FORGE

Fate of Repository Gases

Richard Shaw FORGE Co-ordinator

www.FORGEproject.org

FORGE (Fate of repository gases)

50 months (projected start 1 Feb 2009)

12M Euro (50% from EC)

24 partners with BGS as Co-ordinator including WMOs, regulators and academia

NDA

SKB

ANDRA

NAGRA

SCK.CEN

Posiva

RAWRA

CEA

CIEMAT

CIMNE-UPC

AFCN-FANC

CNRS-GDR-MoMas

LML

EDF

GRS

CTU-CEG

NRI

IRSN

INR

IfG

LEI

HSK

ULg

FORGE specifically designed to tackle key research issues associated with the generation and movement of repository gases.

Of particular importance are the long-term performance of bentonite buffers, plastic clays, indurated mudrocks and crystalline formations.

FORGE consists of 5 Work Packages and Coordination

WP1 Treatment of gas in performance assessment

WP2 Gas generation

WP3 Engineered barrier systems

WP4 Disturbed host rock formations

WP5 Undisturbed host rock formations

WP0 Co-ordination

FORGE – WP 1 Treatment of Gas in Performance Assessment WP Leader - Simon Norris (NDA)

WP 1.1 State of the Art – Gas Generation and Gas Migration

At the outset of the project

• Describe the current treatment of gas issues

in PA;

• Analyse limitation of previous studies and

uncertainties related to gas transport ;

• Discuss needs for additional studies of gas

migration issues, and PA relevance.

• State of the art report published (January 2010)

• Benchmark definitions completed and modelling using different codes by different laboratories about completed using these so that they are consistent.

• WP1.1 has maintained strong interaction with other WPs and is now seeking to finalise key questions, for consideration at the 2012 General Assembly and progression in 2013. These questions that will anchor around linking the outcome, learning and development of understanding from FORGE experiments and modelling to performance assessment and the development of the safety case, leading to a revised WP1.1 “Gas generation and migration: Current state of the art” report in early 2013.

WP 1: Current Status

FORGE – WP 2 Hydrogen generation and migration with radiolysis WP Leader – Delphine Pellegrini (IRSN)

Objectives • Assessment of mass balance of H2 production under

radiolitical conditions;

• H2 migration through iron/bentonite/clay/concrete

samples;

• Sensitivity analysis of the conditions of H2

production/ consumption (influence of near field

materials, water chemistry etc.).

Methods

• Experimental facilities of IRSN and NRI (radiation

cells) using samples (iron powder in contact with

bentonite);

• Numerical modelling (Chemsimul/Macksima, two-

phase/reactive biphase transport).

WP2: Production and migration of hydrogen

NRI H2 breakthrough

Outlines of work

– Corrosion of iron powder under anaerobic conditions including sensitivity analysis;

– Migration of produced H2 through compacted bentonite/clay (iron in contact with bentonite/clay);

– Modelling (using Goldsim);

– Short term experiments with high ionising flux;

– Long term experiment (several years) with low ionising flux.

Experimental procedures include

– Consumption of H2 by reaction with radiolytic products such as OH;

– Inhibition of corrosion by water radiolysis oxidant products consumed by H2 (Allen chain);

– Effect of water composition: influence of carbonates by reaction with OH (modification of Allen Chain, mass balance etc.).

WP 2: Current Status

•The maximum pressure before breakthrough caused by hydrogen accumulation from anaerobic corrosion of iron depends on type and density of bentonite and might reach very high values exceeding 20 MPa before breakthrough •First breakthrough pressure level is always higher than subsequent breakthroughs, without backpressure a very fast breakthrough (min) was observed •Hydrogen can penetrate through compacted bentonite under constant pressure at relatively low pressures even before breakthrough •Breakthrough pressures are much lower than in the case of experiments with hydrogen generated by iron corrosion •Different results of flow of hydrogen were achieved for small and large samples, with flow of hydrogen through samples with 100 mm diameter being slower than through sample with 30mm diameter

FORGE – WP 3 Engineered Barrier Systems WP Leader - Patrik Sellin (SKB)

WP 3.1 Bentonite URL Experiments

• Large Scale Gas Injection Test (Lasgit) - Gas flow at full-scale to examine up-scaling issues.

The Lasgit experiment

WP 3.1 Bentonite URL Experiments

• In situ experiment at Bure site URL – Competition between gas production and seal re-saturation -

Will gas generation affect saturation?

Bentonite plug

with gas injection

during resaturation

Bentonite

plug

without gas

injection

Access drifts (GMR, GEX, GED) Borehole (hydro pressure monitoring) Borehole PGZ (phase 1) Borehole PGZ (phase2)

Bure borehole tests

WP 3.2 Bentonite Laboratory Experiments • Gas migration in bentonite – fundamental issues

Examination fundamental issues related to processes governing gas movement;

• Gas migration in bentonite - stress effects Axi-symmetric dipole tests performed under stress controlled conditions ;

WP 3.2 Bentonite Laboratory Experiments

• Modelling of laboratory experiments - Pore-scale numerical investigations and thermodynamic properties;

• Detailed investigation of gas migration through sand/bentonite mixtures -

S/B transport properties and the hydro-chemical interaction with cement pore water;

• Small scale experiments and modelling - Relation to water retention properties at the atomic level;

• Gas migration at various degrees of saturation - Microstructural investigations on compacted bentonite samples before and after breakthrough.

Nagra Large Column Experiment

WP 3.4 Concrete Laboratory Experiments

• Carbonation reactions of buffer/backfill cements and their impact upon gas and radionuclide migration

Alteration of the physical properties of the buffer/backfill.

CaCO3 replaced

CSH matrix

Enhanced microporosity through CSH dissolution,

locally associated with carbonation and shrinkage

microfractures

2 mm

Altered

cement with

shrinkage

cracks

Unaltered

cement

28 mm

Unaltered

cement

CO2GeoNet: batch experiments (BGS)

• Key outcomes achieved: – Vast number of experiments performed;

– A common understanding of the gas migration process in compacted bentonite has largely been reached;

– Significant development and testing of numerical models.

• Outcomes expected: – Some experiments are still in progress;

– Further understanding of gas migration in concrete.

WP 3: Current Status

FORGE – WP 4 Disturbed Host Rock Formations WP Leader - Jon Harrington (BGS)

WP 4.1 Background and rationale

• Repository construction results in re-distribution of stress causing localised alteration and failure of the host rock;

• While SELFRAC and NF-PRO have

improved understanding of EDZ behaviour, there is still a paucity of data defining HM responses to complex stress paths and of the role of gas migration on issues including fracture self-sealing, tunnel convergence, radionuclide displacement and repository over-pressuring.

Tm 6-9

WP 4.1 Laboratory-scale experiments in argillaceous

and crystalline formations

• Examine the effect of stress field and mechanical deformation on permeability and fracture self-sealing in CoX;

• Examine the relationship between the stress tensor and fracture orientations and its impact on transmissivity;

WP 4.2 Field-scale experiments in argillaceous and crystalline formations

• Insight into the hydro-mechanical behaviour of EDZ in an indurated mudrock formation

(Opalinus Clay) in transporting gas along the backfilled tunnels and seals;

• Examine EDZ-sealing, radionuclide

migration and gas movement in

a plastic clay formation (Boom Clay);

• Investigate the hydro-mechanical

behaviour of the EDZ in a disturbed

crystalline rock formation (granite)

and its role in the movement of

repository gases.

Experimental concept: - Backfill tunnel with sand - Seal-off tunnel with pneumatic packer (sealing length 3 m, packer pressure ≤ 5 MPa)

cont.: - Perform hydraulic / gas injection test (Monitor hydraulic / mechanical responses in rock) - Interpretation / modeling (model validation, parameter estimation)

Nagra HG-A experimental concept

WP 4.3 Modelling of laboratory and field-scale experiments

• Modelling of gas migration through the EDZ in Opalinus and Boom Clays using a modified version of CODE_BRIGHT;

• Modelling gas migration in the Callovo-Oxfordian argillite using both elastic and visco-plastic deformation models;

• Modelling the coupling between gemoechanics and fluid flow in various argillites using the coupled mechanical deformation FEC Lagamine;

• Strong interactive links between modeling and experimental teams will be fostered.

WP 4: Current Status Laboratory experiments are approaching completion - results to date show: •Tracer experiments demonstrate that < 0.5% contaminated water is mobilised during gas flow which is focused on existing weakness in the system •Gas flow is associated with volumetric strain in the COx which exhibits coupled time-dependent deformation following a stress-path suggesting that dilation is a key transport mechanism • The importance of stress-history on flow along fractures which can exhibit episodic flow (fault valve behaviour). •The HGA (Mont Terri), the EDZ Boom Clay experiment (Mol) and hard rock in-situ gas test (Joseph URL) are all operational and providing data for numerical modelling. • 2 and 3D models have been developed and applied to the HGA experimental data and to the lab scale experiments.

FORGE – WP 5 Undisturbed Host Rock Formations WP Leader - Geert Volckaert (SCK•CEN)

WP 5 Background and rationale

Gas impact on the hydro-mechanical properties of host rocks which then impacts on safety function to “retard and spread release of radionuclides”?

From earlier studies

– Ratio gas production rate/gas migration rate and two-phase flow properties determine pressure build-up;

– Classic concepts of porous media two-phase flow are inappropriate.

Main objectives

– Conditions that determine dominance of gas migration processes;

– Identification of methods to model those processes and parameter values;

– Determine parameters of direct long-term safety relevance.

• Radionuclide transport through undisturbed

clay during gas breakthrough in Boom Clay.

WP 5.1 Gas transport laboratory experiments

SCK.CEN test cells

WP 5.2 Gas transport in situ experiments

• Complimentary field-scale experiments will be

undertaken to examine issues relating to up-scaling of process and phenomena;

• The PGZ1 experiment at Bure URL -

New gas injection borehole experiment

Coupling gas flow-geomechanical

Behaviour;

• The HG-C gas injection

experiment at Mont Terri URL;

• Further exploitation of results

of on-going experiment -

Testing similar to PGZ1

but using different clay.

Mont Terri HG-C test

Bure PGZ-1 experiment

WP 5.3 Gas transport in undisturbed host rock modelling

• Focus on geomechanical coupling and gas flow;

• Laboratory experiments;

• Influence of boundary conditions and test protocols -

Heterogeneous distribution of parameters;

• For in situ experiments 2 teams per experiment to allow comparison of different approaches -

PGZ1

HG-C;

• Generic approaches to up-scaling gas dispersion for sequences of geological layers.

WP 5: Current Status

•Developed successful techniques able to look at small scale time-dependant processes and have accrued a significant quantity of data •Examined mechanisms associated with gas entry/breakthrough, gas permeability, saturation and hysteresis •Complex flow behaviour observed including precursor flow, dynamic pathway propagation, pathway instability, temporal evolution of parameters, hysteresis and localised heterogeneity •Developing a new conceptual model for gas flow in the COx based on detailed process understanding in which dilatancy appears to play a significant role in the movement of gas Implications for process understanding •Classic porous medium models are not able to explain many aspects of the data •Some features strongly indicate the development of flow pathways •Rapid changes in pressure/flow indicate highly unstable pathways •The combination of relatively high gas flow rates with relatively slow gas breakthrough also suggests the time-dependent development of discrete pathways

Dissemination

3 Project meetings held to date (one more planned for 4 to 6 Dec 2012 (Gent, Belgium) open to all). Several meetings workshops held on different topics including: • Modelling (Sept 2009 and March 2010) • Bentonite testing (Sept 2011) • Luxembourg Symposium (5 to 7 Feb 2013)

FORGE was very well represented at: • Nantes Clay Barriers meeting (April 2010) • Loughborough Geological Disposal of Radioactive Waste: Underpinning Science and Technology (Oct 2011) • Montpellier Clay Barriers meeting (Oct 2012) 20+ papers/posters

Web site - www.FORGEproject.org

www.FORGEproject.org

With thanks to all FORGE partners for their contribution in developing the FORGE project and especially to those who have (unknowingly!) provided illustrations for

this presentation.

rps@bgs.ac.uk

FORGE receives funding from the European Commission FP7 Euratom Programme under grant agreement 230357