Document: NUREG-0800
Document ID: dd4f84a9-8976-44c4-b631-d7c0254f4efc
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1416/ML14161A594.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
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CFR Title: 

Content:
an 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 reviewer5 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 5 Support from an independent contractor or staff in the Office of Research may be necessary. 19.0-26 Draft Revision 3 –November 2014 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 (e.g., use of nozzle dams, outage schedule, containment status, procedural requirements) have been clearly documented in the FSAR. If licensee practices deviate dramatically from these assumptions in the future, the insights obtained from the shutdown PRA may no longer be valid. It is the COL applicant’s responsibility to confirm the assumptions made at the DC stage, and if done properly should capture any significant differences. 2. The staff