Abstract A multi-layer repository concept is proposed as an alternative to the single-layer repository concept to improve the disposal density of high-level radioactive waste (HLW) in Korea. Numerical simulations are performed to compare the coupled thermo-hydro-mechanical (THM) behavior in the existing Korean reference HLW disposal system (KRS) based on the single-layer repository concept to that in the new multi-layer repository concept. The applicability of the multi-layer repository concept, such as double- and triple-layer repositories, for the disposal of HLW is analyzed with respect to a maximum temperature criterion of 100 °C, evolution of saturation and pore pressure, and mechanical stability. Maximum temperatures are below 100 °C in the double- and triple-layer repository concepts, as in the single-layer reference, although two peaks in simulated temperatures are observed during the evolution of the thermal pulse, resulting from superposition of decay heat at different vertical levels in the multi-layer repository concept. There is no significant difference in the evolution of pore pressure and saturation among the three concepts. The evolutions of mean effective stress at the bentonite blocks and backfill materials are also not significantly different between the single-, double-, and triple-layer repository concepts, because the hydraulic behavior is quite similar, resulting in almost the same change in swelling pressure. Stress states in the rock mass near the tunnels and deposition holes remain below the Mohr-Coulomb failure envelopes at the repositories of 500 m depth in the single-, double-, and triple-layer repository concept simulations. However, the stress states exceed the Mohr-Coulomb failure envelopes at the repositories below 500 m depth (beneath the top layer) in the double- and triple-layer repository concepts. Also, mechanical analysis shows high potential for spalling failure around the deposition holes and tunnel roof in the double- and triple-layer repository concepts. Subsidence in the double- and triple-layer concepts due to the construction of repositories is much deeper than that in the single-layer concept, and uplift induced by heating the rock mass due to the decay heat in the double- and triple-layer concepts is much higher than in the single-layer concept. These results indicate that multi-layer repositories with larger depth intervals between layers are a feasible alternative to the KRS to safely achieve higher disposal density.

中文翻译：

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用于高放废物处置的单层和多层处置库概念中耦合热-水-力学行为的数值分析

摘要 为了提高韩国高放废物（HLW）的处置密度，提出了多层处置库概念作为单层处置库概念的替代方案。进行了数值模拟，以比较基于单层处置库概念的现有韩国参考 HLW 处置系统 (KRS) 与新的多层处置库概念中的耦合热-水力机械 (THM) 行为。从最高温度标准 100 °C、饱和度和孔隙压力的演变以及机械稳定性方面分析了多层处置库概念（例如双层和三层处置库）在处置高放废物方面的适用性。双层和三层存储库概念中的最高温度低于 100 °C，如在单层参考中，尽管在热脉冲演变过程中观察到模拟温度的两个峰值，这是由于多层储存库概念中不同垂直水平的衰变热叠加所致。三个概念之间孔隙压力和饱和度的演变没有显着差异。膨润土块和回填材料的平均有效应力的演变在单层、双层和三层存储库概念之间也没有显着差异，因为水力行为非常相似，导致膨胀压力的变化几乎相同. 在单层、双层和三层储存库概念模拟中，隧道和沉积孔附近岩体的应力状态保持在 500 m 深度的储存库的莫尔-库仑破坏包络线以下。然而，在双层和三层储存库概念中，应力状态超过 500 m 深度以下（顶层以下）储存库的 Mohr-Coulomb 破坏包络。此外，力学分析显示双层和三层储存库概念中沉积孔和隧道顶部周围剥落失效的可能性很高。双层和三层概念由于建造储层而下沉比单层概念深得多，双层和三层概念中由于衰变热加热岩体引起的隆升远高于单层概念。这些结果表明，层与层之间具有较大深度间隔的多层处置库是 KRS 的可行替代方案，可以安全地实现更高的处置密度。