• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.876-883
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• 2023

Radioactive waste should be solidified before being disposed of in the repository to eliminate liquidity or dispersibility. Cement is a widely used solidifying media for radioactive waste, and cement solidified waste should satisfy the minimum compressive strength of the waste acceptance criteria of a radioactive repository. Although the compressive strength of waste should be measured by the test method provided by the waste acceptance criteria, the method differs depending on the operating repository of different countries. Considering the measured compressive strength changes depending on test conditions, the effect of test conditions should be analyzed to avoid overestimation or underestimation of the compressive strength during disposal. We selected test conditions such as the height-to-diameter ratio, loading rate, and porosity as the main factors affecting the compressive strength of cement solidified radioactive waste. Owing to the large variance in measured compressive strength, the effects of the test conditions were analyzed via statistical analyses using parametric and nonparametric methods. The results showed that the test condition of the lower loading rate, with a height-to-diameter ratio of two, reflected the actual cement content well, while the porosity showed no correlation. The compressive strength assessment method that reflects the large variance of strengths was suggested.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.1
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• pp.13-22
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• 2022

The decommissioning of a nuclear power plant generates large amounts of radioactive waste, which is of several types. Radioactive concrete powder is classified as low-level waste, which can be disposed of in a landfill. However, its safe disposal in a landfill requires that it be immobilized by solidification using cement. Herein, a safety assessment on the disposal of solidified radioactive concrete powder waste in a conceptual landfill site is performed using RESRAD. Furthermore, sensitivity analyses of certain selected input parameters are conducted to investigate their impact on exposure doses. The exposure doses are estimated, and the relative impact of each pathway on them during the disposal of this waste is assessed. The results of this study can be used to obtain information for designing a landfill site for the safe disposal of low-level radioactive waste generated from the decommissioning of a nuclear power plant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1452-1461
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• 1997

The hot press apparatus to obtain the solidified rocks with 60mm of diameter against rock waste was developed, and the optimum conditions for solidification were founded out, of which were 300.deg. C of temperature and 1hr of holding time. The solidified rocks reinforced with the fibers (carbon, steel) were made by means of a hydrothermal hot press method. Fracture toughness of those was obtained using the round compact tension(RCT) specimens. Load and displacement behaviours of the solidified rocks reinforced with the fibers were dependent upon the fiber volume fraction and kind of the fibers. Strength and fracture energy of the solidified rocks with steel were much larger than those of the solidified ones with carbon because of the Bridge's effect, multiple cracking and crack branching phenomena.

• Journal of the Korean Society of Industry Convergence
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• v.1 no.1
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• pp.51-58
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• 1998

This study was carried out to investigate the leaching characteristics by the landfill of solidified sludge. pH of leachate was 3.7 - 5.8 and 8.0 - 10.4 in each column using sand as a top-soil layer on filled municipal waste and solidified cake. $NH_3$-N in leachate was increasing in the each column using sand as a top-soil layer on filled dewatered sludge and solidified cake, but decreasing in the each column using sand and solidified cake by top-soil layer on filled municipal waste. Also the concentration of $NO_3$-N was on the way of stabilizing but was difficult to find any tendency until now. Zn and Mn in leachates were the highest in the column filled with the solidified sludge, Cr, Pb and Cd were low concentration at each column.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.244-250
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• 2003

With a recent public concern rising on the radioactive waste, it is disclosed that the problem is more serious than expected. This research has been conducted to find effects of yellow sandy rainwaters on the solidified cement of mid-and-low level radioactive waste. The ANS 16.1 standard test method was chosen for this leaching experiment. Make a cement solidified radioactive waste that contains Co nuclide, and fabricate it for over 28 days. Then, decide on the volume of leaching water and the concentration of ion and metal in leachate from the mass concentration of yellow sands in atmosphere. In this paper, we have taken a short look at characteristics of yellow sand. Before going into the leaching experiment, we decided experimental conditions first. Then, it was evaluated and analyzed how sandy rainfalls have impact on the cement solidified radioactive waste based on data from 90 days of leaching experiment.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1524-1533
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• 2021

The structural stability of a waste package is essential for containing radioactive waste for the long term in a repository. A silo-type disposal facility would require more severe verification for the structural integrity, because of radioactive waste packages staked with several tens of meters and overburdens of crushed rocks and shotcretes. In this study, structural safety was analyzed for a silo-type repository, located approximately 100 m below sea level in Gyeongju, Korea. Finite element simulation was performed to investigate the influence of the loads from the backfilling materials and waste package stacks on the mechanical stress of the disposed of wastes and containers. It was identified that the current design of the waste package and the compressive strength criterion for the solidified waste would not be enough to maintain structural stability. Therefore, an enhanced criterion for the compressive strength of the solidified waste and several reinforced structural designs for the disposal concrete container were proposed to prevent failure of the waste package based on the results of parametric studies.

• 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 environmental and Sanitary engineering
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• v.18 no.4
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• pp.36-44
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• 2003

The cement-based system among S/S(Solidification/Stabilization) is widely used to treat hazardous wastes. In this study, tannery sludge was solidified to evaluate the stabilization effects of using admixtures in the cement-based S/S. Fly ash as substitute also used to increase the strength of the S/S of hazardous waste. The compressive strength measurement and leaching experiment of chromium metal of solidified mortar were carried out to compare and evaluate the physical and chemical characteristics of solidified hazardous waste sludge. From the result of this study, there was increased of compressive strength by using AEW-3(early-hardening AE water reducing agent), and leaching concentration of chromium became low enough to satisfy the regulatory criteria. The successful solidification for the organic contaminant and heavy metal in hazardous waste should enable to treat by cement-based system using early-hardening AE water reducing admixture and fly ash as substituted cement.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.15-22
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• 2001

The key part in risk assessments for disposal sites of solidified/stabilized (S/S) wastes is to predict the contaminant transport from the S/S wastes to the environment under dynamically changing field conditions after characterizing chemical leaching properties of the ash, to evaluate the risk from the predictions, and finally to decide the risk is acceptable. In this paper, a risk assessment framework for disposal and reuse of S/S wastes was developed considering two limiting cases of contaminant leaching. Two types of waste characterization procedures that can determine waste-specific variables for the two limiting cases were developed and verified by applying them to a landfill site of the Municipal Solid Waste incinerator ash solidified/stabilized by cement.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2018.05a
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• pp.194-195
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• 2018