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Modeling and analysis of the coolability of corium interacting with concrete underwater

Alejandro Villareal Larrauri​ has defended his thesis on 10th March 2020, at Nancy

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Authors > VILLAREAL LARRAURI Alejandro

Publication Date > 10/03/2020


In case of a hypothetical severe accident with partial or extensive core meltdown, the superheated magma made of molten steel and fuel, called corium (T > 2500K), may threaten the integrity of the reactor pressure vessel and subsequently the reactor containment building, if long-term coolability is not assured. In the ex-vessel scenario, the coolability from top water injection is analyzed for two expected configurations: particle bed, and fractured crust overlying a corium pool.
The second configuration is linked to the situation of molten corium-concrete interaction (MCCI). The first one is linked to melt fragmentation in water either from the top (melt coming from the vessel), either from the bottom though the crust, during melt ejection episodes throughout MCCI. The phenomena linked to the penetration of water in the corium for these two configurations are examined with the help of in-depth analysis of available experiments, in particular some recent CCI tests (ANL), by the development of an analytical model and finally through the modification and use of the CMFD code MC3D.

 One dimensional analysis yields the proposal of a heat flux model for the water penetration. The mechanism of the water ingression phenomena in fractured crusts is revisited, although the large uncertainties related to the corium mechanical properties limits the prediction of fracture characteristics (permeability). Beside, some experiments and calculations with MC3D show the development of front instabilities and important 2D/3D effects. An analytical two-zone two-phase model is developed to take into account the penetration front heterogeneity and the front instabilities are examined with MC3D calculations. Finally the models are applied to real situations including the impact of residual power. In the case of an initially hot debris bed with the presence of residual power, the developed model shows that the extracted heat flux is less than the commonly used “dryout heat flux” criterion.
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