Editorial: Advanced modeling techniques in radioactive waste disposal

Representation and simplification of complex disposal systems

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 transport-relevant 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.

Process-based near-field modeling

A second aspect concerns the representation of near-field processes, where radionuclide release is controlled by time-dependent degradation and transport mechanisms. Finsterle et al. developed a coupled model for glass degradation and radionuclide release, which accounted for the influence of environmental conditions such as temperature and pH. Their results indicate that predicted peak dose is not a fixed input, but depends on a combination of factors including glass degradation rate, residual rate, temperature, pH, affinity effects, and instantaneous release fraction. This work shows the importance of treating source-term evolution as a process-dependent component of performance assessment rather than as a prescribed boundary condition. Wang proposed an empirical relationship linking dissolution kinetics to the solution volume-to-surface area ratio to examine the dissolution behavior of oxide materials. This approach provides a practical parameterization in cases where thermodynamic data are incomplete, offering a basis for comparing dissolution behavior across different waste-form materials.

Within engineered barrier systems, model resolution and numerical formulation can also influence predicted radionuclide release behavior. Chen et al. developed a three-dimensional near-field release model using COMSOL and reported higher release rates for some radionuclides than those obtained previously using GoldSim calculations. The authors attributed these differences to two factors: coarse discretization, which can alter migration and accumulation behavior, and reduced-dimensional representations, which may omit relevant three-dimensional transport features. Their results indicate that model dimensionality and discretization should be considered carefully in performance assessment calculations, as they can affect the interpretation of release predictions.

Coupled processes and multi-scale modeling

A third challenge concerns the treatment of coupled processes and the integration of mechanisms across scales. Finsterle et al. investigate corrosion-gas generation and transport in a deep borehole disposal concept, taking into account gas production, dissolution, and multiphase flow. The simulations suggest that, for the design conditions considered, hydrogen generated by steel corrosion is likely to remain largely confined to the disposal section or dissipate into the near field, rather than generating pressures high enough to compromise barrier integrity. This study provides a more process-based basis for examining gas-related safety issues in deep borehole disposal and may inform engineering considerations such as casing, sealing, and disposal-section layout. Hu et al. developed a phase-field model to simulate silver dissolution in a cementitious waste form. Their results show that the dissolution behavior and effective release rates were influenced by the interfacial precipitation, oxidation reactions, and particle size. It suggests that microstructural processes can contribute to macroscopic transport behavior, highlighting the value of linking mesoscale simulations with continuum-scale performance assessment.

Concluding remarks

The contributions in this Research Topic indicate that uncertainties in radioactive waste disposal modeling arise not only from incomplete knowledge of parameters, but also from choices in model structure, simplification strategies, and scale representation. Addressing these issues requires careful integration of models across scales and processes, as well as the approaches to model validation. This Research Topic provides a set of studies that clarify several methodologies relevant to performance assessment of geological repositories and illustrate how modeling choices can influence the analysis of disposal-system behavior. Continued work on linking models across scales, comparing alternative formulations, and integrating modeling with experimental evidence will remain important for improving confidence in long-term assessments.

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