Analysis of the passive heat removal enhancement for AP1000 containment due to the partially wetted coverage

AP1000 containment uses the water film evaporation, coupled with containment inner condensation, to remove the core decay heat. However, water film cannot fully cover heat transfer surface and dry-wetted strips appear. As a result, heat transfer within the containment shell is a two-dimension thermal conduction. Current work numerically studied the AP1000 heat removal enhancement due to the partially wetted coverage phenomenon. It used the evaporation and condensation boundary conditions and Fluent software to calculate the local heat fluxes and their distributions. Results show that the maximum heat transfer enhancement can reach 63% and this enhancement peak appears when the dry strip fraction approximately equals 90%. The influences of dry coverage and dry-wet strip width were carefully discussed. It indicates that the heat transfer enhancement for small dry-wet strip is linear with dry strip fraction (0 < α < 80%). Finally, according to the wetted coverage ranges for AP1000 passive containment cooling system, an empirical correlation for heat transfer enhancement is given and it can be used to improve PCCS analysis.