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:
ence between these times should be appropriately considered. This uncertainty could reduce the level of assurance and potentially invalidate a conclusion that operators can perform the action reliably within the time available. For complex situations and for actions with limited margin, such as less than 30 minutes between time available and time required, a more focused staff review will be performed. Diverse manual initiation of safety functions should be performed on a system level or division level basis (depending on the design). Since single failures concurrent with a CCF are not required to be postulated and normal alignment of equipment is assumed, the capability for manual actuation of a single division is sufficient. For plants licensed to allow one division to be continuously out of service, the diverse manual actuation should apply to at least one division that is in service (see section B.3.1, item 9, concerning addressing spurious actuation caused by the diverse means in the design of the diverse means). A CCF that affects normal displays or controls should not prevent the operator from manually initiating safety functions. Prioritization between safety and diverse non-safety systems to ensure the credited safety function can be accomplished by either system is addressed as follows: Safety-related commands that direct a component to a safe state must always have the highest priority and must override all other commands. Commands that originate in a safety-related channel but which only cancel or enable cancellation of the effect of the safe-state command (that is, a consequence of a CCF in the primary system that erroneously forces the plant equipment to a state that is different from the designated “safe state”), and which do not directly support any safety function, have lower priority and may be overridden by other commands. The reasoning behind the proposed priority ranking should be explained in detail. The reviewer should refer the proposed