCF is not risk significant. An applicant can do this by demonstrating the adequacy of the design techniques and prevention and mitigation measures credited in the D3 assessment. If the D3 assessment demonstrates that a CCF can be reasonably prevented or mitigated by other means (e.g., using other installed systems) or that the CCF is not risk significant, then a diverse means of performing the same or a different function may not be needed. When a diverse means is provided, Point 3 allows for the diverse means to be comprised of safety-related equipment