• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.4
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• pp.301-313
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• 2015

The rock cavern storage for spent fuel has been assessed to apply in Korea with reviewing the state of the art of the technologies for surface storage and rock cavern storage of spent fuel. The technical feasibility and economic aspects of the rock cavern storage of spent fuel were also analyzed. A considerable area of flat land isolated from the exterior are needed to meet the requirement for the site of the surface storage facilities. It may, however, not be easy to secure such areas in the mountainous region of Korea. Instead, the spent fuel storage facilities constructed in the rock cavern moderate their demands for the suitable site. As a result, the rock cavern storage is a promising alternative for the storage of spent fuel in the aspect of natural and social environments. The rock cavern storage of spent fuel has several advantages compared with the surface storage, and there is no significant difference on the viewpoint of economy between the two alternatives. In addition, no great technical difficulties are present to apply the rock cavern storage technologies to the storage of domestic spent fuel.

• Tunnel and Underground Space
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• v.23 no.5
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• pp.442-453
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• 2013

A large-scale high-temperature thermal energy storage(TES) was numerically modeled and the heat loss through storage tank walls was analyzed using a commercial code, FLAC3D. The operations of rock cavern type and above-ground type thermal energy storages with identical operating condition were simulated for a period of five consecutive years, in which it was assumed that the dominant heat transfer mechanism would be conduction in massive rock for the former and convection in the atmosphere for the latter. The variation of storage temperature resulting from periodic charging and discharging of thermal energy was considered in each simulation, and the effect of insulation thickness on the characteristics of heat loss was also examined. A comparison of the simulation results of different storage models presented that the heat loss rate of above-ground type TES was maintained constant over the operation period, while that of rock cavern type TES decreased rapidly in the early operation stage and tended to converge towards a certain value. The decrease in heat loss rate of rock cavern type TES can be attributed to the reduction in heat flux through storage tank walls followed by increase in surrounding rock mass temperature. The amount of cumulative heat loss from rock cavern type TES over a period of five-year operation was 72.7% of that from above-ground type TES. The heat loss rate of rock cavern type obtained in long-period operation showed less sensitive variations to insulation thickness than that of above-ground type TES.

• Journal of the Korean Institute of Gas
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• v.28 no.2
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• pp.7-16
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• 2024

This study presents investigation on the technical characteristics and field cases of the salt cavern storage method for large-scale hydrogen storage. The salt cavern storage method enables effective hydrogen storage compared to other methods due to the low porosity and permeability of the rock salt that constitutes the cavern, which is not likely to leak and requires a small amount of cushion gas for operation. In addition, there is no chemical reaction between rock salt and hydrogen, and multiple injection/withdrawl cycles can be performed making it effective for peak shaving and short-term storage. The salt cavern is formed in three stages: leaching, debrining, and filling, and leakage tests are conducted to ensure stable operation. Field applications are currently performing to meet industrial demand in the surrounding area of four sites in the UK and Texas, USA, and salt cavern operation is being prepared for energy storage in European countries such as Germany and France. The investigated results in this study can be utilized as a basic guideline for the design of future hydrogen storage projects.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.189-201
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• 2005

Brittle failure has been detected in over-stressed rock mass during the construction of oil storage cavern. The main characteristics of stress induced brittle failure of the site are introduced. Various evaluation and measures are sought to stabilize the over-stressed rock mass. The major results from numerical analysis of the cavern are presented, and from current microseismic monitoring to detect hazard from brittle failure are presented.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.705-712
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• 2000

The fluid generally flows through fractures in crystalline rocks where most of underground storage facilities are constructed because of their low hydraulic conductivities. The fractured rock is better to be conceptualized with a discrete fracture concept, rather continuum approach. In the aspect of fluid flow in underground, the simultaneous flow of groundwater and gas should be considered in the cases of generation and leakage of gas in nuclear waste disposal facilities, air sparging process and soil vapor extraction for eliminating contaminants in soil or rock pore, and pneumatic fracturing for the improvement of permeability of rock mass. For the purpose of appropriate analysis of groundwater-gas flow, this study presents an unsteady-state multi-phase FEM fracture network simulator. Numerical simulation has been also conducted to investigate the hydraulic head distribution and air tightness around Ulsan LPG storage cavern. The recorded hydraulic head at the observation well Y was -5 to -10 m. From the results obtained by the developed model, it shows that the discrete fracture model yielded hydraulic head of -10 m, whereas great discrepancy with the field data was observed in the case of equivalent continuum modeling. The air tightness of individual fractures around cavern was examined according to two different operating pressures and as a result, only several numbers of fractures neighboring the cavern did not satisfy the criteria of air tightness at 882 kPa of cavern pressure. In the meantime, when operating pressure is 710.5 kPa, the most areas did not satisfy air tightness criteria. Finally, in the case of gas leaking from cavern to the surrounding rocks, the resulted hydraulic head and flowing pattern was changed and, therefore, gas was leaked out from the cavern ceiling and groundwater was flowed into the cavern through the walls.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.168-185
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a large-scale high-temperature cavern thermal energy storage (CTES) at a shallow depth has been investigated, and the effects of hydrological conditions such as water table and rock permeability on the behavior have been examined. The liquid saturation of ground water around a storage cavern may have a small impact on the overall heat transfer and mechanical behavior of surrounding rock mass for a relatively low rock permeability of $10^{-17}m^2$. In terms of the distributions of temperature, stress and displacement of the surrounding rock mass, the results expected from the simulation with the cavern below the water table were almost identical to that obtained from the simulation with the cavern in the unsaturated zone. The heat transfer in the rock mass with reasonable permeability ${\leq}10^{-15}m^2$ was dominated by the conduction. In the simulation with rock permeability of $10^{-12}m^2$, however, the convective heat transfer by ground-water was dominant, accompanying the upward heat flow to near-ground surface. The temperature and pressure around a storage cavern showed different distributions according to the rock permeability, as a result of the complex coupled processes such as the heat transfer by multi-phase flow and the evaporation of ground-water.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.287-296
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• 2011

We performed a numerical modeling study of thermodynamic and multiphase fluid flow processes associated with underground compressed air energy storage (CAES) in a lined rock cavern (LRC). We investigated air tightness performance by calculating air leakage rate of the underground storage cavern with concrete linings at a comparatively shallow depth of 100 m. Our air-mass balance analysis showed that the key parameter to assure the long-term air tightness of such a system was the permeability of both concrete linings and surrounding rock mass. It was noted that concrete linings with a permeability of less than $1.0{\times}10^{-18}\;m^2$ would result in an acceptable air leakage rate of less than 1% with the operational pressure range between 5 and 8 MPa. We also found that air leakage could be effectively prevented and the air tightness performance of underground lined rock cavern is enhanced if the concrete lining is kept at a higher moisture content.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.243-256
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• 2012

Developing efficient and reliable energy storage system is as important as exploring new energy resources. Energy storage system can balance the periodic and quantitative mismatch between energy supply and energy demand and increase the energy efficiency. Industrial waster heat and renewable energy such as solar energy can be stored by the thermal energy storage (TES) system at high and low temperatures. TES system using underground rock carven is considered as an attractive alternative for large-scale storage, because of low thermal conductivity and chemical safety of surrounding rock mass. In this report, the development of available thermal energy storage methods and the characteristics of storage media were introduced. Based on some successful applications of cavern storage and high-temperature storage reported in the literature, the applicabilities and practicabilities of storage media and technologies for large-scale cavern thermal energy storage (CTES) were reviewed.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.192-202
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• 2013

The domestic demand of natural gas has increased continuously due to the sudden rise of oil price and regulations on greenhouse gas to global warming. In order to improve the supply security of natural gas market in Korea, the agreement on supply of pipeline natural gas (PNG) in Russia was signed between Gazprom and Korea Gas Corporation in 2008. If the supply plan of Russian natural gas is realized, underground storage facilities would be required in order to balance supply and demand of natural gas because the gas demand is concentrated in the winter. This study investigated the safety of the storage facility in quantitative way considering several design parameters such as gas pressure, depth of the storage cavern, rock condition and in-situ horizontal stress ratio. Two dimensional stress analyses were conducted using axi- symmetry condition to examine the behavior of cavern depending upon suggested design parameters. Results showed that the factor of safety, defined as the ratio of 'shear strength'/'shear stress', was largely affected by the depth, rock class and gas pressure but was insensitive to the coefficient of lateral pressure(Ko).

• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.56-65
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• 2007

A new underground LNG storage concept in the rock mass has been developed by combining underground cavern construction and new ice-ring harrier technologies with the conventional cryogenic insulation system. Technical feasibility of the storage system has been verified through construction and operation of the pilot storage cavern and a full-scale project is expected to start in the near future. One of the most important issues in the LNG storage system is the operational efficiency of the storage to minimize heat loss during a long period of operation due to the cryogenic heat transfer. This paper presents several important results of heat transfer and coupled hydro-thermal analyses by a finite element code Temp/W and Seep/W. A series of heat transfer analyses for full-scale caverns were performed to determine design parameters such as boil-off gas ratio (BOR), insulation thickness and pillar width. The result of the coupled hydro-mechanical analysis showed that BOR for underground storage system remains at about 0.04 %/day during the early stage of the operation. This value could be even much lower when the discontinuities in the rock masses are taken into consideration.