Multiphase CFD-based critical heat flux predictions for single-element heaters at CANDU reactor conditions.

• CFD modelling undertaken for pressurized heavy water reactor fuel channel conditions. • Developed new wall boiling model for predicting CHF based on liquid film thickness. • Assessed model predictions against CHF tests for single-element configuration. This paper uses Eulerian multiphase computational fluid dynamics (MCFD) simulations to predict the critical heat flux in a simplified CANDU test geometry for typical pressurized heavy water reactor (PHWR) conditions. A diffused liquid film-based wall dryout model is proposed based on the physical description of the dryout phenomenon. Given the adopted ensemble-averaged two-phase framework, this proposed model can represent the film dryout physics but requires some calibration. Simulations are performed for three calibration cases at 9 MPa outlet pressures to determine the appropriate diffused liquid film layer thickness to accurately predict the experimental data for the test geometry. This calibrated layer thickness is then applied to a number of assessment cases for various axial heating profiles, mass fluxes, inlet subcooling levels, and outlet pressures. The accuracies of the assessment simulations are generally within ±11 % of the experimental measurements, with a few exceptions. Specifically, the errors for the cases at lower outlet pressures (6 MPa) and mass fluxes (≲ 2000 kg/m2-s) ranged from about −19 % to –33 %. The lower pressure cases indicate that a separate calibration may be required at low pressures, while the larger errors in the lower mass flux cases suggest that some improvement of the boiling closures is needed to account for conditions at high average outlet quality. [ABSTRACT FROM AUTHOR]