• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.2
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• pp.119-128
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• 2008

Thermal assessment of a new CANDU spent fuel disposal system, which improves the retrievability of the spent fuel and enhances the densification factor compared with the Korean Reference disposal System, is carried out in this study. The canisters for CANDU spent fuels are stored for long term and cooled by natural convection in the proposed disposal system for the retrievability. The steady state thermal analyses for proposed CANDU disposal system are carried out with the ANSYS 10.0 CFX code. The thermal analyses are performed through two steps. At the first step, the sensitivity of the disposal tunnel spacing is analysed. The differences of maximum temperatures by several tunnel spacings are calculated at three points in the disposal tunnel. The result shows that the differences of the temperature at the three points are almost negligible because 99% of the decay heat is removed by natural convection. At the second procedure, 60m tunnel spacing with a ventilation system instead of natural convection is considered. The result is applied to the calculation of the canister surface temperature in disposal tunnel as boundary conditions. Consequently, the average and the maximum surface temperature of disposal canisters are $79.9^{\circ}C$ and $119^{\circ}C$, respectively. The inner maximum temperature of a basket in the disposal canister is calculated as $140.9^{\circ}C$. The maximum temperature of the basket meets the thermal requirement for the CANDU spent fuel cladding.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.429-439
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• 2004

The deep underground High Level Waste (HLW) repository to dispose of 36,000tons of spent fuel from the reactors in Korea needs about $4km^2$ repository area. In this study, the deep undergrond repository layout was optimized to minimize the excavation rock volume as well as underground repository area. In the optimization, the results from thermal analysis were used to define the influence of tunnel and deposition hole spacings on repository layout. The repository area and excavation rock volume could be reduced with longer disposal tunnel length. When it is necessary to reduce the repository area with satisfying thermal criteria, it is better to reduce tunnel spacing and increase deposition hole spacing. In contrast, the excavation rock volume can be reduced by increasing the tunnel spacing and decreasing the hole spacing.

• Tunnel and Underground Space
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• v.9 no.2
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• pp.102-113
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• 1999

Two-dimensional and three-dimensional DEM programs, UDEC and 3DEC, were used to investigate the mechanical stability of the conceptual design of deposition drift and deposition holes constructed in a crystalline rock mass. From the simulations, the influence of discontinuities, the number of deposition holes, and deposition hole interval on the stability of deposition drift and deposition holes could be determined. From the two-dimensional and three-dimensional analysis. it was concluded that three-dimensional analysis should be carried 7ut fur deriving reliable conclusions. Even though the deposition hole interval changed from 8 m to 3 m, which did not damage the mechanical stability of the deposition drift.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.445-471
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• 2023

Long-term safety over millennia is the top priority consideration in the construction of disposal sites. However, ensuring the mechanical stability of deep geological repositories for spent fuel, a.k.a. radwaste, disposal during construction and operation is also crucial for safe operation of the repository. Imposing restrictions or limitations on tunnel support and lining materials such as shotcrete, concrete, grouting, which might compromise the sealing performance of backfill and buffer materials which are essential elements for the long-term safety of disposal sites, presents a highly challenging task for rock engineers and tunnelling experts. In this study, as part of an extensive exploration to aid in the proper selection of disposal sites, the anticipation of constructing a deep geological repository at a depth of 500 meters in an unknown state has been carried out. Through a review of 2D and 3D numerical analyses, the study aimed to explore the range of properties that ensure stability. Preliminary findings identified the potential range of rock properties that secure the stability of central and disposal tunnels, while the stability of the vertical tunnel network was confirmed through 3D analysis, outlining fundamental rock conditions necessary for the construction of disposal sites.

• Tunnel and Underground Space
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• v.23 no.2
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• pp.141-149
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• 2013

The thermal analysis is carried out for a geological disposal system developed for the final disposal of a ceramic high-level waste from pyroprocessing of PWR spent fuel. The horizontal disposal tunnel type is considered with the distance of 2 m between the disposal canisters and the tunnel spacing of 25 m. The temperature distributions around the disposal canisters are calculated for the horizontal tunnel based on the conceptual design. The thermal performance analysis is carried out using a FEM program, ABAQUS. The performance analysis shows that the peak temperature in a disposal system outside the disposal canister is lower than $100^{\circ}$, which meets the thermal criterion of the disposal system. According the analysis, the peak temperature for the disposal canister located boundary of the disposal system is lower by $3^{\circ}$ than that for the canister at the central area. This implies the disposal density can be improved by locating more disposal canisters along the boundary.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.3 no.4
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• pp.349-358
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• 2005

In this study, analysis of the disposal tunnel spacing and disposal pit pitch was carried out, as a factor of the design to estimate the scale and layout of the repository. To do this, based on the reference repository concept and the engineered barrier concept, several cross sections of the disposal tunnel and disposal pit were established. After then, the mechanical and thermal stabilities of the established tunnels were analyzed. Also, an optimized disposal tunnel spacing and the disposal pit pitch reducing the excavation volume was proposed. The results of these analyses can be used in the deep geological repository design. The detailed analyses by the exact site characteristics data to reduce the uncertainty of the site and the modification for the optimization are required.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.315-321
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• 2003

In this study, analysis of the disposal tunnel spacing and disposal pit pitch was carried out, as a factor of the design to estimate the scale and layout of the repository To do this, based on the reference repository concept and the engineered barrier concept, the cross section of the disposal tunnel and disposal pit are established and the mechanical and thermal stabilities of the tunnels are analyzed. Also, the optimized disposal tunnel spacing and the disposal pit pitch which minimize the excavation volume was proposed. The detailed analyses by the exact site characteristics data are needed to reduce the uncertainty of the site in the future.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.4
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• pp.393-400
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• 2006

In design of a deep geological repository for the high level wastes, it is very important that the temperature of the bentonite block should not be over $100^{\circ}C$ to maintain the integrity of the bentonite buffer block from the decay heat. In this study, for the layout of the repository to meet the requirement, the analysis of the disposal tunnel and disposal pit spacing was carried out. To do this, based on the reference repository concept, several cases of cooling times and disposal tunnel and disposal pit spacing were compared. The thermal stabilities of the disposal systems were analyzed in terms of the cooling time and spacing. The results showed that it was more desirable to determine the layout of the repository in terms of disposal pit spacing than the disposal tunnel spacing. The results of these analyses can be used in the deep geological repository design. The detailed analyses with the exact site characteristics data will reduce the uncertainty of the results.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2010.05a
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• pp.171-172
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• 2010

본 논문에서는 하나로폐기물을 처분 원가대상으로 설정하고 처분 단위모듈당 주요 원가를 추정하였다. 추정결과, 처분용기 직접재료비가 제일 많이 소요되며, 그 다음은 처분공 굴착비인 것으로 나타났다. 이러한 이유는 처분공 굴착은 발파공법이 아닌 그라인더로 굴착하는 정밀공법이기 때문에 굴착단가가 1,143,963원/$m^3$으로 매우 비싸기 때문이다. 따라서 주요 원가동인의 비용 점유율은 처분용기 재료비가 44.7%, 처분공 굴착비가 27%로 나타났다. 그리고 처분터널 굴착비는 비교적 비용 점유율이 적은 2.3%로 계산되었다. 이러한 이유는 처분터널은 처분공과 달리 발파기법으로 굴착하기 때문에 굴착단가가 처분공 굴착단가에 비해 저렴하기 때문이다.

• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.26-31
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• 2007

The 11 nuclear power plants have been taking charge of more than 40% of the total electrical power development in Korea. In addition to the existing nuclear power plants at Gori, Wolsung, Youngkwang, etc., the 12 nuclear power plants are expected to be newly established until 2006. So, the 23 nuclear power plants will produce the electric power as much as more than 50% of the national gross production. However the nuclear power plants are inevitably generating the detrimental atomic wastes. Therefore the disposal techniques for the nuclear wastes should be ensured considering a very high safety factor. According to the basic researches in KAERI, the underground disposal repositories are reported to be most favorable for Korea. The KBS-3 disposal system has been strongly suggested by KAERI and this system has a deep tunnel with several disposal boreholes in tunnel floor. The nuclear wastes, which are sealed tightly in a canister, will be disposed in these boreholes. Considering the disposal tunnel in a great depth, the in-situ stress regimes will affect severely the tunnel stability. Consequently the effect of the in-situ stresses on the disposal tunnel and the role of the in-situ stresses in tunnel stability analysis are examined by the numerical studies.