• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.4
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• pp.329-337
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• 2010

Radiotracer experiments were performed over two years using pot cultures in a greenhouse to investigate soil-torice seeds transfer factors of radioiodine and technetium for paddy fields around the radioactive-waste disposal site in Gyeongju. Before transplanting rice seedlings, the top about 20 cm soils were thoroughly mixed with $^{125}I$ (2007) and $^{99}Tc$ (2008), and the pots were irrigated to simulate flooded rice fields. Transfer factors were determined as the ratios of the radionuclide concentrations in dry rice seeds (brown rice) to those in dry soils. Transfer factors of radioiodine and technetium were in the ranges of $1.1{\times}10^{-3}{\sim}6.4{\times}10^{-3}$ (three soils) and $5.4{\times}10^{-4}{\sim}2.5{\times}10^{-3}$ (four soils), respectively, for different soils. It seems that the differences in the clay content among soils played a more important role for such variations than those in the organic matter content and pH. As the representative values of radioiodine and technetium transfer factors for rice seeds, $2.9{\times}10^{-3}$ and $1.1{\times}10^{-3}$, respectively, were proposed. In order to obtain more highly representative values in the future, investigations for the sites of interest need to be carried out continuously.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.4
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• pp.293-301
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• 2010

Optical fiber cable, as a sensor, was installed on the wall of KAERI(Korea Atomic Energy Research Institute) Underground Research Tunnel(KURT) in order to monitor the physical stability of the tunnel, which was constructed for technical development and demonstration of radioactive waste disposal. This monitoring system has two simultaneous measurements of temperature and strain over time using Brillouin backscatter. According to the results of the monitoring from Jan. 2008 to Nov. 2009, there is no significant displacement or movement at the tunnel wall However, the cumulative volume of total strain increased slightly as time passes with the comparison of the reference observation, which was measured in Jan. 2008. The change in cumulative volume of total strain indicates that the strain level had been affected by saturation and de-saturation phenomena due to groundwater fluctuation at several points at KURT. This system is based on the distributed sensing technique concept, not point sensing. By using this system, a displacement can be detected with the range from $20{\mu}{\varepsilon}$ to $28,000{\mu}{\varepsilon}$ every 1m interval in minimum. A temperature variation can be monitored at every 0.5m interval with the resolution of 0.01 in minimum. Based on the study, this monitoring system is potentially applicable to long term monitoring systems for radioactive waste disposal project as well as other structures and underground openings.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.4
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• pp.279-291
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• 2010

To characterize geological features in study area for high-level radioactive waste disposal research, KAERI (Korea Atomic Energy Research Institute) has been performing the several geological investigations such as geophysical surveys and borehole drilling since 1997. Especially, the KURT (KAERI Underground Research Tunnel) constructed to understand the deep geological environments in 2006. Recently, the deep borehole of 500 m depths was drilled to confirm and validate the geological model at the left research module of the KURT. The objective of this research was to identify the geological structures around KURT using the data obtained from the deep borehole investigation. To achieve the purpose, several geological investigations such as geophysical and borehole fracture surveys were carried out simultaneously. As a result, 7 fracture zones were identified in deep borehole located in the KURT. As one of important parts of site characterization on KURT area, the results will be used to revise the geological model of the study area.

• 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 Energy Engineering
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• v.11 no.2
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• pp.106-113
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• 2002

While the demand for energy has shown a sharp increase recently, the supply seems to be limited by the fact that the conventional fossil fuel energy or nuclear energy has its own environmental problems such as, for example, global warming or nuclear waste disposal. To overcome such limited supply of energy, the utilization of natural thermal energy such as river water and sea water as well as treated sewage can be a substantial supplement. The potential use of the unused energy has become more and more feasible these days as the heat pump technology has been advanced. In the present study, the unused energy reserves are estimated on regional and monthly basis for each resource based on the method developed here in order to establish the base data for its utilization. The potential use of the unused energy is also discussed.

• Journal of Radiation Protection and Research
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• v.9 no.2
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• pp.118-128
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• 1984

The analysis of radiological protection at Kori Nuclear Unit #1, which started commercial operation on April 29, 1978, has been carried out in three areas, namely, radiation exposure, radioactive waste disposal and environmental management. The analysis results for radiation exposure and radioactive effluent releases appear to increase gradually with plant operating years. On the other hand, the apex of radiation exposure and radioactive effluent releases was in 1983 and 1982 respectively and then decreased or stabilized. Also, the operation environmental radioactivity seems to be no higher than preoperation environmental radioactivity.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.147-153
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• 2018

Copper is used in various applications in environments favoring and enabling formation of biofilms by naturally occurring microbes. Copper is also the chosen corrosion barrier for nuclear waste in Finland. The copper canisters should have lifetimes of 100,000 years. Copper is commonly considered to be resistant to corrosion in oxygen-free water. This is an important argument for using copper as a corrosion protection in the planned canisters for spent nuclear-fuel encapsulation. However, microbial biofilm formation on metal surfaces can increase corrosion in various conditions and provide conditions where corrosion would not otherwise occur. Microbes can alter pH and redox potential, excrete corrosion-inducing metabolites, directly or indirectly reduce or oxidize the corrosion products, and form biofilms that create corrosive microenvironments. Microbial metabolites are known to initiate, facilitate, or accelerate general or localized corrosion, galvanic corrosion, and intergranular corrosion, as well as enable stress-corrosion cracking. Sulfate-reducing bacteria (SRB) are present in the repository environment. Sulfide is known to be a corrosive agent for copper. Here we show results from corrosion of copper in anoxic simulated ground water in the presence of SRB enriched from the planned disposal site.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.57-64
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• 2012

Since a seismic exceeding design load can result in exposing radioactive material during disposal process of radioactive wastes, the repository should be designed with enough seismic margin. In this paper, a seismic fragility analysis was performed to evaluate the seismic capacity of surface facility structures. According to the analysis results, since inspection & store facility and radioactive waste facility have a rectangle geometry, the seismic capacity was differently presented about 23%~43% according to the axis of structures. The HCLPF capacity of inspection & store facility and radioactive waste facility was 0.52g and 0.93g, respectively. And it was observed that seismic capacity of radioactive waste facility was similar to that of a containment for nuclear power plants.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.2 no.4
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• pp.253-262
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• 2004

Construction of tunnels in a deep crystalline host rock for a potential High-Level Radioactive Waste(HLW) repository inevitably generates an excavation disturbed zone (EDZ). There have been a series of debates on whether a permeability in an EDZ increases or not and what would be the maximum depth of an EDZ. Recent studies show mixed opinions on permeability. However, there has been an international consensus on the thickness of an EDZ; 30 cm for TBM and 1 meter for controlled blast. One of the impacts of an EDZ is on determining the distance between adjacent deposition holes. The void gap by the excavation hinders relaxation of temperature profiles so that the current Korean reference designing distance between holes should be stretched out more to keep the maximum temperature in a buffer region below 100 degrees Celsius. The other impact of an EDZ is on the long-term post closure radiological safety. To estimate the impact, the reference scenario, the well scenario, is chosen. Released nuclides diffuse through a bentonite buffer region experiencing strong sorption and reach a fracture surrounded by a porous medium. Inside a fractured porous region, radionuclides migrate by advection and dispersion with matrix diffusion into a porous medium. Finally, they reach a well assumed to be a source of potable water for local residents. The annual individual dose is assessed on this well scenario to find out the significance of an EDZ. A profound sensitivity study was performed, but all results show that the impact is negligible. Even though the role of an EDZ turns out to be limited on overall safety assessment, still it is worthwhile to study the chemical role of an EDZ, such as a potential source for natural colloids, potential sealing of an open fracture by fine clay particles generated by the process of an EDZ, and alteration of a sorption mechanism by an EDZ in the future.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2174-2181
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• 2024

In this work, Sr_0.5Zr₂(PO₄)₃-SmPO₄ dual-phase ceramics were prepared via in-situ synthesis process, which is a potential novel nuclear waste form for immobilizing the fission product ⁹⁰Sr and the trivalent actinide radionuclides in high-level waste (HLW). And the preparation technology, microstructure and chemical durability of Sr_0.5Zr₂(PO₄)₃-SmPO₄ dual-phase ceramics were systematically investigated. It was confirmed that the optimum microwave-sintering temperature (1050 ℃) and heat preservation time (1.5 h) is estimated by Archimedes method. Besides, the as-prepared samples that were consisted of strontium zirconium phosphate (SrZP) and monazite showed the remarkable densification, in which the two crystalline phases were intermixed well with each other. Meanwhile, the formation and evolution of microstructure was also consistent with the variational rule of Sr_0.5Zr₂(PO₄)₃/SmPO₄, indicating that there was not mutual reaction during the in-situ synthesis process. The PCT and MCC-1 experimental results demonstrated that the elemental normalized leaching rates of tested samples are all at a low level (LR_Sr ~10^-4 g·m^-2·d^-1, LR_Zr ~10^-8-10^-6 g·m^-2·d^-1, LR_Sm ~10^-7-10^-5 g·m^-2·d^-1 and LR_P ~10^-4 g·m^-2·d^-1). It is indicated that Sr_0.5Zr₂(PO₄)₃-SmPO₄ dual-phase ceramics possesses excellent chemical durability for HLW disposal.