Overview of severe accident research activities performed in the Lacomeco Project at Karlsruhe Institute of Technology

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The LACOMECO platform provides European organizations access to experimental facilities at Karlsruhe Institute of Technology (KIT) designed to study the remaining severe accident safety issues, including the coolability of a degraded reactor core, corium coolability in the reactor pressure vessel, melt dispersion to the reactor cavity, and hydrogen mixing and combustion phenomena in the containment. The KIT facilities are unique in its specified field and the experiments are designed to complement other European experimental platforms to form a coherent European nuclear experimental network. The LACOMECO platform includes: 1) QUENCH facility designed for the investigation of early and late phases of core degradation in prototypical geometry for different reactor designs and cladding alloys; 2) LIVE facility, a large-scale 3D facility for the investigation of melt pool behavior in the lower head of reactor pressure vessel; 3) DISCO facility, the only operating facility worldwide able to investigate the melt dispersion to the reactor cavity and direct containment heating; 4) HYKA facility with a number of large and medium scale experimental test vessels addressing hydrogen behavior in containment under well controlled conditions. Six experiments were defined in the LACOMECO project addressing the high and medium priority safety issues defined by the Severe Accident Research Priorities (SARP) group of the Severe Accident Research Network of Excellence (SARNET). Three experiments have already been performed, the main results obtained are discussed in the paper: - QUENCH-16 test in the QUENCH facility test aimed at study the slow oxidation of fuel rod bundle in air; - DISCO-FCI test in the DISCO facility aimed at investigation of ex-vessel fuel coolant interaction; - HYKA-DETHYD tests in the HYKA facility aimed at investigation of the critical layer thickness for hydrogen- air detonation propagation in semi-confined geometry. Three experiments will be performed in 2012, the main objectives and the status of the preparation are presented: - LIVE-CERAM test in the LIVE facility test aimed at examination of the dissolution kinetics of KNO3 ceramic crust by KNO3/NaNO3 melt; - HYKA-HYGRADE test in the HYKA facility aimed at investigation of hydrogen combustion in hydrogen concentration gradients and with obstructed geometries prototypical of conditions in LWR containments: - HYKA-UFPE test in the HYKA facility aimed at scaling- down of hydrogen combustion phenomena in nuclear power plant containments for numerical code validations.dc201

Test and simulation results of LIVE-L4 + LIVE-L5L. (KIT Scientific Reports ; 7593)

The objective of the LIVE program is to study the core melt phenomena during the late phase of core melt progression in the RPV both experimentally in large-scale 3D geometry and with CFD simulation. LIVE-L4 and LIVE-L5L experiments investigate the transient and steady state behaviors of the molten pool and the crust at the melt/vessel wall interface influenced by the several melt relocation numbers and different heat generation rate during external cooling. The melt pool behaviour and crust thickness in L4 test are calculated by CONV-code

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

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.cf201

Results of the LIVE-L3A Experiment. (KIT Scientific Reports ; 7542)

The sequence of a postulated core melt down accident in the reactor pressure vessel (RPV) of a pressurised water reactor (PWR) involves a large number of complex physical and chemical phenomena. The main objective of the LIVE program is to study the core melt phe-nomena during the late phase of core melt progression in the RPV both experimentally in large-scale 3D geometry in supporting separate-effects tests and analytically using CFD codes in order to provide a reasonable estimate of the remaining uncertainty band under the aspect of safety assessment. The main objective of the LIVE-L3A experiment was to investigate the behaviour of the mol-ten pool and the formation of the crust at the melt/vessel wall interface influenced by the melt relocation position and initial cooling conditions. The test conditions in the LIVE- L3A test were similar to the LIVE-L3 test except the initial cooling conditions. In both tests the melt was poured near to the vessel wall. In the LIVE-L3 test the vessel was initially cooled by air and then by water; in the LIVE-L3A test the vessel was cooled by water already at the start of the experiment. The information obtained in the test includes horizontal and vertical heat flux distribution through the RPV wall, crust growth velocity and dependence of the crust properties on the crust growth velocity and cooling conditions. Supporting post-test analysis contributes to the characterization of solidification processes of binary non-eutectic melts. The results of the LIVE-L3 and LIVE-L3A tests are compared in order to characterize the impact of transient cooling condition on the crust solidification characteristics and melt pool behaviour including interface temperature, time to reach thermal hydraulic steady-state and the steady-state heat flux distribution. The report summarizes the objectives of the LIVE program and presents the main results obtained in the LIVE-L3A test compared to the LIVE-L3 test

Live experiments on melt behavior in the reactor pressure vessel lower head

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Behavior of the corium pool in the lower head is still a critical issue in understanding of Pressurized Water Reactor (PWR) core meltdown accidents. One of the key parameter for assessing the vessel mechanical strength is the resulting heat flux at the pool-vessel interface. A number of studies [1]-[3] have already been performed to pursue the understanding of a severe accident with core melting, its course, major critical phases and timing and the influence of these processes on the accident progression. Uncertainties in modeling these phenomena and in the application to reactor scale will undoubtedly persist. These include e.g. formation and growth of the in-core melt pool, relocation of molten material after the failure of the surrounding crust, characteristics of corium arrival in residual water in the lower head, corium stratifications in the lower head after the debris re-melting [4]. These phenomena have a strong impact on a potential termination of a severe accident. The main objective of the LIVE program [5] at Karlsruhe Institute of Technology (KIT) is to study the core melt phenomena both experimentally in large-scale 3D geometry and in supporting separate-effects tests, and analytically using CFD codes 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. The results of these experiments, performed in nearly adiabatic and in isothermal conditions, allow a direct comparison with findings obtained earlier in other experimental programs (SIMECO, ACOPO, BALI, etc.) and will be used for the assessment of the correlations derived for the molten pool behavior. The information obtained from the LIVE experiments includes heat flux distribution through the reactor pressure vessel wall in transient and steady state conditions, crust growth velocity and dependence of the crust formation on the heat flux distribution through the vessel wall. Supporting posttest analysis contributes to characterization of solidification processes of binary non-eutectic melts. Complimentary to other international programs with real corium melts, the results of the LIVE activities provide data for a better understanding of incore corium pool behavior. The experimental results are being used for development of mechanistic models to describe the incore molten pool behavior and their implementation in the severe accident codes like ASTEC. The paper summarizes the objectives of the LIVE program and presents the main results obtained in the LIVE experiments up to now.mp201