Document: NRC Regulatory Guide
Document ID: 82659041-98b0-4721-b25d-c4fb2ea394d0
Document Type: regulatory_guide
Title: An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1635/ML16358A153.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.174
CFR Part: 
CFR Title: 

Content:
ent failures. An example of this type of defense might be fire or flood barriers that limit component failures from fires of floods to only one train of redundant equipment. Another approach to defend against CCFs is to decouple failures as opposed to preventing the cause of failures. This defense effectively decreases the similarity of components and their environment in some way that prevents a particular type of failure cause from affecting all components simultaneously and allows more opportunity for detecting failures before they appear in all components of the group. An example of this type of defense against CCF is using diverse components to provide the same safety function. 5. Maintain multiple fission product barriers. Fission product barriers include the physical barriers themselves (e.g., the fuel cladding, reactor coolant system pressure boundary, and containment) and any equipment relied upon to protect the barriers (e.g., containment spray). In general, these barriers are designed to perform independently so that a complete failure of one barrier does not disable the next subsequent barrier. For example, one barrier, the containment, is designed to withstand a double-ended guillotine break of the largest pipe in the reactor coolant system, another barrier. A plant’s licensing basis might contain events that, by their very nature, challenge multiple barriers simultaneously. Examples include interfacing-system loss-of-coolant accidents (LOCAs), steam generator tube rupture, or crediting containment accident pressure. Therefore, complete independence of barriers, while a goal, might not be achievable for all possible scenarios. 6. Preserve sufficient defense against human errors. Human errors include the failure of operators to perform the actions necessary to operate the plant or respond to off-normal conditions and accidents, errors committed during test and maintenance, and other plant staff performing an incorrect action. Human errors can result in