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

ZRO₂ and UO₂ dissolution by molten Zircalloy

This paper describes the results of the different tests on the dissolution of ZrO2 and UO2 by molten Zircaloy at temperatures about 1000 K below their melting point. The understanding of the mechanisms of this process is important for the modelling of the fuel rod failure during the reactor severe accidents

CoreSOAR Core Degradation State-of-the Art Report Update: Conclusions [in press]

In 1991 the CSNI published the first State-of-the-Art Report on In-Vessel Core Degradation, which was updated to 1995 under the EC 3rd Framework programme. These covered phenomena, experimental programmes, material data, main modelling codes, code assessments, identification of modelling needs, and conclusions including the needs for further research. This knowledge was fundamental to such safety issues as in-vessel melt retention of the core, recovery of the core by water reflood, hydrogen generation and fission product release. In the last 20 years, there has been much progress in understanding, with major experimental series finished, e.g. the integral in-reactor Phébus FP tests, while others have many tests completed, e.g. the electrically-heated QUENCH series on reflooding degraded rod bundles, and one test using a debris bed. The small-scale PRELUDE/PEARL experiments study debris bed quench, while LIVE examines melt pool behaviour in the lower head using simulant materials. The integral severe accident modelling codes, such as MELCOR and MAAP (USA) and ASTEC (Europe), encapsulate current knowledge in a quantitative way. After two EC-funded projects on the SARNET network of excellence, continued in NUGENIA, it is timely to take stock of the vast range of knowledge and technical improvements gained in the experimental and modelling areas. The CoreSOAR project, in NUGENIA/SARNET, drew together the experience of 11 European partners to update the state of the art in core degradation, finishing at the end of 2018. The review covered knowledge of phenomena, available integral experiments, separate-effects data, modelling codes and code validation, then drawing overall conclusions and identifying needs for further research. The final report serves as a reference for current and future research programmes concerning core degradation in NUGENIA, in other EC research projects such as in Horizon2020 and for projects under the auspices of OECD/NEA/CSNI