Assessment of the Effect of the Advanced Drift-Flux Model of ASSERT-PV on CHF, Flow and Void Fraction Distributions

Abstract of the journal article publised in Annals of Nuclear Energy
June 2017

Prepared by:
N. Hammouda
Canadian Nuclear Safety Commission

Y.F. Yao
Canadian Nuclear Laboratories

Abstract

This paper examines the effect of the drift-flux model of ASSERT-PV on critical heat flux (CHF) predictions. More specifically, it looks at how the drift-flux model influences local void fraction and flow distribution across a bundle. Numerical experiments are performed to examine the trends and relative behaviour of the different components of the drift-flux model under various flow conditions.

The drift-flux model of ASSERT-PV is composed of three components: (a) the lateral component or diversion cross-flow, caused by pressure difference between connected subchannels, (b) the turbulent diffusion component or turbulent mixing through gaps in subchannels, caused by instantaneous turbulent fluctuations or flow oscillations, and (c) the void drift component that occurs due to the two-phase tendency toward a preferred distribution.

This study shows that the drift-flux model has a significant impact on CHF predictions. The lateral component of the drift-flux model has a stronger effect on CHF predictions than the axial component, especially for horizontal flow. Predictions of CHF, void fraction and flow distributions are most sensitive to the turbulent diffusion component of the drift-flux model, followed by the void drift component. Buoyancy drift can be significant, but does not have as much influence on CHF and flow distribution predictions as the turbulent diffusion and void drift do.

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