• Nuclear Engineering and Technology
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• v.34 no.5
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• pp.482-493
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• 2002

The MOX fuel for LWR is fabricated either by direct mechanical blending of UO$_2$ and PuO$_2$ or by two stage mixing. Hence Pu-rich particles, whose Pu concentrations are higher than pellet average one and whose size distribution depends on a specific fabrication method, are inevitably dispersed in MOX pellet. Due to the inhomogeneous microstructure of MOX fuel, the thermal conductivity of LWR MOX fuel scatters from 80 to 100 % of UO$_2$ fuel. This paper describes a mechanistic thermal conductivity model for MOX fuel by considering this inhomogeneous microstructure and presents an explanation for the wide scattering of measured MOX fuel＇s thermal conductivity. The developed model has been incorporated into a KAERI＇s fuel performance code, COSMOS, and then evaluated using the measured in-pile data for MOX fuel. The database used for verification consists of homogeneous MOX fuel at beginning-of-life and inhomogeneous MOX fuel at high turnup. The COSMOS code predicts the thermal behavior of MOX fuel well except for the irradiation test accompanying substantial fission gas release. The over-prediction with substantial fission gas release seems to suggest the need for the introduction of a recovery factor to a term that considers the burnup effect on thermal conductivity.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.167-171
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• 2009

We conducted performance test of a 350 kW class wood pellet boiler installed at a dormitory whose total area is $1,354\;m^2$. The maximum heating capacity of the boiler is 350 kW(300,000 kcal/kg). The wood pellet boiler consists of 3 parts; boiler, hot water storage tank and wood pellet storage tank. In testing the boiler, we shut off hot water utility supply and open up floor heating water system in order to measure exact value of the heating output of the wood pellet boiler. To determine the efficiency and heating output of the wood pellet boiler, we measured mass flow rate of wood pellet, the lower heating value(LHV) of the wood pellet, mass flow rate and temperature of water for floor heating and so on. We measured the mass flow rate of fuel, wood pellet with respect to rotational speed of auger, wood pellet feeding screw. We also measured the flue gas concentration of the wood pellet boiler by using a gas analyser. The result shows that the efficiency of the wood pellet boiler is 80.6% based on lower heating value at 124 kW of heating output. At this condition, O2 concentration of the flue gas is 6.0%, CO and NOx concentrations are 85 and 102 ppm.

• Proceedings of the Korean Nuclear Society Conference
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• 1977.06a
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• pp.112-112
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• 1977

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.79-88
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• 2010

Spent $UO_2$ nuclear fuel discharged from a nuclear power plant (NPP) contains fission products, U, Pu, and other actinides. Due to neutron capture by $^{238}U$ in the rim region and a temperature gradient between the center and the rim of a fuel pellet, a considerable increase in the concentration of fission products, Pu, and other actinides are expected in the pellet periphery of high burnup fuel. The characterization of the radial profiles of the various isotopic concentrations is our main concern. For an analysis, spent nuclear fuels originating from the Yeonggwang-2 pressurized water reactor (PWR) were chosen as the test specimens. In this work, the distributions of some actinide isotopes were measured from center to rim of the spent fuel specimens by a radiation shielded laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) system. Sampling was performed along the diameter of the specimen by reducing the sampling intervals from 500 ${\mu}m$ in the center to 100 ${\mu}m$ in the pellet periphery region. It was observed that the isotopic concentration ratios for minor actinides in the center of the specimen remain almost constant and increase near the pellet periphery due to the rim effect apart from the $^{236}U$ to $^{235}U$ ratio, which remains approximately constant. In addition, the distributions of local burnup were derived from the measured isotope ratios by applying the relationship between burnup and isotopic ratio for plutonium and minor actinides calculated by the ORIGEN2 code.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2760-2770
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• 2020

A model for calculation of fuel temperature profile using binary gas mixture of Helium and Xenon for gap gas conductance is proposed here. In this model, the temperature profile of a fuel pencil from fuel centreline to fuel surface has been calculated by taking into account the dilution of Helium gas filled during fuel manufacturing due to accumulation of fission gas Xenon. In this model an explicit calculation of gap gas conductance of binary gas mixture of Helium and Xenon has been carried out. A computer code Fuel Characteristics Calculator (FCCAL) is developed for the model. The phenomena modelled by FCCAL takes into account heat conduction through the fuel pellet, heat transfer from pellet surface to the cladding through the gap gas and heat transfer from cladding to coolant. The binary noble gas mixture model used in FCCAL is an improvement over the parametric model of Lassmann and Pazdera. The results obtained from the code FCCAL is used for fuel temperature calculation in 3-D neutron diffusion solver for the coolant outlet temperature of the core at steady operation at full power. It is found that there is an improvement in calculation time without compromising accuracy with FCCAL.

• Journal of Forest and Environmental Science
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• v.30 no.4
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• pp.362-369
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• 2014

This study investigated physical properties and combustion gas characteristics for 8 types of wood pellets (4 domestic and 4 imported products) distributed in the domestic market. Results showed that most pellet types were first-grade pellets in the wood pellet quality standards in Korea with the exception of 3 pellet types from K company (second-grade in mechanical durability), G company (off-grade in nitrogen content) and P company (second-grade in ash percentage). Mixed pellets which contained more lignin and sap content were higher in mechanical durability (%) than that of white pellets. From the combustion gas analysis results, NOx emitted from all pellets combustion was at acceptable levels for national emission standard of the Clean Air Conservation Act except for pellets from G company. In addition, CO levels from all types of wood pellets were acceptable except for pellets from D company and domestic pellets were higher CO levels than imported pellets. These results indicate the higher CO levels in domestic pellets due to the usage of forest thinning materials including logging debris which usually had the high content of bark.

• Nuclear Engineering and Technology
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• v.40 no.1
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• pp.1-8
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• 2008

One of the major current challenges to nuclear energy lies in its competitiveness. To stay competitive the industry needs to reduce maintenance and fuel cycle costs, while enhancing safety features. Extended burnup is one of the methods applied to meet these objectives However, there are a number of potential fuel failure causes related to increased burnup, as follows: l) Corrosion of zirconium alloy cladding and the water chemistry parameters that enhance corrosion; 2) Dimensional changes of zirconium alloy components, 3) Stresses that challenge zirconium alloy ductility and the effect of hydrogen (H) pickup and redistribution as it affects ductility, 4) Fuel rod internal pressure, 5) Pellet-cladding interactions (PCI) and 6) pellet-cladding mechanical interactions (PCMI). This paper discusses current and potential failure mechanisms of these failure mechanisms.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1333-1344
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• 2019

An integrated approach of model simplification for high burnup spent nuclear fuel is proposed based on material calibration using optimization. The spent fuel rods are simplified into a beam with a homogenous isotropic material. The proposed approach of model simplification is applied to fuel rods with two kinds of interfacial configurations between the fuel pellets and cladding. The differences among the generated models and the effects of interfacial bonding efficiency are discussed. The strategy of model simplification adopted in this work is to force the simplified beam model of spent fuel rods to possess the same compliance and failure characteristics under critical loads as those that result in the failure of detailed fuel rod models. It is envisioned that the simplified model would enable the assessment of fuel rod failure through an assembly-level analysis, without resorting to a refined model for an individual fuel rod. The effective material properties of the simplified beam model were successfully identified using the integrated optimization process. The feasibility of using the developed simplified beam models in dynamic impact simulations for a horizontal drop condition is examined, and discussions are provided.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.48 no.3
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• pp.99-106
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• 2016

Our aim was to identify the potential of reed stalk as a raw materials for biomass pellet production. Compared to woody biomass, reed stalk contained significant levels of ash. The holocellulose content of reed stalk was similar to that of larch, but the lignin content of reed stalk was lower than that of larch. In the elemental analysis, chlorine content of reed stalk was much higher than that of larch, and satisfied only the mixed biomass pellet B of European non-woody pellet standards(EN 14961-6). In quantitative analysis of the ash, heavy metals contents of reed stalk satisfied European non-woody pellet standards. Higher heating value of oven-dried reed stalk pellet was slightly lower than that of larch wood pellet. The durability of reed stalk pellet was lower than that of larch wood pellet. The results of this study indicate that reed stalk might be used as a raw material of mixed biomass pellet B.

• Clean Technology
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• v.24 no.2
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• pp.119-126
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• 2018

This study introduced a treatment process that was developed to treat Indonesian low-rank coal with high-ash content, which has the same characteristics as residual coal from the biosolubilization process. The treatment process includes separation of ash, solid-liquid separation, pelletizing, and drying. To reduce the ash content, flotation was performed using 4-methyl-2-pentanol (MIBC) as frother, and kerosene, waste oil, and cashew nut shell liquid (CNSL) as collectors. The increasing amount of collector had an effect on combustible coal recovery and ash reduction. After flotation, a filter press, extruder, and an oven drier were used to make a dried coal pellet. Then another coal pellet was made using asphalt as a binder. The compressive strength and friability of the coal pellets were tested and compared.