The 'IMPACT Super-Simulation' project for exploring NPP fundamental phenomena

To ensure the safe operation of a nuclear power plant under any normal operating or hypothesized accident conditions, understanding of the physical phenomena involved and tools to calculate such events must exist. The complexity of the fundamental phenomena and their interrelated effects require considerable research and development of software and hardware to produce a audible power plant simulation system. A large-scale project is underway at the Nuclear Power Engineering Corporation to develop the software for a 'Super Simulation' system, capable of analysing scenarios ranging from normal operation to hypothesised accident conditions. Designed as a large-scale system of interconnected, hierarchical modules, IMPACT's distinguishing features include mechanistic models and high speed simulation on parallel processing computers. The present plan is a ten-year program starting from 1993. The IMPACT software will be completed within the year 2000 followed by two years for refinement through extensive verification and validation against test results and available real plant data. Parallelization was completed for the incompressible single phase flow module and on increase in calculation speed of at least 30 times by parallel processing on 64 processors has been attained, depending on a number of mesh. The pre-mixing submodule for analysis of steam explosion phenomena under severe accident conditions has been completed, and was shown to simulate the MIXA tests well. Calculation results of debris spreading model in debris cooling process are compared and showed good agreement with the UC Santa Babara test results. The physical models in the Boiling Transition Code has been completed and partially verified for both BWR fuels and PWR fuels by the comparison with basic experimental results. (author)