Document: NUREG-0800
Document ID: b8d2b8f5-432a-4c0a-81ab-20231f7d0f28
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1508/ML15089A068.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
, and design options to prevent these sequences from occurring and demonstrated that these accident sequences are not significant contributors to risk. These operational strategies should also provide reasonable assurance that there is sufficient ability to mitigate multiple core damages accidents. 2. Shutdown and refueling operations for small, modular reactor designs may be performed in ways which are new and completely different from those used at large traditional LWRs either licensed or under review by the NRC. In these cases, a more in-depth review will be needed to assure that the PRA model is of acceptable scope, level of detail, and technical adequacy. Reviewers should confirm that applicants identify and describe the expected 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 for low power and shutdown modes of operation 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 2 PRA) For DC applications and COL applications not referencing the Level 2 PRA in the DC, the reviewer6 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