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