Title: Study of the processes of corium-melt retention in the reactor pressure vessel (INVECOR)
Citation: Proceedings of ICAPP 2011 p. Paper 11375 (1-9)
Publisher: Société Française d'Energie Nucléaire
Publication Year: 2011
JRC N°: JRC67132
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC67132
Type: Articles in periodicals and books
Abstract: Integral large-scale vessel retention experiments have been performed using up to 60 kg of prototypic corium melt discharged from the electric melting furnace at a height of 1,7 m into a model RPV (Reactor Pressure Vessel- 40cm dia. x 60cm depth) with plasmatrons for decay heating of corium for 1-2 hours. Specific power release in corium was 6-9 W.cm-3 and the maximum temperature of the RPV wall was up to 1400°C. The following has been achieved during the project: 1) Protective coatings on the graphite crucibles and the plasmatron graphite nozzles have been further developed. Numerous trials were carried out to improve the decay heat simulation of corium. 2) Calculations of the corium pool (heating efficiency, thermal fluxes and temperature distributions) were performed with specific tests for validation of the models. 3) 4 large-scale experiments with the model RPV using a molten oxidic corium and oxidic-metallic corium were conducted. 4) Extensive post-test analysis of corium samples and RPV steel has been performed. Post-test examination showed that there was a layer of small fragments above a massive ingot of solidified. There was insignificant erosion of the steel surface of the RPV wall at the impact point of the corium jet. The results lead us to 2 specific conclusions: 1) Relatively low thermal fluxes were noted across the RPV model wall. This was due to: firstly, the thermal insulation on the RPV external surface, which redistributes thermal fluxes in the RPV wall; secondly, there is incomplete UO2 dissolution by the metallic Zr melt and this endothermic UO2 dissolution continues in the corium of the RPV; thirdly, the gap caused by differential expansion between the corium crust and the RPV wall reduces heat transfer; fourthly, the layering of the corium crust effectively reduces its thermal conductivity. 2) The initial transient processes of melt speed onto the lower head and the rate of corium pool formation determine (along with the pool configuration) the steady-state phenomena occurring during its retention in the reactor vessel. However the formation of a fragmented debris layer (with a large surface area for interaction with water) over a corium ingot suggests that corium coolability by internal flooding is possible.
JRC Directorate:Nuclear Safety and Security

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