Influence of Boundary Conditions, Vessel Geometry, and Simulant Materials on the Heat Transfer of Volumetrically Heated Melt in a Light Water Reactor Lower Head

This study investigates heat transfer characters of a volumetrically heated melt pool in LWR lower plenum. Experimental restrictions on prediction reliability are discussed. These restrictions include cooling boundary conditions, vessel geometries, and simulant melt selection on general and localized heat transfer. A survey of existing heat transfer correlations derived from individual experimental definitions is presented. The inconsistency in parameter definitions in Nu–Ra correlations is discussed. Furthermore, the discrepancy of upward Nu depending on the existence of crust is stressed. Several serials of experiments with different combinations boundary condition of external cooling and top cooling were performed in LIVE3D and LIVE2D facilities. The experiments were conducted with simulants with and without crust formation. The influences of cooling boundary conditions, the vessel geometry, and the simulant material on overall heat transfer as well as on heat flux distribution are analyzed. This paper provides own explanations about the discrepancies among the exiting heat transfer correlations and recommends the most suitable descriptions of melt pool heat transfer under different accident management strategies.