Droplet Entrainment and Deposition Rate Models for Determination of Boiling Transition in BWR Fuel Assembly

Abstract

Droplet entrainment and deposition rates are of vital importance for mechanistic determination of critical power and location of boiling transition in a BWR fuel assembly. Data from highpressure, high-temperature steam-water adiabatic experiments conducted in very tall test sections are used to develop a combination of equilibrium entrainment-deposition rate. Application of this combination to the heated tests conducted in a shorter test section of typical height of a BWR fuel assembly shows that correct split of total liquid in form of the film and droplets at the onset of annular-mist flow regime is also important to obtain good prediction of film flow rates/entrainment fraction. The improved model is then applied to simulate critical power tests in annulus and rod bundles.