Two-region 모델을 활용한 벤토나이트 완충재의 장기 침식 정량화 모델 개발 및 완충재 물성 열화 평가
Development of a Long-term Erosion Model for Bentonite Buffer using a Two-region Model and Evaluation of Buffer Property Degradation
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벤토나이트는 고준위방사성폐기물의 심층처분에서 완충재로 사용되며, 뛰어난 팽윤 능력과 낮은 투수 율로 방사성 핵종의 이동을 효과적으로 차단한다. 하지만 장기적으로 팽윤 및 지하수 흐름에 의한 침식 이 발생해 성능 저하 가능성이 있으며, 이는 처분 시스템의 안정성을 저해할 수 있다. 본 연구에서는 벤토 나이트 침식 거동을 정량적으로 평가하기 위해 Two-region 모델을 활용하여 벤토나이트 완충재의 장기 침식 정량화 모델을 개발하였다. 또한 ADioS 기반의 지하수 유동 해석을 바탕으로 처분장 내 발생 가능 한 벤토나이트 완충재 침식량의 범위와 평균값을 도출하였으며, 침식으로 인한 벤토나이트 완충재 물성 열화 정도를 평가하였다. 연구 결과, 균열 간극 크기와 지하수 유속이 침식량에 중요한 영향을 미치며, 약 10만 년 후 평균적으로 벤토나이트의 약 0.78%가 균열을 통해 유실될 가능성이 있음을 확인하였다. 이 러한 장기 침식으로 인해 처분공 내 벤토나이트 완충재의 체적 밀도가 감소하며, 이에 따라 벤토나이트 완충재 물성이 열화되는 것을 확인하였다. 다만, ADioS는 처분공을 관통하는 균열이 아닌 굴착손상영역 (EDZ) 만을 반영하므로, 본 연구에서 도출된 침식량이 실제보다 과소평가 되었을 가능성이 있다. 그럼에 도 본 연구는 벤토나이트 완충재의 장기 성능을 평가하기 위한 효율적이고 체계적인 방법론을 제시하며, 국내 심층처분 시스템의 안전성 및 성능 평가에 기여할 수 있을 것으로 기대된다.
Abstract
Bentonite is used as a buffer material in the deep geological disposal of high-level radioactive waste due to its excellent swelling capacity and low permeability, which effectively inhibit radionuclide migration. However, over the long term, erosion caused by swelling and ground- water flow may occur, potentially degrading its performance and compromising the stability of the disposal system. In this study, a long-term erosion model for bentonite buffer was developed using a Two-region model to evaluate the erosion behavior of bentonite quantitatively. Groundwater flow simulations in ADioS were utilized to estimate the range and average amount of bentonite erosion that could occur in the disposal area, and the degree of buffer property degradation caused by erosion was evaluated. The results indicated that crack aperture size and groundwater flowrate significantly affect erosion rates, with approximately 0.78% of bentonite potentially being lost through cracks over a 100,000–year period. This long-term erosion phenomenon reduces the bulk density of the bentonite buffer, leading to the degradation of its material properties. However, since ADioS accounts only for the excavation damaged zone (EDZ) rather than cracks penetrating the deposition hole, the erosion amounts derived in this study may have been underestimated. Nevertheless, this study proposes an efficient and systematic methodology for evaluating the long-term performance of bentonite buffers, which is expected to contribute to the safety and performance assessment of domestic deep geological disposal systems in the future.
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