Void formation at low pressure and low flow rates

A 2-MW version of the 20 kW SLOWPOKE research reactor is being developed by AECL for low temperature industrial or space heating applications [1]. A design target for the up-rated SLOWPOKE reactor is to achieve similar inherent safety against power excursions to that achieved in the present SLOWPOKE reactors. To accomplish this objective at the relatively high power density of the up-rated SLOWPOKE, the designers must rely on a strong negative void coefficient. Because of this, they must be able to predict the onset of significant void (OSV) and core void fractions under sub-cooled and low-quality conditions at the low pressures (∼150 to 250 kPa) and the low velocities (∼0.5 m/s and less) which will be met in this application. There is considerable information on OSV and void fractions for steam-water flows available in the literature and several well-known correlations exist for these parameters eg, Saha and Zuber and Levy. Most of the information and correlations are for higher pressures and velocities than those anticipated in an up-rated SLOWPOKE. (author)