• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.1
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• pp.83-91
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• 2018

While using an electrokinetic method to analyze the characteristics of cement solidification of radioactive wastes from decontaminated uranium soil and concrete, the compressive strength, pH, electrical conductivity, irradiation effects, and volume expansion were measured for the solidified cement specimens. The workability of cement solidified from radioactive waste was about 170-190%. After the solidified cement was irradiated, the compressive strength decreased by about 15%, but met the criteria ($34kgf{\cdot}cm^{-2}$) of KORAD (Korea Radioactive Waste Agent). According to the results of SEM-EDS for solidified cement, the aluminum phase was well combined with cement, while the calcium phase was separated from cement. The volume of solidified cement in radioactive wastes was dependent on the waste-to-cement ratio and the amount of water, and increased by about 30% under the conditions used in this study. Therefore, it was concluded that permanent disposal of electrokinetically decontaminated radioactive wastes is appropriate.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.3
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• pp.239-256
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• 2017

In the process of site selection for a radioactive waste disposal, site characterization must be carried out to obtain input parameters to assess the safety and feasibility of deep geological repository. In this paper, methodologies of site characterization for radioactive waste disposal in Korea were suggested based on foreign cases of site characterization. The IAEA recommends that site characterization for radioactive waste disposal should be performed through stepwise processes, in which the site characterization period is divided into preliminary and detailed stages, in sequence. This methodology was followed by several foreign countries for their geological disposal programs. General properties related to geological environments were obtained at the preliminary site characterization stage; more detailed site characteristics were investigated during the detailed site characterization stage. The results of investigation of geology, hydro-geology, geochemistry, rock mechanics, solute transport and thermal properties at a site have to be combined and constructed in the form of a site descriptive model. Based on this site descriptive model, the site characteristics can be evaluated to assess suitability of site for radioactive waste disposal. According to foreign site characterization cases, 7 or 8 years are expected to be needed for site characterization; however, the time required may increase if the no proper national strategy is provided.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.215-220
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• 2010

An experiment measuring the concentration ratios of $^{137}Cs$ and $^{85}Sr$ in fish as an index aquatic animal was performed. The species was Chinese minnow (Rhynchocypris Oxycephalus), a Korean native freshwater species. Chinese minnows were reared in acryl aquarium which was 45 cm wide, 85 cm long and 50 cm high. Water in the aquarium was successively purified using filtering devices attached on the floor and the wall. Fish powder in a particulate form was supplied twice a day for feeding. After a radioactive solution was added to make the initial water concentrations approximately $0.02\;{\mu}Ci/l$ and $0.1\;{\mu}Ci/l$ for $^{137}Cs$ and $^{85}Sr$, respectively, the fish and water were sampled 10 times for a month. The concentration ratios were measured to be $0.348lkg^{-1}\sim13.906lkg^{-1}$ for $^{137}Cs$ and $0.474lkg^{-1}\sim13.089lkg^{-1}$ for $^{85}Sr$.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.2
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• pp.159-166
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• 2010

The block-scale groundwater flow system at Olkiluoto site in Finland was simulated. The heterogeneous and anisotropic hydraulic conductivity field for the domain was constructed from the discrete fracture network, which considered only the fractured zones identified in the deep boreholes installed in the study site. The groundwater flow model was calibrated by adjusting the recharge rate and the transmissivities of the fractured zones to fit the calculated hydraulic heads and into- and out-flow rates in the observation intervals of the boreholes with the observed ones. In the calibrated model, the calculated flow rates at some intervals were not in accordance with the observed ones although the calculated hydraulic heads fit well with the observed ones, which revealed that the number of the conduits for groundwater flow is insufficient in the conceptual model for groundwater flow modeling. Therefore, it was recommended that the potential local conduits such as background fractures should be added to the present conceptual model.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.189-199
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• 2010

In a high-level waste (HLW) repository, heat is generated by the radioactive decay of the waste. This can affect the safety of the repository because the surrounding environment can be changed by the heat transfer through the rock. Thus, it is important to determine the heat transfer coefficient of the atmosphere in the underground repository. In this study, the heat transfer coefficient was estimated by measuring the indoor environmental factors in the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) under forced convection. For the experiment, a heater of 5 kw capacity, 2 meters long, was inserted through the tunnel wall in the heating section of KURT in order to heat up the inside of the rock to $90^{\circ}C$, and fresh air was provided by an air supply fan connected to the outside of the tunnel. The results showed that the average air velocity in the heating section after the provision of the air from outside of the tunnel was 0.81 m/s with the Reynolds number of 310,000~340,000. The seasonal heat transfer coefficient in the heating section under forced convection was $7.68\;W/m^2{\cdot}K$ in the summer and $7.24\;W/m^2{\cdot}K$ in the winter.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.247-260
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• 2010

The developement of a HLW disposal canister is under way in KAERI using Cold Spray Coating technique. To estimate corrosion behavior of a cold sprayed copper, a creivice corrosion test was conducted at Southwest Research Institute(SWRI) in the United State. For the measurement of repassivation potential needed for crevice corrosion, three methods such as (1) ASTM G61-86 : Cyclic Potentiodynamic Polarization Measurements, (2) Potentiodynamic Polarization plus intermediate Potentiostatic Hold method, and (3) ASTM G192-08 (THE method) : Potentiodynamic- Galvanostatic-Potentiostatic Method, were introduced in this report. In the crevice corrosion test, the occurrence of corrosion at crevice area was optically determined and the repassivation potentials were checked for three kind of copper specimens in a simulated KURT underground water, using a crevice former dictated in ASTM G61-86. The applied electrochemical test techniques were cyclic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. As a result of crevice corrosion tests, every copper specimens including cold sprayed one did not show any corrosion figure on crevice areas. And the open-cell voltage, at which corrosion reaction initiates, was influenced by the purity of copper, but not their manufacturing method in this experiment. Therefore, it was convinced that there is no crevice corrosion for the cold sprayed copper in KURT underground environment.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.181-188
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• 2010

Metal surface decontamination characteristics were investigated by using a laser ablation method. A second harmonic generation of a Q-switched Nd:YAG laser with a wave length of 532 nm, a pulse energy of 150 mJ and a pulse width of 5 ns was employed to assess the decontamination performance for metal surfaces contaminated with $CsNO_3$, $Co(NH_4)_2(SO_4)_2$, $Eu_2O_3$ and $CeO_2$. The ablation behavior was investigated for the decontamination variables such as a number of laser shots, laser fluence and an irradiation angle. Their optimum values were found to be 8, 13.3 J/$cm^2$ and $30^{\circ}$, respectively. The decontamination efficiency was different depending on the kinds of the contaminated ions, due to their different melting and boiling points and was in the order: $CsNO_3>Co(NH_4)_2(SO_4)_2>Eu_2O_3>CeO_2$. We also evaluated a correlation between the metal ablation thickness and the number of laser shots for the different laser fluences.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.207-213
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• 2010

The effect of temperature on swelling pressure was observed with a Korean domestic Ca-bentonite which has been considered as a potential buffer material in the engineering barrier of a high level radioactive waste (HLW) disposal system. The Ca-bentonite was compacted to a dry density of 1.6 g/$cm^3$, and then de-ionized water was supplied into it with a constant pressure of 0.69 MPa. The equilibrium swelling pressures were measured with different temperatures of $25^{\circ}C$, $30^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$, $60^{\circ}C$, $70^{\circ}C$, respectively. The Ca-bentonite showed a sufficiently high swelling pressure of 5.3 MPa at room temperatures. Then it was clearly showed that the equilibrium swelling pressure was decreased with an increase of temperature. Interestingly, there were some differences in temperature effect on the equilibrium swelling pressure when the environmental temperature is increasing or decreasing. For further clarifying the swelling behaviour of a Korea domestic Ca-bentonite, the change of a compaction level, and the composition variation of a supplied water would be needed to use in conceptual design of HLW disposal system.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.2
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• pp.125-131
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• 2009

An electrolytic system (zinc anode-gallium cathode) was setup to evaluate the performance of several stirrers prepared for this study, where stirrers have been used to prevent uranium from forming dendrite on the cathode in pyrochemical process. In the case of no-stirring condition, zinc dendrites began to grow on the gallium surface in 1 hour and some dendrite grew out of the cathode crucible around 6 hours. When a rectangular stirrer or a tilt stirrer was rotated, at 40${\sim}$150 rpm, to mix the liquid gallium cathode, dendritic growth of zinc metal was prevented irrespective of revolution speed, but some of the deposits overflowed out of the cathode crucible owing to the large centrifugal forces at 150 rpm. The harrow stirrer did not nearly retard the dendrite growth at 40 rpm, but the dendrite growth was retarded at higher than 100 rpm and the zinc deposits also did not overflow at 150 rpm. Pounder could also prevent the dendrite growth to some extent but it had some difficulties in operation compared with other types of stirrers.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.2
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• pp.151-158
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• 2010

In order to measure the deposition velocity of $I_2$ vapor for radish plants and its translocation factor for their roots, radish plants were exposed to $I_2$ vapor for 80 min. at different growth stages between 29 and 53 d after sowing. The exposure was performed in a transparent chamber during the morning time. Deposition velocities ($ms^{-1}$) were on the whole in the range of $1.0{\times}10^{-4}{\sim}2.0{\times}10^{-4}$ showing an increasing tendency with an increase in the biomass density. The results showed some agreement with existing reports that a higher relative humidity would lead to a higher deposition velocity. The acquired deposition velocities were lower than by factors of several tens than some field measurements probably due to a very low wind speed (about $0.2\;ms^{-1}$) in the chamber. Translocation factors (ratio of the total iodine in the roots at harvest to the total plant deposition), estimated in a more or less conservative way, were $1.3{\times}10^{-3}$ for an exposure at 29 d after sowing and $5.0{\times}10^{-3}$ for an exposure at 53 d after sowing. In using the present experimental data, meteorological conditions and chemical and physical forms of iodine need to be carefully considered.