(690f) Numerical Modeling of Sodium Pool Fire Using Homogeneous Flow and Equilibrium Based Chemistry Model

Unlike in the case of hydrocarbon fuel-based fire scenarios, the combustion reactions occurring in a typical sodium pool fire produce multiple stable oxide products which are in condensed form [1]. The products undergo continuous physical and chemical changes depending on the temperature and the environment. Such realism of the combustion chemistry is not considered in many computational fluid dynamics (CFD) simulations of sodium pool fire scenarios [2]. In the present study, the physico-chemical aspects are fully accounted for through an equilibrium thermodynamics-based model coupled to a homogeneous two-phase flow model to account for the thermal hydraulic effects. Thus, in the present model, important physical and chemical processes present in sodium pool fire are taken into account using a distinctly different, reaction pathway-independent, CFD-based approach to simulate sodium fire: (i) the density and the specific heat of the gas-aerosol mixture evaluated on a mass-weighted basis, (ii) Gibbs free energy minimization calculations used to determine the equilibrium composition of the reactant-product mixture as a function of the temperature, mixture fraction variable and the calculated radiative heat exchange as the assigned enthalpy, and (iii) a homogenous two-phase flow model to take account of the presence of the condensed phase. Comparison of the results obtained using this approach with literature data [3] shows that the composition of the aerosols is correctly predicted both above and below the flame sheet for both dry and moist air sodium pool fire cases. However, more experimental work on sodium pool fires needs to be done to get accurate data for modeling and calibrating it.

References

1. Subramani A., Jayanti S., ?Equilibrium considerations in aerosol formation during sodium fire?, Nuclear Engg. Design, 238 (2008) 2739-2745.

2. Yamaguchi A., Tajima Y., ?Sodium pool combustion phenomena under natural convection flow?, Nuclear Eng. Design, 2009 (Article in Press).

3. Hilliard R.K, MCcormack J.D, A.K.Postma, ?Aerosol behavior during sodium pool fires in a large vessel - CSTF tests AB1 and AB2?, Report No. HEDL-TME 79-28 UC-79, 79p, Hanford Engineering Development Laboratory, 1979.