• Journal of Energy Engineering
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• v.24 no.3
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• pp.135-141
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• 2015

The core melts stratifies into lower mixture layer and upper metal layer by density in a severe accident condition. The decay heat generated from the mixture layer threatens the integrity of the reactor vessel. This study simulated the natural convection heat transfer of the mixture layer with volumetric heat source using the mass transfer system. $H_2SO_4-CuSO_4$ electroplating system was used as the mass transfer system. With the modified Rayleigh number of $3{\times}10^{14}$, the Nusselt number showed minimum at the bottom and increased along curvature to the top of the experimental apparatus.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.237-242
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• 1998

Zr합금의 수소화 반응속도에 미치는 합금원소의 영향을 평가하기 위하여 Zr과 Zr-0.8Sn-XNb계열(X=0.2, 0.4, 0.8, 1.0) 및 Zr-0.4Nb-YSn계열(Y=0.5, 0.8, 1.5, 2.0)의 3원계 합금으로 electro-microbalance가 장착된 TGA (thermo-gravimetric apparatus)장치를 이용하여 40$0^{\circ}C$에서 1기압 수소와의 반응에 따른 무게증가를 in-situ로 측정하였다 Sn 첨가량이 증가함에 따라 1.5% 까지는 수소반응에 따른 무게증가율이 낮게 나타났으나 Sn을 2.0% 함유한 Zr-0.4Nb-2.0Sn합금의 경우 가장 높게 나타났다. 이는 Sn의 함량이 증가할수록 수소침투에 대한 저항성이 증가함을 의미하지만 Sn이 고용도 이상 함유되면 Sn을 함유한 다량의 석출물이 대량수소침투의 site로 작용하여 수소침투가 가속화된 것으로 평가된다. Nb의 경우 첨가량을 증가시킬수록 무게증가는 크게 나타났는데 이는 Nb이 수소흡수성이 크기 때문이며 Zr-0.8Sn-0.2Nb 및 Zr-0.8Sn-0.4Nb 합금보다 Zr-0.8Sn-0.8Nb 및 Zr-0.8Sn-1.0Nb 합금의 경우 TEM을 이용한 금속간 석출물(intermetallic precipitates) 분석에서 이러한 석출물들의 평균크기 및 개수가 크게 평가되었고, 또한 Zr-0.8Sn-0.2Nb, Zr-0.8Sn-0.4Nb 합금에서는 관찰이 되지 않는 $\beta$-Zr 석출물이 관찰되었다 이러한 사실로부터 Nb의 큰 수소흡수성에 부가적으로 이러한 석출물들이 수소침투를 가속화 하는 데에 기여하는 것으로 여겨진다.

• The KSFM Journal of Fluid Machinery
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• v.8 no.6 s.33
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• pp.15-25
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• 2005

Check valves playa vital role in the operation and protection of nuclear power plants. Check valves failure in nuclear power plants often lead to a plant transient or trip. The analysis of historical failure data gives information on the populations of various types of check valves, the systems they are installed in, failure modes, effects, methods of detection, and the mechanisms of the failures. A majority of check valve failures are caused by improper application. The experimental apparatus is designed and installed to measure the disc positions with flow velocity, Vopen and Vmin for 3 inch and 6 inch swing check valves. The minimum flow velocity necessary to just open the disc at a full open position is referred to as Vopen, and Vmin is defined as the minimum velocity to fully open the disc and hold it without motion. In the experiments, Vmin is determined as the minimum flow velocity at which the back stop load begins to increase after the disc is fully opened or the oscillation level of disc is reduced below $1^{\circ}$. The results show that the Vmin velocities for 3 inch and 6 inch swing check valves are about 27.3% and 17.5% higher than the Vopen velocities, respectively.

• Nuclear Engineering and Technology
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• v.33 no.1
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• pp.25-33
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• 2001

To determine the pin power distribution without disassembling, HANARO fuel assemblies are gamma-scanned and then the distribution is reconstructed tv using the tomography method. The iterative least squares method (ILSM and the wavelet singular value decomposition method (WSVD) are chosen to solve the problem. An optimal convergence criterion is used to stop the iteration algorithm to overcome the potential divergence in ILSM. WSVD gives better results than ILSM , and the average values from the two methods give the best results. The RMSE (root mean square errors) to the reference data are 5.1, 6.6, 5.0, 6.5, and 6.4% and the maximum relative errors are 10.2, 13.7, 12.2, 13.6, and 14.3%, respectively. It is found that the effect of random positions of the pins is important. Although the effect can be accommodated by the iterative calculations simulating the random positions, the use of experimental equipment with a slit covering the whole range of the assembly horizontally is recommended to obtain more accurate results. We made a new apparatus using the results of this study and are conducting an experiment in order to obtain more accurate results.

• Solar Energy
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• v.18 no.4
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• pp.1-10
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• 1998

Polymer induced turbulent drag reduction in a rotating disk apparatus was investigated using four different molecular weights of poly(ethylene oxide)(PEO) in a synthetic seawater solution for the purpose of potential application to the cold water piping in the Ocean Thermal Energy Conversion(OTEC) system. To apply drag reduction to the OTEC we measured the temperature dependence on the drag reduction efficiency. From this study, it was found that the drag reduction efficiency increases with the temperature and the concentration. To measure the drag reduction efficiency during the operation period, the drag reduction behavior was detected as a function of time and the results obtained from the experiment was compared to the Brostow's model equation.

• Geomechanics and Engineering
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• v.22 no.5
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• pp.375-384
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• 2020

In this study, the application of conventional cubic law to a deep depth condition was experimentally evaluated. Moreover, a modified equation for estimating the rock permeability at a deep depth was suggested using precise hydraulic tests and an effect analysis according to the vertical stress, pore water pressure and fracture roughness. The experimental apparatus which enabled the generation of high pore water pressure (< 10 MPa) and vertical stress (< 20 MPa) was manufactured, and the surface roughness of a cylindrical rock sample was quantitatively analyzed by means of 3D (three-dimensional) laser scanning. Experimental data of the injected pore water pressure and outflow rate obtained through the hydraulic test were applied to the cubic law equation, which was used to estimate the permeability of rock fracture. The rock permeability was estimated under various pressure (vertical stress and pore water pressure) and geometry (roughness) conditions. Finally, an empirical formula was proposed by considering nonlinear flow behavior; the formula can be applied to evaluations of changes of rock permeability levels in deep underground facility such as nuclear waste disposal repository with high vertical stress and pore water pressure levels.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.214-220
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• 2019

Thermochemical cycles have been predominantly used for energy transformation from heat to stored chemical free energy in the form of hydrogen. The thermochemical cycle based on uranium (UTC), proposed by Oak Ridge National Laboratory, has been considered as a better alternative compared to other thermochemical cycles mainly due to its safety and high efficiency. UTC process includes three steps, in which only the first step is unique. Hydrogen production apparatus with hectogram reactants was designed in this study. The results showed that high yield hydrogen was obtained, which was determined by drainage method. The results also indicated that the chemical conversion rate of hydrogen production was in direct proportion to the mass of $Na_2CO_3$, while the solid product was $Na_2UO_4$, instead of $Na_2U_2O_7$. Nevertheless the thermochemical cycle used for hydrogen generation can be closed, and chemical compounds used in these processes can also be recycled. So the cycle with $Na_2UO_4$ as its first reaction product has an advantage over the proposed UTC process, attributed to the fast reaction rate and high hydrogen yield in the first reaction step.

• Analytical Science and Technology
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• v.22 no.5
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• pp.395-406
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• 2009

The determination of iodine in the spent nuclear fuel and the volatile behavior during its acid dissolution have been studied by NAA(neutron activation analysis) and electron probe microanalysis (EPMA). Simulated spent fuels (SIMFUELs) were dissolved in $HNO_3$(1+1) at $90^{\circ}C$ for 8 hours. The iodine remained in a dissolver solution after dissolution, and that condensed in dissolution apparatus and trapped in the adsorbent by volatilization during the dissolution were determined, respectively. The condensed iodine was recovered by the redistillation with $HNO_3$(1+1) after transfer of the dissolver solution. The iodines in the dissolver and redistilled solution were separated by solvent extraction followed by ion exchange or precipitation method and determined by RNAA (radiochemical neutron activation analysis). The ion exchange column and filtration kit used for the isolation of iodine, which were prepared with a polyethylene tube, were used as an insert in the pneumatic tube for neutron irradiation. The iodine volatilized during the dissolution of SIMFUELs was collected in a trapping tube containing Ag-silica gel (Ag-impregnated silica gel) adsorbent, and the distribution of iodine trapped in the adsorbents were determined by EPMA. The adsorbing characteristics shown with the SIMFUELs were compared with those shown with a real spent fuel from the nuclear power plant.

• Nuclear Engineering and Technology
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• v.48 no.1
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• pp.274-284
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• 2016

Purpose: The purpose of this work is to describe the spectrometric analysis of gaseous cloud formation over reactor mixed uranium-and-plutonium (UP) fuel $(U_{0.8}Pu_{0.2})O_2$ samples heated to a temperature $>2,000^{\circ}C$, and thus forecast and evaluate radiation hazards threatening humans who cope with the consequences of any accident at a fission reactor loaded by UP mixed oxide $(U_{0.8}Pu_{0.2})O_2$, such as a mixture of 80% U and 20% Pu in weight. Materials and methods: The UP nuclear fuel samples were heated up to a temperature of over $2,000^{\circ}C$ in a suitable assembly (apparatus) at out-of-pile experiments' implementation, the experimental in-depth study of metabolism of active materials in living organisms by means of artificial irradiation of pigs by plutonium. Spectrometric measurements were carried out on the different exposed organs and tissues of pigs for the further estimation of human internal exposure by nuclear materials released from the core of a fission reactor fueled with UP mixed oxide. Results: The main results of the research described are the following: (1) following the research on the influence of mixed fuel fission products (radioactive isotopes being formed during reactor operation as a result of nuclear decay of elements included into the fuel composition) on living organisms, the authors determined the quantities of plutonium dioxide ($PuO_2$) that penetrated into blood and lay in the pulmonary region, liver, skeleton and other tissues; and (2) experiments confirmed that the output speed of plutonium out of the basic precipitation locations is very small. On the strength of the experimental evidence, the authors suggest that the biological output of plutonium can be disregarded in the process of evaluation of the internal irradiation doses.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.203-204
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• 2002

The wear behaviour of steam generator (SG) tubes (Inconel 600 and 690) against support materials (405 and 409 ferritic stainless steels) has been experimentally studied in room temperature water using reciprocating wear apparatus with tube-an-plate configuration. The results showed that the wear rate of Inconel 690 was lower than that of lnconel 600 with increasing normal loads and sliding amplitudes. Also, plastic deformation layers appear below the surface of both SG tubes, which have a specific thickness and are small compared with their grain size. This means that wear rate of SG tubes in water condition is closely related to the formation and fracture of plastic deformation layers.