• Journal of Radiation Protection and Research
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• v.42 no.1
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• pp.42-47
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• 2017

Background: One of the most urgent issues following the accident at the Fukushima Daiichi nuclear power plant (FDNPP) was the remediation of the land, in particular, for residential area contaminated by the radioactive materials discharged. In this study, the effect of decontamination on reduction of ambient dose equivalent outdoors and indoors was evaluated. The latter is essential for residents as most individuals spend a large portion of their time indoors. Materials and Methods: From December 2012 to November 2014, thirty-seven Japanese single-family detached wooden houses were investigated before and after decontamination in evacuation zones. Outdoor and indoor dose measurements (n = 84 and 114, respectively) were collected based on in situ measurements using the NaI (Tl) scintillation surveymeter. Results and Discussion: The outdoor ambient dose equivalents [$H^*(10)_{out}$] ranged from 0.61 to $3.71{\mu}Sv\;h^{-1}$ and from 0.23 to $1.32{\mu}Sv\;h^{-1}$ before and after decontamination, respectively. The indoor ambient dose equivalents [$H^*(10)_{in}$] ranged from 0.29 to $2.53{\mu}Sv\;h^{-1}$ and from 0.16 to $1.22{\mu}Sv\;h^{-1}$ before and after decontamination, respectively. The values of reduction efficiency (RE), defined as the ratio by which the radiation dose has been reduced via decontamination, were evaluated as $0.47{\pm}0.13$, $0.51{\pm}0.13$, and $0.58{\pm}0.08$ ($average{\pm}{\sigma}$) when $H^*(10)_{out}$ < $1.0{\mu}Sv\;h^{-1}$, $1.0{\mu}Sv\;h^{-1}$ < $H^*(10)_{out}$ < $2.0{\mu}Sv\;h^{-1}$, and $2.0{\mu}Sv\;h^{-1}$ < $H^*(10)_{out}$, respectively, indicating the values of RE increased as $H^*(10)_{out}$ increased. It was found that the values of RE were $0.53{\pm}0.12$ outdoors and $0.41{\pm}0.09$ indoors, respectively, indicating RE was larger outdoors than indoors. Conclusion: Indoor dose is essential as most individuals spend a large portion of their time indoors. The difference between outdoors and indoors should be considered carefully in order to estimate residents' exposure dose before their returning home.

• Textile Coloration and Finishing
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• v.32 no.2
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• pp.73-79
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• 2020

Pursuing the fabric materials for military chemical warfare protective clothing with the improved detoxification properties, this study investigated the simple and effective cotton treatment method using pad-dry-cure process and 3-aminopropyltrimethox ysilane(APTMS) solution for surface amination. Detoxification properties of the untreated and treated cotton fabrics were evaluated via decontamination of chemical warfare agent simulant, DFP(diisopropylfluorophosphate). The surface aminated cotton fabric increased the rate of the hydrolysis of DFP by the factor of 3 and the decontamination ratio reached 88.2% after 24h. Therefore, the surface amination of the cotton fabric with APTMS can be an effective pathway to prepare the material for protective clothing against chemical warfare agents.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.3
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• pp.161-165
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• 2009

To evaluate the efficiency of the decontamination plant for the removal of uranium compounds deposited on the internal surface of $UF_6$ cylinder for its reuse, two demonstration tests of the plant with different ratio of ${Na_2}{CO_3}$ and ${H_2}{O_2}$ were carried out, and each test had 5 steps. The main chemical form removed by the tests was to be identified as ${Na_4}{UO_2}(CO_3)_3$. More than 50% of uranium was removed by water of the first step, and at the following steps the removal amounts were exponentially decreased. On the other hand, the result shows that the injected amount of ${Na_2}{CO_3}$, compared with that of the removed uranium, was stoichiometrically excessed. This suggests that the injected amounts of ${Na_2}{CO_3}$, the generation rate of decontaminated waste, and the decontamination steps could be reduced by a process optimization of the plant.

• Journal of the Korean institute of surface engineering
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• v.34 no.1
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• pp.10-16
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• 2001

Recently plasma etching research has been focused on the metal surfaces in the nuclear industry. In this study, surface etching reaction of metallic Co and Mo, principal contaminants in the spent nuclear components, in CF$_4$/O$_2$, gas plasma has been experimentally investigated to look into the applicability and the effectiveness of the technique for the surface decontamination. Experimental variables are $CF_4$/$O_2$ ratio and substrate temperature between 29$0^{\circ}C$ and 38$0^{\circ}C$. Experimental results Show that the optimum gas composition is 80%CF$_4$-20%$O_2$ and the metallic Co and Mo are etched out well enough in the temperatures range. Cobalt starts to be etched above $350^{\circ}C$ and the etching rate increases with increasing substrate temperature. Maximum rate achieved at 38$0^{\circ}C$ under 220 W r.f. plasma power is 0.06 $\mu\textrm{m}$/min. On the other hand, the metallic Mo is etched easily even at low temperature and the reaction rate drastically increases as the substrate temperature goes up. Highest rate obtained under the same conditions is $1.9\mu\textrm{m}$/min. OES (Optical Emission Spectroscopy) analysis reveals that the intensities of F atom and CO molecule reach maximum at the optimum gas composition, which demonstrates that the principal reaction mechanism is fluorination and/or carbonyl reaction. It is confirmed, therefore, that dry processing technique using reactive plasma is quite feasible and applicable for the decontamination of surface-contaminated parts or equipments.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.4
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• pp.271-280
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• 2013

Since the decommissioning of nuclear plants and facilities, large quantities of slightly contaminated concrete waste have been generated. In Korea, the decontamination and decommissioning of the KRR-1, 2 at the KAERI have been under way. And concrete waste was generated about 800 drums of 200 L. The conditioning of concrete waste is needed for final disposal. The concrete waste is conditioned as follows: mortar using coarse and fine aggregates is filled void space after concrete rubble pre-placement into 200 L drum. Thus, this research has developed an optimizing mixing ratio of concrete waste, water, and cement and has evaluated characteristics of a cement waste form to meet the requirements specified in disposal site specific waste acceptance criteria. The results obtained from compressive strength test, leaching test, thermal cycling test of cement waste forms conclude that the concrete waste, water, and cement have been suggested to have 75:15:10wt% as the optimized mixing ratio. Also, the compressive strength of cement waste form was satisfied that including fine powder up to maximum 40wt% in concrete debris wastes about 75%. As a result of scale-up test, the mixture of concrete waste, water, and cement is 75:10:15wt% meet the satisfied compressive strength because the free water increased with and increased in particle size.

• Journal of Environmental Science International
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• v.24 no.12
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• pp.1601-1608
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• 2015

This study evaluates heavy metal(Cu and Cr) adsorption characteristics produced from food waste charcoal extracted in an optimal operation condition after analyzing activated charcoal of iodine adsorption and heavy metals that derived from an activation process of carbide by the developed by-products of food waste treatment facility using the methods from previous studies. As experiment apparatus, this study used a tube-shaped high temp furnace. The mixing ratio of by-products of food waste treatment facility, carbide, and activation component($ZnCl_2$) was 1:1. The experiment was proceeded as adjusting the activation temperature from 400 to $800^{\circ}C$ and activation time from 30 to 120 minutes. The optimal activation condition for iodine absorption was 90 minutes at $700^{\circ}C$ and by using the produced food waste charcoal, this study conducted an experiment on absorption of heavy metals (Cu and Cr) as changing pH of artificial wastewater and stirring time. As a result, pH 7 showed the highest heavy metal decontamination ratio and in terms of stirring time, it revealed balance adsorption after 10 minutes. This result can be particularly applied as basic data for recyclability of high concentration organic waste, by-products of food waste treatment facility, as an food waste charcoal.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.179-182
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• 2001

The chloride volatilization method for the recovery of zirconium and removal of uranium from zirconium containing metallic wastes formed in spent fuel reprocessing was studied using the simulated alloy waste, i.e. the mixture of Zr foil and UO$_2$/U$_3$O$_{8}$ powder. When the simulated waste was heated to react with chlorine gas at 350- l00$0^{\circ}C$, the zirconium metal changed to volatile ZrCl$_4$showing high volatility ratio (Vzr) of 99%. The amount of volatilized uranium increases at higher temperatures causing lowering of decontamination factor (DF) of uranium. This is thought to be caused by the chlorination of UO$_2$ with ZrCl$_4$vapor. The highest DF value of 12.5 was obtained when the reaction temperature was 35$0^{\circ}C$. Addition of 10 vol.% oxygen gas into chlorine gas was effective for suppressing the volatilization of uranium, while the volatilization ratio of zirconium was decreased to 68% with the addition of 20 vol.% oxygen. In the case of the mixture of Zr foil and U$_3$O$_{8}$, the V value of uranium showed minimum (44%) at 40$0^{\circ}C$ with chlorine gas giving the highest DF value 24.3. When the 10 vol.% oxygen was added to chlorine gas, the V value of zirconium decreased to 82% at $600^{\circ}C$, but almost all the uranium volatilized (Vu=99%), which may be caused by the formation of volatile uranium chlorides under oxidative atmosphere.ere.

• Korean Journal of Food Science and Technology
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• v.49 no.1
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• pp.20-27
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• 2017

Eighteen commercial laver (Porphyra sp.) products were purchased from Korean market and were monitored for their microbial contamination, pre-decontamination, and luminescence properties. The laver samples showed considerable variation in their microbial contamination, from $10-10^7CFU/g$ of total aerobic counts, <$10-10^2CFU/g$ of coliforms in 4 dried laver samples, and <$10-10^6CFU/g$ of yeasts and molds except in 3 samples. In addition, $10^2CFU/g$ of Bacillus cereus was found in one sample. DEFT/APC analysis was suitable for demonstrating whether the samples were pre-decontaminated or not, with DEFT/APC values lower than 2.0 log for non-heated samples and 1.0-8.5 log for heatprocessed samples. In photostimulated luminescence (PSL) calibration, 15 samples irradiated at 1 kGy showed positive (irradiated) values more than 5000 PCs. Furthermore, thermoluminescence (TL) analysis by separating the marker minerals from samples revealed the potential to be employed in identifying irradiation status by determining $1^{st}$ TL glow at $125-175^{\circ}C$ and TL ratio ($TL_1/TL_2$) of all the samples.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.2
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• pp.217-225
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• 2020

Concrete waste accounts for approximately 70~80% of the total waste generated during the decommissioning of nuclear power plants (NPPs). Based upon the concentration of each radionuclide, the concrete waste from the decommissioning can be used in the determination of the clearance threshold used to classify waste as radioactive. To reduce the cost of radioactive concrete waste disposal, it is important to perform decontamination before self-disposal or limited recycling. Therefore, it is necessary to estimate the internal radioactivity distribution of radioactive concrete waste to ensure effective decontamination. In this study, the performance metrics of various Compton reconstruction algorithms were compared in order to identify the best strategy to estimate the internal radioactivity distribution in concrete waste during the decommissioning of NPPs. Four reconstruction algorithms, namely, simple back-projection, filtered back-projection, maximum likelihood expectation maximization (MLEM), and energy-deconvolution MLEM (E-MLEM) were used as Compton reconstruction algorithms. Subsequently, the results obtained by using these various reconstruction algorithms were compared with one another and evaluated, using quantitative evaluation methods. The MLEM and E-MLEM reconstruction algorithms exhibited the best performance in maintaining a high image resolution and signal-to-noise ratio (SNR), respectively. The results of this study demonstrate the feasibility of using Compton images in the estimation of the internal radioactive distribution of concrete during the decommissioning of NPPs.

• Journal of Soil and Groundwater Environment
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• v.8 no.1
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• pp.17-26
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• 2003

The sorption experiment of cobalt was performed after the TRIGA soil was intentionally contaminated with cobalt was found that the sorption equilibrium coeficiency of soil decontamination was high when the ratio of soil mass to the volume of citric acid becomes 1:5 The TRIGA soil contaminated with 0.01 M, 0.001 M, and 0.0001 M of cobalt solution were decontaiminated with 0.01 M citric acid. The cobalt concentrtion in the wastewater were measured to be correspondingly 36.0, 14.0, 1.5 ppm. The results of wastewater recycling experiment by chemical precipitation method revealed that corresponding cobalt removal efficiency were 97% 88%. It was shown that the removal efficiency decreases as the cobalt concentration in the wastewater decreases. During the decontamination experiment, a lot of NaOH had to be added, and the volume of final solid waste reached almost 10% of that of the contaminated soil. The result of wastewater recyling experiment by ion exchange resin meted rethod revealed that to more the strong acid resins are used, the higher the cobalt removal efficiency becomes and the cobalt removal efficiency becomes and the lower the pH of recycling wastewater become. In order to obtain more than 95% removal efficiency, more than 0.625 g of strong acid resin was necessary in each of 3 experiments. There was an unexpected problem that a lot of strong acid resin waste was produced which amounts to 9.2% (volume) of the contaminated soil.