Document: NUREG-0800
Document ID: 8dd882f4-a34f-4415-acd1-ebb441c72786
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1213/ML12132A481.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
s identify and describe all the specific plant operating states (POS) in a refueling outage between the time the output breaker to the grid is opened for plant shutdown and when it is closed to resume power operation after the outage. The reasonableness of the PRA model cannot be judged without a description of each POS that includes an estimate of the expected time in the POS, a description of the expected changes in configuration of the nuclear steam supply system, a description of the methods of removing heat from the fuel during each POS, a description of the automatic and human actions expected to occur during each POS and an assessment of the potential upset conditions and human errors during each POS that could contribute to a loss of decay heat removal. Design-Specific PRA (Level II PRA) For DC applications and COL applications not referencing the Level II PRA in the DC, the reviewer4 carries out an independent assessment of the plant response to selected severe accident scenarios using the latest version of the MELCOR computer code. The assessment should examine accident scenarios from the PRA, which are chosen based on a combination of frequency, consequence, and dominant risk. Some of these scenarios should be similar or identical to sequences analyzed by the applicant and reported in the PRA. The reviewer compares the results of corresponding sequences and release categories in the two studies. If the results of the assessment do not support and confirm the applicant’s simulation of the accident progression, analysis methodology, and interpretations of its analyses of the reactor, containment, and system response to severe accidents, the reviewer engages with the applicant to resolve the differences in results. Design-Specific PRA (PRA for Non-Power Modes of Operation) 1. Given that shutdown risk may be highly outage-specific, the staff reviews the shutdown PRA insights to confirm that operational assumptions used to develop an average shutdown model