Abstract
The objective of this research effort is to study the cool ability of spent fuel pool under various unload scenarios. For example, during full core unload, the fuel rods temporarily stored in the spent fuel pool, it is important to determine whether has proper capability to remove the decay heat. In this research study, we apply CFD (Computational Fluid Dynamics) methodology to develop tool for spent fuel pool thermal hydraulic analysis. The mathematical model, which includes the physical geometry dimension, is established. The large number of fuel rod bundles is approximated with porous media that will impose similar flow resistance to the motion of the fluid. Such treatment enables us to have optimum computational efficiency while maintaining high degree of accuracy of the pool flow behavior. The heat and mass transfer on the air/liquid interface is modeled by using effective heat transfer coefficient. When the power density of the fuel rods exceeds certain criteria, boiling and phase change is possible. A homogeneous two-phase model is implemented. In order to verify the accuracy of the present two-phase model, the result is compared with that computed by COBRA code. It is found that our model has close agreement with the prediction of the COBRA simulations. We conclude that the current model is suitable for the modeling of spent fuel pool thermal hydraulic process. In the case study, we found the current spent fuel pool can meet the requirements of the regulation when it is under the normal operation configurations. However, when the event is beyond the scope of the regulation, it may lead to local boiling if there is no external cooling system included. The temperature distribution and cooling situation could be improved via the layout of the fuel but this effect is limited when abnormals happened. Once those unlikely situations occur in the pool, we may have to start the cooling system for efficient cooling.