Document: NRC Regulatory Guide
Document ID: 8a2332d3-66ca-40af-84e1-507db8b26559
Document Type: regulatory_guide
Title: TRIAL - Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2123/ML21235A008.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.247
CFR Part: 
CFR Title: 

Content:
and relatively constant plant conditions is identified and characterized. • LPSD plant evolutions are divided into POSs based on differences in plant response to initiating events in a given POS to facilitate the practicality and efficiency of the PRA. • Each POS to be considered for the specific application is identified and characterized with respect to all important conditions affecting the delineation and evaluation of event sequence families. • The POS safety functions to consider include reactivity control, reactor coolant chemistry control, decay heat removal control, reactor coolant system (RCS) inventory/barrier control, radionuclide transport barrier control, and ex-vessel fission product control (e.g., off-gas tanks/fuel salt storage tanks/spent fuel pools). • POS definitions should consider decay heat level, RCS configuration, reactor level (i.e., for reactors with liquid coolant), reactor pressure and temperature, radionuclide transport configuration, status of radionuclide transport barriers, status of fire and flood barriers, available and accurate instrumentation necessary to adequately monitor key plant parameters for the specific POS, and any additional plant parameters and assumed representative plant system configurations needed to determine POS success criteria, POS mechanistic source terms, and POS radiological consequences. • POS definitions should include all sources of radioactive material within the scope of the PRA, including ex-vessel sources, unless there is a documented technical justification for excluding ex-vessel sources. RG 1.247, Page 20 • POS definitions should consider any activities that may lead to changes in the above parameters used to define the POS. • POS definitions should be reviewed to ensure they are adequate for all hazard groups evaluated within the scope of the PRA. • POS definitions should include consideration of changing plant conditions that may impair or change the effectiveness of hazard