Validation of the CFX-4 Code for PWR Fault Analysis

This paper presents the current status of the AEA Technology work validating CFX-4 as a tool for modelling fluid transport and mixing in reactor coolant systems. Conclusions are given on the adequacy of this methodology for correctly predicting turbulent mixing in the fault transients of relevance. CFX-4 code predictions have been carried out against pump start-up data from the 1/5 scaled (based on Ringhals) experiments at Vattenfall. These experiments are concerned with the transport of a boron depleted slug of fluid from the cold leg to the vessel. These computational results showed the timescales and concentration of the boron depleted slug reaching the core region to be well predicted. AEA Technology, on behalf of UK Health and Safety Executive, is also participating in the pump start-up ISP at the University of Maryland during 1999/2000. Predictions of thermal mixing have been carried out against Sizewell-B plant data from Emergency Boration System (EBS) commissioning tests. These data provide a stringent test for the code which successfully replicated the broad features but failed to reproduce an observed swirl. This modelling discrepancy is currently under investigation. (authors)