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:
ingle specific cause or event that could simultaneously affect several components important to risk. The cause or event may include an installation or construction deficiency, accidental human action, extreme external environment, or an unintended cascading effect from any other operation or failure within the plant. CCFs can also result from poor design, manufacturing, or maintenance practices. To defend against CCF, one should first identify potential coupling factors between equipment failures. A coupling factor is the condition or mechanism through which multiple components could be affected (or coupled) by the same cause. Coupling factors can be based on, but may not necessarily be limited to the following attributes: • Inadequate design for the environment or other aspect of the application. • Manufacturing error that diminishes the capability of all components of a particular batch or run. DG-1285, Page 16 • Detrimental maintenance practices (e.g., incorrect lubricant type or amount, poor performance of maintenance, etc.). • Support system dependencies (e.g., common power supplies, ventilation, cooling water, etc.). • Inadequate separation or protection from common hazards such as fires or flooding barriers. • Common staff, common procedures, or common maintenance, testing, or calibration schedules. Once coupling factors have been identified, measures may be put in place to minimize the impact of CCF. A variety of defense strategies can be used to decrease the likelihood of component or system unavailability and to minimize the occurrence of CCFs. Preventing and decoupling failures are both important as defenses against CCFs. A defense can prevent the occurrence of failures from the causes and events that could allow simultaneous multiple component 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