Document: NUREG-0800
Document ID: 757b676a-0f71-4094-8677-ca3a50743281
Document Type: srp
Title: Revision 7 – August 2016
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A344.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
port (SAR) using best-estimate methods. The vendor or applicant shall demonstrate adequate diversity within the design for each of these events.” Point 3 “If a postulated common-mode failure could disable a safety function, then a diverse means with a documented basis that the diverse means is unlikely to be subject to the same common-mode failure, shall be required to perform either the same function or a different function. The diverse or different function may be performed by a nonsafety system if the system is of sufficient quality to perform the necessary function under the associated event conditions.” Point 4 “A set of displays and controls located in the main control room shall be provided for manual, system-level actuation of critical safety functions and monitoring of parameters that support the safety functions. The displays and controls shall be independent and diverse from the safety computer system identified in Items 1 and 3 above.” The term “best-estimate methods” in Point 2 is more accurately referred to as “realistic assumptions,” which are defined as normal plant conditions corresponding to the event. For example: • power levels, • temperatures, • pressures, • flows, and • alignment of equipment. Thus, in performing the assessment, the vendor or applicant should analyze each postulated CCF for each event that is evaluated in the SAR section analyzing power operation accidents at the plant conditions corresponding to the event. This analysis may use realistic assumptions to analyze the plant response to DBEs, or the conservative assumptions on which the Chapter 15, SAR analysis is based. If the D3 analysis indicates a postulated CCF could disable a safety function, then Point 3 directs that an applicant should identify an existing diverse means or add a diverse means that may be nonsafety (see Section 1.6, “D3 Assessment”). Point 3 also addresses manual initiation methods of RTS and ESFAS, if subject to a postulated