Document: NUREG-0800
Document ID: dc63e8aa-2a74-4078-9e19-9a26ed1b4d8c
Document Type: srp
Title: Revision 6 – July 2012
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1105/ML110550791.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
ted basis) is necessary. The D3 analysis methods used in ALWR DC applications and for operating plant upgrades are documented in NUREG/CR-6303, which describes an acceptable method for performing such assessments. When the RTS and ATWS mitigation system in an operating plant is modified, the requirements of the ATWS rule, 10 CFR 50.62, must be met. 10 CFR 50.62 requires that the ATWS mitigation system be composed of equipment that is diverse from the RTS. If “sufficient” diversity in manufacturer cannot be demonstrated, a case-by-case assessment of the mitigation system designs should be conducted. This assessment should include differences such as manufacturing division (within a corporate entity), software (including implementation language), equipment (including control processing unit architecture), function, and people (design and verification/validation team). 1.7 The Diverse Means When a diverse means is needed to be available to replace an automated system used to accomplish a credited safety function as a result of the D3 assessment identifying a potential CCF, the credited safety function (or a different function that will accomplish the same desired safety protection) can be accomplished via either an automated system or manual operator actions performed from the MCR. The preferred diverse means is generally an automated system. The primary focus of BTP 7-19 is to identify whether a diverse means of performing protective actions is necessary due to an automated safety function being subject to a postulated CCF. Functions performed manually normally would be expected to still be performed manually in the presence of a CCF (even if different equipment is called upon to function). If the manual actuation method could be adversely affected by the postulated CCF, then a diverse manual means is needed to perform the safety function or an acceptable different function. 1.8 Potential Effects of CCF: Failure to Actuate and Spurious Actuation There are two