Analysis of the LaSalle Unit 2 Nuclear Power Plant, Risk Methods Integration and Evaluation Program (RMIEP)

This report is a description of the internal flood analysis performed on the LaSalle County Nuclear Generating Station, Unit 2. A more detailed integration with the internal events analysis than in prior flood risk assessments was accomplished. The same system fault trees used for the internal events analysis were also used for the flood analysis, which included modeling of components down to the contact pair level. Subsidiary equations were created to map the effects of pipe failures. All component locations were traced and mapped into the fault trees. The effects of floods were then mapped directly onto the internal plant model and their relative importance was evaluated. A detailed screening analysis was performed which showed that most plant areas had a negligible contribution to the flood-induced core damage frequency. This was influenced strongly by the fact that the LaSalle plant was designed with a high level of concern about the effects of external events such as fire and flood and significant separation was maintained between systems in the original design. Detailed analysis of the remaining flood scenarios identified only two that contributed significantly to risk. The flood analysis resulted in a total (mean) core damage frequency of 3.23E-6 per year