Ji-Woong Han

New Design Options Free from a Potential Sodium Freezing Issue for a Passive DHR System of KALIMER

Abstract To enhance the operational reliability of a purely passive decay heat removal system in KALIMER, which is named PDRC, three design options to prevent sodium freezing in an intermediate decay heat removal circuit were proposed, and their feasibilities have been studied for an entire plant operation mode. The potential candidates for the new design options are (a) the partially immersed DHX concept, (b) the cavity air cooling system–coupled PDRC concept, and (c) the advanced PDRC concept with alternative cooling medium. The design features of each concept are quantitatively evaluated in this study. For all the options, more specific design considerations were made to confirm their feasibility to properly materialize their concepts in a practical system design procedure, and the general definitions for a purely passive concept and its design features have been discussed as well.

Transient Performance Analysis of the Reactor Pool in KALIMER-600 with an Inertia Moment of a Pump Flywheel

The effect of an inertia moment of a pump flywheel on the thermal-hydraulic behaviors of the KALIMER-600(Korea Advanced LIquid MEtal Reactor) reactor pool during an early-phase of a loss of normal heat sink accident was investigated. The thermal-hydraulic analyses for a steady and a transient state were made by using the COMMIX-1AR/P code. In the present analysis a quarter of the reactor geometry was modeled in a cylindrical coordinate system, which includes a quarter of a reactor core and a UIS, a half of a DHX and a pump and a full IHX. In order to evaluate the effects of an inertia moment of the pump flywheel, a coastdown flow whose flow halving time amounts to 3.69 seconds was supplied to a natural circulation flow in the reactor vessel. Thermal-hydraulic behaviors in the reactor vessel were compared to those without the flywheel equipment. The numerical results showed a good agreement with the design values in a steady state. It was found that the inertia moment contributes to an increase in the circulation flow rate during the first 40 seconds, however to a decrease of it there after. It was also found that the flow stagnant region induced by a core exit overcooling decelerated the flow rate. The appearance of the first-peak temperature was delayed by the flow coastdown during the initial stages after a reactor trip.

Experimental and Numerical Investigations on Detailed Methane Reaction Mechanisms in Oxygen Enriched Conditions

The burning velocities of conventional and oxygen-enriched methane flame in various equivalence ratio were determined by experiments. The validity of existing reaction mechanisms was examined in oxygen-enriched flame on the basis of the experiment results. Modified reaction mechanism is suggested, which was able to predict burning velocity of oxygen enriched flame as well as methane-air flame. Complementary study on reaction mechanisms shows the following results : Present experiment data were found to be more reliable in comparison with existing ones in a oxygen-enrichment condition. It was found that some modification in existing reaction mechanisms is necessary, since discrepancy between measurements and predictions is increasing with oxygen enrichment ratio. The sensitivity analysis was performed to discriminate the dominantly affecting reactions on the burning velocity in various oxygen enrichment and equivalence ratio. A modified GRI 3.0 reaction mechanism based on our experiment results was suggested, in which reaction rate coefficients of (R38) H+O

An Experimental Study on the NOx Formation of LNG Flame in Fuel Staged Combustor

An experimental study on the NOx formation of LNG flame in fuel staged combustor has been studied. The design concept of multi fuel/air staged combustor is creation of two separate flame, a primary flame is a act as a pilot flame for the secondary combustion stage combustion zone, where most of fuel bums. Experiments were performed on a semi-industrial scale (thermal input 0.233 MW) in a laboratory furnace and Liquefied Natural Gas(LNG) was used as a primary and secondary fuels. This study included parametric study to identify the optimum operating conditions which are primary/secondary fuel ratio, and primary/secondary air ratio for reducing NOx emission with two types of nozzle. The test demonstrated that NOx emission can be reduced by >70% in accordance with operating conditions.

Computation of turbulent natural convection with the elliptic-blending differential and algebraic flux models

ABSTRACT A computation of turbulent natural convection in enclosures with the elliptic-blending based differential and algebraic flux models is presented. The primary emphasis of the study is placed on an investigation of accuracy of the treatment of turbulent heat fluxes with the elliptic-blending second-moment closure for the turbulent natural convection flows. The turbulent heat fluxes are treated by the elliptic-blending based algebraic and differential flux models. The proposed models are applied to the prediction of turbulent natural convections in a 1:5 rectangular cavity and in a square cavity with conducting top and bottom walls. It is shown that both the elliptic-blending based models predict well the mean velocity and temperature, thereby the wall shear stress and Nusselt number. It is also shown that the elliptic-blending based algebraic flux model produces solutions which are as accurate as those by the differential flux model.

Preliminary Performance Test of Mechanical Pump for a Stella-1

In the process of sodium-cooled fast reactor (SFR) design, it is very important to verify thermo-hydraulic performance of each component in the sodium environment. In KAERI (Korea Atomic Energy Research Institute) STELLA (Sodium Integral Effect Test Loop for Safety Simulation and Assessment) project is under a Mid- and Long-term Nuclear R&D Program. The STELLA project is composed of two stages. In the 1st stage the performance for heat exchangers such as DHX (Decay heat exchanger) and AHX (Air heat exchanger) and for PHTS (Primary heat transport system) mechanical pump will be evaluated. The detailed design of each component is based on that of a 600MWe demonstration reactor.Since full-scale components could not be installed in STELLA-1 [1], the model pump is designed to be scaled-down based on the scaling law. Various pump tests have been done in water environment by using model pump.In this study the design features of model pump were described and the scaling parameters were examined. The results of pump performance tests have been also introduced which is essential to perform safety analysis.Copyright

Analysis of Transient Performance of KALIMER-600 Reactor Pool by Changing the Elevation of Intermediate Heat Exchanger

The effect of increasing the elevation of an IHX (intermediate heat exchanger) on the transient performance of the KALIMER-600 reactor pool during the early phase of a loss of normal heat sink accident was investigated. Three reactors equipped with IHXs that were elevated to different heights were designed, and the thermal-hydraulic analyses were carried out for the steady and transient state by using the COMMIX-1AR/P code. In order to analyze the effects of the elevation of an IHX between reactors, various thermal-hydraulic properties such as mass flow rate, core peak temperature, RmfQ (ratio of mass flow over Q) and initiation time of decay heat removal via DHX (decay heat exchanger) were evaluated. It was found that with an increase in the IHX elevation, the circulation flow rate increases and a steep rise in the core peak temperature under the same coastdown flow condition is prevented without a delay in the initiation of the second stage of cooling. The available coastdown flow range in the reactor could be increased by increasing the elevation of the IHX.

Analysis of IHX Vertical Position Effects in the Reactor Vessel of KALIMER-600

In this research the vertical position effects of an IHX (Intermediate Heat eXchanger) during a loss of normal heat sink accident were investigated by varying the distance between the thermal centers of core and IHX. The conceptual design data of KALIMER(Korea Advanced Liquid Metal Reactor)-600(Hahn et al., 2007) was utilized as the reference reactor design. The thermal-hydraulic calculations for the steady and transient state have been done using the COMMIX-1AR/P code(Garner et al., 1992). In order to evaluate the effects of the IHX vertical position, the elevation of the IHX was increased by 1m and 2m respectively in comparison to the reference design and the required numerical analysis was completed. Several coastdown flow conditions were also considered to investigate the variation of the IHX elevation effect. The thermo-hydrodynamic behaviors in a steady and transient state were compared during early-phase of an accident. It was found that the IHX elevation enhances the circulation flow rate and contributes to the decrease of early-phase peak temperature for non-reverse flow coastdown conditions. IHX elevation also contributed to the extension of the non-reverse flow coastdown flow time range.Copyright

Investigation on Flame Characteristics′ Variation by Flue Gas Recirculation and Fuel Injection Recirculation

Investigation on Flue Gas Recirculation(FGR) flame and Fuel Injection Recirculation(FIR) flame was performed with numerical method. Quantitative Reaction Path Diagram(QRPD) is utilized to compare the different chemistry effects between FGR flame and FIR flame. In order to compare flamelets in various oxygen-enrichment conditions reasonably, the adiabatic flame temperature and Damkohler number were held fixed by modulating the amount of diluents to fuel and oxidizer stream and by varying global strain rate of flame respectively. Basic flame structures were compared and characteristics of CH decomposition and NO formation were analyzed based on QRPD analysis between FGR flame and FIR flame.

The Study on the Development of The Non-Gravity Fluidized Dryer

The purpose of this study is to develop the non-gravity fluidized dryer. In this non-gravity fluidized dryer the fluidized zone is produced by two paddles in mixer, which maximizes the surface area of materials and then heated air through the guiding panels dehumidify them. This can conduct the drying process quickly and control moisture contents to lower limits. The ventilation system is closed loop system, which can be changeable to open system, and can be used as a multi-purposed dryer in which mixing, drying, granulating and cooling process is conducted. In order to develop the non-gravity fluidized dryer, in the first fundamental experiments were performed to mixing accuracy and then the other parts of dryer and control system were examined to check whether they were designed properly and operated harmoniously with mixer. Also the preparatory experiments were fulfilled to examine the efficiency and reliability of the dryer. Lastly, on the basis of preparatory experiments, performance test for the non-gravity fluidized dryer carried out for the variation of the initial moisture contents, desired moisture contents, heated air velocity and heating temperature.