The objectives for the ASP large early release frequency (LERF) model development work is to build a Level 2 containment response model that would capture all of the events necessary to define LERF as outlined in Regulatory Guide 1.174, can be directly interfaced with the existing Level 1 models, is technically correct, can be readily modified to incorporate new information or to represent another plant, and can be executed in SAPHIRE. The ASP LERF models being developed will meet these objectives while providing the NRC with the capability to independently assess the risk impact of plant-specific changes proposed by the utilities that change the nuclear power plants' licensing basis. Together with the ASP Level 1 models, the ASP LERF models provide the NRC with the capability of performing equipment and event assessments to determine their impact on a plant's LERF for internal events during power operation. In addition, the ASP LERF models are capable of being updated to reflect changes in information regarding the system operations and phenomenological events, and of being updated to assess the potential for early fatalities for each LERF sequence. As the ASP Level 1 models evolve to include more analysis capabilities, the LERF models will also be refined to reflect the appropriate level of detail needed to demonstrate the new capabilities. An approach was formulated for the development of detailed LERF models using the NUREG-1150 APET models as a guide. The modifications to the SAPHIRE computer code have allowed the development of these detailed models and the ability to analyze these models in a reasonable time. Ten reference LERF plant models, including six PWR models and four BWR models, which cover a wide variety of containment and nuclear steam supply systems designs, will be complete in 1999. These reference models will be used as the starting point for developing the LERF models for the remaining nuclear power plants.
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