First European High-Level First European High-Level Nuclear Waste Repository Nuclear Waste Repository – OLKILUOTO, FINLAND – – OLKILUOTO, FINLAND –
Rock Model Rock Model Verification and ValidationVerification and Validation
Calin Cosma & Nicoleta Calin Cosma & Nicoleta EnescuEnescu
7th International Workshop on the Application of Geophysics to Rock Engineering7th International Workshop on the Application of Geophysics to Rock EngineeringLisbon 2007Lisbon 2007
AcknowledgementsAcknowledgements
Timo ÄikäsTimo Äikäs
Liisa WikströmLiisa Wikström
Kimmo KemppainenKimmo Kemppainen
Turo Ahokas Turo Ahokas
Eero HeikkinenEero Heikkinen
What, Why, Where and What, Why, Where and When?When?• Nuclear wastes don’t go away
– the organic environment has to be protected at all times
– the method shall not require continuous supervision and maintenance
• From all thinkable alternatives– there is an international concensus that– the geologic disposal has been proven to be
the most suitable to provide safe isolation of the long-lived nuclear wastes
• Challenge of the geologic disposal– the time required for isolation, and thus for
assessing the safety, is extremely long– due to long time required, considerable
uncertainty is associated in the assesment
1980 – Start of programme for 1980 – Start of programme for geologic storage in Finlandgeologic storage in Finland
• Power companies responsible for activities and Power companies responsible for activities and costcost
• TVO starts to build an interim storage facilityTVO starts to build an interim storage facility
• International cooperation starts in the area of International cooperation starts in the area of geologic disposal (Stripa)geologic disposal (Stripa)
• Since the ‘90s, TVO has annually invested EUR Since the ‘90s, TVO has annually invested EUR 8.4 - 11.8 million on research and development8.4 - 11.8 million on research and development
Issues for georesearchIssues for georesearch
Understanding groundwater is main research target– radionuclides can enter organic environment only by the
transport of groundwater– chemical conditions can be influenced by groundwater
related processes– performance of engineered barriers can be influenced by
groundwater
In crystalline rock, essentially all groundwater In crystalline rock, essentially all groundwater transport takes place in fractures and fracture zonestransport takes place in fractures and fracture zones
Mapping the fracture zones is fundamental to Mapping the fracture zones is fundamental to evaluating the radionuclide transport from repository evaluating the radionuclide transport from repository to the biosphereto the biosphere
Site Selection Research Site Selection Research Programme 1983-2000Programme 1983-2000
Site identification1983-1985
Preliminary sitecharacterisation
1986-1992
Detailed sitecharacterisation
1993-2000
More than 100 candidatesites were identified
Nuclear Waste Disposal Project in Nuclear Waste Disposal Project in FinlandFinland
The Olkiluoto site has been selected for deep geological disposal of spent nuclear fuel in 2001
Extensive geophysical data and imaging have been used to produce and refine a 3D model of the site
An underground research, testing and demonstration facility, ONKALO, is being built at Olkiluoto for detailed characterisation of the planned nuclear waste repository host rock.
Tentative repository layout green, ONKALO yellow.
The access tunnel will be 5.5 km long.Total length of tunnels for the research facility will be 8.3 km, at
levels 420 m and 520 m.
Objectives of the geo-research Objectives of the geo-research programmeprogramme
Attain sufficient confidence in the plans for the final disposal operations
Identification of bedrock volumes suited for final disposal
Detailed definition of the properties of these volumes
Mapping lithological contacts and structural features
The Olkiluoto Geological The Olkiluoto Geological ModelModel
The almost twenty years of investigations have been recently implemented into geological model, where the geometric and parameter properties are given for four submodels (GeoMTF 2006):
Lithological model, Ductile deformation model, Brittle deformation model, Alteration model.
The bedrock at Olkiluoto consists of multiphase
deformed and fractured granitic and gneissic rocks.
Geophysical Investigations at Geophysical Investigations at OlkiluotoOlkiluoto
• Airborne and ground level geological mapping and geophysical soundings • Surface and borehole seismic reflection imaging • Detailed geophysical logging• Core logging • Hydrological and hydrochemical investigations
40 deep boreholes, over 7 km2 were used
Borehole investigations included
Comprehensive geological mapping
Geophysical logging,
VSP, MSP and Crosshole seismic investigations,
Detailed hydrological studies
Ground level investigations included
geological mapping on outcrops and in trenches,
electrical, electromagnetic, magnetic,
3D reflection and refraction seismic surveys.
Integration/Confirmation – Bridging the Integration/Confirmation – Bridging the scale – scale –
Detailed borehole logs & VSPDetailed borehole logs & VSP
The average trends observed from detailed borehole logging and
from 3D VSP imaging display remarkable consistency.
Lower hemisphere, equal-area stereographic projection. VSP reflectors are displayed in red, contours display fracture (and foliation) orientation distributions over depth ranges.
A comparison of detailed borehole logging with the seismic investigations highlights the petrophysical and geological
connection between features interpreted at different scales.
Model Confirmation from the Model Confirmation from the ONKALO tunnelONKALO tunnel VSP predictions are being VSP predictions are being
verified by direct observationsverified by direct observations
Model Confirmation from the ONKALO Model Confirmation from the ONKALO tunneltunnel
Direct observation of a sub-vertical deformed Direct observation of a sub-vertical deformed shear zoneshear zone
VSP reflector and VSP migrated sections from shots L15 and L25 measured from borehole KR04.
Altered and deformed shear zone (green, transparent), and corresponding VSP reflector (black), same as shown in image A. Small grey disks on tunnel are other VSP reflectors.
The weathered zone as observed in ONKALO wall at 280 m.
A weathered and deformed shear zone oriented 110–170/40–60 (with an extension towards 150/36) has been met at tunnel length 240–282m and 450–453m, on investigation trenches at surface, and in boreholes. This zone is characterized by low seismic velocity.
Cross-validation of geological, hydrological, electrical and VSP models of a series of sub-horizontal brittle fault zones.
Tunnel length 1355 m
Model Confirmation from the Model Confirmation from the ONKALO tunnelONKALO tunnel
3D rock features mapping by 3D rock features mapping by seismicsseismics
Seismic features were found to be associated Seismic features were found to be associated with: with:
fracture zonesfracture zones lithological contactslithological contacts
Reflectors without borehole control data may not directly be used as fracture zone indicators.
From a subset of 29 most pro-eminent seismic features analyzed :
24 (83%) were unambiguously explained.
15 (50%) clearly identified as fracturing-related and
14 (50%) identified as combination of rock type/shearing and fracturing.
ConclusionsConclusions
Previous geophysical determinations, interpretations and models find confirmation by direct observation in the ONKALO tunnel.
The main features met so far form a subset of the predictions made.
The direct verification of the predictions shows a The direct verification of the predictions shows a great potential of the group of investigations and great potential of the group of investigations and interpretation techniques used so far.interpretation techniques used so far.
Models built on large- and medium-scale Models built on large- and medium-scale investigations are easier to validate at the scale of investigations are easier to validate at the scale of the tunnel than in sparsely drilled boreholes.the tunnel than in sparsely drilled boreholes.
Olkiluoto todayOlkiluoto today