Article

Development of mathematical model for optimization of sodium leak collection tray

Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
Nuclear Engineering and Design (Impact Factor: 0.97). 10/2008; 238(10):2684-2692. DOI: 10.1016/j.nucengdes.2008.05.011

ABSTRACT Sodium leaks and resultant fire containment play an important role in the safe operation of a fast breeder reactor. Leak collection tray (LCT) is a passive device which is used to collect the highly reactive liquid sodium in the case of an accidental leakage. The consequences of sodium fire are mitigated by oxygen starvation in the vessel which collects the liquid sodium after leakage. The current paper deals with the optimization of the LCT geometry based on the hydrodynamic characteristics of the leaked liquid sodium. Isothermal numerical simulations have been performed to understand the interfacial dynamics of the hot liquid sodium flow in the top tray part and the variation of sodium draining rate into the holdup vessel for various drainpipe diameters and leak rates. Since the numerical simulations involve very high computational effort, an equivalent semi-analytical sloshing/draining model has also been developed which emulates the flow process in the LCT. The predictions of transient mass distributions in the top part and in the holdup vessel for the semi-analytical model are in close match with the results obtained from the detailed numerical study. The results reveal critical geometric parameters at which the un-burnt sodium collected in the LCT will be maximum.

0 Bookmarks
 · 
119 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Nuclear Engineering and Design 12/2011; DOI:10.1016/j.nucengdes.2011.09.015 · 0.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A sodium cooled fast reactor is one of the fourth generation advanced reactor designs. Liquid sodium is used as a coolant in such a reactor as it has excellent thermophysical properties. However liquid sodium can react violently when exposed to air or water. A sodium-air reaction typically occurs in two dominant modes: spray and pool. Typically, the spray mode of burning is considered as more severe than the pool model of burning. The focus of this paper is on sodium spray combustion. For the safety of a sodium cooled fast reactor, sodium-air reactions should be avoided. To avoid and to mitigate the consequences if a sodium fire occurs, it is essential to understand various physical phenomena involved in a sodium-air reaction. Computational fluid dynamics based numerical methods can be used for this purpose as they are known to resolve all spatial and temporal scales and simulate various physical processes governing sodium-air reaction. The goal of the work presented within this paper is to propose a numerical method to simulate sodium spray combustion and validate this method against experiments. A single sodium droplet combustion experiments is used for the validation. The model predictions of falling velocity and burned mass are in good agreement with experimental data. Additionally, parametric studies were performed to investigate the effects of initial droplet diameter, temperature and oxygen concentration on burning rate and on ignition time delay. Once sufficiently validated, the present method can be used for safety evaluation of a sodium fast reactor.
    Nuclear Engineering and Design 10/2014; 278. DOI:10.1016/j.nucengdes.2013.11.081 · 0.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The risk of sodium-air reaction has received considerable attention after the sodium-fire accident in Monju reactor. The fires resulting from the sodium-air reaction can be detrimental to the safety of a sodium fast reactor. Therefore, predicting the consequences of a sodium fire is important from a safety point of view. A computational method based on CFD is proposed here to simulate sodium pool fire and understand its characteristics. The method solves the Favre-averaged Navier-Stokes equation and uses a non-premixed mixture fraction based combustion model. The mass transfer of sodium vapor from the pool surface to the flame is obtained using a sodium evaporation model. The proposed method is then validated against well-known sodium pool experiments of Newman and Payne. The flame temperature and location predicted by the model are in good agreement with experiments. Furthermore, the trends of the mean burning rate with initial pool temperature and oxygen concentration are captured well. Additionally, parametric studies have been performed to understand the effects of pool diameter and initial air temperature on the mean burning rate. Furthermore, the sodium spray and sodium pool combustion models are combined to simulate simultaneous spray and pool combustion. Simulations were performed to demonstrate that the combined code could be applied to simulate this. Once sufficiently validated, the present code can be used for safety evaluation of a sodium fast reactor.
    Nuclear Engineering and Design 10/2014; 278:739–752. DOI:10.1016/j.nucengdes.2014.05.037 · 0.97 Impact Factor