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DOE OSTI · 2584602

Comparing modelling approaches for a generic nuclear waste repository in salt

LaForce, Tara·Bartol, Jeroen·Becker, Dirk-Alexander·Benbow, Steven·Bond, Alexander·Dietl, Carl Rudolf·Frank, Tanja·Kock, Ingo·Magri, Fabiano·Nicholas, Josh·Jayne, Rick·Pekala, Marek·Stauffer, Philip H.·Stein, Emily·Stone, Jodie·Wolf, Jens
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Abstract

This paper contains a comparison of five modelling approaches for a simplified nuclear waste repository in a domal salt formation. It is the result of a four-year collaboration between five international teams on Task F of the DECOVALEX-2023 project on performance assessment modelling. The primary objectives of Task F are to build confidence in the models, methods, and software used for performance assessment (PA) of deep geologic nuclear waste repositories, and/or to bring to the fore additional research and development needed to improve PA methodologies. This work demonstrates how these objectives are accomplished through staged development and comparison of the models and methods used by participating teams in their PA frameworks. Participating teams made a wide range of model assumptions, ranging from compartmentalized networks to full 3D models of the salt formation and repository. Despite differences in the modelling strategies, all models indicate that salt compaction and diffusion of radionuclides in brine are key processes in the repository. For the isothermal spent nuclear fuel and vitrified waste scenario with multiple early failures considered, all models indicate little of the disposed radionuclides will migrate beyond the repository seal over the 100,000-year simulations. In general, the model output quantities have the largest differences over the short term and near the waste. Disparities between the models are believed to be due to differing simplifications from the conceptual model.

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DECOVALEXDomal saltNuclear waste disposalPerformance assessmentRadionuclide transportSafety assessment

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LaForce, Tara, Bartol, Jeroen, Becker, Dirk-Alexander, Benbow, Steven, Bond, Alexander, Dietl, Carl Rudolf, Frank, Tanja, Kock, Ingo, Magri, Fabiano, Nicholas, Josh, Jayne, Rick, Pekala, Marek, Stauffer, Philip H., Stein, Emily, Stone, Jodie, Wolf, Jens. 2024-11-26. Comparing modelling approaches for a generic nuclear waste repository in salt. https://doi.org/10.1016/j.gete.2024.100621

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DOE OSTI2025

Designing a repository in domal salt: The influence of design variants in different modelling environments

To understand the long-term environmental impact of disposing radioactive waste of in a deep geological repository and to optimise its design, performance assessments are used. In this study, four teams (COVRA, GRS, Quintessa, and DOE) modified the previously developed generic repository of DECOVALEX task F2 to identify commonalities and differences between the teams for specific changes in repository design. The teams tested six design modifications: (1) Replacing concrete abutments with run-of-mine salt; (2) Replacing the salt seal with a concrete abutment and using run-of-mine salt instead for the two concrete abutments in each drift seal; (3) Halving the size of the infrastructure area; (4) Using run-of-mine salt instead of gravel for backfilling the infrastructure area; (5) Disposal of spent nuclear fuel without the POLLUX-10 containers (6); Lower initial saturation of the spent nuclear fuel and vitrified waste disposal drifts. Despite different modelling strategies used, models agreed that a smaller infrastructure area has a limited effect on radionuclide transport. Responses to the absence of the two concrete abutments in each seal, the use of single large concrete abutments (200 m each), or the use of run-of-mine salt in the infrastructure area differ between teams due to differing modelling assumptions. Based on these results, the estimated efficacy of containment depends strongly on the model assumptions of each team. More specifically, it appears to depend on the compaction model used and therefore on the backfill material used in different areas of the repository. However, the drift seal appears to be a critical design element in all models, effectively limiting radionuclide transport by hydrologically disconnecting sections of the repository. Additional beneficial design choices include the use of dry salt in disposal drifts to limit radionuclide transport and reducing the infrastructure area costs and minimizing host rock damage.

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