Document: NRC Regulatory Guide
Document ID: 22ccfd5e-c5d8-4615-a02c-32369aa9f533
Document Type: regulatory_guide
Title: Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1930/ML19308B636.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.200
CFR Part: 
CFR Title: 

Content:
s function. Parameter estimation analysis quantifies the frequencies of the initiating events, as well as the equipment failure probabilities and equipment unavailabilities of the modeled systems. The estimation process includes a mechanism for addressing uncertainties and has the ability to combine different sources of data in a coherent manner, including the actual operating history and experience of the plant when it is of sufficient quality, as well as applicable generic experience. Human reliability analysis identifies and provides probabilities for the HFEs that can negatively impact normal or emergency plant operations. The HFEs associated with normal plant operation include DG-1362, Page 16 the events that leave the system (as defined by the success criteria) in an unrevealed, unavailable state. The HFEs associated with emergency plant operation represent those human actions that, if not performed, do not allow the needed system to function. Quantification of the probabilities of these HFEs is based on plant- and accident-specific conditions, where applicable, including any dependencies among actions and conditions. Quantification provides an estimation of the CDF given the design and/or operation the plant (depending whether the plant is in the design or operating stage). Regardless of the plant stage, the CDF is based on the summation of the estimated CDF from each accident sequence for each initiator group. If truncation of accident sequences and cut sets is applied, truncation limits are set so that the overall model results are not impacted in such a way that significant accident sequences or contributors are eliminated. Therefore, the truncation value is selected so that the required results are stable with respect to further reduction in the truncation value. Table 2 provides a summary of characteristics and attributes needed for the technical elements for a Level 1 PRA for internal events. The characteristics and attributes are provided for at-power