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Econ. Environ. Geol. 2022; 55(1): 1-17

Published online February 28, 2022

https://doi.org/10.9719/EEG.2022.55.1.1

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Rock Mechanics Site Characterization for HLW Disposal Facilities

Jeong-Gi Um1, Seung Gyu Hyun2,*

Author Info. +

1Dept. of Energy Resources Engineering, Pukyong National University
2Dept. of Nuclear Safety Research, Korea Institute of Nuclear Safety

Correspondence to : *Corresponding author : mgodo@kins.re.kr

Received: January 25, 2022; Revised: February 10, 2022; Accepted: February 14, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The mechanical and thermal properties of the rock masses can affect the performance associated with both the isolating and retarding capacities of radioactive materials within the deep geological disposal system for High-Level Radioactive Waste (HLW). In this study, the essential parameters for the site descriptive model (SDM) related to the rock mechanics and thermal properties of the HLW disposal facilities site were reviewed, and the technical background was explored through the cases of the preceding site descriptive models developed by SKB (Swedish Nuclear and Fuel Management Company), Sweden and Posiva, Finland. SKB and Posiva studied parameters essential for the investigation and evaluation of mechanical and thermal properties, and derived a rock mechanics site descriptive model for safety evaluation and construction of the HLW disposal facilities. The rock mechanics SDM includes the results obtained from investigation and evaluation of the strength and deformability of intact rocks, fractures, and fractured rock masses, as well as the geometry of large-scaled deformation zones, the small-scaled fracture network system, thermal properties of rocks, and the in situ stress distribution of the disposal site. In addition, the site descriptive model should provide the sensitivity analysis results for the input parameters, and present the results obtained from evaluation of uncertainty.

Keywords high-level radioactive waste, rock mechanics, site characterization, fractured rock mass, site descriptive model

고준위방사성폐기물 처분시설 부지에 대한 암반역학 부지특성화

엄정기1 · 현승규2,*

1부경대학교 에너지자원공학과
2한국원자력안전기술원 원자력안전연구실

요 약

암반의 역학적 및 열적 특성은 고준위방사성폐기물(high-level radioactive waste; HLW) 심지층 처분시스템 내 방사성 물질의 격리 및 이동 지연 능력과 관련된 성능에 영향을 미칠 수 있다. 이 연구는 HLW 처분시설 부지의 암반역학적 및 열적 특성과 관련된 부지설명모델에 필수적인 항목을 고찰하고 스웨덴과 핀란드의 선행 부지설명모델 사례를 통한 기술적 배경을 논의하였다. 스웨덴 SKB (Swedish Nuclear and Fuel Management Company)와 핀란드 Posiva는 암반역학적 및 열적 특성 조사·평가에 필수적인 항목을 제시하고 부지의 안전성 분석과 처분시설의 건설을 위한 암반역학 부지설명모델을 도출하였다. 암반역학 부지설명모델은 처분시설 부지 내 응력 분포와 더불어 신선암, 절리, 절리성 암반에 대한 강도 및 변형특성과 대규모 변형대의 기하학적 구조, 소규모 불연속면의 연결망 구조 및 암석의 열적 특성에 대한 조사·평가 결과를 포함한다. 또한, 암반역학 부지설명모델은 입력변수에 대한 민감도 분석결과와 입력변수의 불확실성에 대한 평가 결과를 제시하여야 한다.

주요어 고준위방사성폐기물, 암반역학, 부지특성화, 절리성 암반, 부지설명모델

Article

Review

Econ. Environ. Geol. 2022; 55(1): 1-17

Published online February 28, 2022 https://doi.org/10.9719/EEG.2022.55.1.1

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Rock Mechanics Site Characterization for HLW Disposal Facilities

Jeong-Gi Um1, Seung Gyu Hyun2,*

1Dept. of Energy Resources Engineering, Pukyong National University
2Dept. of Nuclear Safety Research, Korea Institute of Nuclear Safety

Correspondence to:*Corresponding author : mgodo@kins.re.kr

Received: January 25, 2022; Revised: February 10, 2022; Accepted: February 14, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The mechanical and thermal properties of the rock masses can affect the performance associated with both the isolating and retarding capacities of radioactive materials within the deep geological disposal system for High-Level Radioactive Waste (HLW). In this study, the essential parameters for the site descriptive model (SDM) related to the rock mechanics and thermal properties of the HLW disposal facilities site were reviewed, and the technical background was explored through the cases of the preceding site descriptive models developed by SKB (Swedish Nuclear and Fuel Management Company), Sweden and Posiva, Finland. SKB and Posiva studied parameters essential for the investigation and evaluation of mechanical and thermal properties, and derived a rock mechanics site descriptive model for safety evaluation and construction of the HLW disposal facilities. The rock mechanics SDM includes the results obtained from investigation and evaluation of the strength and deformability of intact rocks, fractures, and fractured rock masses, as well as the geometry of large-scaled deformation zones, the small-scaled fracture network system, thermal properties of rocks, and the in situ stress distribution of the disposal site. In addition, the site descriptive model should provide the sensitivity analysis results for the input parameters, and present the results obtained from evaluation of uncertainty.

Keywords high-level radioactive waste, rock mechanics, site characterization, fractured rock mass, site descriptive model

고준위방사성폐기물 처분시설 부지에 대한 암반역학 부지특성화

엄정기1 · 현승규2,*

1부경대학교 에너지자원공학과
2한국원자력안전기술원 원자력안전연구실

Received: January 25, 2022; Revised: February 10, 2022; Accepted: February 14, 2022

요 약

암반의 역학적 및 열적 특성은 고준위방사성폐기물(high-level radioactive waste; HLW) 심지층 처분시스템 내 방사성 물질의 격리 및 이동 지연 능력과 관련된 성능에 영향을 미칠 수 있다. 이 연구는 HLW 처분시설 부지의 암반역학적 및 열적 특성과 관련된 부지설명모델에 필수적인 항목을 고찰하고 스웨덴과 핀란드의 선행 부지설명모델 사례를 통한 기술적 배경을 논의하였다. 스웨덴 SKB (Swedish Nuclear and Fuel Management Company)와 핀란드 Posiva는 암반역학적 및 열적 특성 조사·평가에 필수적인 항목을 제시하고 부지의 안전성 분석과 처분시설의 건설을 위한 암반역학 부지설명모델을 도출하였다. 암반역학 부지설명모델은 처분시설 부지 내 응력 분포와 더불어 신선암, 절리, 절리성 암반에 대한 강도 및 변형특성과 대규모 변형대의 기하학적 구조, 소규모 불연속면의 연결망 구조 및 암석의 열적 특성에 대한 조사·평가 결과를 포함한다. 또한, 암반역학 부지설명모델은 입력변수에 대한 민감도 분석결과와 입력변수의 불확실성에 대한 평가 결과를 제시하여야 한다.

주요어 고준위방사성폐기물, 암반역학, 부지특성화, 절리성 암반, 부지설명모델

    Fig 1.

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    Figure 1.Scale dependent strength and deformability (SKB, 2001).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 2.

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    Figure 2.Distribution of (a) uniaxial compressive strength, (b) crack initiation strength and (c) indirect tensile strength of main rock types in Olkiluoto, Finland (Posiva, 2012a).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 3.

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    Figure 3.Hoek-Brown and Mohr-Coulomb failure envelopes for main rock types in Forsmark, Sweden (SKB, 2007a).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 4.

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    Figure 4.Distribution of (a) Young’s modulus and (b) Poisson’s ratio of main rock types at Forsmark, Sweden (SKB, 2007a)
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 5.

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    Figure 5.Estimated Q and RMR values from Forsmark, Sweden (SKB, 2007a).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 6.

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    Figure 6.Histogram of GSI values estimated from Olkiluoto, Finland; (a) top part (Z > -125m) and (b) bottom part (Z < -125m) (Posiva, 2012b).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 7.

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    Figure 7.Generated DFN model for diorite in Forsmark, Sweden (SKB, 2002a).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 8.

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    Figure 8.Maximum and minimum P-wave velocities with respect to depth of the borehole KMF01A (SKB, 2003).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 9.

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    Figure 9.Direction of maximum horizontal stress around Forsmark, Sweden (modified from www.world-stress-map.org).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 10.

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    Figure 10.Recommended stress gradients for Forsmark area (SKB, 2007b).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 11.

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    Figure 11.Estimated in-situ stresses at Olkiluoto, Finland; (a) magnitude of maximum horizontal stress, (b) magnitude of minimum horizontal stress and (c) direction of maximum horizontal stress (Posiva, 2012a).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 12.

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    Figure 12.3-D conceptual model for a brittle deformation zone at Forsmark, Sweden (SKB, 2007c).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 13.

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    Figure 13.3-D model of the deformation zone at Forsmark, Sweden (SKB, 2007c).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 14.

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    Figure 14.Fracture domain delineated form Forsmark, Sweden; (a) 2-D and (b) 3-D (SKB, 2007d).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 15.

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    Figure 15.Examples of fracture survey at a outcrop of Forsmark, Sweden: (a) fracture outcrop mapping and (b) final fitted fracture sets (SKB, 2007d).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Fig 16.

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    Figure 16.Distribution of thermal conductivity with respect to depth at Forsmark, Sweden (SKB, 2008).
    Economic and Environmental Geology 2022; 55: 1-17https://doi.org/10.9719/EEG.2022.55.1.1

    Table 1 . Strength and deformability of Olkiluoto gneisses (GN) and pegmatite granite (PGR) at Onkalo tunnel, Finland (POPSIVA, 2012b).

    ParameterRock typeMean valueStandard deviation95% conf. limitsNumber of samples
    Young’s modulus, E (GPa)GN601031/81109
    PGR60847 / 7313
    Poisson’s ratio, v (mm/mm)GN0.250.040.15/0.33109
    PGR0.290.060.14/0.3413
    Uniaxial compressive strength, UCSGN1082658/16194
    (MPa)PGR1022756/14613
    Crack damage stress, σCD(MPa)GN992651/15384
    PGR851756/11313
    Crack initiation stress, σCD(MPa)GN521234/8385
    PGR571235/7712
    Indirect tensile strength, σT,I(MPa)GN12.12.96.6/17.498
    PGR8.92.14.6/12.051
    Direct tensile strength, σT,D (MPa)GN7.61.55.9/10.318
    PGR--0
    Mode I fracture toughness, K*ICGN2.290.571.43/3.019
    Chevron bend, (MPa1/2)PGR1.580.21.39/1.773
    Mode I fracture toughness, K*ICGN1.580.510.96/2.399
    Brazilian disk experiment, (MPa1/2)PGR1.120.11.02/1.213
    Mode II fracture toughness, K*IICGN3.470.392.87/4.049
    Punch-through with conf. (MPa1/2)PGR3.300.472.89/3.773

    Table 2 . Estimated Hoek-Brown strength parameters from rock domain RFM029 at Forsmark, Sweden (SKB, 2007a).

    Fracture domainRock typeNumber of samplesMin. strength1Mean strengthMax. strength2
    UCS (MPa)miUCS (MPa)miUCS (MPa)mi
    FFM01Granite to granodiorite, metamorphic, medium grained86149312252829926
    FFM01Granite, granodiorite and tonalite, metamorphic, fine-to medium-grained4136501654619442
    FFM01Pegmatite, pegmatitic granite15165192271828917
    FFM03Granite to granodiorite, metamorphic, medium grained25196292212824628
    FFM03Tonalite to granodiorite, metamorphic8142131511316013

    1 Lower envelope, 95% probability..

    2 Upper envelope, 95% probability..

    Table 3 . Estimated Mohr-Coulomb strength parameters from rock domain RFM029 at Forsmark, Sweden (SKB, 2007a).

    Fracture domainRock typeNumber of samplesMin. strength1Mean strengthMax. strength2
    C (MPa)Φ (°)C (MPa)Φ (°)C (MPa)Φ (°)
    FFM01Granite to granodiorite, metamorphic, medium grained86195928603661
    FFM01Granite, granodiorite and tonalite, metamorphic, fine to medium grained4176219632263
    FFM01Pegmatite, pegmatitic granite15245533564256
    FFM03Granite to granodiorite, metamorphic, medium grained25246027603061
    FFM03Tonalite to granodiorite, metamorphic8245125512651

    1 Lower envelope, 95% probability..

    2 Upper envelope, 95% probability..

    Table 4 . Summary of strength properties from direct shear tests for the fracture domains at Forsmark, Sweden (SKB, 2007a).

    Fracture domainPeak friction (°)Peak cohesion (MPa)Residual friction (°)Residual cohesion (MPa)
    mean/std. dev.mean/std. dev,mean/std. dev.mean/std. dev.
    min - maxmin - maxmin - maxmin - max
    uncertainty of μuncertainty of μuncertainty of μuncertainty of μ
    FFM0136.6/2.90.8/0.334.9/3.40.3/0.2
    29.3 - 42.00.2 - 1.327.9 - 41.90.1 - 0.8
    ±2.9%±13.7%±3.6%±24.3%
    FFM0236.4/2.50.5/0.434.8/7.30.4/0.6
    34.4 - 40.00.2 - 1.024.1 - 40.30.1 - 1.3
    ±6.7%±78.4%±20.6%±147.0%
    FFM0337.0/1.70.6/0.234.2/6.20.5/0.4
    34.2 - 39.00.3 - 0.925.7 - 41.50.2 - 1.1
    ±3.0%±21.8%±11.8%±52.3%
    FFM0432.0/3.30.9/0.432.2/2.50.3/0.1
    28.5 - 35.00.6 - 1.429.6 - 34.60.2 - 0.4
    ±11.7%±50.3%±8.8%±37.7%
    FFM0537.0/1.80.8/0.234.3/3.00.4/0.1
    35.7 - 38.20.7 - 0.932.2 - 36.40.4 - 0.5
    ±6.7%±34.7%±12.1%±34.7%
    DZ35.3/2.40.8/0.534.8/2.00.3/0.2
    32.5 - 38.40.0 - 1.730.3 - 36.80.0 - 0.6
    ±4.2%±38.7%±3.6%±41.3%

    Note: The uncertainty of the mean is quantified for a 95% confidence interval. Minimum and maximum truncation values are based on the observed min. and max. for the tested population..

    Table 5 . Summary of deformability properties from direct shear tests for the fracture domains at Forsmark, Sweden (SKB, 2007a).

    Fracture domainNormal stiffness, Kn (GPa/m)Shear stiffness, KS0.5 (GPa/m)Shear stiffness, KS5.0 (GPa/m)Shear stiffness, KS20.0 (GPa/m)
    mean/std. dev.mean/std. dev.mean/std. dev.mean/std. dev.
    min - maxmin - maxmin - maxmin - max
    uncertainty of μuncertainty of μuncertainty of μuncertainty of μ
    FFM01656/39610/626/934/10
    159 - 1,8331 - 237 - 4618 - 52
    ±22.0%±21.8%±12.6%±10.7%
    FFM02248/1658/426/433/8
    115 - 4834 - 1221 - 3125 - 41
    ±65.2%±49.0%±15.1%±23.8%
    FFM03293/1938/431/735/10
    152 - 7344 - 1523 - 4320 - 49
    ±43.0%±32.7%±14.8%±18.7%
    FFM041,385/2838/616/523/5
    1,072 - 1,6241 - 1212 - 2218 - 29
    ±23.1%±84.9%±35.4%±24.6%
    FFM05599/576/320/725/2
    559 - 6394 - 814 - 2523 - 26
    ±13.2%±69.3%±48.5%±11.2%
    DZ662/72912/1026/931/8
    167 - 2,4453 - 357 - 4119 - 44
    ±68.3%±51.7%±21.5%±16.0%

    Note: The uncertainty of the mean is quantified for a 95% confidence interval. Minimum and maximum truncation values are based on the observed min. and max. for the tested population..

    Table 6 . Comparison of the results from SDM 1.2 and modelling stage 2.2 for the rock mass outside deformation zones in domain RFM029 (SKB, 2007a).

    Rock mass parameterForsmark v1.2Forsmark v2.2
    minmean/std devmaxminmean/std devmax
    Q*7370 [86]2,1332363 [100]2,133
    RMR7387/6987187/698
    Em (GPa)3769/10753469/1076
    Vm0.120.22/0.030.270.110.22/0.030.30
    UCSm (H-B) (MPa)1880/291532384/28153
    Φm (°)4049/2513249/252
    cm (MPa)1525/4351226/435
    UCSm (M-C) (MPa)63134/2619644138/25196
    Tm (MPa)0.32/150.52/15

    * Mode values are shown in brackets..

    Table 7 . Estimated strength and deformability of fractured rock mass at Forsmark, Sweden (SKB, 2002b).

    LithologyRock mass strengthRock mass modulusPoisson’s ratio
    mean (MPa)5/95 percentiles (MPa)covmean (GPa)5/95 percentiles (MPa)covmean5/95 percentiles (MPa)cov
    Äspö diorite140.183 - 1980.2537.225 - 490.200.340.28 - 0.420.15
    Småland granite124.373 - 1750.2542.028 - 560.200.320.28 - 0.400.15
    Fine grained granite114.468 - 1610.2536.424 - 480.200.310.28 - 0.390.15
    Mixed lithology75.044 - 1060.2536.424 - 480.200.320.28 - 0.390.15

    Table 8 . Inter relationships between Vp, Em and Qc (Barton, 2002).

    Qc0.0010.010.11.0101001000
    Vp0.51.52.53.54.55.56.5 km/s
    Em1.02.24.61021.546.4100 GPa

    Table 9 . Measured thermal conductivity (W/(m·K)) at Forsmark, Sweden (SKB, 2008).

    Rock codeRock nameMeanSt. dev.MaxMinNo. of samples
    101057Granite to granodiorite， metamorphic, medium-grained3.680.174.013.25741
    101056Granodiorite, metamorphic3.040.093.202.985
    101054Tonalite to granodiorite, metamorphic2.730.192.942.455
    101051Granite, granodiorite and tonalite, metamorphic, fine- to medium-grained2.850.263.392.4612
    101058Granite, metamorphic, aplftic3.850.134.063.68122
    101061Pegmatite, pegmatitic granite3.330.203.503.074
    102017Amphibolite2.330.102.482.2112
    111058Granite, fine- to medium-grained3.470.173.623.225
    103076Felsic to intermediate volcanic rock, metamorphic2.542.992.092
    101033Diorite, quartz diorite and gabbro, metamorphic2.281

    1Includes four oxidised samples. 2Both altered and unaltered samples included..

    Table 10 . Measured thermal expansion (m/(m·K)) at Forsmark, Sweden (SKB, 2008).

    Rock codeRock nameMeanSt. dev.MinMaxNo. of samples
    101057Granite to granodiorite7.7 · 10-62.2 · 10-62.1 · 10-61.5 · 10-556
    101056Granodiorite8.1 · 10-63.4 · 10-65.2 · 10-61.4 · 10-56
    101054Tonalite to granodiorite7.2 · 10-65.3 · 10-68.2 · 10-53
    101051Granite, granodiorite and tonalite7.8 · 10-61.2 · 10-66.5 · 10-61.0 · 10-56
    101058Granite, aplitic7.5 · 10-66.9 · 10-68.0 · 10-53

    KSEEG
    Dec 31, 2024 Vol.57 No.6, pp. 665~835
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