Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
on). The preferred resolution to this would be a request for re-solution with the appropriate changes made to all affected SSCs. Section A.9 of this SRP chapter discusses this in more detail. SSCs may not be included in the logic model structure because HEPs are so high that they are assumed to dominate the unavailability of a function, and therefore the associated hardware is not modeled. However, the hardware could still be a contributor to the calculation of risk importance. For example, the hardware (as a group) will have the same risk importance (in terms of Risk Achievement Worth) as the associated HFIE. This suggests that the licensees should identify the important operator actions for applications in RIR, as well as the equipment required to perform the specific function associated with the action. The equipment should then be dispositioned in accordance with its importance in achieving that function. For some complexy groups of operator actions (e.g., the response to an ATWS in a BWR, or the choice to go to recirculation rather than RHR in response to a small LOCA in a PWR), the PRA analysts may have chosen to adopt a bounding approach to the accident scenarios which precludes having to address subsequent actions. This could mean that the equipment associated with those actions might be overlooked in the change process. c. Evaluation Findings The staff safety evaluation report should include language equivalent in effect to the following: The modeling of human performance is appropriate. Post-accident recovery of failed components is modeled in a defensible way. Recovery probabilities are realistically quantified. The formulation of the model shows decisionmakers the degree to which the apparently low risk significance of certain items is dependent on credit for recovery of failed components (restoration of component function, as opposed to actuation of a compensating system). When human actions are proposed as compensatory measures as part of a proposed