Near-Field Processes and Evolution toward to Assessment of Radionuclide Migration in Geological Disposal of High-Level Radioactive Waste

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Clays and Engineered Mineral Materials".

Deadline for manuscript submissions: closed (27 October 2023) | Viewed by 2477

Special Issue Editors

Near-Field Research Group, Radioactive Waste Processing Research Department, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1184, Japan
Interests: radioactive waste disposal; groundwater geochemistry; thermodynamic data of minerals; geochemical modeling; water-rock interactions; cement-rock interactions; iron-bentonite interactions; cement-bentonite interactions; colloid characterization; dissolved organic matter characterization
Department of Geological Disposal Research, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1194, Japan
Interests: geological disposal; radionuclide migration modelling; sorption and diffusion processes; bentonite/clay minerals
Dr. Randy Arthur
E-Mail Website
Guest Editor
INTERA Incorporated, Austin, TX 78759, USA
Interests: geochemical modeling; performance assessment of geologic repositories for nuclear waste; multiphase reactive-transport processes
Dr. James Wilson
E-Mail Website
Guest Editor
Wilson Scientific Ltd., Warrington WA3 6TR, UK
Interests: bentonite; iron–bentonite interactions; cement/concrete chemistry; cement–clay interactions; geochemical modelling; chemotoxic species
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Special Issue Information

Dear Colleagues,

This Special Issue of Minerals will focus on the key processes and evolution of the near-field (NF) towards the assessment of radionuclide migration for high-level radioactive waste (HLW) disposal. The NF comprises the engineered barrier system (EBS) and the surrounding host rock in its immediate proximity that is significantly affected by repository construction and waste emplacement. Topics related to the following aspects, including laboratory experiments, in situ experiments, and modeling studies, will be considered for this Special Issue:

Early processes and the evolution of the EBS:

  • The corrosion of the canister/container/overpack;
  • THM processes and the evolution of the bentonite buffer (e.g., thermal processes, hydraulic/gas processes, mechanical processes, coupled processes and evolution);
  • Geochemical processes and the evolution of the bentonite buffer (e.g., salt accumulation, cementation, buffer chemical evolution);
  • Piping and/or erosion.

Long-term processes and the evolution of the NF:

  • Interactions of different materials (e.g., iron–bentonite interactions, cement–bentonite interactions, or cement–rock interactions);
  • Organic/microbe/colloid influence on radionuclide migration;
  • Sorption and/or diffusion behavior in the EBS and the surrounding rock mass;
  • Coupled modeling with radionuclide migration.

Dr. Hiroshi Sasamoto
Dr. Yukio Tachi
Dr. Randy Arthur
Dr. James Wilson
Guest Editors

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Keywords

  • iron corrosion
  • bentonite alteration
  • cement hydration and degradation
  • coupled modeling
  • organic, microbe and colloid influence
  • radionuclide migration

Published Papers (2 papers)

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Research

26 pages, 12172 KiB  
Article
Modelling of the Corrosion-Induced Gas Impact on Hydraulic and Radionuclide Transport Properties of Geological Repository Barriers
Minerals 2024, 14(1), 4; https://doi.org/10.3390/min14010004 - 19 Dec 2023
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Abstract
The geological disposal of high-level radioactive waste is the final step in the nuclear fuel cycle. It is realized via isolating the high-level radioactive waste in the geological environment with an appropriate system of engineered barriers. Radionuclides-containing materials must be isolated from the [...] Read more.
The geological disposal of high-level radioactive waste is the final step in the nuclear fuel cycle. It is realized via isolating the high-level radioactive waste in the geological environment with an appropriate system of engineered barriers. Radionuclides-containing materials must be isolated from the biosphere until the radioactivity contained in them has diminished to a safe level. In the case of high-level radioactive waste, it could take hundreds of thousands of years. Within such a long timescale, a number of physical and chemical processes will take part in the geological repository. For the assessment of radionuclide migration from a geological repository, it is necessary to predict the repository’s behavior once placed in the host rock as well as the host-rock response to disturbances due to construction. In this study, the analysis of repository barriers (backfill, concrete, inner excavation disturbed zone (EDZ), outer EDZ, host rock) thermo–hydraulic–mechanical (THM) evolution was performed, and the scope of gas-induced desaturation was analyzed with COMSOL Multiphysics. The analysis was based on modelling of a two-phase flow of miscible fluid (water and H2) considering important phenomena such as gas dissolution and diffusion, advective–diffusive transport in the gaseous phase, and mechanical deformations due to thermal expansion of water and porous media. The importance of proper consideration of temperature-dependent thermodynamic properties of water and THM couplings in the analysis of near-field processes was also discussed. The modelling demonstrated that such activities as 50 years’ ventilation of the waste disposal tunnel in initially saturated porous media, and such processes as gas generation due to corrosion of waste package or heat load from the waste, also led to desaturation of barriers. H2 gas generation led to the desaturation in engineered barriers and in a part of the EDZ close to the gas generation place vanishing soon after finish of gas generation, while the host rock remained saturated during the gas generation phase (50–100,000 years). Radionuclide transport properties in porous media such as effective diffusivity are highly dependent on the water content in the barriers determined by their porosity and saturation. Full article
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20 pages, 5942 KiB  
Article
Evolution of the Reaction and Alteration of Granite with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive Transport Modelling
Minerals 2022, 12(7), 883; https://doi.org/10.3390/min12070883 - 13 Jul 2022
Viewed by 1309
Abstract
The construction of a repository for the geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository, and the extensive use of cement will result in the development of a highly alkaline porewater, pH [...] Read more.
The construction of a repository for the geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository, and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially with high Na and K concentrations, evolving to a Ca-rich fluid, and finally returning to the natural background groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a granite, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the granite with the cement leachates resulted in small changes in pH and the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions, of greatest abundance with the Ca-rich fluid. As the system evolved, secondary C-(A-)S-H phases redissolved, partly replaced by zeolites. This general sequence was successfully simulated using reactive transport modelling. Full article
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