Numerical prediction of fire extinguishment characteristics of sodium leak collection tray in a fast breeder reactor

Sodium leak collection tray (LCT) is an efficient passive device used for the extinguishment of liquid sodium fire in case of an accidental leakage from the secondary circuit of a fast breeder reactor. The LCT essentially isolates the leaking sodium into closed containers where the resulting fire is extinguished due to limited availability of oxygen. The current work aims to highlight the combustion extinguishment characteristics of LCT through a lumped formulation by conserving the mass and energy of liquid sodium and constituent gases in various parts of the LCT. Here, the complex hydrodynamics of liquid sodium is emulated through a semi-analytical draining/sloshing model and its burning rates are predicted through a three-dimensional open pool combustion model for the tray region and a closed pool combustion model for the holdup vessel. These simulations evaluate the burning rates at discrete levels of liquid sodium which are subsequently interpolated to establish correlations involving instantaneous liquid levels and oxygen concentration. Using the correlations obtained from the draining and combustion models, the overall lumped formulation directly predicts the un-burnt sodium recoverable after the extinguishment of fire in the LCT. The predicted results of this model compare well with the available experimental data.