Document: NUREG-0800
Document ID: b8d2b8f5-432a-4c0a-81ab-20231f7d0f28
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1508/ML15089A068.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
ion. Hardware CCF between different safety 19.0-30 Revision 3 – December 2015 functions using the same hardware should be identified. Dependencies between hardware and software should be identified. The applicant should provide the rationale for the degree of dependency assumed for DI&C CCF. An important expectation is that the applicant included sufficient equipment in the CCF groups. The evaluation should address why various channels, trains, systems, etc., were or were not placed in each CCF group. The justification should discuss common software/hardware among the equipment considered and the level(s) of dependency among them. The reviewer should work with the I&C reviewer to evaluate the applicant’s justifications. D. It is important to evaluate claims by applicants regarding the credit that should be given for defensive design features. Design features such as fault tolerance, diagnostics, and self testing are intended to increase the safety of DI&C systems, and therefore are expected to have a positive effect on the system’s safety. However, these features may also have a negative impact on the safety of DI&C systems if they are not designed properly or fail to operate appropriately. The potentially negative effects of these features should be included in the probabilistic model. The PRA should account for the possibility that after a failure is detected, the system may fail to reconfigure properly, may be set up into a configuration that is less safe than the original, may fail to mitigate the failure altogether, or the design feature itself may contain the fault. The benefits of these features also may be credited in the PRA. Care should be taken to ensure that design features intended to improve safety are modeled correctly (e.g., ensuring that the beneficial impacts of these features are only credited for appropriate failure modes and that the limitations, including failure of the design feature itself, is considered in the model). An issue