  The Burns turbulent dispersion force is the most commonly used turbulent
dispersion in the twofluid RANS bubbly-flow literature. However, its derivation
is based on a series of hypothesis that are difficult to justify in industrial
flows. It is shown that in low-void fraction vertical pipe flow, the Burns
turbulent dispersion formulation is equivalent to considering the radial
movement of the gas phase like a passive scalar that follows turbulent eddies.
This is not apparent in the derivation of the force. As bubbles in pressurized
water reactor (PWR) conditions have a low Stokes number ($\sim$ 10--1),
considering bubbles are transported by turbulence is a good approximation for
bubble dispersion in pipe flow. Therefore, the Burns turbulent dispersion force
is appropriate to represent bubble dispersion in low-void fraction PWR flows.
