Host laboratory: Corium Physics Study Laboratory (LEPC)
Beginning of the thesis: October 2014
Ali SwaidanSubject description
accidents arising from the fusion of the nuclear reactor core must be
anticipated to enhance the efficiency of its mitigation. Such accidents
have occurred at TMI-2 in the USA- 1979, Chernobyl-1984 and in
Fukushima, Japan-2011 where 3 reactors were destroyed.
a loss of coolant accident, the reactor core gets uncovered and starts
to accumulate residual heat. As the accident evolves, core heating and
oxidation of the fuel cladding by the coolant vapor provoke core
degradation. In this case, injection of water into the core (reflooding)
to remove the residual heat is vital for stopping the progressive
degradation and saving the core from melting down.
can cause a thermal shock and the embrittlement of the cladding, hence
forming a porous debris bed in the core. The arrival of steam that is
generated by cooling the lower zones may activate the oxidation of
Zircaloy at high temperature zones, the reaction is very exothermic and
leads to partial melting of materials. Those molten materials tend to
move within the porous medium and thus reducing the porosity in the
accumulation zones and increasing it in the zones from which they
migrate. Due to this heterogeneity and the varying degrees of
degradation, the coolant flow becomes multidimensional.
is a multiphase system including 4 phases: gas, liquid (water), liquid
(molten material) and solid particles constituting the porous debris
bed. The first initiative was to establish the Mass, Energy and Species
conservation equations in a form that accounts for porosity evolution
and the chemical reaction (Zircaloy oxidation). Averaging techniques are
applied to get the volume-averaged form of the governing equations,
followed by considering several assumptions to simplify these equations.
should integrate with future initiatives into improving the previously
developed model in order to deal with local geometrical modifications
consequent to partial melting of the porous medium, and include a
refined structure of the medium as the two-phase flow is very sensitive
to the evolution of this structure. This model would either be
integrated into the ICARE/CATHARE code – a tool developed by IRSN for
core degradation studies – or into a stand-alone code. The models
developed in this thesis will be used by IRSN to improve the ASTEC code
(IRSN’s reference code for simulating core meltdown accidents).