Investigation of film boiling thermal hydraulics under FCI conditions: results of analyses and a numerical study

Film boiling on the surface of a high-temperature melt jet or of a melt par ticle is one of key phenomena governing the physics of fuel-coolant interac tions (FCIs) which may occur during the course of a severe accident in a li ght water reactor (LWR). A number of experimental and analytical studies ha ve been performed, in the past, to address film boiling heat transfer and t he accompanying hydrodynamic aspects. Most of the experiments have, however , been performed for temperature and heat flux conditions, which are signif icantly lower than the prototypic conditions. For ex-vessel FCIs, liquid su bcooling is big and can significantly affect the FCI thermal hydraulics. Pr esently, there are large uncertainties in predicting natural convection fil m boiling of subcooled liquids on high-temperature surfaces. In this paper, research conducted at the Division of Nuclear Power Safety, Royal Institut e of Technology (RIT/NPS), Stockholm, concerning film boiling thermal hydra ulics under FCI condition is presented. Notably, the focuses are placed on the effect of water subcooling, high-temperature steam properties, the radi ation heat transfer and mixing zone boiling dynamics on the vapor film char acteristics. Numerical investigation is performed using a novel CFD modelli ng concept named as the local homogeneous slip model (LHSM). Results of the analytical and numerical studies are discussed with regards to boiling dyn amics under FCI conditions. (C) 1999 Elsevier Science S.A. All rights reser ved.