International Bentonite Longevity (IBL) project: an introduction

W.R.Alexander1, M.Ito2 & H.M.Reijonen3

1. Bedrock Geosciences, Auenstein, Switzerland (russell@bedrock-geosciences.com) 2. Kunimine Industries, Miyagi, Japan (masa.ito@kunimine.co.jp) 3. Geological Survey of Finland (GTK), Espoo, Finland (heini.reijonen@gtk.fi)

Why IBL? Geological disposal of radioactive waste

2

PREVENTany releases reaching

people and the environment in harmful

concentrations

CONTAINradioactivity for many

thousands of years until 99.9% has decayed

MAINTAIN a stable ‘geological cocoon’

for engineered containment system for hundreds of

thousands of years

ISOLATE radioactivity from

people by deep burial in rock

Repository typically 300 -1000 m deep

Bentonite

Bentonite

Bentonite

Bentonite

Bentonite

Bentonite

Where

geological

disposal (and

the

involvement

of bentonite)

began

USNAS (1957)

Why IBL?

Why natural systems (or analogues)?

Link very short term laboratory studies, medium

term in situ studies and geological (ie very long

term) time periods of relevance to repository

safety (10 ka to 1 Ma)

Realistic spatial scales too (cf small lab samples)

Ability to access the true complexity/heterogeneity

of real systems

Ease of understanding of nature (compared to

models of the repository behaviour)

Location

Japanese bentonite quarries & mines

(Takagi, 2005)

5

Plan figure and cross section of the Tsukinuno bentonite deposit after

Kobayashi and Itoh (1992)

6

7

The mine

• Kunimine Industries Company’s

(KIC) Tsukinuno bentonite mine

is a source for Miocene age Na-

bentonite (with Ca-bentonite

near-surface)

• Mining ongoing

• Direct access to surface

exposures in the area

• Access via drifts and shafts

in the mine

• Access to KIC drill cores and

existing database

8

Mine – layout and ongoing activities

採掘終了

Yellow: Bentonite／Hard mudstone interbed,

Red: Inclined shaft, Cross cut

Dip≒60°

Dip≒45°

Dip≒0-10°

East

Footwall rock “Green Tuff”

月布鉱山の模式断面図

川向鉱床 梅ノ木田鉱床

採掘中

Kawanukai

Deposit

Now Working

West

Old

Working

Umenokida Deposit

Bentonite produced

9

10

Bentonite produced

11

Features of interest to radioactive waste disposal

Feature Safety relevance Examples of FEPs of

interest

Bentonite deposit outcrops at the surface,

including in nearby river bed

Potential to study fresh water bentonite

interactions

Saturation, water-rock

(clay)interaction, cation

exchange, colloid formation,

erosion^n

Bentonite occurs as bands with varying

thicknesses (from few cm to ca. 7 m)

Repository relevant size, scale effects. Clay – rock interaction. Clay

based buffer, backfill designs

plus tunnel and borehole

seals.

Bentonite occurs at various depths (0 – ca.

200m below ground surface)

Repository relevant depth (hydrostatic and

lithostatic pressures)

Saturation, groundwater flow,

groundwater diffusion

Hosted by sandy siltstone Brittle host rock: fractures and water conducting

features

Advection/diffusion, water-

rock (clay) interaction, colloid

formation

Area has faults cutting bentonite bearing rocks Deformed bentonite? Faulting, bentonite

deformation, host rock

deformation

Some of the bentonite appears dry Unsaturated bentonite? Saturation, homogenisation

General: special focus on bentonite sampling

Sampling to obtain in situ densities/structures

Recent reviews of drilling practices (e.g Ewy, 2015; Alexander et al., 2017) indicate that currently utilised methods induce damage in the samples ranging from artificial fracturing to altering the in situ density

Approaches for minimising such damage to clay cores are already utilised in the oil industry and it is proposed to adopt these practices here to assess their relevance to future radioactive waste R&D, including sub-sampling laboratory material and drilling cores from full-scale experiments in URLs

Courtesy Geoinvest, Cyprus

13

Fresh water/groundwater – bentonite interactions

• The stability of bentonite is of interest across a range of groundwater salinities, but

especially in relation to potential dilute water intrusion into a repository

• Chemical erosion of bentonite is related to conditions where there is dilute enough

groundwater to produce bentonite colloids and high enough flow to transport them

away from the repository

• The chemical erosion process has been acknowledged in several recent repository

Safety Assessments, but ongoing modelling studies supported by dedicated, short-

term laboratory programmes have produced ambiguous results

• This indicates that longer-term ‘experiments’ are required to obtain better

conceptual models

• cf NAWG – www.natural-analogues.com

14

Fresh water/groundwater – bentonite interactions

Cation exchange

at river bed, outcrops (meteoric) and within deposit

(groundwater)

Na-bentonite changes to Ca-bentonite

Other effects of mineralogical properties?

Gel and colloid formation and erosion?

Groundwater seeping into tunnels

River water

Rain water

Bentonite erosion

Erosion of bentonite around a canister by fresh water could increase

release of radionuclides (see Reijonen & Marcos, 2015 for details)

Bentonites in North

Dakota (Bluemle, 1991)

Natural bentonite erosion can be studied in IBL (schematic cross

section through the Tsukinuno bentonite mine) Locations of sampled

groundwater (A - C) and their depths (above the sea level) are

indicated. Kuno et al. (2002).

Repository-

relevant

16

Saturation

• Bentonites in the repository engineered barrier system (EBS) will be subjected to natural hydrostatic pressures

• Saturation processes dictate the type and rate of many geochemical processes taking place in the bentonite and full saturation is assumed in most repository designs as a long-term condition for the bentonite

• However, the period before full saturation can be very long when the decay heat of the waste affects near-field conditions, especially in cases where the host rock is relatively dry

Relationship between buffer

material thickness and density to

satisfy design requirements

(JNC, 2000)

17

Saturation

• Potential implications including

• incomplete seals formed by the bentonite

• fracturing and/or cementation of the bentonite

• canister sinking

• So, by looking at bentonite occurrences at repository relevant depths, some open questions can be answered:

• What is the natural saturation state of bentonite and how does it vary as a function of the surrounding rock hosting it?

• Why is all bentonite not fully saturated, even when near water-saturated host rocks?

• In the Tsukinuno mine, dryer and wetter bentonites are clearly observed, need to understand why this difference occurs. What are the implications for the repository buffer, backfill and seals?

18

Deformation/extrusion

• Description of bentonite deformation in fault system

• Analogue to earthquake/rock shear scenarios

• Description of bentonite extrusion into fracture systems

• Sealing of fractures is assumed in repository designs, but it has not been documented in natural settings (conceptual model confirmation)

• Documentation of the sealing properties of bentonite in fractured rock

• Description of bentonite fracturing

• Analogue self sealing properties of bentonite in case of fracturing (e.g. due to drying)

19

Bentonite – host rock interaction

• Assess if there are differences between host rock/bentonite interaction for:

• thick bentonite beds (backfill relevant)

• medium beds (relevant for buffer around

waste packages)

• thin beds (borehole seal relevant)

• Examine changes in cation exchange capacity (CEC) and exchangeable cation composition (EC) in bentonite

• Salinity: comparison of the Perapedhi bentonite (Cyprus) with a range of industrial bentonites, indicates that exposure to marine saline conditions for nearly 90 million years had no significant impact on its swelling capacity (Kremer & Alexander, 2015)

Alexander (2018)

20

Stakeholder communications

• As an integral part of the overall

project, material will be produced

which can be utilised for more

general, technical and non-technical

communication purposes

• The main aim is to produce multi-

media material which will clarify the

role of bentonite in repository

performance to a range of

stakeholders (cf Norris et al., 2015)

Project status

Current status

• Preliminary site visits -concluded

• Literature review, data mining –concluded

• Selection of topics – concluded

• Detailed project planning –initiated - influence matrix =>

• Sampling – early November*

• Analysis – mid-November*

• Reporting and publishing in 2019 – 2021

* NB preliminary sampling and analysis reported in Reijonen et al. (2018), this conference, session F, 10:50 on Wednesday, 19th

September

sampling

saturation

state: wet

host rock

saturation

state: dry

host rock

bed

thickness

bentonite

/rock

reaction

erosion/

colloid

formation

fracturing/

faulting

stakeholde

r comms

swelling/

creep

saturation

state: wet

host rock

saturation

state: dry

host rock

bed

thickness

bentonite/

rock

reaction

erosion/

colloid

formation

fracturing/

faulting

stakeholde

r comms

swelling/

creep

References

Alexander. W.R. (2018). Sealing site investigation boreholes: Phase 2. The use of natural, industrial and archaeological analogues in support of the borehole sealing project, Amec

Foster Wheeler report 202580/07 for RWM Ltd, Harwell, UK.

Alexander, W.R., Reijonen, H.M., MacKinnon, G., Milodowski, A.E., Pitty, A.F. & Siathas, A. (2017). Assessing the long-term behaviour of the industrial bentonites employed in a

repository for radioactive wastes by studying natural bentonites in the field. Geosciences Special Issue on Geological Disposal of High Level Radioactive Waste - The Relationship

between Engineered and Natural Barriers. Geosciences Special Issue on Geological Disposal of High Level Radioactive Waste - The Relationship between Engineered and Natural

Barriers, eds. R.Lunn, S.Harley, S.Norris & J.Martinez-Frias. Geosciences 7, 5; doi:10.3390/geosciences7010005

Bluemle, J.B. 1991. The face of North Dakota, revised edition: North Dakota Geological Survey Educational Series 21, 177 p, North Dakota Geological Survey, USA.

Ewy, R.T. (2015): Shale/claystone response to air and liquid exposure, and implications for handling, sampling and testing.- International Journal of Rock Mechanics and Mineral

Sciences 2015, 80, 388–401.

JNC (2000). H12: Project to establish the scientific and technical basis for HLW disposal in Japan, Project Overview Report, 2nd progress report on research and development for

the geological disposal of HLW in Japan, JNC TN1410 2000-001, JNC, Tokai, Japan.

Kobayashi, K. and Itoh, K. (1992) Recent bentonite production process at Kunimine Industries. Journal of the Clay Science Society of Japan, vol. 31, 222-230. (in Japanese).

Kremer, E.P. & Alexander, W.R. (2015). Long-term durability of shaft sealing materials under highly saline groundwater conditions. In Alexander, W.R., Ruskeeniemi, T. and

Reijonen, H.M. (eds) (2015). Proceedings of the NAWG-14 Workshop, Rauma, Finland, 9-11 June, 2015. Geological Survey of Finland (GTK) Guide No. 61. GTK, Espoo, Finland.

Kuno, Y., Kamei, G. And Ohtani, H. 2002. Natural Colloids in Groundwater from a Bentonite Mine - Correlation between Colloid Generation and Groundwater Chemistry. Mat. Res.

Soc. Symp. Proc. Vol. 713 © 2002 Materials Research Society. JJ8.4.1- JJ8.4.8.

W.M.Miller, W.R.Alexander, N.A.Chapman, I.G.McKinley & J.A.T.Smellie (2000). Geological disposal of radioactive wastes and natural analogues. Waste management series, vol. 2,

Pergamon, Amsterdam, The Netherlands.

Norris, S., Alexander, W.R., Milodowski, A.M., West, J.M. & McEvoy, F. (2015). USING NATURAL ANALOGUES TO BUILD STAKEHOLDER CONFIDENCE IN GEOLOGICAL DISPOSAL

- A CATALOGUE OF NATURAL ANALOGUES FOR RADIOACTIVE WASTE MANAGEMENT. Proceedings of the NAWG-14 Workshop, Rauma, Finland, 9-11 June, 2015. Geological

Survey of Finland (GTK) Guide No. 61. GTK, Espoo, Finland.

Reijonen, H.M. & Marcos, N. (2015). Chemical erosion of bentonite – true or false? Proceedings of the NAWG-14 Workshop, Rauma, Finland, 9-11 June, 2015. Geological Survey of

Finland (GTK) Guide No. 61. GTK, Espoo, Finland.

Reijonen, H.M., Kuva, J. & Laxtröm, H. (2018). Benefits of 3D X-ray tomography (XCT) analysis on textural bentonite characterisation. Session F, MECC2018, Zagreb, Croatia.

Takagi, T. (2005): Bentonite in Japan – Geology and Industries. Open file report of Geological Survey of Japan (AIST), no. 425, AIST, Tsukuba, Japan.

USNAS (1957). The disposal of radioactive wastes on land. Report of the committee on waste disposal of the division of earth sciences. US National Academy of Sciences,

Washington, USA.

.