Evaluation of Debris Transport Augmentation by Turbulence During the Recirculation Cooling Phase of a LOCA

The determination of the debris transport fraction during a LOCA of a PWR is very important in the sizing of the sump screen area. In this study, the debris transport fraction during the recirculation cooling phase is evaluated with and without consideration of turbulence effect. To do this, first experiments involving tumbling velocities measurements and supplementary CFD analyses are performed to verify the turbulence effect on debris transport. From these findings, the turbulence effect on the degree of debris tumbling augmentation was found to be represented by the algebraic sum of the mean velocity and the fluctuating velocity. Then, a CFD analysis of the flooding containment floor during the recirculation cooling phase of the OPR1000 plant is performed. Based on these studies, the debris transport fraction is evaluated for NUKON. The result shows a considerable increase in the debris transport fraction when a turbulence effect is implemented compared to when it is not. Increases of 5.55 and 2.06 times are observed for large NUKON and small/fine NUKON, respectively. This result implies that the turbulence effect should be considered in the debris transport quantification for conservatism.