Thermal-hydraulic modeling and analysis of a tank in pool reactor for normal operation and loss of flow transient

A transient thermal-hydraulic model entitled Tank in Pool Reactor Thermal-Hydraulic Analysis (TPRTHA) has been developed to simulate the steady-state operation and loss of flow transient for a tank in pool type research reactor. The model solves the momentum equation, energy equation and general conduction equation in cylindrical coordinates in order to predict the coolant velocity, coolant temperature and fuel rod temperature distribution respectively. The analytical solution is utilized for steady-state calculation while the finite difference technique with implicit scheme is adopted for transient calculation. The model divides the active core into a specified axial regions and the fuel rod into a specified radial zones, then a nodal calculation is performed for both average and hottest rods with a chopped cosine shaped heat generation flux. The model also predicts the heat flux leading to onset of nucleate boiling and the critical heat flux as well as the flow inversion phenomenon. The model is used to simulate a 2 MW reactor with downward flow direction and different types of fuel bundles of different powers and different flow rates. The best-estimate thermal-hydraulic safety margins are determined and the model results are analyzed and discussed.