Live experiments on melt pool heat transfer in the reactor pressure vessel lower head

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

The main objective of the LIVE program at Karlsruhe Institute of Technology (KIT) is to study the core melt phenomena both experimentally in large-scale 2D and 3D geometry and in supporting separate-effects tests in order to provide a reasonable estimate of the remaining uncertainty band under the aspect of safety assessment. Within the LIVE experimental program several tests have been performed with water and with non-eutectic melts (mixture of KNO3 and NaNO3) as simulant fluids to study the heat flux distribution in the conditions when the melt pool is covered by water from the top. The tests were performed in LIVE-3D and LIVE-2D facilities using different simulant materials and under different external cooling condition. The upward and downward heat transfer was compared between the 2D and 3D geometries. Although similar heat flux distribution through the vessel wall is observed for LIVE-3D and LIVE-2D tests, LIVE-2D test results have shown higher heat transfer from the top of the melt pool as compared to the LIVE-3D tests and to results from previous studies. Using water as simulant material resulted in a lower heat transfer both to the top of the pool and to the vessel wall. The outcomes of the LIVE top-cooling tests provide new insights for the evaluation of the established Nu-Ra correlations. The results of these experiments allow a direct comparison with findings obtained earlier in other experimental programs (SIMECO, ACOPO, BALI, etc.) and are used for the assessment of the correlations derived for the molten pool behavior. Besides the investigation of molten pool heat transfer behavior, melting process of debris in the reactor lower plenum after relocation of liquid melt in a large scale hemispherical geometry is also investigated in LIVE-3D facility using a noneutectic nitrate to simulate the debris bed material. Two experiments have been performed with different volume of the relocated liquid melt. The onset of melting, the form and the volume of the melt pool and the timing of important events during the melting process were identified.