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Wilson, J.*; Sasamoto, Hiroshi; Tachi, Yukio; Kawama, Daisuke*
Applied Clay Science, 275, p.107862_1 - 107862_15, 2025/05
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)High-Level Radioactive Waste (HLW) repositories include iron or steel-based containers/overpack and bentonite buffers. Over the last 25 years or so, research efforts have attempted to elucidate the nature of iron-bentonite interactions, especially the potential for the deleterious alteration of the swelling clay component (smectite), to iron-rich layer silicates, some of which lack the capacity for intracrystalline swelling. This could result in a reduction or loss in swelling pressure in the bentonite buffer which is designed to protect waste containers from shear forces and also acts to restrict water and solute transport, as part of an engineered barrier system. Most data on iron-bentonite interactions come from experimental and geochemical modelling studies, as natural analogue data are lacking. The data suggests that there is the potential for the development of an iron-rich bentonite alteration zone with smectite (generally present as the aluminous montmorillonite type) undergoing alteration to iron-rich solids, including layer silicates and steel corrosion products such as green rust or magnetite. The evidence available is complex, arguably incomplete, with many potential complex couplings. Many uncertainties remain despite efforts taken over the last 25 years, but plausible scenarios for iron-bentonite interactions have been identified and possible implications for buffer properties have been suggested.
Metcalfe, R.*; Benbow, S. J.*; Kawama, Daisuke*; Tachi, Yukio
Science of the Total Environment, 958, p.177690_1 - 177690_17, 2025/01
Uplifting fractured granitic rocks occur in substantial areas of countries such as Japan. A repository site would be selected in such an area only if it is possible to make a safety case, accounting for the changing conditions during uplift. The safety case must include robust arguments that chemical processes in the rocks around the repository will contribute sufficiently to minimise radiological doses to biosphere receptors. To provide confidence in the safety arguments, numerical models need to be sufficiently realistic, but also parameterised conservatively (pessimistically). However, model development is challenging because uplift involves many complex couplings between groundwater flow, chemical reactions between water and rock, and changing rock properties. The couplings would affect radionuclide mobilisation and retardation, by influencing diffusive radionuclide fluxes between groundwater flowing in fractures and effectively immobile porewater in the rock matrix and radionuclide partitioning between water and solid phases, via: (i) mineral precipitation/dissolution; (ii) mineral alteration; and (iii) sorption/desorption. It is difficult to represent all this complexity in numerical models while showing that they are parameterised conservatively. Here we present a modelling approach, illustrated by simulation cases for some exemplar radioelements, to identify realistically conservative process conceptualisations and model parameterisations.
Metcalfe, R.*; Tachi, Yukio; Sasao, Eiji; Kawama, Daisuke*
Science of the Total Environment, 957, p.177375_1 - 177375_17, 2024/12
A safety case for an underground radioactive waste repository must show that groundwater will not in future transport radionuclides from the repository to the near-surface environment (the biosphere) in harmful quantities. Safety cases are developed step-wise throughout a programme to site and develop a repository. At early stages, before a site is selected, safety cases are generic and based on simplified safety assessment models of the disposal system that have conservative parameter values. Later, when site-specific conditions are known, more realistic models are needed for the long-term geo-environmental evolution and their impacts on radionuclide migration/retention. Uplift is one such environmental change, which may be particularly important in countries near active tectonic plate boundaries, such as Japan. Here we review the state of knowledge about how the properties of fractured granitic rocks evolve during uplift, based on studies in Japan. Hence, we present conceptual models and a generic scenario for mass transport and retardation processes in uplifting granitic rocks as a basis for realistic numerical models to underpin safety assessment.
Oda, Chie; Kawama, Daisuke*; Shimizu, Hiroyuki*; Benbow, S. J.*; Hirano, Fumio; Takayama, Yusuke; Takase, Hiroyasu*; Mihara, Morihiro; Honda, Akira
Journal of Advanced Concrete Technology, 19(10), p.1075 - 1087, 2021/10
Times Cited Count：0 Percentile：0.00(Construction & Building Technology)Concrete in a transuranic (TRU) waste repository is considered a suitable material to ensure safety, provide structural integrity and retard radionuclide migration after the waste containers fail. In the current study, coupling between chemical, mass-transport and mechanical, so-called non-linear processes that control concrete degradation and crack development were investigated by coupled numerical models. Application of such coupled numerical models allows identification of the dominant non-linear processes that will control long-term concrete degradation and crack development in a TRU waste repository.
Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio
Applied Clay Science, 195, p.105741_1 - 105741_11, 2020/09
Times Cited Count：4 Percentile：14.74(Chemistry, Physical)Safety functions for the clay buffer in a repository for high-level radioactive waste (HLW) are fulfilled if the presence of montmorillonite with high swelling capacity and low permeability is maintained in the long-term. The transformation of montmorillonite to the non-swelling mineral likely illite is addressed in most safety assessments by using simple semi-empirical kinetic models, but this approach contrasts with more complex reactive-transport simulations. In the present study, reactive-transport simulations are compared with simple semi-empirical kinetic models. Results suggest that reactive-transport simulations err on the side of conservatism, but may produce unrealistic estimates of illitization. This comparison demonstrates that reactive-transport models may be carefully applied to simulate the long-term evolution of near field environment for HLW disposal.
Benbow, S. J.*; Kawama, Daisuke*; Takase, Hiroyasu*; Shimizu, Hiroyuki*; Oda, Chie; Hirano, Fumio; Takayama, Yusuke; Mihara, Morihiro; Honda, Akira
Crystals (Internet), 10(9), p.767_1 - 767_33, 2020/09
Times Cited Count：4 Percentile：36.66(Crystallography)Details are presented of the development of a coupled modeling simulator for assessing the evolution in the near-field of a geological repository for radioactive waste disposal where concrete is used as a backfill. The simulator uses OpenMI, a standard for exchanging data between simulation software programs at run-time, to form a coupled chemical-mechanical-hydrogeological model of the system. The approach combines a tunnel scale stress analysis finite element model, a discrete element model for accurately modeling the patterns of emerging cracks in the concrete, and a finite element and finite volume model of the chemical processes and alteration in the porous matrix and cracks in the concrete, to produce a fully coupled model of the system. Combining existing detailed simulation software in this way with OpenMI has the benefit of not relying on simplifications that might be necessary to combine all of the modeled processes in a single piece of software.
Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio
Applied Clay Science, 179, p.105146_1 - 105146_10, 2019/10
Times Cited Count：13 Percentile：49.60(Chemistry, Physical)Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability was evaluated. Thermodynamic modeling using three different TDBs shows that stability fields for montmorillonite exist from 0 to 140
C, but at low values of silica activity, a stability field for illite replaces that for montmorillonite. Pore fluid chemical and mineralogical data for sediments from ODP sites from offshore Japan show a trend from montmorillonite + amorphous silica stability at temperatures up to 60C to that for illite + quartz at higher temperatures. However, even over very long timescales (
1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80C.
Takubo, Yusaku*; Takayama, Yusuke; Kawama, Daisuke*; Mitsuyama, Kazuaki*; Sugita, Yutaka; Ishida, Keisuke*
no journal, ,
In order to understand the phenomena and conditions that should be noted when evaluating the infiltration behavior of water in the buffer material during the re-saturation process of the engineered barrier system, Authors are working on a comparative evaluation of previous test results and coupled analysis results. The development status of the technology to evaluate the influence of thermal, chemical, and mechanical processes using coupled analysis is presented.
Wilson, J.*; Bateman, K.*; Kawama, Daisuke*; Tachi, Yukio
no journal, ,
Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio
no journal, ,
Safety functions for the clay buffer in a repository for HLW are fulfilled if the presence of montmorillonite is maintained in the long-term. Its transformation to non-swelling minerals (e.g. illite) is addressed in most safety assessments by using semi-empirical kinetic models. However, this approach contrasts with all other near-field geochemical modelling activities that employ complex reaction-transport simulations. Here we investigate the consistency of these two approaches by modelling the montmorillonite to illite transformation in the marine sediment profile penetrated by the Ocean Drilling Program (ODP) Site 1174. Illitisation of smectite at Site 1174 using the semi-empirical approach has been modeled by previous studies, and shown to provide a reasonable match to the gradual change of illite content with depth. In comparison, the initial results of reaction-transport simulations showed rapid (conservative) conversion of montmorillonite to illite. The cause of this rapid conversion appears to be the transformation of amorphous silica to quartz over a similar timescale. Subsequent simulations have focused on alternative mechanisms for mineral growth that may explain the discrepancies between the semi-empirical and reaction-transport approaches.
Metcalfe, R.*; Kawama, Daisuke*; Benbow, S. J.*; Tachi, Yukio
no journal, ,
