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.
[Show abstract][Hide abstract] ABSTRACT: We recorded electroencephalogram (EEG) and electrocardiogram (ECG) from 20 infants monthly between 5 and 10 months of age during baseline and during performance on the looking A-not-B task of infant working memory. Analyses of baseline data showed age-related increases in EEG power (medial frontal, central, temporal, medial parietal, lateral parietal, and occipital electrode sites) and coherence (frontal pole-medial frontal, medial frontal-lateral frontal, medial frontal-medial parietal, and medial frontal-occipital electrode pairs), and decreases in heart rate (HR). Patterns of age-related change were similar for EEG power, EEG coherence, and HR. Analyses of task data relative to baseline revealed task-related increases in EEG power (all electrode sites), but no task-related changes in EEG coherence (medial frontal pairings) and HR. There was some evidence of localized task-related changes in EEG power by 10 months of age. These data highlight age-related changes in EEG and ECG, as well as the functional significance of these psychophysiological measures during baseline and during cognitive processing in the first year.
International journal of psychophysiology: official journal of the International Organization of Psychophysiology 02/2011; 80(2):119-28. DOI:10.1016/j.ijpsycho.2011.02.009 · 2.88 Impact Factor
[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.
[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.
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