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:
Water Reactor (LWR) Certification Issues and Their Relationships to Current Regulatory Requirements” (Ref. 38). The CDF and LERF metrics are defined in a functional sense as follows: • Core damage frequency is defined as the sum of the frequencies of those accidents that result in uncovery and heatup of the reactor core to the point at which prolonged oxidation and severe fuel damage are anticipated and involving enough of the core, if released, to result in offsite public health effects. • Large early release frequency is defined as the sum of the frequencies of those accidents leading to rapid, unmitigated release of airborne fission products from the containment to the environment occurring before the effective implementation of offsite emergency response and protective actions such that there is the potential for early health effects. (Such accidents generally include unscrubbed releases associated with early containment failure shortly after vessel breach, containment bypass events, and loss of containment isolation.) • As discussed in SECY-13-0029, the staff has not developed a definition of large release frequency (Ref. 39). The staff encourages DC and COL applicants to review approved DC and COL applications (including the associated staff safety evaluation reports) and Section 5.1.1 of DC/COL-ISG-020 when developing a definition of large release frequency. In accordance with SRM-SECY-12-0081 (Ref. 40), COL holders transition from the use of LRF to the use of LERF when the fuel-load PRA required by 10 CFR 50.71(h)(1) is developed. Issues related to the reliability of barriers (in particular, containment integrity and consequence mitigation) are addressed by other parts of the decision-making process, such as consideration of defense- DG-1362, Page 13 in-depth. To provide the risk perspective for use in decision-making, a Level 1 PRA assesses the CDF risk metric and a limited Level 2 PRA assesses the LERF risk metric. DC and COL applicants should meet