The Basalt/Water System: Considerations for a Nuclear Waste Repository

ABSTRACTHigh-level nuclear Waste emplaced in a repository in basalt will lead to elevated temperatures and chemical reactions between the basalt and repository groundwater. The resultant changes in groundwater chemistry and the formation of secondary minerals will affect radionuclide release rates from the repository. In this study, Grande Ronde Basalt and synthetic groundwater were reacted at temperatures of 100°, 150°, and 300°C at a pressure of 30 MPa. Dickson-type sampling autoclaves were used to follow solution composition changes with time. Solution PH remained weakly alkaline, while steady state concentrations of F-, Cl-, SO4-2, and total Carbon were similar to or lower than initial values. Alteration assemblages at 300°C included silica, zeolites, potassium feldspar, and iron smectite. These assemblages are metastable, and prediction of alteration in the basalt and packing material depends on “accelerated” tests results and must be supplemented by study of metastable assemblages in natural analog systems and by tests in open systems with varying flow rates. Experimental data are consistent with rapid adjustment of Eh to reducing values; however, more work on reaction rates and buffering capacity is in progress.

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Does Fully Radioactive Glass Behave Differently than Simulated Waste Glass?

MRS Proceedings ◽

10.1557/proc-294-207 ◽

1992 ◽

Vol 294 ◽

Cited By ~ 4

Author(s):

X. Feng ◽

J. K. Bates ◽

C. R. Bradley ◽

E. C. Buck

Keyword(s):

Radiation Field ◽

Nuclear Waste ◽

Potassium Feldspar ◽

Waste Glass ◽

Solution Ph ◽

Static Tests ◽

Leach Rate ◽

Nuclear Waste Glass ◽

Surface Alteration ◽

Leach Behavior

ABSTRACTStatic tests at SA/V (ratio of surface area of glass to solution volume) 20,000 m−1 on SRL 200 glass compositions show that, at long test periods, the simulated nuclear waste glass (nonradioactive) leaches faster than the corresponding radioactive glass by a factor of about 40, although comparative tests, done through 560 days, at lower SA/V, 2000 m−1, indicate little difference in the leach behavior of the two types of glasses. The similarity in leach behavior between radioactive and simulated glasses at SAN of 2000 m−1 or lower is also observed for SRL 165/42 and 131/11 compositions. The accelerated glass reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or potassium feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH. This lower pH, in turn, may retard the onset of increased reaction rate. The radiation field generated by the radioactive glasses does not directly affect the stability of the glass surface alteration layer under those conditions where the radioactive and simulated glasses react at the same rate. These results suggest that the fully radioactive nuclear waste glass 200R may maintain a much lower leach rate than the simulated 200S, if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests.

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Reactions in the System Basalt/Simulated Spent Fuel/Water

MRS Proceedings ◽

10.1557/proc-26-137 ◽

1983 ◽

Vol 26 ◽

Cited By ~ 3

Author(s):

D.E. Grandstaff ◽

G.L. Mckeon ◽

E.L. Moore ◽

G.C. Ulmer

Keyword(s):

Water System ◽

Potassium Feldspar ◽

Nuclear Waste Repository ◽

Spent Fuel ◽

Secondary Phases ◽

Glass Dissolution ◽

Ph Values ◽

C 30 ◽

High Level ◽

Radionuclide Release

ABSTRACTThe Grande Ronde Basalts underlying the Hanford Site are being evaluated as a possible site for a high-level nuclear waste repository. Experiments, in which basalt from the Umtanun flow of the Grande Ronde Basalt and basalt with simulated spent fuel were reacted with synthetic Hanford groundwater, were conducted to determine steady state concentrations which can be used in radionuclide release-rate models. Tests were performed at temperatures of 100°, 200°, and 300°C; 30 MPa pressure, and a solution:solid mass ratio of 10:1 for durations up to 7,000 hr. Solution aliquots were extracted periodically during the experiments for analysis. The pH was measured at 250°C and recalculated to higher temperatures. In the basalt-water system the stable high-temperature pH values achieved were 7.2 (100°C), 7.5 (200°C), and 7.6 (300°C). Solution composition variations are due to mesostasis (glass) dissolution and precipitation of secondary phases. Solution measurements indicate a redox potential (Eh) of about -0.7 volts at 300°C. Secondary phases produced include silica, potassium feldspar, iron oxides, clays, scapolite, and zeolites. Tests in the basalt + simulated spent fuel + water systen show that calculated pH values stabilized near 7.6 (100°C), 7.2 (200°C), and 7.7 (300°C). At higher temperatures, solution concentrations were controlled by secondary phases similar to those found in basalt-water tests. Less than 1% of uranium, thorium, samarium, rhenium, cerium, and palladium were released to solution while somewhat higher amounts of iodine, molybdenum, and cesium were released. The UO2 component was unreactive; however, other components (e.g., cesium-bearing phases) were almost completely dissolved. Secondary phases incorporating radionuclide-analog elements include clays, palladium sulfide, powellite, coffinite, and a potassium-uranium silicate.

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Heating-induced creep and potential creep rupture of clay liners for nuclear waste repository

E3S Web of Conferences ◽

10.1051/e3sconf/202020510002 ◽

2020 ◽

Vol 205 ◽

pp. 10002

Author(s):

Karam A. Jaradat ◽

Sherif L. Abdelaziz

Keyword(s):

High Temperatures ◽

Nuclear Waste ◽

Elevated Temperatures ◽

Creep Rupture ◽

Nuclear Waste Repository ◽

Clay Liners ◽

Model Soil ◽

Dem Simulations ◽

Waste Repository ◽

Rate Process Theory

The aim of this study is to assess the potential of encountering a heating-induced creep rapture of clay liners in nuclear waste repository. Groundwater and soil contaminations may occur if the elevated temperatures, expected in the vicinity of nuclear waste repository, trigger creep rapture of the clay liners. In this study, we utilize simulations based on the discrete element method (DEM) to understand the conditions under which heating-induced creep rupture can take place. In lieu of the conventional local/non-local damping mechanism usually utilized in DEM simulations to dissipate energy, the DEM simulations presented in this study incorporate the rate process theory as a damping mechanism to model soil creep. The results of a base anisotropic model at 70 °C show a dramatic increase in the creep rate at high temperatures showing creep rupture. Such undesired behavior can be mitigated by engineering clay liner materials to sustain and resist the expected high temperatures expected around nuclear waste repository.

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Application of Coupled Thermo-Hydro-Mechanical-Chemical (THMC) Processes in Hydrothermal Systems to Processes Near a High-Level Nuclear Waste Repository

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B ◽

10.1115/icem2011-59246 ◽

2011 ◽

Author(s):

Geoffrey J. Peter

Keyword(s):

Nuclear Waste ◽

Transport Theory ◽

Reaction Rates ◽

Hydrothermal Systems ◽

Coupled Processes ◽

Nuclear Waste Repository ◽

High Level Nuclear Waste ◽

Waste Repository ◽

High Level ◽

Waste Repositories

Modeling of coupled processes in the geology near a high-level nuclear waste repository is similar to the modeling of coupled Thermo-Hydro-Mechanical-Chemical (THMC) processes that occur in magma-hydrothermal systems. Former Professor Denis Norton and his colleagues at the Geoscience Department at University of Arizona studied magma-hydrothermal systems extensively. These hydro-thermal codes were verified by obtaining excellent matches between calculated δ18O–values and measured δ18O–values in three principal rock units: basalt, gabbro, and gneiss. This paper reviews the concept of transport theory used in the formulation of the conservation principle used to model the hydrothermal systems. In addition, the paper reviews conservation of mass, momentum, energy, and chemical component equations as applied to the multicomponent-multiphase systems related to hydrothermal systems and obtains parallels to reaction rates and radionuclide transport in the geology of a high level nuclear water repository. Further, this paper compares published results obtained by other researchers modeling coupled THMC process in the geology of high-level nuclear waste repositories.

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Investigating the Temperature Limits of Bentonite Backfilled Repositories: Coupled THMC Modeling, Lab Mockup Testing and Field Experiments

10.5194/egusphere-egu2020-3191 ◽

2020 ◽

Author(s):

Jens Birkholzer ◽

Liange Zheng ◽

Jonny Rutqvist ◽

Sharon Borglin ◽

Chun Chang ◽

...

Keyword(s):

Nuclear Waste ◽

Field Experiments ◽

Elevated Temperatures ◽

Spent Nuclear Fuel ◽

The United States ◽

Transport Processes ◽

Maximum Temperature ◽

Nuclear Waste Repository ◽

Swelling Properties ◽

Clay Formation

Compacted bentonite is commonly considered for use as backfill material in emplacement tunnels of nuclear waste repositories because of its low permeability, high swelling pressure, and retardation capacity of radionuclide. To assess whether this material can maintain its favorable features when undergoing heating from the waste package and hydration from the host rock, we need a thorough understanding of the thermal, hydrological, mechanical, and chemical evolution under disposal conditions. Laboratory and field tests integrated with THMC modeling have provided an effective way to deepen such understanding; however, most of this work has been conducted for maximum temperatures around 100&#176;C. In contrast, some international disposal programs have recently started investigations to understand whether local temperatures in the bentonite of up to 200&#176;C could be tolerated with no significant changes in safety relevant properties. For example, the United States disposal program is evaluating the feasibility of geological disposal of large spent nuclear fuel canisters that are currently in dry storage. Direct disposal of these canisters is attractive for economical and safety reasons, but faces the challenge of exposing the bentonite to significant temperatures increases. As a result, strong thermal gradients may induce complex moisture transport processes and bentonite-rock interactions while cementation and perhaps also illitization effects may occur, all of which could &#160;strongly affect the bentonite properties.Here, we present initial investigations of bentonite behavior exposed to strongly elevated temperatures. We first show results from coupled thermal, hydrological, mechanical and chemical (THMC) simulations of a generic nuclear waste repository in a clay formation with a bentonite-based buffer exposed to a maximum temperature of 200&#176;C. Modeling results illustrate possible performance impacts, such as the time frame and condition of the early unsaturated phase during bentonite hydration, the porosity and permeability after the bentonite becomes fully saturated, and changing in swelling properties. We then discuss preliminary data from a bench-scale laboratory mockup experiment which was designed to represents the strong THMC gradients occurring in a &#8220;hot&#8221; repository, and we briefly touch on a full-scale field experiment to be conducted soon in the Grimsel Test Site underground research laboratory in Switzerland (referred to as HotBENT, with bentonite exposure from up to 200oC).&#160;

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MULTIPHASE FLOW, HYDROMECHANICS AND UNDERPRESSURED GROUNDWATER AT THE SITE OF A PROPOSED DEEP GEOLOGIC NUCLEAR WASTE REPOSITORY IN CANADA

10.1130/abs/2020am-350361 ◽

2020 ◽

Author(s):

Michael Plampin ◽

Keyword(s):

Multiphase Flow ◽

Nuclear Waste ◽

Nuclear Waste Repository ◽

Waste Repository

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Electric-Field Effects on Reactions Between Oxides

MRS Proceedings ◽

10.1557/proc-481-303 ◽

1997 ◽

Vol 481 ◽

Author(s):

Matthew T. Johnson ◽

Shelley R. Gilliss ◽

C. Barry Carter

Keyword(s):

Solid State ◽

Electric Field ◽

Elevated Temperatures ◽

Ionic Current ◽

Reaction Rates ◽

Solid State Reactions ◽

Interfacial Stability ◽

Electric Field Effects ◽

Thin Film Diffusion ◽

Microscopy Techniques

ABSTRACTThin films of In2O3 and Fe2O3 have been deposited on (001) MgO using pulsed-laser deposition (PLD). These thin-film diffusion couples were then reacted in an applied electric field at elevated temperatures. In this type of solid-state reaction, both the reaction rate and the interfacial stability are affected by the transport properties of the reacting ions. The electric field provides a very large external driving force that influences the diffusion of the cations in the constitutive layers. This induced ionic current causes changes in the reaction rates, interfacial stability and distribution of the phases. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated in these spinel-forming systems, to gain a better understanding of the influence of an electric field on solid-state reactions.

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Chemical, Physical and Engineering Characterization Of Candidate Backfill Clays and Clay Admixtures for a Nuclear Waste Respository-Part I

MRS Proceedings ◽

10.1557/proc-6-413 ◽

1981 ◽

Vol 6 ◽

Author(s):

Sudesh K. Singh

Keyword(s):

Nuclear Waste ◽

Morphological Changes ◽

Deionized Water ◽

Engineering Properties ◽

Nuclear Waste Repository ◽

Exchange Cation ◽

Mineral Components ◽

Waste Repository ◽

Mineralogical Compositions

ABSTRACTFourteen Canadian clays and clay admixtures were subjected to simulated nuclear waste repository environments. The present work is concerned with the montmorillonite-dominant materials only. The montmorillonite-dominant samples showed significant leaching on interaction with deionized water. On heating the samples at 200°C for 500 hours, montmorillomites lost intermicellar water completely and acquired cusp-like to cylindrical morphologies. The loss of water and the morphological changes in montmorillonites significantly altered the engineering characteristics. Permeability, shrinkage limits, compactability and shear strength varied in response to the dominant exchange cation in the structure of montmorillonites and the presence of other mineral components in the materials. The synthetic granite water reacted with montmorillonites and led to changes in chemical and mineralogical compositions, crystalline state and engineering properties.

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