Document: NUREG-0800
Document ID: 65f2433f-2c4a-4580-b173-0c6da7fa4d73
Document Type: srp
Title: Draft Revision 7 – August 2015
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A996.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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CFR Title: 

Content:
ols should not prevent the operator from manually initiating safety functions. Prioritization between safety and diverse nonsafety systems to ensure the credited safety function can be accomplished by either system is addressed as follows: BTP 7-19-16 Draft Revision 7 – August 2015 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 priority ranking and the explanation to appropriate systems experts for review. The priority module itself should be shown to apply the commands correctly in order of their priority rankings, and should meet all other applicable guidance. It should be shown that the unavailability or spurious operation of the actuated device is accounted for in, or bounded by, the plant safety analysis. This recommendation does not prohibit the use of manual controls for operating individual safety system components after the corresponding safety system functions have been actuated. 3.6 Applicability to Current or New Plants This guidance applies to both the currently operating NPPs licensed under 10 CFR Part 50 and new NPPs licensed under 10 CFR Part 52. The potential for CCF in digital safety systems should be considered whether the systems are to be used in new plants or for upgrades in existing plants. The main difference is that new NPPs predominantly will use digital technology, whereas currently operating plants may introduce