Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site

ABSTRACTMatrix diffusion is a key process for radionuclide retention in crystalline rocks. Within the LTD project (Long-Term Diffusion), an in-situ diffusion experiment in unaltered non-fractured granite was performed at the Grimsel Test Site (www.grimsel.com, Switzerland). The tracers included 3H as HTO, 22Na+, 134Cs+ and 131I- with stable I- as carrier.The dataset (except for 131I- because of complete decay) was analyzed with different diffusion-sorption models by different teams (NAGRA / IDAEA-CSIC, UJV-Rez, JAEA, Univ. Poitiers) using different codes, with the goal of obtaining effective diffusion coefficients (De) and porosity (ϕ) or rock capacity (α) values. A Borehole Disturbed Zone (BDZ), which was observed in the rock profile data for 22Na+ and 134Cs+, had to be taken into account to fit the experimental observations. The extension of the BDZ (1-2 mm) was about the same magnitude as the mean grain size of the quartz and feldspar grains.De and α values for the different tracers in the BDZ are larger than the respective values in the bulk rock. Capacity factors in the bulk rock are largest for Cs+ (strong sorption) and smallest for 3H (no sorption). However, 3H seems to display large α values in the BDZ. This phenomenon will be investigated in more detail in a second test starting in 2013.

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Background analysis of actinide and 99Tc tracers in the frame of an in-situ bentonite diffusion experiment at the Grimsel Test Site

10.7185/gold2021.7629 ◽

2021 ◽

Author(s):

Francesca Quinto ◽

Ingo Blechschmidt ◽

Thomas Faestermann ◽

Karin Hain ◽

Dominik Koll ◽

...

Keyword(s):

Test Site ◽

Diffusion Experiment ◽

Grimsel Test Site

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Studies on radionuclide transport behaviour–The next generation of in-situ experiments at the Grimsel Test Site

MRS Proceedings ◽

10.1557/proc-1193-159 ◽

2009 ◽

Vol 1193 ◽

Author(s):

Andrew James Martin ◽

Ingo Blechschmidt

Keyword(s):

Shear Zone ◽

Diffusion Processes ◽

Test Site ◽

Core Material ◽

Laboratory Studies ◽

Grimsel Test Site ◽

And Migration ◽

Colloid Formation

AbstractTwo recent ongoing major projects at the Grimsel Test Site (GTS) (www.grimsel.com) that were initiated to simulate the long-term behaviour of radionuclides in the repository near-field and the surrounding host rock are presented: the Colloid Formation and Migration (CFM) project, which focuses on colloid generation and migration from a bentonite source doped with radionuclides and the Long-Term Diffusion (LTD) project, which aims at in-situ verification and understanding of the processes that control the long-term diffusion of repository-relevant radionuclides. So far, the CFM project has principally involved: development and implementation of a state-of-the-art sealing concept to control hydraulic gradients in a shear zone to imitate repository-relevant conditions; extensive laboratory studies to examine bentonite erosion and colloid formation in a shear zone; and, development of models to estimate colloid formation and migration. The next stage will be to assess the behavior of bentonite colloids generated from a radionuclide spiked bentonite source-term emplaced into the controlled flow field of the shear zone. This will be coupled with further extensive laboratory studies in order to refine and evaluate the colloid models currently used in performance assessments. The LTD project consists of: a monopole diffusion experiment where weakly sorbing and non-sorbing radionuclides (3H, 22Na, 131I, 134Cs) have been circulating and diffusing into undisturbed rock matrix since June 2007; experiments to characterise pore space geometry, including determination of in-situ porosity with 14C doped MMA resin for comparison with laboratory derived data; a study of natural tracers to elucidate evidence of long-term diffusion processes; and, an investigation of the in-situ matrix diffusion paths in core material from earlier GTS experiments. Future experiments will focus on diffusion processes starting from a water-conducting feature under realistic boundary conditions.

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The seismo-hydro-mechanical behaviour during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in-situ stimulation experiment

10.5194/se-2017-79 ◽

2017 ◽

Cited By ~ 1

Author(s):

Florian Amann ◽

Valentin Gischig ◽

Keith Evans ◽

Joseph Doetsch ◽

Reza Jalali ◽

...

Keyword(s):

Rock Mass ◽

Geothermal Energy ◽

Numerical Models ◽

Test Site ◽

Crystalline Rock ◽

Coupled Processes ◽

Small Scale ◽

Intermediate Scale ◽

Grimsel Test Site

Abstract. In this contribution we present a review of scientific research results that address seismo-hydro-mechanical coupled processes relevant for the development of a sustainable heat exchanger in low permeability crystalline rock and introduce the design of the In-situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to study such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydro-mechanical processes that would enhance process understanding in a way that aids future stimulation design. Small scale laboratory experiments provide a fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from 1) difficulties and uncertainties in upscaling the results to the field-scale and 2) relatively homogeneous material and stress conditions that lead to an over-simplistic fracture flow and/or hydraulic fracture propagation behaviour that is not representative for a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales, and for which access to the target rock mass with a comprehensive monitoring system is possible. Only few intermediate-scale hydro-shearing and hydro-fracturing experiments have recently been performed in a densely instrumented rock mass. No such measurements have been performed on faults in crystalline basement rocks. The In-situ Stimulation and Circulation (ISC) experiment currently performed in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland) is designed to address open research questions, which could not be investigated in the required detail so far. Two hydraulic injection phases were executed to enhance the permeability of the rock mass: a hydro-shearing phase and then a hydraulic fracturing phase. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation and the micro-seismic response were monitored at a high spatial and temporal resolution.

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A fully 3-D anisotropic numerical model of the DI-B in situ diffusion experiment in the Opalinus clay formation

Physics and Chemistry of the Earth Parts A/B/C ◽

10.1016/j.pce.2006.04.017 ◽

2006 ◽

Vol 31 (10-14) ◽

pp. 531-540 ◽

Cited By ~ 30

Author(s):

J. Samper ◽

C. Yang ◽

A. Naves ◽

A. Yllera ◽

A. Hernández ◽

...

Keyword(s):

Numerical Model ◽

Opalinus Clay ◽

Diffusion Experiment ◽

In Situ Diffusion ◽

Clay Formation

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In-Situ Diffusion Experiment In Sparsely Fractured Granite

MRS Proceedings ◽

10.1557/proc-824-cc7.4 ◽

2004 ◽

Vol 824 ◽

Cited By ~ 1

Author(s):

Peter Vilks ◽

Neil H. Miller ◽

Mark Jensen

Keyword(s):

Field Experiments ◽

Effective Diffusion ◽

Rock Properties ◽

Experimental Program ◽

Diffusion Experiment ◽

Stress Regime ◽

In Situ Experiments ◽

In Situ Diffusion ◽

Conservative Values

AbstractThe in-situ diffusion experiment was conducted at AECL's Underground Research Laboratory (URL) to improve the understanding of diffusive solute transport in sparsely fractured or intact granitic rock (SFR). The experimental program used a comparative series of laboratory and in-situ field experiments to evaluate the ability of laboratory measurements to estimate in-situ rock properties and to explore issues surrounding the influence of stress relaxation, rock texture, porosity, pore geometry, and anisotropy on derived effective diffusion coefficients (De). In-situ experiments yielded iodide Debetween 1.4 × 10−13 and 1.1 × 10−12 m2/s. Unlike laboratory results, the in-situ De estimates did not exhibit correlation with sample depth or varied stress regime. Laboratory-derived measurements of De, porosity and permeability were found to systematically increase for samples removed from greater depths and higher stress regimes. Laboratory-derived iodide De values consistently trended higher than in-situ values by a factor of 1 to 15, except on the shallowest 240-m Level (σ1 ≍ 30 MPa) where differences were negligible. Laboratory-derived estimates of permeability were consistently higher than in-situ derived values by a factor of 2 to 100. This experimental program provides evidence that laboratory steady-state diffusion experiments are most likely to yield conservative values of De for simulation of diffusive mass transport in SFR.

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Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

Clays and Clay Minerals ◽

10.1007/s42860-019-00012-5 ◽

2019 ◽

Vol 67 (2) ◽

pp. 111-131 ◽

Cited By ~ 6

Author(s):

Jebril Hadi ◽

Paul Wersin ◽

Vincent Serneels ◽

Jean-Marc Greneche

Keyword(s):

Test Site ◽

In Situ Test ◽

Grimsel Test Site

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Grimsel Test Site - Phase VI: Review of Accomplishments and Next Generation of In-Situ Experiments Under Repository Relevant Boundary Conditions

MRS Proceedings ◽

10.1557/proc-1107-547 ◽

2008 ◽

Vol 1107 ◽

Author(s):

Ingo Blechschmidt ◽

Stratis Vomvoris ◽

Joerg Rueedi ◽

Andrew James Martin

Keyword(s):

Near Field ◽

Planning Horizon ◽

Test Site ◽

Low Ph ◽

Swiss Alps ◽

In Situ Experiments ◽

Grimsel Test Site ◽

And Migration

AbstractThe Grimsel Test Site owned and operated by Nagra is located in the Swiss Alps (www.grimsel.com). The Sixth Phase of investigations was started in 2003 with a ten-year planning horizon. With the investigations and projects of Phase VI the focus has shifted more towards projects assessing perturbation effects of repository implementation and projects evaluating and demonstrating engineering and operational aspects of the repository system. More than 17 international partners participate in the various projects, which form the basic organisational “elements” of Phase VI. Scientific and engineering interaction among the different projects is ensured via an annual meeting and several experimental team meetings throughout the year. On-going projects include: evaluation of full-scale engineered systems under simulated heat production and long-term natural saturation (NF-Pro/FEBEX), gas migration through engineered barrier systems (GMT, finished this year), emplacement of a shotcrete low-pH plug (ESDRED/Module IV), testing and evaluation of standard monitoring techniques (TEM).Numerous in-situ experiments with inactive tracers and radionuclides were successfully carried out over the past few years at the Grimsel Test Site (GTS). For the GTS Phase VI, three major projects have been initiated to simulate the long-term behaviour of contamination plumes in the repository near-field and the surrounding host rock:•The CFM (Colloid Formation and Migration) project, which focuses on colloid generation and migration from a bentonite source doped with radionuclides•The LCS (Long-Term Cement Studies) project, which aims at improving the understanding of low-pH cement interaction effects in water conducting features•The LTD (Long-Term Diffusion) project, which aims at in-situ verification of long-term diffusion concepts for radionuclidesAs Phase VI approaches its mid-term point, what are the next steps planned? The accomplishments assessed to date and the opportunities with the on-going projects as well as new projects – currently under discussion – are presented herein

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The “FEBEX” Project: A Demonstration and Testbench of the Spanish Concept for Crystalline Rock Repositories

MRS Proceedings ◽

10.1557/proc-506-937 ◽

1997 ◽

Vol 506 ◽

Cited By ~ 1

Author(s):

J.L. Fuentes-Cantillana ◽

F. Huertas ◽

J.L. Santiago

Keyword(s):

Test Site ◽

Crystalline Rock ◽

Test Length ◽

In Situ Test ◽

Preliminary Results ◽

Compacted Bentonite ◽

Automatic Mode ◽

Grimsel Test Site ◽

Total Test

ABSTRACTA full-scale “In situ” test is currently being conducted as part of the FEBEX project. This test is being carried out at the Grimsel Test Site in Switzerland and reproduces the “AGP-Granite” concept of the Spanish agency ENRESA for HLW repositories. Two heaters, of the same dimensions and weight as the canisters in the reference concept, have been placed in a horizontal drift of 2,28 m diameter and backfilled with a total of 115.7 t of highly compacted bentonite blocks, up to a total test length of 17 m. More than 600 sensors have been installed in the experiment, which runs basically in an automatic mode and is being remotely controlled and monitored from Spain. This paper addresses the engineering, installation and instrumentation aspects of this test. In addition, some preliminary results are shown

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