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Journal Articles

Modelling concrete degradation by coupled non-linear processes

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(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.

Journal Articles

Using natural systems evidence to test models of transformation of montmorillonite

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:1 Percentile:13.07(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.

Journal Articles

A Coupled modeling simulator for near-field processes in cement engineered barrier systems for radioactive waste 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:2 Percentile:43.54(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.

Journal Articles

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

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:7 Percentile:58.58(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$$^{circ}$$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 60$$^{circ}$$C to that for illite + quartz at higher temperatures. However, even over very long timescales ($$gg$$ 1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80$$^{circ}$$C.

Journal Articles

A Comparative study of the modelling of cement hydration and cement-rock laboratory experiments

Savage, D.*; Soler, J. M.*; Yamaguchi, Kohei; Walker, C.; Honda, Akira; Inagaki, Manabu; Watson, C.*; Wilson, J.*; Benbow, S.*; Gaus, I.*; et al.

Applied Geochemistry, 26(7), p.1138 - 1152, 2011/07

 Times Cited Count:16 Percentile:46.86(Geochemistry & Geophysics)

The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for rad wastes creates potential issues concerning chemical reactivity. From a long term safety perspective, it is desirable to be able model these interactions and changes quantitatively. As part of the LCS (Long-term Cement Studies) project programme, a modelling inter-comparison has been conducted, involving the modelling of two experiments describing cement hadration and cement-rock reaction, with teams representing the NDA (UK), Posiva (Finland), and JAEA. This modelling exercise showed that the dominant reaction pathways in the two experiments are fairly well understood and are consistent between the different modelling teams, although significant differences existed amongst the precise parameterisation. Future modelling exercises of this type should focus on a suitable natural or industrial analogue that might aid assessing mineral-fluid reactions at these longer timescales.

Journal Articles

Natural systems evidence for the alteration of clay under alkaline conditions; An Example from Searles Lake, California

Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*; Ono, Kaori*; Oda, Chie; Honda, Akira

Applied Clay Science, 47(1-2), p.72 - 81, 2010/01

 Times Cited Count:30 Percentile:69.07(Chemistry, Physical)

Mudstones containing smectite have been altered under mildly alkaline conditions (9 $$<$$ pH $$<$$ 10) at Searles Lake, California over a 3 million-year time period. This natural alteration has been simulated incorporating time-dependent boundary conditions of sedimentation and fluid composition, a Pitzer model for activities of aqueous species, and a coupled hydrogeological model for time-dependent flow in the sediment layers. Kinetic dissolution of detrital smectite under alkaline conditions was described using one of two models based on departure from thermodynamic equilibrium or by an empirical rate dependent upon aqueous Si concentrations. The zonal pattern of smectite dissolution observed at Searles Lake was reproduced reasonably well by the "Cama-TST" model of montmorillonite dissolution. This assessment provides a test of the accuracy and reliability of published data in the application of models of smectite dissolution in the long-term.

Oral presentation

Natural analogue in relation to alkaline alteration of clayey buffer material; An Example from the Searles Lake, California, 2; A Geochemical-transport modelling

Oda, Chie; Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*

no journal, , 

An natural clay alteration at Searles Lake, California has been investigated using reaction-transport modelling with the computer code employing time-dependent boundary conditions of sedimentation and fluid composition. The evidence in natural systems can demonstrate that alkaline alteration will be controlled by kinetic-geochemical reaction and transport coupling process, and that advective fluid flow and the salinity of the pore fluid eill be important factors.

Oral presentation

Groundwater patterns in a Playa Lake Basin, California; Analogue studies for geological disposal

Gallardo, A.*; Savage, D.*; Benbow, S.*; Takase, Hiroyasu*; Oda, Chie

no journal, , 

A numerical model was constructed to understand the groundwater flow dynamics and salinity distribution in the Searles Lake, California, a dry and alkaline playa lake, as a natural analogue for processes in a potential geological repository. The result shows that vertical flow would prevail at the center of the lake, and under this condition, salts would be dissolved from shallow evaporitic horizons being redistributed downwards and away from the lake surface. Concentrations up to 220 g/L would occur within an area approximately 6 by 4 km, extending to a depth of 200 m after 200,000 years. Although several uncertainties remain, the model is consistent with many observations, and provides a framework to address geochemical processes in the basin.

Oral presentation

Natural analogue in relation to alkaline alteration of clayey buffer material; An Example from the Searles Lake, California

Oda, Chie; Yamaguchi, Kohei; Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*

no journal, , 

Mudstones containing smectite have been altered under mildly alkaline conditions (9 $$<$$ pH $$<$$ 10) at Searles Lake. This natural alteration has been investigated using reaction-transport modelling. These data demonstrate that smectite alteration will be controlled by the kinetics of dissolution-precipitation reaction and the salinity of the pore fluid.

Oral presentation

Reactive transport modelling of iron-bentonite interface evolution

Wilson, J.*; Watson, C.*; Benbow, S.*; Savage, D.*; Sasamoto, Hiroshi

no journal, , 

Iron steel overpack will be surrounded by bentonite buffer as a engineering barrier system for the high-level radioactive waste disposal. It is concerned that iron-bentonite interactions result in the alteration of montmorillonite to non-swelling Fe-rich minerals. In the present study, reactive transport modeling of iron-bentonite interface evolution has been conducted to evaluate the long-term behavior of bentonite stability. A number of model cases were produced in order to assess which processes are likely to dominate at iron-bentonite interfaces.

Oral presentation

Using natural systems data to test models of transformation of montmorillonite

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.

Oral presentation

Evolution of radionuclide transport and retardation processes in uplifting crystalline rocks

Metcalfe, R.*; Kawama, Daisuke*; Benbow, S. J.*; Tachi, Yukio

no journal, , 

12 (Records 1-12 displayed on this page)
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