Use of RETRAN for determination of some BWR success criteria

The evaluation of the risks associated with severe accident and transient conditions of nuclear power plants by means of probabilistic risk assessment has increased significantly in the past few years. The determination of core melt frequency, for this evaluation, has previously been based on conservative assumptions of the system success criteria. System success criteria are the minimum available system configuration, operator actions, etc. required to safely shutdown a nuclear plant for a given accident or transient initiating event. This paper discusses the use of the RETRAN thermal-hydraulic system analysis code to determine bestestimate success criteria of the Wm. H. Zimmer plant for two operational transients with dominant risk potential. The risk implications resulting from the application of these realistic, best-estimate success criteria will also be examined