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Furthermore, LPS PSA models and results can be used to identify enhancements to procedures (either normal procedures used during shutdown or emergency procedures) or hardware modifications. An accurate representation of the plant during shutdown conditions requires extensive and detailed interaction between the PSA analysis team and all organizations at the plant which are involved in work performed during the shutdown. Thus, sufficient time and resources should be allocated to ensure these interactions can take place.

This identification and quantification guidance should be specifically developed for shutdown conditions where multiple human actions may be ongoing and where the time to respond may range from very short to very long. This methodological guidance should ensure that the following human actions are included in the analysis: • • those occurring before the initiating event; those causing or contributing to an initiating event; • those in response to procedural steps; • those that recover or repair failed equipment.

In order to get a realistic picture of the nature and safety significance of a LPS event, it is sometimes necessary to do a very detailed and comprehensive analysis. A good example of this is a boron dilution event for which models of mixing and 3D neutron kinetics are needed in combination with modelling of primary circuit thermal hydraulics. Currently the analysis for LPS has been performed only for a small number of cases. However, because of their safety significance, there is a need to perform these analyses for inclusion in final safety analysis reports, for development of emergency operating procedures, and for further development of technical specifications.