Analysis of the Availability of In-Vessel Retention of Molten Core Debris Strategy for AP1000 Available to Purchase

The availability of IVR (In-vessel Retention of Molten Core Debris) strategy at severe reactor accident depend upon the capacity of ERVC (External Reactor Vessel Cooling), i.e. the CHF (Critical Heat Flux) of the external reactor vessel should be higher than the related location heat flux. In this paper, an analysis model of CHF on the downward facing curved surface for pool boiling has been proposed, which adopts the Helmholtz instability analysis of vapor-liquid interface of the vapor jets which penetrating in the thin liquid film underneath the elongated bubble adhering to the lower head outer surface. When the heat flux closing to the CHF point, the vapor-liquid interface becomes highly distorted which resulted in obvious vapor blanket, it will block liquid to feed the thin liquid film underneath the vapor blanket from the bulk region. As a result, the thin liquid film will dry out gradually. As a consequence, the CHF occurs. Based upon this model, spatial variation of CHF about the downward facing curved surface in different subcooling are obtained, and the safety margin of IVR strategy for AP1000 increase with the increase of the subcooling. However, the IVR strategy may be invalid by comparing the CHF with the related local heat flux under the condition of saturated.