international bentonite longevity (ibl) project: an ... · 13 fresh water/groundwater –bentonite...
TRANSCRIPT
International Bentonite Longevity (IBL) project: an introduction
W.R.Alexander1, M.Ito2 & H.M.Reijonen3
1. Bedrock Geosciences, Auenstein, Switzerland ([email protected]) 2. Kunimine Industries, Miyagi, Japan ([email protected]) 3. Geological Survey of Finland (GTK), Espoo, Finland ([email protected])
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.
.