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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CFR Title: 

Content:
ting 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 methods using realistic assumptions identified in point 2, the 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 D3 assessment independently. For example, if the initiating event is the loss of offsite power, the assessment does not need to assume another concurrent DBE. If the D3 assessment shows that a postulated CCF could disable a safety function, then point 3 directs that a diverse means be provided to perform that safety function or a different function. The diverse means may already exist in the facility or may be installed in connection with the DI&C modification. The diverse means may comprise NSR equipment, together with a documented basis that this equipment is of sufficient quality and is not vulnerable to the same CCF. Methods for demonstrating sufficient quality include application of the alternative treatment provided in 10 CFR 50.69(d)8 and quality controls or measures developed in accordance with GL 85-06. SECY-18-0090 clarifies that either automatic or manual actuation within an acceptable time frame is a permissible diverse means of actuation. If the D3 assessment demonstrates that a possible CCF can be reasonably mitigated by other means (e.g., using other installed systems), a diverse means that performs the same or a different function may not be needed. For example, an ATWS system may be credited as the diverse means of tripping the reactor, provided it is not vulnerable to the same CCF that could disable the safety function. If a diverse