Document: NUREG-0800
Document ID: dd4f84a9-8976-44c4-b631-d7c0254f4efc
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1416/ML14161A594.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
he same DI&C hardware is used for implementing several DI&C systems that perform different functions, a failure in the hardware, software, or system of the DI&C platform may adversely affect all these functions. Should these functions be needed at the same time, they would be affected simultaneously. This impact should be explicitly included in the probabilistic model. The DI&C system probabilistic model should be fully integrated with the probabilistic model of other systems. Coordinate with the I&C reviewer. B. Ensure that spurious actuations of diverse backup systems or functions are evaluated and the overall risk impact documented. C. Common cause failures can occur in areas where there is sharing of design, application, or functional attributes, or where there is sharing of environmental challenges. Review the extent to which the DI&C systems were examined by the applicant to determine the existence of such areas. Each of the areas found to share such attributes should be evaluated in the DI&C analysis to determine where CCF should be modeled and to estimate their contribution. Based on the results of this evaluation, D&IC software and/or hardware/software dependent CCFs may need to be applied in several areas within subsystems (e.g., logic groups), among subsystems of the same division, across divisions or trains, and across systems. For example, CCF assignments should be based on similarity in design and function of component or system modules. The CCF events should be identified and modeled by the applicant. The CCF probabilities and their bases should be evaluated and provided based on an evaluation of coupling mechanisms (e.g., similarity, design defects, external events, and environmental effects) combined with an evaluation of defensive measures meant to protect against CCF (e.g., separation and independence, operational testing, maintenance, diagnostics, self-testing, fault tolerance, and software/hardware design/development techniques and processes).