Editorial: Advanced modeling techniques in radioactive waste disposal

Numerical modeling therefore plays an important role by enabling the analysis of coupled processes and the prediction of system behavior under conditions that cannot be directly observed. A central challenge is how to construct models that represent these processes consistently across scales while remaining suitable for performance assessment [4]. This Research Topic brings together seven contributions on modeling techniques relevant to radioactive waste disposal, with particular focus on multiscale and multi-physics coupling, numerical method development, and the integration of modeling with experimental observations.A first challenge lies in how complex geological and engineered systems are represented in models. In fractured host rocks, flow and transport behavior are strongly influenced by the structure and connectivity of fracture networks. Darcel et al.examined the transformation of discrete fracture networks into equivalent continuum representations and show that this simplification affects predicted flow velocity and transport times. Their results indicate that continuum models may overestimate connectivity, whereas process-based upscaling methods may better preserve transportrelevant features. This study suggests that the evaluation of long-term transport behavior will be compromised by an excessive reliance on simplified continuum representations of sparsely fractured rock. Therefore, higher-fidelity upscaling approaches are important for repository assessment. A related issue concerns the level of complexity required in performance assessment models. In practice, only a limited number of radionuclides contribute significantly to long-term dose. Finsterle et al.proposed a systematic screening approach to identify safety-relevant radionuclides based on inventory, half-life, mobility, and dose contribution. By clearly defining this selection process, their work provides a transparent way to reduce model complexity while retaining the radionuclides most relevant to system response.A second aspect concerns the representation of near-field processes, where radionuclide release is controlled by time-dependent degradation and transport mechanisms. Within engineered barrier systems, model resolution and numerical formulation can also influence predicted radionuclide release behavior. Chen et al. developed a threedimensional near-field release model using COMSOL and reported higher release rates for some radionuclides than those obtained previously using GoldSim calculations. The