Performance assessment (PA) of geologic radioactive waste repositories requires three-dimensional simulation of highly nonlinear, thermo-hydro-mechanical-chemical (THMC), multiphase flow and transport processes across many kilometers and over tens to hundreds of thousands of years. Integrating the effects of a near-field geomechanical process (i.e. buffer swelling) into coupled THC simulations through reduced-order modeling, rather than through fully coupled geomechanics, can reduce the dimensionality of the problem and improve computational efficiency. In this study, PFLOTRAN simulations model a single waste package in a shale host rock repository, where re-saturation of a bentonite buffer causes the buffer to swell and exert stress on a highly fractured disturbed rock zone (DRZ). Three types of stress-dependent permeability functions (exponential, modified cubic, and Two-part Hooke’s law models) are implemented to describe mechanical characteristics of the system. Our modeling study suggests that compressing fractures reduces DRZ permeability, which could influence the rate of radionuclide transport and exchange with corrosive species in host rock groundwater that could accelerate waste package degradation. Less permeable shale host rock delays buffer swelling, consequently retarding DRZ permeability reduction as well as chemical transport within the barrier system.

地质放射性废物处置库的性能评估 (PA) 需要对高度非线性、热-水-机械-化学 (THMC)、多相流和传输过程进行多公里和数万到数十万年的三维模拟。通过降阶建模将近场地质力学过程（即缓冲区膨胀）的影响整合到耦合 THC 模拟中，而不是通过完全耦合的地质力学，可以减少问题的维度并提高计算效率。在这项研究中，PFLOTRAN 模拟模拟了页岩母岩储存库中的单个废物包，其中膨润土缓冲区的再饱和导致缓冲区膨胀并对高度破裂的扰动岩石带 (DRZ) 施加应力。实现了三种类型的应力相关渗透率函数（指数、修正三次和两部分胡克定律模型）来描述系统的机械特性。我们的建模研究表明，压裂裂缝会降低 DRZ 渗透率，这可能会影响放射性核素传输和与基质岩地下水中腐蚀性物质的交换速率，从而加速废物包降解。渗透性较低的页岩主岩延迟了缓冲膨胀，从而延缓了 DRZ 渗透率的降低以及屏障系统内的化学传输。这可能会影响放射性核素传输和与基质地下水中腐蚀性物质的交换速率，从而加速废物包的降解。渗透性较低的页岩主岩延迟了缓冲膨胀，从而延缓了 DRZ 渗透率的降低以及屏障系统内的化学传输。这可能会影响放射性核素传输和与基质地下水中腐蚀性物质的交换速率，从而加速废物包的降解。渗透性较低的页岩主岩延迟了缓冲膨胀，从而延缓了 DRZ 渗透率的降低以及屏障系统内的化学传输。