Recent progress in the LIVE program (late in-vessel phase experiments) and first results of the LIVE-L1 experiment within the Lacomera project

Full text of publication follows: The demonstration of in-vessel coolability of melt pools still requires a more profound basis, experimentally and theoretically. The knowledge about melt mass relocation from the core to the lower plenum, formation of a melt pool and its coolability and the role of the gaps between the solidified melt crust and Reactor Pressure Vessel (RPV) should be improved. Generally computer models have uncertainties in modelling the molten pool formation and cooling in the lower head even though the modelling has recently advanced considerably. Some models for the molten pool behaviour in the lower head have been developed, but for a soundly based validation further experimental data are required. The LIVE (Late In-Vessel Phase Experiments) Program at the Forschungszentrum Karlsruhe is started to study the late phase of core degradation, onset of melting and the formation and stability of melt pools in the RPV. Additionally, the regaining of cooling and melt stabilisation in the RPV by flooding the outer RPV or by internal water supply will be investigated. The core of the experimental facility is the RPV scaled 1:5 made of special steel. The lower head has an internal diameter of 1 m and a wall thickness of {approx}25 mm. To simulate the decay heat, electrical heaters are used, which provide in different layers a representative and homogeneous heating of the melt in the lower head. The core melt is simulated by different materials. To investigate special problems a nitrate is used with a melting temperature of about 350 deg. C, and with a similar phase diagram as the expected core melt. In more integral tests the use of oxides is planned with a melting temperature of approximately 900 deg. C. These oxide compositions provide a sufficiently high melting temperature and, due to their phase diagram, allow a comparison with the core melt in various scenarios of core meltdown. LIVE experiments are part of the LACOMERA project of the 5. Framework Program of the EU. Overall objective of this project is to offer research institutions from the EU member countries access to four large-scale experimental facilities (QUENCH, LIVE, DISCO-H, and COMET) at the Forschungszentrum Karlsruhe to investigate core melt scenarios from the beginning of core degradation to melt formation and relocation in the vessel, possible melt dispersion to the reactor cavity, and finally corium concrete interaction and corium coolability in the reactor cavity. LIVE-L1 experiment within the LACOMERA project aims at the simulation of melt relocation into the RPV lower head for VVER conditions. The experiment will study the melt pool behaviour during the stages of air circulation at the outer RPV surface with a subsequent flooding of the lower head. It will provide information on time dependent local heat flux distribution to the lower head, and the development of crusts, depending on internal melt heating and external cooling modes. Presented paper gives an overview of main objectives and results expected from the LIVE experiments and presents the first results of the LIVE-L1 test which is scheduled for the fall 2004. (authors)