Incorporating FLEX into PRA Models

There are substantial benefits and good reasons for incorporating and crediting FLEX equipment in industry PRA models, for all hazard types (not just seismic and external flooding). Reactor safety is improved by allowing operators the flexibility to use FLEX in a variety of scenarios - not just in beyond design basis external event scenarios, which are the subject of the previously issued Mitigation Strategies under Order EA-12-049. The benefits of crediting FLEX - both in procedures and in PRA models, and for risk applications (such as RICT and SDP cases) - outweigh any potential regulatory uncertainties. The NRC’s recent enforcement policy found in Inspection Manual Chapter (IMC) 0609 Appendix A was recently reconsidered for FLEX equipment deficiencies, both in how these are screened, and in how the cases would be quantified (i.e., which hazard models are used) when performing more detailed significance analysis. FLEX component reliabilities and associated deployment actions (HRA) are evolving and being closely studied and evaluated by industry and the NRC. In the meantime, our models should reasonably reflect the as-built/as-operated plant, as required by the ASME Standard and Regulatory Guide 1.200. The option to deploy FLEX strategies is an important defense in depth measure in any/all scenarios when an extended loss of power is present, and is an improvement in reactor safety. It’s acknowledgement in PRA models should not be discouraged or unduly challenged.

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