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Corium liquid jets instability and dispersion: analysis of physical process and modelisation on the MC3D code

​Sebastian Castrillon Escobar has defended his thesis on 13th September 2016 at University of Lorraine (France).

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/PSN-RES/SAG/LEPC

Authors > CASTRILLON ESCOBAR Sebastian

Publication Date > 13/09/2016

Summary

In the case of a severe accident in a nuclear power plant, the molten core may flow into water and interact with it. The consequences of this fuel-coolant interaction (FCI) for the follow-up of the accident may be numerous so the phenomenon needs to be described accurately, one of them called “steam explosion” can lead to the failure of the nuclear reactor containment. FCI is a complex multiphase interaction involving several physical phenomena. The premixing phase of the interaction consists in the fragmentation and dispersion of corium in the coolant pool. This phase is driven by the fragmentation process which modifies heat transfers (coolant boiling dynamics) and chemical reactions (corium oxidation and hydrogen generation).


This thesis brings new elements about the corium jet and droplet breakup with the main goal of improve fragmentation models on the MC3D multiphase code, developed by the IRSN. Our study is based on a multi-scale fragmentation process where the jet fragmentation rate and final droplet dimensions are not coupled themselves. We suppose a fragmentation process resulting from a primary instability (mass transfer within jet and big droplets) depending on the large flow scales and a secondary instability depending on the small flow scales (leading to final droplet breakup). This model has been implemented in MC3D in combination with the MUSIG method recently added to MC3D. In this method, droplets are represented using several classes, each of them with their own droplet diameter, mass and energy fields. Despite new improvements on modeling corium fragmentation, there is still a lack on the comprehension and characterization on the liquid droplet fragmentation, particularly on liquid/liquid configurations. In this thesis, we study in detail droplet breakup using the computational fluid dynamics software GERRIS. As a result, we find a new droplet breakup classification in liquid/liquid configurations, we improve the droplet breakup dynamics comprehension and we analyze the droplet-vortex interaction to determine breakup regime transition.

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