• 한국재료학회지
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• 제30권10호
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• pp.533-541
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• 2020

UO₂ kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 ㎛-sized UO₂ particles using an external gelation process, contact length extension of the NH₃ gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 M-NH₄OH solution are used to form 3,000 ㎛-sized liquid droplets. To produce high-sphericity and high-density UO₂ particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO₂ spheres that undergo the subsequent treatment is 10.78 g/㎤; the sphericity is analyzed and found to be 0.948, indicating good experimental results.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(2)
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• pp.623-629
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• 1995

To investigate the effects of powder shape on U loading density of fuel meat, two kinds of fuel meats were prepared with atomized and comminuted U$_3$Si$_2$ powders by extrusion or rolling process. Extruded fuel meats with atomized spherical U$_3$Si$_2$ powder appeared to have much less porosity than those with comminuted irregular U$_3$Si$_2$ powder at higher U$_3$Si$_2$ fraction- The U$_3$Si$_2$ particles with spherical shape are less fractured in extrusion than in rolling. Most of atomized particles on the whole maintained to have spherical shapes in the extrusion. It has been shown that atomized spherical particles are expected to approach similar upper loading limits comparing with comminuted particles in rolled plates, but exceed comminuted powder loading limits in extruded rods.

• 한국분말재료학회지
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• 제16권2호
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• pp.115-121
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• 2009

The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for $UO_2$ kernel preparation. In this study, ADU compound particles were calcined to $UO_3$ particles in air and Ar atmospheres, and these $UO_3$ particles were reduced and sintered in 4%-$H_2$/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to $UO_3$ phases at $500^{\circ}C$. At $600^{\circ}C$, the $U_3O_8$ phase appeared together with $UO_3$. After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric $UO_2$. As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of $U_3O_7$ and $U_4O_9$.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
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• pp.55-58
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• 2013

A new soot particle generation system has been developed and tested. The soot generation system consists of two sections, a fuel supply and a soot production. In the fuel supply module, either liquid fuel precisely controlled by a syringe pump is mixed with preheated carrier gas and rapidly evaporated or gaseous fuel controlled by a MFC is diluted with dilution gas. The soot production module contains a heater that can raise the gas/fuel temperature up to $1400^{\circ}C$. The physical and chemical properties of produced soot particles depend on the type and concentration of fuel, the residence time, and temperature in the soot production section. The soot generation system will be utilized to produce well-defined soot particles for soot studies such as the evaluation of experimental sampling and analysis processes for the quantitative assessment of PM and BC from ships and the adverse health effects on pulmonary and cardiovascular systems of human body.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.595-595
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• 2016

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1729-1737
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• 2019

This paper presents neutronics design of VVER-1000 fuel assembly using burnable poison particles (BPPs) for controlling excess reactivity and pin-wise power distribution. The advantage of using BPPs is that the thermal conductivity of BPP-dispersed fuel pin could be improved. Numerical calculations have been conducted for optimizing the BPP parameters using the MVP code and the JENDL-3.3 data library. The results show that by using $Gd_2O_3$ particles with the diameter of $60{\mu}m$ and the packing fraction of 5%, the burnup reactivity curve and pin-wise power distribution are obtained approximately that of the reference design. To minimize power peaking factor (PPF), total BP amount has been distributed in a larger number of fuel rods. Optimization has been conducted for the number of BPP-dispersed rods, their distribution, BPP diameter and packing fraction. Two models of assembly consisting of 18 BPP-dispersed rods have been selected. The diameter of $300{\mu}m$ and the packing fraction of 3.33% were determined so that the burnup reactivity curve is approximate that of the reference one, while the PPF can be decreased from 1.167 to 1.105 and 1.113, respectively. Application of BPPs for compensating the reduction of soluble boron content to 50% and 0% is also investigated.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.839-846
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• 2013

This paper describes a finite element model of the microstructure of dispersion type nuclear fuels, which can be used to determine the effective thermal conductivity of the fuels during irradiation. The model simulates a representative region of the fuel as a prism shaped unit cell made of brick elements. The elements within the unit cell are assigned material properties of either the fuel or the matrix depending on position, in such a way as to represent randomly distributed fuel particles with a size distribution similar to that of the as manufactured fuel. By applying an appropriate heat flux across the unit cell it is possible to determine the effective thermal conductivity of the unit cell as a function of the volume fraction of the fuel particles. The presence of a fuel/matrix interaction layer is simulated by the addition of a third set of material properties that are assigned to the finite elements that surround each fuel particle. In this way the effective thermal conductivity of the material may also be determined as a function of the volume fraction of the interaction layer. Work is on going to add fission gas bubbles in the fuel as a fourth phase to the model.

• 한국분무공학회지
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• 제12권1호
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• pp.65-70
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• 2007

This paper is to investigate the characteristics of exhaust emissions and nano-particle emission from diesel passenger vehicle according to using biodiesel fuel as an alternative fuel. In this work, the particulate matters (PM) of exhaust emissions in diesel engine were investigated by number of particles and mass measurement. The mass of the total PM was measured using the standard gravimetric measurement method, the total number concentrations were measured on a ECE15+EUDC driving cycle using Condensation Particle Counter (CPC). Total PM emission was reduced $2{\sim}38%$ and number concentration was reduced $1{\sim}27%$ according to increasing blended ratio of biodiesel with diesel fuel. Total PM emission was reduced more than particle number emission because volatile particles were measured in total PM but were not measured in particle number emissions.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.279-286
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• 2009

Improving over a previous study [1], this paper provides a Monte Carlo method for the heat conduction analysis of problems with complicated geometry (such as a pebble with dispersed fuel particles). The method is based on the theoretical results of asymptotic analysis of neutron transport equation. The improved method uses an appropriate boundary layer correction (with extrapolation thickness) and a scaling factor, rendering the problem more diffusive and thus obtaining a heat conduction solution. Monte Carlo results are obtained for the randomly distributed fuel particles of a pebble, providing realistic temperature distributions (showing the kernel and graphite-matrix temperatures distinctly). The volumetric analytic solution commonly used in the literature is shown to predict lower temperatures than those of the Monte Carlo results provided in this paper.

• 한국자동차공학회논문집
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• 제17권4호
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• pp.55-62
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• 2009

As an experiment investigation, the effects of ethanol blended gasoline fuel with different injection method on nano-sized particle emission characteristics were examined in a 0.5L spark-ignited single-cylinder engine with a compression ratio of 10. Because this engine nano-particles are currently attracting interest due to its adverse health effects and their impact on the environments. So a pure gasoline and an ethanol blended gasoline fuels, namely E85 fuel, used for this study. And, as a particle measuring instrument, a fast-response particle spectrometer (DMS 500) with heated sample line was used for continuous measurement of the particle size and number distribution in the size range of 5 to 1000nm (aerodynamic diameter). As this research results, we found that the effect of ethanol blending gasoline caused drastic decrease of nano-particle emissions when port fuel injection was used for making better air-fuel mixture than direct fuel injection. Also injection timing, specially direct fuel injection, could be a dominant factor in controlling the exhaust particle emissions.