Single-phase and two-phase flow computational fluid dynamics (CFD) simulations were performed for the coolant flow inside a CANDU thirty-seven element fuel string and the results are presented in this paper. The geometrical models represent original and modified 37-element fuel bundles inside un-crept and 5.1% crept pressure tubes. A Reynolds Averaged Navier Stokes (RANS) method with parallel processing was employed to limit the computational requirements to a reasonable level. The energy equations, decoupled from the momentum equations, were incorporated with a Conjugate Heat Transfer (CHT) model to investigate the element heat conduction effects. An inhomogeneous scheme in conjunction with a wall boiling and partitioning model was used for the two-phase flow analysis. Experiments were performed in a water loop with electrically-heated fuel bundles to simulate the fuel channel under a variety of operating conditions. Single-phase temperature and pressure and two-phase pressure data were used to evaluate the CFD model; good agreement was found. The CFD model was capable of predicting the pressure and temperature trends inside the flow channel as well as the bundle geometrical effects on the fuel thermalhydraulic performance.
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