JAEA-Review
2016-014
DOI:10.11484/jaea-review-2016-014

Synthesized Research Report in the Second Mid-term
Research Phase－ Mizunami Underground Research Laboratory Project, Horonobe UndergroundResearch Laboratory Project and Geo-stability Project －(Translated Document)(Translated by) Katsuhiro HAMA, Eiji SASAO, Teruki IWATSUKI, Hironori ONOE
Toshinori SATO, Tomoo FUJITA, Hiroshi SASAMOTO, Toshiyuki MATSUOKA
Masaki TAKEDA, Kazuhei AOYAGI, Masashi NAKAYAMA, Kazuya MIYAKAWA
Takuya OHYAMA, Kenichi YASUE, Koichi ASAMORI, Masakazu NIWA
Hideaki OSAWA, Hiroaki ITO, Isako NAGAE, Ryoko NATSUYAMA
Takeshi SENBA and Kenji AMANO

Geoscientific Research Department
Tono Geoscience Center
Sector of Decommissioning and Radioactive Waste Management

August 2016
Japan Atomic Energy Agency

日本原子力研究開発機構

本レポートは国立研究開発法人日本原子力研究開発機構が不定期に発行する成果報告書です。
本レポートの入手並びに著作権利用に関するお問い合わせは、下記あてにお問い合わせ下さい。
なお、本レポートの全文は日本原子力研究開発機構ホームページ（http://www.jaea.go.jp）
より発信されています。
国立研究開発法人日本原子力研究開発機構 研究連携成果展開部 研究成果管理課〒319-1195 茨城県那珂郡東海村大字白方 2 番地4
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Tel +81-29-282-6387, Fax +81-29-282-5920, E-mail:ird-support@jaea.go.jp© Japan Atomic Energy Agency, 2016

JAEA-Review 2016-014
Synthesized Research Report in the Second Mid-term Research Phase－Mizunami Underground Research Laboratory Project, Horonobe Underground ResearchLaboratory Project and Geo-stability Project－(Translated Document)(Translated by) Katsuhiro HAMA, Eiji SASAO, Teruki IWATSUKI,
Hironori ONOE, Toshinori SATO, Tomoo FUJITA+1, Hiroshi SASAMOTO+1,
Toshiyuki MATSUOKA+1, Masaki TAKEDA+1, Kazuhei AOYAGI+1, Masashi NAKAYAMA+1,
Kazuya MIYAKAWA+1, Takuya OHYAMA+3, Kenichi YASUE, Koichi ASAMORI,
Masakazu NIWA, Hideaki OSAWA, Hiroaki ITO+1, Isako NAGAE, Ryoko NATSUYAMA,
Takeshi SENBA+2 and Kenji AMANO+2
Geoscientific Research Department, Tono Geoscience Center
Sector of Decommissioning and Radioactive Waste Management
Japan Atomic Energy Agency
Akiyo-cho, Mizunami-shi, Gifu-ken(Received May 27, 2016)
We have synthesized the research results from the Mizunami/Horonobe UndergroundResearch Laboratories (URLs) and geo-stability projects in the second mid-term researchphase. This report can be used as a technical basis for the Nuclear Waste Management
Organization of Japan/Regulator at each decision point from siting to beginning of disposal(Principal Investigation to Detailed Investigation Phase). High-quality construction
techniques and field investigation methods have been developed and implemented, which will
be directly applicable to the National Disposal Program (together with general assessments ofhazardous natural events and processes). Acquisition of technical knowledge on decisions ofpartial backfilling and final closure from actual field experiments in the Mizunami/Horonobe
URLs will be crucial as the main theme for the next phases.
Keywords: Mizunami Underground Research Laboratory, Horonobe Underground ResearchLaboratory, Long-term Stability of Geological Environment, Second Mid-term Research Phase,
Geological Disposal of HLWThis document is the English translation of “Synthesized Research Report in the Second
Mid-term Research Phase” (JAEA-Research 2015-007).
+1 Horonobe Underground Research Center+2 Geological Disposal Research and Development Department+3 Fukushima Environmental Safety Center, Sector of Fukushima Research andDevelopmenti

JAEA-Review 2016-014
第 2 期中期計画期間における研究成果取りまとめ報告書－深地層の研究施設計画および地質環境の長期安定性に関する研究－（翻訳資料）
日本原子力研究開発機構
バックエンド研究開発部門
東濃地科学センター
（訳）濱

克宏，笹尾

笹本

広+1，松岡大山卓也+3，安江
長江

輝希，尾上

博則，佐藤

稔紀，藤田

朝雄+1，

匡樹+1，青柳

和平+1，中山雅+1，宮川

和也+1，

浩一，丹羽

正和，大澤

英昭，伊藤

洋昭+1，

毅+2，天野

健治+2

英嗣，岩月

稔幸+1，武田地層科学研究部

健一，浅森衣佐子，夏山諒子，仙波（2016 年 5 月 27 日受理）
国立研究開発法人日本原子力研究開発機構は，高レベル放射性廃棄物の地層処分の実現に向けた国の第 2 期中期目標（平成 22～26 年度）に基づき中期計画を策定し，処分事業と国による安全規制の両面を支える技術基盤を整備するため，地層処分研究開発と深地層の科学的研究の 2 つの領域において研究開発を進めている。今般，本中期計画期間における深地層の科学的研究分野（超深地層研究所計画，幌延深地層研究計画，地質環境の長期安定性に関する研究）の成果を取りまとめるにあたり，処分事業におけるサイト選定から処分開始に関する意思決定ポイントまでに必要な技術情報を事業者・規制機関が活用し易い形式で体系化し，所期の目標の精密調査（前半）の段階に必要となる技術基盤として整備した。
本成果で体系化された調査解析技術は，地層処分場の許認可段階にある国外の地層処分事業（スウェーデン，フィンランド）での適用技術と比肩しうる網羅性と品質を有しており，地震・断層，
火山などの天然現象の高精度調査解析技術との組み合わせにより，わが国の地質環境に適応したより幅広い地質環境特性のシナリオに対応可能である。
今後は，部分的埋め戻しや廃棄体定置終了，最終閉鎖に関する意思決定ポイントに必要な技術基盤を整備するために，これらに関する先進的な研究開発を深地層の研究施設において実施し，世界をリードする地層処分技術として国内外に広く発信していく。
本報告書は，「第 2 期中期計画期間における研究成果取りまとめ報告書－深地層の研究施設計
画および地質環境の長期安定性に関する研究」（JAEA-Research 2015-007）を英訳したものである。
東濃地科学センター：〒509-6132

岐阜県瑞浪市明世町山野内 1-64

+1 幌延深地層研究センター+2 地層処分研究開発推進部+3 福島研究開発部門

福島環境安全センター

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Contents
1.

Introduction ...........................................................................................................................1
1.1 Background and current status of the Underground Research Laboratory project andresearch on geosphere stability for long-term isolation of radioactive waste .................1
1.2 Integration of research results and chronological framework for reporting ...................2
1.3 Core messages of major research results in the second mid-term research phase .........4
References..................................................................................................................................62.

Understanding of the initial geo-environmental conditions ................................................7
2.1 Geology ...............................................................................................................................7
References................................................................................................................................20
2.2 Hydrogeology ....................................................................................................................26
References................................................................................................................................44
2.3 Hydrogeochemistry ..........................................................................................................49
References................................................................................................................................60
2.4 Rock mechanics ................................................................................................................61
References................................................................................................................................72
2.5 Mass transport .................................................................................................................75
References................................................................................................................................82
2.6 Engineering technology for deep underground applications ..........................................85
References................................................................................................................................91
2.7 Geosphere stability for long-term isolation of radioactive waste...................................94
References..............................................................................................................................103

3.

Understanding impact of construction in geo-environmental conditions .......................107
3.1 Geology ...........................................................................................................................107
References.............................................................................................................................. 111
3.2 Hydrogeology .................................................................................................................. 112
References..............................................................................................................................123
3.3 Hydrogeochemistry ........................................................................................................125
References..............................................................................................................................142
3.4 Rock mechanics ..............................................................................................................143
References..............................................................................................................................150
3.5 Mass transport ...............................................................................................................152
References..............................................................................................................................171
3.6 Engineering technology for deep underground applications ........................................174
References..............................................................................................................................185
3.7 Performance and setting condition of the engineering barrier ....................................188
References..............................................................................................................................194iii

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4.

Understanding long-term changing/recovering behavior of geo-environmental conditions............................................................................................................................................195
4.1 Geology ...........................................................................................................................195
References..............................................................................................................................206
4.2 Hydrogeology ..................................................................................................................209
References..............................................................................................................................219
4.3 Hydrogeochemistry ........................................................................................................221
References..............................................................................................................................233
4.4 Rock mechanics ..............................................................................................................235
References..............................................................................................................................238
4.5 Mass transport ...............................................................................................................241
References..............................................................................................................................247
4.6 Geosphere stability for long-term isolation ..................................................................249
References..............................................................................................................................258

5.

Tool development for integration of knowledge from each research result.....................261
5.1 Introduction ....................................................................................................................261
5.2 Concept of ISIS ...............................................................................................................262
5.3 Results ............................................................................................................................264
5.4 Summary ........................................................................................................................270
References..............................................................................................................................271

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目次
1.

はじめに ..................................................................................................................................1
1.1 深地層の研究施設計画および地質環境の長期安定性に関する研究の経緯と現状............................................................................................................................................1
1.2 研究成果の統合化に向けた基本方針と成果の構造 ..............................................................2
1.3 第 2 期中期計画における主要成果のコアメッセージ ..........................................................4
参考文献 .....................................................................................................................................62.

地質環境の初期状態の理解（成果ダイジェスト A1 群） .......................................................7
2.1 地質・地質構造 ...................................................................................................................7
参考文献 ...................................................................................................................................20
2.2 岩盤水理 ............................................................................................................................26
参考文献 ...................................................................................................................................44
2.3 地下水の地球化学特性 .......................................................................................................49
参考文献 ...................................................................................................................................60
2.4 岩盤力学 ............................................................................................................................61
参考文献 ...................................................................................................................................72
2.5 物質移動 ............................................................................................................................75
参考文献 ...................................................................................................................................82
2.6 深地層における工学技術 ...................................................................................................85
参考文献 ...................................................................................................................................91
2.7 地質環境の長期安定性 .......................................................................................................94
参考文献 .................................................................................................................................103

3.

地質環境の短期変動・回復挙動の理解（成果ダイジェスト A2 群）..................................107
3.1 地質・地質構造 ...............................................................................................................107
参考文献 ................................................................................................................................. 111
3.2 岩盤水理 .......................................................................................................................... 112
参考文献 .................................................................................................................................123
3.3 地下水の地球化学特性 .....................................................................................................125
参考文献 .................................................................................................................................142
3.4 岩盤力学 ..........................................................................................................................143
参考文献 .................................................................................................................................150
3.5 物質移動 ..........................................................................................................................152
参考文献 .................................................................................................................................171
3.6 深地層における工学技術 .................................................................................................174
参考文献 .................................................................................................................................185
3.7 人工バリアの設置環境と性能 ..........................................................................................188
参考文献 .................................................................................................................................194v

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4.

地質環境の長期変動・回復挙動の理解（成果ダイジェスト A3 群）..................................195
4.1 地質・地質構造 ...............................................................................................................195
参考文献 .................................................................................................................................206
4.2 岩盤水理 ..........................................................................................................................209
参考文献 .................................................................................................................................219
4.3 地下水の地球化学特性 .....................................................................................................221
参考文献 .................................................................................................................................233
4.4 岩盤力学 ..........................................................................................................................235
参考文献 .................................................................................................................................238
4.5 物質移動 ..........................................................................................................................241
参考文献 .................................................................................................................................247
4.6 地質環境の長期安定性 .....................................................................................................249
参考文献 .................................................................................................................................258

5.

成果の統合および知識の伝達・伝承ツールの整備 .............................................................261
5.1 はじめに ..........................................................................................................................261
5.2 ISIS の概要 .....................................................................................................................262
5.3 実施内容と成果 ...............................................................................................................264
5.4 まとめと今後の課題 ........................................................................................................270
参考文献 .................................................................................................................................271

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List of Figures
Fig. 1.1-1

Bird’s-eye/cutaway view of the Underground Research Facilities (Mizunami andHoronobe; prepared in September 2014) ..............................................................2

Fig. 1.2.1-1

Chronological history of CoolRep ..........................................................................3

Fig. 1.2.2-1

Structure of the kernel of the URL project and research on geosphere stability................................................................................................................................4

Fig. 1.3-1

An example of core messages in the results and issues digest map (part of theA2 group) ................................................................................................................6

Fig. 2.1.3-1Comparison of the geological models constructed during the surface-based
investigation phase (Phase I) and in the second mid-term research phase ........9

Fig. 2.1.3-2

Confirmation of the boundary the between Koetoi and Wakkanai Formations..............................................................................................................................10

Fig. 2.1.3-3

Distribution of faults on the basis of geophysical investigation from groundsurface (left), and the estimated distribution of Fault A (right) ........................12

Fig. 2.1.3-4

Geological model of the Horonobe area prepared on the basis of the Phase I
investigation results ............................................................................................13

Fig. 2.1.3-5

Geological map of the ventilation and east shafts of the Horonobe URL .........14

Fig. 2.1.3-6

Shear fractures related to faults in the upper Wakkanai Formation (G.L. −250
m in the ventilation shaft)...................................................................................15

Fig. 2.1.3-7

Change in self-potential (upper) and hydraulic head in the MIZ-1 borehole withan inflow rate into the shafts (lower) .................................................................16

Fig. 2.1.3-8

Interpretation around the Omagari Fault by seismic reflection survey andborehole investigations ........................................................................................17

Fig. 2.1.3-9

Interpretation of the geological structure by AMT survey and borehole
investigations .......................................................................................................18

Fig. 2.1.3-10 Distribution of tensile fractures and ductility measurements (∝-1BRI)...........18
Fig. 2.1.3-11 Rock domain classified by the competence factor, and geological and hydraulicproperties of fractures in each domain ...............................................................19
Fig. 2.2.3-1

Stepwise evolution of the results of groundwater flow analyses (MIU) ............28

Fig. 2.2.3-2

Stepwise evolution of the results of groundwater flow analyses (Horonobe)....29

Fig. 2.2.3-3

Groundwater inflow rate into the underground facilities (MIU) ......................31

Fig. 2.2.3-4

Hydraulic responses caused by construction of underground facilities (MIU)..............................................................................................................................31

Fig. 2.2.3-5

Concept of hydrogeological modeling taking hydrogeological heterogeneity into
account (MIU) ......................................................................................................32

Fig. 2.2.3-6

Procedure for revising the hydrogeological model .............................................32

Fig. 2.2.3-7

Comparison of measured and modeled groundwater inflow rates (MIU) .........33

Fig. 2.2.3-8

Comparison of measured and modeled hydraulic responses (MIU) ..................33

Fig. 2.2.3-9

Improvement in understanding of groundwater flow conditions with stepwise
progress of the investigations .............................................................................34vii

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Fig. 2.2.3-10 Changes in Cl− concentrations based on advection–dispersion analysis ..........34
Fig. 2.2.3-11 Stepwise evolution of the results of groundwater flow analyses (MIU) ............35
Fig. 2.2.3-12 Groundwater inflow rate into the underground facilities (Horonobe) ..............36
Fig. 2.2.3-13 Hydraulic responses because of inflow into the ventilation shaft andhydrogeological model (Horonobe) ......................................................................37
Fig. 2.2.3-14 Comparison of measured and modeled groundwater inflow rates (Horonobe)..............................................................................................................................37
Fig. 2.2.3-15 Comparison of measured and modeled hydraulic responses (Horonobe) ..........38
Fig. 2.2.3-16 Improvements in understanding of the groundwater flow conditions withstepwise progress of the investigations (Horonobe) ...........................................38
Fig. 2.2.3-17 Evolution of the hydrogeological model around the shafts (Horonobe) ............39
Fig. 2.2.3-18 Discrete fracture network model for estimation of the inflow rate into
underground facilities .........................................................................................40
Fig. 2.2.3-19 Example of a risk curve showing the risk regarding cost variation for thecountermeasures..................................................................................................41
Fig. 2.2.3-20 Tools for supporting the rapid construction of geological environmental models..............................................................................................................................41
Fig. 2.2.4-1

Sequential hydraulic testing procedure (MIU) ..................................................43

Fig. 2.2.4-2

Sequential hydraulic testing procedure (Horonobe) ..........................................43

Fig. 2.2.4-3

Example of fluid logging (MIU)...........................................................................44

Fig. 2.3.3-1

Distribution of groundwater chemistry and the hydrochemical model
constructed from surface-based investigations (MIU) .......................................50

Fig. 2.3.3-2

Distribution of groundwater chemistry (salinity) and the hydrochemical model
constructed from surface-based investigations (Horonobe) ...............................51

Fig. 2.3.3-3Comparison of Cl concentrations in groundwater estimated by surface-based
investigations and by investigations during the construction phase ................52

Fig. 2.3.3-4

Results of surface-based electrical surveys and resistivity logging using
boreholes (upper), and the distribution of Cl concentrations in groundwater(lower) ..................................................................................................................53

Fig. 2.3.3-5

Contamination by iron compounds on a borehole wall caused by drilling (left:
immediately after drilling, right: after formation of films) ...............................54

Fig. 2.3.3-6

pH and redox conditions of groundwater obtained by surface-based
investigation and by investigation during the construction phase (MIU) ........55

Fig. 2.3.3-7

Variation in physicochemical parameters during pumping at borehole MIZ-1,
Section 9 (1150 mabh (meter along borehole)) ...................................................55

Fig. 2.3.3-8

pH and redox conditions of groundwater obtained during the surface-based
investigation and construction phases (Horonobe) ............................................56

Fig. 2.3.3-9

Groundwater residence time estimated based on 36Cl and 4He, and groundwaterevolution process estimated from δ18O and δD depth profiles (Horonobe)........57

Fig. 2.3.4-1

Procedure for hydrogeochemical modelling during surface-based investigations..............................................................................................................................59

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Fig. 2.4.3-1

Comparison of the in situ stress distributions from measured and analyzed
values (Mizunami) ...............................................................................................63

Fig. 2.4.3-2

Countermeasures against inflow during initial stress measurement by compact
conical-ended borehole overcoring technique .....................................................63

Fig. 2.4.3-3

Locations of the stress measurements in the galleries ......................................65

Fig. 2.4.3-4

Stress magnitudes and orientations obtained in the galleries indicated on Wolf
net diagrams, lower-hemisphere projections......................................................66

Fig. 2.4.3-5

Values of maximum and minimum horizontal stress measured in the galleries
and HDB-1 ...........................................................................................................67

Fig. 2.4.3-6

Orientations of the maximum horizontal stress measured in the galleries and
HDB-1, 3, 6, and 11 .............................................................................................67

Fig. 2.4.3-7

Depth distribution of the physical and mechanical properties of rock (Mizunami)..............................................................................................................................68

Fig. 2.4.3-8

Conceptual model of rock mechanics (Mizunami) ..............................................69

Fig. 2.4.3-9

Locations of the plate-loading tests and direct shear tests ...............................70

Fig. 2.4.3-10 Results of the plate-loading tests ........................................................................70
Fig. 2.4.3-11 Results of the direct shear tests..........................................................................71
Fig. 2.5.1-1

Geosynthesis data flow diagram (mass transport study) ..................................75

Fig. 2.5.3-1

Laboratory through-diffusion testing equipment...............................................77

Fig. 2.5.3-2

Results from the laboratory experiment.............................................................78

Fig. 2.5.3-3

Advanced through-diffusion/reservoir-depletion method ..................................78

Fig. 2.5.3-4

Depth profiles of (a) sulfate-reducing bacteria, (b) iron-related bacteria, and (c)colloidal particles in the groundwater in the Mizunami area ...........................79

Fig. 2.5.3-5

Humic substances in groundwater at the Horonobe ..........................................80

Fig. 2.5.3-6

Microbial populations related to geological setting in the Horonobe area........81

Fig. 2.6.3-1

Measurement results of the axial forces of the steel support for the Main Shaft(G.L. −250 m) (Mizunami) ...................................................................................86

Fig. 2.6.3-2

Measured maximum acceleration values of earthquakes (Mizunami) .............87

Fig. 2.6.3-3

Comparison of measured and analyzed motion of the Suruga Bay earthquake(2009.8.11) ............................................................................................................87

Fig. 2.6.3-4

Distribution of circumferential stress on concrete lining ..................................89

Fig. 2.6.3-5

Measured and analyzed results of circumferential stresses in a concrete lining..............................................................................................................................90

Fig. 2.6.3-6

Relationship between excavation rate and fracture density in Drifts I and II..............................................................................................................................91

Fig. 2.7.3-1

Spatial distribution of 3He/4He ratios in groundwater around the source regionof the 2000 western Tottori earthquake .............................................................96

Fig. 2.7.3-2

Spatial distribution of 3He/4He ratios along the Itoigawa–Shizuoka Tectonic
Line (ISTL)...........................................................................................................97

Fig. 2.7.3-3

An example of improvement in MT data quality ...............................................98ix

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Fig. 2.7.3-4

3-D resistivity structure in the source region of the Kagoshima earthquake
doublet..................................................................................................................98

Fig. 2.7.3-5

Results of K–Ar dating for fault gouges from the Toki Granite ......................100

Fig. 2.7.3-6

Results of K–Ar dating for fault gouges from the Arima–Takatsuki Tectonic Line............................................................................................................................100

Fig. 2.7.3-7Results of particle size distribution analysis and K–Ar dating for clay fractions
from fractures containing clay infillings in the Kojaku Granite .....................101

Fig. 2.7.3-8(a) Distribution of circular abandoned channels in Japan interpreted from
1:25,000 topographic maps and (b) Histograms of the heights of circular
abandoned channels in Japan relative to present-day channels .....................102

Fig. 2.7.3-9(a) Topographical map of the study area showing the locations and sample codesaround the Suzuka Mountains and (b) Latitude versus apatite fission-track(AFT) ages across the Suzuka Mountains ........................................................103

Fig. 3.1.3-1

Conceptual models showing the fracture formation process before excavation (aand b) and after excavation (c) on the floor of the gallery ...............................109

Fig. 3.1.3-2

Fracture mapping showing all fractures (a), fractures with grout (b), andfractures with grouts and faults (c) .................................................................. 110

Fig. 3.2.3-1

Groundwater inflow rate into the underground facilities (MIU) .................... 114

Fig. 3.2.3-2

Sectional groundwater inflow rate into the underground facilities (MIU) ..... 114

Fig. 3.2.3-3

Hydraulic head distribution in the vicinity of the shafts (MIU) ..................... 115

Fig. 3.2.3-4

Groundwater inflow rate into the underground facilities (Horonobe) ............ 115

Fig. 3.2.3-5

Hydraulic responses caused by construction of underground facilities (MIU)............................................................................................................................ 116

Fig. 3.2.3-6

Method of data processing for specifying hydraulic changes........................... 117

Fig. 3.2.3-7

Changes in the groundwater level of the unconfined aquifer (MIU)............... 117

Fig. 3.2.3-8

Hydraulic responses caused by construction of underground facilities(Horonobe).......................................................................................................... 118

Fig. 3.2.3-9

Changes in the groundwater level of the unconfined aquifer (Horonobe) ...... 119

Fig. 3.2.3-10 Tilt changes during construction of underground tunnels (Horonobe) ........... 119
Fig. 3.2.3-11 Changes in groundwater pressure/moisture and temperature/humidity in thetunnel (Horonobe) ..............................................................................................121
Fig. 3.3.3-1

Hydrochemical monitoring boreholes in and around the MIU ........................127

Fig. 3.3.3-2

Accumulated inflow in each water-collection ring (Apr. 2004–May 2012) ...........
............................................................................................................................129

Fig. 3.3.3-3

Temporal variations of Cl concentrations in groundwater at the Main Shaft andthe Ventilation Shaft .........................................................................................130

Fig. 3.3.3-4

Temporal variations of Cl concentrations in groundwater in the boreholes drilledfrom the gallery .................................................................................................131

Fig. 3.3.3-5

Temporal variations of CFC gas in each monitoring section ...........................131

Fig. 3.3.3-6

Principal component analysis of groundwater chemistry related to shaft sinking............................................................................................................................132x

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Fig. 3.3.3-7

Hydrological/hydrochemical monitoring boreholes at the Horonobe ..............134

Fig. 3.3.3-8

Salinity distribution around the Horonobe ......................................................136

Fig. 3.3.3-9

Salinity evolution related to shaft sinking (Horonobe) ....................................137

Fig. 3.3.3-10 Principal component analysis based on hydrochemical data of Horonobe
groundwater .......................................................................................................138
Fig. 3.4.3-1

Results of equivalent continuum analysis using the crack tensor model .......145

Fig. 3.4.3-2

Strain measurement during shaft sinking .......................................................145

Fig. 3.4.3-3

Comparison of measured and analyzed rock mass displacement ...................145

Fig. 3.4.3-4

Results of discontinuity observations obtained at the shaft wall ....................146

Fig. 3.4.3-5

Relative error of crack tensor vs. relative interval ..........................................146

Fig. 3.4.3-6

Image of the layout of the in situ surveys used for determining the EDZ in thegallery ................................................................................................................147

Fig. 3.4.3-7

Representative results of seismic tomography surveys conducted in the
G.L. −250 m gallery ...........................................................................................148

Fig. 3.4.3-8

Microcracking region around the gallery from the results of FEM analysis............................................................................................................................149

Fig. 3.4.3-9

Conceptual model of the fracture distribution around the gallery..................149

Fig. 3.5.1-1

Geosynthesis data flow diagram (mass transport study) ................................153

Fig. 3.5.3-1

Overview of the test equipment used in the in situ tracer test .......................156

Fig. 3.5.3-2

Reproducibility verified by duplicated tracer migration tests .........................156

Fig. 3.5.3-3

Packer inflation/deflation procedure under gaseous conditions ......................157

Fig. 3.5.3-4

Results of tracer migration tests using uranine and deuterium .....................157

Fig. 3.5.3-5Conceptual model of the relationship between petrography and flow-path
fractures .............................................................................................................158

Fig. 3.5.3-6

Discontinuous geological structures around the Horonobe URL ....................159

Fig. 3.5.3-7

Size distribution of rare earth elements in groundwater in the Toki Granite............................................................................................................................160

Fig. 3.5.3-8

Drilling fluid sterilization system .....................................................................160

Fig. 3.5.3-9

Results of microbial genetic analysis of the groundwater ...............................161

Fig. 3.5.3-10 Normalized concentrations of rare earth elements in groundwater ...............163
Fig. 3.5.3-11 Groundwater analysis using a size-exclusion chromatography coupled plasma
mass spectrometry technique............................................................................163
Fig. 3.5.3-12 Humic substances in groundwater at the Horonobe URL ...............................164
Fig. 3.5.3-13 Sorption in the element/organic substance/sedimentary rock ternary system............................................................................................................................164
Fig. 3.5.3-14 Reservoir-depletion curves (circles) and breakthrough curves (squares) withcoexisting humic substances (laboratory diffusion experiments for Eu and Th)............................................................................................................................165
Fig. 3.5.3-15 Overview of microbial effects on mass transport in the geological environment............................................................................................................................166
Fig. 3.5.3-16 The hydrochemical monitoring system on the circulation line .......................166xi

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Fig. 3.5.3-17 Biofilms collected at the Horonobe URL and imaged using a confocal laser
scanning microscope ..........................................................................................166
Fig. 3.5.3-18 Biofilm diffusion experiment using Cu2+ ..........................................................167
Fig. 3.5.3-19 Results of dipole test simulation .......................................................................168
Fig. 3.5.3-20 Best-fit calculation for the one-dimensional solute transport model ..............168
Fig. 3.6.3-1

Actual excavation cycle time of the Main Shaft ...............................................175

Fig. 3.6.3-2

Designed and actual excavation cycle times of the Main Shaft ......................175

Fig. 3.6.3-3

Calculated results of changes in vertical stress with development of spalling of
the rock mass around the shaft wall in the concrete lining.............................176

Fig. 3.6.3-4

Flowchart for selecting the optimum support pattern in the Ventilation Shaft............................................................................................................................177

Fig. 3.6.3-5

Model for groundwater flow analysis................................................................178

Fig. 3.6.3-6

Results of groundwater flow analysis for post-excavation grouting ...............178

Fig. 3.6.3-7

Post-excavation grouting test............................................................................179

Fig. 3.6.3-8

Results of post-excavation grouting test...........................................................179

Fig. 3.6.3-9Pre-excavation grouting plan for shaft sinking ................................................179

Fig. 3.6.3-10 Confirmation of effectiveness of grouting (groundwater pressure monitoring in
the borehole) ......................................................................................................180
Fig. 3.6.3-11 Countermeasures against spalling at the Main Shaft wall .............................180
Fig. 3.6.3-12 Distribution of faults and volume of grout material injected in two shafts............................................................................................................................181
Fig. 3.6.3-13 Conceptual image of fractures with grout material on the shaft wall ............182
Fig. 3.6.3-14 Ventilation system for Mizunami......................................................................183
Fig. 3.6.3-15 Examination items for ventilation network analysis .......................................183
Fig. 3.6.3-16 Observation of the concrete liner of the shaft using a video camera ..............183
Fig. 3.6.3-17 Durability test of the crack detection sensor using optical fiber .....................184
Fig. 3.6.3-18 Results of the ventilation network analysis in the excavations of the
G.L. −350 m galleries ........................................................................................184
Fig. 3.7.3-1

The areas where HFSC was applied for support and grouting at the Horonobe
URL ....................................................................................................................190

Fig. 3.7.3-2

Test pit excavation method ...............................................................................191

Fig. 3.7.3-3

Emplacement method of the buffer (vacuum hoisting method) ......................191

Fig. 3.7.3-4

Tunnel sealing technology .................................................................................192

Fig. 3.7.3-5

Engineered barrier system experiment at the Horonobe URL .......................192

Fig. 3.7.3-6

Image view of the overpack corrosion test........................................................193

Fig. 4.1.3-1

Uplift and subsidence rates estimated from the change in thickness of different
strata ..................................................................................................................196

Fig. 4.1.3-2

Estimated paleo-geography from the Kiso Mountains (upper right) to the Nobi
Plains (lower left)...............................................................................................197

Fig. 4.1.3-3

Evolution histories of geological structures and paleo-stress fields in the
Mizunami area ...................................................................................................198

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Fig. 4.1.3-4

Evolution of the geological events in the Mizunami area ................................199

Fig. 4.1.3-5

Plot of uplift versus time for a sequence of marine-terrace surfaces ..............200

Fig. 4.1.3-6

Uplift and subsidence history in the Horonobe area .......................................201

Fig. 4.1.3-7

Amount of erosion in the URL area ..................................................................203

Fig. 4.1.3-8

Diagram of the considered geological events....................................................205

Fig. 4.1.3-9

Topographical and geological evolution model constructed by the sequential
modeling system (SMS) of the impact of geological evolution on groundwaterflow .....................................................................................................................205

Fig. 4.2.3-1

Results of restoration of paleo-topography and groundwater flow analysis basedon the paleo-topography in the region from the Kiso Mountains to Ise Bay (Tonoregion) ................................................................................................................212

Fig. 4.2.3-2

Modeled hydraulic head distributions from groundwater flow analyses focusing
on the impact of recharge rate (Tono region)....................................................212

Fig. 4.2.3-3

Paleo-topography restored based on river terraces and groundwater flow
analysis based on the paleo-topography (Tono region) ....................................213

Fig. 4.2.3-4

Results of landform development simulation and groundwater flow analysis
based on topography estimated by the simulation (Tono region) ....................213

Fig. 4.2.3-5

Results of groundwater flow analysis taking into account topographic changes
and fault distributions (Tono region) ................................................................214

Fig. 4.2.3-6

Groundwater pressure changes caused by the 2011 off the Pacific coast of
Tohoku Earthquake (Tono region) ....................................................................214

Fig. 4.2.3-7

Geological synthesized scenario for modeling the long-term evolution ofgroundwater flow conditions (Tono region) ......................................................215

Fig. 4.2.3-8

Relationship between mean annual temperature and evapotranspiration (left),and between latitude and evapotranspiration (right) ......................................215

Fig. 4.2.3-9Overall procedure used in SMS ........................................................................216

Fig. 4.2.3-10 Geological evolution model and results of groundwater flow analysis (Horonobe
region) ................................................................................................................217
Fig. 4.2.3-11 Groundwater pressure changes caused by the 2011 off the Pacific coast of
Tohoku Earthquake (Horonobe region) ............................................................217
Fig. 4.2.3-12 Geological synthesized scenario for modeling the long-term evolution ofgroundwater flow conditions (Horonobe region) ..............................................218
Fig. 4.3.3-1

Overview for modeling hydrochemical characteristics based on mineralogicalinvestigation ......................................................................................................222

Fig. 4.3.3-2

Spatial distribution of fracture-filling calcite...................................................223

Fig. 4.3.3-3

Fluid inclusions in fracture-filling calcite in the Toki Granite ........................224

Fig. 4.3.3-4

Changes in groundwater pressure and hydrochemistry related to earthquakes............................................................................................................................225

Fig. 4.3.3-5

Schematic illustration of the long-term hydrochemical evolution in the Tono
area.....................................................................................................................227

Fig. 4.3.3-6

Scenario of long-term hydrochemical evolution in the Tono area ...................228

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Fig. 4.3.3-7

Schematic illustration showing long-term hydrochemical evolution in the
Horonobe area ....................................................................................................229

Fig. 4.3.3-8

Long-term scenario related to hydrochemical evolution in the Horonobe area............................................................................................................................229

Fig. 4.3.3-9

Long-term variations of redox potential and pH based on mineralogicalequilibrium conditions .......................................................................................231

Fig. 4.3.4-1

Generic procedure for estimation of long-term hydrochemical evolution .......231

Fig. 4.3.4-2Synthesized scenario for analysis of medium- and long-term hydrochemical
evolution (MIU) .................................................................................................233

Fig. 4.4.3-1

Results of long-term creep testing (Tage tuff) ..................................................236

Fig. 4.4.3-2

Pressure-solution testing of quartz...................................................................236

Fig. 4.4.3-3

The relationship between axial strain and stress in strength recovery tests............................................................................................................................237

Fig. 4.4.3-4

The result of hydraulic tests in strength recovery tests ..................................237

Fig. 4.4.3-5

The relationship between saturation and axial strain in measurement of dryinginduced deformation ..........................................................................................237

Fig. 4.4.3-6

The relationship between saturation and elastic modulus ..............................237

Fig. 4.5.3-1

Correlation of minor elements with Al in the rock samples ............................243

Fig. 4.5.3-2

Discontinuous geological structures around the Horonobe URL ....................245

Fig. 4.5.3-3

Topographic and geological evolution model constructed by SMS (Sequential
Modeling System of geological evolution impact on groundwater flow) .........246

Fig. 4.5.3-4

Processing the formation of the lateral fault....................................................246

Fig. 4.6.3-1

Volumetric strain changes in Eastern Japan after the Tohoku Earthquake
described by Coulomb 3.1 ..................................................................................251

Fig. 4.6.3-2

Evaluation of landform changes using the old topography restored to theoriginal ...............................................................................................................253

Fig. 4.6.3-3

Comparison between the results of a landform development simulation and thespatial distribution of real low terraces............................................................254

Fig. 4.6.3-4

Differences in terms of summit plane between the simulation landforms and thereal landforms ....................................................................................................254

Fig. 4.6.3-5

Distribution of late Miocene to late Pleistocene sedimentary rocks in Japan .....
............................................................................................................................256

Fig. 4.6.3-6Frequency histogram and cumulative distribution of onset times for active fault
movements .........................................................................................................256

Fig. 4.6.3-7

Onset times of consistent mode and rate of crustal deformation in Japan basedon simulations of temporal changes in mean altitude developed underconcurrent tectonics and denudation processes ...............................................257

Fig. 4.6.3-8

Probability of the occurrence of a new volcanic event over the next 1 Myr ....257

Fig. 5.1-1

Relationship between each field of knowledge in construction of a safety case............................................................................................................................262

Fig. 5.2-1

Concept of ISIS ..................................................................................................263

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Fig. 5.2-2

Four tabs in the management cockpit ..............................................................264

Fig. 5.3.1-1

The GEM historical management tool ..............................................................265

Fig. 5.3.1-2

Knowledge linkable to the GEM historical management tool .........................266

Fig. 5.3.1-3

Registration of tasks to the research programme management tab ...............267

Fig. 5.3.1-4

Task flow diagram constructed using the registered tasks .............................267

Fig. 5.3.2-1

Discussion using a view.....................................................................................268

Fig. 5.3.2-2

An example of a story board ..............................................................................268

Fig. 5.3.3-1

Development of rule-bases using the rule-base development interface ..........270

Fig. 5.3.3-2

Development of case-bases using the case-base development interface .........270

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List of Tables
Table 1.3-1Core messages of the research result from the URL project and research on thegeosphere stability kernel .....................................................................................5

Table 2.1.2-1 Performance target of R&D for perceiving three-dimensional geologicalstructures (baseline condition) ..............................................................................7
Table 2.1.3-1 Depth of the boundary surface between the Koetoi and Wakkanai Formations..............................................................................................................................10
Table 2.2.2-1 Performance target of R&D for perceiving hydrological baseline conditions ...27
Table 2.3.2-1 Performance target of R&D for the hydrochemistry ..........................................49
Table 2.4.2-1 Performance target of R&D for rock mechanical characterization ...................61
Table 2.5.2-1 Performance target of R&D for the mass transport study ................................76
Table 2.6.2-1 Performance target of R&D for engineering technology ....................................85
Table 2.6.3-1 Evaluation of B-measurement results for the Main Shaft (Mizunami) ............87
Table 2.7.2-1 Performance target of R&D on geosphere stability for long-term isolation......95
Table 3.1.2-1 Performance target of R&D for perceiving the extent of the EDZ ..................107
Table 3.2.2-1 Performance target of R&D perceiving the short-term evolution and recovery
behavior of groundwater flow conditions .......................................................... 113
Table 3.3.2-1 Performance target of R&D for the short-term evolution and recovery behaviorof hydrochemical conditions ..............................................................................125
Table 3.3.3-1 Hydrological/hydrochemical monitoring sections at the Mizunami ................128
Table 3.3.3-2 Hydrological/hydrochemical monitoring sections at the Horonobe .................135
Table 3.3.4-1 Remaining R&D issues for perceiving the evolution and recovery behavior of thehydrochemical conditions ..................................................................................141
Table 3.4.2-1 Performance target of R&D for rock mechanical characterization .................143
Table 3.5.2-1 Performance target of R&D in the mass transport study ................................154
Table 3.5.3-1 Classification of types of discontinuous structures in the Toki Granite .........158
Table 3.5.4-1 Future themes in the next research phase .......................................................171
Table 3.6.2-1 Performance target of R&D for engineering technology ..................................174
Table 3.7.2-1 Performance target of R&D for geological disposal technology .......................188
Table 3.7.3-1 Mixing proportions of HFSC shotcrete used in the G.L. −250 m gallery ........190
Table 3.7.3-2 Compressive strength at the material age of 28 days used in the G.L. −250 m
deep gallery ........................................................................................................190
Table 3.7.3-3 Specifications of the buffer and electric heater ................................................191
Table 3.7.3-4 Design requirements and specification of backfill ...........................................192
Table 4.1.2-1 Performance target of R&D for perceiving topographical/geological long-term
evolution.............................................................................................................195
Table 4.2.2-1 Performance target of R&D for perceiving the long-term evolution and recovery
behavior of groundwater flow conditions ..........................................................209
Table 4.2.3-1 Hypothesized long-term evolution of groundwater flow conditions ................210

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Table 4.3.2-1 Performance target of R&D on long-term variation of hydrochemical conditions............................................................................................................................221
Table 4.4.2-1 Performance target of R&D for rock mechanical characterization .................235
Table 4.5.2-1 Performance target of R&D in the mass transport study ................................242
Table 4.5.3-1 Classification of types of discontinuous structures in the Toki Granite .........244
Table 4.6.2-1 Performance target of R&D on geosphere stability for long-term isolation....250
Table 4.6.3-1 Comparison of the theoretical coseismic groundwater level changes with theobserved ones at boreholes more than 1 km distant from the MIU ................252

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1. Introduction
1.1 Background and current status of the Underground Research Laboratory project and researchon geosphere stability for long-term isolation of radioactive waste
The Japan Atomic Energy Agency (JAEA) has conducted R&D programs on the UndergroundResearch Laboratory (URL) project and geosphere stability research during the second midterm program (fiscal years 2010–2014). Specific goals were set on the basis of past researchachievements and the government’s research policy, as listed below:- Evaluation of applicability of investigation techniques and modeling methodologies
through excavation of underground facilities up to approximately 500 m depth at
Mizunami and up to approximately 350 m depth at Horonobe.
- Verification of the applicability of engineering technologies in the deep underground.
- Development of prediction and evaluation technologies for understanding the long-term
evolution of the geological environment in terms of important natural phenomena duringsite characterizations of the planned geological disposal program.
With regard to the URL project, excavations over a five-year period and relevant
investigations were conducted. At the end of September 2014, two shafts with a depth of 500
m and horizontal tunnels with a length of 430 m at that depth had been excavated at the
Mizunami Underground Research Laboratory, and three shafts with a depth of 350 m andinvestigation tunnels with a length of 760 m at that depth had been excavated at the Horonobe
Underground Research Laboratory (Fig. 1.1-1). In these laboratories, the geologicalenvironment data required to achieve the goals were obtained and analyzed/evaluated inparallel with the excavation. In addition, R&D on geological disposal, including validation ofengineering technologies such as engineered barrier systems (EBS), was conducted in
Horonobe. With regard to the geosphere stability research, more detailed R&D items werefocused on (a) development and systematization of investigation techniques; (b) developmentof models for long-term estimation and effective assessment; and (c) development of dating
techniques, in order to consolidate investigation and analysis technologies and the related
knowledge and skills applicable to the Japan-specific geological environment within themobile belt.

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Fig. 1.1-1 Bird’s-eye/cutaway view of the Underground Research Facilities (Mizunami andHoronobe; prepared in September 2014)
1.2 Integration of research results and chronological framework for reporting
1.2.1 Integration of research results
The results of R&D on geological disposal technologies were reported on the JAEA website
after integration to form a knowledge base to support safety cases for geological disposal inorder to allow readers to utilize the results easily1). This newly invented reporting system was
employed after the first mid-term research program was issued (CoolRepH22). This systemallows presentation of the meaning and significance of the results of different areas of R&D to
support the construction of safety cases, by which utilization of the results will be promoted
and timely communication of information will become possible. The total number of visits tothe website of CoolRepH22 was over 39,000 by August 2014. This number indicates that thesite has played an important role as a tool to communicate with and provide information on
R&D results to a variety of public groups.
In this kernel, specific utilization of the results of site characterization, particularly the sitecharacterization techniques applicable to the early stages of siting processes in the planned
geological disposal program, were compiled, with a focus on the systematic processes involvedin the construction of a safety case (Fig. 1.2.1-1). More specifically, instead of the conventional
message that “technologies required for constructing a site description model were developed,”-2-

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this kernel shows where and when to incorporate the results, and what points should be noted
in incorporating the results (e.g., limitations of the investigation) as specifically as possible.
In addition, a knowledge management system (JAEA KMS)2) and a next-generation sitecharacterization data integration system (ISIS) developed by JAEA were merged to provide amore convenient environment for the main end-users, i.e., the Japanese implementer (NUMO:
Nuclear Waste Management Organization of Japan) and the Japanese regulator (NRA:
Nuclear Regulation Authority).

Fig. 1.2.1-1 Chronological history of CoolRep
1.2.2 Chronological framework
The research results were compiled considering each decision-making step of the geologicaldisposal project (Fig. 1.2.1-1) and were described as a hierarchy in order to make the purposeof the reflection clear. The decision-making steps were divided into three groups: group A1(understanding the initial state of the geological environment); group A2 (understanding theshort-term evolution and recovery behavior of the geological environment); and group A3(understanding the long-term evolution and recovery behavior of the geological environment),
based on the general activity phases of projects defined by ICRP and NEA3),4). Results relating
to the period from before starting the tunnel excavation to the time of starting the tunnel
excavation were assumed to belong to group A1; those for the period from completion of thetunnel excavation to tunnel closure to group A2; and those for the period after the closure to-3-

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group A3. The results of the development of tools to integrate each result were defined asgroup B (development of tools to integrate the knowledge obtained in each R&D activity). In
addition, construction of a structured system was attempted for gaining knowledge andinformation on geological disposal that could be complex and divided into a variety of
disciplines with respect to time (lateral axis) and description level (vertical axis) (Fig. 1.2.2-1),
wherein individual results for each R&D area and summaries of each result were collected as“results digests” a meaning was assigned to the results digests in each project and a total
meaning was assigned as a core message.

Fig. 1.2.2-1 Structure of the kernel of the URL project and research on geosphere stability
This type of structure allowed the contribution of individual research results to the overall
goals to be more specifically shown and the knowledge base to support the construction of asafety case more easily referred to. Compilation using this format is expected to be useful inextracting issues to be addressed with priority in the future, streamlining of research topics,
and creation of new research topics.
1.3 Core messages of major research results in the second mid-term research phase
The core messages and their meaning for groups A1 to A3 and group B as described above(section 1.2.2) are listed in Table 1.3-1, and their relationship with the results digest that
supports the basis of the core message is mapped in Fig. 1.3-1 (only part of the total map is-4-

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illustrated). These messages will help to clarify the significance of the results in the decisionmaking points for each project phase and allow easy and accurate identification ofrelationships between individual results and issues, which could not be sufficiently elicitedfrom conventional compilation.
Table 1.3-1 Core messages of the research result from the URL project and research on thegeosphere stability kernelCore message

Technical meaning in decision points

Understanding initialstate of geologicalenvironment(A1 Group) Synthesize overall investigation
methodologies to construct site
descriptive models under limited
investigations
 Can evaluate/reduce uncertainty ofgeo-environmental models by using
multiple lines of evidence Be compatible with a complex
geological environment and a
resource-constrained environment
based upon the developed techniques
and the obtained technical knowhow
 Exemplify important investigation
techniques and their combinations
including investigation limitations

Understanding
impact of
construction in geoenvironmental
conditions(A2 Group) Develop and test methods to evaluate
the impact of URL construction andany potential impact on long-term
safety performance Acquire new insights into engineering
technologies for reducing excavation
effects around shafts and drifts

 Can utilize technical information forcharacterizing Excavation Damaged
Zone (ex. functionally-usefulinvestigation techniques, effective
investigation layout and optimized
planning scheme etc.)

 Develop comprehensive evaluation
methodology for understanding longterm geological evolution and its
impact on deep underground Can evaluate long term geoenvironmental evolutions and theirimpact process by multidisciplinary
approach Understand tolerant and resilient
function of geo-environmental system
to some degree

Understanding longtermchanging/recovering
behavior of geoenvironmental
conditions(A3 Group)

Tools development
 Develop tools that can share andfor integration oftransfer expert knowledges on siteknowledge from eachcharacterization/engineeringresearch result
techniques, repository design and(B Group)
safety assessment-5- Can transfer expert knowledge in a
traceable manner for constructing
safety case

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Result digest

Fig. 1.3-1 An example of core messages in the results and issues digest map (part of the A2
group)
These core messages are also considered to be summaries of the R&D results obtained overa five-year period in the second mid-term program (146 technical reports, 124 academic
publications, and 268 conference abstracts). In section 2 and the subsequent sections in thiskernel, more specific explanations will be provided with respect to individual research results
to be used as a basis for the core messages of groups A1 to A3 and group B.
References
1) (Eds.) Umeki, H., Hioki, K., Osawa, H., Fujita, T., Shibata, M., Makino, H., Iwatsuki, T.,
Takeuchi, S. and Ishimaru, A.: “CoolRep H22; Synthesis report on R&D results on
geological disposal up to 2009”, JAEA-Review 2010-073 (2011), 255p. (in Japanese)
2) (Eds.) Notoya, S., Ota, K. and Shimizu, K.: “Conference on progress in development of JAEA
knowledge management system (Conference report)”, JAEA-Conf 2009-005 (2010), 58p. (inJapanese)3) Weiss, W., Larsson, C. M., McKenney, C., Minon, J. P., Mobbs, S., Schneider, T., Umeki, H.,
Hilden, W., Pescatore, C. and Vesterlind, M.: “Radiological Protection in Geological
Disposal of Long-lived Solid Radioactive Waste”, ICRP Publication 122, Annals of the ICRP,
Volume 42, Issue 3, pp.1-57 (2013).
4) NEA: “The Nature and Purpose of the Post-closure Safety Cases for Geological Repositories”,
NEA/RWM/R(2013)1 (2013).

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2. Understanding of the initial geo-environmental conditions
2.1 Geology
2.1.1 Introduction
Since both the geology and geological structure could control the capability of a site to act asa repository, the understanding of these fields of study is essential for understanding
groundwater flow, hydrochemistry and mass transport conditions, as well as for the design ofunderground facilities. Therefore, we proceeded with the investigation, analysis andassessment of the distribution of geological structures from the ground surface in terms ofsafety assessments1),2), including an understanding of the following:(1) distribution and shape of the targeted rock mass,(2) geological inhomogeneity of rock mass, and(3) important structures acting as paths for mass transport.
2.1.2 Objectives in the second mid-term research phase
The following studies as shown in Table 2.1.2-1 have been carried out to reach theperformance target of R&D for perceiving three-dimensional geological structure, which was
confirmed by the surface-based investigation performed during the first mid-term researchphase.
Table 2.1.2-1 Performance target of R&D for perceiving three-dimensional geologicalstructures (baseline condition)
Focus

Performance target of R&D

Tasks

Siting decision

Enable to select a geologically favorable
domain• Demonstration of technique tounderstand three-dimensional
distribution of geological structure fromground surface

Enable to judge appropriateness ofconstruction of underground facility
taking into account important geologicalstructure which acts as path for masstransport• Demonstration of technique ofinvestigation and interpretation toconfirm distribution of fault in deep
underground from ground surface• Demonstration of technique ofinvestigation and modeling to confirm
distribution of geological structure
which acts as path for groundwaterand mass transport• Demonstration of technique ofinvestigation and interpretation toestimate distribution of fault aroundshaft/gellery

Construction
decision-7-

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2.1.3 Project details and outcomes(1) Understanding of the distribution and shape of the targeted rock mass
As a result of the surface-based investigation (Phase I), characteristics of the geologicalenvironment and processes important for deep geological disposal have been understood bystepwise investigations including existing data analysis, airborne and surface based
investigations, and borehole investigations in the region, including URL construction sites. A
technical basis has been also established through the iteration of investigation, interpretation,assessment and construction of geological models3),4).
In the second mid-term research phase, we accumulated all technical knowledge regarding
the distribution and shape of the targeted rock mass and confirmed the validity of thegeological model established in the Phase I investigation through the understanding of therock mass distribution, and of geological structures such as fractures by observations in andaround the URL site and by borehole and geophysical investigations from galleries.
1) Mizunami
As a result of the Phase I investigation, the distribution of the Toki Granite (late Cretaceous)and overlying Mizunami Group (Miocene) and the faults were estimated through stepwise
investigations such as the interpretation of existing geological maps, surface geological andgeophysical surveys (seismic reflection survey) and borehole investigations3). Two structural
domains, named the upper highly-fractured domain (UHFD) and lower sparsely-fractured
domain (LSFD), were recognized by surface-based borehole investigations. The distributionsof the domains were modeled based on the results of the borehole investigations and seismicreflection survey3). We investigated the distribution of the UHFD and LSFD, and the obtained
results are described below.
The thickness of the UHFD is related to the thickness of the overlying Mizunami Group, andis thicker in areas where the Mizunami Group is thick5). The Mizunami Group is very thick in
the Mizunami URL site, because the Group buried a channel structure developed on the
granite. Thus, the UHFD was estimated to be located at G.L. −467 m3),6).
The pilot borehole drilled from the bottom of Ventilation Shaft7) revealed that the lower limitof the UHFD was located at approximately G.L. −460 m. Observations of the walls in the
Ventilation Shaft8) revealed that the frequency of fractures decreased at approximately G.L.
−460 m (Fig. 2.1.3-1)9). These results implied that two structural domains were confirmed by
the surface-based investigations with an error of approximately 10 m.

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Fig. 2.1.3-1 Comparison of the geological models constructed during the surface-based
investigation phase (Phase I) and in the second mid-term research phase2) Horonobe
The distribution of the Neogene Koetoi and Wakkanai Formations, overlying Yuchi andSarabetsu Formations and major faults have been confirmed by stepwise investigations suchas interpretations of existing geological maps, surface geological and geophysical surveys(seismicreflection

surveyandaudiomagnetotelluric(AMT)

survey)andborehole

investigations4). The boundary between the Koetoi and Wakkanai Formations is indicated by
the occurrence of a silica mineral phase10); that is, the Wakkanai Formation contains Opal-CT
which formed by the diagenesis of diatom remains (Opal-A), while the Koetoi Formation does
not contain Opal-CT11). The boundary of the two formations estimated by the Phase I result
was determined within a few meters, compared with the Phase II result obtained by thegeological observation of the shaft walls and mineralogical analysis of drill core samples
obtained from research galleries (Fig. 2.1.3-2 and Table 2.1.3-1)12).
From the above mentioned points, we concluded that the geological model established by thePhase I result contained enough information to understand the stratigraphy in and aroundthe URL, and that the estimation of the distributions of each geological formation on the basisof the Phase I result4) was reasonable.
Based on the results of the previous investigations, we established a methodology to confirm
the distribution and thickness of each formation in sedimentary rock and less fractured
domains in granite. Thus, geological classification of the target rock in terms of the
distribution of faults and frequency of fractures was achieved by a combination of surface-9-

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geological, geophysical and borehole investigations. We also prepared a flow diagram toestablish the geological model summarized by the result of various kinds of investigations on
the basis of a “top-down” approach from “investigation” through to “data,” and“interpretation/data set” to “conceptualization /modeling”13).

Fig. 2.1.3-2 Confirmation of the boundary the between Koetoi and Wakkanai Formations
Table 2.1.3-1 Depth of the boundary surface between the Koetoi and Wakkanai Formations
No.
I
II
III
IV

Investigation/Location
Geological mapping on the floor/250m pumping station
Analysis of Core
/Grout hole in the East shaft
Analysis of core
/Borehole from 250m Niche off the West
Shaft No.1
Analysis of core
/borehole from 250m Niche off the West
Shaft No.1

Estimated depth

Observed depth

G.L. −249 m

G.L. −251 m

G.L. −260 m

G.L. −261 m

G.L. −275 m

G.L. −274 m

G.L. −276 m

G.L. −275 m(2) Understanding the geological inhomogeneity of the rock mass
The geological inhomogeneity of the rock mass could result from variations in the rock facies
and lithology (rock type, grain size and so on) and structural development (fracture frequency,
distribution of faults and so on)14). We prepared a technical basis to understand the geologicalinhomogeneity by confirmation of the distribution of the rock mass and fracture zones on thebasis of geological observations, as well as from borehole and geophysical investigations fromresearch galleries.

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1) Mizunami
Toki Granite has been lithologically divided into muscovite-biotite, hornblende-biotite andbiotite granites on the basis of the petrography (mineralogical and modal compositions) of drill
cores drilled from the ground surface15). These three litho-facies are systematically changed
from biotite granite in the core of the rock mass through hornblende-biotite granite tomuscovite-biotite granite in the rim15).
A petrographic study of the MIZ-1 core revealed that hornblende-biotite and biotite granites
are distributed above and below the G.L. −500 m point at the MIU site, respectively15).
Hornblende is generally fine-grained and rarely contained in hornblende-biotite granite.
The granite observed in the shaft and galleries is generally equigranular and medium tocoarse-grained with a long axis of 5 to 7 mm in each mineral, and is occasionally fine tomedium-grained with long axis of 1 to 5 mm9),16). Pegmatite and aplite dykes are locally
distributed in the granite and basic lamprophyre is distributed along the main-shaft fault9),16).
Since these intrusions show limited distribution, we concluded that the rock mass was
homogeneous as a whole.
In terms of fractures, a difference in the frequency of fractures was confirmed as mentionedin (1). The frequency of fractures is considered to be related to the cooling speed17),18),19),20).
Based on statistical analysis and the response surface of the spatial relationship between
regional geological structures and the fracture density, the fracture density may beinterpolated in the uninvestigated area21). Spatial modeling of the regional geology andfracture density could be applied to understand the fracture density with each strikedirection22).
Some faults were confirmed by detailed surface geological investigations and were estimatedby reflection seismic surveys3) during Phase I5). Most of the faults around the URL site were
not described in previous publications. The fault strikes indicate NS to NW-SE and EW to
WNW-ESE with small displacements. Since some of the faults cannot be associated with thefaults confirmed at the surface, such faults are not appeared at the surface, or are notpresently active3).
In Phase II (construction phase), we confirmed the locations and distributions of faults bygeological observation of the walls in shafts and research galleries, borehole and geophysicalinvestigations from research galleries. Based on the results of the Phase I and II investigations,
we established a technical basis to understand the minor faults that were not described inprevious publications (Fig. 2.1.3-3)9),16). In some cases, however, different faults were regarded
as a single fault, and vice versa6),9),16),23). Estimations of the fault locations appear to contain a
few tens of meters of error, because the position of some faults could not be confirmed byborehole investigations from galleries or reverse vertical seismic profiling surveys 24),25).
Strong alterations are pervasive around the main-shaft fault. The mode of occurrence ofalterations in drill cores could be divided into white-colored clayey alterations in the entire
core near the fault, and pale green to dark green-colored alterations along fractures 23),26).
The fault zone is generally fragile and thus core-loss often occurs. We developed a technology
to estimate the location and characteristics of faults without core recovery by combining the- 11 -

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data from geophysical loggings of the boreholes27).

Fig. 2.1.3-3 Distribution of faults on the basis of geophysical investigation from groundsurface (left), and the estimated distribution of Fault A (right)
2) Horonobe
The geological model established in Phase I contains the distributions of the target rock
(Neogene Koetoi Formation: diatomaceous mudstone, and Wakkanai Formation: siliceous
mudstone), Omagari Fault and minor faults (Fig. 2.1.3-4)4).
The boundary between the Koetoi and Wakkanai Formations was determined by theoccurrence of a silica mineral phase, as mentioned (1). In the Phase II investigation, we
confirmed that the methodology applied in Phase I is adequate to distinguish between the twoformations, and the physical properties obtained in the Phase II investigation such as porosityand hardness are concordant with those obtained in the Phase I investigation12).
The apertures and interconnections of faults and fractures in the Koetoi Formation are lessprevalent than those in the Wakkanai Formation28). The faults and fractures in the Wakkanai
Formation are characterized by those crossing bedding planes at a high angle, and those thatare parallel to bedding planes29). In the Wakkanai Formation, the faults mainly grew bylinking with adjacent faults via numerous splay cracks, formed by tensile failures above
roughly 400 m depth at the URL site30). In the Phase II investigation, geological observationsof the shaft walls and floor revealed that the lengths of faults and fractures in the Koetoi
Formation are generally less than a few meters and a few tens of centimeters, respectively(Fig. 2.1.3-5)31),32).
Geological observations of the shaft walls and floor in the Wakkanai Formation revealed thedevelopment of a tensile failure crossing a bedding plane at a high angle (Fig. 2.1.3-6)33).
Nineteen faults were confirmed in the Wakkanai Formation by borehole investigations fromthe ground surface. Six faults were estimated to be present at the G.L. −350 m gallery.
Geological observations at this gallery indicated that the distribution of faults was concordant- 12 -

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with results of the Phase I investigation34). As a result of the above mentioned points, thedistribution and characteristics of faults and fractures could be estimated by surface based
investigations.
As a result of the Phase I and II investigations, we confirmed the distribution and frequency
of unknown faults in previous publications by a combination of surface geological, geophysicaland borehole investigations, and classified target rocks in terms of the distribution of the fault
and fracture density. Faults in granite that were difficult to confirm without borehole
investigations could be estimated by reverse vertical seismic profiling surveys35),36). We
developed a technology to estimate the location of minor faults by a combination of data fromthe geophysical loggings of boreholes. We also examined a method to show the change ofunderstanding of the geological environment and the uncertainty in the geologicalmodel37),38),39).

Fig. 2.1.3-4 Geological model of the Horonobe area prepared on the basis of the Phase I
investigation results- 13 -

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Fig. 2.1.3-5 Geological map of the ventilation and east shafts of the Horonobe URL- 14 -

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Fig. 2.1.3-6 Shear fractures related to faults in the upper Wakkanai Formation(G.L. −250 m in the ventilation shaft)(3) Understanding of the important structures acting as paths for mass transport
Primary structures such as pores in grains, bedding planes, unconformities and schistose,and secondary structure such as fractures and faults are listed as the important structuresthat act as paths for mass transport40). We prepared a technical basis to understand theseimportant structures through the investigation of discontinuities such as pores, fractures andfaults by geological, borehole and geophysical investigations.
1) Mizunami
In the Mizunami URL, faults and flow-path fractures are the important structures that act
as paths for mass transport. As mentioned in (2), we understood the distribution of the faults
and extracted future issues to improve the accuracy of estimation.
We confirmed the flow-path fractures by geological observation of the gallery walls8),9),16),41).
We also discussed a technique to detect flow-path fractures on the basis of the mineralcomposition and mode of occurrence of fracture fillings42).
At the time of large inflow during the drilling of a pilot borehole at the G.L. − 300 m
Access/Research Gallery, a positive self-potential was observed at the northeastern side of themain-shaft fault (Fig. 2.1.3-7)43). This result suggested the groundwater had flowed to the
inflow point, and thus self-potential monitoring during shaft/gallery excavation could be used
as a tool to estimate the distribution of structures influencing groundwater flow.

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Fig. 2.1.3-7 Change in self-potential (upper) and hydraulic head in the MIZ-1 borehole withan inflow rate into the shafts (lower)
A positive self-potential was observed in the northeastern part of the main-shaft fault,suggesting the occurrence of groundwater flow to the inflow point.
2) Horonobe
In the Horonobe URL, discontinued structures such as faults and fractures are listed as theimportant structures acting as paths for mass transport4). As a result of the Phase I
investigation, a major fault (Omagari Fault) could be confirmed by a combination of surface
geological and geophysical surveys (seismic reflection and AMT surveys) and borehole
investigations (Fig. 2.1.3-8 and Fig. 2.1.3-9)4),44). Minor faults and fractures are also listed, andtheir distribution and characteristics were estimated as mentioned in (2). In terms of
permeability, the faults and fractures in the Koetoi Formation do not appear to act as major
flow paths28), while some faults and fractures that cross a bedding plane at a high angle in the
Wakkanai Formation act as a major flow path29). In the Wakkanai Formation, the fault
crossing a bedding plane at a high angle and tensile splay fault both possess highpermeability30).
In the Phase II investigation, geological observations of gallery walls and floor revealed thatmost of the faults and fractures in the Koetoi Formation were not accompanied by water inflow(Fig. 2.1.3-5)31),32). In the Wakkanai Formation, the fault crossing a bedding plane at a high- 16 -

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angle and the accompanying fractures acted as major flow paths33). An increase in water inflow
has been observed at the crossing point of faults crossing a bedding plane at a high angle andparallel to the bedding plane. Therefore, we performed the geological investigation at thesurface exposure in a similar geological setting. As a result, we found evidence of past waterflow in a fracture zone around the fault parallel to a bedding plane near the crossing pointwith a fault crossing the bedding plane at a high angle34).
The differences in the density and permeability of faults and fractures in the Koetoi and
Wakkanai Formations are estimated to result from differences in brittleness (Fig. 2.1.310)45),46),47). Based on this estimation, the target rock was divided in terms of permeability (Fig.
2.1.3-11)48). According to the estimation, the Wakkanai Formation below G.L. −500 m would
have low permeability without developments of tensile faults (Fig. 2.1.3-11).

Fig. 2.1.3-8 Interpretation around the Omagari Fault by seismic reflection survey andborehole investigations
HDB-1,3,4 and 5 shows the location of boreholes projected to the survey line.

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Fig. 2.1.3-9 Interpretation of the geological structure by AMT survey and borehole
investigations

Fig. 2.1.3-10 Distribution of tensile fractures and ductility measurements (∝-1BRI)45)- 18 -

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Fig. 2.1.3-11 Rock domain classified by the competence factor, and geological and hydraulicproperties of fractures in each domain
2.1.4 Summary
The techniques and accumulated technical knowledge regarding the investigation, analysis,
and assessment for understanding the three-dimensional distribution of geological structuresin the Mizunami and/or Horonobe URLs are stated as follows:(1) Understanding the distribution and shape of the targeted rock mass
- A technique to understand the distribution and shape of the target and surrounding rockwas established by a combination of surface geological, geophysical, and borehole
investigations (both URLs).
- A technique to construct the geological model was established by an arrangement of
results obtained by each investigation using a “top-down” approach (both URLs).
(2) Understanding geological inhomogeneities of the rock mass
- A technique to classify the target rock on the basis of the distribution of the fault andfracture density was established by a combination of surface geological, geophysical, and- 19 -

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borehole investigations (both URLs).
- A technique to estimate the distribution and strike of unknown faults was established by
a combination of surface geological and borehole investigations (both URLs).
- A technique to understand minor faults in the deep underground was established byusing a multi-dataset obtained by borehole investigations (both URLs).
- A technique to show the change in understanding of the geological environment anduncertainty in the geological model with an advance of the investigation phase wasestablished (both URLs).
(3) Understanding the important structures that act as paths for mass transport- A technique to model the rock domain with different permeabilities was established on
the basis of the frequency of fractures (Mizunami URL; crystalline rock) and competence
factor (Horonobe URL; sedimentary rock).
- A technique to obtain information about the hydrogeological conceptual model, such as
the distributions of faults and fractures and permeability, was demonstrated in a casewhere the target rock had visible outcrops at the surface (both URLs).
- A technique to confirm the presence of faults in granite, which was difficult to confirm
without borehole investigations, was demonstrated by a reverse vertical seismic profilingsurvey. This technique should be applicable to rocks without a large change in elastic
wave velocity (Mizunami URL).
- An applicability of technique for wall rock observations was confirmed by anunderstanding of the detailed distribution and characteristics of faults and fractures byobservation of the shafts and gallery (both URLs).
- A technique to confirm the distribution of geological structures influencing groundwaterflow was demonstrated by self-potential monitoring during shaft/gallery excavation. This
technique should allow for the detection of highly permeable structures such as fracturezones in granites and conglomerates (Mizunami URL).
As mentioned above, the techniques and procedures for understanding the distribution of thetarget rock and important structures acting as paths for mass transport have been prepared
to date.
In further studies, an accumulation of knowledge on the heterogeneous distribution of
fractures and their formative processes is needed through further studies on A2 and A3, as
described in the following chapters. This knowledge will feed- back to the technique forsurface-based investigation.
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Ishibashi, M., Takeuchi, R., Matsuoka, T., Mizuno, T. and Tagami, M. : “Mizunami
Underground Research Laboratory Project; Results of the Borehole Investigations to
Understand the Geological Environment in and around the Main-shaft Fault”, JAEATechnology 2012-001 (2012), 134p. (in Japanese).
27) Abumi, K., Amano, K., Koike, K., Tsuruta, T. and Matsuoka, T. : “Fault zone determination
and bedrock classification through multivariate analysis -Case study using a dataset froma deep borehole in the Mizunami Underground Research Laboratory-”, Geoinformatics,
vol.22, pp171-188 (2011). (in Japanese).
28) Funaki, H., Ishii, E. and Tokiwa, T. : “Evaluation of the role of fractures as the majorwater-conducting features in Neogene sedimentary rocks”, Journal of the Japan Society ofEngineering Geology, Vol.50, No. 4, pp.238-247 (2009). (in Japanese).
29) Ishii, E. and Fukushima, T. : “A Case study of analysis of faults in Neogene siliceous rocks”,
Journal of the Japan Society of Engineering Geology, Vol.47, No.5, pp280-291 (2006). (inJapanese).
30) Ishii, E., Funaki, H., Tokiwa, T. and Ota, K. : “Relationship between fault growthmechanism and permeability variations with depth of siliceous mudstones in northern
Hokkaido, Japan”, Journal of Structural Geology, 32, pp.1792-1805 (2010).
31) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2009 fiscal year”, JAEA-Review
2010-039 (2010), 67p. (in Japanese).
32) (Eds.) Nakayama, M., Sawada, S. and Sugita, Y. : “Horonobe Underground ResearchLaboratory Project Investigation Report for the 2010 Fiscal Year”, JAEA-Review 2011-033(2011), 80p. (in Japanese).
33) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2008 fiscal year”, JAEA-Research
2009-032 (2009), 68p. (in Japanese).
34) (Ed.) Hanamuro, T. : “Horonobe Underground Research Laboratory Project; Investigation
report for the 2013 fiscal year”, JAEA-Review 2014-039 (2014), 69p. (in Japanese).
35) Matsuoka, T., Hodotsuka, Y. and Yamada, N. : “Reverse Vertical Seismic Profiling using
vibration during the construction of underground facility”, JAEA-Research 2012-028 (2012),
70p. (in Japanese).

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36) Yamada, N., Matsuoka, T., Ishigaki, K., Kanazawa, Y., Tokuyasu, S. and Nakahara, J. :“Reverse vertical seismic profiling using the research gallery in granite”, Abstract of the129th (2013 FALL) SEGJ CONFERENCE, pp.152-155 (2013). (in Japanese).
37) Kurihara, A., Matsuoka, T. and Martin, A. J. : “Quantitative evaluation of fault
distribution uncertainty: Applicability of an analytical method for evaluating 3-D geologicalmodels in the Mizunami Underground Research Laboratory Project”, Proceedings ofInternational symposium on earth science and technology 2010 (by CINEST), December 78, 2010, Fukuoka, Japan, 2010, pp.453-456 (2010).
38) Hama, K., Mikake, S., Nishio, K., Matsuoka, T., Ishibashi, M., Sasao, E., Hikima, R.,
Tanno, T., Sanada, Y., Onoe, H., Sato, S., Karino, T., Takeuchi, R., Shingu, S., Ohmori, K.,
Iwatsuki, T., Yuguchi, T., Morikawa, K., Ogata, N., Koide, K., Ikeda, K., Yamamoto, M.,
Shimada, A., Sato, T., Ito, H. and Sugihara, K. : “Mizunami Underground ResearchLaboratory Project Annual Report for Fiscal Year 2012”, JAEA-Review 2013-050 (2014),
114p. (in Japanese).
39) Hama, K., Mikake, K., Nishio, K., Kawamoto, N., Yamada, M., Ishibashi, H., Murakami,
H., Matsuoka, T., Sasao, E., Sanada, H., Ohnuki, K., Sato, S., Beppu, S., Onoe, H., Takeuchi,R., Saegusa, H., Ohmori, K., Hasegawa, T., Munemoto, T., Yuguchi, T., Iwatsuki, T.,
Iwasaki, R., Ikeda, K., Horiuchi, Y., Sato, T., Osawa, H., Koide, K. and Sugihara, K. :“Mizunami Underground Research Laboratory Project Annual Report for Fiscal Year 2013”,
JAEA-Review 2014-038 (2014), 137p. (in Japanese).
40) Japan Nuclear Fuel Cycle Development Institute : “H12 Project to establish the scientificand technical basis for HLW disposal in Japan, Supporting report 1: Geologicalenvironment in Japan”, JNC-TN1410 2000-002 (2000), 391p. (in Japanese).
41) Kawamoto, K., Kuboshima, K., Ishibashi, M., Tsuruta, T., Sasao, E., Ikeda, K., Mikake, S.,
Hara, I. and Yamamoto, M. : “Mizunami Underground Research Laboratory Project
Compilation of Results of Geological Investigation at the Shafts and Research Galleries”,
JAEA-Data/Code 2012-009 (2012), 47p. (in Japanese).
42) Ishibashi, M., Ando, T., Sasao, E., Yuguchi, T., Nishimoto, S. and Yoshida, H. :“Characterization of water conducting fracture and their long-term behavior in deep
crystalline rock; A Case study of the Toki granite”, Journal of the Japan Society ofEngineering Geology, Vol.55, No.4, pp.156-165 (2014). (in Japanese).
43) Tokuyasu, S., Matsuoka, T. and Hodotsuka, Y. : “Studies on Estimation of Hydrogeological
Structure using Self-potential Monitoring around Mizunami Underground ResearchLaboratory (MIU)”, JAEA-Research 2012-007 (2012), 55p. (in Japanese).
44) Ishii, E., Yasue, K., Tanaka, T., Tsukuwi, R., Matsuo, K., Sugiyama, K. and Matsuo, S. :“Three-dimensional distribution and hydrogeological properties of the Omagari Fault in
the Horonobe area, northern Hokkaido, Japan”, Journal of the Geological Society of Japan,
Vol.112, pp.301-314 (2006). (in Japanese).
45) Ishii, E., Sanada, H., Funaki, H., Sugita, Y. and Kurikami, H. : “The relationships among
brittleness, deformation behavior, and transport properties in mudstones: An example fromthe Horonobe Underground Research Laboratory, Japan”, Journal of Geophysical Research,- 24 -

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Vol. 116, B09206, p.15 (2011).
46) Ishii, E., Sanada, H., Iwatsuki, T., Sugita, Y. and Kurikami, H. : “Mechanical strength of
the transition zone at the boundary between opal-A and opal-CT zones in siliceous rocks”,
Engineering Geology, 122, pp.215-221 (2011).
47) Ishii, E. : “Microstructure and origin of faults in siliceous mudstone at the Horonobe
Underground Research Laboratory site, Japan”, Journal of Structural Geology, 34, pp.2029 (2012).
48) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Project Investigation
Report for the 2012 Fiscal Year”, JAEA-Review 2013-037 (2014), 63p. (in Japanese).

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2.2 Hydrogeology
2.2.1 Introduction
The objective of the study is to establish the following techniques:- Comprehensive

techniquesofinvestigation,

analysis,

andassessment

forcharacterization of groundwater flow conditions- Techniques of investigation and analysis for prediction of the volume of inflow into
underground facilities
From these hydrogeological points of view, the focused features and processes to be
characterized and the resulting data requirements relevant to safety assessment, design, andconstruction were identified1).
(1) Groundwater flow field
In order to estimate deep groundwater flow conditions on a scale of several kilometers using
groundwater flow analysis, it is important to understand the following:- The area containing a deep groundwater flow system within the recharge area to thedischarge area
- State of groundwater flow conditions, such as advection or diffusion- Type of driving force of the deep groundwater flow (potential flow, density flow, or thermal
flow)
The major factors influencing groundwater flow are the topography and geological conditions.
(2) Spatial variability of groundwater flux
The three-dimensional spatial variability of groundwater flux is to be determined by spatial
variability of hydraulic properties and hydraulic gradient. As the hydraulic properties show
heterogeneity caused by faults, joints, and geological layers, it is important to estimate the 3D
spatial variability of the hydraulic properties.
(3) Spatial variability of water fluxes in higher-permeability rocks and aquifers
Knowledge of the spatial variability of water fluxes in higher-permeability rocks and aquifers
is important to understand dilution effects. The concentrations of solutes in the groundwater
are diluted because of changes in the groundwater flux along groundwater flow paths fromlow-permeability rock zones to high-permeability zones or highly permeable structures.
Therefore, thick aquifers with high hydraulic conductivities that extend over a large area andare associated with highly fractured zones were considered to be important for diluting solutes.
(4) Volume of inflow into underground facilities
Prediction of the volume of inflow into underground facilities from the viewpoints of designand construction of underground facilities is important. In particular, planning of grouting
based on the prediction is necessary if a large volume of the inflow interferes with construction.
2.2.2 Objectives in the second mid-term research phase
The following studies have been carried out to reach the performance target of R&D forperceiving hydrological baseline conditions (Table 2.2.2-1):- Monitoring of groundwater pressure and inflow volumes during construction ofunderground facilities- 26 -

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JAEA-Review 2016-014- Hydraulic tests using boreholes drilled at underground facilities- Testing the prediction results of the surface-based investigation phase- Examining the investigation and analytical techniques for prediction of the volume of
inflow into underground facilities
Table 2.2.2-1 Performance target of R&D for perceiving hydrological baseline conditions
Focus

Performance target of R&D

Tasks

Siting decision

Enable to select a area with low
groundwater flux and long flow path.

• Comprehensive techniques ofinvestigation, analysis and assessment
for characterization of groundwaterflow condition• Method for groundwater flow modelingbased on geo-synthesized information

Construction
decision

Enable to judge appropriateness ofconstruction and operation ofunderground facility taking into accountgroundwater flow.

• Techniques of investigation andanalysis for prediction of volume of
inflow into underground facilities

2.2.3 Project details and outcomes(1) Groundwater flow field
The hydrogeological model and boundary conditions for the groundwater flow analyses at thearea from recharge area to the discharge area, which were constructed during the surfacebased investigation phase (Phase I), have been modified and a groundwater flow analysis has
been carried out. The results of the analysis will be used for assignment of boundary conditions
for the groundwater flow analysis in the region measuring several km2.
1) Mizunami
Low hydraulic heads, which are similar to river water levels, were observed at the MIU site2).
The river is located 1.5 km from the MIU site and the altitude is 50 m lower than that of the
MIU site. Groundwater flow analyses at Phase I could not express the hydraulic head
distribution. Therefore, improvement of hydrogeological model and analytical conditions
taking into account the following uncertain points have been carried out in order to match theobserved and analyzed hydraulic heads.
- Trace length and hydraulic parameters of large-sized discontinuities- Trace length and hydraulic parameters of hydrogeological elements continuing from the
MIU site to the river- Side boundary conditions in the river part- 27 -

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The hydrogeological model of Phase I has been tested by comparison between the results ofgroundwater flow analyses obtained using the Phase I model and the improved Phase II model(Fig. 2.2.3-1). In detail, the analyzed distributions of the hydraulic head and hydraulicgradient were used for the comparison. Significant differences could not be recognized. This
result indicates the reasonableness of the Phase I hydrogeological model.

Fig. 2.2.3-1 Stepwise evolution of the results of groundwater flow analyses (MIU)
2) Horonobe
Although the measured and analyzed hydraulic head distribution on the downstream side(west side) of the Omagari Fault was consistent, significant differences in the hydraulic head
distribution were recognized at upper stream side (east side) of the fault3). Improvement of thehydrogeological model and analytical conditions taking into account the following uncertain
points has been carried out to reduce the difference.
- Geometry and hydraulic parameters of the Omagari Fault- Continuity of the Omagari Fault- Recharge rate
As in the Mizunami case, the hydrogeological model of Phase I was tested by comparing theresults of groundwater flow analyses obtained using the Phase I model and the improved
Phase II model (Fig. 2.2.3-2). As significant differences could not be detected, the Phase I
model was concluded to be reasonable.

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JAEA-Review 2016-014(a) Surface-based investigation phase (Phase 1)(b) Revised model on construction phase (Phase 2)
Fig. 2.2.3-2 Stepwise evolution of the results of groundwater flow analyses (Horonobe)(2) Spatial variability of groundwater flux
The groundwater inflow rate into underground facilities and groundwater pressure responses
during excavation and operation of the underground facilities have been monitored4),5),6).
Groundwater pressure monitoring was carried out using two types of multi-packer system,
one that measures the groundwater pressure directly in the measurement interval and onethat measures the groundwater level in a piezometer tube over a certain interval. The total
inflow rate and depth profile of inflow rate were also monitored. In addition, tilt
monitoring7),8),9),10) was conducted to complement the groundwater pressure monitoring. In
advance of installation of the monitoring system, single-hole hydraulic tests were performed
for hydrogeological characterization of the pilot borehole investigations11). In addition,
continuous surface hydrological investigations and meteorological observations were carriedout to obtain the boundary conditions of groundwater flow analysis and to assess the changes- 29 -

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in groundwater level resulting construction of underground facilities.
The hydrogeological models in the region measuring several km2 were calibrated using themonitoring results. The hydrogeological model of Phase I has been tested by comparison of theresults of groundwater flow analyses obtained using the Phase I model and the improved
Phase II model. In particular, the analyzed hydraulic gradient, groundwater flux, andgroundwater flow path were used in the comparison.
1) Mizunami
In addition to the investigations described above, a long-term pumping test was carried out
using the boreholes drilled from underground facilities at the Mizunami site12).
The main achievements and technical findings from the investigations can be summarized
as follows:- The inflow rate increased during construction of facilities in the area of highly permeable
structures (Fig. 2.2.3-3).
- The hydraulic responses differ for each hydraulic compartment that is formed with lowpermeability structures (Fig. 2.2.3-4).
- The hydraulic conductivity of the lower sparsely fractured domain is one order ofmagnitude lower than that of the upper highly fractured domain.
- Fluid conductivity logging13),14), which can identify water-conducting features withtransmissivity values higher than 10−9 to 10−8 m2/s using boreholes drilled from theground surface, is not applicable because of the larger inflow of water in the boreholes
drilled from the underground facility.
- There is spatial variability in the recharge rate, which is affected by the location, thegeological conditions of the ground surface, and the size of the catchment. The time
variability of the recharge rate is also large because of fluctuations in the meteorologicalconditions15). The results indicate that surface hydrological investigations in a catchmentof similar size to that of the groundwater flow analysis is effective for obtaining accurateboundary conditions.
The main achievements and technical findings from the hydrogeological modeling andgroundwater flow analysis can be summarized as follows:- A hydrogeological conceptual model was constructed using the groundwater pressure
responses16).
- The hydrogeological model was improved by taking into account the hydraulicheterogeneity caused by the water-conducting features in the fractured domain17),18) (Fig.
2.2.3-5).
- A procedure for improvement of the hydrogeological model during Phase II was developed(Fig. 2.2.3-6).
- The hydrogeological model has been improved using data on inflow rate and hydraulicresponses during construction of underground facilities and long-term cross-hole
hydraulic tests (Fig. 2.2.3-7, Fig. 2.2.3-8).

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JAEA-Review 2016-014- The hydrogeological model could be improved step-wise as site characterization proceeds(Fig. 2.2.3-9).
- During the model improvement, geochemical changes during the construction ofunderground facilities as well as groundwater pressure changes were simulated19) (Fig.
2.2.3-10).
- The reasonableness of the Phase I model was confirmed by comparing the models before
and after improvement (Fig. 2.2.3-11). Significant differences could not be recognized.

Fig. 2.2.3-3 Groundwater inflow rate into the underground facilities (MIU)

Fig. 2.2.3-4 Hydraulic responses caused by construction of underground facilities (MIU)- 31 -

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Fig. 2.2.3-5 Concept of hydrogeological modeling taking hydrogeological heterogeneity into
account (MIU)

Fig. 2.2.3-6 Procedure for revising the hydrogeological model- 32 -

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Fig. 2.2.3-7 Comparison of measured and modeled groundwater inflow rates (MIU)

Fig. 2.2.3-8 Comparison of measured and modeled hydraulic responses (MIU)- 33 -

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Fig. 2.2.3-9 Improvement in understanding of groundwater flow conditions with stepwise
progress of the investigations

Fig. 2.2.3-10 Changes in Cl− concentrations based on advection–dispersion analysis- 34 -

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Fig. 2.2.3-11 Stepwise evolution of the results of groundwater flow analyses (MIU)
2) Horonobe
The main achievement and technical findings from the investigations are summarized asfollows:- The inflow rate increases during construction of facilities in the area with highly
permeable structures (Fig. 2.2.3-12).
- Clear hydraulic responses were recognized in the zone of water-conducting fault withtensional fractures (Fig. 2.2.3-13).
- The network of splay fractures of fault in the upper part of the Wakkanai Formation
forms a high-permeability zone9).
- The recharge rate is affected by the geology and spatial distribution and the hydrogeologyof the fractured zone rather than the topographic conditions and vegetation. The
characteristics of recharge in snowy cold region are identified, which are: 1) 40%–50 %of the annual amount of precipitation is snowfall; and 2) the maximum recharge occurs
during the snowmelt season20),21).
The main achievements and technical findings from the hydrogeological modeling andgroundwater flow analysis are summarized as follows:- 35 -

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JAEA-Review 2016-014- A hydrogeological conceptual model was constructed using the groundwater pressure
responses10).
- The improved model could comprehensively simulate the changes of inflow rate into
underground facilities and groundwater pressure responses (Fig. 2.2.3-14, Fig. 2.2.3-15).
- Based on the models, which underwent step-wise improvements as the sitecharacterization proceeded, the relationship between accuracy of prediction results andnumber of boreholes could be clarified (Fig. 2.2.3-16).
- By comparing the models before and after improvement, it was confirmed that thehydrogeological model in the Wakkanai Formation is different (Fig. 2.2.3-17). In
particular, the Wakkanai Formation has been divided into a shallow part with high-angle
fractures and a lower part.

Inflow rate into Ventilation shaft （Measured）

200

300

Inflow rate into East shaft （Measured）
Total inflow （Mesured）
Excavation depth （Ventilation shaft）

180

Excavation depth （East shaft）

250

160

200

120
150

100
80

100

60
40

50

20
0

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

0
1500

Elapsed time （day）

Fig. 2.2.3-12 Groundwater inflow rate into the underground facilities (Horonobe)- 36 -

Excavation depth（GL-m）

Inflow rate （m3/d）

140

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Fig. 2.2.3-13 Hydraulic responses because of inflow into the ventilation shaft andhydrogeological model (Horonobe)

Inflow rate into Ventilation shaft （Simulated）
Inflow rate into East shaft （Simulated）
Inflow rate into Ventilation shaft （Measured）
Inflow rate into East shaft （Measured）
Total inflow （Mesured）
Total inflow （Simulated）
Simulated excavation （Ventilation shaft）
Simulated excavation （East shaft）

Inflow rate （m3/d）

250

300

250

200

200

150

150

100

100

50

50

0

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

Excavation depth（GL-m）

300

0
1500

Elapsed time （day）

Fig. 2.2.3-14 Comparison of measured and modeled groundwater inflow rates (Horonobe)- 37 -

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Fig. 2.2.3-15 Comparison of measured and modeled hydraulic responses (Horonobe)

Fig. 2.2.3-16 Improvements in understanding of the groundwater flow conditions withstepwise progress of the investigations (Horonobe)22)- 38 -

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Fig. 2.2.3-17 Evolution of the hydrogeological model around the shafts (Horonobe)(3) Spatial variability of water fluxes in higher-permeability rocks and aquifers
The dilution effect was estimated by comparing the distribution of the Darcy velocity in thehydrogeological units assumed to form the aquifer that extends over a large area in Phase I23).
The Darcy velocity was also calculated using the improved hydrogeological model of Phase II.
The reasonableness of the estimation result in Phase I has been confirmed by comparison with
the Phase II result. Significant differences between the estimation results could not berecognized for both Mizunami and Horonobe.
(4) Volume of inflow into underground facilities
Groundwater flow analyses with the aim of predicting the inflow rate into the undergroundfacilities were conducted using the hydrogeological model taking into account hydraulicheterogeneity24). Pilot borehole investigations were carried out to predict the inflow rate andto specify inflow points. Based on the investigation results, inflow reduction measures havebeen planned24),25),26),27),28),29),30),31).
An overview of the prediction results using groundwater flow analyses are summarized asfollows:- The inflow volume rapidly increases in the zone crossed by a high-permeability fault.
- The highly permeable structures were found to affect the volume of the inflow
significantly.
- The number and locations of the highly permeable structures intersecting theunderground facilities will be influenced strongly by uncertainties in the geometry of
those structures.
Overview of the pilot borehole investigation results are summarized as follows:- 39 -

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JAEA-Review 2016-014- Pilot borehole investigations could be used to specify inflow points.
- The geological and hydrogeological characteristics of the inflow points were described.
- The actual inflow volume could be reduced by grouting that was planned based on thepilot borehole investigations.
The probability of generation of water inflow has been estimated based on a stochastic
discrete fracture network model. The relationship between the amount of information becauseof the progress of the investigations and the risk regarding cost variation for thecountermeasures has been studied32),33),34),35),36),37) (Fig. 2.2.3-18, Fig. 2.2.3-19). The mainachievements are summarized as follows:- Pilot borehole investigations are effective for understanding the geological andhydrogeological characteristics.
- It is important to characterize the water-conducting features located around theunderground facilities as well as in the vicinity of the facilities.
- For rational characterization of water-conducting features, an effective method is toconduct detailed borehole investigations following investigations on a wider area using
techniques that yield 2D information to identify the open issues for which more detailed
information is required.

Fig. 2.2.3-18 Discrete fracture network model for estimation of the inflow rate into
underground facilities- 40 -

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Fig. 2.2.3-19 Example of a risk curve showing the risk regarding cost variation for thecountermeasures(5) Tools developed and adopted
The system for geological and hydrogeological modeling and visualization has been developed
to provide an efficient modeling platform that allows users to modify their models quickly inresponse to the acquisition of new data38) (Fig. 2.2.3-20). This system has the advantages thatthe modeling and numerical analysis are integrated and both discontinuities and rock matrix
zones can be considered simultaneously. Using the system, the 3D grid of groundwater flow
analysis is constructed automatically, even for complex geological models. The automatic
generation function of the discrete model is particularly effective in reducing the effort
required for modeling complicated geological structures and conducting groundwater flow
analyses based on the model, and also for developing a number of models (e.g., for sensitivity
analysis). The visualization of the results obtained by the groundwater flow analysis allowed
effective evaluation of the analytical results.

Fig. 2.2.3-20 Tools for supporting the rapid construction of geological environmental models- 41 -

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2.2.4 Summary
Techniques and accumulated technical knowledge regarding investigation, analysis, andassessment for characterization of groundwater flow conditions and for prediction of volume
of inflow into underground facilities are listed below.
(1) Generic techniques- The procedure described below is effective to characterize the hydrogeologicalenvironment.
• Preliminary characterization of hydrogeological structures affecting groundwaterflow field in a wider area using techniques providing 2D information• Identification of open issues requiring more detailed information• Borehole investigations addressing the investigation items- Preferentially investigating the uncertain items identified by groundwater flow analysis
with sensitivity analysis is effective.
- A modeling system allowing users to quickly construct and modify models in response to
the acquisition of new data was developed.
- The technical findings for hydrogeological characterization are summarized and areavailable for inspection23),39),40).
(2) Groundwater flow field- In order to characterize the groundwater flow field, preferential investigation of thehydraulic characteristics of faults across to the major groundwater flow direction isnecessary.
- The major groundwater flow direction is in line with the overall topography.
(3) Spatial variability of groundwater flux
- The spatial distributions of hydraulic head are different in the areas divided by faults
with low hydraulic conductivity across to the major groundwater flow direction. The
hydraulic gradient in the areas bounded by such faults with low hydraulic conductivity
tends to be low.
- Monitoring of hydraulic responses in the hydrogeological compartment is useful tocharacterize the connectivity and hydrogeological characteristics of hydrogeologicalstructures forming hydrogeological compartments.
- In order to ensure sufficient quality of test data for rocks with a wide range of hydrauliccharacteristics, a series of improvements was successfully undertaken on packer test
equipment, and efficient testing procedures and data evaluation methods weredeveloped41),42) (Fig. 2.2.4-1, Fig. 2.2.4-2).
- The fluid electrical conductivity logging method is capable of detecting water-conducting
features with a transmissivity two orders of magnitude lower than that detected by theflow-meter logging method using impellers or electric-magnetic flow-meters (Fig. 2.2.43).

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Fig. 2.2.4-1 Sequential hydraulic testing procedure (MIU)

Fig. 2.2.4-2 Sequential hydraulic testing procedure (Horonobe)- 43 -

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Fig. 2.2.4-3 Example of fluid logging (MIU)(4) Spatial variability of water fluxes in higher-permeability rocks and aquifers- Techniques of investigation, analysis, and assessment to characterize the spatial
variability of water fluxes in higher-permeability rocks and aquifers are the same as
those used to characterize the spatial variability of groundwater flux.
(5) Volume of inflow into underground facilities- Pilot borehole investigations are useful for the improvement of prediction accuracy.
In further studies, development of effective investigation techniques for continuous dataacquisition on fractures with a wide range of hydraulic characteristics in a continuous manner
will be performed in A2-1 and fed back to A1-1. The development of the discrete fracture
modeling methodology is also important.
References
1) Saegusa, H., Matsui, H., Hama, K., Sato, T., Tsuruta, T., Takeuchi, R., Kunimaru, T.,
Matsuoka, T. and Mizuno, T. : “Concept and Procedure of Geoscientific Study in the
Mizunami Underground Research Laboratory Project - Study Plan on Construction Phase(Phase II) and Operation Phase (Phase III) to 500 m Depth”, JAEA-Review 2011-022 (2011),
78p. (in Japanese).

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2) Onoe, H., Saegusa, H., Ohyama, T. and Endo, Y. : “Stepwise hydrogeological modeling andgroundwater flow simulation on Site scale (Step 4)”, JAEA-Research 2007-034 (2007), 106p.
(in Japanese).
3) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Project; Investigation
report for the 2012 fiscal year”, JAEA-Review 2013-037 (2014), 63p. (in Japanese).
4) Karino, T. and Takeuchi, R. : “Data of Long Term Hydro-pressure Monitoring on Tono
Regional Hydrogeological Study Project for Fiscal Year 2010”, JAEA-Data/Code 2012-001(2012). (in Japanese).
5) Karino, T. and Takeuchi, R. : “Data of Long Term Hydro-pressure Monitoring on Mizunami
Underground Research Laboratory Project for Fiscal Year 2010”, JAEA-Data/Code2012-002(2012), 54p. (in Japanese).
6) Sato, S., Ogata, N., Takeuchi, R. and Saegusa, H. : “Monitoring of groundwater inflow into
research galleries in the Mizunami Underground Research Laboratory Project (MIU
Project); From fiscal year 2004 to 2011”, JAEA-Data/Code 2013-020 (2014), 38p. (inJapanese).
7) Ohyama, T., Takeuchi, R., Saegusa, H., Onoe, H. and Matsuki, K. : “Applicability of themethod to estimate hydrogeological structures using a tilt data”, Proceeding of the 37th
symposium on rock mechanics, pp.245-250 (2008). (in Japanese).
8) Ohyama, T., Saegusa, H., Takeuchi, R., Takeuchi, S. and Matsuoka, T. : “Multiple lines ofevidence for characterization of hydrogeological structures at the Mizuami undergroundresearch laboratory in Tono area, Japan”, 2009 Annual Conference and General Assemblyof Korean Society for Rock Mechanics, pp.245-252 (2009).
9) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2008 fiscal year”, JAEA-Research
2009-032 (2009), 68p. (in Japanese).
10) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2009 fiscal year”, JAEA-Review
2010-039 (2010), 67p. (in Japanese).
11) Daimaru, S., Takeuchi, R., Onoe, H. and Saegusa, H. : “Results of single borehole hydraulictesting in Mizunami Underground Research Laboratory Project (Phase 2)”, JAEAData/Code 2012-020 (2012), 44p. (in Japanese).
12) Daimaru, S., Takeuchi, R. and Onoe, H. : “Study on hydrogeology in the Mizunami
Underground Research Laboratory Project; Hydrogeological investigation to evaluate
hydraulic characteristic of Main-shaft fault”, JAEA-Research 2012-008 (2012), 70p. (inJapanese).
13) Takeuchi, S., Shimo, M., Doughty, C. and Tsang, C.-F. : “Identification of the WaterConducting Features and Evaluation of Hydraulic parameters using Fluid Electric
Conductivity Logging”, Proceedings of the Second International Symposium on Dynamics
of Fluids in Fractured Rock, pp.349-354 (2004).
14) Takeuchi, S., Shimo, M., Jho, M. and Tsang, C.-F. : “Evaluation of the water-conducting
features and their hydraulic parameters using fluid electric conductivity logging”,- 45 -

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Proceedings of the 33rd Symposium on Rock Mechanics, Japan Society of Civil Engineers,
pp.451-456 (2004). (in Japanese).
15) Sato, S., Ogata, N., Takeuchi, R. and Takeda, M. : “Annual data compilation of waterbalance observation in the Mizunami Underground Research Laboratory Project (MIU
Project) - For the fiscal year 2010 to 2011 -”, JAEA-Data/Code 2013-016 (2013), 50p. (inJapanese).
16) Onoe, H., Takeuchi, R., Saegusa, H., Daimaru, S. and Karino, T. : “Interpretation of
Hydrogeological Characteristics based on Data from Long-Term Cross-Hole Pumping Test”,
Proceedings of the 19th International Conference on Nuclear Engineering, CD-ROM (2011).
17) Shimo, M., Kumamoto, S., Onoe, H. and Saegusa, H. : “Mizunami Underground ResearchLaboratory Project (Study on hydrogeology in crystalline fractured rock) Hydrogeologicalmodeling and groundwater flow simulation based on data of hydraulic impacts during
construction of MIU facilities (FY2006 - 2007)”, JAEA-Research 2011-017 (2011), 132p. (inJapanese).
18) Ando, K., Tanaka, T., Hashimoto, S., Saegusa, H. and Onoe, H. : “Study for establishmentof the methodology for hydrogeological modeling using hydraulic discrete fracture networks(Study on hydrogeology in crystalline fractured rock)”, JAEA-Research 2012-022 (2012),
60p. (in Japanese).
19) Hishiya, Y., Maemura, T., Kimura, H., Onoe, H., Saegusa, H. and Mizuno, T. : “Study ofhydrogeology in the Mizunami Underground Research Laboratory Project; Hydrogeologicalmodeling and groundwater flow simulation based on data of hydraulic and geochemical
impacts during the construction of the MIU facilities; FY 2010”, JAEA-Research 2013-023(2013), 84p. (in Japanese).
20) Yamamoto, Y., Maekawa, K., Yokota, H. and Yamazaki, M. : “Estimation of groundwater
recharge rate and spatial distribution of hydrological quantities in surface hydrogeologicalinvestigation basin of Horonobe URL Project - From December 2004 to November 2009 -”,JAEA-Research 2011-042 (2012), 97p. (in Japanese).
21) Yokota, H., Yamamoto, Y. and Maekawa, K. : “A Study of shallow groundwater flow basedon groundwater level and geological structures in the Horonobe area, Hokkaido”, Journalof groundwater hydrology, Vol.53, No.2, pp.193-206 (2011). (in Japanese).
22) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Ohyama, T., Amano, Y., Murakami,
H., Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S.,
Ohhara, M. and Jin, K. : “Horonobe Underground Research Laboratory Project;
Investigation report for the 2008 fiscal year”, JAEA-Review 2012-035 (2012), 63p. (inJapanese).
23) (Eds.) Saegusa, H. and Matsuoka, T. : “Final report on the Surface-based Investigation
Phase (Phase I) at the Mizunami Underground Research Laboratory Project”, JAEAResearch 2010-067 (2011), 377p.
24) Mikake, S., Yamamoto, M., Ikeda, K., Sugihara, K., Takeuchi, S., Hayano, A., Sato, T.,
Takeda, S., Ishii, Y., Ishida, H., Asai, H., Hara, M., Kuji, M., Minamide, K., Kuroda, H.,
Matsui, H., Tsuruta, T., Takeuchi, R., Saegusa, H., Matsuoka, T., Mizuno, T. and Oyama,- 46 -

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T. : “Studies on planning and conducting for reducing water inflow because of undergroundconstruction in crystalline rock”, JAEA-Technology 2010-026 (2010), 146p. (in Japanese).
25) Tsuruta, T., Takeuchi, S., Takeuchi, R., Mizuno, T. and Ohyama, T. : “Result of the pilot
borehole investigations conducted from bottom of shafts at the Mizunami UndergroundResearch Laboratory”, JAEA-Research 2008-098 (2009), 116p. (in Japanese).
26) Funaki, H., Tokiwa, T., Ishii, E., Hatsuyama, Y., Matsuo, S., Tsuda, K., Koizumi, A.,
Ishikawa, T., Daijo, Y. and Sugiyama, K. : “Horonobe Underground Research Laboratory
project - Overview of the pilot borehole investigation of the ventilation shaft (PB-V01) Geological investigation -”, JAEA-Data/Code 2008-013 (2008), 65p. (in Japanese).
27) Funaki, H., Asamori, K., Sanada, H., Hatsuyama, Y., Yamamoto, T., Ijiri, Y., Matsuoka, K.,
Kimura, K., Lin, S. and Kumagai, T. : “Horonobe Underground Research Laboratory project- Overview of the pilot borehole investigation of the ventilation shaft (PB-V01) Geophysical loggings -”, JAEA-Data/Code 2010-002 (2010), 151p. (in Japanese).
28) Yabuuchi, S., Kunimaru, T., Ishii, E., Hatsuyama, Y., Ijiri, Y., Matsuoka, K., Ibara, T.,
Matsunami, S. and Makino, A. : “Horonobe Underground Research Laboratory project Overview of the pilot borehole investigation of the ventilation shaft (PB-V01);
Hydrogeological investigation”, JAEA-Data/Code 2008-026 (2009), 62p. (in Japanese).
29) Ishii, Y., Watanabe, K., Kamiya, A., Hayano, A., Mikake, S., Takeuchi, S., Ikeda, K.,
Yamamoto, M. and Sugihara, K. : “Results and considerations on the pre-excavation
grouting below four hundreds meter depth of the Ventilation Shaft”, JAEA-Technology
2010-044 (2011), 92p. (in Japanese).
30) Sawada, S., Nakayama, M. and Ishikawa, M. : “Collection of pre-grouting data in the URL
at the Horonobe Underground Research Laboratory Project - Data of Ventilation Shaft -”,JAEA-Data/Code 2013-018 (2013), 25p. (in Japanese).
31) Tsuyuguchi, K., Kuroiwa, H., Kawamoto, K., Yamada, N., Ohnuki, K., Iwatsuki, T.,
Takeuchi, R., Ogata, N., Suto, M. and Mikake, S. : “Results of pilot borehole investigationin -500 m Access/Research Gallery-North (12MI27 and 12MI33 boreholes)”, JAEATechnology 2013-044 (2014), 89p. (in Japanese).
32) Motoshima, T., Ijiri, Y., Onoe, H., Saegusa, H. and Ohtsu, H. : “A study of risk assessmentof rapid inrush of water into the underground facility at the Mizunami undergroundresearch laboratory project (part 1) - development of risk assessment methodology of water
inrush using discrete fracture network model -”, EIT-JSCE Joint Seminar on RockEngineering (2007).
33) Onoe, H., Saegusa, H., Motoshima, T., Ijiri, Y. and Ohtsu, H. : “A study of risk assessmentof rapid inrush of water into the underground facility at the Mizunami undergroundresearch laboratory project (part 2) - Relationship between progress of investigations andcost variation related to water inrush -”, EIT-JSCE Joint Seminar on Rock Engineering(2007).
34) Ohtsu, H., Hotta, Y., Saegusa, H., Ijiri, Y. and Onoe, H. : “An application of risk assessment
method of water inrush in fractured rock masses to actual underground construction
project”, Journal of Japan society of civil engineers, F, Vol.64, No.4, pp.353-368 (2008). (in- 47 -

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Japanese).
35) Ohtsu, H., Arizono, H. and Saegusa, H. : “A Consideration on the value on geologicalinvestigation focusing on water inrush in discontinuous rock masses from viewpoints ofconstruction contract”, Journal of Japan society of civil engineers, F, Vol.66, No.1 (2010).
(in Japanese).
36) Ohtsu, H., Ohkawa, J., Takeuchi, R., Saegusa, H. and Ota, Y. : “A Study on the meaning ofgeological investigation focusing on water inrush from viewpoint of geological risk”,
Proceeding of the 41st symposium on rock mechanics (2012). (in Japanese).
37) Motoshima, T., Onoe, H., Ijiri, Y., Ohtsu, H. and Saegusa, H. : “A study on risk assessment
approach of water inflow into a shaft in fractures rock mass”, Journal of Japan society ofcivil engineers, C, Vol.66, No.2, pp.370-386 (2010). (in Japanese).
38) Ohyama, T. and Saegusa, H. : “GEOMASS System”, JAEA-Testing 2008-007 (2009), 248p.
39) Ohsawa, H., Ota, K., Hama, K., Sawada, A., Takeuchi, S., Amano, K., Saegusa, H.,
Matsuoka, T., Miyamoto, T., Toyoda, G., Iwatsuki, T., Maekawa, K., Kunimaru, T., Niizato,
T., Asamori, K., Hiraga, M., Yamanaka, Y., Shigehiro, M., Shimada, A., Abe, H. and Umeki,
K. : “Establishment of advanced integration technology for site characterization of deep
geological repository - Development of information synthesis and interpretation system Annual report 2007”, JAEA-Research 2008-085 (2008), 741p. (in Japanese).
40) Saegusa, H., Takeuchi, S., Maekawa, K., Osawa, H. and Semba, T. : “Technical know-how
for modeling of geological environment (1) Overview and groundwater flow modeling”, The
13th International Conference on Environmental Remediation and Radioactive Waste
Management (2010).
41) Saegusa, H., Niizato, T., Yasue, K., Onoe, H. and Doke, R. : “Technical know-how of site
descriptive modeling for site characterization”, The 14th International conference on
Environmental Remediation and Radioactive Waste Management (2011).
42) (Eds.) Ota, K., Abe, H. and Kunimaru, T. : “Horonobe Underground Research Laboratory
Project Synthesis of Phase I Investigations 2001-2005 Volume “Geoscientific Research”,
JAEA-Research 2010-068 (2011), 370p.

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2.3 Hydrogeochemistry
2.3.1 Introduction
Aspects of groundwater chemistry such as the chemical composition (salinity), pH, and redox
potential are indispensable parameters for safety assessment of HLW disposal. Knowledge ofthese parameters is necessary for decision-making during site selection and the subsequent
underground facility construction. Investigation of groundwater chemistry needs to be
conducted considering the three-dimensional geology, hydrogeological structure, andgroundwater flow, because the chemistry evolves by the mixing of chemically distinct waters
and water–mineral–microbe interactions. This chapter provides basic knowledge on surfacebased investigation techniques to evaluate the hydrogeochemical conditions prior to theconstruction of underground facility.
2.3.2 Objectives in the second mid-term research phase
Most of the surface-based investigations were conducted during the first mid-term plan. The
reliability of the estimated hydrogeochemical preliminary condition was confirmed byobservations during the facility construction. The performance target of R&D in the second
mid-term research phase is listed in Table 2.3.2-1.
Table 2.3.2-1 Performance target of R&D for the hydrochemistry
Focus

Performance target of R&D

Tasks

Siting decision

To provide an investigation techniqueand determination method to determine
chemically favorable or unfavorable
domains.

• Methodology for borehole layout andobservation to identify spatial
groundwater chemistry• Methodology for data traceability andtransparency• Analysis and modeling procedure

Construction
decision

To provide an investigative techniqueand determination method to judge;• Whether drainage during facility
construction satisfies environmentallaw• Hydrochemical changes during
facility construction and operation• Borehole investigation methods toestimate chemical composition ofdrainage• Approach on design and layout ofgallery to suppress hydrochemical
disturbance• Technique for estimatinghydrochemical disturbance caused bylong-term drainage

2.3.3 Project details and outcomes
Groundwater was sampled from three boreholes (MSB-2, MSB-4: 100–200 m deep insedimentary rocks; MIZ-1: 1,200 m deep in granitic rock) at the Mizunami URL site. In
addition, data obtained from the regional hydrological study (DH-2: 500 m deep in granitic
rock; DH-15: 1,000 m deep in sedimentary and granitic rocks) were used to estimate the spatial
distribution of groundwater chemistry and its evolution. The results are summarized in Fig.
2.3.3-1.

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Hydrogeochemical data were obtained from water collection rings in the shafts, inflow fromthe excavation wall, and boreholes drilled from galleries and the ground surface. Based oncomparison of the newly obtained data with the results of previous surface-based
investigations1),

theinvestigation

techniques

andprocedures

tounderstandthehydrogeochemical baseline conditions were confirmed.

Fig. 2.3.3-1 Distribution of groundwater chemistry and the hydrochemical model constructedfrom surface-based investigations (MIU)
Groundwater chemistry around the MIU is classified into three types: 1) Na–Ca–HCO3–SO4type in the shallower sedimentary rocks; 2) Na–Ca–Cl type with relatively low salinity in the
deeper sedimentary rocks and shallower granite; and 3) Na–Cl type with relatively highsalinity in deeper granite. The hydrochemical spatial distribution is controlled by mixing ofthese groundwater types1).
In the Horonobe area, groundwater was pumped from 11 deep boreholes (HDB-1 to -11, withborehole lengths of approximately 500 m to 1,000 m), which were drilled from the surface. In- 50 -

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addition, pore waters were also squeezed from core samples of each borehole. In collaboration
with other research organizations such as National Institute of Advanced Industrial Scienceand Technology (AIST) and Central Research Institute of Electric Power Industry (CRIEPI),
pumped waters and pore waters were also collected from additional boreholes such as HCD-1(300 m depth) and SAB-1 (500 m depth). Chemical analyses of pumped and pore waters were
performed to identify the variation and evolution of groundwater chemistry (e.g., salinity) in
the Horonobe area. Salinity distribution and a hydrochemical model based on the results
obtained through surface-based investigation phase are illustrated in Fig. 2.3.3-2. According
to the hydrochemical model, the followings are considered to have been important processes
in the evolution of groundwater chemistry in Horonobe: diagenetic processes forming the fossil
seawater during sedimentation, mixing processes affecting the salinity distribution (mixing
between the fossil seawater and young meteoric water), and dilution processes derived fromwater of dehydration from biogenic silica during diagenesis. Based on the measurements ofphysicochemical parameters (pH and oxidation–reduction potential: ORP), appears to beslightly alkaline and weakly reducing (approximately −100 mV value of Eh).
In the second mid-term research phase plan, the applicability of prediction methods
developed in the surface-based investigation phase has been confirmed. For validation of theprediction methods, comparative studies for the predicted parameters (e.g., pH, ORP, andprobable groundwater salinity) and the measurements obtained from the shafts/boreholes
during the construction phase of the URL until G.L. −350 m were performed.

Fig. 2.3.3-2 Distribution of groundwater chemistry (salinity) and the hydrochemical model
constructed from surface-based investigations (Horonobe)
The groundwater in the Horonobe area is considered to have originated as fossil seawater
trapped during sedimentation. The spatial distribution of hydrochemistry could have been
controlled by mixing of fossil seawater, meteoric water, and water of dehydration from biogenic
silica during diagenesis.
(1) Groundwater chemistry (salinity)
1) Mizunami
Chlorine is not susceptible to water–mineral interaction. The Cl concentrations in WRs up to- 51 -

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the depths of 500 m are shown in Fig. 2.3.3-3. The groundwater chemistry that was identified
immediately after facility construction was almost the same as the results of surface-based
investigations. Thus, the investigation techniques and procedures applied during surfacebased investigation phase are suitable for understanding the hydrochemistry. The chemical
type of the groundwater and the salinity distribution was influenced by specifichydrogeological structures (e.g., faults, low-permeability layers, and fracture zones). A
borehole layout taking these structures into account is essential during surface-based
investigations to confirm the relationship between the hydrogeological structure and thethree-dimensional hydrochemical distribution. The investigation techniques and proceduresfor surface-based investigations are summarized by Saegusa et al. (2011)2).

Fig. 2.3.3-3 Comparison of Cl concentrations in groundwater estimated by surface-based
investigations and by investigations during the construction phase2) Horonobe
Comparison between the measured salinity variations of groundwater during the surfacebased investigation phase and the relevant data obtained through the construction phase of
the URL until G.L. −350 m level was performed. The results show that the groundwatersalinity in a lower-permeability zone was almost identical to the predictions obtained during
the surface-based investigation phase. Therefore, it was suggested that the method ofpredicting the salinity distribution used in the surface-based investigation phase is anappropriate technique. In addition, multivariate statistical analysis could be considered as asuitable method for comparison of data obtained in the surface-based investigation andconstruction phases of the URL, excluding data affected by engineering materials used in thedrifts/shafts. Because the groundwater chemistry can change in higher-permeability zones
after the construction of URL, it should be noted that determination of variations in salinity
corresponding to the hydraulic properties and geological structures may be a key issue in thesurface-based investigation phase.

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Furthermore, the efficiency of using electric resistivity surveys to evaluate the salinity
distribution has also been demonstrated by the good agreement between the results ofextrapolation of salinity variations based on the chemical analysis and resistivity logging dataobtained from deep boreholes (Fig. 2.3.3-4). The reason for this good agreement might be thecorrelation of the electric resistivity and salinity. This empirical knowledge implies that theresults of geophysical exploration would be useful to complement the lack of salinity
distribution data between the boreholes by extrapolation. Electric exploration at the surface
could obtain variations in the specific resistivity in the depth of 200 m as a maximum; however,certain conditions might be necessary in order to evaluate the salinity distributions
appropriately: 1) a significant contrast in electric resistivity between rock matrix andgroundwater; 2) homogeneity of electric resistivity in the rock matrix.

Salinity distribution

Fig. 2.3.3-4 Results of surface-based electrical surveys and resistivity logging using
boreholes (upper), and the distribution of Cl concentrations in groundwater (lower)(2) pH and redox conditions
The pH and redox conditions can be measured by installing in situ sensors into boreholes
during the surface-based investigation phase. The observed values can be evaluated using
theoretical calculations based on the chemical composition of groundwater. However, it isdifficult to investigate at a large number of sites because of limitations of the budget and the- 53 -

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schedule of the surface-based investigation phase2). Moreover, formation of iron-compound
films, possibly of redox-controlling material, has been observed on the walls of several
boreholes3) (Fig. 2.3.3-5). Thus, the quality of the redox data observed from the surface is
uncertain.
During construction phase, pH and redox values were directly measured under pressurized
and anaerobic conditions in the boreholes drilled from the gallery to confirm the redox
conditions. In addition, periodic redox measurements were obtained in the boreholecontaminated by iron-compound films to understand the influence of this contamination
during borehole drilling.

Fig. 2.3.3-5 Contamination by iron compounds on a borehole wall caused by drilling(left: immediately after drilling, right: after formation of films)
1) Mizunami
The redox potentials measured in the surface-based investigation phase and construction
phase are illustrated in Fig. 2.3.3-63). The redox potentials measured immediately after
interrupting borehole drilling from surface tend to correspond with the values measured at
the gallery. Measurement of groundwater immediately after drilling is probably important tominimize contamination. The pH and redox potential plots for near the calcite/bicarbonate ionboundary, ferric iron/ferrous hydroxide, and ferric iron/sulfide minerals are illustrated. These
reactions may control the pH/redox conditions of groundwater.
In the periodic redox measurement in the borehole with iron-compound films at MIZ-1, redox
potential approached the initial reducing value obtained immediately after drilling (approx.
−300 mV) with an increase in the pump-out water volume (Fig. 2.3.3-7). This would have been
because the contamination by iron compounds was removed by flushing with a large volumeof groundwater. There are many outstanding questions about the formation process of the ironcompound. Iron derived from the drill bits used for borehole drilling may be reduced andabsorbed on the borehole wall. The elucidation of this process and development of a removal
method for the iron compound are future tasks.

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Fig. 2.3.3-6 pH and redox conditions of groundwater obtained by surface-based investigation
and by investigation during the construction phase (MIU)

Fig. 2.3.3-7 Variation in physicochemical parameters during pumping at borehole MIZ-1,
Section 9 (1150 mabh(meter along borehole))
2) Horonobe
Fig. 2.3.3-8 shows pH–Eh diagrams including data obtained both at the surface andunderground. Dissolution/precipitation reactions of calcite might control the pH of- 55 -

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groundwater because of the fact that the measured partial pressure of CO2 (PCO2) and the pHof groundwater showed good agreement with the theoretically calculated value assuming
calcite equilibrium. Moreover, the effect of CO2(g) degassing on the pH of pumped water has
been evaluated for the groundwater sampled from the borehole at 500 mbgl (meter below
ground level). The measured pH of groundwater at the surface was higher by approximately
0.4 compared to the in situ pH value. A correction method for pH changes caused by CO2(g)degassing has been proposed; this method involves measuring the amount of degassed CO2(g)and calculating the PCO2, which corresponds to the in situ condition4). Fig. 2.3.3-8 (a) shows
the pH and redox conditions of the groundwater measured in deep boreholes. Data obtained
at a depth of around 500 mbgl are plotted on the equilibrium lines of redox reactions related
to sulfate ions and ferric sulfide or pyrite (lines 2 and 3 in Fig. 2.3.3-8 (a)). In contrast, data
derived from a depth of around 600 mbgl are plotted on the equilibrium line of sulfate ionsand hydrogen sulfide ions (line 1 in Fig. 2.3.3-8 (a)). The results obtained in the tunnel at 140
mbgl are plotted in Fig. 2.3.3-8 (b). Although the data in Fig. 2.3.3-8 (b) were obtained from
depths different from those in Fig. 2.3.3-8 (a), the measured values are also plotted around theline of bicarbonate ions and pyrite and/or that of sulfate ions and pyrite. Therefore, it issuggested that these reactions are important in the redox reactions of groundwater in thesedimentary rocks in the Horonobe area4).
(a) Surface-based investigation(b) Investigation during shaft construction

Fig. 2.3.3-8 pH and redox conditions of groundwater obtained during the surface-based
investigation and the construction phases (Horonobe)(3) Groundwater residence time
The practicability of using chemical tracers (e.g., 14C, 36Cl, 37Cl, and 4He) to estimate
groundwater residence time was confirmed for various hydrogeological conditions (e.g., rocktype and groundwater flow conditions)5).

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1) Mizunami
Groundwater dating using the 14C concentration in dissolved inorganic carbon (DIC) has
primordial uncertainty due to contamination by “dead” (14C-free) carbon derived fromcarbonate minerals. In the crystalline rock (MIU) without solid organics, a 14C dating method
using dissolved organic matter (DOM) was developed. In this method, a procedure forseparating artificial organics (e.g., fluorescent dyes) from natural DOM was also presented6).
2) Horonobe
A method of groundwater dating using radioactive chlorine (36Cl), helium (4He), andradioactive iodine (129I) was developed to allow more precise estimation of residence time ofgroundwater (Fig. 2.3.3-9). In deeper locations, where the contribution of meteoric water
infiltration is faint, the groundwater age showed a good agreement with the sedimentation
age of geological formation. In consequence, the estimated age of the groundwater supports
the scenario of groundwater evolution in which the present-day groundwater was formed
from mixing of fossil altered seawater that was trapped in sedimentary rocks from the time of
sedimentation and meteoric water. In addition, several notations regarding the applicationsof these geochronological methods (i.e., attention to the correction of the degassing effect ofhelium at the time of sampling) were summarized.

Fig. 2.3.3-9 Groundwater residence time estimated based on 36Cl and 4He, and groundwaterevolution process estimated from δ18O and δD depth profiles (Horonobe)
2.3.4 Summary
The techniques and procedures for understanding the hydrochemical baseline conditions
prior to facility construction have been prepared to date (Fig. 2.3.4-1). R&D will be completed
by performing feedback of knowledge relevant to the facility closure into surface-based- 57 -

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investigations in future.
The messages in this section are summarized as follows:- Make a plan of monitoring taking the hydrogeological compartments and potential
permeable zones (e.g., conglomerates, faults, unconformities, and fractured zones) into
consideration.
- For areas with homogeneous geology and saline water, the spatial distribution ofgroundwater salinity between boreholes can be interpolated based on electric andelectromagnetic surveys at the ground surface and electrical logging in boreholes.
- New redox-controlled secondary minerals may precipitate on borehole walls duringborehole investigations. Borehole walls should be observed using BTV observation prior
to redox measurement. The preliminary measurements of redox conditions at the surface
should be observed by measurements in the gallery.
- The measured redox values should be checked using theoretical calculations (withparticular attention paid to carbonates and sulfide minerals–water interactions).
Data for 3H and 14C are available for piston-flow conditions in homogeneous sedimentaryrocks. Several isotopic measurements (36Cl, 4He, and oxygen isotope shifts) are indexes of longterm residence conditions of seawater. Data for 14C of DOM are available for non-piston-flow
conditions in fractured granite.

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Fig. 2.3.4-1 Procedure for hydrogeochemical modelling during surface-based investigations- 59 -

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References
1) Iwatsuki, T., Furue, R., Mie, H., Ioka, S. and Mizuno, T. : “Hydrochemical baseline conditionof groundwater at the Mizunami underground research laboratory (MIU)”, Applied
Geochemistry, 20, pp.2283-2302 (2005).
2) (Eds.) Saegusa, H. and Matsuoka, T : “Final report on the Surface-based investigation phase(Phase I) at the Mizunami Underground Research Laboratory Project”, JAEA-Research
2010-067 (2011), 377p.
3) Iwatsuki, T., Hagiwara, H., Ohmori, K., Munemoto, T. and Onoe, H. : “Hydrochemical
disturbances measured in groundwater during the construction and operation of a largescale underground facility in deep crystalline rock in Japan.”, Environ Earth Sci, Volume
74, Issue 4, pp. 3041-3057 (2015).
4) Sasamoto, H., Arthur, R. C. and Hama, K.: “Interpretation of undisturbed hydrogeochemical
conditions in Neogene sediments of the Horonobe area, Hokkaido, Japan”, Applied
Geochemistry, 26(8), pp.1464-1477 (2011).
5) Hama, K. and Metcalfe, R. : “Groundwater dating applied for geological disposal ofradioactive waste - A review of methods employed worldwide -”, J. Jap. Assoc. Hydrol. Sci.,
44, pp.39-64 (2014).
6) Nakata, K., Kodama, H., Hasegawa, T., Hama, K., Iwatsuki, T. and Miyajima, T. :“Groundwater dating using radiocarbon in fulvic acid in groundwater containing
fluorescein”, Journal of Hydrology 489, pp.189-200 (2013).

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2.4 Rock mechanics
2.4.1 Introduction
In situ stress and rock properties are important in the design and construction of large anddeep underground structures. In fact, in situ stress is recognized as the primary factor in thedevelopment of an excavation damaged zone (EDZ). An EDZ is likely to be less stable than theundisturbed rock mass and to provide higher-permeability pathways for groundwater flow inthe vicinity of excavations. Thus, development of an EDZ is recognized as a key issue both forthe design and construction of disposal facilities and for safety assessment. In Phase I, it isnecessary to understand the initial state of the rock conditions using borehole investigations
and laboratory tests using core samples. In Phase II, it is necessary to obtain detailed
information by investigation from the shaft and gallery and to compare with the information
obtained during Phase I.
The subjects of rock mechanical studies are as follows:- In situ stress- Rock properties- Thermal gradient- Thermal properties
2.4.2 Objectives in the second mid-term research phase
The objectives of rock mechanics investigations during construction phase (Phase II) is tounderstand the detailed in situ stress conditions and rock mechanical properties by borehole
investigations from the shaft and gallery, and laboratory tests during extension of the shaft
and gallery at depths of 500 m (Mizunami) and 350 m (Horonobe). Also, it is necessary toconfirm the validity of the conceptual model and analysis technique applied in Phase I. Table
2.4.2-1 lists the target level of R&D, achievement items, and reflection of the results of R&D.
In Phase I, the thermal gradient and thermal properties of rock were also obtained.
Table 2.4.2-1 Performance target of R&D for rock mechanical characterization
Focus

Siting decision

Performance target of R&D

Decision-making for selection of goodrock conditions.

Tasks• Technology of rock mechanicalinvestigation from the surface• Technology of modeling and numericalanalysis to estimate the regional stressfield

2.4.3 Project details and outcomes(1) In situ stress conditions
1) Mizunami
During the surface-based investigation phase (Phase I), hydraulic fracturing tests were
performed in borehole MIZ-1 and core-based in situ stress measurements (AE (Acoustic
Emission) /DRA (Deformation Rate Analysis), ASR (Anelastic Strain Recovery), DSCA

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JAEA-Review 2016-014(Differential Strain Curve Analysis)) were also obtained1). A conceptual model for rockmechanics was developed on the basis of the data obtained, and numerical analysis was
performed to estimate the regional stress and excavation damaged zone (EDZ). In Phase II,
the Compact Conical-ended Borehole Overcoring (CCBO) technique was performed in eachgallery to understand the 3D in situ stress state. Based on the results of these investigations,the conceptual model and analysis technique applied in the Phase I was confirmed2),3),4),5),6).
The conclusions are as follows:- The direction of horizontal maximum principal stress is NW–SE based on the results ofhydraulic fracturing tests in the MIZ-1 borehole. The results correspond to the regional
stress state estimated from movement of plates and GPS surveys. The stress state isreverse-fault type in the upper part to a depth of 400 m and normal-fault type to strikeslip-fault type in the lower part to a depth of 600 m, estimated from vertical stress andhorizontal stresses1).
- The direction of horizontal maximum principal stress is NW–SE based on the CCBO
results in the G.L. −100 m, 200 m and 300 m galleries. The results show good agreementwith the hydraulic fracturing tests in borehole MIZ-1 (Fig. 2.4.3-1)2),3),4),6).
- For individual elemental technology, a high-compliance system of hydraulic fracturing
was applied and the quality of data for the maximum principal stresses improved
compared to that from the ordinary system7). We developed a groundwater inflow
countermeasure tool and applied it to in situ stress measurement using the CCBO
technique8) (Fig. 2.4.3-2). The applicability of the core-based method (DSCA: Differential
Strain Curve Analysis) was tested against the hydraulic fracturing tests and overcoring
method9).
- To estimate simultaneously the regional stress fields and the elastic modulus of the rockmass from the in situ stress measurements, back-analysis based on three-dimensional
finite element analysis and the boundary element method were developed; subsequently,
the direction and principal stress magnitudes at MIU were predicted10),11),12),13). The trend
in the analyzed results coincides with the results obtained from hydraulic fracturing tests
performed in the MIZ-1 borehole and using the CCBO technique in the G.L. −200 m and−300 m galleries14).

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Fig. 2.4.3-1 Comparison of the in situ stress distributions from measured and analyzed
values (Mizunami)

Fig. 2.4.3-2 Countermeasures against inflow during initial stress measurement by compact
conical-ended borehole overcoring technique2) Horonobe
Hydraulic fracturing tests and observations of the breakout were conducted in the boreholes
around the URL (Phase I), and in the G.L. −140 m, 250 m, and 350 m galleries in the URL
during Phase II (Fig. 2.4.3-3). In each location, three boreholes, 76 mm in diameter and 20 m
in length, were drilled. The orientation (trend and plunge) was different for each borehole.
Hydraulic fracturing tests in the galleries were conducted using a high compliance hydraulicfracturing system in order to obtain reliable values of the fracture reopening pressure. The
conclusions obtained from the results can be summarized as follows:- The values and orientations (trend and plunge) of in situ stress in the G.L. −140 m- 63 -

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galleries (Fig. 2.4.3-4(a)) showed good agreement with each other15).
- The values and orientations of in situ stress are scattered in the G.L. −250 m galleries,
which are located near the transition zone of the Koetoi and Wakkanai Formations (Fig.
2.4.3-4(b)). No principal stresses act in the vertical direction15).
- The maximum principal stress is oriented NNW–SSE, plunging about 45° to the north in
the G.L. −350 m pumping gallery16). In the G.L. −350 m loop gallery east, the orientationof one of the principal stress was vertical; the value of the maximum and intermediate
principal stress was almost identical. The values of the stress in the 350 m galleries were
smaller than the results from the surface-based investigation (Fig. 2.4.3-4(c)).
- The ratio of the maximum horizontal stress measured in the gallery to that obtained in
the surface-based investigation was 0.4 to 0.9. On the other hand, the ratio of theminimum horizontal stress in the gallery to that obtained in the surface-based
investigation was 0.5 to 0.6 (Fig. 2.4.3-5)15). This phenomenon is considered to be theresult of decreased pore pressure resulting from shaft sinking and excavation ofgalleries16).
It is estimated that geological structures such as faults and folds affect the direction of in situ
stress (Fig. 2.4.3-6). Therefore, for the assessment of in situ stress, it is essential to integrate
the results of other measurement method such as analysis of borehole breakouts or
measurement methods using rock specimens from cores15),16).

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JAEA-Review 2016-014(a) G.L. −140 m gallery(b) G.L. −250 m gallery(c) G.L. −350 m gallery
Fig. 2.4.3-3 Locations of the stress measurements in the galleries
Circles indicate measurement locations. The colors of the circles correspond to the colors used in Figs.
2.4.3-4 and 5.

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JAEA-Review 2016-014(a) G.L. −140 m gallery(b) G.L. −250 m gallery(c) G.L. −350 m gallery
Fig. 2.4.3-4 Stress magnitudes and orientations obtained in the galleries indicated on Wolf
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σH(HDB-1)
σh(HDB-1)
σH(140V)σh(140V)σH(140E)σh(140E)
σH(250V)σh(250V)σH(250E)σh(250E)
σH(250W)σh(250W)
σH(350P)σh(350P)
σH(350E)σh(350E)100

Depth (m)200300

H=1.3×v
400

Estimated geologicalboundary (HDB‐6)500

h=0.9×v
Vertical stress：v(HDB‐6)

600
700
0

2

4

6

8

10

12

14

Horizontal stress (MPa)Fig. 2.4.3-5 Values of maximum and minimum horizontal stress measured in the galleries
and HDB-1

0

HDB-1
HDB-3
HDB-6
HDB-11
140V
140E
250V
250E
250W

100
200
300
400
500
600
700
-90 -60 -30
0
30
60
90
N
W
E
Orientation of the maximum horizontal stress (°)

Fig. 2.4.3-6 Orientations of the maximum horizontal stress measured in the galleries and
HDB-1, 3, 6, and 11- 67 -

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As the strength of the rock is different between Mizunami and Horonobe, there arelimitations in the use of in situ stress measurements because the former is in hard rock andthe latter in soft rock. It is difficult to apply in situ measurements because of the occurrenceof borehole wall collapses in the soft rock. Hydraulic fracturing tests cannot be used incollapsed boreholes. Moreover, overcoring techniques cannot be used in this type of boreholeas the technique assumes elastic behavior. In the case of collapse, borehole breakout can beused to estimate direction of maximum stresses. Although the CCBO technique can be usedin many rock types, the strain gauge cell could not be glued to the sedimentary rocks in
Horonobe.
(2) Physical and mechanical properties of rock1) Mizunami
The physical and mechanical properties of rock were obtained by laboratory tests (e.g.,
uniaxial compressive test, triaxial compressive test, and Brazilian test) in Phase I (Fig. 2.4.37). Based on the results of these tests, a conceptual model was developed. Laboratory tests
were also performed using cores obtained from boreholes drilled from the galleries and waste
rock from shaft excavation in Phase II, and a conceptual model was revised2),3),4),5). The
conclusions are as follows:- The physical and mechanical properties of rock obtained from MIZ-1 in the surface-based
investigation show good consistency with those obtained in Phase II and thecorresponding geological conditions.
- A conceptual model was developed on the basis of laboratory test results (Fig. 2.4.3-8). A
comparison of the statistical properties of Toki Granite obtained from MIU and thoseobtained from the literature survey of the second progress report17) was performed4).

Fig. 2.4.3-7 Depth distribution of the physical and mechanical properties of rock (Mizunami)- 68 -

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Fig. 2.4.3-8 Conceptual model of rock mechanics (Mizunami)2) Horonobe
To investigate the rock mass properties on the scale of the disposal facility, plate-loading tests
and direct shear tests were conducted in the G.L. −250 m and G.L. −350 m galleries (Fig. 2.4.39). In the direct shear tests, specimens 600 mm long, 600 mm wide, and 300 mm high wereprepared on the floor of the gallery, then a vertical load and a shear load were applied to thespecimen to obtain the failure stress state. In the plate-loading tests, a loading plate with adiameter of 600 mm was set on the floor and a vertical load was applied. The deformation
modulus and elastic modulus were obtained from the tests. On the basis of these in situ tests,
the properties of the rock mass were evaluated. The results can be summarized as follows:- In the plate-loading tests (Fig. 2.4.3-10), the deformation modulus and elastic modulus of
the Koetoi Formation in the G.L. −250 m gallery were almost same values as detected insurface-based investigation. On the other hand, in the G.L. −350 m gallery, the values of
the two moduli were larger than those from the surface-based investigation. From theperspective of designing facilities, the estimation of the deformation characteristics ofrock was almost valid18).
In the direct shear tests (Fig. 2.4.3-11), the shear stress of failure at low vertical stress wasalmost the same as the failure criterion detected in the surface-based investigation18).

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JAEA-Review 2016-014(a) GL−250 m gallery(b) GL−350 m gallery

Fig. 2.4.3-9 Locations of the plate-loading tests and direct shear tests(a) GL−250 m gallery(b) GL−350 m gallery
Fig. 2.4.3-10 Results of the plate-loading tests- 70 -

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Fig. 2.4.3-11 Results of the direct shear tests
The investigation methods, modeling, and analysis techniques for the rock mechanical field
are not dependent on the rock type.
(3) Thermal gradient distribution
1) Mizunami
Temperature logging was performed in borehole MIZ-1, which was drilled from the groundsurface. The calculated thermal gradient was approximately 1.9°C /100 m, in good agreementwith the value obtained from boreholes around MIU (about 2.0°C /100 m)19).
2) Horonobe
After the surface-based investigation, a long-term hydraulic monitoring system was inserted
in borehole HDB-3. The temperature was measured using the system at various depths. The
results showed that the geothermal gradient around the Horonobe URL is approximately
4.6°C /100 m17).
(4) Thermal properties of rock1) Mizunami
The thermal properties of Toki Granite obtained from borehole MIZ-1 were: thermal
conductivity 2.77–3.04 W/m ・ K; specific heat 0.74–0.93 J/g ・ K; and thermal expansion
coefficient 4.0–5.6 × 10−6 /°C20). Comparison of the statistical properties between Toki Granite
obtained from MIU and those obtained from the literature survey was performed. It was
confirmed that there was no great difference between them.
2) Horonobe
In the surface-based investigation, the thermal properties of the rock mass were also obtained.
The results showed that the thermal conductivity of the Koetoi Formation was 0.88 to 1.17

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W/m·K and the value for the Wakkanai Formation was 1.24 to 1.61 W/m·K. The specific heatin saturated conditions of the Koetoi Formation was 1.88 to 2.67 J/g·K; that of the Wakkanai
Formation was 1.34 to 1.53 J/g·K. In dry conditions, the specific heat values of both formations
were 1.34 to 1.53 J/g·K. The thermal expansion coefficients were about 5 to 7 × 10−6/°C in the
Koetoi Formation and 9 to 14 × 10−6/°C in the Wakkanai Formation. The coefficients of thermal
expansion decrease as temperature increases21).
Techniques to understand the thermal properties of rock by laboratory tests using core
specimens are applicable to many rock types.
2.4.4 Summary
The principal stresses and the directions were understood by in situ stress measurements,
and the applicability of the techniques and analysis methods was tested at Mizunami andHoronobe. An analysis method for regional stress field was developed. The statistics and depth
distribution of physical and mechanical properties of rock were understood. In situ loading
tests and direct shear tests were conducted at Horonobe.
It was shown that evaluation of the in situ stress field and mechanical properties of rock arepossible using in situ and laboratory tests together with numerical analysis.
Accumulation of knowledge about the in situ stress and mechanical properties of rock isnecessary to provide information for the design of the underground facility at a disposal site.
References
1) Hirano, T., Nakama, S., Yamada, A., Seno, Y. and Sato, T. : “Mizunami UndergroundResearch

Laboratory

Project(Rockmechanicalinvestigations);

MIZ-1

borehole

investigations”, JAEA-Research 2009-031 (2009), 58p. (in Japanese).
2) Hirano, T., Nakama, S., Yamada, A., Seno, Y. and Sato, T. : “Mizunami UndergroundResearch

Laboratory

Project(Rockmechanicalinvestigations);

In

situ

stressmeasurements and the laboratory tests using core on GL.-100m level of research gallery”,
JAEA-Research 2010-002 (2010), 48p. (in Japanese).
3) Hirano, T., Seno, Y. and Matsui, H. : “Mizunami Underground Research Laboratory Project;Rock mechanical investigations in situ stress measurements and laboratory tests using
core on the GL.-200m level of research galley”, JAEA-Research 2010-013 (2010), 51p. (inJapanese).
4) Tanno, T., Sato, T., Sanada, H. and Hikima, R. : “Mizunami Underground ResearchLaboratory Project; Rock mechanical investigations in situ stress measurements andlaboratory tests using core on the GL.-300m and GL.-400m level of research galley”, JAEAResearch 2013-044 (2014), 257p. (in Japanese).
5) Matsui, H. and Hirano, T. : “Preliminary validation of a rock mechanical conceptual model
developed during the surface-based investigation phase in the Mizunami URL project”,
Proc. of the 39th Symposium on Rock Mechanics, pp.48-53 (2010). (in Japanese).
6) Sato, T., Tanno, T., Hikima, R., Sanada, H. and Kato, H. : “In situ stress measurement in
the Mizunami Underground Research Laboratory, Japan”, Proceedings on the 6th- 72 -

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International Symposium on In-Situ Rock Stress, 20-22 August 2013, Sendai, Japan,
pp.354-359 (2013).
7) Sato, T., Tanno, T., Hikima, R., Sanada, H. and Kato, H. : “Data quality of in-situ stresses
by hydraulic fracturing method; Applicability of high-compliance system and evaluation of
maximum stress based on the results in granite”, Journal of MMIJ, Vol.128, No.7, pp.449454 (2012). (in Japanese).
8) Sato, T., Tanno, T., Hikima, R., Sanada, H. and Kato, H. : “Study of core disking phenomenonon compact conical-ended borehole overcoring technique; A Case study for measurement inborehole with inflow at Toki Granite”, Journal of MMIJ, Vol.129, No.2,3 (2013). (inJapanese).
9) Sanada, H., Hikima, R., Tanno, T., Matsui, H. and Sato, T. : “Application of differential
strain curve analysis to the Toki Granite for in situ stress determination at the Mizunami
underground research laboratory, Japan”, International Journal of Rock Mechanics andMining Sciences, 59, pp.50-56 (2013).
10) Kimura, N., Matsuki, K., Nakama, S. and Sato, T. : “Estimation of Regional Stress for
Heterogeneous Rock Mass”, Shigen to Sozai, Vol.119, pp.655-662 (2003). (in Japanese).
11) Matsuki, K., Nakama, S. and Sato, T. : “Estimation of regional stress by FEM for aheterogeneous rock mass with a large fault”, International Journal of Rock Mechanics andMining Sciences, Volume46, Issue 1, pp.31-50 (2009).
12) Li, G., Mizuta, Y., Ishida, T., Li, H., Nakama, S. and Sato, T. : “Stress field determinationfrom local stress measurements by numerical modeling”, International Journal of RockMechanics and Mining Science Volume46, Issue 1, pp.138-147 (2009).
13) Nara, Y., Cho, S. H., Yoshizaki, T., Kaneko, K., Sato, T., Nakama, S. and Matsui, H. :“Estimation of three-dimensional stress distribution and elastic moduli in rock mass of the
Tono area”, Internet Journal of the JCRM, Vol.7, No.1, pp.1-9 (2011).
14) Tanno, T., Hirano, T. and Matsui, H. : “Development of method for evaluation of three
dimensional distribution of in situ stress state and preliminary estimation of applicability”,
Rock Stress and Earthquakes, Xie (ed.), Taylor & Francis Group, London, pp.521-526(2010).
15) Kondo, K., Tsusaka, K., Inagaki, D., Sugita, Y., Kato, H. and Niunoya, S. : “Initial stressmeasurement by hydraulic fracturing method in diatomaceous mudstone in the Horonobe
Underground Research Laboratory”, Journal of The 13rd Japan Symposium on RockMechanics (CD-ROM), pp.583-588 (2013). (in Japanese).
16) Aoyagi, K., Tsusaka, K., Tokiwa, T., Kondo, K., Inagaki, D. and Kato, H. : “A study of theregional stress and the stress state in the galleries of the Horonobe Underground ResearchLaboratory”, Proceedings on the 6th International Symposium on In-Situ Rock Stress, 2022 August 2013, Sendai, Japan, pp.331-338 (2013).
17) Japan Nuclear Cycle Development Institute : “H17: Development and Management of theTechnical Knowledge Base for the Geological Disposal of HLW (H17 report)”, JNC TN1400
2005-014, pp.4-145 (2005). (in Japanese).
18) Tsusaka, K., Inagaki, D., Niunoya, S. and Jo, M. : “An investigation on mechanical- 73 -

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properties of in-situ rock mass at the Horonobe Underground Research Laboratory”,
Proceedings of 2014 ISRM International Symposium - 8th Asia Rock Mechanics
Symposium, pp.591-599 (2014).
19) (Eds.) Saegusa, H. and Matsuoka, T. : “Final Report on the Surface-based Investigation(Phase I) at the Mizunami Underground Laboratory Project”, JAEA-Research 2010-067(2007), 377p.
20) Fukui, K. : “The heat characteristic test and the fracture toughness test using the corefrom borehole MIZ-1”. JNC-TJ7400 2005-038 (2004), 162p. (in Japanese).
21) Yamamoto, T., Matsui, H., Horiuchi, Y. and Tominaga, E. : “Thermal properties on soft
sedimentary rock of Horonobe Underground Research Program”, Proceedings of the 34th
symposium on Rock Mechanics, pp.153-158 (2005). (in Japanese).

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2.5 Mass transport
2.5.1 Introduction
As part of the study of mass transport conducted for understanding the retardation effects
on mass transport in rock masses and groundwater, we have been working toward
understanding the initial conditions of the geological environment as assessed by surfacebased investigations, with the aim of developing and applying investigative, analytical, andevaluation techniques with a focus on the properties and processes in the geologicalenvironment as shown in (1) and (2) below1),2) (Fig. 2.5.1-1).
(1) Understanding the sorption and diffusion properties of rock mass
From the perspective of safety assessment of geological disposal, it is important tounderstand the initial conditions of a rock mass in terms of sorption and diffusion properties.
Moreover, it is essential to establish techniques to obtain reliable data for such properties, inaddition to the techniques for analyzing and evaluating them.
(2) Understanding the effects of colloids, organics, and microbes
As the presence of colloids, organics, and microbes in the geological environment affects themass transport properties of a rock mass in various ways, it is necessary to develop individual
elemental techniques that can be used to understand the factors in a specific given geologicalenvironment as well as to systematize the investigation, analysis, and evaluation techniques.
These tools are essential to understand the initial conditions of the geological environment.

Fig. 2.5.1-1 Geosynthesis data flow diagram (mass transport study)2)- 75 -

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2.5.2 Objectives in the second mid-term research phase
Research in the underground facilities must produce outcomes and scientific knowledge thatcan be reflected in the decision-making concerning site selection, construction of facilities,
commencement of disposal, completion of placement of waste packages, and final sealing in
the actual disposal operation. The level of technical development in the context ofunderstanding the initial conditions of the geological environment, is the establishment ofinvestigation and evaluation techniques for identification of favorable environmental
conditions in terms of mass transport in a rock mass by means of surface-based investigations
and the confirmation of the applicability of such techniques, as well as the systematization of
the series of techniques from investigation to analysis/evaluation (Table 2.5.2-1).
During the second mid-term research phase, we conducted investigations and studies
addressing themes (1) and (2) described in 2.5.1. These investigations and studies wereconducted using the boreholes drilled from the surface, drillcore and groundwater samples,and vertical shafts and horizontal galleries reaching depths of 500 m at Mizunami and 350 m
at Horonobe. We conducted laboratory tests, analyses, and evaluations concerning masstransport to establish investigation techniques and accumulate data/knowledge.
Table 2.5.2-1 Performance target of R&D for the mass transport study
Focus

Siting decision

Performance target of R&D

Tasks

To identify the domain that is favorable
for the mass transport study.

Sorption capacity and diffusivity of rockmatrix and of transport pathways• Development of high-reliability
technologies and methods forinvestigation, analysis andevaluation• To obtain mass transportparameters by laboratory
experiment
Effect of colloid/organics/microbe on
nuclide transport/retardation• Development of investigation
technologies for understanding
phenomena affecting mass transport
by laboratory experiment2.5.3 Project details and outcomes(1) Understanding rock mass sorption and diffusion properties
Sorption and diffusion in the geological environment are important phenomena controlling
the retardation of nuclide transport. The sorption and diffusion phenomena vary greatly
depending on the solid-phase mineral composition and pore structure, the groundwaterchemistry and porewater chemistry, the state of dissolved nuclides in water (chemical species),and other physicochemical conditions. From this perspective, we performed various analyses
and laboratory tests to obtain basic data such as chemical composition and mineral- 76 -

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composition of the rock masses selected for study and to understand the sorption and diffusion
properties of rock.
1) Mizunami
We acquired lithological and mineralogical data such as whole-rock chemical composition andmineral composition using rock samples obtained from boreholes drilled from the surface3). In
addition, we started laboratory through-diffusion tests using the drillcore samples, with theaim of obtaining a detailed understanding of the relationship between fracture characteristics
and mass transport parameters. In intact Toki Granite, we determined that the effective
diffusion coefficient for substances such as non-sorbing tracer uranine (a fluorescent dye)
ranged from 10−14 to 10−13 (m2/s)4),5) (Fig. 2.5.3-1).

Fig. 2.5.3-1 Laboratory through-diffusion testing equipment
2) Horonobe
We acquired lithological and mineralogical data such as whole-rock chemical composition andmineral composition using rock samples obtained by surface geological investigations andsurface-based borehole investigations6),7),8), and also acquired data concerning mass transport
properties, including porosity, pore size distribution, and other physical properties9),10). In
addition, using core samples obtained from surfaced-based borehole investigations, we
performed laboratory mass transport tests and determined the effective diffusion
coefficient11),12),13),14),15). Furthermore, we developed methods for laboratory mass transport
tests to obtain highly reliable sorption and diffusion parameters for a variety of elements andenvironmental conditions, and the measured sorption and diffusion parameters using nonsorbing tracers (Cs, I, and HTO) and highly sorbing tracers (e.g., Ni, Np, Am, Th, and Se)16),17)(Fig. 2.5.3-2). The laboratory test methods employed were the batch method and the newly
developed expanded through-diffusion/reservoir depletion method18),19) (Fig. 2.5.3-3).

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Fig. 2.5.3-2 Results from the laboratory experiment(a) batch sorption, (b) advanced through-diffusion experiments

Fig. 2.5.3-3 Advanced through-diffusion/reservoir-depletion method(2) Understanding the effects of colloids, organics, and microbes
We developed investigative techniques to understand the effects of colloids, organics, andmicrobes on mass transport in the underground environment. Because the mass transport ina rock mass depends on fluid media, and one of these fluids is groundwater, we conductedinvestigations and analyses to understand the phenomena that occur in the geologicalenvironment, focusing on groundwater–rock–colloids/organics/microbes interactions and thecharacteristics of mass transport. This enabled us to confirm the presence of colloids, organics,
and microbes in the geological environment, demonstrating the necessity of future studies of
their possible effects on the characteristics of mass transport and evaluation of these effects.

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1) Mizunami
Confirmation of the presence or absence of microbes in groundwater and measurement of
viable cell counts for sulfate-reducing bacteria and iron bacteria were performed using
groundwater obtained from boreholes drilled from the surface. The results showed a total cellcount of approximately 106 cells/ml, which is comparable to the abundance of marine
bacteria20). In addition, it was demonstrated that sulfate-reducing bacteria were only found atparticular depths, suggesting the formation of a microbial community structure reflecting thegeochemical conditions20),21) (Fig. 2.5.3-4).

Fig. 2.5.3-4 Depth profiles of (a) sulfate-reducing bacteria, (b) iron-related bacteria, and (c)colloidal particles in the groundwater in the Mizunami area20)2) Horonobe
We examined the composition of natural colloids in groundwater and their interactions with
substances such as rare earth elements in order to understand the forms and transport
behavior of colloids in groundwater. The results showed that colloidal particles in groundwater
mainly consisted of silicate minerals, phosphate minerals, carbonate minerals, and sulfate
minerals. In addition, it was determined that lighter rare earth elements became incorporated
in colloids more readily than heavier rare earth elements.
Groundwater from this site had a total organic carbon concentration between several andseveral tens of mg/l22). The concentration of dissolved organic matter at the Horonobe site ishigher than that in groundwater in crystalline rocks (such as the groundwater at Mizunami),- 79 -

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and hence the influence of mass transport behavior on organic matter is likely to be obvious.
The study of the properties of organic matter (mainly humic substances) in groundwater fromshallow and deep layers conducted for this reason indicated that the molecular weight
distribution of humic substances may be uneven23). In addition, a study using dissolved humic
substances isolated and purified from groundwater from the Koetoi and Wakkanai Formations(Fig. 2.5.3-5) showed that those humic substances had low molecular weights (similar to thosefrom other locations in Japan24)), were rich in aliphatic carbon, and there were no differencesin structural characteristics between the two formations. The structural characteristics
resemble those of humic substances originating from organic matter derived from aquatic life
(e.g., in Lake Biwa).
To assess the effects of microbes in groundwater, we conducted measurements of total cellcounts and genetic analysis using groundwater obtained from boreholes drilled from thesurface. The total cell count ranged from 104 to 106 cells/ml with no depth-dependence22). In
addition, the presence of microbes that influence degradation of aromatic compounds,
ammonia oxidation, nitrite oxidation, sulfur oxidation, methane oxidation, nitrate reduction,sulphate reduction, and denitrification in the nitrogen cycle was confirmed, as well as thedominance of a single strain of methane-producing microbes25). The results suggested atendency for microbial composition to differ greatly across a fault25) and a possibility of a
relationship between geological structure and the structure and activity of microbialcommunities26) (Fig. 2.5.3-6).

Fig. 2.5.3-5 Humic substances in groundwater at the Horonobe- 80 -

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Fig. 2.5.3-6 Microbial populations related to geological setting in the Horonobe area26)
2.5.4 Summary
We obtained the basic information required to understand the characteristics of masstransport in the geological environment by means of surface-based investigations. The
following list summarizes our technical findings.
(1) Understanding the sorption and diffusion properties of rock mass
- From the analysis of core samples, we obtained the whole-rock chemical composition,mineral composition, porosity, pore size distribution, and other data providing basic
information concerning mass transport in rock masses (for both sites).
- Using laboratory mass transport tests, we obtained the sorption and diffusion parameterssuch as the effective diffusion coefficient (for both sites).
- Using the expanded through-diffusion/reservoir depletion method, we made it possible toobtain highly reliable sorption and diffusion parameters for various elements andenvironmental conditions (for Horonobe).
(2) Understanding the effects of colloids, organics, and microbes- Colloid particles in groundwater mainly consist of silicate minerals, phosphate minerals,
and sulfate minerals, and are considered to affect the mass transport behavior of
substances such as rare earth elements (Horonobe).
- Although no relationship was detected between the organic matter concentration in
groundwater and the major chemical concentrations, the influence of mass transport- 81 -

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behavior on organic matter concentrations is likely to become obvious (Horonobe).
- Because the humic substances in the groundwater from Horonobe are similar to those in
the groundwater at other locations in Japan, it is necessary to evaluate the effects oforganic matter in groundwater on mass transport as a generic property (Horonobe).
- The total cell counts of microbes in groundwater are comparable to the abundance ofmarine bacteria. As the microbial composition varies depending on fault structures andparticular depths, it is possible that there are relationships linking geological structuresand geochemical environments to the distribution and activity of microbes (Mizunamiand Horonobe).
For understanding the sorption and diffusion properties of a rock mass, the concrete themeof a future study is to perform in situ tests in the galleries and laboratory tests for the purposeof establishing techniques and collecting data on mass transport in the rock mass as well as
sorption and diffusion parameters.
With respect to the effects of colloids, organics, and microbes, which have been difficult toassess using surface-based investigations, the concrete theme for another future study is toassess these issues using samples of controlled quality.
From the perspective of safety assessment, it is extremely important to understand thecharacteristics of mass transport in the geological environment by surface-based
investigations in decision-making concerning site selection. Therefore, an important theme isprovision of examples of investigation, analysis, and evaluation techniques through theinvestigations and research at the Mizunami URL and the Horonobe URL.
References
1) (Eds.) Iwatsuki, T., Sato, H., Tanai, K., Inagaki, M., Sawada, A., Niinuma, H., Ishii, E.,
Maekawa, K., Tomura, G., Sanada, H., Kunimaru, T., Asamori, K., Niizato, T., Tokiwa, T.,
Sugita, Y., Yamazaki, M., Nakamura, T., Fujita, T., Taniguchi, N., Kobayashi, Y., Hayashi,K., Saito, Y., Tachi, Y., Iijima, K. and Sasamoto, H. : “Horonobe Underground ResearchLaboratory project research and development plan in Phase 2; H20-21”, JAEA-Research
2009-002 (2009), 156p. (in Japanese).
2) Hama, K., Sato, T., Sasao, E., Iwatsuki, T., Kunimaru, T., Matsuoka, T., Takeuchi, R., Onoe,
H. and Mikake, S. : “Mizunami Underground Research Laboratory Project; Preparation ofgeosynthesis data flow diagram (Construction phase)”, JAEA-Data/Code 2013-010 (2013),
58p. (in Japanese).
3) Yuguchi, T., Tsuruta, T., Mizuno, T. and Kunimaru, T. : “Petrological and mineralogical datacollected from the Mizunami Underground Research Laboratory construction site; Bulk
chemical composition, mineral occurrence and mineral composition”, JAEA-Data/Code
2011-009 (2011), 85p. (in Japanese).
4) Kunimaru, T., Morikawa, K., Tachi, Y., Kuno, Y., Hosoya, S., Shimoda, S., Kato, H.,
Nakazawa, T., Ikuse, H. and Kubota, M. : “Measurement of sorption, diffusion and pore
physicality for granite sample, [document], [errata]”, JAEA-Data/Code 2012-013 (2012),- 82 -

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96p. (in Japanese).
5) Kunimaru, T., Mikake, S., Nishio, K., Tsuruta, T., Matsuoka, T., Ishibashi, M., Ueno, T.,
Tokuyasu, S., Daimaru, S., Takeuchi, R., Saegusa, H., Onoe, H., Takeda, M., Karino, T.,
Mizuno, T., Hagiwara, H., Sato, T., Sanada, H., Tanno, T., Hikima, R., Morikawa, K.,
Yuguchi, T., Ogata, N., Hama, K., Ikeda, K., Yamamoto, M., Shimada, A., Matsui, H., Ito,
H. and Sugihara, K. : “Mizunami Underground Research Laboratory Project annual reportfor fiscal year 2010”, JAEA-Review 2012-020 (2012), 178p. (in Japanese).
6) Takahashi, K. : “Data book of measurements and analyses on geological and drilling surveys
for Horonobe URL Project”, JNC TN5400 2005-010 (2005), 72p. (in Japanese).
7) Hiraga, N. and Ishii, E. : “Mineral and chemical composition of rock core and surface gas
composition in Horonobe Underground Research Laboratory Project (Phase 1)”, JAEAData/Code 2007-022 (2008), 100p. (in Japanese).
8) Funaki, H., Tokiwa, T., Ishii, E., Hatsuyama, Y., Matsuo, S., Tsuda, K., Koizumi, A.,
Ishikawa, T., Daijo, Y. and Sugiyama, K. : “Horonobe Underground Research Laboratory
project overview of the pilot borehole investigation of the ventilation shaft (PB-V01);
Geological investigation”, JAEA-Data/Code 2008-013 (2008), 65p. (in Japanese).
9) Hara, A. : “Data Acquisition for Hydrology and Transport Properties of Sedimentary Rocks,
Pore Size Distribution and Chemical Composition of the Horonobe Area”, JNC TN8400
2003-052 (2004), 148p. (in Japanese).
10) Hara, A. : “Data acquisition of groundwater flow and mass transport properties in
sedimentary rocks, 2; Considerations of mass transport properties based on pore size
distribution, chemical composition and air permeability of the Horonobe specimen”, JAEAResearch 2006-020 (2006), 137p. (in Japanese).
11) Shimo, M. and Kumamoto, S. : “Data acquisition for hydrology and mass transport
properties of sedimentary rocks in subsurface layer”, JNC TJ5410 2005-003 (2005), 40p. (inJapanese).
12) Shimo, M., Kumamoto, S. and Maekawa, K. : “Study on flow and mass transport throughfractured soft sedimentary rocks (Contract research)”, JAEA-Research 2007-016 (2007),
141p. (in Japanese).
13) Shimo, M., Kumamoto, S., Karasaki, K., Sawada, A., Maekawa, K. and Sato, H. : “Studyon flow and mass transport through fractured sedimentary rocks (Contract research)”,
JAEA-Research 2008-029 (2008), 95p. (in Japanese).
14) Shimo, M., Kumamoto, S., Karasaki, K., Sato, H. and Sawada, A. : “Study on flow andmass transport through fractured sedimentary rocks, 2”, JAEA-Research 2008-101 (2009),
70p. (in Japanese).
15) Shimo, M., Kumamoto, S., Ito, A., Karasaki, K., Sawada, A., Oda, Y. and Sato, H. : “Studyon flow and mass transport through fractured sedimentary rocks, 3”, JAEA-Research 2009060 (2010), 70p. (in Japanese).
16) Tachi, Y., Seida, Y., Doi, R., Xia, X. and Yui, M. : “Sorption and diffusion of Cs in HoronobeURL’s sedimentary rock: comparison and model prediction of retardation parameters fromsorption and diffusion experiments”, In: Scientific Basis for Nuclear Waste Management- 83 -

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XXXII, Mater. Res. Soc. Symp. Proc., 1124, pp.573-579 (2009).
17) Tachi, Y., Yotsuji, K., Seida, Y. and Yui, M. : “Diffusion and sorption of Cs+, I– and HTO insamples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Claybased modeling”, Geochim. Cosmochim. Acta 75, pp. 6742-6759 (2011).
18) Tachi, Y., Yotsuji, K., Seida, Y. and Yui, M. : “Diffusion of cesium and iodine in compacted
sodium montmorillonite under different saline conditions, In: Scientific Basis for Nuclear
Waste Management XXXIII”, Mat. Res. Soc. Symp. Proc., Vol.1193, pp.545-552 (2009).
19) Tachi, Y., Nakazawa, T., Ochs, M., Yotsuji, K., Suyama, T., Seida, Y., Yamada, N. and Yui,
M. : “Diffusion and sorption of neptunium(V) in compacted montmorillonite : Effects ofcarbonate and salinity”, Radiochimica Acta, Vol.98, pp.711-718 (2010).
20) Murakami, Y., Iwatsuki, T. and Naganuma, T. : “Microbial Activity in the Subsurface
Environment of the Tono Area and its Relation to Groundwater Chemistry”, Journal of
Geography, No. 112, Vol. 2, pp.277-287 (2003).
21) Saegusa, H., Seno, Y., Nakama, S., Tsuruta, T., Iwatsuki, T., Amano, K., Takeuchi, R.,
Matsuoka, T., Onoe, H., Mizuno, T., Oyama, T., Hama, K., Sato, T., Kuji, M., Kuroda, H.,
Semba, T., Uchida, M., Sugihara, K. and Sakamaki, M. : “Final report on the surface-based
investigation (phase I) at the Mizunami Underground Laboratory project”, JAEA-Research
2007-043 (2007), 337p. (in Japanese).
22) Ota, K., Abe, H., Yamaguchi, T., Kunimaru, T., Ishii, E., Kurikami, H., Tomura, G., Shibano,K., Hama, K., Matsui, H., Niizato, T., Takahashi, K., Niunoya, S., Ohara, H., Asamori, K.,
Morioka, H., Funaki, H., Shigeta, N. and Fukushima, T. : “Horonobe UndergroundResearch Laboratory project synthesis of phase I investigations 2001-2005 volume"Geoscientific Research"”, JAEA-Research 2007-044 (2007), 434p. (in Japanese).
23) Nagao, S., Iwatsuki, T. and Hama, K. : “Characterization of groundwater humic substancesby high-performance size exclusion chromatography with fluorescence detection”, Abstract.
International Workshop on Waste Management in Sapporo, pp.3-4 (2005).
24) Terashima, M., Nagao, S., Iwatsuki, T., Sasaki, Y., Seida, Y. and Yoshikawa, H. :“Structural Characteristic of Deep Groundwater Humic Substances in Horonobe Area,
Hokkaido, Japan”, Advances in natural organic matters and humic substances 2008 - 2010,
Proceedings Book of the Communications presented to the 15th Meeting of theInternational Humic Substances Society, Tenerife - Canary Islands, 3, pp.24-27 (2010).
25) Shimizu, S., Akiyama, M., Ishijima, Y., Hama, K., Kunimaru, T. and Naganuma, T. :“Molecular characterization of microbial communities in fault-bordered aquifers in the
Miocene formation of northernmost Japan”, Geobiology, Vol. 4, Issue 3, pp.203-213 (2006).
26) Kato, K., Nagaosa, K., Kimura, H., Katsuyama, C., Hama, K., Kunimaru, T., Tsunogai, U.
and Aoki, K. : “Unique distribution of deep groundwater bacteria constrained by geologicalsetting”, Environmental Microbiology Reports, Vol. 1, Issue 6, pp.569-574 (2009).

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2.6 Engineering technology for deep underground applications
2.6.1 Introduction
The underground research laboratory projects will provide the opportunity to demonstrate
the feasibility of safe and reliable construction, maintenance, and management of anunderground research facility by applying conventional and state-of-the-art engineering
technology in a deep geological environment. Engineering technologies, such as design,
construction planning, construction, countermeasures, and safety management, have been
applied to Mizunami and Horonobe.
2.6.2 Objectives in the second mid-term research phase
The objectives of engineering technology for deep underground application during the second
mid-term plan are to test the applicability of construction and countermeasure technologies,
maintenance technology during extensions of shaft and gallery at depths of 500 m (Mizunami)
and 350 m (Horonobe). Design and construction planning technologies have been also
estimated during this phase. Table 2.6.2-1 shows the performance target level of technicaldevelopment for engineering technology.
Table 2.6.2-1 Performance target of R&D for engineering technology
Focus

Performance target of R&D

Decision-making for Decision and planning the construction
start of construction of underground facilities.

Tasks• Design methodology of construction ofunderground facilities
Stability of underground operation
Design of support
Earthquake-resistant design• Technology of planning of undergroundfacilities

2.6.3 Project details and outcomes(1) Design and construction planning technologies
1) Mizunami
The shafts and galleries were excavated based on the results of the design and construction
plan at the Phase I. Confirmation of the design and construction plan was carried out by
evaluation of data obtained during excavation to a depth of 500 m. The conclusions are as
follows1),2),3):- Parameters, such as rock mass classification, rock properties, and stress release ratio,
which were used for numerical analysis of rock mass behavior of the Ventilation Shaft
excavated in good rock conditions during the surface-based investigation phase, werevariable (Fig. 2.6.3-1, Table 2.6.3-1).
- On the other hand, a fault with an altered zone was observed at the Main Shaft. The
support system which was designed during Phase I were applied with minor changes tothe specifications to the excavation of the Main Shaft. As deformation of the supports was- 85 -

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not observed, the design methodology applied to the Mizunami can be used in a wide
range of geological conditions.
- Pilot borehole investigations are useful for both estimation of the applicability of the
support system and also for planning countermeasures to water inflow at the Ventilation
Shaft and the −300 m access/research gallery4).
- It was observed that the intensity of earthquake motion increases from deep undergroundto the shallow surface. Numerical simulations were carried out to compare the analyticalresults with observed records. The calculated results agreed well with the observed
values (Fig. 2.6.3-2, Fig. 2.6.3-3)5).
- The excavation cycle time was recorded during Ventilation Shaft sinking and comparedwith the planned excavation cycle time for evaluation of the baseline design plan. The
recorded results indicate that actual cycle time was longer than those listed in the plan
because of safety matters and maintenance of the equipment6),7).

Fig. 2.6.3-1 Measurement results of the axial forces of the steel support for the Main Shaft(G.L. −250 m) (Mizunami)- 86 -

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Table 2.6.3-1 Evaluation of B-measurement results for the Main Shaft (Mizunami)
Measurement
depth

G.L. −250 m

G.L. −450 m

Steel support

There were some data exceed
management level II, steel support
were functioning, in general.

There were some data exceed
management level II, steel support
were functioning, in general.

Concrete liner

All the data were within managementlevel II.

All the data were within managementlevel I.

Convergence

Anisotropic displacement closed to
management level II, but it converged.

Displacement was within managementlevel I, it converged.

Evaluation

Stress of concrete lining was 17N/mm2.
Shaft was stable, but it is necessary tomonitor concrete liner.

Stress of concrete lining was 12N/mm2.
Shaft was stable, but it is necessary tomonitor concrete liner.

Fig. 2.6.3-2 Measured maximum acceleration values of earthquakes (Mizunami)

Fig. 2.6.3-3 Comparison of measured and analyzed motion of the Suruga Bay earthquake(2009.8.11)- 87 -

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2) Horonobe
In the Horonobe URL, the stability of the support and the mechanical behavior of the rockmass around shafts and horizontal galleries were analyzed on the basis of in situ
measurements such as stress on lining, steel arch libs, and rock bolts, and numericalsimulations (three-dimensional excavation analysis). In shaft sinking and excavations ofhorizontal galleries, consuming time for excavation and mucking, i.e., cyclic time wasanalyzed; then compared with geological observations and laboratory tests. On the basis ofthese investigations, the validity of the design and plan of construction were assessed. The
results are summarized as follows:- The relationship between the initial deformation rate, the final deformation, and thestress of the concrete lining was suggested for use as a practical guide in shaft sinking8),9).
- Analyses of the relationship between the initial deformation rate, observed deformation,
ratio of the modulus of elasticity of rock mass to the initial stress, and magnitude of
inelastic behavior of rock based on convergence measurements and investigation of rockmass properties on shaft walls were conducted to construct a classification of rock mass
behavior in shaft sinking8),10). This classification is useful to predict the rock mass
behavior and stress on the lining caused by excavation work at the earlier stage.
- From analysis of the effects of rock bolts on the deformation of rock and lining in shaft
sinking, a support pattern that omits the installation of rock bolts was suggested andapplied in subsequent shaft sinking11).
- The results of three-dimensional stress analysis showed that the minimum andmaximum stresses on the concrete lining occurred in the direction of the maximum andminimum horizontal stress, respectively (Fig. 2.6.3-4). Considering the result of stressanalysis of a concrete lining, a stress meter for a concrete lining should be installed at an
inner and lower position in the direction of the minimum horizontal stress in order toestimate the stability of the support system of a shaft (Fig. 2.6.3-5)12),13),14).
- Fractures were newly created and developed around the wall of the shaft during the
excavation process. After the concrete lining was installed, these fractures would beclosed. As a result of this behavior, it was determined that the concrete lining gradually
deformed from an original cylindrical form to an elliptical shape with the long axis
parallel to the direction of the minimum horizontal principal stress15).
- In shaft sinking, the mechanical behavior of the concrete lining and the rock mass aroundthe shaft wall is affected by inhomogeneity of the stress conditions and construction
procedures. For the design of a support pattern and planning of in situ measurements, itis necessary to understand the behavior of the support and the rock mass prior to
excavation on the basis of the results of three-dimensional excavation analysis
considering the stress conditions and construction procedure.
- The relationship between the progress of shaft sinking (cyclic time) and rock massclassification was analyzed. The results showed that the time required for shaft sinking
by mechanical excavation and by the drill-and-blast method were almost identical. Also,
the relationship between rock mass classification and cyclic time has a correlation16).

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JAEA-Review 2016-014- In shaft sinking, analysis of the relationship between the specific energy required for
excavation using a boom header and the mechanical properties of rock was conducted. As
a result, the rock mass property will be determined using the measurement value of
specific energy17),18),19).
The excavation of galleries perpendicular to the orientation of the natural fractures yielded
faster excavation rates than the excavation of galleries parallel to the orientation of natural
fractures when tunneling through the soft sedimentary rocks using an impact hammer in the
Horonobe URL (Fig. 2.6.3-6)20).

Fig. 2.6.3-4 Distribution of circumferential stress on concrete lining14)- 89 -

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JAEA-Review 2016-014(a) Layout of stress meters in the concrete lining between 218 m and 220 m depth(b) Change in circumferential stresses as an excavation face advances(+: compressive, −: tensile)Fig. 2.6.3-5 Measured and analyzed results of circumferential stresses in a concrete lining13)- 90 -

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Fig. 2.6.3-6 Relationship between excavation rate and fracture density in Drifts I and II(Drift I: excavated perpendicular to the orientation of pre-existing fractures; Drift II:
excavated parallel to the orientation of pre-existing fractures)20)
The design and construction planning technologies applied during the excavation of shafts
and galleries at Mizunami and Horonobe are considered as the generic engineering technology
for road and railway tunnels and could be applied to the various kinds of rock types. These
technologies should be treated carefully as countermeasures against large amounts of water
inflow are required at Mizunami, and a mechanical stability and support system is necessaryat Horonobe. However, insufficient preliminary investigations have been performed in
excavations of road and railway tunnels. Pilotborehole investigations are useful for decreasing
the uncertainty related to the geological environment. The results at Mizunami and Horonobe
are recognized as good practice.
2.6.4 Summary
The effectiveness of estimation of the mechanical stability of underground openings andsupport systems and the earthquake-resistance design has been confirmed based on the
results of excavation of shafts and galleries at Mizunami and Horonobe. It was determinedthat the intensity of earthquake motion increases from deep underground to the shallow
surface. For construction planning technology, the excavation cycle time was recorded duringshaft sinking then compared with the planned excavation cycle time for the purpose ofevaluating the baseline design plan.
References
1) Hashizume, S., Matsui, H., Horiuchi, Y., Hata, K., Akiyoshi, K., Sato, S., Shibata, C.,
Niunoya, S. and Noda, M. : “Study on dynamic behavior of a shaft excavated throughfaulted crystalline rock mass”, Proc. of the 13th Japan Symposium on Rock Mechanics,
JSCE, pp.121-126 (2013). (in Japanese).
2) Ijiri, Y., Noda, M., Nobuto, J., Matsui, H., Mikake, S. and Hashizume, S. : “Study on- 91 -

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engineering technologies in the Mizunami Underground Research Laboratory; FY20092010 (Contract research)”, JAEA-Technology 2013-047 (2014), 819p. (in Japanese).
3) Fukaya, M., Noda, M., Hata, K., Takeda, Y., Akiyoshi, K., Ishizeki, Y., Kanata, T., Sato, S.,
Shibata, C., Ueda, T., Toda, A., Kobayashi, S., Niimi, K., Okihara, M., Tsuji, M., Yamada,T., Sato, T., Mikake, S., Horiuchi, Y. and Hashizume, S. : “Study on Engineering
Technologies in the Mizunami Underground Research Laboratory (FY. 2012) (Contract
Research)”, JAEA-Technology 2014-019 (2014), 495p. (in Japanese).
4) Niunoya, S., Matsui, H., Mikake, S., Sato, S., Noda, M. and Hata, K. : “Study for
effectiveness of rock mechanical model estimated from pilot boring survey”, Proc. of the
41th Symposium on Rock Mechanics, JSCE, pp.214-219 (2012). (in Japanese).
5) Niimi, K., Kobayashi, S., Nobuto, J., Matsui, H. and Yamamoto, M. : “Analysis andNumerical Simulation of Seismic Events Recorded in the Ventilation Shaft at the
Mizunami URL”, Proceedings of European Rock Mechanics Symposium (EUROCK 2012)(CD-ROM) (2012).
6) Sato, T., Mikake, S., Noda, M. and Kobayashi, S. : “Evaluation of shaft excavation
technology based on construction results up to a depth of 500m at Mizunami UndergroundResearch Laboratory”, Tunnel and Underground, Vol.45, No.7, pp.501-510 (2014). (inJapanese).
7) Sanada, H., Sato, T., Horiuchi, Y., Mikake, S., Okihara, M., Yahagi, R. and Kobayashi, S. :“Analysis of excavation cycle time during sinking of the Ventilation Shaft at the Mizunami
Underground Research Laboratory”, Proceedings of 2014 ISRM International Symposium- 8th Asia Rock Mechanics Symposium, pp.1263-1269 (2014).
8) Tsusaka, K., Yamazaki, M. and Hatsuyama, Y. : “Rock deformation and support load in shaft
sinking in Horonobe URL Project”, Rock Engineering in Difficult Ground Conditions; SoftRocks and Karst (EUROCK 2009), pp.589-594 (2009).
9) Yamasaki, M., Tsukasa, K., Hatsuyama, Y., Minamide, M. and Takahashi, A. : “Correlation
between initial deformation ratio of convergence and lining stress in shaft excavation”, Proc.
of the 38th Symposium on Rock Mechanics, JSCE, pp.196-201 (2009). (in Japanese).
10) Tsusaka, K. : “Proposal of rock mass behavior classification based on convergencemeasurement in shaft sinking through sedimentary soft rocks”, Journal of Japan Societyof Civil Engineers, Ser. F, Vol.66, No.1, pp.181-192 (2010). (in Japanese).
11) Inagaki, D., Tsusaka, K., Ijiri, Y., Koike, M. and Hatsuyama, Y. : “Study on the Behavior ofConcrete Liner and Rock Mass during Shaft Excavation in the Horonobe URL Project (Part1)”, Proc. of the 40th Symposium on Rock Mechanics, JSCE, pp.1-6 (2011). (in Japanese).
12) Tsusaka, K., Inagaki, D., Koike, M., Ijiri, Y. and Hatsuyama, Y. : “A study on mechanicalbehaviors of concrete lining and rock caused by shaft sinking at the Horonobe undergroundresearch laboratory”, Proceedings of the 12th Congress of International Society for RockMechanics, pp.305-308 (2011).
13) Tsusaka, K., Inagaki, D., Koike, M., Ijiri, Y. and Hatsuyama, Y. : “Study on the Behaviorof Concrete Liner and Rock Mass during Shaft Excavation in the Horonobe URL Project- 92 -

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JAEA-Review 2016-014(Part 2)”, Proc. of the 40th Symposium on Rock Mechanics, JSCE, pp.7-12 (2011). (inJapanese).
14) Tsusaka, K., Inagaki, D., Hatsuyama, Y., Koike, M. and Ijiri, Y. : “A Study on MechanicalBehavior of Support Elements Induced by Shaft Sinking”, Journal of Japan Society of Civil
Engineers, Ser. F1, Vol.68, No.1, pp.7-20 (2012). (in Japanese).
15) Tsusaka, K., Tokiwa, T., Inagaki, D., Hatsuyama, Y., Koike, M. and Ijiri, Y. : “A Study on
Rock Mass Behavior induced by Shaft Sinking in the Horonobe Underground ResearchLaboratory”, Journal of Japan Society of Civil Engineers, Ser. F1, Vol.68, No.2, pp.40-54(2012). (in Japanese).
16) Yamasaki, M., Sekiya, M., Fujikawa, D. and Kitagawa, Y. : “Progress of shaft construction
and cyclic time analysis in the Horonobe Underground Research Laboratory Project”,
Underground Research Symposium, JSCE, 14, pp.191-196 (2009). (in Japanese).
17) Fukui, K., Okubo, S., Inagaki, D., Hatsuyama, Y. and Yamamoto, T. : “Specific energy of aboom header in excavation and properties of a rock mass”, Proc. of the Fall meeting 2009
The Mining and Materials Processing Institute of Japan, pp.109-112 (2009). (in Japanese).
18) Yamasaki, M., Hatsuyama, Y., Yamamoto, T. and Fukui, K. : “Estimation of the strengthof soft rock with specific energy of tunneling machine”, Proc. of the 44th JNCGE, pp.12671268 (2009). (in Japanese).
19) Yamasaki, M., Fukui, K., Minamide, K. and Hatsuyama, Y. : “A study of correlation
between specific energy of tunneling machine and crack frequency of mudstone”, Japan
Society of Civil Engineers 2009 Annual Meeting, CS5-060 (2009). (in Japanese).
20) Tsusaka, K. and Tokiwa, T. : “Influence of fracture orientation on excavatability of soft
sedimentary rock using a hydraulic impact hammer: A case study in the Horonobe
Underground Research Laboratory”, Tunneling and Underground Space Technology
incorporating Trenchless Technology Research, Volume 38, pp.542-549, (2013).

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2.7 Geosphere stability for long-term isolation of radioactive waste
2.7.1 Introduction
The framework of the research on geosphere stability for long-term isolation of high-level
radioactive waste is structured into three categories to contribute to the site selection and thenational safety regulation of the final disposal. These three categories are: development andsystematization of investigation techniques; development of models for long-term estimationand effective assessment; and development of dating techniques. Development andsystematization of investigation techniques aims to construct the technical bases whether thegeological environments at the candidate disposal sites satisfy the stepwise site selection
requirements of the Specified Radioactive Waste Final Disposal Act, the environmental
requirements of safety regulations, and other considerations, through the preliminary
investigation and the detailed investigation. This report documents the main results from theresearch and development.
2.7.2 Targeted level of technology development
The scientific program for fiscal years 2010–2014 was set taking into account the importanceand urgency of the needs of the implementing bodies and the regulatory agencies1),2),3),4),5) withattention to acts and reports after having investigated the trend of basic research inuniversities as well as related research institutes (Table 2.7.2-1).

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Table 2.7.2-1 Performance target of R&D on geosphere stability for long-term isolation
Focus

Decision on site
selection

Performance target of R&D

Tasks

Enable investigation of faults with
unclear tectonic landforms.

Investigation techniques for active faults
with unclear tectonic landforms• Development of investigation
technique using the geochemical
characteristics of gas released fromthe fault

Enable estimation of the presence orabsence of an earthquake source fault
and high-temperature fluid in deep
underground.

Investigation techniques for earthquake
source faults in the crust• Development of an investigation
technique using the resistivity
structure determined by themagnetotelluric method

Enable understanding the activity offault which can’t apply the approach
using cover sediments.

Investigation techniques for fault activity
in basement rock
• Development of an investigation
technique with the material scienceand radiometric age of faulted
materials infilling fractures

Enable estimation of the uplift,
subsidence, and erosion rates in inland
areas that have poorly developed riverterraces.

Investigation techniques for estimation of
uplift and erosion rates in inland areas• Development of an investigation
technique for erosion rate using an
old river valley around a detachedmeander core
• Development of an investigation
technique for uplift and erosion rates
based on thermochronology

2.7.3 Project details and outcomes(1) Investigation techniques for active faults with unclear tectonic landforms
Earthquake faulting is one of the most important factors affecting the long-term stability ofa geological disposal system, because a faulting could cause dynamic destruction of basement
rocks. Recently, some large earthquakes have occurred in several areas where active faults
with geomorphological signature6),7) have not been detected, implying the existence ofconcealed active faults. Therefore, we developed a geochemical approach based on terrestrial
gases along faults to detect concealed active faults. In the second mid-term research phase,
we observed a wide variety of chemical components (He, Ar, CO2, and H2) of terrestrial gases
along faults, indicating that active faults may be major leaks or pathways in the crust forthese gases8). In particular, helium isotopes provide an excellent geochemical tracer to detect
immature faults at an early stage of their evolution (i.e., concealed active faults without
geomorphological and geological expression), as suggested by observations in and around theseismic source region of the western Tottori earthquake and the Itoigawa–Shizuoka Tectonic
Line (ISTL).
An inland earthquake (M 7.3) with no noticeable surface expression of faulting occurred in- 95 -

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western Tottori in 2000, where no active fault was related to the earthquake. Groundwater
samples collected in the aftershock area are characterized by helium isotope ratios (3He/4He)
several times higher than the atmospheric value. The helium isotope ratios decrease with
distance from the inferred fault segments9) (Fig. 2.7.3-1). In addition, magnetotelluric
soundings were taken in the aftershock area in order to estimate the subsurface electricalresistivity structure. These measurements detected an anomalous conductive body, which may
be attributed to latent magma and related fluids, on the southwestern side of the source fault.
These findings indicate that mantle helium is leaking from latent magma through theconcealed faults10).
The ISTL fault system can be divided into three distinct segments: northern, middle, andsouthern. The northern and southern segments are characterized by reverse faults. The
middle segment of the ISTL contains strike-slip faults. The spatial variation of the helium
isotope ratios of groundwater samples along the ISTL revealed that a high helium isotope ratio
can be detected along active faults11),12) (Fig. 2.7.3-2), which can be interpreted as leakage ofmantle helium within the crust migrating upward through reverse and strike-slip faults. The
central Nagano earthquake (M 5.4) occurred near the Gofukuji fault, located in the middle
segment of the ISTL, in 2011. The helium isotope ratio of groundwater samples collected before
and after the earthquake showed no significant change11),13), indicating stable leakage ofmantle helium along the active faults.
In future studies, geochemical data in a different area with different tectonics should becollected. In addition, construction of a technique that jointly incorporates geomorphological,
geological, and geophysical findings for detecting concealed active faults will also be important.

Fig. 2.7.3-1 Spatial distribution of 3He/4He ratios in groundwater around the source region of
the 2000 western Tottori earthquake (after Umeda and Ninomiya (2009)9)).

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Fig. 2.7.3-2 Spatial distribution of 3He/4He ratios along the Itoigawa–Shizuoka Tectonic Line(ISTL) (after Umeda et al. (2013)11))(2) Investigation techniques for earthquake source faults in the crust
Earthquake faulting and volcanism are important factors affecting the long-term stability ofgeological disposal systems, because the intrusion of magma and fault movement could cause
dynamic destruction of basement rocks. Recent studies have argued that the existence ofaqueous fluids and melts in the crust may affect long-term fault evolution and earthquake
generation14) as well as volcanism. Magnetotelluric (MT) sounding is a powerful tool for
detecting crustal fluids. However, there are several problems in correctly determining thecrustal structure in Japan. The reliability of the resistivity structure determined by MT
inversion analysis is affected by strong artificial noise, such as leakage currents from DC
railways, and complicated three-dimensional (3-D) subsurface structure in and around theobservation area.
We developed a weighted stacking method for use with data degraded by strong artificial
noise, and demonstrated the validity of the method using synthetic and observed MT data15),16)(Fig. 2.7.3-3). We also developed a 3-D MT inversion code with a heterogeneous smoothnessconstrained least-squares method to allow modeling of resistivity boundaries in the subsurface
structure17). In addition, we performed 3-D MT modeling in the source region of the 1997
Kagoshima earthquake doublet (Mj 6.5, Mj 6.3), where there have not been any obvious
indications of active faulting at the surface prior to the events. A prominent conductive zone
was revealed in the vicinity of the main shocks. The source faults of the earthquake doublet
are located near the boundary between the conductive and the resistive part of the crust18)- 97 -

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These results indicate that the distribution of crustal fluids could contribute to detecting theexistence of concealed source faults. A joint approach using the above-mentioned geochemicaland geophysical techniques including MT sounding could reveal the distribution of partiallymelted zones 10),19),20),21),22). In future studies, seismological techniques such as seismic
tomography should also be incorporated into this approach for detecting concealed source
faults.

Fig. 2.7.3-3 An example of improvement in MT data quality. Observed (a) and stacked (b)apparent resistivity.

Fig. 2.7.3-4 3-D resistivity structure in the source region of the Kagoshima earthquake
doublet (after Umeda et al. (2014)18)). Resistivity distribution at a depth of 10 km (a) andalong cross-section AA’ (b).
(3) Investigation techniques for fault activity in basement rockExamination of fault activity is essential for safety assessment of a candidate site forgeological disposal. In general, identification of recent fault activity is based on dating of- 98 -

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faulted sediments, such as radiocarbon dating and tephrochronology. In that case, the age of
undeformed sediments covering a fault provides information about the timing of the latest
activity of the fault. However, this type of approach using cover sediments is not applicable toassessment of faults in basement rocks, for example, faults that are newly detected duringborehole drilling or tunnel excavation23),24). Mineralogical and chemical analyses of material
infilling faults25) and radiometric dating of fault rocks26) have been proposed for theassessment of faults in basement rocks. During second mid-term plan, we carried out K–Ar
dating of authigenic clay minerals formed as a result of fault activity.
JAEA possesses an installation for noble gas mass spectrometry that can be used for argon
isotope analysis and flame photometry for measurement of potassium concentration.
Specifically, the mass spectrometry in JAEA enables measurement of argon isotope ratios
using the sensitivity method27), which is advantageous for precise dating for ages younger than
1 Ma. We collected <0.1 μm particle size fractions from fault gouge samples using a repetitive
freezing and thawing technique and high-speed centrifugation28). The particle size distributionof each fraction was examined using a laser diffraction-scattering particle size distribution
analyzer. As a case study, we carried out K–Ar dating on clay fillings from fractures or faults
in the Toki, Rokko, and Kojaku Granites of southwest Japan.
There are many faults in the Toki Granite, which is overlain by the Miocene Mizunami Group.
K–Ar dating of two clay samples from these faults indicated that the finer fractions haveyounger K–Ar ages (Fig. 2.7.3-5). The K–Ar ages of the <0.1 μm fractions are 46.5 Ma and 42.7
Ma29). These results suggest that the age of the finer clay minerals corresponds to the timingof more recent hydrothermal activity along faults, i.e., more recent fault activity. Thus, precise
separation and collection of finer particle size fractions are important for identification ofyounger fault activity28). The depositional age of the Mizunami Group (ca. 20 Ma) and thecooling history of the Toki Granite30) are consistent with the results of K–Ar dating29).
The K–Ar ages of fault gouge samples from the Arima–Takatsuki Tectonic Line in the Rokko
Granite also indicated that finer fractions have younger K–Ar ages31). The youngest age in thefinest fractions is 23 Ma (Fig. 2.7.3-6). There is still a discrepancy between the K–Ar age andthe age of the latest activity of the Arima–Takatsuki Tectonic Line. K–Ar dating may bedifficult to apply to any determination of the timing of subsurface fracturing, at least in thestudied area28),32). However, K–Ar dating could be informative for assessment of coupling of
main faults and subfaults, and estimation of the extent of fault damage.
The K–Ar ages of clay fillings in fractures in the Kojaku Granite in the Tsuruga Peninsula
also show that finer fractions have younger K–Ar ages (Fig. 2.7.3-7). In electron microscopy,
specular illite, which is typically formed as a result of fault activity and subsequenthydrothermal alteration, was invisible in the fine clay fractions. Most clay minerals are flakyor platy. These clay infillings could have been derived from hydrothermal alteration at ca. 50
Ma and subsequent weathering33).
As future work, application of radiometric dating to veins such as carbonates displaced byfaults, as well as mineralogical and chemical analysis of faulted materials, are recommended.

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Sample A

Sample B

AgeFig. 2.7.3-5 Results of K–Ar dating for fault gouges from the Toki Granite
Error bars indicate standard deviation (2σ)31).

①

②

①

①

②

③

③

① Brownish-red gouge, ② Gray gouge, ③ Charcoal-gray gouge
Fig. 2.7.3-6 Results of K–Ar dating for fault gouges from the Arima–Takatsuki Tectonic Line
Error bars indicate standard deviation (2σ)31).

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Frequency (％）

Fraction A
Fraction B
Fraction C

Particle size (μm）
Fig. 2.7.3-7 Results of particle size distribution analysis and K–Ar dating for clay fractions
from fractures containing clay infillings in the Kojaku Granite(4) Investigation techniques for estimation of uplift and erosion rates in inland areas
The uplift and erosion rates for the past tens of thousands of years and the past hundreds ofthousands of years can be calculated from the age and height of terrace surfaces, such as
marine terraces along the shore and river terraces inland34). However, it is difficult to apply
the calculation technique of the uplift rate using river terraces in the inland areas35) of
southwest Japan and the upper reaches of rivers, because terraces are lacking in these areas.
Therefore, a new investigation technique to clarify the uplift and erosion rates in inland areas
is necessary. We focused on “circular abandoned channels”, which are old valleys arounddetached meander cores formed by the cut-off of incised meandering rivers in inland
mountains with a small river terraces. We considered the estimation approach of uplift anderosion rates from the emergence age and elevation. Approximately 800 circular abandoned
channels, interpreted from topographic maps with a scale of 1 to 25,000, were detected
throughout the Japanese Islands. These channels can be useful for estimating uplift anderosion rates because they occur at a range of elevations throughout the Japanese Islands (Fig.
2.7.3-8)36),37). We undertook a case study to determine the uplift and erosion rates using acircular abandoned channel in the middle reaches of the Kumanogawa (Totsukawa) River. The
old river channel deposits that overlie the circular abandoned channel have been emergent
since approximately MIS7 (i.e., 214 ka), based on analyses of the soil color and volcanic ash
grains in the deposits, and the distribution of fluvial terraces around the Kumanogawa
River38). The incision rate, as calculated from this age and the difference in elevation between
the deposit and present channel (112 m), is about 0.5 m/ky or less. Matsushi et al. (2012)39)
calculated an incision rate of 4.4±0.3 mm/y from the 10Be exposure ages of gravels on theabandoned channel in the uppermost reaches of the Totsukawa River. That rate is different
from the rate calculated in this study.
It is necessary to study the reliability of the estimates of the uplift and erosion rates in inland
mountains obtained using circular abandoned channels.

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Thermochronometric methods using cooling ages and closure temperatures of multi-systems
have conventionally been applied to estimate uplift and denudation histories on timescales of
one million years or longer40). (U–Th)/He thermochronometry, which has a lower closure
temperature, has been recently put to practical use41),42) and applied to estimate later upliftand denudation histories43). We carried out fission-track dating and track length
measurements of apatites in granites collected from the Suzuka Mountains as a case study of
estimation of the uplift and denudation histories over the past few million years in
medium-sized mountains (Fig. 2.7.3-9). The results showed that the thermochronologic
methods were effective for obtaining an estimate of vertical crustal movement. On the other
hand, the result showed that apatite FT thermochronometry cannot readily detect the
Quaternary uplift and denudation histories of <1,000-m-high mountains in the JapaneseIslands31).
We are planning to measure exposure ages of bedrocks using in situ terrestrial cosmogenic
nuclides, such as 10Be and 26Al, to estimate the amounts of uplift and denudation in inland
areas over shorter periods.

Fig. 2.7.3-8 (a) Distribution of circular abandoned channels in Japan interpreted from
1:25,000 topographic maps and(b) Histograms of the heights of circular abandoned channels in Japan relative topresent-day channels37)- 102 -

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Fig. 2.7.3-9 (a) Topographical map of the study area showing the locations and sample codesaround the Suzuka Mountains and(b) Latitude versus apatite fission-track (AFT) ages across the Suzuka Mountains31)
2.7.4 Summary
We developed techniques to investigate past and present natural phenomenon that must be
considered during the site selection phase in the final disposal. These investigation techniques
cannot be used to observe faults directly, but instead are used to infer the existence of faults
on the basis of indirect evidence. Therefore, in addition to the accumulation of examples,
important themes include construction of a comprehensive investigation technique thatincorporates different types of data.
References
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Project - for the Selection of Detailed Investigation Areas -”, NUMO-TR-10-02 (2010), p.58.
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study for radioactive waste disposal (Fiscal Year 2010-2014)” (2009), 36p.
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4) Agency for Natural Resources and Energy and Japan Atomic Energy Agency :“Fundamental R&D Program for the Geological Disposal of HLW” (2009), 114p.
5) Agency for Natural Resources and Energy and Japan Atomic Energy Agency :“Fundamental R&D Program for the Geological Disposal of HLW and TRU” (2010), 139p.
6) The Working Group for Compilation of 1:2,000,000 Active Faults Map of Japan : “New
1:2,000,000 Active Faults Map of Japan”, Active Fault Research, no.19, pp.3-12 (2000).

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7) Nakata, T. and Imaizumi, T. (eds.) : “Digital active fault map of Japan”, University of Tokyo
Press (2002).
8) Niwa, M., Kurosawa, H., Shimada, K., Ishimaru, T. and Kosaka, H. : “Identification of
Pathways for Hydrogen Gas Migration in Fault Zones with a Discontinuous, Heterogeneous
Permeability Structure and the Relationship to Particle Size Distribution of Fault
Materials”, Pure Appl. Geophys., 168, pp.887-900 (2011).
9) Umeda, K. and Ninomiya, A. : “Helium isotopes as a tool for detecting concealed active
faults”, Geochem. Geophys. Geosyst., 10, Q08010 (2009).
10) Umeda, K., Asamori, K., Negi, T. and Kusano, T. : “A large intraplate earthquake triggeredby latent magmatism”, J. Geophys. Res., 116, B01207 (2011).
11) Umeda, K., Asamori, K. and Kusano, T. : “Release of mantle and crustal helium from afault following an inland earthquake”, Appl. Geochem., Volume 37, pp.131-141 (2013).
12) Umeda, K., Kusano, T., Ninomiya, A., Asamori, K. and Nakajima, J. : “Spatial variationsin 3He/4He ratios along a high strain rate zone, central Japan”, J. Asian, Earth Sci., Volume
73, pp.95-102 (2013).
13) Umeda, K., Asamori, K., Komatsu, R., Kakuta, C., Kanazawa, S., Ninomiya, A., Kusano,T. and Kobori, K. : “Postseismic leakage of mantle and crustal helium from seismically
active regions”, In Helium: Occurrence, Applications and Biological Effects, edited by S. B.
Davis, pp.115-178 (2013).
14) Zhao, D. and Negishi, H. : “The 1995 Kobe earthquake, seismic image of the source zone
and its implications for the rupture nucleation”, J. Geophys. Res., Volume 103, Issue 5,
pp.9967-9986 (1998).
15) Negi, T., Umeda, K., Matsuo, K., Asamori, K., Yokoi, K. and Ohara, H. : “An efficient andeffective stacking method for MT spectrum data; - Effectiveness against coherent noise -”,Geophys. Explor., 63, pp.395-408 (2010).
16) Negi, T., Umeda, K., Matsuo, K., Asamori, K., Yokoi, K. and Ohara, H. : “An efficient andeffective stacking method for MT spectrum data; - A validation study using survey data -”,Geophys. Explor., 64, pp.153-165 (2011).
17) Negi, T., Mizunaga, H., Asamori, K. and Umeda, K. : “Three-dimensional magnetotelluric
inversion using a heterogeneous smoothness-constrained least-squares method”, Explor.
Geophys., 44(3), pp.145-155 (2013).
18) Umeda, K., Asamori, K., Makuuchi, A. and Kobori, K. : “Earthquake doublet in an active
shear zone, southwest Japan: Constraints from geophysical and geochemical findings”,
Tectonophysics, Volume 634, pp.116-126 (2014).
19) Asamori, K., Umeda, K., Ogawa, Y. and Oikawa T. : “Electrical Resistivity Structure andHelium Isotopes around Naruko Volcano, Northeastern Japan and Its Implication for theDistribution of Crustal Magma”, Inter. J. Geophys., 2010, ID738139 (2010).
20) Asamori, K., Umeda, K., Ninomiya, A. and Negi, T. : “Manifestations of Upwelling Mantle
Flow on the Earth’s Surface”, In The Earth's Core: Structure, Properties and Dynamics,edited by J. M. Phillips, pp.77-94 (2011).
21) Umeda, K., Asamori, K., Ninomiya, A., Kanazawa, S. and Oikawa, T. : “Multiple lines of- 104 -

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evidence for crustal magma storage beneath the Mesozoic crystalline Iide Mountains,
northeast Japan”, J. Geophys. Res., 112, B05207 (2007).
22) Umeda, K., Ninomiya, A. and Asamori, K. : “Release of mantle helium and its tectonic
implications”, in Helium: Characteristics, Compounds, and Applications, edited by L. A.
Becker, pp.81-101 (2011).
23) Umeda, K., Yasue, K. and Asamori, K. : “Currents status and perspective of faulting
studies for high level radioactive waste disposal”, Chikyu Monthly, 32, pp.52-63 (2010).
24) Yamada, K., Yasue, K., Iwano, H., Yamada, R., Umeda, K. and Omura, K. :“Thermochronological study of the dip-slip displacement and timing of initiation of the
Atera fault”, he Journal of the Geological Society of Japan, 118, pp.437-448 (2012).
25) Manaka, M., Fukushi, K., Miyashita Y., Itoh, J., Watanabe, Y., Kobayashi, K. and Kamei,
A. : “Comparison of fault gouges in the aftershock area and the non aftershock area of the2000 Tottori-ken Seibu earthquake”, The Journal of the Geological Society of Japan, 118,
pp.459-475 (2012).
26) Murakami, M. and Tagami, T. : “Dating pseudotachylyte of the Nojima fault using thezircon fission-track method”, Geophys. Res. Lett., Vol. 31, L12604 (2004).
27) Yamasaki, S., Zwingmann, H. and Tagami, T. : “Intermethod Comparison for K-Ar Datingof Clay Gouge”, Mineralogical Magazine, 77(5) p.2542 (2013).
28) Yamasaki, S., Yamada, K., Tagami, T. and Zwingmann, H. : “K-Ar dating of fault clays Case studies and precise separation of authigenic clay minerals -”, Fission Track News
Letter, No.26, pp.6-8 (2013).
29) Yamasaki, S., Zwingmann, H., Yamada, K., Tagami, T. and Umeda, K. : “Constraining thetiming of brittle deformation and faulting in the Toki granite, central Japan”, Chem. Geol.,
Volume 351, pp.168-174 (2013).
30) Yamasaki, S. and Umeda, K. : “Cooling history of the Cretaceous Toki granite in theeastern Sanyo Belt, Central Japan”, Japanese Magazine of Mineralogical and Petrological
Sciences, 41, pp.39-46 (2012).
31) Yasue, K., Asamori, K., Niwa, M., Hanamuro, T., Kokubu, Y., Sueoka, S., Makuuchi, A.,
Ikuta, M., Matsubara, A., Tamura, H., Kobori, K., Ishimaru, T. and Umeda, K. : “Annual
report for research on geosphere stability for long-term isolation of radioactive waste infiscal years 2012”, JAEA-Research 2013-047 (2014), 109p.
32) Tamura, H. and Sato, K. : “K-Ar geochronology of fault”, Engineering Geology of Japan, 3,
pp.21-25 (2013).
33) Niwa, M., Shimada, K., Yasue, K., Ishimaru, T. and Umeda, K. : “Faulting gouges and clayveins developed in granite”, Abstracts of the 120th Annual Meeting of the GeologicalSociety of Japan, R24-P-3 (2013).
34) Niizato, T., Yasue, K., Doke, R. and Nakayasu, A. : “An Externalization of Technical Knowhow and Decision-Making Processes in a Geoscientific Investigation - An Example of an
Estimation of Uplift Rate -”, Geoinformatics, 25, pp.3-20 (2014).
35) Yoshiyama, A. and Yanagida, M. : “Uplift Rates Estimated from Relative Heights of
Fluvial Terrace Surfaces and Valley Bottoms”, Journal of Geography (Chigaku Zasshi), 104,

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pp.809-826 (1995).
36) Takatori, R., Yasue, K., Tanikawa, S., Ninomiya, A. and Tanase, A. : “Development of
database on circular abandoned channel in Japan”, JAEA-Data/Code 2012-028 (2013), 15p.
37) Yasue, K., Asamori, K., Tanikawa, S., Yamada, K., Yamasaki, S., Kokubu, Y., Niwa, M.,
Doke, R., Kusano, T., Hanamuro, T., Ishimaru, T. and Umeda, K. : “Annual report for
research on geosphere stability for long-term isolation of radioactive waste in fiscal years
2010”, JAEA-Research 2011-023 (2011), 113p.
38) Asamori, K., Niwa, M., Hanamuro, T., Yamada, K., Kusano, T., Makuuchi, A., Takatori, R.,
Kokubu, Y., Matsubara, A., Ishimaru, T. and Umeda, K. : “Annual report for research on
geosphere stability for long-term isolation of radioactive waste in fiscal years 2011”, JAEAResearch 2012-024 (2012), 132p.
39) Matsushi, Y., Chigira, M., Hiraishi, N. and Matsuzaki, H. : “Incision Rate of Uppermost
Reaches in the Totsukawa River, Kii Peninsula Japan : an Approach from Exposure Datingof Abandoned Channels using Terrestrial Cosmogenic Nuclides”, Disaster Prevention
Research Institute Annuals., Vol.55B, pp.241-245 (2012).
40) Wagner, G. A., Reimer, G. M. and Jäger, E. : “Cooling ages derived by apatite fission-track,
mica Rb-Sr and K-Ar dating: the uplift and cooling history of the Central Alps”, Memoir of
the Institute of Geology and Mineralogy, University of Padova, 30, pp.1-27 (1977).
41) Yamada, K. : “(U-Th)/He dating of a pseudotachylyte collected from the Ryoke Granite,
Taki area, Mie Pref”, Chikyu Monthly, 32, pp.30-39 (2009).
42) Yamada, K., Hanamuro, T., Tagami, T., Shimada, K., Takagi, H., Yamada, R. and Umeda,
K. : “The first (U-Th)/He thermochronology of pseudotachylyte from the Median Tectonic
Line, southwest Japan”, J. Asian, Earth Sci., Volume 45, pp.17-23 (2012).
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Methods”, J. Geography (Chigaku Zasshi), 120, pp.1003-1012 (2011).

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3. Understanding impact of construction in geo-environmental conditions
3.1 Geology
3.1.1 Introduction
Knowledge of the distribution and characteristics of the Excavation Damaged Zone (EDZ)
induced by the excavation of underground facilities is important for understanding the shortterm evolution and recovery behavior of the geological environment around the undergroundfacility. In the construction phase (Phase II) and operation phase (Phase III), detailed
information concerning the EDZ needs to be obtained by geological investigations at the shaft
and galleries during and after the facility excavation. Therefore, we proceeded with R&D toidentify the extent of the EDZ that should be characterized for the safety assessment1),2).
3.1.2 Objectives in the second mid-term research phase
Geological mapping of the excavated shaft and gallery walls and borehole investigations at
the underground facilities were conducted to reach the performance target of R&D, in order
to identify the extent of the EDZ induced by excavation of the underground facilities shown in
Table 3.1.2-1.
Table 3.1.2-1 Performance target of R&D for perceiving the extent of the EDZ
Focus

Performance target of R&D

Tasks

Decision to begin
disposal

Enable to understand an extent of EDZ
around a gallery.

• Demonstration of technique tounderstand extent of EDZ induced byconstruction of underground facility

3.1.3 Project details and outcomes(1) Understanding the extent of the EDZ
Fracture observations by geological mapping of the excavated shaft and gallery walls andborehole investigations at the underground facilities were carried out in the Horonobe URL to
identify the extent of the EDZ in soft sedimentary rock. However, the EDZ that were inducedby the excavation of granitic rocks in the Mizunami URL could not be identified by visualobservations such as geological mapping. The results of the studies around the Horonobe URL
are summarized as follows:- Fractures observed on the floor of the Pumping Drift in the 250 m gallery could be divided
into pre-existing fractures (shear fractures) and EDZ fractures (extension fractures). The
EDZ fractures were not controlled by the orientation of the excavation, and could beclassified into two sets by focusing on their orientation. The first set was from NW-SE to
N-S strike, dipped slightly westward, and was parallel to the bedding plane. The second
set was from E to W strike and dipped steeply north or south. This fracture set wasparallel to the E-W shear fractures and weak planes inferred from the paleo-stress field.
These EDZ fractures were terminated against the pre-existing shear fractures. The
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including bedding and transgranular fractures, and was controlled by pre-existing
fractures (Fig. 3.1.3-1)3).
- Several pre-excavation grouting boreholes were drilled from the 250 m depth in andaround the Ventilation Shaft, and grouting was carried out from 250 to 380 m depth.
After grouting, the Ventilation Shaft from 250 to 350 m depth was excavated, andgeological mapping was carried out. Based on the mapping results, EDZ fractures withgrout were observed until several meters depth from the floor at the 250 m gallery (Fig.
3.1.3-2)4). These fractures with grout were assumed to be induced by the excavation of
the 250 m gallery.
- The total trace length of the newly created fractures was small in the areas where thetotal trace length of the pre-existing fractures was large while the total trace length of
the newly created fractures was large where the total trace length of pre-existing
fractures was small5). Thus, there was a negative correlation between the total trace
length of pre-existing fractures and that of the newly created fractures. The number offractures around the gallery drastically increases after gallery excavation, and theresulting stress release and formation of the EDZ occur due to the formation of the newly
created and pre-existing fractures. From these studies, conceptual models of the EDX
showing characteristics of the formation of the newly created and pre-existing fractures
around the gallery were constructed5).

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Fig. 3.1.3-1 Conceptual models showing the fracture formation process before excavation (aand b) and after excavation (c) on the floor of the gallery3)- 109 -

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Fig. 3.1.3-2 Fracture mapping showing all fractures (a), fractures with grout (b), andfractures with grout and faults (c)4)
3.1.4 Summary
The common knowledge regarding the potential investigation techniques for understanding
the extent of the EDZ induced by the construction of underground facilities is as follows:- For soft sedimentary rocks such as those found in the Horonobe area, the distribution
and characteristics of the EDZ could be identified, and a conceptual model of theformation of the EDZ could be constructed based on the results obtained from geologicalmapping and borehole investigations in the gallery. On the other hand, for granitic rocks
such as those found in the Mizunami area, the EDZ induced by the excavation could not
be easily identified from visual observations such as geological mapping investigations.
Future issues include the development of investigation techniques for understanding theevolution of the EDZ during construction and operation phases, which will require the- 110 -

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following R&D:
- Development of investigation techniques for understanding the evolution of the extent
and characteristics of the EDZ fractures- Accumulation of data and knowledge regarding infilling and sealing of fractures during
the post–closure gallery
References
1) Saegusa, H., Matsui, H., Hama, K., Sato, T., Tsuruta, T., Takeuchi, R., Kunimaru, T.,
Matsuoka, T. and Mizuno, T. : “Concept and Procedure of Geoscientific Study in the
Mizunami Underground Research Laboratory Project -Study Plan on Construction Phase(Phase II) and Operation Phase (Phase III) to 500m Depth”, JAEA-Review 2011-022 (2011),
78p.
2) (Eds.) Iwatsuki, T., Sato, H., Nohara, T., Tanai, K., Sugita, Y., Amano, K., Yabuuchi, S.,
Oyama, T., Amano, Y., Yokota, H., Niizato, T., Tokiwa, T., Inagaki, D., Abe, H., Nakayama,
M. and Kurikami, H. : “Horonobe Underground Research Laboratory Project Research andDevelopment Plan(H22-H26)”, JAEA-Research 2011-009 (2011), 73p.
3) Tokiwa, T., Tsusaka, K., Matsubara, M., Ishikawa, T. and Ogawa, D. : “Formation
mechanism of extension fractures induced by excavation of a gallery in soft sedimentaryrock, Horonobe area, Northern Japan”, Geoscience Frontiers, Volume 4, Issue 1, pp.105-111(2013).
4) Tokiwa, T., Sawada, S., Ochiai, S. and Miyakawa, K. : “Occurrence of high-permeability
fracture estimated by grouting in Horonobe URL of Japan”, 13th Japan Symposium on
Rock Mechanics & 6th Japan-Korea Joint Symposium on Rock Engineering, pp.1021-1025(2013).
5) Tokiwa, T., Tsusaka, K., Matsubara, M. and Ishikawa, T. : “Fracture characterization
around a gallery in soft sedimentary rock in Horonobe URL of Japan”, International
Journal of Rock Mechanics & Mining Sciences, 65, pp.1-7 (2014).

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3.2 Hydrogeology
3.2.1 Introduction
The objective of the study was to establish the following techniques:- Comprehensive techniques of investigation, analysis, and assessment, including amonitoring method, for characterization of the evolution of groundwater flow conditions
during construction and operation of underground facilities- Techniques of investigation, analysis, and assessment for characterization ofgroundwater flow conditions near the field of the disposal gallery
From these hydrogeological points of view, the focused features and processes to be
characterized and the resulting data requirements relevant to safety assessment, design, andconstruction were identified1).
(1) Volume of inflow into underground facilities
It is necessary to understand the volume of inflow into underground facilities from thefollowing points of view:- Design, construction, and maintenance of underground facilities- Prediction of recovery behavior during backfilling of underground tunnels(2) Impact on groundwater table and pressure
It is also necessary to understand the impact of construction and operation of undergroundfacilities on the groundwater table and pressure from the following points of view:- Design, construction, and maintenance of underground facilities- Prediction of recovery behavior during backfilling of underground facilities- Environmental impact assessment(3) Spatial variability of groundwater flux
The three-dimensional spatial variability of groundwater flux is determined from the spatial
variability of hydraulic properties and hydraulic gradient. In order to assess the masstransport and retardation characteristics, it is important to characterize the spatial variabilityof the groundwater flux near the field of the underground facilities, which includes the
excavation damaged zone.
3.2.2 Objectives in the second mid-term research phase
The following studies were carried out to achieve the R&D performance target for perceiving
the short-term evolution and recovery behavior of groundwater flow condition (Table 3.2.2-1):- Monitoring of groundwater pressure and inflow volume during construction of theunderground facilities- Hydraulic testing using boreholes drilled at underground facilities to characterize thehydrogeological heterogeneity near the field of the underground facilities- 112 -

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Table 3.2.2-1 Performance target of R&D perceiving the short-term evolution and recovery
behavior of groundwater flow conditions
Focus

Performance target of R&D

Tasks

Construction
decision

Enable judging of appropriateness ofconstruction and operation ofunderground facility taking into accountgroundwater flow.

• Method for measurement of inflow
volume during construction ofunderground facility• Method for monitoring of changes ofgroundwater pressure during
construction of underground facility

Enable estimation of recovery of feasible
groundwater flow conditions post closure.

• Techniques of investigation andanalysis for prediction of recovery
behavior of groundwater flow
conditions post closure

Enable prediction and confirmation of
the spatial variability of hydrauliccharacteristics and groundwater flux
near field of disposal gallery.

• Techniques of investigation, analysis
and assessment for prediction ofgroundwater flow conditions near fieldof disposal gallery

Decision to begin
disposal

3.2.3 Project details and outcomes(1) Volume of inflow into underground facilities
The total volume of inflow into the underground facilities has been monitored. In addition,
the inflow rate monitoring was carried out at measured intervals along the shafts tounderstand the depth profile of the inflow volume2).
1) Mizunami
It is estimated that the influence of the hydrogeological characteristics near the tunnel on
the inflow rate are significant, because artificial structural materials, such as lining concreteor drainage materials installed behind the lining or grout, may function as a skin. Therefore,
data regarding the skin has been obtained3) as well as regarding the inflow volume.
The main achievements and technical findings from the investigations can be summarized
as follows:- The total and sectional inflow rates into the underground tunnel have been monitored.
The inflow rate increased during construction of facilities at the area with highpermeability structures (Fig. 3.2.3-1, Fig. 3.2.3-2).
- The applicability of each technique for inflow rate monitoring was evaluated.
Steep hydraulic drawdown was recognized in the vicinity of shafts caused by skin effects (Fig.
3.2.3-3).

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Inflow rate(m3/d)

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Fig. 3.2.3-1 Groundwater inflow rate into the underground facilities (MIU)

Fig. 3.2.3-2 Sectional groundwater inflow rate into the underground facilities (MIU)- 114 -

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Fig. 3.2.3-3 Hydraulic head distribution in the vicinity of the shafts (MIU)
2) Horonobe
The main achievements and technical findings from the investigations can be summarized
as follows:- As it is estimated that the inflow rate into the underground tunnel is high in the highpermeability zone along the shafts, impermeable walls in the underground area havebeen constructed to reduce the inflow rate4),5).
The total inflow rate into underground tunnel has been monitored. The inflow rate increased
during construction of facilities in the area with high-permeability structures (Fig. 3.2.3-4).
Inflow rate into Ventilation shaft （Measured）

200

300

Inflow rate into East shaft （Measured）
Total inflow （Mesured）

180

Excavation depth （Ventilation shaft）
Excavation depth （East shaft）

250

160

200

120
100

150

80
100

60
40

Excavation depth（GL-m）

Inflow rate （m3/d）

140

50

20
0

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

0
1500

Elapsed time （day）

Fig. 3.2.3-4 Groundwater inflow rate into the underground facilities (Horonobe)- 115 -

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Groundwater pressure has been monitored using several boreholes drilled from the surface
and underground tunnels6),7). Tilt monitoring8),9),10),11),12),13), self-potential monitoring14)(Mizunami only), and surface hydrological monitoring15) have also been carried out assupplementary methods of groundwater pressure monitoring.
1) Mizunami
The main achievements and technical conclusions from the investigations are summarized
as follows:- The hydraulic responses differ for each hydraulic compartment that is estimated to beformed by low-permeability structures (Fig. 3.2.3-5).
- Degassing of dissolved gas causes measurement errors if the piezometer tube is thin. A
method was developed as a countermeasure.
- A method of data processing has been developed for specifying hydraulic changes
resulting from construction of underground facilities and elimination of other components
such as hydraulic changes caused by earth tides, atmospheric pressure variations, andearthquakes (Fig. 3.2.3-6).
- The groundwater level in the unconfined aquifer near the surface fluctuates
synchronously with rain fall (Fig. 3.2.3-7).
Tilt monitoring and self-potential monitoring are useful methods to understand the hydraulicresponses in the horizontal plane and can be supplementary methods of groundwater pressure
monitoring.

Fig. 3.2.3-5 Hydraulic responses caused by construction of underground facilities (MIU)- 116 -

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Fig. 3.2.3-6 Method of data processing for specifying hydraulic changes

Fig. 3.2.3-7 Changes in the groundwater level of the unconfined aquifer (MIU)- 117 -

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2) Horonobe
The main achievements and technical findings from the investigations can be summarized
as follows:- Clear hydraulic responses have been recognized only in the zone of water-conducting
faults with tensional fractures16) (Fig. 3.2.3-8).
- The groundwater level in the unconfined aquifer near the surface fluctuates
synchronously with rain fall17) (Fig. 3.2.3-9).
Tilt monitoring is a useful method to understand the hydraulic responses in the horizontal
plane and can be used as a supplementary method of groundwater pressure monitoring (Fig.
3.2.3-10).

150

50

0

Relatively large response of pressure
drop corresponding to the increase of
inflow75

HDB‐3

Pressure drop response
postdating with time lag(Wakkanai Fm, deep zone)

70
65
60

Koetoi Fm

HDB-3
GL-226.71m
GL-329.85m
GL-401.00m
GL-438.69m

55
50
80

KoetoiFm
Wakkanai
Fm

HDB‐6

75

Wakkanai Fm (shallow)

70(highly permeable domain)

65

HDB-6
GL-74.80m Koetoi Fm
GL-229.14m
GL-292.15m
GL-365.85m Wakkanai
GL-400.77m Fm
01

01

08
/0

08
/1

09
/0

09
/0

09
/0

09
/1

10
/0

10
/0

10
/0

10
/1

11
/0

20

20

20

20

20

20

20

20

20

20

20

3/

2/

01

01

08
/0

9/

6/

3/

2/

01

01

01

01

9/

01

Wakkanai Fm (deep)

20

9/

6/

01

01

50

01

55

6/

60

2/

Hydraulic head (masl)

80

Hydraulic head (masl)

the last 3‐year after the drop started (HDB‐3, HDB‐6: a maximum of ca. 0.15 MPa)

100

3/

y
a
d
/
m

Inflow from Shaft Amount of groundwater pressure drop for

Ventilation shaft reached highly
permeable domain of Wakkanai
Fm (shallow) at ca. 250 m in
depth

200

3

3/day)
Inflowrate(m
Inflow
volume
) /d)
湧水量(
³ (m

250

Pressure drop response
postdating with time lag (Koetoi
Fm)

Date

Fig. 3.2.3-8 Hydraulic responses caused by construction of underground tunnels (Horonobe)- 118 -

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Fig. 3.2.3-9 Changes in the groundwater level of the unconfined aquifer (Horonobe)

Fig. 3.2.3-10 Tilt changes during construction of underground tunnels (Horonobe)- 119 -

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JAEA-Review 2016-014(3) Spatial variability of groundwater flux
1) Mizunami
A hydrogeological model based on a discrete fracture network approach was constructedusing data obtained from investigations at the underground facilities and from boreholes
drilled underground18),19). The main achievements and technical findings from theinvestigations can be summarized as follows:- A method of discrete fracture network modeling and continuum modeling taking into
account the hydraulic heterogeneity were developed.
- Sensitive parameters for discrete fracture network modeling were specified taking into
account the influence of the geological and hydrogeological characteristics of fractures ongroundwater flow and mass transport phenomena.
- Data acquisition for fractures with a wide range of hydraulic characteristics in acontinuous manner was difficult because of the high groundwater pressure condition (itwas difficult to replace borehole fluid for fluid logging) and time constraints (it wasnecessary to carry out short-interval hydraulic tests for a long time along the whole
length of the borehole).
2) Horonobe
The short-term phenomena of geological and hydrogeological characteristics in the EDZ has
been investigated to understand the spatial variability of groundwater flux20),21),22). The mainachievements and technical findings from the investigations can be summarized as follows;- Changes in groundwater pressure stabilized within 1.5 years after construction of theunderground facilities, and saturation also stabilized at 70% to 80% humidity (Fig. 3.2.311).
- Changes in the hydraulic properties and pore structure at distances greater than 3
meters from the wall of the underground tunnel were not recognized.
- A hydro-testing method has been developed for an environment in which degassing of
dissolved gas occurs.

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25

Humidity
坑内湿度

80

20

60

15

40

55

Start of excavation of 140m stage
Breakthrough of 140m east connection drift
Start of excavation of 140m west connection drift

20
00
0.6

Completion of excavation of 140m stage

0.5

0.5

0.4

0.4

0.3
Moisture(2m from tunnel wall)
水分量（坑壁から2m）
Moisture(1m from tunnel wall)
水分量（坑壁から1m）

0.2

GW
pressure (8.6-9.1m from tunnel wall )間隙水圧（孔口からの距離8.6-9.1m）

0.2

GW
pressure (10.0-10.5m from tunnel wall )間隙水圧（孔口からの距離10.0-10.5m）
GW
pressure (11.5-12.0m from tunnel wall)
間隙水圧（孔口からの距離11.5-12.0m）

0.1

0.1

0.0

0

間隙水圧 (MPa)0.3

Groundwater pressure (MPa)

10

0.6

Volume体積含水率
water content

100
Temperature
坑内気温

Daily mean humidity (%)

30

日平均湿度 (%)(℃)
Daily日平均気温
mean temperature(℃)

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日付

Date

Fig. 3.2.3-11 Changes in groundwater pressure/moisture and temperature/humidity in thetunnel (Horonobe)
3.2.4 Summary
The techniques and accumulated technical knowledge regarding investigation, analysis, andassessment for characterization of the evolution of groundwater flow conditions during
construction and operation of underground facilities and for characterization of groundwaterflow conditions near the field of the disposal gallery are summarized below.
(1) Volume of inflow into underground facilities- Pilot borehole investigations are capable of yielding improvements to the prediction
accuracy.
- Measurement of the sectional inflow rate is useful for interpretation of hydrogeologicalheterogeneity.
- The influence of the hydraulic characteristics near the tunnel on the groundwater inflow- 121 -

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rate is quite significant, because artificial structural materials, such as lining concrete,
grout, and drainage material, may function as a skin.
- A method for maintenance of measurement equipment has been established.
- The technical findings for the measurements have been accumulated, and a method for
quality control of the measurements has been developed.
(2) Impact on groundwater table and pressure- Assignment of hydraulic monitoring intervals, taking into account hydrogeologicalheterogeneity including hydrogeological compartmentalization, is useful for estimationof hydraulic characteristics.
- A method for maintenance of measurement equipment, including countermeasuresagainst gas, has been established.
- The technical findings for the measurement have been accumulated, and a method for
quality control of the measurements, under gaseous condition, has been developed.
(3) Spatial variability of groundwater flux
- The necessity to develop techniques of investigation, analysis, and assessment forcharacterization of hydrogeological heterogeneity and groundwater flow conditions in
low-permeability domains using boreholes drilled from tunnels has been identified.
The future studies will be performed to solve the open issues described below:
1) Development of techniques of investigation, analysis, and assessment for prediction of the
post-closure recovery behavior of groundwater flow conditions.
- Applicability checking of techniques of investigation, analysis, and assessment forevaluation of the influences of heterogeneous inflow into the underground on theperformance of material for back-filling by groundwater recovery experiment and tunnel
back-filling experiments.
- Durability enhancement of measurement equipment, development of a wirelessmonitoring technique, development of a method for maintenance of measurement
equipment (including countermeasures against gas), accumulation of technical know-how,and development of quality control methods.
- Accumulation of technical knowledge regarding the post-closure recovery behavior ofgeological environments.
2) Development of effective techniques of investigation, analysis, and assessment forcharacterization of hydrogeological heterogeneity and groundwater flow conditions in lowpermeability domains.
- Development of effective investigation techniques for continuous data acquisition on
fractures with a wide range of hydraulic characteristics.
- Development of a method for discrete fracture network modeling taking into account theactual characteristics of fractures.

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References
1) Saegusa, H., Matsui, H., Hama, K., Sato, T., Tsuruta, T., Takeuchi, R., Kunimaru, T.,
Matsuoka, T. and Mizuno, T. : “Concept and Procedure of Geoscientific Study in the
Mizunami Underground Research Laboratory Project - Study Plan on Construction Phase(Phase II) and Operation Phase (Phase III) to 500m Depth”, JAEA-Review 2011-022 (2011),
78p. (in Japanese).
2) Sato, S., Ogata, N., Takeuchi, R. and Saegusa, H. : “Monitoring of groundwater inflow into
research galleries in the Mizunami Underground Research Laboratory Project (MIU
Project); From fiscal year 2004 to 2011”, JAEA-Data/Code 2013-020 (2014), 38p. (inJapanese).
3) Takeuchi, R., Saegusa, H., Ohyama, T., Keya, H., Sato, A., Kosaka, H., Takeda, M., Daimaru,
S. and Takeuchi, S. : “Study on hydrogeology on the Mizunami Underground ResearchLaboratory Project Annual report for fiscal year 2008”, JAEA-Research 2010-018 (2010),
133p. (in Japanese).
4) Shibano, K., Orukawa, G., Yasue, K., Funaki, H. and Kurikami, H. : “Prediction ofgroundwater flow rate into shaft to the depth of 50m”, JAEA-Research 2008-033 (2008),
27p. (in Japanese).
5) Orukawa, G., Matsui, H., Kurimaki, H., Funaki, H. and Morioka, H. : “Problem and countermeasures in construction of underground research shaft and drift of Horonobe
Underground Research Laboratory Project”, The Japanese Geotechnical Society, 56(1),pp.32-35 (2008). (in Japanese).
6) Karino, T. and Takeuchi, R. : “Data of Long Term Hydro-pressure Monitoring on Tono
Regional Hydrogeological Study Project for Fiscal Year 2010”, JAEA-Data/Code 2012-001(2012), 54p. (in Japanese).
7) Karino, T. and Takeuchi, R. : “Data of Long Term Hydro-pressure Monitoring on Mizunami
Underground Research Laboratory Project for Fiscal Year 2010”, JAEA-Data/Code 2012002 (2012), 110p. (in Japanese).
8) Ohyama, T., Takeuchi, R., Saegusa, H., Onoe, H. and Matsuki, K. : “Applicability of themethod to estimate hydrogeological structures using a tilt data”, Proceeding of the 37th
symposium on rock mechanics, pp.245-250 (2008). (in Japanese).
9) Ohyama, T., Saegusa, H., Takeuchi, R., Takeuchi, S. and Matsuoka, T. : “Multiple lines ofevidence for characterization of hydrogeological structures at the Mizuami undergroundresearch laboratory in Tono area, Japan”, 2009 Annual Conference and General Assemblyof Korean Society for Rock Mechanics, pp.245-252 (2009).
10) Matsuki, K., Nakatani, K., Arai, T., Ohmura, K., Takeuchi, R., Arai, Y. and Takeuchi, S. :“A quadratic element method for evaluating groundwater flow by the inversion of surface
tilt with application to the Tono Area, Japan”, Journal of Hydrology, Volume 360, Issues 14 pp.217-229 (2008).
11) Narukawa, T., Matsuki, K., Arai, T., Ohyama, T., Takeuchi, R. and Takeuchi, S. :“Estimation of groundwater flow at the site of Mizunami Underground ResearchLaboratory by the inversion of surface tilt during drainage, submergence and re-drainage- 123 -

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in excavation of shafts”, Journal of Japan Society of Civil Engineers, C, Vol.65, No.2,
pp.442-455 (2009). (in Japanese).
12) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2008 fiscal year”, JAEA-Research
2009-032 (2009), 68p. (in Japanese).
13) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project; Investigation report for the 2009 fiscal year”, JAEA-Review
2010-039 (2010), 67p. (in Japanese).
14) Tokuyasu, S., Matsuoka, T. and Hodotsuka, Y. : “Studies on estimation of hydrogeologicalstructure using self-potential monitoring around Mizunami Underground ResearchLaboratory (MIU)”, JAEA-Research 2012-007 (2012), 55p. (in Japanese).
15) Sato, S., Ogata, N., Takeuchi, R. and Takeda, M. : “Annual data compilation of waterbalance observation in the Mizunami Underground Research Laboratory Project (MIU
Project) - For the fiscal year 2010 to 2011 -”, JAEA-Data/Code 2013-016 (2013), 50p. (inJapanese).
16) Amano, Y., Nanjo, I., Murakami, H., Yabuuchi, S., Yokota, H., Sasaki, Y. and Iwatsuki, T. :“Validation of surface-based hydrochemical investigation and the impact of undergroundfacility construction at Horonobe URL”, Journal of groundwater hydrology, Vol.54, No.4,
pp.207-228 (2012). (in Japanese).
17) Yokota, H., Yamamoto, Y. and Maekawa, K. : “A Study of shallow groundwater flow basedon groundwater level and geological structures in the Horonobe area, Hokkaido”, Journalof groundwater hydrology, Vol.53, No.2, pp.193-206 (2011). (in Japanese).
18) Ishibashi, M., Onoe, H., Sawada, A., Atsumi, H., Masumoto, K. and Hosoya, S. : “Discrete
fracture network modeling based on in-situ data at underground gallery (Part I)”,
Proceeding of the 42nd symposium on rock mechanics, pp.101-106 (2014). (in Japanese).
19) Nakajima, M., Seno, S., Onoe, H., Ishibashi, M., Saegusa, H. and Sawada, A. : “Discrete
fracture network modeling based on in-situ data at underground gallery (Part II)”,
Proceeding of the 42nd symposium on rock mechanics, pp.107-112 (2014). (in Japanese).
20) Yabuuchi, S., Kunimaru,T., Kishi, A. and Komatsu, M. : “Monitoring of pore water pressure
and water content around a horizontal drift through excavation - Measurement at the 140m
gallery in the Horonobe URL -”, Journal of Japan Society of Civil Engineers, C, Vol.67, No.4,
pp.464-473 (2011). (in Japanese).
21) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Ohyama, T., Amano, Y., Murakami,
H., Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S.,
Ohhara, M. and Jin, K. : “Horonobe Underground Research Laboratory Project;
Investigation report for the 2011 fiscal year”, JAEA-Review 2012-035 (2012), 63p. (inJapanese).
22) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Project; Investigation
report for the 2012 fiscal year”, JAEA-Review 2013-037 (2014), 63p. (in Japanese).

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3.3 Hydrogeochemistry
3.3.1 Introduction
The geological environment will probably be influenced for several decades by changes
resulting from the construction and operation of a large underground facility. In the excavateddamaged zone [EDZ], mechanically and chemically damaged rock properties will not recoverafter facility closure. In the excavated disturbed zone [EdZ] comprising EDZ, hydraulic andchemical disturbance may possibly recover over time after closure of the facility1). During theconstruction and operation of the facility, the tunnels have atmospheric pressure andgroundwater inflow into the tunnel occurs depending on the hydrogeological properties of therock. Large amounts of groundwater inflow will alter the hydraulic conditions as well as thegroundwater chemistry around the facility2).
3.3.2 Objectives in the second mid-term research phase
Basic knowledge of changes in the hydrochemical baseline conditions based on long-termmonitoring is required during the construction, operation, and post closure around deep large
underground facilities similar to HLW repository. The R&D listed in Table 3.3.2-1 has been
conducted in both URLs.
Hydrochemical changes during the facility construction phase are mainly caused by thefollowing processes. In an EDZ, the mechanical and hydrogeological properties of rock change
intensely because of fracturing during excavation, and the chemical properties are modified
by factors such as shotcrete, grouting, and air circulation. In an EdZ, the groundwaterchemistry possibly changes because of mixing of chemically distinct waters induced bychanges in the hydraulic conditions. The hydrochemical changes and their processes in the
EdZ/EDZ were summarized based on hydrochemical monitoring during the facility
construction phase.
Table 3.3.2-1 Performance target of R&D for the short-term evolution and recovery behaviorof hydrochemical conditions
Focus

Start of isolation

Performance target of R&D

Tasks• Demonstrate the monitoring andsimulation technique for hydrochemicalchanges during facility construction,
To judge that favorable chemical
operation, and post closure
conditions can be presumed after facility
closure.
• Provide an appropriate design tofacilitate recovery of favorablehydrochemical conditions post closure- 125 -

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3.3.3 Project details and outcomes(1) Changes in groundwater chemistry (salinity)
1) Mizunami
Hydrochemical monitoring was conducted in and around the MIU during the shaft
construction down to G.L. −500 m depth (Fig. 3.3.3-1, Table 3.3.3-1). Hundreds of cubic metersof inflowing groundwater have been draining every day. From October 2005 to February 2006,
when the shafts had been excavated to 180 m depth (uppermost part of granite), groundwater
discharge from the shafts had to be reduced while the effluent treatment facility was being
expanded. As a result, the shafts were temporarily flooded by groundwater up to 50 m
underground.
Water-collection rings (WR) were placed every 25 m in the shafts to direct the water inflow
and reduce the water pressure on the concrete lining. The inflow rate was measured at each
WR in the shafts (Fig. 3.3.3-2). The highest water inflow occurred from the conglomerate layer;
this is probably the dominant groundwater flow path in the sedimentary rock. Water inflow
increased in the weathered granite below the unconformity or low angle fractured zone (LAFZ),
and at the G.L. −300 m access/research gallery. The connectivity and continuity of fractures of
the LAFZ may be higher than those of the upper highly-fractured domain (UHFD). The water
inflow volume at the G.L. −300 m access/research gallery, having a length of about 100 m, isrelatively higher than that from both shafts in the granite part at depths of 170–500 m. The
reason for this may be differences in the encounter rate of excavations and higher-angle
fractures in granite. The volume of water inflow into the Main Shaft tends to be less comparedto that into the Ventilation Shaft. Such differences are attributed to the low permeability of
the Main Shaft fault.
The groundwater chemistry in the WRs is possibly affected by water–cement interactions
caused by contact with the concrete liner. Incidentally, Cl is not susceptible to water–mineralinteractions. The variations in chlorine (Cl) concentration in WRs and the water chemistry inboreholes drilled from the gallery are illustrated in Figs. 3.3.3-3 and 3.3.3-4, respectively. The
Cl concentrations in the WRs and boreholes increased during the initial observation period
but subsequently decreased with time. The groundwater chemistry at depth was affected by
the upconing in the initial period. After the excavation of the shaft had advanced to deeper
depths, the upconing point also moved to a greater depth. In the upper depths, upconing was
reduced and the impact of shallower groundwater infiltration increased with time3). To assessshallow water infiltration, stable isotopes, tritium (3H), and chlorofluorocarbons (CFCs) as
tracers of shallow groundwater were monitored in granitic rock for 5 years (Fig. 3.3.3-5). The
results showed that the shallow groundwater infiltrates into the groundwater at depths of
200–400 m after 10 years of drainage (hundreds ton/day). The mixing ratio of surface waterin deep groundwater can be approximately estimated using CFC-12 data. The hydrochemicalchanges in groundwater were estimated by principal components analysis (PCA) (Fig. 3.3.36)3). It is presumed that deep groundwater will be replaced by shallow groundwater in the
future.

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Fig. 3.3.3-1 Hydrochemical monitoring boreholes in and around the MIU
Drawdown occurred at the boundary between the conglomerate layer and the weathered
granite (700–800 kPa below baseline conditions); and in the deep granite (1.0–1.5 MPa below
baseline conditions). The drawdown values in the 09MI21 borehole on the G.L. −300 m
access/research gallery drilled to the north of the Main Shaft fault were less than those in the
09MI20 borehole, and the drawdown was larger to the south of the Main Shaft fault comparedto the north. Any potential hydraulic impact caused by the Ventilation Shaft was shielded by
the Main Shaft fault from impacts on the north side of the fault.
Cl is not susceptible to water–mineral interaction. Variations in Cl concentrations in WRs
are shown in Fig. 3.3.3-3; the Cl concentrations in these WRs increased during the initialobservation period but subsequently decreased with time. The WRs were sequentiallyinstalled in the deepest part of the shaft as the excavation progressed; therefore, theobservation at each WR was affected by upconing during the initial period. Increases in Cl
concentrations from baseline levels because of upconing were observed to be of the order ofseveral tens to hundreds mg 1−1 in the Ventilation Shaft. Groundwater movement by upconing
is illustrated using these groundwater chemistry data. For example, the Cl concentration at
WR 13 (300 m depth) in the Ventilation Shaft was approximately 250 mg 1−1 during upconing
periods (December 2009). This value corresponds to the Cl concentration observed at
approximately 450 m depth prior to shaft excavation. This finding implies that groundwaterfrom approximately 150 m below moved upward to the bottom of the shaft. As excavation of
the shaft advanced to deeper depths, the upconing point also moved to deeper depths.
Meanwhile, in the upper depths, upconing was reduced and the impact of shallow groundwater
infiltration increased with time3).

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Table 3.3.3-1 Hydrological/hydrochemical monitoring sections at the Mizunami- 128 -

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Fig. 3.3.3-2 Accumulated inflow in each water-collection ring (Apr. 2004–May 2012)
The groundwater in 07MI07, 09MI20, and 10MI26 initially had relatively high Na, Ca, andCl and low DIC and SO4 concentrations, which subsequently changed to relatively low Na, Ca,
and Cl and high DIC and SO4 concentrations (Fig. 3.3.3-4). This tendency was clearly observed
near the borehole collars in the excavations (e.g., zones 5 and 6). Horizontal monitoring
boreholes were drilled sequentially in the deepest gallery during excavation. Therefore, theobservations at each borehole were affected by upconing during the initial period. In boreholes
07MI07, 09MI20, and 10MI26 on the south side of the Main Shaft fault, groundwater withrelatively high levels of Na, Ca, and Cl and low DIC and SO4 concentrations during earlyobservations was representative of the upconed-water around the Ventilation Shaft. Since
then, relatively shallow groundwater has infiltrated to the area around the Ventilation Shaft
and is characterized by low levels of Na, Ca, and Cl, and high DIC and SO4 concentrations.
This process of groundwater replacement is most likely occurring at a faster rate on the south
side of the Main Shaft fault than on the north side of the fault, reflecting the extent ofhydraulic impact. However, such trends were not observed in borehole 09MI21 on the northside of the Main Shaft fault. Borehole 09MI21 is located approximately 100 m north of theMain Shaft fault and was drilled into LSFD. Hydrochemical changes in the groundwater here
were most likely caused by mixing with groundwater at 300 m depth without having been
influenced by the upconing along the shaft. In general, mixing with shallower groundwater
became the dominant process on the south side of the Main Shaft fault whereas mixing withdeeper groundwater dominated groundwater chemistry on the north side of the fault3).
To infer the infiltration of shallow groundwater as a result of the long-term drawdown into
the shafts, measurements of tritium and chlorofluorocarbon (CFC) concentrations were used
as an index of surface water infiltration (Fig. 3.3.3-5). Tritium was detected at several
monitoring zones even though the concentrations dropped to zero at around 200 m depth prior- 129 -

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to shaft excavations3). CFC-12 was first detected in 2010, and the concentrations gradually
increased with time as observed in boreholes 07MI07 (200 m depth), 09MI20 and 09MI21 (300m depth), and 10MI26 (400 m depth). This implies that surface water containing CFC-12
penetrated up to 400 m depth within a few years.
Principal component analysis (PCA) was performed to identify the chemical composition ofgroundwater end-members using the chemical data obtained from over 1,000 groundwater
samples located below the low-permeability clay layer, but excluding the areas considered tohave been contaminated during drilling or subsequently by cement materials.
The first principal component (PC 1) and second principal component (PC 2) values ofgroundwater are shown in Fig. 3.3.3-6. PC 1 is dominated by Na, Ca, and Cl concentrations,and PC 2 is dominated by DIC, SO4, and F concentrations. The PCA results also indicated thatgroundwater displacement of high-salinity deep groundwater by infiltration of low-salinity
shallow groundwater occurred.

Fig. 3.3.3-3 Temporal variations of Cl concentrations in groundwater at the Main Shaft andthe Ventilation Shaft- 130 -

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Date

Date

Fig. 3.3.3-4 Temporal variations of Cl concentrations in groundwater in the boreholes drilledfrom the gallery
Borehole 09MI20 has six monitoring sections (section 1 is located at the bottom of theborehole) and was drilled from the G.L. −300 m sub-stage. Borehole 09MI21 has four
sections (section 4 is located at the bottom of the borehole) and was drilled from the G.L.
−300 m access/research gallery.

Fig. 3.3.3-5 Temporal variations of CFC gas in each monitoring section- 131 -

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Fig. 3.3.3-6 Principal component analysis of groundwater chemistry related to shaft sinking2) Horonobe
In the second mid-term research phase, three shafts (the East Shaft, the West Shaft, and theVentilation Shaft) were excavated down to a depth of G.L. −350 m and the G.L. −350 m gallery
was also constructed. The daily outflow rate of groundwater due to the shaft and drift
excavation was normally less than about 200 m3/day, except the period during the excavationof the G.L. −350 m gallery, which caused the maximum groundwater outflow (e.g., 700 m3/day)in February, 2013.
The amount of groundwater outflow in the Horonobe URL is generally lower than that in the- 132 -

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Mizunami URL. This may be explained by 1) general differences in the permeability of theparent rocks (i.e., permeability of the sedimentary rock at the Horonobe URL is lower thanthat of the crystalline rock at the Mizunami URL) and 2) the effect of pregrouting on thepermeable zone predicted before the construction of URL below the G.L. −250 m level in the
Horonobe.
During the excavation of shafts, a hydrological response was observed in the surface-based
borehole PB-V01 close to the Ventilation Shaft (borehole PB-V01 is located ca. 17 m north of
the Ventilation Shaft). This response suggests that hydrological effects may be active in thepart deeper than G.L. −350 m because a decrease in the hydraulic head in the packed-off
section of G.L. −479 to −520 m was observed.
Additionally, similar hydrological responses were recorded both in the surface-based
boreholes HDB-3 (located ca. 210 m west of the East Shaft) and HDB-6 (located ca. 160 m
south of the Ventilation Shaft). In HDB-6, a decrease in salinity was identified in themonitoring zone around G.L. −500 m after shaft sinking. Based on these hydrologicalmonitoring results, the extent of EdZ around the Horonobe URL seems to be several tens tohundreds of meters.
Sampling and analysis of groundwater (results shown in both Fig. 3.3.3-7 and Table 3.3.3-2)
have been performed. For the groundwater collected from the water ring in the shafts,
sampling and analysis have been conducted in both the East and Ventilation Shafts but notin the West Shaft. The groundwater sampling and analysis have been performed in theboreholes (e.g., borehole length from 20 m to 100 m) drilled from the G.L. −140 m and G.L.
−250 m galleries.
Fig. 3.3.3-8 shows variations with time in the groundwater salinity for each sampling pointin the drift from 2006 to 2013. The results of chemical analysis of groundwater indicate that
there are different tendencies of salinity variations at the sampling points; at some points, thesalinity increases with time (i.e., WR-V-98.0, WR-V-132.0, WR-V-202.0, WR-V-242.0, WR-E63.8, and WR-E-202.0) and at others, the salinity decreases with time (i.e., WR-V-310.0, WRV-343.9, WR-E-276.0, and WR-E-340.0). The maximum change in salinity observed was ca. 0.8
g/L. These changes in the groundwater salinity might be caused by a probable change in the
mixing ratio between fossil sea water and meteoric water resulting from the URL excavation.
Fig. 3.3.3-9 shows the temporal variations around the URL during shaft construction. As
shown in Fig. 3.3.3-9, the groundwater salinity in the west part of the URL and in the deeper
part around the URL area was higher than that in the other part. During shaft construction,
the groundwater salinity around the East Shaft appeared to change because of the intrusionof higher-salinity groundwater in the west part of the URL through the boundary between the
Koetoi and Wakkanai Formations. To understand the process of salinity change, amultivariate statistical analysis (principal component analysis; PCA) was performed.

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Ventilation shaft
West shaft

East shaft

Water collection rings

Borehole
HDB-3

Borehole
HDB-6

Fig. 3.3.3-7 Hydrological/hydrochemical monitoring boreholes at the Horonobe- 134 -

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Table 3.3.3-2 Hydrological/hydrochemical monitoring sections at the Horonobe- 135 -

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Fig. 3.3.3-8 Salinity distribution around the Horonobe
Fig. 3.3.3-10 shows the results of PCA including the 13 major components (Na+, K+, Ca2+,
Mg2+, Si, Sr, Cl−, Br−, I−, SO42−, HCO3−, δD, and δ18O). The first principal component (PC 1) has
loading factors dominated by Na+, K+, Ca2+, Cl−, Br−, δD, and δ18O, which implies that its
variation corresponds to differences in the mixing ratio of groundwaters with different salinity.
In Fig. 3.3.3-10, the data are mostly plotted along the line between the data of WR-V-28.5(water ring in the Ventilation Shaft) and of HDB-3 (surface-based borehole). Borehole HDB-3
is located in the west of the URL where the groundwater salinity is relatively higher (Fig.
3.3.3-9). On the other hand, the groundwater sampled from WR-V-28.5 is low-salinity andsimilar to meteoric water. Therefore, it is suggested that the Horonobe groundwater chemistry
can be understood as mixing of these endmembers (Fig. 3.3.3-10).
In contrast, the second principal component (PC 2) has loading factors of Mg2+, SO42−, andHCO3−. Because these ions are common in major components of concrete material, PC 2
probably reflects the mixing proportions of the groundwater and the concrete material used
for the construction of the URL. In the time variation of WR-V-28.5 in Fig. 3.3.3-10(a), forexample, only PC 2 decreased while PC 1 showed small variation. Although the pH ofgroundwater sampled from WR-V-28.5 had an initial value of 10, the value decreased to pH
7–8 over four successive years. This result suggested that the groundwater was influenced by
the surrounding concrete materials at the beginning of the monitoring, and the influence
reduced with time. This is also consistent with the results of PCA analysis, because thedecrease in groundwater pH corresponds to the decrease in the scores for PC 2 (Fig. 3.3.310(a)).

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WSW

E. ShaftElevation (m)KoetoiFm.

BeforeBefore construction
construction
第1段階調査時（坑道掘削前）
E. ShaftElevation (m)Oomagari Fault

2008年
2008

E. ShaftElevation (m)ENE

塩分濃度（g/L）
Salinity(g/L)

Oomagari Fault

ENE

Salinity(g/L)
塩分濃度（g/L）

Wakkanai
Fm.

WSW

E. ShaftElevation (m)Koetoi
Fm.

Salinity(g/L)
塩分濃度（g/L）

Wakkanai
Fm.

WSW

KoetoiFm.

ENE

Wakkanai
Fm.

WSW

KoetoiFm.

Oomagari Fault

2010年
2010

Oomagari Fault

ENE

塩分濃度（g/L）
Salinity(g/L)

Wakkanai
Fm.

2012
2012年

Fig. 3.3.3-9 Salinity evolution related to shaft sinking (Horonobe)
Additionally, the lack of major variation of score plots with time suggests no significant
changes of groundwater chemistry in each sampling point. However, strictly speaking, thedata belonging to the sampling points WR-V-98.0, WR-V-132.0, and WR-V-168.0 appear to shift
with time from the left upper part to the right lower part on the PCA score plot. These trends
reflect the decreasing effect of concrete degradation and increasing influence of groundwatersalinity changes. This salinity increase can be interpreted as an increase in the mixing ratioof higher-salinity groundwater in borehole HDB-3.
The relationships between 1) the area of groundwater salinity change and thehydrogeological structure, and 2) the timing of groundwater salinity change and thehydrological conditions have not been well understood. The shallow part of the Wakkanai- 137 -

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Formation (just below the boundary of the Koetoi and Wakkanai Formations) has a highpermeability where fractures are developed. When the construction of the URL reached thehigh-permeability zone (i.e., after September 2008), the groundwater outflow rate rose and the
distribution of the groundwater salinity changed. Hence, the observed salinity changes
probably had a close relationship to both the hydrogeology structure system and groundwaterflow conditions. However, the range of variation of the groundwater salinity and its area will
be limited in the future because the groundwater flow rate is relatively slower than at the
Mizunami URL and the rock permeability in the Horonobe area is very low.

(a)

(b)

Fig. 3.3.3-10 Principal component analysis based on hydrochemical data ofHoronobe groundwater(2) Change of groundwater chemistry (pH and redox conditions)
Possible processes to change the pH and redox conditions during facility construction andoperation are: 1) groundwater alkalization by degassing in the EdZ; 2) groundwater mixing
with relatively shallower water by drawdown in the EdZ; 3) alkalization by grout andshotcrete in the EDZ; and 4) oxidation by air circulation in galleries in the EDZ.
1) Alkalization by degassing
As an example, the pH value changed by approximately 0.2–0.4 by degassing of dissolved
carbon dioxide (according to the decrease in water pressure from a depth of 500 m to theground surface in the Horonobe). The pH changes depending on Pco2 during degassing andthe inorganic carbon concentration. In the Mizunami, groundwater drawdown by the facility
construction ranged from 100 to 150 m, but the pH values were stable in the range 8–9 during
facility construction3). In the Horonobe, the pH ranged from 6.5 to 7.5 during facility
construction, excluding the area around the cement materials used. The amount ofalkalization by degassing during the facility construction and operation appears to have beensmall.
2) Groundwater mixing subsequent to drawdown- 138 -

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Groundwater mixing has been mainly observed in the Mizunami3). The groundwaterchemistry at depth tends to vary with time from high-Na, Ca, Cl, low-DIC, SO4 type to highDIC, SO4, low-Na, Ca, Cl type. Though the pH and redox potential (weakly alkaline, reducing
conditions) almost never show changes over time at the present day, long-term monitoring isrequired to evaluate the influence of shallow-water infiltration and the pH and redox buffer
capacity of rock minerals. Groundwater chemistry at deep depths can change to that of theshallow depths because of long-term drainage. Changes in the pH and redox potential arecontrolled by chemical interactions in mixed groundwaters and buffer minerals. If sufficientlevels of pH–redox buffer minerals are present in the bedrock, the pH–redox conditions can beinferred based on the future groundwater chemistry and dominant pH–redox buffer reactions.
The possible dominant buffer reactions at depths of 200–400 m are thought to be as follows:
Fe(OH)3 + 3H+ + e− = Fe2+ + 3H2O (E0 = 0.95 V)
Fe(OH)3(am) + 3H+ + e− = Fe2+ + 3H2O (E0 = 0.975 V)
FeCO3 + 3H2O = Fe(OH)3 + 2H+ + HCO3− + e− (E0 = 1.078 V)
Future pH–redox conditions can be theoretically inferred by substituting the chemicalcomposition of these solutes. For instance, if the solute concentrations in the deep groundwaterchange to those of the shallow groundwater as follows:
pH: 7.5–8.5
Fe2+: 0–3.6 μM (0–0.2 mg/L)
HCO3−: 1.3–1.7 mM (IC: 15–20 mg/L)
SO42−: 0.17–0.21 mM (SO42−: 15–20 mg/L),
the redox potential ranges from −230 to −10 mV at G.L. −200 m to G.L. −400 m and −250 to−180 mV at deeper than G.L. −400 m. However, the pH–redox conditions would markedly
change if buffer minerals such as iron hydroxides on fracture surfaces are all used up in thereactions or the groundwater flow around the facility is faster than the buffer reactions
between the groundwater and buffer minerals. Thus, long-term monitoring of groundwaterchemistry and pH–redox conditions at the gallery is indispensable to demonstrate the natural
buffer capacities of bedrock on the impact of facility construction and operation.
3) Alkalization by shotcrete and grout
For conditions of groundwater inflow and no inflow in Mizunami, the pH was 7–9 and 11–12
for several years, respectively. This implies a low pH-buffering capacity of granite for cement
material. The pH values of ordinary Portland cement (OPC) and high fly-ash silica-fume
cement (HFSC: low-alkaline cement) were observed in the HOR. In this monitoring, the pH
did not increase in either cement for two years because of groundwater replacement.
These observations suggest that alkalization around drift occurs heterogeneously according
to the extent of water inflow in various hydrogeological conditions. Additional alkalization ofgroundwater by cement may possibly occur in stagnant conditions after facility closure.
4) Oxidation by air circulation
The redox buffer capacity for air diffusion from gallery to rock was mainly researched in the- 139 -

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HOR. An infiltration experiment of O2-saturated water into a borehole drilled from the gallery
showed that the redox potential recovers to the baseline reducing condition within a few days
as a result of water–mineral–microbe interactions. Organic-rich sedimentary rock has asufficient redox buffer capacity for air infiltration. On the other hand, no obvious increase inredox potential was observed in the vicinity of the gallery in the granitic rocks of the MIU.
3.3.4 Summary
The R&D in the second mid-term research phase focused on demonstrating monitoring
techniques during facility construction and operation. Based on the results from MIU/HOR,
knowledge of the mid-term variations in the geological environment around the undergroundfacilities is as follows.
Points to keep in mind for facility construction/operation and monitoring- Based on comparison between Mizunami and Horonobe, chemical disturbance is lesser
in low-permeability sedimentary rock with a smaller amount of water inflow.
- The hydrochemical conditions change markedly with time if a facility is constructed in
fractured rock with a large volume of groundwater inflow. Design of gallery layout taking
into account the low-permeability rock domain identified in the surface-based
investigation is indispensable to avoid and reduce disturbance.
- Hydrochemical monitoring in each hydrogeological compartment during facility
construction/operation enables assessment of a panel division that should be
preferentially closed to prevent expansion of the disturbed zone.
- The mid-term changes in groundwater chemistry during the operation phase are
predicted based on monitoring of the permeable zone and multivariate analysis such as
principal component analysis. Shallow water is likely to infiltrate to depth in a facility
with a large volume of groundwater inflow. Tritium and CFCs are essential tracers thatshould be observed from baseline conditions.
- During facility construction and operation, it is important not to disturb the performanceof the natural barrier. It is essential to maintain minimum disturbance by predicting the
distribution of high-permeability domains around the facility area. However, excessive
water-tight grout may cause unanticipated inflow accidents. This is a trade-off withsafety management.
Points to keep in mind for pH and redox conditions:- During facility operation and after closure, alkalization around drift will occur
heterogeneously according to the water inflow conditions. Geophysical surveys andhydrochemical integrated analyses are available to identify the area of alkalization.
- Sedimentary rock with abundant organic matter has an efficient redox buffer capacity
for oxidation by air in drift.
- Replacement of the shallower groundwater infiltrated during facility operation to original
deep groundwater is required for recovery of chemical conditions. Then the facility closure
procedure should be considered based on data such as the groundwater inflow rate ateach depth, chemical composition, and preliminary modeling of water pressure recovery.

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JAEA-Review 2016-014- In the low-permeability rock domain, an unsaturated zone around gallery may persist
locally and possess heterogeneous hydrochemical properties after closure.
Regarding the approach used to consider the variation of hydrochemical conditions, it isimportant to compare the magnitude relation between short-term and medium-term
variation caused by facility construction/operation and long-term variation resulting fromnatural geological phenomena. The magnitude relations are listed in Table 3.3.4-1.
Table 3.3.4-1 Remaining R&D issues for perceiving the evolution and recovery behavior of thehydrochemical conditions
pH

PorousmediumGW chemistry

Changewith GW
flow

ChangewithcementChange with GW
flow

Change withmaterial transport
from drift

Change with
GW flow

Construction/
operation

A>B

B>A

B>A ?

A>B

B>A

Post closure

A>B

B>A

B>A ?

B>A ?

B>A ?

Construction/
operation

A>B

B>A

A>B

A>B

A>B

Post closure

A>B

B>A

A>B

B>A ?

A>B

Small
variation

A longterm
steadystate

Buffer capacity for
infiltrated
oxidizing water

Impact of
backfillingmaterial

GW
replacement

Main process

Fracture
mediumRedox

Importance

A: long-term variation caused by natural geological phenomena
B: short-term and medium-term variation caused by facility construction/operation
The subjects denotes as A > B and B > A require R&D on the long-term phenomena andshort, mid-tem monitoring for each geological medium. For instance, changes in the redox
conditions caused by shallow-water infiltration during facility construction/operation in a
fractured medium resemble accelerated testing of long-term infiltration of shallow oxidized
water related to uplift/erosion. If no changes in redox conditions were identified bymonitoring during facility construction/operation, the rock probably has a sufficient redox
buffer capacity. In other words, the redox conditions do not change over the long term unlessthe impact of long-term geological phenomena is greater than the impact of facility
construction/operation. On the other hand, pH changes caused by cement materials are muchlarger than changes from long-term geological phenomena. The long-term pH variation after
closure is an important future problem.
R&D on the variation in the geological environment after facility closure, such as therecovery process and features are planned as indispensable subjects in the next researchphase of Mizunami and Horonobe.

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References
1) Tsang, Chin-Fu, Bernier, F. and Davies, C. : “Geohydromechanical processes in the
Excavation Damaged Zone in crystalline rock ,rock salt, and indurated and plastic clays in the context of radioactive waste disposal”, International Journal of Rock Mechanics &Mining Sciences Volume 42, Issue 1, pp.109-125 (2005).
2) SKB : “Long-term safety for the final repository for spent nuclear fuel at Forsmark Main
report of the SR-Site project. Volume II”, Svensk Kärnbränslehantering AB, (2011).
3) Iwatsuki, T., Hagiwara, H., Ohmori, K., Munemoto, T. and Onoe, H. : “Hydrochemical
disturbances measured in groundwater during the construction and operation of a largescale underground facility in deep crystalline rock in Japan.”, Environ Earth Sci. (2015).

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3.4 Rock mechanics
3.4.1 Introduction
An EDZ (Excavation Damaged Zone) and an EdZ (Excavation disturbed Zone) are likely tobe less stable than the undisturbed rock mass and to provide higher-permeability pathwaysfor groundwater flow in the vicinity of excavations. Thus, development of an EDZ and EdZ isrecognized as a key issue in both the design and construction of disposal facilities and safetyassessment. Knowledge of the initial conditions of in situ stress and mechanical properties of
the rock before shaft sinking is necessary in the surface-based investigation phase (Phase I).
In the construction phase (Phase II) and operation phase (Phase III), the predicted geologicalconditions have been evaluated based on additional data obtained during these phases andinformation about the EDZ and EdZ around the shaft and gallery should be obtained. The
subjects of study regarding rock mechanics are as follows:
1) Mechanical stability around openings- In situ stress- Physical and mechanical properties- Discontinuities
2) Thermal condition- Thermal gradient- Thermal properties
3) Geological environment of the EDZ- Width of the EDZ- Physical and mechanical properties of the EDZ- In situ stress state in the EDZ- Thermal properties of rock
The geological environment of the EDZ is discussed below.
3.4.2 Objectives in the second mid-term research phase
As shown in section 2.4, the objectives of rock-mechanics investigation during Phase II areto understand the detailed in situ stress conditions and rock mechanical properties by borehole
investigations from the shafts and galleries and laboratory tests during extension of the shafts
and galleries at depths of 500 m (Mizunami) and 350 m (Horonobe). Also, it is necessary toconfirm the validity of the conceptual model and analysis technique applied in Phase I. An
additional objective of this phase is to understand the geological changes caused by shaft andgallery excavation. Table 3.4.2-1 lists the performance target of R&D, achievement items, andreflection on the R&D results.
Table 3.4.2-1 Performance target of R&D for rock mechanical characterization
Focus

Performance target of R&D

Decision-making for Decision-making for excavation ofstart of construction underground facility.

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3.4.3 Project details and outcomes(1) Geological environment of the EDZ
1) Mizunami
Two- and three-dimensional and numerical simulations using crack tensor model and an
MBC (Micromechanics Based Continuum) model considering the EDZ were performed to
predict the rock mass behavior based on the results of in situ stress measurements andlaboratory tests during Phase I. The distribution of rock mass stress and strain, fracture
openings, shear strain, and the local safety factor were predicted at depths of 500 m and 1,000m.
Strain measurement during shaft sinking was performed to estimate the width of EDZ
caused by blasting at the shaft wall1). The simulation results were compared withmeasurements and the validity of the simulation was confirmed2). The scale effect of the crack
tensor calculated using the geometric properties of discontinuities based on geologicalmapping at the shaft wall was discussed to reflect the modeling method for fractured media3).
The conclusions are as follows:- Based on the results of equivalent continuum analysis using information obtained from
Phase I, the distribution of rock mass stress and strain, fracture openings, shear strain,
and local safety factor were influenced by the in situ stress field, existing fractures, andthe orientation and length of induced fractures. The changes in the hydraulic conductivityof the EDZ were assessed in terms of the relation between fracture opening and hydraulicconductivity (Fig. 3.4.3-1). An increase in hydraulic conductivity by two orders ofmagnitude of the EDZ was predicted as a result of opening of fractures parallel to thegallery wall.4),5),6). Investigation of the length and spacing of fractures is important formodeling of the EDZ.
- Rock mass stress and strain were measured during Ventilation Shaft sinking at a depthof 200 m (Fig. 3.4.3-2). The magnitude of the rock strain was equal to the value predictedby elastic analysis, and slightly less than the limiting value. The measured lateral strain
was compressive, but the predicted strain was tensional. Rock mass behavior caused by
excavation was dominated by changes in fractures1) (Fig. 3.4.3-3).
- The relative error of the crack tensor calculated from the results of geological mapping of
the shaft and gallery was estimated to examine the variation of relative error to the scaleof observation areas for suitable modeling of the Toki Granite3) (Fig. 3.4.3-4, Fig. 3.4.3-5).

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Fig. 3.4.3-1 Results of equivalent continuum analysis using the crack tensor model

換気立坑

Ventilation(掘削径D :5.3mshaft)( D= 5 .3 m)
深度200ｍ
GL.200m
ボーリ
ング横坑

1.15D ((6.1m)
6.1m )(1.1m)
0.2D (1.
1m )

Niche

掘削方向

Shaft depth
立坑深度
Shaft
depth
200m

07M I12号孔07M I11号孔07M I10号孔Buried- typestrain
meter
埋設型

立坑深度
Shaft
depth
216m

ひずみ計①

Buriedtype
埋設型
ひずみ計②
strainmeter

Opticalfiber
光ファイバ式
ひずみ計①
strain
meter
立坑深度
Shaft
depth
225m
光ファイバ式
Opticalfiber
ひずみ計②
strain
meter
立坑深度
Shaft
depth

Buried- type
埋設型
strain
meter
ひずみ計③

234m

Insertion- type
連続式
clinometer
挿入型傾斜計Fig. 3.4.3-2 Strain measurement during shaft

Fig. 3.4.3-3 Comparison of measured

sinking

and analyzed rock mass displacement- 145 -

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Fig. 3.4.3-4 Results of discontinuity observations obtained at the shaft wallFig. 3.4.3-5 Relative error of crack tensor vs. relative interval2) Horonobe
Investigation of an EDZ was conducted in the G.L. −140 m and G.L. −250 m galleries and theEast Access Shaft at 160 m depth. In the G.L. −140 m and G.L. −250 m galleries, seismic,
resistivity, and acoustic tomography surveys had been conducted before excavation and during
excavation of the tomography area. After excavation of the tomography area, these surveys
have been conducted about two to four times a year. Fig. 3.4.3-6 shows the layout of theinvestigation conducted in the G.L. −250 m gallery. In addition, hydraulic tests andmeasurements of pore pressure, displacement, and pressure of a shotcrete were conducted tounderstand the hydrogeological properties in an EDZ in detail. In the East Access Shaft,- 146 -

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hydraulic tests were conducted; then the hydraulic conductivity before and after excavation
was compared. The results of these tests can be summarized as follows:- For the tomography survey in the presence of flammable gases such as methane, thesimplified seismic velocity survey system was developed. This system consists of ahammer to transfer seismic energy to receivers. In addition, this system is well suited torepetitive surveying7),8).
- In the G.L. −140 m gallery, a desaturation zone was detected from the measurements ofwater content and pore pressure9).
- In the G.L. −250 m gallery, the layer with low seismic velocity (LVL) has changed withtime; however, the layer did not exceed the extent detected shortly after excavation (Fig.
3.4.3-7)10),11).
- From numerical analysis, microcracks were expected to be induced in the LVL (Fig. 3.4.38)12).
- In the LVL, hydraulic conductivity was increased by about two orders of magnitude
compared with undamaged rock13).
- A conceptual model of the distribution of fractures in the G.L. −250 m gallery wasconstructed based on fracture mapping on the wall (Fig. 3.4.3-9)14).
- Hydraulic conductivity within approximately 1 m of the East Access Shaft wall increased
by one order of magnitude15).
- A multi-interval displacement sensor using Fiber Bragg Grating (FBG) technology wasdeveloped to measure the long-term deformation behavior of the rock mass16). Using
comparison with measurement data from conventional extensometers, the applicabilityof the FBG sensor was investigated.

Fig. 3.4.3-6 Image of the layout of the in situ surveys used for determining the EDZ
in the gallery- 147 -

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Ex.3
Ex.4
Ex.5
Ex.6
Ex.7

Ex.7

Ex.8
(m) 4

3

2

1

0

Ex.8
(m) 4

(a) Pre-excavation

(m) 4

3

2

1

0

(d) 64 days after the preexcavation

3

2

1

0

(m) 4

(b) Excavation 6

(m) 4

3

2

1

3

2

1

0

(g) 561 days after the preexcavation

0

(m) 4

(e) 214 days after the preexcavation

(m) 4

3

2

1

2

1

0

(c) Excavation 12

3

2

1

0

(f) 369 days after the preexcavation

1.1

(m) 4

3

0

1.3 1.5 1.7 1.9Seismic velocity (km/s)

Rocks of pre-excavation
Excavated gallery(h) 743 days after the preexcavation

Fig. 3.4.3-7 Representative results of seismic tomography surveys conductedin the G.L. −250 m gallery- 148 -

2.1

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Fig. 3.4.3-8 Microcracking region around the gallery from the results of FEM analysis10)

Fig. 3.4.3-9 Conceptual model of the fracture distribution around the gallery14)3) Generic results
There are differences between the rock mechanical model, the elasto-plastic model for porous
media, and the crack tensor model for fractured media, and the rock strength of soft rocks andhard rocks. Almost all investigation techniques and numerical analysis techniques areapplicable to both rock types.
3.4.4 SummaryRock mass displacement and strain measurements were performed to understand the widthof the EDZ in Mizunami. The modeling methodology for the rock mass using the equivalentcontinuum model was discussed. Water pressure monitoring, tomography measurements, andhydraulic test were performed to understand the EDZ, and an instrument for use in conditions- 149 -

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with flammable gas was developed in Horonobe. An EDZ model considering induced fracturescaused by excavation was also developed.
The data concerning EDZ have been obtained, and the mechanism of EDZ development has
also been determined. Future plans are as follows:- Understanding of coupled behavior in the EDZ- Failure mechanism because of thermal effect, and measurement examples- Understanding the behavior of the EDZ during gallery closure and development of aprediction methodology
References
1) Hirano, T., Seno, Y., Hikima, R. and Matsui, H. : “Mizunami Underground ResearchLaboratory Project; Rock mechanical investigations measurement of the rock strain anddisplacement during shaft excavation at the GL.-200m level of research galley”, JAEAResearch 2011-019 (2011), 51p.
2) Matsui, H., Tanno, T., Hirano, T., Gohke, M., Kumasaka, H., Tada, H. and Ishii, T. :“Estimation of crack tensor for evaluating excavation disturbance of research gallery at the
Mizunami Underground Research Laboratory”, JAEA-Research 2010-043 (2010), 87p.
3) Tanno, T., Sato, T., Sanada, H., Hikima, R., Kumasaka, H. and Tada, H. : “Fundamental
study on REV based on crack tensor at the Mizunami Underground Research Laboratory”,
Proc. of the 13th Japan Symposium on Rock Mechanics, JSCE, pp.109-113 (2013). (inJapanese).
4) Gohke, M., Tada, H., Seno, Y., Nakama, S. and Sato, T. : “Excavation disturbance analysis
in consideration of excavation damaged zone for research drift of Mizunami UndergroundResearch Laboratory”, Journal of Tunnel Engineering, JSCE, Vol.16, pp.35-45 (2006). (inJapanese).
5) Nakama, S., Aoki, T., Sato, T., Gohke, M. and Mori, T. : “Analysis of rock mass behavior
based on MBC and crack tensor model in consideration of Excavation Damaged Zone”, Proc.
of the 34th Symposium on Rock Mechanics, JSCE, pp.33-40 (2005). (in Japanese).
6) Sato, T., Mikake, S., Nakama, S., Seno, Y., Mori, T., Iwano, K., Gohke, M. and Tada, H. :“Japanese underground research laboratory project and prediction of rock mass behavioraround deep shafts and galleries using continuous and discontinuous models”, ICADD-7,
the Seventh International Conference on Analysis of Discontinuous Deformation, held in
Honolulu, Hawaii, December 10-12 (2005).
7) Sugita, Y., Nakamura, T., Sanada, H., Aizawa, T. and Ito, S. : “Seismic Tomography
Investigation in 140m Gallery in the Horonobe URL project”, Mater. Res. Soc. Symp. Proc.
Vol. 1265, AA06-03 (2010).
8) Sugita, Y., Nakamura, T. and Sanada, H. : “Application of seismic tomography survey formonitoring EDZ development”, Proceedings of the 40th symposium on Rock Mechanics,
pp.230-235 (2011). (in Japanese).
9) Yabuuchi, S., Kunimaru, T., Kishi, A. and Komatsu, M. : “Monitoring of pore water pressure
and water content around a horizontal drift through excavation - measurement at the 140- 150 -

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m gallery in the Horonobe URL -”, Journal of Japan Society of Civil Engineers ser. C, Vol.67,
No.4, pp.464-473 (2011). (in Japanese).
10) Aoyagi, K., Tsusaka, K., Kondo, K. and Inagaki, D. : “Quantitative assessment of an
Excavation Damaged Zone from variations in seismic velocity and fracture distribution
around a gallery in the Horonobe Underground Research Laboratory”, Rock Engineeringand Rock Mechanics; Structures in and on Rock Masses, pp.487-492 (2014).
11) Aoyagi, K., Tsusaka, K., Kubota, K., Tokiwa, T., Kondo, K. and Inagaki, D. : “Investigations
for a change of an Excavation Damaged Zone with time at the 250 m gallery in the Horonobe
Underground Research Laboratory”, Journal of Japan Society of Civil Engineers ser. C,
Vol.70, No.4, pp.412-423 (2014). (in Japanese).
12) Aoyagi, K., Tsusaka, K., Tokiwa, T., Kondo, K. and Inagaki, D. : “Geomechanicalassessment of excavation damaged zone in the Horonobe Underground ResearchLaboratory, Japan”, Proceedings of the 6th Japan-Korea Joint Symposium on RockEngineering, pp.905-910 (2013).
13) Aoyagi, K., Tsusaka, K., Nohara, S., Kubota, K., Kondo, K. and Inagaki, D. :“Hydrogeomechanical investigation on an Excavation Damaged Zone based on seismic
surveys and hydraulic tests in the Horonobe Underground Research Laboratory”,
Proceedings of 2014 ISRM International Symposium - 8th Asia Rock Mechanics Symposium,
pp.2804-2811 (2014).
14) Tokiwa, T., Tsusaka, K., Matsubara, M. and Ishikawa, T. : “Fracture characterization
around a gallery in soft sedimentary rock in Horonobe URL of Japan”, International
Journal of Rock Mechanics and Mining Sciences, Volume 65, pp.1-7 (2014).
15) Sanada, H., Nakamura, T. and Sugita, Y. : “Mine-by Experiment in a deep shaft in Neogene
sedimentary rocks at Horonobe, Japan”, International Journal of Rock Mechanics andMining Sciences, Volume 56, pp.127-135 (2012).
16) Sanada, H., Sugita, Y. and Kashiwai, Y. : “Development of a multi-interval displacement
sensor using Fiber Bragg Grating technology”, International Journal of Rock Mechanics
and Mining Sciences, Volume 54, pp.27-36 (2012).

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3.5 Mass transport
3.5.1 Introduction
As part of the study of mass transport, we have been working on themes (1) through (3) below
for the purpose of understanding the retardation effects on mass transport in rock masses andgroundwater1) (Fig. 3.5.1-1), as well as theme (4) from the perspective of the establishment
and systematization of techniques for investigation and evaluation of mass transport tosupport safety assessment2),3).
(1) Understanding the sorption and diffusion properties of rock mass
From the perspective of the safety assessment of geological disposal, it is important tounderstand the sorption and diffusion properties of rock masses. It is also necessary toestablish techniques for acquisition of highly reliable data on these properties and for analysis
and evaluation.
(2) Understanding mass transport fields
From the perspective of safety assessment of geological disposal, it is necessary to understandthe initial conditions concerning geological structures, groundwater pressure, permeability ofrocks, and groundwater chemistry. In addition, it is also necessary to establish techniques foracquisition of the highly reliable data needed for this purpose and for analysis and evaluation.
(3) Understanding the effects of colloids, organics, and microbes
As the presence of colloids, organics, and microbes in the geological environment affects themass transport properties of a rock mass in various ways, it is necessary to develop individual
elemental techniques for the characterization of the factors in a specific given geologicalenvironment, as well as to systematize investigation, analysis, and evaluation techniques, asessential means for understanding the initial conditions of the geological environment.
(4) Establishment of techniques for analysis and evaluation of mass transport properties
From the perspective of conducting safety assessment for geological disposal, it is importantto establish analysis and evaluation techniques for appropriate understanding of the masstransport phenomena occurring in the geological environment based on the acquired data on
the characteristics of mass transport.

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Fig. 3.5.1-1 Geosynthesis data flow diagram (mass transport study)1)
3.5.2 Objectives in the second mid-term research phase
The study at underground facilities needs to produce outcomes and scientific knowledge thatcan be reflected in the decision-making concerning site selection, construction of facilities,
commencement of disposal, completion of placement of waste packages, and final sealing in
the actual disposal operation. From this perspective, the level of technical development we
aim to achieve for use in decision-making concerning the construction of facilities and thecommencement of disposal, in the context of understanding the short-term changes andrecovery behavior in the geological environment, is the establishment of survey and evaluation
techniques that can indicate the favorable underground facility layout and disposal hole layout
in terms of mass transport and the confirmation of the in situ applicability of such techniques,as well as the systematization of the series of techniques from survey to analysis/evaluation
enabling us to obtain the mass transport properties and their heterogeneity in the geologicalenvironment during facility construction and operation (Table 3.5.2-1).
During the second mid-term research phase, we conducted investigation and study
addressing themes (1) to (4) described above in vertical shafts and horizontal galleries
reaching depths of 500 m at Mizunami and 350 m at Horonobe. We conducted laboratory tests,
in situ tests, and modeling and analysis concerning mass transport and started theaccumulation of in situ data and knowledge.

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Table 3.5.2-1 Performance target of R&D in the mass transport study
Focus

Performance target of R&D

Tasks
Sorption capacity and diffusivity of rockmatrix and of transport pathways• Methodology development tounderstand sorption/diffusion
property by in-situ experiment

Decision to
construct, to begin
disposal, to end
emplacing waste
and on final closure

To identify the domain that is favorable
for the mass transport study.

Geometry of transport pathways; depthof diffusion-accessible rock mass
• Methodology development tounderstand transport pathway by insitu experiment
Effect of colloid/organics/microbe on
nuclide transport/retardation• Methodology development tounderstand the effect on masstransport

To evaluate the safety of geologicaldisposal system.

Evaluation technology for thecharacterization of mass transport
property• Methodology development toevaluate mass transport property(investigation, modeling, analysis)

3.5.3 Project details and outcomes(1) Understanding the sorption and diffusion properties of rock mass
For the purpose of understanding the mass transport properties of a rock mass, we developed
techniques for acquiring relevant parameters from in situ tests using non-sorbing and sorbing
tracers. In the Mizunami and Horonobe URLs, we developed in situ mass transport test
apparatuses and test methods that can be applied to various underground environments, suchas those with high groundwater pressure and groundwater containing dissolved gases andgeological environments containing rock masses with different properties, and confirmed theapplicability of such techniques. As mass transport in the underground environment is acomplex phenomenon involving sorption and diffusion in a rock mass, advection accompanying
the flow of groundwater, and other factors, this part of the study also included development oftechniques for understanding the properties of mass transport caused by advection.
1) Mizunami
We started in situ mass transport tests focusing on fractures in crystalline rocks. Specifically,
we aimed to examine the applicability to an actual underground environment using the test
apparatuses developed by the Central Research Institute of Electric Power Industry (CRIEPI),
and started in situ tests at the −300 m stage. We drilled multiple boreholes and conductedgeological and hydrogeological investigations to obtain basic data for the evaluation andselection of test sections, where we plan to perform in situ mass transport tests using tracers.

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In addition, we conducted laboratory through-diffusion tests using drillcore samples for the
purpose of detailed examination of the relationship between fracture characteristics and masstransport parameters4),5).
2) Horonobe
By adding tracer injection and recovery functions to existing cross-hole hydraulic test
apparatus, we developed a test apparatus that can perform in situ tests using tracers6) (Fig.
3.5.3-1). In the in situ tests using this apparatus, we conducted borehole drilling, core logging,
various physical logging, fluid logging, single-hole, cross-hole hydraulic tests, and tracer tests
at the 250 m Niche off Ventilation Shaft No. 1 focusing on fractures in rock masses. During
this in situ testing, we conducted duplicate tests under varying conditions, including tracer
injection flow rate, pumping flow rate, and injected tracer concentration, for the purpose of
establishing the test apparatus and test methods and confirming their applicability (Fig. 3.5.32). For the purpose of application to tests under gaseous conditions, we established a functionthat can remove gases from the test section in the borehole and a procedure for test apparatus
installation that minimizes the generation of free gases in the test section (Fig. 3.5.3-3). This
made it possible to perform tests in the presence of dissolved gases and obtain reliable data.
Our method also improved the reliability of test results obtained in the presence of dissolved
gases, as it became possible to confirm the effective exclusion of the influence of dissolved
gases based on the fluid compressibility in the test interval. The results demonstrated thevalidity of permeability tests based on injection and tracer tests using low injection andpumping rates and a dipole ratio (the ratio of injection flow rate to pumping rate) of 1 in theunderground environment near the test site.
Regarding the development of techniques for in situ analysis of tracers, we constructed asystem consisting of flow cells for online fluorescence analysis, which were installed in the test
intervals in both the injection and pumping boreholes and connected via optical fibers (Fig.
3.5.3-1), and confirmed the applicability of the in situ analysis techniques to the sedimentaryrock environment through duplicated tests using uranine. Although the analytical value fromthe flow cell on the recovery side differed from the values for samples of pumped water,suggesting the possibility of fluorescent scattering caused by microbubbles in the flow cell, it
was confirmed that reliable data can be obtained by correcting the in situ data with theanalytical value of pumped water. We also examined the application of deuterium as a nonsorbing tracer for in situ tests (Fig. 3.5.3-4). With an eye to the application of a flow cell online
analysis technique, we performed absorption spectrophotometric analysis of deuterium
concentrations: the results supported the prospect of using deuterium as a tracer in in situ
tests. On the other hand, it became clear that online analysis would require further
improvement of analytical accuracy through an increase in optical length and integration of
scattered light.

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Flow Meter

Water Tank

PackerInjection
Pump

Pump for
Permutation

Water Quality
Sensor

Water/Tracer
Permutation Tank
Gas/Water
Separator

Drain Tank

PackerFlow Meter

Flow Cell
For Fluorescence
Analysis

Injection
Well

Withdrawal
Well
Water Quality
SensorFraction
Collector
Control PC

Withdrawal Pump
Pore Pressure
Meter

Spectrometer

Light Source Flow Cell (in test intervals)
Fluorescence analysis device

Monitoring
Well

Fig. 3.5.3-1 Overview of the test equipment used in the in situ tracer test6)

Concentration of Uranine (ppm)

Injection well

Data on Flow Cell (corrected)
Data on Flow Cell (corrected, 1/23)
Data on Flow Cell (corrected, 1/20)
Data on Flow Cell (corrected, 1/19)
Data on Flow Cell (corrected, 1/18)
Values of collected samples (1/23)
Values of collected samples (1/20)
Values of collected samples (1/19)
Values of collected samples (1/18)

Withdrawal
wellTime (s)Fig. 3.5.3-2 Reproducibility verified by duplicated tracer migration tests- 156 -

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Fig. 3.5.3-3 Packer inflation/deflation procedure under gaseous conditions

Deuterium:
30 vol%
重水 30 vol%（注水濃度）(Injection)

Uranine on Flow Cell (corrected)
注水孔フローセル（補正）Uranine on Flow Cell (corrected)
揚水孔フローセル（補正）Uranine of collected samples
揚水分析値（ウラニン）
Deuterium of collected samples
揚水分析値（重水：補正）

1030Concentrationof Deuterium
重水濃度（vol%）(vol%)

Concentration of Uranine(ppm)
ウラニン濃度（ppm）

10

1

1
3.0

0.1

0.1
0.3

0.03
0.01

0.01
0

1000

2000 3000 4000 5000 6000 7000
経過時間
Time (s) (sec)Fig. 3.5.3-4 Results of tracer migration tests using uranine and deuterium(2) Understanding mass transport fields
We developed investigation techniques to understand the mass transport pathways. The
mass transport pathways in a rock mass are formed by interconnected spaces (cavities), suchas pores between mineral particles and clastic particles occurring in the rock matrix andfractures and discontinuous structures present in the rock mass. Of these types of spaces, we
focused on fractures and discontinuous structures, where relatively rapid mass transport is
likely to be caused by advection, and classified these structures as a means of clarifying thetargets of our efforts to understand the characteristics of mass transport.
1) Mizunami
Faults and fractures that could form mass transport pathways were identified based on the
results of surface-based borehole investigations, investigations during shaft excavation, and- 157 -

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investigations in the underground facilities. These faults and fractures were classified into
five types according to the type and presence/absence of fracture-filling minerals, the degreeof alteration and color of host rock near the fracture, permeability, and the ages of the faultsand fractures 5) (Table 3.5.3-1, Fig. 3.5.3-5). We plan to proceed with in situ tests, laboratory
tests, and modeling focusing on discontinuous structures such as fractures and faults.
Table 3.5.3-1 Classification of types of discontinuous structures in the Toki Granite
Type

Fracturefillings

Wall rock alteration
around fracture

Hydraulicconductivity

Age and temperature

I : Fractures

Chlorite

Not alteredLow

69-43Ma
300-200℃

II : Fault-

Strongly altered

Very low

64-43Ma
400-300℃

III : Fractures

Chlorite(wall rocks show greenish
or white-tinged color)Low64-43Ma
300-200℃

IV : Fractures

Calcite,Chlorite ornot(wall rocks show grayish ororange color)High69-24Ma<200℃

V : Low-angle
Fractures

Calcite ornot

Not alteredHigh

43-22Ma<100℃

AlteredAlteredFig. 3.5.3-5 Conceptual model of the relationship between petrography and flow-path
fractures (Fracture type I and type II in the Table 3.5.3-1)
2) Horonobe
Discontinuous structures that can form the mass transport pathways were identified basedon the results of surface-based borehole investigations, investigations during shaft excavation,and investigations in the underground facilities. These structures were classified into fourtypes according to the mechanism of fracture formation (tensile and shear), thepresence/absence of fault rock accompanying shear fractures7), and the presence/absence of
shear band formation8) (Fig. 3.5.3-6).

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Fig. 3.5.3-6 Discontinuous geological structures around the Horonobe URL(a, c, d7) ; b8))(3) Understanding the effects of colloids, organics, and microbes
We developed investigation techniques to understand the effects of colloids, organics, andmicrobes as phenomena contributing to mass transport in the geological environment.
Because the medium for material transport in a rock mass is groundwater, we conductedinvestigations to understand the phenomena occurring in the underground environment andestablished investigation and analysis techniques for this purpose, focusing on groundwater–rock–colloid/organics/microbe interactions and the characteristics of mass transport. Thisclarified that the effects of colloids in groundwater on mass transport phenomena varydepending on the chemical elements involved and the environment of colloid formation, andenabled us to develop mathematical models of sorption and diffusion phenomena in a diffusion
system featuring organic matter in groundwater. In addition, we developed investigation andanalysis methods to evaluate the effects of microbial activities in groundwater on masstransport phenomena and understand the effects of biofilms on diffusion and sorption
phenomena.
1) Mizunami
For the development of in situ investigation techniques to understand the effects of colloids
in groundwater on mass transport, we constructed a system for collecting colloids ingroundwater using ultrafiltration under in situ groundwater pressure in a borehole drilledfrom the gallery, and confirmed its applicability to in situ investigations9). In this system, theparts that come in contact with groundwater are protected by passivation treatment, which
minimizes the elution of iron from materials. To address the effects of organic matter in- 159 -

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groundwater, we conducted investigations of rare earth elements that work effectively as
analog elements for radionuclides. After size fractionation using ultrafiltration was conductedon the colloids in groundwater, the concentrations of rare earth elements in each size fraction
were analyzed. The results showed, based on thermodynamic calculations, that rare earth
elements form complexes with organic matter (humic acid) and occur in groundwater in a
colloidal state5),10) (Fig. 3.5.3-7). With respect to the effects of microbes in groundwater, weconstructed a system in which the water for drilling is used after sterilization with ultraviolet
light to avoid contamination that would affect the results (Fig. 3.5.3-8), and applied thissystem in the investigations. The use of this system reduced the viable cell count in drilling
water to 1/4–1/5 of the level prior to application of the system. In addition, we performed
genetic analysis of microbial populations after the addition of various electron donors togroundwater to evaluate the activity of microbes in groundwater. The results demonstrated
that the dominant microbial species changes in response to the addition of different electron
donors5),11) (Fig. 3.5.3-9).

Fig. 3.5.3-7 Size distribution of rare earth elements in groundwater in the Toki Granite

Fig. 3.5.3-8 Drilling fluid sterilization system- 160 -

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Fig. 3.5.3-9 Results of microbial genetic analysis of the groundwater2) Horonobe
To understand the forms and mass transport behavior of elements in groundwater, we
examined the interactions between natural colloids and substances such as rare earth
elements that are effective analogs for minor actinide (MA) elements. The results showed thatcolloid particles in groundwater mainly consist of silicate minerals, phosphate minerals,
carbonate minerals, and sulfate minerals and that lighter rare earth elements were
distributed more readily in colloids than heavier rare earth elements. In addition, weestablished a method for pre-treatment of groundwater with high salinity and a method forquantitative determination using mass spectroscopy to evaluate the state of polyvalent metal
ions (uranium, thorium, and rare earth elements) (Fig. 3.5.3-10). The results of tests using
these methods indicated that tetravalent ions of uranium and thorium may increase theapparent solubility as a result of colloid formation and interactions with natural organic acids
in groundwater, and hence we need to examine in greater detail their states in solution. In
addition, the results of experiments taking organic matter into consideration suggested thepossibility that MAs in the groundwater environment around the tunnel may exhibit limited
solubility because of formation of phosphate precipitates and may be transported ingroundwater as pseudo-colloidal particles with MA-humic substance complexes12). To clarify
the mass transport behavior of radionuclides in the underground environment, we conducted
qualitative analysis using an SEC-ICP-MS chromatogram technique, which consisted of sizeexclusion chromatography coupled on-line to ultraviolet–visible detection and inductively
coupled plasma mass spectrometry (Fig. 3.5.3-11). The results showed that uranium is boundto low-molecular-weight silica that does not contain metallic elements such as alkaline metals
and aluminum, and that organic colloids completely lack radioactive waste-relevant elements
such as selenium, strontium, iodine, cesium, thorium, and uranium13). This study provided thefirst evidence for the fact that the carrier associated with transport of uranium is not colloids
but low-molecular-weight silica.
With respect to the effects of organic matter in groundwater, we aimed to develop
investigation and evaluation methods for quantitative evaluation of whether these effects
constitute a scenario relevant to performance assessment of a geological disposal system. We
examined dissolved humic substances that had been separated and purified from thegroundwater from Horonobe (Fig. 3.5.3-12) and investigated sedimentary rocks forcharacterization and evaluation, and studied realistic models based on these investigations(Fig. 3.5.3-13). A comparison was made between the humic substances separated and purified
from groundwater sampled at Horonobe URL and the results of simulation using the data for- 161 -

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Eu3+ complexation and existing model parameters14), as well as laboratory diffusion tests toinvestigate the possibility of matrix diffusion of element–humic substance complexes in
sedimentary rock15) (Fig. 3.5.3-14). The results showed that sorption of europium in the
ternary system (element–organic matter–host rock) can be modeled using the additive law
approach, which combines a model for complexation equilibrium with organic matter and amodel for sorption to the rock mass, and that the matrix diffusion of humic substancecomplexes into sedimentary rock is negligible, suggesting that the matrix diffusion of trivalentelements in the ternary system can be described by a model for complexation of organic matterand a model for rock sorption and diffusion. On the other hand, these findings obtained fromthe groundwater samples from Horonobe URL cannot be applied to generic groundwater–organic matter systems, indicating the need for further study to be able to form
generalizations.
With respect to the effects of microbes in groundwater, we developed and improved research
and analysis methods for the purpose of understanding the changes in groundwater chemistrycaused by microbes and the impact of biofilm formation on mass transport and the safety
performance of geological disposal systems. We investigated sedimentary rock andgroundwater samples obtained in the gallery under different redox conditions, and assessed
the results in comparison with the model analysis for evaluation of microbial effects (Fig. 3.5.315). The involvement of microbial activities depending on redox condition changes in theunderground environment has been confirmed by laboratory tests and analysis16). However,
because of the importance of in situ evaluation of groundwater–rock–microbe reactions, we
performed in situ tests using an analysis apparatus. The system was designed to monitor
water chemistry in a circulatory line connecting the parts in the borehole and in the gallery,
and the test result demonstrated its applicability to in situ study. The inclusion of a pressure
filtration tank in the analysis system provided an addition to the volume of circulating test
water, reducing the influence of periodical water sampling on monitoring results and ensuring
a sufficient supply of samples (Fig. 3.5.3-16). The results showed that air exposure in theunderground environment caused oxidation of porewater and a pH rise, while in the presenceof sufficient electron donors, the microbial activities were likely to induce rapid recovery to a
reduced state.
Observation of biofilm morphology showed that the channel structure arising from celldensity differences in biofilms affected the mass transport (Fig. 3.5.3-17). According todiffusion tests and sorption tests (Fig. 3.5.3-18), the presence of biofilm coverage on rocksurfaces causes slow diffusion of elements into biofilms, and after reaching very highconcentrations, elements are transferred into the rock through matrix diffusion.

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Fig. 3.5.3-10 Normalized concentrations of rare earth elements in groundwater

Fig. 3.5.3-11 Groundwater analysis using a size-exclusion chromatography coupled plasma
mass spectrometry technique13)- 163 -

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Fig. 3.5.3-12 Humic substances in groundwater at the Horonobe URL

Fig. 3.5.3-13 Sorption in the element/organic substance/sedimentary rock ternary system- 164 -

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Fig. 3.5.3-14 Reservoir-depletion curves (circles) and breakthrough curves (squares) withcoexisting humic substances (laboratory diffusion experiments for Eu and Th)- 165 -

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Fig. 3.5.3-15 Overview of microbial effects on mass transport in the geological environment

Fig. 3.5.3-16 The hydrochemical monitoring system on the circulation line

Fig. 3.5.3-17 Biofilms collected at the Horonobe URL and imaged using a confocal laser
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Fig. 3.5.3-18 Biofilm diffusion experiment using Cu2+ (A: reservoir-depletion andbreakthrough curves, B: breakthrough curve and calculated approximate curve)(4) Establishment of techniques for analysis and evaluation of mass transport properties
Regarding the techniques for analysis and evaluation of mass transport characterizations,
we conducted the following studies with an eye to direct and indirect use in safety assessment
studies: development and construction of procedures and methodologies for investigation andmeasurement, modeling, parameter setting, and evaluation; study of the methods for planningin situ tests through modeling of heterogeneous mass transport behavior on fracture planes
based on analysis of the mass transport heterogeneity of permeability depending on fracture
structure and in situ data; and development of detailed test protocols.
1) Horonobe
We conducted dipole tracer migration test simulation using models considering the control offracture structure on the heterogeneity of permeability and examined the effects of theheterogeneous distribution of permeability on fractures, the test scale, and background flowof groundwater (Fig. 3.5.3-19). The results revealed that the dispersion length identified in
the one-dimensional model was larger than that identified in the two-dimensional model
irrespective of the heterogeneity of permeability in fracture planes, and when the backgroundflow of ground water was perpendicular to the direction between boreholes, this tendency ismore likely to increase than when increasing the dipole ratio (the ratio of injection flow rate
to withdrawal flow rate) and the hydraulic gradient. In addition, in a field with a small
background flow of groundwater, the uncertainty of the results in analysis using the onedimensional parallel plane model was observed to decrease when the dipole ratio was small
and the direction between boreholes was parallel to the background flow of groundwater17),18).
Furthermore, based on the results of in situ mass transport tests conducted in the −250 m
gallery, we conducted a preliminary analysis using the one-dimensional analytical solution19)(Fig. 3.5.3-20) and examined the heterogeneity of mass transport characterization in fracture
planes considering asymmetrical permeability and the relationship between the tracer
migration test conditions and the recovery rate. These results suggested the presence of two
or more mass transport pathways in fracture planes. Based on these study results and- 167 -

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considering the geological environment in the Horonobe area, we developed detailed plans forin situ diffusion tests in intact rock focusing on diffusion systems, in situ dipole tests in
fracture zones focusing on advection/dispersion systems, and in situ tracer migration tests insingle fractures focusing on the evaluation of heterogeneity in the fracture plane andsorption/matrix diffusion, and commenced in situ tests in the −350 m gallery.

Fig. 3.5.3-19 Results of dipole test simulation(The left-hand figure shows transmissivities distributed heterogeneously in a twodimensional parallel plate fracture model. The right-hand figure shows the simulated tracer
distribution in the model. 【 Dipole ratio: 0.2, background groundwater flow direction:
injected borehole to withdrawn one, hydraulic gradient: 0.1】)

Fig. 3.5.3-20 Best-fit calculation for the one-dimensional solute transport model19)
3.5.4 Summary
This section summarizes the technical findings concerning the understanding of short-termchanges and recovery behavior in the geological environment obtained from the surface-based
investigations, investigations during shaft excavation, and investigations in the undergroundfacilities concerning mass transport.

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JAEA-Review 2016-014(1) Understanding the sorption and diffusion properties of rock mass
- We commenced in situ mass transport tests focusing on fractures in crystalline rock inthe underground facility, obtained the basic in situ data for evaluation and selection oftest areas, and commenced laboratory through-diffusion tests to evaluate the relationshipbetween fracture characteristics and mass transport parameters (Mizunami).
- We conducted in situ mass transport tests focusing on fractures in sedimentary rocks in
the underground facility, established test apparatuses and test methods, and confirmed
their applicability to in situ tests (Horonobe).
- We established a test apparatus that can perform in situ mass transport tests based on
an existing hydraulic test apparatus (Horonobe).
- We employed flow cell online fluorescence analysis in test intervals and confirmed theapplicability of the in situ analysis techniques to the sedimentary rock environment(Horonobe).
- We confirmed that the absorption spectrophotometric analysis of the concentration of
deuterium can be applied to the in situ tracer migration tests (Horonobe).
- We developed apparatuses and test methods that can limit the influence of dissolved
gases on in situ mass transport tests: these methods enabled acquisition of highly reliabledata (Horonobe).
(2) Understanding material transport fields- We categorized the discontinuous structures that can be the mass transport pathways
into five types at Mizunami and four types at Horonobe to clarify the targets of study on
characteristics of mass transport (both sites).
(3) Understanding the effects of colloids, organics, and microbes- We established a system for collecting colloids in groundwater based on ultrafiltration
under artesian conditions (Mizunami).
- We established the methods for pre-analysis treatment of groundwater containing highsalinity and quantitative determination for the purpose of evaluating the state ofmultivalent metal ions in groundwater, and confirmed their applicability to in situ study(Horonobe).
- We demonstrated that rare earth elements in groundwater form complexes with organic
matter and occur in the form of colloids (Mizunami).
- We showed that the colloid particles in groundwater mainly consist of silicate minerals,
phosphate minerals, carbonate minerals, and sulfate minerals, and more readily containlighter rare earth elements than heavier rare earth elements. (Horonobe).
- We provided the first proof of the fact that the carrier for uranium in the undergroundenvironment is not colloids but low-molecular-weight silica in groundwater (Horonobe).
- We demonstrated that the sorption of a trivalent element in the ternary system (element–
organic matter–host rock) can be modeled using the additive law approach and that thematrix diffusion of trivalent elements can be described by a model for complexation withorganic matter and a model for rock sorption and diffusion into rock mass (Horonobe).
- The humic substances in groundwater at Horonobe had similar properties to humic- 169 -

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substances in groundwater from other areas in Japan (Horonobe).
- The investigation system with ultraviolet sterilization, which was applied to in situ
borehole investigations, can reduce contamination of microbes from drilling fluid(Mizunami).
- We confirmed a monitoring system with a circulation line from in the gallery to in theborehole can be used to obtain sufficient samples without an influence of volume change
in the system (Horonobe).
- We demonstrated that different microbial species become dominant after the addition ofdifferent electron donors and that microbes enable rapid recovery of groundwatercontaining sufficient electron donors from an oxidizing to a reducing state (both sites).
- We showed that cell density differences in biofilms affect mass transport and that thebiofilm covering on rock surfaces buffers the matrix diffusion of elements into rock
(Horonobe).
(4) Establishment of techniques for analysis and evaluation of mass transport characterizations- Based on the tracer migration test simulation considering the heterogeneity ofpermeability depending on fracture structure, we proposed test conditions that can
reduce the uncertainty produced in analysis using the one-dimensional parallel platemodel (Horonobe).
- We showed that there are two or more mass transport pathways in the fracture plain in
sedimentary rock mass using the results from in situ mass transport tests (Horonobe).
- Considering the above results and the geological environment in the Horonobe area, wedeveloped detailed plans for in situ mass transport tests and commenced these tests(Horonobe).
An important requirement for future studies of mass transport is to continue research on anddevelopment of investigation and analysis/evaluation techniques, which are needed forappropriate understanding of the phenomena and characteristics involved in mass transportin rock beds. The future themes are summarized in Table 3.5.4-1.
With respect to understanding the sorption and diffusion properties of rock mass, concrete
themes are to clarify the possibility and limitations of application of various tracers togroundwater and rock, to develop in situ test and analysis methods for geologicalenvironments, and to accumulate data from such tests.
With respect to understanding mass transport fields, concrete themes are to understand the
distribution of discontinuous structures such as fractures that contribute to mass transport inrock masses, and to understand the mass transport phenomena that occur therein. In addition,
it is necessary to develop investigation techniques for identifying and understanding thestructures that contain mass transport pathways.
With respect to understanding the effects of colloids, organic matter, and microbes, concrete
themes are to accumulate in situ and laboratory test data concerning the effects of colloids,organic matter, and microbes as a whole, to develop investigation techniques to obtain in situ
data with little uncertainty, to investigate the state of dissolved elements in detail, and to- 170 -

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confirmtheapplicabilityof

constructed

techniques

concerning

colloids/organic

matter/microbes and mass transport for other geological environments.
With respect to the establishment and systematization of techniques for analysis/evaluationof mass transport properties supporting safety assessment, concrete themes are to confirm theapplicability of the evaluation technique of mass transport characterizations and safetyassessment methodologies to actual geological environments.
Study of mass transport is placed as an important theme in Phase III (investigations in theunderground facilities) both in the Mizunami20) and Horonobe URLs. Construction ofhorizontal galleries for in situ tests and other works are making good progress at Mizunamiand Horonobe URLs. In the timeframe of the second mid-term research phase, we have justcommenced the in situ study on mass transport. In the future, we plan to conduct masstransport tests and other in situ tests and proceed with modeling of fracture networks andmass transport analysis. Building on the outcomes of such study, we will evaluate the effects
of disturbance of the geological environment resulting from the construction of tunnels on
mass transport characterizations and also evaluate the alteration of material transport
properties caused by long-term changes in the geological environment.
Table 3.5.4-1 Future themes in the next research phase
Focus

R&D performancetargetDecision to
construct, to Favorable URL layout
begin disposal, and disposal pit canto endbe designed from theemplacingviewpoint of solutewaste and on transport property.
final closure

Tasks

IssuesCharacterization
methodology• Methodology for the characterization ofmass transport pathway• Methodology for the characterization ofimportant factor affecting masstransport property• Generalization of characterization
methodology

Example proposal• Show example through the executionof URL project

References
1) Hama, K., Sato, T., Sasao, E., Iwatsuki, T., Kunimaru, T., Matsuoka, T., Takeuchi, R., Onoe,
H. and Mikake, S. : “Mizunami Underground Research Laboratory Project; Preparation ofgeosynthesis data flow diagram (Construction phase)”, JAEA-Data/Code 2013-010 (2013),
58p.
2) (Eds.) Iwatsuki, T., Sato, H., Tanai, K., Inagaki, M., Sawada, A., Niinuma, H., Ishii, E.,
Maekawa, K., Tomura, G., Sanada, H., Kunimaru, T., Asamori, K., Niizato, T., Tokiwa, T.,
Sugita, Y., Yamazaki, M., Nakamura, T., Fujita, T., Taniguchi, N., Kobayashi, Y., Hayashi,K., Saito, Y., Tachi, Y., Iijima, K. and Sasamoto, H. : “Horonobe Underground ResearchLaboratory project research and development plan in Phase 2; H20-21”, JAEA-Research
2009-002 (2009), 156p.
3) (Eds.) Iwatsuki, T., Sato, H., Nohara, T., Tanai, K., Sugita, Y., Amano, K., Yabuuchi, S.,- 171 -

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Oyama, T., Amano, Y., Yokota, H., Niizato, T., Tokiwa, T., Inagaki, D., Abe, H., Nakayama,
M. and Kurikami, H. : “Horonobe Underground Research Laboratory Project; Research anddevelopment plan (H22-H26)”, JAEA-Research 2011-009 (2011), 73p.
4) Kunimaru, T., Morikawa, K., Tachi, Y., Kuno, Y., Hosoya, S., Shimoda, S., Kato, H.,
Nakazawa, T., Ikuse, H. and Kubota, M. : “Measurement of sorption, diffusion and pore
physicality for granite sample”, JAEA-Data/Code 2012-013 (2012), 96p.
5) Kunimaru, T., Mikake, S., Nishio, K., Tsuruta, T., Matsuoka, T., Ishibashi, M., Ueno, T.,
Tokuyasu, S., Daimaru, S., Takeuchi, R., Saegusa, H., Onoe, H., Takeda, M., Karino, T.,
Mizuno, T., Hagiwara, H., Sato, T., Sanada, H., Tanno, T., Hikima, R., Morikawa, K.,
Yuguchi, T., Ogata, N., Hama, K., Ikeda, K., Yamamoto, M., Shimada, A., Matsui, H., Ito,
H. and Sugihara, K. : “Mizunami Underground Research Laboratory Project annual reportfor fiscal year 2010”, JAEA-Review 2012-020 (2012), 178p.
6) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Oyama, T., Amano, Y., Murakami, H.,
Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S., Ohara,
M. and Jin, K. : “Horonobe Underground Research Laboratory Project; Investigation reportfor the 2011 fiscal year”, JAEA-Review 2012-035 (2012), 63p.
7) Ishii, E., Funaki, H., Tokiwa, T. and Ota, K. : “Relationship between fault growthmechanism and permeability variations with depth of siliceous mudstones in northern
Hokkaido, Japan”, Journal of Structural Geology, 32(11) , pp.1792-1805 (2010).
8) Ishii, E., Sanada, H., Funaki, H., Sugita, Y. and Kurikami, H. : “The Relationships among
brittleness, deformation behavior, and transport properties in mudstones; An Example
from the Horonobe Underground Research Laboratory, Japan”, Journal of GeophysicalResearch, 116(B09), p.B09206_1-B09206_15 (2011).
9) Aosai, D., Yamamoto, Y. and Mizuno, T. : “Development of New Ultrafiltration Techniques
Maintaining In-Situ Hydrochemical Conditions for Colloidal Study”, 13th International
Conference on Environmental Remediation and Radioactive Waste Management (ICEM'10),
Tsukuba, Japan, Proceedings of ICEM2010-40074, (CD-ROM) (2010).
10) Yamamoto, Y., Aosai, D. and Mizuno, T. : “Evaluation of Behavior of Rare Earth Elements
Based on Determination of Chemical State in Groundwater in Granite”, 13th International
Conference on Environmental Remediation and Radioactive Waste Management (ICEM'10),
Tsukuba, Japan, Proceedings of ICEM2010-40072, (CD-ROM) (2010).
11) Fukuda, A., Hagiwara, H., Ishimura, T., Kouzuka, M., Ioka, S., Amano, Y., Tsunogai, U.,
Suzuki, Y. and Mizuno, T. : “Geomicrobiological Properties of Ultra-Deep Granitic
Groundwater from the Mizunami Underground Research Laboratory (MIU), Central
Japan”, Microbial Ecology, vol.60, no.1, pp.214-225 (2010).
12) Kirishima, A., Kuno, A., Amamiya, H., Murakami, H., Amano, Y., Iwatsuki, T., Mizuno, T.,
Kubota, T., Sasaki, T. and Sato, N. : “Interaction of rare earth elements and suspended
matters contained in Horonobe deep groundwater, Abstracts Book Migration 2013”, 14th
International Conference on the Chemistry and Migration Behaviour of Actinides andFission Products in the Geosphere, PA6-1 (2013).
13) Kozai, N., Ohnuki, T. and Iwatsuki, T. : “Characterization of saline groundwater at- 172 -

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Horonobe, Hokkaido, Japan by SEC-UV-ICP-MS: Speciation of uranium and iodine”, Water
Research, Volume 47, Issue 4, pp.1570-1584 (2013).
14) Terashima, M., Okazaki, M., Iijima, K. and Yui, M. : “Application of NICA-Donnan model
to modelling of Eu(III) solubility in the presence of deep groundwater humic substances”,
Mineralogical Magazine, 75, p.1999 (2011).
15) Seida, Y., Terashima, M., Tachi, Y., Iijima, K., Nakazawa, T., Yamada, M. and Yui, M. :“Sorption and diffusion of Eu in sedimentary rock in the presence of humic substance”,
Radiochim. Acta 98, pp.703-709 (2010).
16) Amano, Y., Sasao, E., Niizato, T. and Iwatsuki, T. : “Redox buffer capacity in water-rockmicrobe interaction system in subsurface environments” , Geomicrobiol. J., Vol. 29, Issue 7,
pp. 628-639 (2012).
17) Ijiri, Y., Naemura, Y., Amano, K., Maekawa, K., Sawada, A., Ota, K. and Kunimaru, T. :“Study on the Estimation Error Caused by Using One-Dimensional Model for the
Evaluation of Dipole Tracer Test”, Proceedings of the ASME 13th International Conference
on Environmental Remediation and Radioactive Waste Management, ICEM2010-40077,(CD-ROM) (2010).
18) Yokota, H., Amano, K., Maekawa, K., Kunimaru, T., Naemura, Y., Ijiri, Y., Motoshima, T.,
Suzuki, S. and Teshima, K. : “Study on development of evaluation technique of in-situ tracer
test in Horonobe Underground Research Laboratory Project (Contract research)”, JAEAResearch 2013-002 (2013), 281p.
19) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Project; Investigation
report for the 2012 fiscal year”, JAEA-Review 2013-037 (2013), 63p.
20) Japan Atomic Energy Agency : “Master plan of the Mizunami Underground ResearchLaboratory Project”, JAEA-Review 2010-016 (2010), 37p.

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3.6 Engineering technology for deep underground applications
3.6.1 Introduction
The underground research laboratory projects will provide the opportunity to demonstrate
the feasibility of safe and reliable construction, maintenance, and management of anunderground research facility by applying conventional and state-of-the-art engineering
technology in a deep geological environment. Engineering technologies, such as design,
construction planning, construction, countermeasures, and safety management, have been
applied to Mizunami and Horonobe.
3.6.2 Objectives in the second mid-term research phase
The objectives of engineering technology for deep underground applications in the second
mid-term research phase is to test the applicability of construction and countermeasuretechnologies and maintenance technology during extension of shafts and galleries at depthsof 500 m (Mizunami) and 350 m (Horonobe). Design and construction planning technologies
have been also estimated in this phase. Table 3.6.2-1 shows the performance target level oftechnical development for engineering technology.
Table 3.6.2-1 Performance target of R&D for engineering technology
Focus

Performance target of R&D

Tasks

Decision-making for Application of construction technology
start of construction and countermeasures.

• Construction technology forunderground facilities• Countermeasures during constructionof underground facilities
Water inflow, inflammable gas
Spalling, rock burst

Decision-making for Security of underground facility.
start of operation Maintenance of underground facilities.

• Technology for security andmaintenance of underground facility

3.6.3 Project details and outcomes(1) Construction technologies
1) Mizunami
Two consecutive drill, blast, and mucking steps (1.3 m + 1.3 m) and one shaft-lining step (2.6m) per cycle to optimize cycle time for shaft excavations were adopted in Mizunami. The
designed cycle time was compared to the actual cycle time: the applicability of the short-step
shaft sinking method is valid. This results in reduction of cycle time for preparation of theconcrete lining and the geological survey at the shaft wall. The applicability of the revised
shaft-sinking method is evaluated by comparison of the designed and actual cycle times. The
conclusions are as follows1),2),3),4),5):- The cycle times for drilling, explosive insertion, and blasting are short due to the
distribution of fractured rock at the Main Shaft. In contrast, the cycle time for the- 174 -

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concrete lining and other operations increased. Other operations consisted of trouble andrepair of facilities, auxiliary methods, and moving scaffolding (Fig. 3.6.3-1).
- The cycle time for all works did not increase with depth. Some works decreased withdepth as the skill of the work increased (Fig. 3.6.3-2).
- The cycle times for the Ventilation Shaft also increased. The cycle times for drilling,
explosive insertion, and blasting were shorter due to the distribution of fractured rock at
the Main Shaft.
- The short-step shaft-sinking method was applied in different conditions in the Main Shaft
and the Ventilation Shaft. Thus, the applicability of this method was evaluated for a wide
range of geological environments.

Fig. 3.6.3-1 Actual excavation cycle time ofFig. 3.6.3-2 Designed and actual

the Main Shaft

excavation cycle times of the Main Shaft

2) Horonobe
In Horonobe, by June 2014, excavation of the G.L. −140 m, −250 m, and −350 m galleries had
been accomplished. The Ventilation and East Access Shafts had been excavated to 380 m
depth; the West Access Shaft had been excavated to 365 m depth. During shaft sinking at
depths greater than 250 m, severe breakout and spalling in the shaft wall was induced in
response to shaft sinking in a region with a fault zone and a low competence factor zone. The
three-dimensional shape of the shaft wall was detected using a three-dimensional laser
scanner together with geological surveys of the shaft wall. At some depths, measurement of- 175 -

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stress in the lining and displacement of rock mass around the wall of the shaft were conducted.
The results are as follows:- In shaft sinking, there is a high possibility of severe breakout and spalling in the directionof minimum principal stress owing to stress concentration. In the fractured zone, thepossibility of spalling becomes high at the top and bottom of the faults with size greaterthan the shaft diameter. Overlapping of these two effects leads to an increase in the depthof spalling6),7).
- In the Ventilation Shaft, vertical tensile stress developed in the concrete lining installed
above the location where spalling developed. This tensile stress was greater than thetensile strength of the concrete lining when the spalling had developed more than 100 cm
into the wall of the shaft. This tensile stress induced a circumferential crack in theconcrete lining (Fig. 3.6.3-3)8).
- Spalling affects the stability of the concrete lining; subsequently, the spalling depth of
the rock mass around the shaft wall was considered to be a practical guideline for theselection of support pattern to prevent the occurrence of severe open cracks (Fig. 3.6.3-4).
The applicability of this guideline has been being verified during the construction of theEast and West Access Shafts9),10).
- In the fault zone, the spalling depth was decreased with shortening the installation spanof concrete lining and additional rock bolts9),10).

(a) Excavation up to
287 m depth(b) Spalling up to
60 cm depth(c) Spalling up to
140 cm depth

Tensile(d) Spalling behind theconcrete linimg

Compressive
StressFig. 3.6.3-3 Calculated results of changes in vertical stress with development of spalling of
the rock mass around the shaft wall in the concrete lining- 176 -

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Fig. 3.6.3-4 Flowchart for selecting the optimum support pattern in the Ventilation Shaft10)3) Generic results
The matters that should be treated carefully are not greatly different between Mizunami andHoronobe. Excavation technologies applied to both sites are based on engineering technology
for road and railway tunnel excavation and mining technology, so the technologies can apply
to many rock types.
(2) Countermeasure technology
1) Mizunami
Pre-excavation grouting as a countermeasure against groundwater inflow to shafts andgallery using normal Portland cement, super-fine Portland cement, and liquid-type colloidal
silica were performed corresponding to geological conditions at depths of 200, 300, 400, and
500 m. Post-excavation grouting testing was performed at the depth of 145 m in the Ventilation
Shaft11),12),13),14),15),16). Numerical analysis to understand the effect of grouting was also
performed17),18),19),20),21). The conclusions are as follows:- Fig. 3.6.3-5 and Fig. 3.6.3-6 show the results of parametric groundwater flow analysis forpost-excavation grouting at the Ventilation Shaft. A 50% reduction of inflow to the shaft
was predicted under conditions of a one-order decrease of hydraulic conductivity in a 6 m
grouting area with a length of 80 m16). The results of post-excavation grouting were that
injection rate decreased with the amount of grouting, and inflow to the injection holes
also decreased (Fig. 3.6.3-7, Fig. 3.6.3-8).
- Pre-excavation grouting using normal Portland cement was performed at the G.L. −300
m access/research gallery. The total amount of inflow to this gallery was several 10 to 100- 177 -

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L/min after excavation with pregrouting, in spite of the large amount of inflow (over 1,000
L/min) in a pilot borehole investigation before excavation of the gallery12).
- Pre-excavation grouting using super-fine Portland cement was performed at a depth
deeper than 400 m in the Ventilation Shaft. This cement can improve low-permeability
rock with an initial value of approximately 1 Lugeon, which normal Portland cement
could not improve. The rate of decline for total head of groundwater decreased with shaft
excavation progress in the area where pre-excavation grouting had been performed13) (Fig.
3.6.3-9, Fig. 3.6.3-10).

RadiusFig. 3.6.3-5 Model for groundwater flow

Fig. 3.6.3-6 Results of groundwater flow

analysisanalysis for post-excavation grouting- 178 -

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Permanent grout
curtain zone

No groutingzone

Temporary grout
curtain zone

Shaft

4m
1m

5m

4m
5m
1m

Fig. 3.6.3-7 Post-excavation grouting test

Fig. 3.6.3-8 Results of post-excavation
grouting test

The unit in numbers is a millimeter.

Fig. 3.6.3-9 Pre-excavation grouting plan for shaft sinking- 179 -

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Fig. 3.6.3-10 Confirmation of effectiveness of grouting(groundwater pressure monitoring in the borehole)
A vertical fault with gauge is present at the location of the Main Shaft. One of themechanisms of spalling is “Takanuke”22), so countermeasures for spalling at the shaft wall
were designed. Rock bolts with silica resin were used as reinforcement and the forepolingmethod of shaft sinking at the depth of 150 m. The effectiveness of the countermeasures wasvalid based on the volume of concrete liner (Fig. 3.6.3-11)3),12).

Fig. 3.6.3-11 Countermeasures against spalling at the Main Shaft wall

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2) Horonobe
From borehole surveys, it was found that a fracture zone with high permeability existed
below the depth of 250 m. To properly control the groundwater inflows to the shafts and drifts,
pre-excavation grouting operations were conducted for the permeable zone detected from
borehole surveys prior to shaft sinking below 250 m depth. The operation was planned toreduce permeability in rock to less than 0.1 Lugeon value within 3.0 m of the wall of theVentilation Shaft and 4.0 m of the wall of the East Access Shaft. Ultra-fine-grained cement
was mainly used as the grout material. The results can be summarized as follows:- From the information on the three-dimensional distribution of the injected volume ofgrouting material, additional faults were detected and integrated into the 3D
visualization system. The revised distribution of faults was applied to select the optimal
support patterns for the Ventilation and East Access Shafts (Fig. 3.6.3-12)7).
- From fracture mapping on the shaft wall, grouting material was mainly observed on the
branching part from the fault rather than the fault itself (fault core); nevertheless, thefault has high continuity. Fig. 3.6.3-13 shows a conceptual image of grout injection to thefault23). This result will lead to construction of an effective plan for grouting and thelocation of injection holes.

Fig. 3.6.3-12 Distribution of faults and volume of grout material injected in two shafts7)- 181 -

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Fig. 3.6.3-13 Conceptual image of fractures with grout material on the shaft wall23)3) Generic results
The matters which should be treated carefully are little different between Mizunami andHoronobe. The countermeasure technologies applied to both sites are based on engineering
technology for road and railway tunnel excavation and mining technology, so the technologies
can apply to many rock types.
(3) Technology for security and maintenance of underground facility1) Mizunami
Based on the results of ventilation network analysis, the required air volume versus velocity
limits, gas inflow, and dust generated by shotcreting were calculated, and capacity andoptimum location of the ventilation equipment were determined. The results of non-steadystate airflow analysis and the state of the airways (smoke-filled, smoke-free) in the event of afire in the URL during each construction step were evaluated and an evacuation and a refuge
plan were confirmed24) (Fig. 3.6.3-14, Fig. 3.6.3-15).
The effectiveness of the safety and maintenance technology for the concrete liner has beenvalidated from photographs taken using a video camera and a crack detection sensor using
optical fiber (Fig. 3.6.3-16, Fig. 3.6.3-17).

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Design of ventilation system
・Shaft：fan & duct ventilation→ shaft & gallery ventilation(at G.L. −500 m)
・Gallery：Extension of fan & duct

Ventilation analysis
・Specification of ventilation system(fan & duct)Fire gas analysis
・Fire detection
・Refuge concept
・Specification of refuge

Fig. 3.6.3-14 Ventilation system for Mizunami

Fig. 3.6.3-15 Examination items forventilation network analysis

Fig. 3.6.3-16 Observation of the concrete liner of the shaft using a video camera- 183 -

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Fig. 3.6.3-17 Durability test of the crack detection sensor using optical fiber2) Horonobe
In excavation of shafts and galleries in the presence of flammable gas such as methane, it isimportant to predict the behavior of fire gases as part of emergency planning. The behavior ofventilation air was investigated experimentally using a model of underground galleries. On
the basis of the results of these experiments, a system for ventilation network analysis thatcan simulate various types of aerial behavior was developed25).
The results of the ventilation network analysis were applied to the ventilation plan. A toolfor estimation of the behavior of fire gases was prepared to improve the reliability of disasterprevention in the galleries. Considering the behavior of fire gases obtained from the analysis,
an evacuation route was secured by controlling the gate (Fig. 3.6.3-18).

Fig. 3.6.3-18 Results of the ventilation network analysis in the excavations of the
G.L. -350m galleries
3) Generic results
The technologies for security and maintenance of the underground facility applied to bothsites are based on engineering technology for road and railway tunnel excavation and mining
technology, so the technologies can apply to many rock types.

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3.6.4 Summary
The effectiveness of construction technology and countermeasures for inflow and spalling
have been confirmed. The safety management technology has also been confirmed. Additional
studies are necessary in the future:- Post-excavation grouting- Estimation of the influence of countermeasures on the geological environment- Development of safety management technology and closure technology- Estimation of the safety of the underground facility against large earthquakes
References
1) Ijiri, Y., Noda, M., Nobuto, J., Matsui, H., Mikake, S. and Hashizume, S. : “Study onengineering technologies in the Mizunami Underground Research Laboratory; FY20092010 (Contract research)”, JAEA-Technology 2013-047 (2014), 819p. (in Japanese).
2) Fukaya, M., Noda, M., Hata, K., Takeda, Y., Akiyoshi, K., Ishizeki, Y., Kanata, T., Sato, S.,
Shibata, C., Ueda, T., Toda, A., Kobayashi, S., Niimi, K., Okihara, M., Tsuji, M., Yamada,T., Sato, T., Mikake, S., Horiuchi, Y. and Hashizume, S. : “Study on Engineering
Technologies in the Mizunami Underground Research Laboratory (FY. 2012) (Contract
Research)”, JAEA-Technology 2014-019 (2014), 495p. (in Japanese).
3) Sato, T., Mikake, S., Noda, M. and Kobayashi, S. : “Evaluation of Shaft Excavation
Technology based on Construction Results up to a depth of 500m at Mizunami
Underground Research Laboratory”, Journal of JTA-Tunnel and Underground, Japan
Tunnelling Association, Vol. 45, No.7, pp.501-510 (2014).
4) Sanada, H., Sato, T., Horiuchi, Y., Mikake, S., Okihara, M., Yahagi, R. and Kobayashi, S. :“Analysis of excavation cycle time during sinking of the Ventilation Shaft at the Mizunami
Underground Research Laboratory”, Proceedings of 2014 ISRM International Symposium- 8th Asia Rock Mechanics Symposium, pp.1263-1269 (2014).
5) Hashizume, S., Matsui, H., Horiuchi, Y., Hata, K., Akiyoshi, K., Sato, S., Shibata, C.,
Niunoya, S. and Noda, M. : “Study on dynamic behavior of a shaft excavated throughfaulted crystalline rock mass”, Proc. of the 13th Japan Symposium on Rock Mechanics,
JSCE, pp.121-126 (2013). (in Japanese).
6) Tsusaka, K., Inagaki, D., Nago, M. and Matsubara, M. : “Spalling in Response to Shaft
Sinking at Grate Depth in Soft Sedimentary Rock”, Underground Research Symposium,
JSCE, 17, pp.155-162 (2012). (in Japanese).
7) Tsusaka, K., Inagaki, D., Tokiwa, T., Yokota, H., Nago, M., Matsubara, M. and Shigehiro,
M. : “An Observational construction management in the Horonobe Underground ResearchLaboratory Project”, Proceedings of World Tunnel Congress 2012 (2012).
8) Tsusaka, K., Inagaki, D., Nago, M., Matsubara, M. and Sugawara, K. : “Influence of rockspalling on concrete lining in shaft sinking at the Horonobe Underground ResearchLaboratory, Japan.”, Proceedings of the 6th Japan-Korea Joint Symposium on RockEngineering, pp.911-916 (2013).
9) Tsusaka, K., Inagaki, D., Nago, M., Kamemura, K., Matsubara, M. and Shigehiro, M. :- 185 -

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JAEA-Review 2016-014“Relationship between rock mass properties and damage of a concrete lining during shaft
sinking in the Horonobe Underground Research Laboratory Project”, Proceedings of World
Tunnel Congress 2013, pp.2014-2021 (2013).
10) Tsusaka, K., Inagaki, D., Nago, M., Aoki, T. and Shigehiro, M. : “Rock spalling andcountermeasures in shaft sinking at the Horonobe Underground Research Laboratory”,
Proceedings of the 6th International Symposium on In-Situ Rock Stress, pp.339-346 (2013).
11) Kuji, M., Hara, M., Minamide, M., Takeuchi, S., Mikake, S. and Sato, T. : “Pre-excavation
Grouting for Reduction of Water Inflow into a Deep Shaft”, Proc. of the 37th Symposium on
Rock Mechanics, JSCE, pp.251-256 (2008). (in Japanese).
12) Mikake, S., Yamamoto, M. and Ikeda, K. : “Applicability of countermeasures during
excavation and construction of the Mizunami Underground Research Laboratory”, Proc. of
the 40th Symposium on Rock Mechanics, JSCE, pp.191-196 (2011). (in Japanese).
13) Ishii, Y., Mikake, S., Kamiya, A., Watanabe, K., Nobuto, J. and Kusano, T. : “Pre-excavation
grouting with micro-fine cement below four hundreds meter depth”, Proc. of the 40th
Symposium on Rock Mechanics, JSCE, pp.185-190 (2011). (in Japanese).
14) Nobuto, J., Tsuji, M., Kusano, T., Mikake, S., Kamiya, A. and Ishii, Y. : “Test execution ofliquid-type grout at depth of 300m of Mizunami Underground Research Laboratory”, Proc.
of the 40th Symposium on Rock Mechanics, JSCE, pp.179-184 (2011). (in Japanese).
15) Kobayashi, S., Nobuto, J., Sugiyama, H., Kusano, T., Tsuji, M., Mikake, S. and Matsui,
H. : “Grouting experiment with colloidal silica at 300 m depth of the Mizunami URL”,
Proceedings of European Rock Mechanics Symposium (EUROCK 2012) (2012).
16) Kuji, M., Sato, T., Mikake, S., Minamide, M., Hara, M. and Sugihara, K. :“Countermeasures planned for reducing water inflow into deep shafts at the Mizunami
Underground Research Laboratory”, Journal of Power and Energy Systems, Vol. 2, No. 1,
Special Issue on 15th International Conference on Nuclear Engineering I, pp.153-163(2008).
17) Nobuto, J., Kobayashi, S., Nishigaki, M., Mikake, S. and Sato T. : “Grouting Methodology
in Crystalline Rock”, Proceedings of ICONE15, 15th International Conference on Nuclear
Engineering, April 22-26, 2007, Nagoya, Japan, ICONE15-10445 (2007).
18) Nobuto, J., Nishigaki, M., Mikake, S., Kobayashi, S. and Sato, T. : “Prevention of clogging
phenomenon with high-grouting pressure”, Journal of Japan Society of Civil Engineers, Ser.
C (Geosphere Engineering), Vol.64, No.4, pp.813-832 (2008). (in Japanese).
19) Nobuto, J., Mikake, S. and Nishigaki, M. : “Proposal of efficient pre-excavation grouting
concept for deep underground rock excavation”, Journal of Japan Society of Civil Engineers,
Ser. C (Geosphere Engineering), Vol.65, No.4, pp.806-821 (2009). (in Japanese).
20) Mikake, S., Nishigaki, M. and Sato, T. : “Establishment of the theoretical evaluation ofgrouting zone with consideration of seepage forces”, Journal of Japan Society of Civil
Engineers, Ser. C (Geosphere Engineering), Vol.70, No.1, pp.33-43 (2014). (in Japanese).
21) Horiuchi, Y., Mikake, S. and Sato, T. : “Changes in water inflow and water pressure
response after earthquakes in Mizunami Underground Research Laboratory”, Proc. of the
42nd Symposium on Rock Mechanics, JSCE, pp.96-100 (2014). (in Japanese).

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22) Sakurai, S., Shimizu, N., Akutagawa, S., Yoshida, H., Sato, T. and Yamachi, H. :“Investigation on collapse mechanism of super-deep vertical shaft”, Journal of Japan
Society of Civil Engineers, Ser. F (Tunneling Engineering), Vol.62, No.4, pp.662-673 (2006).
(in Japanese).
23) Tokiwa, T., Sawada, S., Ochiai, S. and Miyakawa, K. : “Occurrence of high-permeability
fracture estimated by grouting in Horonobe URL of Japan”, Proceedings of the 6th JapanKorea Joint Symposium on Rock Engineering, pp.1021-1025 (2013).
24) Sakai, T., Kashiwase, Y., Mikake, S. and Sato, T. : “Establishment of integrated
underground information management system for underground facilities”, UndergroundResearch Symposium, JSCE, 12, pp.161-168 (2007). (in Japanese).
25) (Eds.) Nakayama, M., Sano, M., Sanada, H. and Sugita, Y. : “Horonobe UndergroundResearch Laboratory Project Annual Report for Fiscal Year 2009”, JAEA-Review 2010-039,
pp.32-33 (2010). (in Japanese).

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3.7 Performance and setting condition of the engineering barrier
3.7.1 Introduction
R&D for contribution to the selection of the detailed investigation areas and the conceptual
design of the repository based on the results of the preliminary investigation by NUMO
(Nuclear Waste Management Organization of Japan), and the formulation of the safety review
basic guideline by safety regulation authority has been performed in phase II of the basic
technology program on geological disposal in Japan (FY2007–2012) based on the master plan1).
Thus, in the basic technology program regarding repository design and engineering technology
in Japan, it is important to improve the design and engineering technology of a deep geologicalrepository and the evaluation technology of the integrity of the engineered barrier system(EBS) as a technical basis. Especially, it is essential to demonstrate some technologies used in
the construction and operation phase of geological repository prior to the implementation andsafety regulation of geological disposal.
3.7.2 Objectives in the second mid-term research phase
In R&D on geological disposal technology at the Horonobe Underground Research Laboratory(URL) project during the second mid-term research phase, "development of an evaluation
technology applicable to actual geological environment and presentation of its engineering
implementability" was set as the whole target. Table 3.7.2-1 shows the performance targets of
R&D for geological disposal technology at the Horonobe URL project.
Table 3.7.2-1 Performance target of R&D for geological disposal technology
Focus

Construction
decision

Operation decision

Performance target of R&D

Task

Underground facilities of repository canbe designed and constructed.

• Development of usable construction
material for underground facilities of arepository with a low long-term
influence on the geologicalenvironment• Development of design & construction
technology of underground facilities ofa repository

EBS can be designed, constructed, andevaluated.

• Development of design & construction
technology of EBS

Tunnel sealing can be designed,
constructed and, evaluated.

• Development of design & construction
technology of tunnel sealing (backfill &plug)

Disposal pit can be designed,
constructed and, evaluated.

• Development of design & construction
technology of a disposal pit

3.7.3 Project details and outcomes
The research results on geological disposal technology at Horonobe URL project are divided
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JAEA-Review 2016-014(1) Design and engineering technology of a deep geological repository- Low-alkaline cement, which has been developed for the long-term stability of the barriersystems and is named high fly-ash silica-fume cement (HFSC), was used in constructionof the underground facility as shotcrete and lining and in grouting at the Horonobe URL(Table 3.7.3-1, 3.7.3-2, Fig. 3.7.3-1). As a result, it was confirmed that the initial strength,
workability, and hydraulic conductivity of support and grout made of HFSC wereequivalent to those of conventional material. Then, it was confirmed that support andgrout made of HFSC was able to be applied in the construction of an underground facility
in a repository2),3),4),5),6).
- Demonstration of the auger machine with casing as an excavation technology for adisposal pit was performed (Fig. 3.7.3-2)6).
- The buffer and overpack which were presented in H12 report were manufactured. The
surface temperature of the overpack can be controlled with electric heaters.
Demonstration of the vacuum hoisting method as an emplacement technology for anengineered barrier system (EBS) was performed (Table 3.7.3-3, Fig. 3.7.3-3)6).
- In consideration of the geological environment at the Horonobe URL, backfill material
that uses the debris (rock fragments) generated in tunnel excavation and bentonite wasdesigned and constructed. Specifically, the specification of the backfill material was
determined on the design requirements relating to water permeability and swelling
ability and the results of laboratory and in situ tests (Table 3.7.3-4, Fig. 3.7.3-4)6).
- The HFSC plug was designed and constructed taking into account the geologicalenvironment at the Horonobe URL.
(2) Evaluation technology of the integrity of the EBS- The experiment on EBS focusing on overpack corrosion, re-saturation phenomena in thenear-field, displacement of buffer into backfill, interactions between bentonite, cement,
and carbon steel, and intrusion of buffer into the host rock was started (Fig. 3.7.3-5, Fig.
3.7.3-6).

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Table 3.7.3-1 Mixing proportions of HFSC shotcrete used in the G.L. −250 m gallery
Water toUnit weight (kg/m3)
Sand
Type ofBinderBinderRatio
Fine
CoarseSuper
Ratio
cementWater(%)
Aggregate
Aggregate
Plasticizer
OPC
SF
FA
(%)
HFSC
35.0
60.2
175
200
100
200
945
638
5.25
BB
40.0
55.7
170
400
25
990
802
2.40
HFSC: High Fly-ash Silica-fume Cement, OPC: Ordinary Portland Cement, BB: Blastfurnace slag cement type B, SF: Silica-fume, FA: Fly ash
Table 3.7.3-2 Compressive strength at the material age of 28 days used in the

HFSC shotcretecore
BB shotcrete core

G.L. −250 m gallery
Result at the
Result at the surface
underground(N/mm2)(N/mm2)
45.9

41.2

51.1

-

Design strength(N/mm2)36.0

The results show the average of three test replicates.

Fig. 3.7.3-1 The areas where HFSC was applied for support and grouting
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JAEA-Review 2016-014(a) Edge cutting - Circumference casing(b) Excavation by augering inside casing

Fig. 3.7.3-2 Test pit excavation method
Table 3.7.3-3 Specifications of the buffer and electric heater(1)Buffer (H12 reference)･Material
Sodium Bentonite Blocks (70% bentonite and 30% quartz sand)･ShapeTwo shapes, 82 cm diameter columns and a fan-shaped typewith 45°central angles, an outside radius of 113 cm, and a
thickness of 70 cm.
･Design dry
1.87 g/cm3 (ω = 10.5%) (the average dry density may be 1.6
densityg/cm3 when the gap between blocks is filled.)･Emplacementa vacuum hoisting method (Fig. 3.7.3-3)
method(2)Electric heater (Simulated overpack)･Material
Carbon steel to simulate the overpack･Dimensions
82 cm in diameter, 173 cm in height, and 5.8 ton in weight.

Fig. 3.7.3-3 Emplacement method of the buffer (vacuum hoisting method)- 191 -

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Table 3.7.3-4 Design requirements and specification of backfill(1)Design requirements
To prevent tunnels from becoming preferential flow･Hydraulic conductivity
paths, they must be backfilled with materials that<10−9 m/s
have a hydraulic conductivity as low or lower than
the surrounding rock.
･Swelling pressure
Backfill materials need to have swelling properties to>0.1 MPa
ensure close contact with the walls of a tunnel, thus
sealing boundaries and voids between the rock andthe backfill.
(2)Specification･Material
60/40 mixture of debris (rock fragments) and sodium
bentonite･Design dry density≥1.2 g/cm3･Construction method
spreading and compaction (lower part), preformedblock laying (upper part)(a) Image view(b) Spreading & compaction method

Fig. 3.7.3-4 Tunnel sealing technology(a) Image view(b) Emplacement of simulated overpack

Fig. 3.7.3-5 Engineered barrier system experiment at the Horonobe URL- 192 -

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JAEA-Review 2016-014(a) Image view(b) Simulated overpack for corrosion test

Fig. 3.7.3-6 Image view of the overpack corrosion test
3.7.4 Summary
The following results were obtained from R&D on geological disposal technology at the
Horonobe URL project during the second mid-term research phase:(1) Design and engineering technology of a deep geological repository- Confirmation of applicability of the design method for buffer, backfill, plug, support, andgrout to the geological environment of the Horonobe URL.
- The demonstration of an excavation technology of a disposal pit, an emplacement
technology of EBS, a tunnel sealing technology, and a countermeasure against
groundwater inflow.
(2) Evaluation technology of the integrity of the EBS- The embarking upon the experiment on EBS focusing on overpack corrosion, resaturation phenomena in the near-field, displacement of buffer into backfill, interactions
between bentonite, cement, and carbon steel, gas migration in buffer, and intrusion of
buffer into host rock.
The issues in the future R&D on geological disposal technology at the Horonobe URL project
are as follows:- Data acquisition focusing on modeling to evaluate the long-term performance of lowalkaline cement in the geological environment.
- Improvement of the evaluation model for the long-term behavior of EBS and sealingmaterials of drift.
- Demonstration of technologies necessary for operation of the repository including
procedures relating to retrievability from the actual geological environment.
- Demonstration of options for the repository components in the real geologicalenvironment.

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References
1) Ministry of Economy, Trade and Industry and Japan Atomic Energy Agency : “The masterplan about basic R&D program on geological disposal of high-level radioactive wastes andTRU waste in Japan” (2010). (in Japanese).
2) (Eds.) Nakayama, M. Sawada, S. and Sugita, Y. : “Horonobe Underground ResearchLaboratory Program Investigation Report for the 2010 Fiscal Year”, JAEA-Review 2011033 (2011), 80p. (in Japanese).
3) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Oyama, T., Amano, Y., Murakami,
H., Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S., Ohara,
M. and Jin, K. : “Horonobe Underground Research Laboratory Program

Investigation

Report for the 2011 Fiscal Year”, JAEA-Review 2012-035 (2012), 63p. (in Japanese).
4) Nakayama, M., Sawada, S., Sato, H. and Sugita, Y. : “Study on applicability of low alkaline
cement in Horonobe Underground Research Project; In-situ experiment at 250m gallery”,
JAEA-Research 2012-023 (2012), 65p. (in Japanese).
5) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Program Investigation
Report for the 2012 Fiscal Year”, JAEA-Review 2013-037 (2014), 63p. (in Japanese).
6) (Ed.) Hanamuro, T. : “Horonobe Underground Research Laboratory Program Investigation
Report for the 2013 Fiscal Year”, JAEA-Review 2014-039 (2014), 69p. (in Japanese).

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4. Understanding long-term changing/recovering behavior of geo-environmental conditions
4.1 Geology
4.1.1 Introduction
Prediction analysis of the long-term evolution of geological environments, such ashydrogeological, geochemical, and geomechanical conditions, and thermal rock properties, isessential for the safety assessment of a site to be used as a repository.
In terms of this issue, we considered the transition of geological phenomena from the past to
the present, based on an approach to estimate the future evolution by extrapolating highly
probable processes to the future that takes into account a sufficient understanding of major
geological processes and their long-term evolution from the past to the present.
4.1.2 Objectives in the second mid-term research phase
The existing data obtained in the Mizunami and Horonobe areas have been reviewed to reachthe performance target of R&D, as shown in Table 4.1.2-1.
Table 4.1.2-1 Performance target of R&D for perceiving topographical/geologicallong-term evolution
Focus

Performance target of R&D

Decision to begin
disposal

Enable to estimate long-term evolutionof host rock.

Tasks• Demonstration of technique ofinvestigation and interpretation toestimate long-term evolution of
topography and geological structure

4.1.3 Project details and outcomes
The R&D has been carried out for estimating the transition of geological phenomena that
could affect the long-term evolution of the geological environment, such as uplift, subsidence,erosion, topographical changes, folding, as well as discontinuities such as paleo-stress fields,
faults, and fractures. Through these activities, data and technical knowledge regarding thelong-term evolution of the topography and geological structures from the past to the present
have been accumulated.
1) Mizunami
Discontinuities such as fractures are considered to be the major groundwater flow paths incrystalline rocks. Therefore, the histories of uplift, subsidence, and related topographicalchanges and stress field changes that are considered to affect the development process offractures were studied in and around the Mizunami area. Results of these studies are
summarized as follows.
In regards to the uplift and subsidence processes, histories after sedimentation of the
Mizunami Group have been considered around the Mizunami URL site1). The thickness ofeach formation in the Mizunami Group was measured from the borehole investigation dataobtained from the Tono mine located to the west of the site, and the changes in elevation of- 195 -

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the unconformity between the Toki Granite and the Mizunami Group at the time period of thesedimentation of each formation and the unconformity of each formation were estimated,
respectively (Fig. 4.1.3-1). The sea-level change in this estimation was based on results from
Haq et al. (1987)2), while the consolidation and erosion of the stratum at the unconformity
period were not considered. The paleo-topography at the unconformity period was also set toEL-0 m.

Age(x10ka)(10ka)
Age

Fig. 4.1.3-1 Uplift and subsidence rates estimated from the change in thickness of different
strata1)
In addition, Amano et al. (2003)3) estimated the uplift rate using plural methods that focusedon the uplift after sedimentation of the Tokai Group.
Four methods were applied to estimate the average uplift rate from the sedimentation periodof the Tokai Group (estimated to be ca. 1.5 Ma) to the present as a target:
i. Estimation using the dating of the Toki Granite and cooling rate.
ii. Estimation using the altitude of the low relief surface by erosion observed in the TokaiGroup.
iii. Estimation using the height and age of the terrace surfaces.
iv. Estimation using vertical crustal movement during the past 100 years measured by theleveling.
From the results of these estimations, the uplift from 1 Ma to the present in this area wasconsidered to be approximately 250 m to 300 m, and the estimated uplift rates obtained by thefour methods listed above were as follows: i. 0.10–0.14 mm y-1 (assuming that the cooling rate
reflected the uplift rate under the condition of a constant geothermal gradient), ii. 0.25–0.30- 196 -

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mm y-1, iii. 0.10–0.24 mm y-1, and iv. 0.15–0.30 mm y-1.
Though there were differences in the assumption conditions and investigation accuracies
between the different methods, the results showed approximately the same rate. Thus, upliftwith a constant rate was assumed to have occurred from 1 Ma to the present in this area, andthe average uplift rate was considered to be within 0.10–0.30 mm y-1 3).
According to the latest research result, the age of the top part of the Tokai Group (Toki sandy
gravel layer) was estimated to be 1.5 Ma4). Based on this result, the uplift rate of method ii
was estimated to be 0.16–0.2 mm y-1.
The uplift rate (0.11–0.16 mm y-1)5) of the Toki River basin, estimated from the height andage of the terrace surfaces based on the detailed classification of the terrace surfaces of theToki River, was within the above estimated rate.
To evaluate the influence of topographical changes on groundwater flow, a restoration of thepaleo-geography was carried out in the area from the Kiso Mountains to the Nobi Plains6). In
this study, five time section models (ca. 1.5 Ma, 1.1 Ma, 0.6 Ma, 0.2 Ma and present) wereconstructed considering the uplift starting time of major mountains and the transition of eachfault displacement (Fig. 4.1.3-2). However, since the uplift and erosion rates were assumed tobe constant in the study, the actual uplift and erosion rates might not have been properlyreflected.

Fig. 4.1.3-2 Estimated paleo-geography from the Kiso Mountains (upper right) to the Nobi
Plains (lower left)6)
In regard to the stress field changes, the direction of the fault displacement and paleo-stressfields at the age of fault activity was estimated by the multiple inverse method based on the
direction of striations and shear senses of the fault identified by borehole cores drilled at theunderground facility and around the Mizunami URL site7).
The results showed that the maximum principal stress in the target fault in this study wasin a N-S direction with a low angle, the minimum stress was in an E-W direction with a low
angle, the stress ratio was approximately 0.3, and the paleo-stress fields of the lateral fault- 197 -

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were universally obtained. These paleo-stress fields indicated the paleo-stress states at 60
Ma7), as suggested by a previous study using the micro-cracks around the Mizunami URL
site8). The paleo-stress fields estimated to reflect the lifting deformation during the extensionof the Sea of Japan were also confirmed. The paleo-stress changes based on the results of thesestudy and the evolution histories of geological structures around the Mizunami area aresummarized in Fig. 4.1.3-37).
Phase

Age（Ma)Inferred casualstress state

fracture &rotation

σ1
69-64
Intrusion and emplacement of Toki granite

σ1

σ3

64-43
Forming of share zone and faults

43-37

Change the subduction directionof Pacific plate

σ3

σ1

37-20
Exposure of granite

σ3
20-15
Rifting / deposition of
the First Setouchi Supergroup

15-14

Clockwise rotation of the Southwest
Honshu arc/
activation of the Setouchi volcanic rocks

σ1
14-12
Reveres faulting and rapid uplifting

σ2
σ3
12-1

Deposition of
the Second Setouchi Surpergroup
aF
er
At
lt
au

σ1
＜1
Compression deformation of E-W directionaamuy Faultob
ByFig. 4.1.3-3 Evolution histories of geological structures and paleo-stress fields in the
Mizunami area7)
From the above results and the geological history in the Mizunami area (Fig. 4.1.3-4), theformation period of fractures observed by geological mapping at the underground facilities can
be classified as follows: i. the cooling period of the granite, ii. the exposure period of the granite
before sedimentation of the Mizunami Group, and iii. the fault activity period9). Low-angle
fractures in the upper part of the granite were assumed to have been formed by the unloadingof the vertical load induced by erosion during period ii, and high-angle fractures distributed- 198 -

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in the lower part of the granite were assumed to have been formed during periods i and iii.
The fractures observed by geological mapping at the underground facilities were assumed tohave been formed from the time of granitic intrusion to before sedimentation of the Mizunami
Group, because period iii likely occurred before the sedimentation of the Mizunami Group9).
The evolution of geological events in the Mizunami area is summarized in Fig. 4.1.3-4.
70Ma

20Ma
Emergence tosurface(weathering)

17Ma

16Ma

15Ma

Tsukiyoshi Fault activity(nornmal fault)

Fracturing (highand low‐angles
fractures)(Start of
opening ofJapan Sea)

12Ma

Tsukiyoshi Fault
activity (reverse
fault)
Emergence(unconformity)(Termination of opening of Japan Sea)

Tectonism

Emergence(unconformity)
and progress ofstrongweathering

Onset ofexhumation?

Present

Activation of fault
activity?
Activation of
exhumation?
Supply of gravel
Formation of gentle slope

Formation of low‐relief surface

Formation of small
collapse basin (depositionof Tokiguchi Porcelain Clay
Formation)

Tokai Group(c. 12 to 1.5Ma)
Supply of mud andsand (quartz grain)

Deposition of fresh Deposition of
Deposition of deep
Mizunamiwater formation
shallow marine
marine formation(Toki
Lignite‐formation(Akeyo(OidawaraGroupbearing and Hongo Formation)
Formation)
Formations)(c.20 toEmergence
15Ma) Supply of gravel(unconformity)
and sand

1.5Ma

Onset of fault
activity?

Progressive diagenesis?

Exhumation of granite

Supply of gravel

Emergence(unconformity)

Period of erosion(exposed granite
was strongly
weathered)

Formation of weathered zone
Cooling (exhumation)
Solidification of
granitic magma

Formation of large‐
scale river(Deposition of Toki
Sand and Gravel
Formation)

Onset of uplift ofbasement rockarea?

Basement rock(mainly Toki Granite)

Fig. 4.1.3-4 Evolution of the geological events in the Mizunami area
2) Horonobe
Sedimentary rocks are generally treated as porous media. However, groundwater isconsidered to flow through not only the pores of the particles in sedimentary rocks but also
through faults and fractures formed in solid sedimentary rocks due to the progression of burial
diagenesis.
The histories of uplift, subsidence, erosion from the past to the present and related
topographical changes, and burial diagenesis and changes in stress fields from the past to thepresent were studied, as these phenomena were expected to influence the evolution of
sedimentary structures. The results of these studies are summarized as follows.
In regard to the uplift and subsidence, the uplift rate was estimated from marine terrace
surfaces and the crustal horizontal strain rate was estimated from a geodetic method using
GPS observation data and triangular survey data, as well as a geological method based on
active tectonics10),11).

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The uplift rate was calculated by subtracting the eustatic change in sea level from the former
shore line level of the marine terrace according to Koike and Machida (2001)12) and Koaze etal. (2003)13). The rates estimated from the marine terraces in the western part of the Horonobe
area are shown in Fig. 4.1.3-510),11). A maximum difference of approximately a factor of two
was observed in the uplift rate estimations, which was attributed to the differences in the MIS(Marine oxygen Isotope Stage) correlation of the marine terraces reported in Koike andMachida (2001)12) and Koaze et al. (2003)13). Koike and Machida (2001)12) based their uplift
rate estimation on MIS 7 and obtained a value of 0.29–0.34 m ky-1, whereas Koaze et al.
(2003)13) reported an estimated value of 0.16–0.26 m ky-1. The uplift rate near the Sarobetsu
Anticline, which is an active fold, was estimated to be larger than that for the surroundingarea based on the MIS correlation reported by Koike and Machida (2001) 12). Taking MIS 5e as
an example, the rate is approximately 0.60 m ky-1 at the anticlinal axis and 0.48 m ky-1 at thefold limb, indicating the presence of local uplift at the anticlinal axis owing to the activity of
the Sarobetsu Anticline14).

Fig . 4.1.3-5 Plot of uplift versus time for a sequence of marine-terrace surfaces10)(Modified from Niizato and Yasue, (2005)14)).
The solid circles for estimation by Koike and Machida (2001)12) and Koaze et al., (2003)13).
The open triangles indicate marine-terrace surfaces at the Sarobetsu Anticline in this study.
The uplift/subsidence history for the Horonobe area is summarized in Fig. 4.1.3-611), basedon the present depth, thickness, depositional age15), and depositional environment of eachformation and paleogeography in the area. The thickness and depositional age of eachformation in the Sarobetsu Lowland were taken from existing information16),17). The
palaeowater depth during the time of sedimentation of each formation was estimated from thesedimentary facies of each formation18) on the basis of the relationship between thesedimentary facies and water depth19),20). Altitudes relative to the current sea level wereobtained from sea levels during the period of sedimentation of each formation using theeustatic change curve of sea-level2),21) and palaeowater depth. Fig. 4.1.3-6 represents theoverall trend of uplift/subsidence in the Horonobe area, although it is based on someassumptions such as the exclusion of a potential decrease in the thickness of the formation- 200 -

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due to compaction, isostatic uplift, and subsidence.

Fig. 4.1.3-6 Uplift and subsidence history in the Horonobe area11)
The amount and rate of erosion were estimated on the basis of the ambient air temperature,
paleogeothermal gradients, and the transformation of the silica minerals11). Palaeogeothermal
gradients in and around the Horonobe area have been obtained in the north (MITI Tenpoku
borehole) and the southeast (Kitakawaguchi SK-1 borehole) of Horonobe Town22). From these
data, the palaeogeothermal gradient in the Horonobe area was estimated to be 3.5 °C per 100
m. For the ground surface temperature of the Horonobe area, the average temperature at themouth of 13 boreholes (including MITI Tenpoku borehole11) and the average ambient air
temperature observed at the JMA Teshio Weather Station from 1979 to 2000 were 15 °C and6.2 °C, respectively. The amount of erosion (denudation) was estimated by taking thesetemperatures as the ground surface temperature at the time when the palaeogeothermal
gradients were obtained11). The transformations of the silica minerals were attributed toburial diagenesis and were not influenced by igneous and hydrothermal activity after
diagenesis, based on results from the surface geological surveys and borehole investigationsin and around the Horonobe area. Given the above conditions, the depth where amorphous- 201 -

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silica (opal A) became low-temperature cristobalite (opal CT) in the past was assumed to occur
at approximately 860–1,250 m. The amount of erosion could be estimated from the differences
between these depths and the depth of the current boundary between opal A and opal CT. As
a result, the amount of erosion at the locations of the borehole investigation was estimated to
be at least 435–820 m11). The boundary between the Wakkanai Formation and the Koetoi
Formation exposed at the ground surface was consistent with the boundary between opal A
and opal CT. Thus, the boundary could be used as the reference surface for estimating theamount of erosion (denudation). A contour map was drawn for the amount of erosion in the
Hokushin district of Horonobe Town based on the boundary between opal A and opal CT ateach borehole location and between the Wakkanai Formation and Koetoi Formation on the
ground surface (Fig. 4.1.3-7).
In the case where the temperature for opal A to become opal CT is 45 °C and the groundsurface temperature is taken as 15 °C, the amount of erosion was presumed to be in excess of
860 m at the anticlinal axis and approximately 275 m around borehole HDB-7 at the limb of
the anticline. For the areas in and around the Hokushin district, distances of approximately
860 m and 1,250 m above the boundary between opal A and opal CT corresponded to locations
at the base of the Sarabetsu Formation and within the Sarabetsu Formation, respectively.
Therefore, the Hokushin district could be considered to not have been a subsidence area since
0.7–1.3 Ma, which is the depositional age of the Sarabetsu Formation23). The values of theerosion amount were converted to erosion rates (per 1,000 years), resulting in estimated valuesof approximately 0.66–1.79 m ky-1 at the anticlinal axis, where the uplift was the largest, andapproximately 0.21–0.86 m ky-1 at the limb of the anticline, where the uplift was smaller11).

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Fig. 4.1.3-7 Amount of erosion in the URL area11)
The orange circles indicate the location of the boreholes used for estimating the amount oferosion.
The Koetoi and Wakkanai formations, which are composed of biogenic fine-grained siliceous
rocks, are distributed in the Horonobe area. Silica minerals contained in siliceous sediments
were transformed from opal A to opal CT and then to low-temperature quartz24) owing to burial
processes and temperature increases. The transformation of silica minerals, along with zeolite
and feldspar with an abundance of Na and Ca, is known as the mineral index of burial
diagenesis. The transformation of silica minerals, in particular, is strongly controlled bychanges in temperature owing to the burial of sediments25).
Based on the results of visible and electron microscopic observations and X-ray diffraction
analysis26), the typical minerals that constitute the Koetoi and Wakkanai formations wereidentified as silica minerals (opal CT/opal A) with minor amounts of quartz, feldspar, clay
minerals (kaolinite, smectite, illite, chlorite), pyrite, and carbonate minerals (siderite,
magnesite). However, there was a large difference in the silica mineral phase between the
Wakkanai Formation and the Koetoi Formation, where the Wakkanai Formation wasconstituted mainly of opal CT formed by the burial and diagenesis of diatom remains (opal A),
while the Koetoi Formation did not contain opal CT.
In regard to the horizontal strain rate, the amount of horizontal shortening and thehorizontal strain rate around the Horonobe area were estimated by a geodetic method using
GPS observation data and triangular survey data, and by a geological method using active
tectonics data and geological cross-sections. The estimate for the strain rate in the Horonobe
area was 10-8–10-7 y-1 with the geodetic method and 10-9–10-8 y-1 with the geological method.

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The values obtained using the two methods were similar, and the strain rate obtained fromthe geological method was smaller than that obtained from the geodetic method by less thana factor of 10. It is generally the case that estimates using the geological method based on dataon active faults and historical earthquakes tend to be smaller than those obtained by thegeodetic method by a factor of around 10.
From the viewpoint of long-term stability of the geological environment, the trend of thecrustal movement and the horizontal crustal strain rate should be obtained using thegeological method that covers a duration of more than several tens of thousands of years11).
In regard to the change in stress states, analysis using GPS observation data and the
direction of striations and shear planes of minor faults were carried out to understand thepaleo-stress fields around the northern part of Hokkaido. From the results, horizontal
displacement vectors based on GPS observations displayed E-W compressive stress. This
result coincided with the direction of maximum principal stress obtained by hydraulicfracturing tests carried out using boreholes. Therefore, the present stress field in the Horonobe
area appeared to be in an E-W compressive stress state27). The direction of the maximum
principal stress obtained by analysis using minor faults was several tens of degrees of rotation
counterclockwise from the E-W direction27). The difference of these stress fields could becorrected by taking the folding process into account during the deposition state28),29). This
result suggested that the E-W compressive stress field had not changed since the time offormation of these minor faults in the Horonobe area. Although the present stress state andpaleo-stress state had been discussed individually, the results enabled the estimation of thetransition of stress states from the past to the present by considering the evolution of thegeological structures.
An analog model experiment using a sandbox device was carried out to develop thetechniques for understanding the evolution process of geological structures (such as a fault
and a fold) and estimating the quantitative uplift and subsidence rates induced by theevolution. From the experiment, the trend of the geological displacement associated with theevolution process of faults could be observed quantitatively30).
Based on the R&D to date, natural events and processes in the Horonobe area could besummarized31). Furthermore, the techniques for modeling and analysis enabled threedimensional geological modeling and groundwater flow analysis to consider the evolution of
the geological environment including folds, faults, uplift/subsidence, erosion, decreases in the
thickness of the formation owing to compaction, and changes in the groundwater recharge andshoreline (Fig. 4.1.3-8 and Fig. 4.1.3-9)32),33). In addition, technical knowledge for estimating
topographical and geological long-term evolution could be accumulated, and an approach andprocedure for constructing the topographical and geological evolution model could be
developed.

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Uplift, Erosion

Change of groundwater recharge rate
Sedimentation interrestrial
environment

Sedimentation,
Subsidence

Sea-level change

・Folding
・Displacement of fault

・Compaction
・Change of waterpressure and effective
stressFig. 4.1.3-8 Diagram of the considered geological events

Fig. 4.1.3-9 Topographical and geological evolution model constructed by the sequential
modeling system (SMS) of the impact of geological evolution on groundwater flow32)
4.1.4 Summary
Techniques and accumulated technical knowledge regarding the investigation, analysis, andassessment for estimating the long-term evolution of the topography and geological structurefrom the past to the present are as stated below:- In regard to the transition of stress states from the past to the present, the present stressstate and paleo-stress state were discussed individually. The results enabled thedevelopment of a technique to estimate the stress states by considering the formation andevolution of geological structures.
- Technical knowledge for estimating topographical/geological long-term evolution has
been

accumulated,

and

an

approachandprocedure

for

constructing

thetopographical/geological evolution model have been developed.
- Techniques for modeling and analysis enabled three-dimensional geological modeling and- 205 -

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groundwater flow analyses to consider the evolution of the geological environment
including folding, fault activity, uplift/subsidence, erosion, decreases in the thickness ofthe formation owing to compaction, and the change in groundwater recharge andshoreline.
In future studies, improvement in the accuracy of the constructed model based on theaccumulation of knowledge of long-term geological phenomena is required. Furthermore, thedevelopment of techniques for evaluating uncertainties in modeling and analyzing and therange of influence of natural events such as faults and fractures is needed.
Reference
1) Sasao, E., Amano, K. and Ota, K. : “Natural analogue study in the Tono uranium deposit Quantitative estimation of uplift and subsidence, and vertical displacement rate -”, Journalof Nuclear Fuel Cycle and Environment, Vol.11, No.2, pp.167-180 (2005). (in Japanese)
2) Haq, B.U., Hardenbol, J. and Vail, P.R. : “Chronology of Fluctuating Sea Levels Since theTriassic”, Science, Vol.235, pp.1156-1167 (1987).
3) Amano, K., Sasao, E. and Ota, K. : “Tono Natural Analogue Project-Exhumation processes
at the Tono area”, Abstract of 2003 Annual Meeting of the Atomic Energy Society of Japan,
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4) Todo Collaborative Research Group : “Fault bounded inland basin of multiple blocks : anexample from the sedimentary basin of the Tokai Group around Tajimi City in Gifu
Prefecture, central Japan”, Earth Science(Chikyu Kagaku), vol.53, pp.291-306 (1999). (inJapanese).
5) Tajikara, M., Yasue, K., Yanagida, M., Furusawa, A., Tanaka, N., Morita, Y. and Sugai, T. :“Fluvial terrace and geomorphology in the Tokigawa (Shonaigawa) river basin since themiddle Pleistocene”, Geographical Review of Japan Series A, Vol.84, No.2, pp.118-130(2011). (in Japanese).
6) Onoe, H., Sasao, E., Saegusa H. and Kosaka H. : “Numerical Assessment of the Influenceof Long-Term Topographic Change on Deep Groundwater Flow Conditions”, Transaction of
the Atomic Energy Society of Japan, Vol.8, No.1, pp.40-53 (2009). (in Japanese).
7) Tagami, M., Yamada, Y., Yamashita, Y., Miyakawa, A., Matsuoka, T., Xeu, Z., Tsuji, T.,
Tsuruta, T., Amano, K., Hama, K. and Sasao, E. : “Development of Geological Structure
Modeling Technology Based on Regional Tectonic Process (Joint Research)”, JAEAResearch 2012-036 (2013), 110p. (in Japanese).
8) Takagi, H., Miwa, S., Yokomizo, Y., Nishijima, K., Enjoji, M., Mizuno, M. and Amano, K. :“Estimation of the paleostress field from the 3-D orientation distribution of microcracks
and their geothermal conditions in the Toki Granite, central Japan” Journal of theGeological Society of Japan, Vol.114, No.7, pp.321-335 (2008). (in Japanese).
9) Sasao, E. and Ishibashi, M. : “Long-term history of geological environment at the Mizunami
Underground Research Laboratory from the perspective of formative process of fractures”,
Annual Meeting of the Geological Society of Japan, Vol.2013 (2013). (in Japanese).

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10) Ota, K., Abe, H., Yamaguchi, T., Kunimaru, T., Ishii, E., Kurikami, H., Tomura, G.,
Shibano, K., Hama, K., Matsui, H., Niizato, T., Takahashi, K., Niunoya, S., Ohara, H.,
Asamori, K., Morioka, H., Funaki, H., Shigeta, N. and Fukushima, T. : “Horonobe
Underground Research Laboratory Project Synthesis of Phase I Investigations 2001 - 2005
Volume "Geoscientific Research"”, JAEA-Research 2007-044 (2007), 434p. (in Japanese).
11) (Eds.) Ota, K., Abe, H. and Kunimaru, T. : “Horonobe Underground Research Laboratory
Project Synthesis of Phase I Investigations 2001 - 2005 Volume "Geoscientific Research"”,
JAEA-Research 2010-068 (2011), 370p.
12) Koike, K. and Machida, H. : “Atlas of Quaternary Marine Terraces in the Japanese Islands”,
Univ. Tokyo Press (2001). (in Japanese).
13) Koaze, T., Nogami, M., Ono, Y. and Hirakawa, K. (Eds.) : “Geomorphology of Hokkaido”,
Regional geomorphology of the Japanese Islands, 2, Univ. Tokyo Press (2003). (in Japanese).
14) Niizato, T. and Yasue, K. : “A study on the long-term stability of the geologicalenvironments in and around the Horonobe area -Consideration of the site specific featuresin assessing of the long-term stability of the geological environments-”, Journal of Nuclear
Fuel Cycle and Environment, Vol.11, No.2, pp.125-138 (2005). (in Japanese).
15) Yasue, K., Akiba, A., Ohira, H. and Ishii, E. : “The upper Pliocene diatom zone and fissiontrack age of the upper Koetoi Formation around the Sarobetsu anticline, northern
Hokkaido”, Journal of the Geological Society of Japan, Vol.112, No.4, pp.284-293 (2006). (inJapanese).
16) Advanced Industrial Science and Technology : “Paleoseismology and Activity Study of theSarobetsu Fault Zone”, Report of the additional and complementary survey of the fault zone
in the fundamental earthquake survey, No. H17-1 (2005). (in Japanese).
17) Oka, T., Igarashi, Y. and Hayashi, M. : “Study of the alluvial deposits (Alluvium) in theTeshio plain by the analyzing drilling data and pollen analysis”, Rep. Geol. Surv. Hokkaido,
No.77, pp. 17-75(2006). (in Japanese).
18) Fukusawa, H., Hoyanagi, K. and Akiyama, M. : “Stratigraphic and paleoenvironmental
study of the Neogene formations in northern Central Hokkaido, Japan”, Mem. Geol. Soc.
Japan, 37, pp.1-10 (1992). (in Japanese).
19) Walker, R.G. : “Wave- and storm-dominated shallow marine systems, In Facies Models;
response to sea level change (R.G. Walker & N.P. James eds.)”, Geological Association of
Canada, pp.219-238 (1992).
20) Seibold, E., Berger, W.H. and Niitsuma, N. : “Origin and topography of the ocean margin”,
In: Seibold, E., Berger, W.H. and Niitsuma, N. The Sea Floor – An Introduction to Marine
Geology, Springer-Verlag Tokyo, pp.25-48 (1986). (in Japanese).
21) Chappell, J. : “Upper Quaternary Sea Levels, Coral Terraces, Oxygen Isotopes and Deepsea Temperatures”, Journal of Geography, 103(7), pp.828-840 (1994).
22) Japan National Oil Corporation : “Report on the MITI Tenpoku Drilling” (1995). (inJapanese).
23) Oka, T. and Igarashi, Y. : “Latest Cenozoic formations in the northern part of Teshio Plain,
Hokkaido -Sedimentary facies and pollen stratigraphy-”, In: Kawamura M., Oka T. and- 207 -

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Kondo T. (Eds.) Commem. Vol. Prof. M. Kato, pp. 341-365 (1997). (in Japanese).
24) Aoyagi, K. and Kazama, T. : “Transformational changes of clay minerals, zeolites and silica
minerals during diagenesis”, Sedimentology, Volume 27, Issue 2, pp.179-188 (1980).
25) Iijima, A. and Tada, R. : “Silica diagenesis of Neogene diatomaceous and volcaniclastic
sediments in northern Japan”, Sedimentology, Volume 28, Issue 2 pp.185-200 (1981).
26) Ishii, E., Hama, K., Kunimaru, T. and Sato, H. : “Change in groundwater pH by infiltrationof meteoric water into shallow part of marine deposits”, Journal of the Geological Societyof Japan, Vol.113, No.2, pp.41-52 (2007). (in Japanese).
27) Tokiwa, T., Asamori, K., Ishii, E. and Funaki, H. : “Stress transition estimated by GPS
observation and fault-striation analysis in the Horonobe area, northern Hokkaido”, Annual
Meeting of the Geological Society of Japan, Vol.2009 (2009). (in Japanese).
28) Ishii, E., Sanada, H., Funaki, H., Sugita, Y. and Kurikami, H. : “The relationships among
brittleness, deformation behavior, and transport properties in mudstones: An example fromthe Horonobe Underground Research Laboratory, Japan”, Journal of Geophysical Research,
Vol.116, B09206, pp.1-15 (2011).
29) Ishii, E. : “Microstructure and origin of faults in siliceous mudstone at the Horonobe
Underground Research Laboratory site, Japan”, Journal of Structural Geology, Vol.34,
pp.20-29 (2012).
30) Matsuzaki, T., Tokiwa, T., Nakatsukasa, M., Yamada, Y., Akamine, S., Amano, K. andNiizato, T. : “An Attempt at quantitative estimation of the uplift rate by using of analogue
model experiments; a case study of Horonobe area, northern Hokkaido”, Annual Meetingof the Geological Society of Japan, Vol.2012 (2012). (in Japanese).
31) Niizato, T., Amano, K., Ota, K., Kunimaru, T., Lanyon B. and Alexander W.R. :“Development of Comprehensive Techniques for Coastal Site Characterisation: Part 3 Conceptualisation of Long-Term Geosphere Evolution”, Proceedings of 13th International
Conference on Environmental and Radioactive Waste Management (ICEM2010), ASME,ICEM2010-40052 (2010).
32) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Ohyama, T., Amano, Y., Murakami,
H., Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Niizato, T., Tanaka, S., Ohhara, M.
and Jin, K. : “Horonobe Underground Research Laboratory Project Investigation Report forthe 2011 Fiscal Year”, JAEA-Review 2012-035 (2012), 63p. (in Japanese).
33) (Ed.) Nakayama, M. : “Horonobe Underground Research Laboratory Project Investigation
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4.2 Hydrogeology
4.2.1 Introduction
The objective of the study is to establish the following techniques of investigation, analysis,
and assessment for estimation of long-term evolutionary ranges of groundwater flow
conditions over geological time scales.
It is assumed that the groundwater flow field, which contains the following, and the spatial
variability of groundwater flux will evolved as a result of natural events and processes suchas landform and climatic changes over geological time scales.
- Groundwater flow system from recharge area to discharge area
- Type of groundwater flow condition (advective field and diffusive field)- Type of driving force of groundwater flow (hydraulic gradient, density flow, and thermal
convection)
From these hydrogeological points of view, the features to be focused on and processes to be
characterized and the resulting data requirements relevant to safety assessment, design, andconstruction were identified1),2)(1) Long-term evolution of the groundwater flow field(2) Long-term evolution of the spatial variability of groundwater flux
4.2.2 Objectives in the second mid-term research phase
The following studies have been performed to achieve the performance target of R&D forperceiving long-term evolution and recovery behavior of groundwater flow conditions (Table
4.2.2-1):- Enable estimation of the long-term stabilities of hydraulic characteristics andgroundwater flow conditions
Table 4.2.2-1 Performance target of R&D for perceiving the long-term evolution and recovery
behavior of groundwater flow conditions
Focus

Performance target of R&D

Tasks

Decision to begin
disposal

Enable estimation of long-term stabilities
of hydraulic characteristics andgroundwater flow condition.

• Techniques of investigation, analysis,
and assessment for estimation of longterm evolutionary ranges ofgroundwater slow conditions overgeological time scales

4.2.3 Project details and outcomes
Features and processes that mainly affect the long-term evolution of groundwater flow
condition are specified and the hypothesized long-term evolution of groundwater flow
conditions is listed in Table 4.2.3-1.

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Table 4.2.3-1 Hypothesized long-term evolution of groundwater flow conditions
Feature &process

Hypothesized long-term evolution of groundwater flow conditions

Landform• Evolution of topography such as mountain making affects groundwater flow
system (recharge and discharge area, and flow path) and hydraulic gradientHydraulicproperty• Evolution of hydraulic property of rock affects groundwater flow velocity• Evolution of hydraulic property of large-scale discontinuous structures such as
fault affects groundwater flow system and hydraulic gradient(Evolution of hydraulic property is occurred by changes of porosity of rock, anddensity, orientation, trace length and mineral filling of fracture, which may becaused by evolution of overburden pressure due to geological processes suchas subsidence and sedimentation.)

Thermalgradient• Evolution of thermal gradient may cause additional driving force ofgroundwater flow, such as thermal convection

Salinity
concentration• Evolution of salinity concentration may cause additional driving force ofgroundwater flow, such as density flow

Fault motion(Earthquake
activity)• Fault motion may cause volumetric strain of rock and change hydraulicproperty, which then affect spatial variability of groundwater pressure

Recharge rate

• Evolution of recharge rate, which occurs as a result of climatic andtopographic evolution, affects groundwater level distribution, and then it affectgroundwater flow system, hydraulic gradient and dilution effectSea levelchange• See level change affects groundwater flow system (location of discharge area)

1) Mizunami
In the case of the Tono region, it is supposed that thermal convection because of hydrothermal
activity had occurred and the hydraulic properties had evolved for several million years.
Therefore, influential factors have been identified based on the following groundwater flow
analyses taking into account landform and climatic changes3). Climatic change has beenmodeled as changes of recharge rate.
- Regional groundwater flow analysis taking into account paleo-topography and climaticchange4) (Fig. 4.2.3-1, Fig. 4.2.3-2)- Local groundwater flow analysis based on restored paleo-topography using riverterraces5),6) (Fig. 4.2.3-3)- Local groundwater flow analysis based on topography estimated by the landform
development simulation7) (Fig. 4.2.3-4)- Local groundwater flow analysis taking into account landform changes and change offault distributions such as hydrogeological continuity in the depth direction andconnectivity in the lateral direction8) (Fig. 4.2.3-5)
The results of these groundwater flow analyses demonstrate that landform and climaticchanges have the potential to affect hydraulic gradient. On the other hand, these results show

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that some groundwater flow systems are not affected by the landform and climatic changes.
Based on the results, the areas of groundwater flow analyses in Fig. 4.2.3-3 and Fig. 4.2.3-4
have been assigned. Additionally, it was inferred that the influence of changes in fault
distribution is smaller than those of landform and climatic changes.
Groundwater pressure changes have been measured in several boreholes in Mizunami (Fig.
4.2.3-6). An overview of the changes caused by the 2011 off the Pacific coast of Tohoku
Earthquake can be summarized as follows9):- Groundwater pressure changes shortly after the earthquake were caused by volumetricstrain induced by the earthquake.
- Groundwater pressure recovery took at most two years after the earthquake.
- Changes in the vertical and horizontal hydraulic gradient after the earthquake were
negligibly small.
- Different trends of changes in groundwater pressure indicate that faults are likely
boundaries of groundwater flow zones.
Based on the results of groundwater flow analyses and measurements of groundwaterpressure changes, the geological synthesized scenario for modeling long-term evolution ofgroundwater flow conditions is summarized in Fig. 4.2.3-7.
For the groundwater flow analysis, development of a method for estimation of the recharge
rate during glacial stages is important. Therefore, existing information on climate, which is
the important parameter of surface hydrological conditions, was reviewed. The relationships
between mean annual temperature and evapotranspiration and between latitude andevapotranspiration display an approximately positive correlation (Fig. 4.2.3-8)6). The
correlation suggests that approximate evapotranspiration rates can be estimated using themean annual temperature value and latitude.

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Fig. 4.2.3-1 Results of restoration of paleo-topography and groundwater flow analysis basedon the paleo-topography in the region from the Kiso Mountains to Ise Bay (Tono region)

Fig. 4.2.3-2 Modeled hydraulic head distributions from groundwater flow analyses focusing
on the impact of recharge rate (Tono region)- 212 -

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Fig. 4.2.3-3 Paleo-topography restored based on river terraces and groundwater flow
analysis based on the paleo-topography (Tono region)

Fig. 4.2.3-4 Results of landform development simulation and groundwater flow analysis
based on topography estimated by the simulation (Tono region)- 213 -

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Fig. 4.2.3-5 Results of groundwater flow analysis taking into account topographic changes
and fault distributions (Tono region)

Fig. 4.2.3-6 Groundwater pressure changes caused by the 2011 off the Pacific coast of Tohoku
Earthquake (Tono region)- 214 -

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Fig. 4.2.3-7 Geological synthesized scenario for modeling the long-term evolution ofgroundwater flow conditions (Tono region)

Fig. 4.2.3-8 Relationship between mean annual temperature and evapotranspiration (left),and between latitude and evapotranspiration (right)
2) Horonobe
In Horonobe, regional groundwater flow analysis has been performed taking into accountlandform changes including sea level change, change of recharge rate because of climaticchange, and evolution of hydraulic properties because of burial and compaction10),11),12).
An unsteady state groundwater flow simulation system named SMS (Sequential Modeling
System for evolution of groundwater flow), which can take into account natural events andprocesses such as topographical, geological, and hydrogeological changes because of uplift and- 215 -

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denudation and temporal changes in recharge rate caused by climate change, has beendeveloped and applied13) (Fig. 4.2.3-9, Fig. 4.2.3-10). The results of groundwater flow analysis
using SMS show that landform and climatic changes including sea level change and evolutionof hydraulic properties resulting from burial and compaction have the potential to affect thehydraulic gradient.
Groundwater level changes were also measured in several boreholes in Horonobe14),15) (Fig.
4.2.3-11). An overview of the changes caused by the 2011 off the Pacific coast of Tohoku
Earthquake can be summarized as follows:- Groundwater level changed as a result of the earthquake in the zone with relatively highhydraulic conductivity (≧10−6 m/sec：C, D, E in Fig. 4.2.3-11).
- Groundwater level recovery took several months after the earthquake.
- There is no clear relationship between the recovery period and the hydraulic conductivity.
Based on the results of groundwater flow analysis and measurements of groundwaterpressure changes, the geological synthesized scenario for modeling the long-term evolution ofgroundwater flow condition is summarized in Fig. 4.2.3-12.

Fig. 4.2.3-9 Overall procedure used in SMS- 216 -

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Fig. 4.2.3-10 Geological evolution model and results of groundwater flow analysis(Horonobe region)

Fig. 4.2.3-11 Groundwater pressure changes caused by the 2011 off the Pacific coast of
Tohoku Earthquake (Horonobe region)- 217 -

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Fig. 4.2.3-12 Geological synthesized scenario for modeling the long-term evolution ofgroundwater flow conditions (Horonobe region)
4.2.4 Summary
Techniques and accumulated technical knowledge regarding individual techniques ofinvestigation and analysis for estimation of the long-term evolutionary ranges of groundwaterflow conditions over geological time scales are as stated below:- To understand the effects of long-term geological phenomena on groundwater flow
conditions, groundwater flow modeling taking into account topographic and climaticchanges is useful.
- Groundwater pressure changed shortly after the 2011 off the Pacific coast of Tohoku
Earthquake, and groundwater pressure recovery took at most two years after theearthquake.
- Changes in the vertical and horizontal hydraulic gradient after the earthquake were
negligibly small.
In further, studies will be done to solve the open issues described below:- Development of techniques of investigation, analysis, and assessment for identificationof long-term geological phenomena affecting groundwater flow conditions and estimationof the long-term evolutionary ranges of groundwater flow condition.
- Understanding of the mechanisms generating groundwater pressure changes and theirinfluences on hydraulic characteristics and groundwater flow conditions.

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References
1) Ohsawa, H., Ota, K., Hama, K., Sawada, A., Takeuchi, S., Amano, K., Saegusa, H.,
Matsuoka, T., Miyamoto, T., Toyoda, G., Iwatsuki, T., Maekawa, K., Kunimaru, T., Niizato,
T., Asamori, K., Hiraga, M., Yamanaka, Y., Shigehiro, M., Shimada, A., Abe, H. and Umeki,
H. : “Establishment of advanced integration technology for site characterization of deep
geological repository - Development of information synthesis and interpretation system Annual report 2007”, JAEA-Research 2008-085 (2008), 742p. (in Japanese).
2) Saegusa, H., Matsui, H., Hama, K., Sato, T., Tsuruta, T., Takeuchi, R., Kunimaru, T.,
Matsuoka, T. and Mizuno, T. : “Concept and Procedure of Geoscientific Study in the
Mizunami Underground Research Laboratory Project - Study Plan on Construction Phase(Phase II) and Operation Phase (Phase III) to 500m Depth”, JAEA-Review 2011-022 (2011),
78p. (in Japanese).
3) Kusano, T., Asamori, K., Kurosawa, H., Saito-Kokubu, Y., Tanigawa, S., Negi, T., Hanamuro,T., Yasue, K., Yamasaki, S., Yamada, K., Ishimaru, T. and Umeda, K. : “Research on
geosphere stability for long-term isolation of radioactive waste (Progress report for fiscal
years 2005-2009: H22 report)”, JAEA-Research 2010-044 (2011), 153p. (in Japanese).
4) Onoe, H., Sasao, E., Saegusa, H. and Kosaka, H. : “Numerical assessment of the influenceof long-term topographic change on deep groundwater flow conditions”, Transactions of theAtomic Energy Society of Japan, Vol.8, No.1, pp.40-53 (2009). (in Japanese).
5) Kosaka, H., Saegusa, H., Kusano, T., Yasue, K., Takeuchi, R., Tajikara, M., Onoe, H. andShiomi, T. : “Study of the methodology for estimation of the influence of long-term
topographic and climatic change on deep groundwater flow conditions in the case of Tono
area (Part 2) - Groundwater flow modeling and simulation considered of long-term
topographic and climatic change -”, Proceedings of the 2009 fall Meeting, Japanese
Association of Groundwater Hydrology, pp338-343 (2009). (in Japanese).
6) Kosaka, H., Saegusa, H., Yasue, K., Kusano, T. and Onoe, H. : “Development of a
Methodology for the Characterisation of the Long-term Geosphere Evolution (2) Estimationof the Long-term Evolution of Groundwater Flow Conditions in a Tono Area Case Study”,
19th International Conference on Nuclear Engineering Chiba, Japan, May 16-19 (2011).
7) Saegusa, H., Yasue, K., Onoe, H., Moriya, T. and Nakano, K. : “Numerical assessment of theinfluence of topographic and climatic perturbations on groundwater flow conditions, In
Stability and Buffering Capacity of the Geosphere for Long-term Isolation of Radioactive
Waste: Application to Crystalline Rock”, edited by Nuclear Energy Agency, Workshop
Proceedings Manchester, United Kingdom 13-15 November 2007, Organization for
Economic Co-operation and Development (OECD), pp.257-267, Paris (2009).
8) Kawaguchi, T., Saegusa, H., Niwa, M., Shimada, K., Yasue, K., Kurosawa, H., Kamataki, T.
and Tosaka, H. : “Regional hydrogeological analysis factored in tectonics and climaticchanges; Case study in Tono Area, Gifu Prefecture”, Proceedings of the 2007 fall Meeting,Japanese Association of Groundwater Hydrology, pp.36-41 (2007). (in Japanese).
9) Niwa, M., Takeuchi, R., Onoe, H., Tsuyuguchi, K., Asamori, K., Umeda, K. and Sugihara,
K. : “Groundwater pressure changes on Central Japan induced by the 2011 off the Pacific- 219 -

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coast of Tohoku Earthquake”, Geochemistry Geophysics Geosystems, vol.13(5), Q05020(2012).
10) Niizato, T., Yasue, K., Kurikami, H., Kawamura, M. and Ohi, T. : “Synthesizing
geoscientific data into a site model for performance assessment: a study on the long-term
evolution of the geological environment in and around the Horonobe URL, Hokkaido,
northern Japan”, Proceedings of an OECD/NEA third AMIGO workshop, Approaches andchallenges for the use of geological information in the safety case for deep disposal ofradioactive waste, 15-17 April 2008, Nancy, France, pp.222-234 (2009).
11) Niizato, T., Amano, K., Ota, K., Kunimaru, T., Lanyon, B. and Alexander, W. R. :“Development of Comprehensive techniques for coastal site characterisation (3)Conceptualisation of long-term geosphere evolution”, Proceedings of the 13th International
Conference on Environmental Remediation and Radioactive Waste Management,
ICEM2010-40052 (2010).
12) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Ohyama, T., Amano, Y., Murakami,
H., Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S.,
Ohhara, M. and Jin, K. : “Horonobe Underground Research Laboratory Project;
Investigation report for the 2008 fiscal year”, JAEA-Review 2012-035 (2012), 63p. (inJapanese).
13) Imai, H., Yamashita, R., Shiozaki, I., Urano, K., Kasa, H., Maruyama, Y., Niizato, T. andMaekawa, K. : “Study on the effects of long-term evolution of geological environment on
groundwater flow”, JAEA-Research 2009-001 (2009), 116p. (in Japanese).
14) Miyakawa, K., Nohara, T., Yamazaki, M. and Tokiwa, T. : “Groundwater level changes
related to Tohoku-oki earthquake at deep monitoring boreholes in Northern Hokkaido”,
Proceedings of the 2011 fall Meeting, Seismological society of Japan, p.269 (2011). (inJapanese).
15) (Eds.) Nakayama, M., Sawada, S. and Sugita, Y. : “Horonobe Underground ResearchLaboratory Project; Investigation report for the 2010 fiscal year”, JAEA-Review 2011-033(2011), 80p. (in Japanese).

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4.3 Hydrogeochemistry
4.3.1 Introduction
For the issues surrounding geological isolation of HLW, estimation of the long-termhydrogeological and hydrochemical conditions of the groundwater system is required for thesafety assessments. To satisfy this requirement, paleo-hydrogeological analysis was performed
with construction of a scenario conception on past groundwater compositions, groundwaterflow rates, and flow directions, using a combination of geological evidence, chemical andisotopic compositions of groundwater, mineralogical data, and hydraulic measurements. The
following approaches were applied:i. Documentation of past geological events and their impact on geological features
ii. Highlight the most important geological phenomena and their relationships, and scenario
documentationiii. Inference of future scenarios and their impact on geological features
Scenario documentation was performed based on the international FEP (Feature, Event,
Process) list and paleo-hydrogeological study1),2),3). FEP analysis is an efficient method forconstruction of a scenario on the long-term relations between various geological events andvariation of features.
4.3.2 Objectives in the second mid-term research phase
In the second mid-term research phase, the R&D shown in Table 4.3.2-1 has been conductedusing the results from the previous phase (surface-based investigation). The main aims of
R&D are to provide and demonstrate methodology to show a long-term hydrochemicalvariation for making a decision on the implementation of disposal.
Table 4.3.2-1 Performance target of R&D on long-term variation of hydrochemical conditions
Focus

Performance target of R&D

Siting
To identify the long-term chemical
Facility construction conditions.

Tasks• Estimate long-term variations inhydrochemistry

4.3.3 Project details and outcomes(1) Methodology for estimation of past hydrochemical conditions
pH conditions
As described in section 2.3, the dominant processes controlling the pH and redox conditionsof the present groundwater are buffering reactions by carbonate minerals and microbial
catalytic reactions including iron and sulfur minerals both in Mizunami and Horonobe. The
spatial distribution and occurrence of these minerals probably reflects the chemical conditions.
For instance, because carbonate minerals are unstable in acidic pH conditions, the presenceof carbonates implies neutral to alkaline conditions. Similarly, sulfide minerals imply reducing
conditions4) (Fig. 4.3.3-1). Such minerals form over the long-term in terms of the geologicaltime scale. By identifying the precipitation age of these minerals, it is possible to estimate the- 221 -

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long-term stability of the chemical conditions.
Observations of the spatial distribution of these minerals at Mizunami showed thatcarbonates precipitate in fractures within granite at depths below approximately 200 m. The
depths from the surface to 200 m possibly correspond to the zone in which pH is buffered bycarbonate–water interactions.
In contrast, a signature of past dissolution of fossil shells has been observed at depths from50 to 300 m in the Horonobe area. It should be taken into account, however, that the
dissolution of fossil shells can also occur under the partially acidic conditions resulting fromorganic degradation by microbiological processes. Therefore, it is necessary to consider
carefully what might be the dominant phenomenon in the interpretation of dissolution of fossil
shells. In the Mizunami and Horonobe areas, iron oxide, which could be an indicator for
intrusion of shallow oxygenated water, has been observed within a depth of 30 m. A zone ofseveral tens of meters below the surface would correspond to the pH buffering zone. The pHof groundwater deeper than the buffering zone might be maintained in neutral to alkalineconditions over the long term5) (Fig. 4.3.3-2). The results obtained in both the Tono andHoronobe areas show that the pH of groundwater is within the range 6–10 where carbonate
minerals have been identified.

Fig. 4.3.3-1 Overview for modeling hydrochemical characteristics based onmineralogical investigation- 222 -

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Fig. 4.3.3-2 Spatial distribution of fracture-filling calcite
The precipitation age of carbonates can be estimated on the basis of isotopes (δ13C, δ18O, and14C),

morphology, and geohistory6),7),8),9). These methods can be applied to areas in which

groundwaters with a distinct isotopic and chemical signature has been replaced in the past.
The methods may not be suitable for areas where the groundwater has been isolated in thegeological formation since the time of deposition. In the Mizunami, the carbonate origins
identified by these methods are the past hydrothermal water, seawater, and fresh water. The
carbonates deeper than 200 m have been preserved for more than a few millions of years10).
On the other hand, it is difficult to estimate the precipitation age of secondary carbonate
minerals because the evolutionary processes of heavy δ13CPDB values of DIC in groundwaterin the Horonobe area are poorly understood. Isotopically heavy carbonate minerals such as
calcite would be formed from biochemical processes during organic maturation. Regarding the
pH condition of groundwater, neutral to alkaline conditions would be estimated at the depthof fossil shell occurrence.
Redox conditions
The occurrence of iron oxy-hydroxide and sulfide minerals can be used as a guide to infer past
long-term changes (Fig. 4.3.3-1). Iron oxides, which imply oxidizing conditions, precipitate to
the depths of 30 m and sulfide minerals, indicating reducing conditions, occur deeper than 60
m in the sedimentary rocks overlying granite in the Tono area (including the MIU). In thebasement granite, iron oxides occur on fracture surfaces at depths shallower than 200 m;
sulfide minerals also occur on fracture surfaces without iron oxides in the depths11). Oxidized
shallow water heterogeneously inflows into the deep controlled by the continuity andconnectivity of fractures in the granite. The present groundwater shows reducing conditions- 223 -

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at depths deeper than 200 m.
In the Horonobe area, the presence of iron oxide has been observed in the lower limit of depth
at approximately 30 m. In the parts deeper than 30 mbgl, pyrite (which is believed to form
during early diagenetic processes in marine sediment) has been identified ubiquitously in therock matrix.
The present redox boundary in terms of depth can be evaluated based on the distribution ofiron and iron sulfide minerals in the rocks. However, a method to evaluate the long-term
stability of redox conditions has not yet been well established, although a method to evaluate
the long-term stability of pH of groundwater has been developed by estimating the origin andprecipitation age of carbonate minerals12). Recently, several methods (e.g., interpretation of
the concentration patterns of metal elements such as uranium and iron in carbonate minerals
and interpretation of the degree of metal-element substitution for the cations Mg and Ca incarbonate minerals depending on their concentrations and speciation in groundwater) thattake into account the results for precipitation age of carbonate minerals have been tested toevaluate the redox condition over the long term13),14); however, the applicability of thesemethods has not been fully confirmed.
Salinity of past groundwater
The salinity of past groundwater can possibly be inferred by analysis of fluid inclusions insecondary minerals such as calcite. The freezing temperature of an inclusion relates to its
salinity. Observations of inclusions under cooling conditions enable estimation of thegroundwater salinity at which the carbonates precipitated13). The result of this research at the
MIU suggests that some carbonates precipitated from groundwater with a salinity of 0.47–
4.53 wt% (1 wt% NaCl Eq. corresponds to approx. 10,000 ppm NaCl) during the period oflacustrine to marine sedimentation (Fig. 4.3.3-3).
If fluid inclusion samples are not available, the variation of past salinity cannot be directly
estimated. Other approaches such as methods based on FEP and scenario analysis (see next
section) are required.

Fig. 4.3.3-3 Fluid inclusions in fracture-filling calcite in the Toki Granite- 224 -

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In addition, the impact of past earthquake (e.g. 2011 off the Pacific coast of Tohoku
Earthquake) on the groundwater pressure and chemistry were observed in the researchgallery of Mizunami (Fig. 4.3.3-4). Groundwater chemistry varies from changes in the mixing
proportion between chemically distinct waters according to the change of groundwater flow.
The variation of groundwater chemistry would fall within the range of end-member waters in
the area.

▼

▼

100

‐165
‐170

95
90

‐175

85
80

‐180

75

‐185

70

‐190

65
60

‐195

55

50
‐200
2011/1 2011/3 2011/5 2011/6 2011/8 2011/10 2011/12 2012/2 2012/4

全水頭 E.L.(m) （区間6）

Hydraulichead (E.L.m) zone 1-5
全水頭 E.L.(m) （区間1～5）

105

Earthquake

Hydraulic head (E.L.m) zone 6

Earthquake

Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6400

Cl- (mg/L)

300
Zone 1
Zone 3200

Zone 4
Zone 5
Zone 6100

0
2011/01 2011/03 2011/05 2011/07 2011/10 2011/12 2012/02

Fig. 4.3.3-4 Changes in groundwater pressure and hydrochemistry related to earthquakes
The groundwater pressure was raised immediately after the earthquakes, and afterward decreased to theinitial conditions. Cl concentrations were altered in several monitoring zones, and subsequently also showed
recovery. The groundwater chemistry will change as a result of mixing of salinity-distinct waters because of
hydraulic changes. The changes in groundwater chemistry are probably within the range of the mixing endmember waters.

(2) Methodology of scenario analysis for long-term variation
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when using long-term variation of chemical conditions in the past estimated based onmineralogical evidence for safety analysis1). It is important to infer future variation byfocusing on the geological events that would have a heavy impact if they took place. In otherwords, understanding of past geological events in the chemically long-term stability area
detected using mineralogical evidence provides an insight into the influence of each geologicalevent in future.
In the second mid-term research phase, FEPs around the Mizunami and Horonobe URLs in
the past and their relations to chemical conditions were analyzed. We summarized long-termchanges in groundwater recharge, uplift/erosion, and faulting activity in the past and theirrelation with the geology, geological structure, hydrology, and groundwater chemistry.
Moreover, we considered long-term scenarios based on probable processes to estimate thevariations of chemical conditions.
In the Mizunami, Miocene lacustrine and marine sediments overlies Cretaceous basement
granite. Saline, brackish, and fresh waters probably inundated the formations. Fresh waterand slightly saline water occur in the upstream and downstream, respectively, in the present.
Long-term hypothetical scenarios of groundwater replacement are illustrated in Fig. 4.3.3-5.

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Fig. 4.3.3-5 Schematic illustration of the long-term hydrochemical evolution in the Tono area
FEPs regarding hydrochemistry in the Tono area are shown in Fig. 4.3.3-6. The dominantgroundwater in deep granite had experienced replacement from the initial hydrothermal
water to seawater and to fresh water during sedimentation of rock, marine transgression, andregression. Carbonate minerals had precipitated from groundwater during each period.
It is not known exactly when the sulfide minerals (the presence of which indicates reducing
conditions) were precipitated, but groundwater rich in sulfate ions is required for formation ofthese minerals. The sulfide minerals possibly originated from hydrothermal water or seawater.
Carbonate and sulfide minerals generally occur in fractures deeper than 200 m.
Geological events such as climate change and groundwater replacement since the marine
regression that took place a few million years ago have possibly influenced chemical conditions
down to a depth of 200 m, and neutral to alkaline pH and reducing conditions would have beenpreserved for a long time period. Calculating from the uplift rate in this area (0.1 to 0.3- 227 -

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m/1,000 yrs)15), uplift of 200–300 m occurs over hundreds of thousand years. It is supposedthat new fractures occur and the rock permeability increases during reduction of rock pressure
by uplift/erosion. This process facilitates intrusion of shallow water at depth, and the salinityof the groundwater will be diluted. The pH and redox conditions of groundwater at depth may
be preserved by buffer reactions with carbonate and sulfide minerals; however, these minerals
in the current depths down to 400–500 m would possibly been dissolved and eliminated byshallow water infiltration.

Fig. 4.3.3-6 Scenario of long-term hydrochemical evolution in the Tono area
In the case of Horonobe, a long-term hydrologically and hydrochemically stagnant area would
be present in the deeper part because of the closed system formed during the burial diagenesisstage (Fig. 4.3.3-7). An FEP (Feature, Event, and Process) scenario focused on geochemical
evolution from the past to the present is shown in Fig. 4.3.3-8. Because of the mineral–waterinteractions and organic maturation catalyzed by biochemical reactions, the deep groundwaterat Horonobe might have a neutral pH and reducing conditions. Based on the assumption of
the average uplift/erosion rate being 0.3 m/ky16), the geological and geochemical conditions
after a hundred thousand years would still be similar to the present-day conditions in the part
deeper than 700 m. However, in the part shallower than 700 m, it is suggested that several
significant changes may occur (e.g. decrease in salinity from saline to fresh, increase in pH bycation exchange reactions, and increase in permeability in the fault zone 17),18)).

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Fig. 4.3.3-7 Schematic illustration showing long-term hydrochemical evolution in the
Horonobe area

Fig. 4.3.3-8 Long-term scenario related to hydrochemical evolution in the Horonobe area

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It is supposed that the pH of groundwater may be buffered by interactions with carbonate
minerals over the long term. Regarding the redox conditions of groundwater, thedissolution/precipitation reactions of iron oxide or iron hydroxide and of pyrite would control
the conditions in the shallower and deeper parts, respectively. These redox buffering reactions
will continue in the future; however, they may gradually become weakened or exhausted ifshallow oxygenated groundwater intrudes because of the permeability increase following
uplift/erosion. A geochemically stable area is suggested by considering the averaged
uplift/erosion rate. For example, the area that maintains neutral to weakly alkaline pH andstrongly reducing conditions (e.g., −300 mV vs. standard hydrogen electrode (SHE), suitablefor pyrite occurrence) after the forthcoming several hundred thousand years, might be thepresent depth deeper than 700 to 800 m in Tono and deeper than approximately 700 m in
Horonobe.
Regarding the area in which both carbonate and sulfide minerals may not be exhausted in
the future, it is possible to calculate the long-term variations of the redox conditions byassuming equilibrium with redox-controlling minerals. In the calculations, both estimation of
past groundwater composition and prediction of future potential groundwater composition will
be considered. When considering the groundwater composition, expected scenarios and/or
conditions will be assumed broadly; e.g., groundwater compositions in the upstream or
downstream of the groundwater flow regime, and the ancient sea water composition that wasrecharged in the past.
As described in section 3.3, shallow water infiltrates into the depths around the shaft in
Mizunami. This is likely to accelerate experiments on long-term shallow water infiltration todepth. Long-term monitoring of pH and redox conditions around the shaft is essential
research .
In the Horonobe area, it is considered that reactions related to sulfide minerals such as pyrite
might control the redox conditions of the groundwater. According to this finding, the range ofredox potential of groundwater from the past to the present can be estimated using the pH–
Eh diagram shown in Fig. 4.3.3-9. Salinity change (dilution) will occur by infiltration ofshallow fresh water because of the uplift/erosion event; however, the pH and Eh ofgroundwater could be buffered against such perturbations in the future. This is because of thepresence of large amounts of pH/Eh buffering minerals (e.g., carbonate and sulfide minerals)
in the sedimentary rock. With regard to pH/Eh buffering phenomena, the occurrence of fossil
shells and pyrite in the formation deeper than dozens of meters indicates long-term buffering
evidence, in contrast to shallow oxygenated water intrusion by the uplift/erosion event during
the most recent 1 to 2 million years.

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Fig. 4.3.3-9 Long-term variations of redox potential and pH based on mineralogicalequilibrium conditions
The chemical compositions of present groundwater and seawater as a past end-member groundwater are
included. Solid line and hatched part: present groundwater; dotted line and shadowed part: seawater.

4.3.4 Summary
The procedure for estimation of long-term hydrogeochemical variation using mineralogicalmethods and scenario analysis is shown in Fig. 4.3.4-1. We propose that the following genericknow-how and point should be considered.
Present hydrochemical condition(groundwater chemistry, pH, redox,
residence time)
Understanding of dominant processes
Identify dominant FEPs
Scenario development relating each FEPs
Identify dominant hydrochemical
process in each time scaleConfirm mineralogical evidence
Modelling on long-termhydrochemical evolution
Estimate the long-term variation ofgroundwater chemistry, pH, redox

Fig. 4.3.4-1 Generic procedure for estimation of long-term hydrochemical evolution- 231 -

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JAEA-Review 2016-014(1) Estimation methods of past hydrogeochemical variation using minerals- The past pH, redox state, and salinity of groundwater can be inferred by using
mineralogical signatures such as chemical and isotopic composition and morphology.
- Carbonate minerals can be applied to estimate the long-term pH conditions for the area
where chemically distinct groundwaters have been replaced10),13),19). However, the method
may not be applicable to the area in which the groundwater has been isolated without
replacement. In addition, the carbon isotopic ratio of carbonate minerals in rockcontaining abundant organic matter, such as sedimentary rocks, might be significantly
affected by microbial processes.
- Redox conditions can be estimated based on the occurrence of iron oxy-hydroxide andsulfide minerals regardless of rock type. However, the long-term redox conditions cannot
be identified because we do not possess a method to estimate the precipitation age ofthese minerals.
- The observational results of hydrochemical changes in groundwater caused byearthquake suggest that the chemical variation occurs by mixing of end-member
groundwaters. The changes in groundwater chemistry probably lie in the range of endmember groundwaters.
(2) Inference of future hydrochemical variation by scenario analysis- Classify the investigation area into sub-systems based on hydrogeological features.
Summarize the various past geological events and hydrochemical changes (FEPs)1) in the
sub-system where construction of an underground facility is planned.
- Illustrate the FEPs and hydrochemical response as a history table, paying attention tocycles or irreversible phenomena.
- Identify the interactions with a high probability for each time period, e.g., microbial
sulfate reduction causes pyrite precipitation, which decreases the sulfate ion
concentration. The pore size is reduced by compaction, which lowers the hydraulicconductivity and suppresses the material supply for chemical reactions.
- Consider the responsiveness of geochemical conditions and the robustness for a pastgeological event. Then, extrapolate past inter relations to the future and infer the longterm range of hydrogeochemical variation. Groundwater residence time is a key featurein this process. For instance, groundwater with a residence time of ten thousand years
would be influenced by climate (recharge rate) change over tens of thousands of years,
whereas groundwater with a residence time of millions of years would not be affected byshort-term climate change.
- Estimate the long-term stability area and depths based on this scenario analysis.
The development of dating methods for minerals, such as sulfides, that are related to redox
conditions is a future subject to demonstrate long-term redox stability. Additionally,
integration of FEPs on facility construction and on long-term natural environmental change
is required to clarify the important issues during facility construction (Fig. 4.3.4-2).

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Fig. 4.3.4-2 Synthesized scenario for analysis of medium- and long-term hydrochemical
evolution (MIU)
References
1) OECD/NEA : “Features, Events and Processes (FEPs) for Geologic Disposal of Radioactive
Waste”, An international database, OECD/NEA (2000).
2) SKB : “Project SAFE Scenario and system analysis”, SKB Report R-01-13, Swedish Nuclear
Fuel and Waste Management Co. (2001).
3) MoDeRn Partners : “MODERN Case Studies Final report”, EC Deliverable D-4.1, Eds.
Jobmann, M. (2013).
4) Iwatsuki, T., Hagiwara, H., Ohmori, K., Munemoto, T. and Onoe, H. : “Hydrochemical
disturbances measured in groundwater during the construction and operation of a largescale underground facility in deep crystalline rock in Japan.”, Environ Earth Sci. (2015).
5) Iwatsuki, T., Mizuno, T., Hama, K. and Kunimaru, T. : “Mineralogical analysis of a longterm groundwater system in Tono and Horonobe area, Japan”, Groundwater Response to
Changing Climate, Eds. M. Taniguchi and I. P. Holman, CRC Press, pp.87-98 (2010).
6) Folk, R. L. : “The Natural History of Crystalline Calcium Carbonate: Effect of Magnesium
Content and Salinity”, Sedimentary Petrology, Vol.44, pp.40-53 (1974).
7) Milodowski, A.E., Gillespie, M.R., Naden, J., Fortey, N.J., Shepherd, T.J., Pearce, J.M. andMetcalfe, R. : “The petrology and paragenesis of fracture mineralisation in the Sellafield
area, west Cumbria”, Proceedings of the Yorkshire Geological Society, 52(2), pp.215-241(1998).
8) Tullborg, E.-L., Drake H. and Landstrom B. : “Palaeohydrogeology: A methodology based on
fracture mineral studies”, Applied Geochemistry, Volume23, Issue 7, pp.1881-1897 (1999).
9) Bath, A.H., Milodowski, A.E., Ruotsalainen, P., Tullborg, E-L., Cortéz Ruiz, A. andAranyossy, J-F. : “Evidence from mineralogy and geochemistry for the evolution ofgroundwater systems during the quaternary for use in radioactive waste repository safetyassessment (EQUIP project)”, European Commission Nuclear Science and Technology- 233 -

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Project Report EUR 19613 (2000).
10) Iwatsuki, T., Satake, H., Metcalf, R., Yoshida, H. and Hama, K. : “Isotopic andmorphological features of fracture calcite from granitic rocks of the Tono area, Japan: apromising paleohydrogeological tool”, Applied Geochemistry, Volume 17, Issue 9, pp.12411257 (2002).
11) Iwatsuki, T. and Yoshida, H. : “Groundwater chemistry and fracture mineralogy in thebasement granitic rock in the Tono uranium mine area, Gifu Prefecture, Japan Groundwater composition, Eh evolution analysis by fracture filling minerals -”,Geochemical Journal, Vol.33, pp.19-32 (1999).
12) Shikazono, N. and Utada, M. : “Stable isotope geochemistry and diagenetic mineralization
associated with the Tono sandstone-type uranium deposit in Japan”, Mineralium Deposita,
Volume 32, Issue 6, pp.596-606 (1997).
13) Milodowski, A.E., Tullborg, E.-L., Buil, B., Gómez, P., Turrero, M.J., Haszeldine, S.,
England G., Gillespie, M.R., Torres, T., Ortiz, J.E., Zachariáŝ, J., Ŝilar, J., Chvátal A.L, M.,
Strnad, L., Ŝebek, O., Bouch, J.E., Chenery, S.R., Chenery, C., Shepherd, T.J. and McKervey,
J.A. : “Application of Mineralogical, Petrological and Geochemical Tools for Evaluating the
Palaeohydrogeological Evolution of the PADAMOT Study Sites”, PADAMOT ProjectTechnical Report WP2, EU FP5 Contract No. FIKW-CT2001-20129 (2005).
14) Arthur, R. C., Iwatsuki, T., Sasao, E., Metcalfe, R., Amano, K. and Ota, K. : “Geochemical
constraints on the origin and solubility of the Tono uranium deposit, Japan. Geochemistry:
Exploration”, Environment, Analysis 6, pp.33-48 (2006).
15) Sasao, E., Ota, K., Iwatsuki, T., Niizato, T., Arthur, R.C., Stenhouse, M.J., Zhou, W.,
Metcalfe, R., Takase, H. and Mackenzie, A.B. : “An overview of a natural analogue study of
the Tono Uranium Deposit, central Japan”, Geochemistry: Exploration Environment
Analysis, 6(1), pp.5-12 (2006).
16) Kurikami, H., Niizato, T. and Yasue, K. : “A study on timeframe definition and reference
evolution of the geological system for safety assessment - case study on the Horonobe URL
site -”, Paper presented at 19th International Conference on Nuclear Engineering, Chiba,
Japan, pp.16-19 (2011).
17) Ishii, E., Funaki, H., Tokiwa, T. and Ota, K. : “Relationship between fault growthmechanism and permeability variations with depth of siliceous mudstones in northern
Hokkaido, Japan”, Journal of Structural Geology, Volume 32, Issue 11, pp.1792-1805 (2010).
18) Ishii, E., Sanada, H., Funaki, H., Sugita, Y. and Kurikami, H. : “The relationships among
brittleness, deformation behavior, and transport properties in mudstones: An example fromthe Horonobe Underground Research Laboratory, Japan”, Journal of Geophysical Research- Solid Earth, Volume 116, Issue B9 (2011).
19) Blyth, A., Frape, S., Ruskeeniemi, T. and Blomqvist, R. : “Origins, closed system formationand preservation of calcites in glaciated crystalline bedrock: evidence from Palmottu
natural analogue site, Finland”, Applied Geochemistry, Volume 19, Issue 5, pp.675-686(2004).

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4.4 Rock mechanics
4.4.1 Introduction
The in situ stress and rock properties are important in the design and construction of large
and deep underground structures. In fact, in situ stress is recognized as the primary factor in
the development of an excavation damaged zone (EDZ). An EDZ is likely to be less stable thanthe undisturbed rock mass and to provide higher-permeability pathways for groundwater flowin the vicinity of excavations. Thus, development of an EDZ is recognized as a key issue in thedesign and construction of disposal facilities and in safety assessment. During surface-based
investigation (Phase I), it is necessary to understand initial state of rock condition by borehole
investigations and laboratory tests using core samples. In the construction phase (Phase II)
and operation phase (Phase III), it is necessary to obtain detailed information by
investigations from shafts and galleries and to compare the results with those obtained during
Phase I, and also to obtain data on EDZ.
On the other hand, rock and rock masses show time-dependent behavior such as termed creep,
stress relaxation. In this section, we discuss our knowledge of the long-term mechanicalbehavior of rock mass.
4.4.2 Objectives in the second mid-term research phase
The objectives of rock mechanics investigations in the second mid-term research phase is tounderstand the detailed in situ stress condition and rock mechanical properties by borehole
investigations from shafts and galleries, and laboratory tests during shaft and gallery
extension at depths of 500 m (Mizunami) and 350 m (Horonobe). Also, it is necessary to confirm
the validity of the conceptual model and analysis technique applied in Phase I. An additional
objective is to understand the changes in the geological environment caused by the excavation.
Table 4.4.2-1 shows the performance target of R&D and tasks in this session. These are not
set as goals of the second mid-term research phase.
Table 4.4.2-1 Performance target of R&D for rock mechanical characterization
Focus

Performance target of R&D

Decision-making for Decision-making for excavation ofstart of operaion
disposal pit and emplacement of waste.

Tasks• Technology of prediction of EDZ andlong-term rock mass behavior

4.4.3 Project details and outcomes(1) Long-term behavior of rock1) Mizunami
Long-term creep testing and stress relaxation testing have been performed to understand thetime-dependent behavior of rock1),2),3),4),5),6),7),8),9),10),11),12),13),14),15),16),17). Observation of the
microstructure of rock has been performed, and important factors that influence the long-term
behavior have been discussed18),19),20),21),22),23),24),25),26). The main conclusions are as follows:- Long-term creep testing, over 10 years, of the Tage tuff has been performed to obtain data

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to estimate the long-term behavior of rock and openings27),28) (Fig. 4.4.3-1).
- Unconfined compressive testing under microscopic observation was performed tounderstand the mechanism of micro-fracturing and dissolution of quartz (Fig. 4.4.3-2).
- The creep phenomenon of Toki Granite around the shaft caused by excavation waspredicted by numerical simulation using a compliance variable equation.

Fig. 4.4.3-1 Results of long-term creep

Fig. 4.4.3-2 Pressure-solution testing of

testing (Tage tuff)

quartz2) Horonobe
Strength recovery, generalized stress relaxation, tensile strength tests (Brazilian anduniaxial tensile tests), and drying-induced deformation tests were performed using siliceous
mudstone sampled from the Wakkanai Formation. The results are summarized as follows:- From the results of compaction tests (strength recovery tests) on fractured rock, theuniaxial compressive strength of the specimens after failure was increased withincreasing axial strain induced by compaction after failure of the specimen (Fig. 4.4.33)29). The uniaxial compressive strength increases with an increase in the time ofcompaction. Also, as illustrated in Fig. 4.4.3-4, the permeability of the specimen after
failure was decreased with an increase in the axial strain induced by compaction29). These
results are useful for investigation of the mechanism of self-sealing of fractures induced
around the gallery.
- A constitutive equation focusing on time-dependent strength recovery and the effect of
bedding planes was modified30).
- From the results of generalized stress relaxation tests, changes in the creep strain andrelaxation stress are small when the strain rate during loading is small. Also, under dry
conditions, the changes in the creep strain and relaxation stress are smaller than thosein saturated conditions31).
- From Brazilian tests and the uniaxial tensile strength tests under saturated condition,
the tensile strengths of specimens that were loaded perpendicular to bedding were twotimes larger than those that were loaded parallel to the bedding31).
- The dependence of the deformation behavior (elastic modulus and strength) of siliceous- 236 -

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mudstone on water content was investigated. From the results, the relationship between
elastic modulus and water content and the relationship between the strength of rock andwater content can be explained as exponential functions30) (Fig. 4.4.3-5 and Fig. 4.4.3-6).
The constitutive equation considering the effect of drying-saturated-induced deformation

Stress （MPa）

will be improved in future.

160

Axial
Lateral 1
Lateral 2
Lateral 3
Lateral 4

120
80
40
0
-40

0

5

10
15
20
Strain （%）

25

Fig. 4.4.3-3 The relationship between axial

Fig. 4.4.3-4 The result of hydraulic tests instrain and stress in strength recovery

strength recovery tests29)

tests30)
0-0.4

Elastic modulus (GPa)Axial strain (%)

3.5

Specimen 1
Specimen 2
Specimen 5
Estimated value

-0.2

-0.6
-0.8
-1
-1.2

2.5

1.5

0.5

0

20

40
60
Saturation (%)

80

100

Fig. 4.4.3-5 The relationship between
saturation and axial strain in measurementof drying-induced deformation30)

0Saturated

Air-dried (7 hours)

Air dried (2 days)

Completely dried

20

40
60
Saturation (%)

80

100

Fig. 4.4.3-6 The relationship between
saturation and elastic modulus30)

3) General knowledge
Understanding of creep and relaxation phenomena is important to estimate the long-term
behavior of rock. In the case of soft rock, understanding of the controlling factors is also
important, as strength recovery is expected in association with loading. Accumulation of data
is important, as there is no information about the long-term behavior of EDZ.

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4.4.4 Conclusions and future plan
The available information about the long-term behavior of rock and its controlling factors has
been increased from laboratory tests and observations. Future plans are as follows:- Understanding the behavior of EDZ caused by earthquakes- Understanding the range of variation of EDZ before closure of the facility- Understanding the self-sealing mechanism of EDZ and its model
References
1) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 2005-044 (1995), 50p. (in Japanese).
2) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, PNC-TJ1602 96-004 (1996), 80p. (in Japanese).
3) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, PNC-TJ1602 97-004 (1997), 141p. (in Japanese).
4) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, PNC-TJ1602 98-004 (1998), 87p. (in Japanese).
5) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 99-003 (1999), 100p. (in Japanese).
6) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 2000-002 (2000), 74p. (in Japanese).
7) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 2001-003 (2001), 134p. (in Japanese).
8) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 2001-010 (2002), 100p. (in Japanese).
9) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic Pointof View”, JNC-TJ7400 2002-011 (2003), 86p. (in Japanese).
10) Okubo, S. : “Fundamental Study on Long-Term Stability of Rock from the Macroscopic
Point of View”, JNC-TJ7400 2004-002 (2004), 115p. (in Japanese).
11) Okubo, S. : “Phenomenological Study on Crystalline Rock Aiming at Evaluation of LongTerm Behaviour of Rock Mass”, JNC-TJ7400 2005-004 (2005), 107p. (in Japanese).
12) Okubo, S., Seno, Y., Nakama, S., Sato, T. and Hirano, T. : “Phenomenological study on
crystalline rock for evaluating of long-term behavior (Contract research)”, JAEA-Research
2007-088 (2008), 118p. (in Japanese).
13) Okubo, S., Seno, Y., Hirano, T., Nakama. S. and Matsui, H. : “Phenomenological study on
crystalline rock for evaluating of long-term behavior (Contract research)”, JAEA-Research
2008-065 (2008), 51p. (in Japanese).
14) Okubo, S., Hirano, T. and Matsui, H. : “Phenomenological study on crystalline rock forevaluating of long-term behavior (Contract research)”, JAEA-Research 2009-020 (2009),
36p. (in Japanese).
15) Okubo, S., Hikima, R., Hirano, T. and Matsui, H. : “Phenomenological study on crystalline
rock for evaluating of long-term behavior (Contract research)”, JAEA-Research 2010-031- 238 -

JAEA-Review
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JAEA-Review 2016-014(2010), 45p. (in Japanese).
16) Okubo, S., Fukui, K., Hashiba, K., Hikima, R., Tanno, T., Sanada, H., Matsui, H. and Sato,T. : “Phenomenological study on crystalline rock for evaluating of long-term behavior(Contract research)”, JAEA-Research 2011-040 (2012), 54p. (in Japanese).
17) Fukui, K., Hashiba, K., Tanno, T., Hikima, R., Sanada, H. and Sato, T. : “Study on
crystalline rock for evaluating method of long-term behavior; FY2012 (Contract research)”,
JAEA-Research 2013-031 (2013), 52p. (in Japanese).
18) Ichikawa, Y. : “Microscopic Study of Rock for Estimating Long-Term Behavior”, JNCTJ7400 2003-002 (2003), 91p. (in Japanese).
19) Ichikawa, Y. : “Microscopic Study of Rock for Estimating Long-Term Behavior”, JNCTJ7400 2004-014 (2004), 98p. (in Japanese).
20) Ichikawa, Y. : “Microscopic Study of Rock for Estimating Long-Term Behavior”, JNCTJ7400 2005-003 (2005), 60p. (in Japanese).
21) Ichikawa, Y., Seno, Y., Nakama, S. and Sato, T. : “Theoretical study on crystalline rock forevaluating of long-term behavior (Contract research)”, JAEA-Research 2008-005 (2008),
60p. (in Japanese).
22) Ichikawa, Y., Seno, Y., Hirano, T., Nakama, S. and Matsui, H. : “Theoretical study on
crystalline rock for estimating long-term behavior (Contract research)”, JAEA-Research
2008-090 (2008), 52p. (in Japanese).
23) Ichikawa, Y., Cho. J. H, Hirano, T. and Matsui, H. : “Theoretical study of rock for
estimating long-term behavior (Contract research)”, JAEA-Research 2009-027 (2009), 48p.
(in Japanese).
24) Ichikawa, Y., Tanno, T., Hikima, R., Sanada, H., Matsui, H. and Sato, T. : “Theoretical
study of rock for estimating long-term behavior; FY2010 (Contract research)”, JAEAResearch 2012-003 (2012), 34p. (in Japanese).
25) Ichikawa, Y., Choi. J. H, Tanno, T., Hirano, T. and Matsui, H. : “Theoretical study of rockfor estimating long-term behavior; FY2009 (Contract research)”, JAEA-Research 2011-007(2011), 91p. (in Japanese).
26) Ichikawa, Y., Kimoto, K., Sato, T., Tanno, T., Hikima, R. and Sanada, H. : “Theoretical
study of rock for estimating long-term behavior; FY2012 (Contract research)”, JAEAResearch 2013-045 (2014), 69p. (in Japanese).
27) Okubo, S. and Fukui, K. : “Long-Term Creep Test and Constitutive Equation of Tage Tuff”,
Journal of Shigen to Sozai, Vol.118, pp.36-42 (2002). (in Japanese).
28) Hashiba, K., Okubo, S. and Fukui, K. : “Ten-Year Creep Test of Tage Tuff”, Journal of
Shigen to Sozai, Vol.124, pp.741-747 (2008). (in Japanese).
29) Sugita, Y., Sanada, M., Fujita, T., Hashiba, K., Fukui, K. and Okubo, S. : “Strength andimpermeability recovery of siliceous mudstone from complete failure”, Proceedings of the
13th Japan Symposium on Rock Mechanics and 6th Japan-Korea Joint Symposium on RockEngineering, pp.207-212 (2013). (in Japanese).
30) Japan Atomic Energy Agency : “Senshinteki Chisou Shobun Gainen Seinou Hyouka
Gijutsu Koudoka Kaihatsu”, pp.88-100 (2014). (in Japanese).

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31) Sanada, M., Kishi, H., Sugita, Y., Hayashi, K., Takebe, A. and Okubo, S. : “Studies aboutstrength recovery and generalized relaxation behavior of rock (V)”, JAEA-Research 2012025 (2012), 130p. (in Japanese).

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4.5 Mass transport
4.5.1 Introduction
As part of the study of mass transport, which involves understanding retardation effects inrock masses and groundwater, we have been working on themes (1) and (2) (listed below) toestablish techniques of investigation/analysis/evaluation focusing on the long-term changes
and processes in geological environments.
(1) Understanding long-term changes in the sorption and diffusion properties of rock mass
From the perspective of safety assessment of geological disposal, it is important tounderstand long-term changes in the sorption and diffusion properties of rock masses. It isalso necessary to establish techniques for analysis and evaluation of these long-term changes.
(2) Understanding long-term changes in mass transport fields
From the perspective of safety assessment of geological disposal, it is necessary to understandlong-term changes in groundwater pressure, rock-mass permeability, and distribution ofgroundwater chemistry. It is also necessary to establish the techniques for acquisition of highly
reliable data on these changes and for analysis and evaluation.
4.5.2 Objectives in the second mid-term research phase
Studies at underground facilities must produce outcomes and scientific knowledge that canbe reflected in the decision-making concerning site selection, construction of facilities,
commencement of disposal, completion of placement of waste packages, and final sealing in
the actual disposal operation.
From this perspective, the level of technical development we aim to achieve for use indecision- making concerning the commencement of disposal, completion of placement of waste
packages, and final sealing, in the context of understanding long-term changes and recovery
behavior in geological environments, is the establishment of investigation and evaluation
techniques that can predict the changes in mass transport characteristics on a geological timescale and indicate the long-term changes in environmental conditions concerning materialtransport, as well as the systematization of a series of techniques from investigation to
analysis/evaluation (Table 4.5.2-1).
During the second mid-term research phase, we conducted investigations in the boreholes
drilled from the surface, laboratory tests using core and groundwater samples, andinvestigations in the vertical shafts and horizontal galleries reaching depths of 500 m at
Mizunami and 350 m at Horonobe. We established investigation, analysis, and evaluation
techniques to estimate mass transport phenomena on a geological time scale and the range ofthe long-term changes in mass transport characteristics.

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Table 4.5.2-1 Performance target of R&D in the mass transport study
Focus

Performance target of R&D

Decision toLong-term evolution of geologicalconstruct, to end
environment can be evaluated from theemplacing waste
viewpoint of solute transport property.
and on final closure

Tasks
Long-term evolution of sorption capacityand diffusivity of rock matrix and oftransport pathways• Methodology development for thecharacterization
Long-term evolution of geometry oftransport pathways; depth of diffusionaccessible rock mass
• Methodology development for thecharacterization

4.5.3 Project details and outcomes(1) Understanding long-term changes in the sorption and diffusion properties of rock mass
Sorption and diffusion in the geological environment are important phenomena that control
the retardation of mass transport. The sorption and diffusion of nuclides vary greatly
depending on the solid-phase mineral composition and interstice structure, the groundwaterand porewater chemistry, the state of dissolved nuclides in water (chemical species), and otherphysicochemical conditions. However, it is difficult to understand directly the long-termchanges in these properties on a geological time scale from laboratory and in situ tests. It is,therefore, important to establish investigation techniques for the evaluation of the changes insorption and diffusion properties using natural analogs and to obtain data using suchtechniques. From this perspective, we conducted several investigations for the purpose ofobtaining basic data, such as the chemical composition and mineral composition of the rockmasses and the distribution of elements.
1) Mizunami
Mainly using cores from boreholes drilled from the surface, we estimated the depth of matrix
diffusion from the distribution profiles of uranium-series nuclides (238U, 234U, and 230Th)
occurring near permeable fractures in the Toki Granite. The results showed that matrix
diffusion near permeable fractures can extend as much as more than several tens of
millimeters. This use of natural analogs is considered capable of evaluating long-term masstransport characteristics.
2) Horonobe
Using cores from the boreholes drilled from the surface, we conducted mineral and chemical
analyses of the Koetoi Formation and the Wakkanai Formation around the gallery to examine
the heterogeneity in the concentration distribution of analog elements and the relationships
linking geological structures, groundwater flow, and geochemical environment to theconcentration of analog elements. The results of analysis and examination showed that no
significant movement of elements occurred in intact rock, and some faults that show

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accumulation of elements were important as mass transport pathways1) (Fig. 4.5.3-1).

Fig. 4.5.3-1 Correlation of minor elements with Al in the rock samples1)- 243 -

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JAEA-Review 2016-014(2) Understanding long-term changes in mass transport fields
We started a review of information that might assist with prediction of long-term changes inmass transport fields, focusing on geological structures that affect mass transport and theprocesses of their formation, and also the geologic history such as uplift and subsidence. As aresult, it was found possible to estimate the long-term transitions of mass transport fields
based on understanding of geologic history and the process of permeable fracture formation.
1) Mizunami
For the purpose of understanding long-term changes in mass transport fields, we extracted
the faults and fractures that could act as mass transport pathways from the results of surfacebased borehole investigations, investigations during tunnel excavation, and investigations in
the underground facilities. These faults and fractures were classified into five types mainly
from a geological standpoint according to the type and presence/absence of fracture-fillingminerals, the degree of alteration and color of host rock near the fracture, and the age of thefault or fracture2) (Table 4.5.3-1). We plan to proceed with the investigation into the origins
and development processes of these fractures, faults, and other discontinuous structures, andaccumulate knowledge that will contribute to the evaluation of long-term mass transport.
Table 4.5.3-1 Classification of types of discontinuous structures in the Toki Granite

Type

Fracturefillings

Wall rock alteration
around fracture

Hydraulicconductivity

Age andtemperature

I : Fractures

Chlorite

Not alteredLow

69-43Ma
300-200℃

II : Fault-

Strongly altered

Very low

64-43Ma
400-300℃

III : Fractures

Chlorite(wall rocks show greenish
or white-tinged color)Low64-43Ma
300-200℃

IV : Fractures

Calcite,Chlorite ornot(wall rocks show grayish ororange color)High69-24Ma<200℃

V : Low-angle
Fractures

Calcite ornot

Not alteredHigh

43-22Ma<100℃

AlteredAltered2) Horonobe
For the purpose of understanding the long-term changes in mass transport fields, we
extracted the discontinuous structures that could act as mass transport pathways from theresults of surface-based borehole investigations, investigations during tunnel excavation, andinvestigations in the underground facilities. We classified the extracted discontinuous
structures into four types on the basis of the mechanism of fracture formation (tensile andshear), the presence/absence of fault rock accompanying shear cracks3), and the- 244 -

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presence/absence of shear bands4) (Fig. 4.5.3-2).
We constructed models for the transition of geology and geological structures based on thegeologic history in the Horonobe area.5) (Fig. 4.5.3-3). In addition, the processes of theformation of permeable fractures and lateral faults were clarified based on the relationships
linking uplift, subsidence, and other phenomena that affect the diagenesis of the strength andbrittleness of rock6) (Fig. 4.5.3-4). Based on understanding of these processes of geologicalstructure development and fracture formation, it is considered possible to estimate the longterm transition of mass transport fields on a geological time scale.

Fig. 4.5.3-2 Discontinuous geological structures around the Horonobe URL(a, c, d 3) ; b 4))- 245 -

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Fig. 4.5.3-3 Topographic and geological evolution model constructed by SMS (Sequential
Modeling System of geological evolution impact on groundwater flow)5)

Fig. 4.5.3-4 Processing the formation of the lateral fault6)
4.5.4 Summary
This section summarizes the technical findings concerning understanding of long-termchanges and recovery behavior in the geological environment obtained from surface-based
investigations, investigations during tunnel excavation, and investigations in theunderground facilities.
(1) Understanding long-term changes in the sorption and diffusion properties of rock mass
- The distribution profiles of uranium-series nuclides occurring near permeable fracturesin the Toki Granite showed that matrix diffusion can extend as much as more thanseveral tens of millimeters. Analyses of the mineral and chemical composition of
sedimentary rocks around the tunnel showed that no significant movement of elements- 246 -

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occurred in intact rock, and some faults were important as mass transport pathways. It
was demonstrated that long-term mass transport characteristics can be evaluated bymethods that use natural analogs (both sites).
(2) Understanding the long-term changes in mass transport fields- We classified the discontinuous structures that can act as mass transport pathways into
five types at Mizunami and four types at Horonobe for the prediction of long-term changes
in material transport fields. This result shows that it is possible to estimate the longterm transitions of material transport fields by considering the origins and development
processes of these discontinuous structures (both sites).
- The modeling of the long-term transition of geology and geological structures, which wasconstructed based on the geologic history of the Horonobe area and understanding of theprocesses of formation of permeable fractures and lateral faults, enables estimation of
the long-term transitions in mass transport fields. (Horonobe).
With respect to understanding of the long-term changes and recovery behavior in thegeological environment related to mass transport, we commenced development ofinvestigation, analysis, and evaluation techniques for estimating material transportphenomena in the geological environment on a geological time scale and the long-term rangeof changes in these characteristics.
In study of mass transport from the perspective of long-term changes and recovery behavior
in the geological environment, it is important to develop investigation, analysis, andevaluation techniques to understand the long-term changes in mass transport characteristics
that occur both near to and far from the underground facilities, and also to understand thechanges in mass transport fields accompanying the long-term changes in the geologicalenvironment.
An additional important theme is to provide examples of investigation, analysis, andevaluation techniques at the Mizunami and Horonobe underground facilities.
The study of mass transport is placed as an important theme in the Phase III (construction
phase) in the underground research project7). Construction of horizontal tunnels for in situ
tests and field investigations have been making progress at the Mizunami and Horonobe. In
the second mid-term research phase, we have just commenced the study of mass transport. In
the future, while continuing organization of information for prediction of long-term changes
in mass transport phenomena, we plan to proceed with the development of investigation andevaluation techniques that can estimate the long-term range of changes in mass transportcharacteristics in and around the underground facilities. We also plan to establish techniques
for modeling of changes in mass transport characteristics on a geological time scale.
References
1) Iwatsuki, T., Ishii, E., Mizuno, T. and Honda, T. : “Natural analogue study on trace element
migration in geological formation at Horonobe area, Japan”, Report of Tokyo City
University, Atomic Energy Research Laboratory, 36, pp.1-13 (2009).
2) Kunimaru, T., Mikake, S., Nishio, K., Tsuruta, T., Matsuoka, T., Ishibashi, M., Ueno, T.,- 247 -

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Tokuyasu, S., Daimaru, S., Takeuchi, R., Saegusa, H., Onoe, H., Takeda, M., Karino, T.,
Mizuno, T., Hagiwara, H., Sato, T., Sanada, H., Tanno, T., Hikima, R., Morikawa, K.,
Yuguchi, T., Ogata, N., Hama, K., Ikeda, K., Yamamoto, M., Shimada, A., Matsui, H., Ito,
H. and Sugihara, K. : “Mizunami Underground Research Laboratory Project annual reportfor fiscal year 2010”, JAEA-Review 2012-020 (2012), 178p. (in Japanese).
3) Ishii, E., Funaki, H., Tokiwa, T. and Ota, K. : “Relationship between fault growthmechanism and permeability variations with depth of siliceous mudstones in northern
Hokkaido, Japan”, Journal of Structural Geology, 32(11), pp.1792-1805 (2010).
4) Ishii, E., Sanada, H., Funaki, H., Sugita, Y. and Kurikami, H. : “The Relationships among
brittleness, deformation behavior, and transport properties in mudstones; An Example
from the Horonobe Underground Research Laboratory, Japan”, Journal of GeophysicalResearch, 116(B09), pp.B09206_1-B09206_15 (2011).
5) Nakayama, M., Amano, K., Tokiwa, T., Yamamoto, Y., Oyama, T., Amano, Y., Murakami, H.,
Inagaki, D., Tsusaka, K., Kondo, K., Yokota, H., Nanjo, I., Niizato, T., Tanaka, S., Ohara,
M. and Jin, K. : “Horonobe Underground Research Laboratory Project; Investigation reportfor the 2011 fiscal year”, JAEA-Review 2012-035 (2012), 63p. (in Japanese).
6) Ishii, E. : “Microstructure and origin of faults in siliceous mudstone at the Horonobe
Underground Research Laboratory site, Japan”, Journal of Structural Geology, 34, pp.2029 (2012).
7) Japan Atomic Energy Agency : “Master plan of the Mizunami Underground ResearchLaboratory Project”, JAEA-Review 2010-016 (2010), 37p. (in Japanese).

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4.6 Geosphere stability for long-term isolation
4.6.1 Introduction
The framework of research on geosphere stability for long-term isolation of high-level
radioactive waste is structured into three categories to contribute to the site selection and thenational safety regulation of the final disposal. These three categories are: development andsystematization of investigation techniques; development of models for long-term estimationand effective assessment; and development of dating techniques. Development of models forlong-term estimation and effective assessment aims at technical preparation to show theoccurrence possibility of a scenario relating to the influence of natural phenomena on thegeological environment, and the variation range of the geological environment including theuncertainty in forecast As an important study and technical preparation for estimation andevaluation relating to the safety assessments based on less likely scenarios, we performed thework described below. This report documents the main results of the research anddevelopment.
4.6.2 Objectives in the second mid-term research phase
The scientific program for fiscal years 2010–2014 was set taking into account the importanceand urgency of the needs of the implementing bodies and the regulatory agencies1),2),3),4),5) withattention to acts and reports after having investigated the trend of basic research inuniversities as well as related research institutes (Table 4.6.2-1).

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Table 4.6.2-1 Performance target of R&D on geosphere stability for long-term isolation
Focus

Decision on the
beginning ofdisposal andrepository closure

Performance target of R&D

Tasks

Enable understanding the variation
range of the geological environment
affected by a Rare Natural Event.

Estimation techniques for hydrologicalchanges with faulting• Development of estimation
techniques for hydrological changeusing analysis of volumetric strain
with subduction-zone earthquakes• Technique validation based on theobservation on the 2011 off the
Pacific coast of Tohoku Earthquake

Enable simulation of landform changes
for approximately 100,000 years.

Simulation techniques for landformchanges• Validation of simulation techniques
using the previously developed
physical model

Enable understanding of the uncertainty
in long-term estimation over a period ofa hundred thousand years in general.

Estimation and evaluation techniques forvery-long-term natural phenomena• Development of estimation andevaluation techniques for very-longterm natural phenomena• Development of quantitative
methodology on the uncertainty ofthe estimation and evaluation

4.6.3 Project details and outcomes(1) Estimation techniques for hydrological change with faulting
The 2011 off the Pacific coast of Tohoku Earthquake (M9.0) triggered earthquakes andearthquake-induced changes in water level and the quality of groundwater and hot springwater6),7). These are considered to be phenomena caused by changes in crustal stress resulting
from trench-type megathrust earthquake. Understanding these phenomena is important forassessment of the long-term stability of the geological environment because these events canaffect the regularity and continuity of regional tectonics. In our study, the relationshipbetween the calculated stress changes induced by trench-type earthquakes and the results ofgroundwater observation was examined.
We focused on changes in groundwater pressure in and around MIU (Mizunami UndergroundResearch Laboratory) induced by the Tohoku Earthquake. For the calculation of volumetricstrain changes because of the earthquake, we used the program Coulomb3.18),9) and input fault
slip models reconstructed from previously reported rupture processes. The calculation outputs
dilation in most of the Eastern Japan (Fig. 4.6.3-1). Next, strain response sensitivity for waterpressure changes of artesian groundwater was estimated based on calculation from earth tidevariations. Finally, theoretical groundwater level changes were determined by multiplying theestimated dilation around MIU because of the Tohoku Earthquake; these theoretical values
were compared to the observed data. The theoretical groundwater level changes indicate a- 250 -

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range of several tens centimeters, consistent with single-day drawdowns for the earthquake
observed in boreholes more than 1 km distant from the MIU (Table 4.6.3-1)10).
This study obtained a typical relationship between changes in crustal stress and groundwaterpressure caused by the trench-type earthquake. This can contribute to a safety assessment
considering geologic events with a recurrence interval of more than 1,000 years.

Fig. 4.6.3-1 Volumetric strain changes in Eastern Japan after the Tohoku Earthquake
described by Coulomb 3.110). The fault model is from Yagi and Fukahata (2011)11).
The star means the epicenter of the Tohoku Earthquake.

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Table 4.6.3-1 Comparison of the theoretical coseismic groundwater level changes with theobserved ones at boreholes more than 1 km distant from the MIU10)
boreholeinterval

DH-7
DH-7
DH-7
DH-7
DH-11
DH-11
DH-11
DH-11
DH-13
DH-13
DH-13
DH-13
AN-1
AN-1
AN-1
AN-1
AN-3
AN-3
AN-3
AN-3
MIU-2
MIU-2
MIU-2
MIU-2
MIU-3
MIU-3
MIU-3
MIU-3
MIU-4
MIU-4
MIU-4
MIU-4

No.1
No.2
No.3
No.5
No.1
No.3
No.4
No.5
No.1
No.4
No.5
No.7
No.1
No.6
No.10
No.12
No.1
No.3
No.4
No.5
No.2
No.5
No.9
No.12
No.1
No.4
No.6
No.8
No.6
No.8
No.9
No.10

groundwater level change (cm)theoreticalobserved*
44
62
33
46
54
88
65
35
68
19
65
33
84
35
78
39
77
80
48
77
50
75
68
6
37
72
61
49
58
35
64
45
49
72
42
69
60
74
34
69
49
18
51
19
64
26
96
54
81
15
50
46
73
46
73
57
57
36
64
29
68
25
77
37

*Single-day groundwater level change calculated from the data between 14:30 local timeon 11 and 12 March 2011.

(2) Simulation techniques for landform changes
It is assumed that landform changes cause changes in geological environments such as
movement and quality of groundwater12). The landform changes over the next hundred
thousand years are basically extrapolated or analogized from the uplift, erosion, and climate
cycle for the past hundreds of thousands of years. We developed a program that included asimulation method for river depositional processes based on changes in particle sizes tounderstand the wider topographic changes on a scale of more than 10 km of one cycle of a
glacial-interglacial cycle (Patent No. 5422833)13). However, it is difficult to prove the validityof future prospects of irreversible phenomena such as landform development. Thus, methods
to simulate the current topography starting from restorations of the past topography based on
topographical and geological data are effective (Fig. 4.6.3-2). This study compared the current
landforms with the result of the numerical simulation that started from the restored
topography for approximately 100,000 years ago.
A case study was conducted around the middle and upper stream on the Toki River, whichflows through the neighborhood of the border between the Mikawa Highlands and the Mino

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Highlands. The old landforms of approximately 140,000 years ago were estimated based on
the river terrace formed in Marine Isotope Stage 6 and the longitudinal current river profiles.
The results of the simulation that started from the old landforms were similar to the current
landforms in broad altitude and distribution and relative height of the river terraces (Fig.
4.6.3-3, Fig. 4.6.3-4). This finding supports the validity of the landform change simulation for
approximately 100,000 years in the future14). In addition, the old landforms were restored at
the conceivable present-day maximum and minimum erosion rates. These simulation results
showed the elevation difference that reflected difference in initial state (Fig. 4.6.3-4)14). Thisdifference is interpreted as the width of uncertainly in the estimate of erosion rate in themountain slope. This result demonstrates that the landform change simulation technique overapproximately 100,000 years using the physical model is valid.
Improvement of the reliability of the forecast by comparison between the numericalsimulation results and the results of extrapolation or analogy will be a theme in future work.

Fig. 4.6.3-2 Evaluation of landform changes using the old topography restored to the original(conceptual diagram)14)- 253 -

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Case : initial elevation= present elevation

Elevation change

Elevation change from 15,000 yrs.
to the present by the simulation(Positive change corresponds to
the Low-terraces)

Elevation

Real distribution of
the Low-terraces(Present)

Fig. 4.6.3-3 Comparison between the results of a landform development simulation and thespatial distribution of real low terraces14)

Fig. 4.6.3-4 Differences in terms of summit plane between the simulation landforms and thereal landforms14)(3) Estimation and evaluation techniques for very-long-term natural phenomena
The estimation and evaluation of natural phenomena such as upheaval, subsidence, erosion,and sedimentation are important in safety assessment based on less likely scenarios. However,estimation using extrapolation is important because these phenomena take place over the longterm in a framework of slow plate motion over a wide area15). According to Tanaka (2011)16),
estimation by extrapolation is performed using the following procedure: (1) statement andextraction of the natural law related to a phenomenon from the past to the present; (2) causeof the occurrence of the phenomenon and clarification of the mechanism; (3) obtaining of
information on the duration of a factor controlling the natural phenomenon; and (4)- 254 -

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extrapolation to the future using the tendency for past change based on (1) to (3). Therefore
the duration of a factor (e.g., crustal movement in the broad sense, including plate motion)
controlling a geologic phenomenon is important in assuring the reliability of estimation by
extrapolation. Kasahara and Sugimura (1978)17) and Matsuda (1988)18) determined theuniformity of the displacement direction and velocity in the crustal movement in the
Quaternary concerning the causation and continuity of a past geological phenomenon, andcalled these the uniform mode and rate. Subsequently, the Japan Association for Quaternary
Research (1987)19) suggested that extrapolation to the future of the same period is possible
based on a variable trend and speed from the past to the present when a uniform mode andrate are in operation. It is necessary to clarify the area and period of the uniform mode andrate from the available topographical and geological information to confirm the validity of
estimation of the future by extrapolation.
Fig. 4.6.3-5 shows the distribution of sedimentary rock from the late Miocene (about 7 million
years ago) to the Late Pleistocene (about 125,000 years ago). The distribution shown for eachage does not facilitate exact discussion, because the distribution does not distinguish between
marine and non-marine deposits. However, it is thought that marine deposits are distributed
widely in the shore area. For example, for the Lower Pleistocene, the sediment of the seabed
after approximately 2.6 Ma is included in sediment distributed over the land after
approximately 0.78 Ma. In other words, the part of the area where this sediment was
distributed became an area of uplift rather than subsidence after approximately 0.78 Ma. This
demonstrates that ongoing crustal movement began in the area along the shore after hundredsof thousands of years ago. Fig. 4.6.3-6 shows the frequency histogram and cumulative
distribution of onset times for active fault movements every 100,000 years for a 6-million-year
period from Doke et al. (2012)20). The onset times of many active faults are after approximately
2.5 Ma. In addition, more than half of the onset times of faulting are after 1 Ma. This
distribution of onset times suggests that the uniform mode and rate of crustal deformation
were present after 1 Ma. Furthermore, Umeda et al. (2013)21) estimated the onset time of theconstant uplift rate of representative mountainous based on the model of mountain
development by concurrent tectonics and denudation of Ohmori (1978)22) (Fig. 4.6.3-7).
According to this deductive estimate, the onset times of the uniform mode and rate of crustal
deformation vary by area. However, the onset times are at least after from hundreds ofthousands of years ago to 1 million years ago. This result does not contradict the inductive
estimate obtained from geomorphological and geological data.
Concerning the possibility that new faults and volcanoes may occur, estimation of the future
occurrence probability can be obtained from the frequency, scale, and range of pastoccurrence23). Previous studies have modeled the long-term spatio-temporal characteristics of
volcanism using probabilistic approach with geological information such as the location,
occurrence time, and magnitude24),25). We developed a multiple-inference model that included
geophysical and geochemical data using a Bayesian method to improve the reliability of
estimation in the second mid-term research phase(Fig. 4.6.3-8)26),27).

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Fig. 4.6.3-5 Distribution of late Miocene to late Pleistocene sedimentary rocks in Japan21)

Fig. 4.6.3-6 Frequency histogram and cumulative distribution of onset times for active fault
movements21)- 256 -

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Fig. 4.6.3-7 Onset times of consistent mode and rate of crustal deformation in Japan basedon simulations of temporal changes in mean altitude developed under concurrent tectonics
and denudation processes21)

Fig. 4.6.3-8 Probability of the occurrence of a new volcanic event over the next 1 Myr27)
The probabilities were calculated using a multiple-inference model that included geophysicaldata and geochemical data using the Bayesian approach.
(a) Calculation using the distribution of volcanoes, age, and seismic velocity structure(b) Calculation including the helium isotope ratio distribution in (a)- 257 -

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4.6.4 Summary
As an important study and technical preparation for estimation and evaluation relating to
the safety assessment based on the less likely scenarios, we performed the following:- Validation of simulation techniques for landform changes over approximately 100,000
years.
- Development of estimation techniques for hydrological changes using analysis ofvolumetric strain with subduction-zone earthquakes.
- Development of estimation and evaluation techniques for very-long-term natural
phenomena.
- Development of quantitative methodology for the uncertainty of the estimation andevaluation.
The future theme is technical upgrading and quantification of the uncertainty.
References
1) Nuclear Waste Management Organization of Japan : “R&D Needs for Geological Disposal
Project - for the Selection of Detailed Investigation Areas -”, NUMO-TR-10-02 (2010), 58p.
2) Radioactive Waste Safety Subcommittee, Nuclear and Industrial Safety Subcommittee ofthe Advisory Committee for Natural Resources and Energy : “About the regulation support
study for radioactive waste disposal (Fiscal Year 2010-2014)” (2009), 36p. (in Japanese).
3) Agency for Natural Resources and Energy and Japan Atomic Energy Agency :“Fundamental R&D Program for the Geological Disposal of HLW” (2006), 110p. (inJapanese).
4) Agency for Natural Resources and Energy and Japan Atomic Energy Agency :“Fundamental R&D Program for the Geological Disposal of HLW” (2009), 114p. (inJapanese).
5) Agency for Natural Resources and Energy and Japan Atomic Energy Agency :“Fundamental R&D Program for the Geological Disposal of HLW and TRU” (2010), 139p.
(in Japanese).
6) Kawabe, T. and Nakano, K. : “Change of water level and its temperature and tectonic
movements in southern Tohoku District by the 2011 off the Pacific coast of Tohoku
Earthquake”, Abstracts (Section B) 2011 Joint Annual Meeting of Japan Association of
Mineralogical Sciences and The Geological Society of Japan, R22-P-9 (p.252) (2011).
7) Kitagawa, Y. and Koizumi, N. : “Changes in groundwater levels, groundwater pressuresand discharge rates a day after the 2011 Off the Pacific Coast of Tohoku Earthquake(M9.0)”, Annual Report on Active Fault and Paleoearthquake Researches, No.11, pp.309318 (2011).
8) Lin, J. and Stein, R. S. : “Stress triggering in thrust and subduction earthquakes, and stressinteraction between the southern San Andreas and nearby thrust and strike-slip faults”,
Journal of Geophysical Research: Solid Earth, Volume 109, Issue B2 (2004).
9) Toda, S., Stein, R. S., Richards-Dinger, K. and Bozkurt, S. : “Forecasting the evolution ofseismicity in southern California: Animations built on earthquake stress transfer”, Journal- 258 -

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of Geophysical Research: Solid Earth, Volume 110, Issue B5 (2005).
10) Niwa, M., Takeuchi, R., Onoe, H., Tsuyuguchi, K., Asamori, K., Umeda, K. and Sugihara,
K. : “Groundwater pressure changes in Central Japan induced by the 2011 off the Pacificcoast of Tohoku Earthquake”, Geochemistry, Geophysics, Geosystems, Volume 13, Issue 5(2012).
11) Yagi, Y. and Fukahata, Y. : “Rupture process of the 2011 Tohoku-oki earthquake andabsolute elastic strain release”, Geophysical Research Letters, Volume 38, Issue 19 (2011).
12) Kawamura, M., Ebashi, T., Makino, H., Niizato, T., Yasue, K., Inagaki, M. and Ohi, T. :“Study on Evaluation Method of Potential Geological Environmental Changes of ‘Uplift and
Erosion’ for Performance Assessment on a High Level Radioactive Waste Geological
Disposal System”, Journal of the Japan Society of Engineering Geology, 51, pp.229-240(2010).
13) Kusano, T., Asamori, K., Kurosawa, H., Kokubu, Y., Tanikawa, S., Negi, T., Hanamuro, T.,
Yasue, K., Yamasaki, S., Yamada, K., Ishimaru, T. and Umeda, K. : “Research on geospherestability for long-term isolation of radioactive waste (Progress report for fiscal years 2005 2009: H22 report)”, JAEA-Research 2010-044 (2011), 153p. (in Japanese).
14) Yasue, K., Asamori, K., Tanikawa, S., Yamada, K., Yamasaki, S., Kokubu, Y., Niwa, M.,
Doke, R., Kusano, T., Hanamuro, T., Ishimaru, T. and Umeda, K. : “Annual report for
research on geosphere stability for long-term isolation of radioactive waste in fiscal years
2010”, JAEA-Research 2011-023 (2011), 113p. (in Japanese).
15) Committee for Geosphere Stability Research : “Geological Leaflet 4, Japanese Island Arc
and Geosphere Stability”, Geological Society of Japan (2011).
16) Tanaka, K. : “Can we predict the future geological environments?: Aiming at siting
conditions and safety design of nuclear power facilities”, Electric Power Civil Engineering,
351, pp.8-13 (2011). (in Japanese).
17) Kasahara, K. and Sugimura, A. : “Evolving Earth, vol. 1”, Iwanami Shoten (1978).
18) Matsuda, T. : “the Neogene/Quaternary boundary on the basis of crustal movement uniform mode and rate of crustal movements during the Quaternary”, Chikyu Monthly, 10,
pp.599-603 (1988).
19) Japan Association for Quaternary Research ed. : “Quaternary Research Looks at the
Future of Nature in Japan”, Kokon Shoin (1987).
20) Doke, R., Tanikawa, S., Yasue, K., Nakayasu, A., Niizato, T., Umeda, K. and Tanaka, T. :“Spatial patterns of initiation ages of active faulting in the Japanese Islands”, Active Fault
Research, no.37, pp.1-15 (2012).
21) Umeda, K., Tanikawa, S. and Yasue, K. : “Geological Predictions for the Long-term
Isolation of Radioactive Waste Based on Extrapolating Uniform Mode and Rate of Crustal
Movements”, Journal of Geography (Chigaku Zasshi), pp.385-397 (2013).
22) Ohmori, H. : “Relief structure of the Japanese mountains and their stages in geomorphic
development”, Bulletin of Department of Geography, University of Tokyo, 10, pp.31-85,(1978).
23) Takahashi, M. and A. J. Martin : “Where is the volcano formed for the next 100,000 years?

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JAEA-Review 2016-014- About the long-term stability of the magma-plumbing system”, Chikyu Monthly, 26,
pp.386-394 (2004). (in Japanese).
24) Martin, A. J., Umeda, K. and Yusa, Y. : “Probabilistic Approaches for Predicting the LongTerm Spatial and Temporal Characteristics of Monogenetic Volcanoes; Application to Two
Monogenetic Volcano Fields in Japan”, JNC Technical Review, 18, pp.59-70 (2003).
25) Martin, A. J., Takahashi, M., Umeda, K. and Yusa, Y. : “Probabilistic methods for
estimating the long-term spatial characteristics of monogenic volcanoes in Japan”, Acta
Geophysica Polonica, 51, pp.271-289 (2003).
26) Martin, A. J., Umeda, K., Connor, C. B., Weller, J. N., Zhao, D. and Takahashi, M. :“Modeling long-term volcanic hazards through Bayesian inference : An example from the
Tohoku volcanic arc, Japan”, Journal of Geophysical Research: Solid Earth, Volume 109,
Issue B10 (2004).
27) Martin, A. J., Umeda, K. and Ishimaru, T. : “Application of the Bayesian Approach toIncorporate Helium Isotopes Ratios in Long-Term Probabilistic Volcanic Hazard
Assessments in Tohoku, Japan”, In Updates in Volcanology - New Advances inUnderstanding Volcanic Systems, edited by K. Nemeth, pp.117-146 (2012).

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5. Tool development for integration of knowledge from each research result
5.1 Introduction
A specific feature of the geological disposal of radioactive waste is to ensure extremely longterm safety, extending several tens of thousands years in the future. Such extreme long-term
safety of geological disposal is difficult to demonstrate in actuality. It is being widely
recognized that there is a need to gain the understanding of the public for the safety byexplaining the safety case that is an integration of the arguments and evidence for the safety
and reliability of the geological disposal system.
The arguments to demonstrate the safety of geological disposal involve a great deal ofknowledge in a variety of disciplines. The related knowledge will be increased over the several
decades of the disposal project period. Compilation of such knowledge of geological disposal in
the framework of explanation of the safety and sharing of this knowledge among relevant
persons will be important. JAEA has developed the JAEA KMS (Knowledge Management
System) and CoolRep as frameworks for that purpose1),2).
The knowledge obtained at the URLs will become important information for the design andsafety evaluation of the repository. In developing a safety case, integration of information inthree R&D areas (site characterization, repository design, and performance assessment) will
be required, rather than use of each of these areas individually, which will requirecommunication.
A geological environment model is used to communicate the knowledge obtained at the URLs
to the people in charge of design and performance assessment of a repository (Fig. 5.1-1).
However, direct use of the geological environment model in the communication will result in
unclear understanding of the validity of the model and the data used for the persons in chargeof design and performance assessment.
JAEA developed the Information Synthesis and Interpretation System (ISIS) as part of the“Development of advanced integration system of the geological environment” (2007–2012)
supported by the Agency for the Natural Resources and Energy, METI2),3),4),5),6),7),8),9),10),11),12).
In chapter 5, traceability from the geological environment model to the data used for themodel and communication strategy will be shown, focusing on ISIS.
It should be noted that descriptions, including both overviews and detailed ones, can be
structured in the CoolRep because it is a report on a web site. The CoolRep can ensure
traceability of the knowledge, because access to detailed descriptions, technical reports or
KMS could be possible as appropriate.

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Fig. 5.1-1 Relationship between each field of knowledge in construction of a safety case
5.2 Concept of ISISThe ISIS consists of an expert system that supports construction of geological environment
models and planning and implementation of a research program, a visualization tool for theconstructed geological environment model, an expert system development tool, an
investigation process management and geological environment electric document system, anda management cockpit that integrates these tools8),9) (Fig. 5.2-1). The management cockpit isa tool to integrate the other tools and knowledge under four tabs (Fig. 5.2-2) together withdifferent management tools and search tools such as a document management tool to manage
relevant documents and users.
The four tabs contain various tools, as described below8),9):- “Research program management tab”: To manage work plans such as investigation,
analysis, and evaluation; with tools to register different types of work (tasks) related tothe site characterization and to display them as a Gantt chart.
- “GEM” viewer tab: to display constructed 3D geological environment models or plans(views); possible to manage discussion or history of discussions on the view.
- “My page tab”: A groupware with tools to register tasks relevant to each person or request
tasks to other workers.
- “KMS tool group tab”: Arranged buttons to initiate tools or tools developed as part of the
ISIS such as a tool to elicit experts’ knowledge (expert system developing interface).
Utilizing the tools described above, ISIS can promptly and effectively support the decisionmaking by managers taken in various situations in the site characterization through the
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and ensure traceability of that knowledge.
In developing ISIS, potential major users were assumed to be those involved in the sitecharacterization (managers, persons in charge of in situ tests, design and performanceassessors) in the implementation body of the geological disposal (NUMO), and regulators in
the regulatory body on safety. With the aim of supporting different works related to thepreliminary investigation or the preceding stage of the site characterization stages, ISIS wasdeveloped to allow information considered to be useful for conducting site characterization at
potential sites for geological disposal, the results of R&D conducted at the URLs in JAEA, theresults of R&D on the geological environment conducted in and outside of Japan, and theexperiences, knowledge, and skills obtained by applying these results to be used effectively, byutilizing knowledge engineering methodology and IT as much as possible8),9).

Fig. 5.2-1 Concept of ISIS

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Fig. 5.2-2 Four tabs in the management cockpit
5.3 Results
As described in section 5.1, geological environment models are used for communicatingknowledge of the site characterization with the persons in charge of the design andperformance assessment of a repository. In providing knowledge of the site characterization to
the persons in charge of the design and performance assessment of a repository, the following
points are important:
1) Method to ensure traceability of knowledge, such as the validity of the geologicalenvironment model, the data used for the modeling, and the methods used to obtain thedata;2) Communication method – a method to reflect knowledge of persons in charge of design
and performance assessment;
3) Knowledge-eliciting method – a method to elicit arguments for the judgment by experts;
4) Knowledge-sharing method – a method to elicit the knowledge described in 1) to 3) above.
These methods for utilizing ISIS are described in detail below.
5.3.1 Method to ensure traceability of knowledge
This section describes the method of ensuring traceability of knowledge for the geologicalenvironment model.
In constructing a geological model, several options generated because of uncertainties in thegeological structure or several versions produced associated with the progress of theinvestigation will be studied. To manage these options or versions, the “geological environment
model history management tool” is equipped8),9).
The tool will be run from the KMS tool group tab. The geological environment models thatwere studied can be displayed in a tree-like structure to identify the relationships between
those options or versions of the studied geological environment models (Fig. 5.3.1-1).
A general description of each geological environment model can be displayed and linked to
the related knowledge as in a) through e) listed below. In addition, the system allows features- 264 -

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of the concerned geological environment model and data used for developing the model to bechecked. This tool will allow knowledge related to the geological environment model to be
traceable (Fig. 5.3.1-2).
a) Rule-base: Decision points, procedures, and concepts for developing a concerned geologicalenvironment modelb) Case-base: Note to be reminded in developing a geological environment modelc) Relevant documents: Technical reports, academic literatures, used data books, andrelated web sites that describe the characteristics of the geological environment modeld) Related images: Figures of geological environment models, etc.
e) Related tasks: Information related to the task of “development of concerned geologicalenvironment model” (including objective, responsible persons, duration, and used
information or results)

Fig. 5.3.1-1 The GEM historical management tool

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Fig. 5.3.1-2 Knowledge linkable to the GEM historical management tool
Item e) described above is the one registered to the research programme management tab in
ISIS.
By registering the task to the tab, the processes for developing a geological environment
model and the data-obtaining process used in developing a concerned geological environment
model can be displayed on this tab (Fig. 5.3.1-3).
The information listed below could be registered and linked to each task:f) General description of task: Description of concerned tasks (objective, specific task,
discrepancy between plan and record, and responsible persons)g) Information used to implement the task: Link to existing rule-base or case-base, link torelated task and external web site, registration of documents in the management cockpit,
and other information (note to be reminded in implementing the task)h) Output obtained by implementing the task: Description of overviews, registration of
documents additionally compiled and registered in the management cockpit.
The system has a tool to make a task flow using tasks registered in the research program
management tab. The tool will allow correlation of the geological environment model and theinvestigation in which data used for developing the model was obtained, which will help toensure traceability (Fig. 5.3.1-4).

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Fig. 5.3.1-3 Registration of tasks to the research programme management tab

Fig. 5.3.1-4 Task flow diagram constructed using the registered tasks
5.3.2 Communication method
The information used for developing a geological environment model can be obtained by using
the tools shown in section 5.3.1. However, communication between related persons will be
required for developing a geological environment model in practice or checking conformity
with other geological environment models with respect to characteristics of the geologicalenvironment, or providing a geological environment model to persons in charge of the design
and performance assessment. In addition, people involved in different disciplines may require
cooperation in preparing a research program for the subsequent phases.

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The methods for supporting communication and cooperative work will be described in thissection.
The “GEM viewer” tab can be utilized for communication8),9) (Fig. 5.2-2).
In the “GEM viewer” tab, geological environment models and figures among related persons
can be registered as a view, which can be displayed Fig. 5.3.2-1. By writing on the marker set
on the view, discussions can be developed on the web site (Fig. 5.3.2-1), which will facilitatecommunication. As the conclusion of the discussion can be recorded, this can be checked as
information related to the geological environment model by correlating to the task that wasmade using the geological environment model history management tool or research program
management tab, as described in section 5.3.1.
The discussion on the web site will allow cooperation in planning subsequent phases.
A “story board” tool is also equipped as a tool to support cooperative work. As an example,
evolution of the geological environment at a certain location or T-H-M-C evolution around theengineered barriers can be defined by cooperative work8),9) (Fig. 5.3.2-2). The story board will
be run from the KMS tool group tab.

Fig. 5.3.2-1 Discussion using a viewFig. 5.3.2-2 An example of a story board- 268 -

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5.3.3 Knowledge-eliciting method
Site characterization will be conducted using different knowledge and skills that are owned
by experts. Such knowledge and skills are unlikely to be described in reports, and experts
often possess their own knowledge and skills. It will be important to obtain this type ofknowledge as much as possible in passing information on to future generations, developing
human resources, and transferring technologies. The knowledge-eliciting method will be
described in this section.
In order to elicit the knowledge possessed by experts and facilitating utilization of thisknowledge by other persons, repeated communications between knowledge engineers and sitecharacterization experts are required in general. However, eliciting knowledge using thismethod is time-consuming. The time available for site-characterization experts to share forinterview were limited, and this process was thus a bottle-neck in gaining knowledge. In
addition, although the site-characterization experts do not necessarily have knowledge of the
program language; knowledge of program language is essential for storing the extracted
knowledge. Therefore, in order to enable the experts to elicit knowledge by themselves as muchas possible, a knowledge-eliciting method was constructed by developing a task flow anddecision-making flow diagram4),5),6),7),8),9),13). In addition, based on the decision-making flow
diagram, an interface to develop an expert system was developed to allow extraction ofknowledge and storage of the extracted knowledge by inputting knowledge that the experts
have using natural language through a web site8),9),14).
The expert system for the ISIS consists of a rule-base and a case-base.
The knowledge that is expressed as a rule such as an “if…then format” can be elicited byusing a rule-base development interface (Fig. 5.3.3-1). Information such as those referred toin implementing similar events in the future including failure or successful experiences could
be elicited by using a case-base development interface, though these cases can not be definedby rules (Fig. 5.3.3-2).
Experts in site characterization can prepare a rule-base or case-base by themselves using
these interfaces. As these bases can be corrected, existing rule-bases or case-bases will be
updated or newly prepared as appropriate when new knowledge is obtained.
Researchers in JAEA and other institutes have compiled knowledge by developing a task flow
and decision-making flow diagram to date. Based on the decision-making flow diagram, therule-bases have been developed and case-bases based on experiences obtained throughinvestigations and analyses have also been constructed13),15),16),17),18),19),20),21),22),23),24),25),
26),27),28),29),30),31),32),33),34),35),36),37),38),39).

Interfaces for the rule-base and case-base will be run from the KMS tool group tab.

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Fig. 5.3.3-1 Development of rule-bases using the rule-base development interface

Fig. 5.3.3-2 Development of case-bases using the case-base development interface
5.3.4 Knowledge sharing method
As described in section 5.2, the ISIS management cockpit has tools to manage documents tobe shared in addition to knowledge in the rule-base and case-base. The system can manage
them while correlating with tasks and other ISIS tools, which can assist with sharing
knowledge among related persons during the progress of the project. After completing the
project, the system can provide information correlated to each other, by which it can support
sharing knowledge between different generations8),9).
5.4 Summary
In developing a safety case, the results of site characterization and design of a repository andperformance assessment need to be integrated. The geological environment model will be used
for communicating between those persons in charge of these three areas. However, the use of
the geological environment model directly will result in unclearness regarding the model
validity and data used for the persons in charge of the design and performance assessment.
Assuming that knowledge of the site characterization be provided to the persons in charge ofdesign and performance assessment of a repository, traceability of knowledge must be ensured
and communication between these persons will be required. Knowledge about the project
including the validity of the method to obtain the provided knowledge is also required to beshared between the related persons. Eliciting experts’ knowledge will be important for
fostering human resources and communicating knowledge.
The chapter 5 demonstrated that a tool to support ensuring traceability of knowledge aboutsite characterization, communication, eliciting of knowledge, and knowledge sharing could be
successfully developed using ISIS for use in JAEA KMS, i.e., a system related to the site

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characterization.
This system will allow communication and sharing of information with traceability inconstructing a safety case. Such knowledge will be further improved and increased by utilizing
ISIS in the future.
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Sekiya, A. : “Collection and analysis of existing information on applicability of investigation
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and Radioactive Waste Management ICEM2011, ICEM2011-59171, September 25-29, 2011,
Reims, France (CD-ROM) (2011).
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20) Iwatsuki, T., Mizuno, T., Kunimaru, T., Amano, Y., Matsuzaki, T. and Semba, T. : “Expert
system of hydrochemical modeling methods for geological disposal of HLW - Know-how onhydrochemical investigation and modeling in Literature survey stage to Detailinvestigation stage -”, Journal of Nuclear Fuel Cycle and Environment, 19(2), pp.51-63(2012). (in Japanese).
21) Iwatsuki, T., Mizuno, T., Amano, Y., Kunimaru, T. and Semba, T. : “Expertize ofHydrochemical Investigation Know-how for Deep Underground”, JAEA-Research 2011-049(2012), 68p. (in Japanese).
22) Kunimaru, T., Ota, K., Amano, K. and Alexander, W. R. : “Development of a Quality
Management System (QMS) for Borehole Investigations: (2) Evaluation of Applicability of
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23) Kunimaru, T., Takeuchi R. and Matsuzaki, T. : “Technical Know-how of Selection Process
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Waste Management ICEM2011, September 25-29, 2011, ICEM2011-59088, Reims, France(CD-ROM) (2011).
24) Kurihara, A., Matsuoka, T. and Martin, A. J. : “Quantitative evaluation of fault
distribution uncertainty: Applicability of an analytical method for evaluating 3-D geologicalmodels in the Mizunami Underground Research Laboratory Project.”, Proc. of theInternational Symposium on Earth Science and Technology 2010,12, Fukuoka, Japan(2010).
25) Matsuoka, T., Amano, K., Osawa, H. and Semba, T. : “Information Synthesis andInterpretation System (4) Procedure for Geological Modeling”, Japan Geoscience Union
Meeting 2010 Abstract, SCG084-P02 (CD-ROM) (2010). (in Japanese).
26) Matsuoka, T., Amano, K., Osawa, H. and Semba, T. : “Technical Know-how for Modelingof Geological Environment (2) Geological Modeling”, Proc. ICEM 2010: 13th International
Conference on Environmental and Radioactive Waste Management, October 3-7, 2010,
Tsukuba, Japan, ICEM2010-40066 (CD-ROM) (2010). (in Japanese).
27) Matsuzaki, T., Iwatsuki, T., Nakayasu, A. and Semba, T. : “Information Synthesis andInterpretation System(6) Development of Expert system for planning method ofinvestigations”, Japan Geoscience Union Meeting 2010 Abstract, SCG084-P04 (CD-ROM)(2010). (in Japanese).
28) Mizuno, T., Takeuchi, R., Tsuruta, T., Matsuoka, T., Kunimaru T. and Saegusa, H. :“Technical know-how

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based on resistivity data for a rock mass”, AGU Fall Meeting 2012, H33J-1477 (2012).
30) Nakatsukasa, M. and Yamada, Y. : “Modeling of fold-and-thrust belt by analogue
experiment and simulation considering erosion”, Japan Geoscience Union Meeting 2012
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31) Nakayasu, A., Doke, R., Urabe, A., Ono, E. and Niizato, T. : “Evaluation of uncertainty
using Evidential Support Logic, case study of the research on estimation of uplift rate”,
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32) Niizato, T., Yasue, K., Doke, R., Nakayasu A. and Shigehiro, M. : “Technical know-how
and decision process for geoscientific investigation of geological disposal (2) An
externalization of tacit knowledge in a geoscientific investigation; an example ofinvestigations for an estimation of uplift rate”, Societies -Muroto Geopark-, August 23-25,
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33) Saegusa, H., Maekawa, K., Oyama, T. and Semba, T. : “Information Synthesis andInterpretation System (3) Modeling Area Setting and Groundwater Flow Modeling”, Japan
Geoscience Union Meeting 2010 Abstract, SCG084-P01 (CD-ROM) (2010). (in Japanese).
34) Saegusa, H., Takeuchi, S., Maekawa, K., Osawa, H and Semba, T : “Technical Know-how
for Modeling of Geological Environment (1) Overview and Groundwater Flow Modeling.”,
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35) Saegusa, H., Niizato, T., Yasue, K., Onoe, H. and Doke, R. : “Technical Know-how of Site
Descriptive Modeling for Site Characterisation.”, Proceedings of the ASME 14th
International Conference on Environmental Remediation and Radioactive Waste
Management ICEM2011, September 25-29, 2011, ICEM2011-59089, Reims, France (CDROM) (2011).
36) Semba, T., Takeuchi, S., Tokiwa, T., Niizato, T. and Osawa, H. : “Technical know-how anddecision process for geoscientific investigation of geological disposal of HLW (1) Overview ofInformation Synthesis and Interpretation System (ISIS) and application of investigation
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国際単位系（SI）
表１．SI 基本単位
SI 基本単位

基本量

名称
記号
長
さメ ートル m
質
量 キログラム kg
時
間
秒
s
電
流ア ンペア A
熱力学温度 ケ ル ビ ン K
物 質 量モル mol
光度 カ ン デ ラ cd

表２．基本単位を用いて表されるSI組立単位の例
SI 組立単位
組立量
名称
記号
面
積 平方メートルm2
体
積 立方メートルm3
速 さ ， 速 度 メートル毎秒m/s
加速度 メートル毎秒毎秒
m/s2
波
数 毎メートルm-1
密 度 ， 質 量 密 度 キログラム毎立方メートル
kg/m3
面
積
密
度 キログラム毎平方メートル
kg/m2
比
体
積 立方メートル毎キログラム
電流
密
度 アンペア毎平方メートル
磁 界 の 強 さ アンペア毎メートル
量 濃 度 (a) ， 濃 度 モル毎立方メートル
質量
濃度 キログラム毎立方メートル輝
度 カンデラ毎平方メートル屈折率 (b) （数字の） １
比 透 磁 率 (b) （数字の） １

乗数
24

10
1021
1018
1015
1012
109
106
103

3

m /kg
A/m2
A/m
mol/m3
kg/m3
cd/m2
1
1

102
101

ヨ

表５．SI 接頭語
記号
乗数
名称
タ
Ｙ
シ
10-1 デ

ゼ
タ
エ ク サ

Ｚ
Ｅ

10-2

ペ
テ

タ
ラ

Ｐ
Ｔ

ギ
メ

ガ
ガ

Ｇ
Ｍ

マイクロ
ノ
10-9 ナコ
10-12 ピ
10-15 フェムト

キ
ロ
ヘ ク ト
デ
カ

ｋ
ｈ
da

10-3
10-6

記号

セ ン チ
ミ
リ

ト
10-18 ア
10-21 ゼ プ ト
10-24 ヨ ク ト

d

c
m
µ
n
p
f
a
z
y

表６．SIに属さないが、SIと併用される単位
名称
記号
SI 単位による値
分
min 1 min=60 s
時
h 1 h =60 min=3600 s（a）量濃度（amount concentration）は臨床化学の分野では物質濃度（substance concentration）ともよばれる。
（b）これらは無次元量あるいは次元１をもつ量であるが、そのことを表す単位記号である数字の１は通常は表記しない。

d
°
’

日
度
分

表３．固有の名称と記号で表されるSI組立単位
SI 組立単位
組立量
他のSI単位による SI基本単位による
名称
記号
表し方
表し方
（ｂ）
平
面
角 ラジアン(ｂ)
rad
m/m
1
（ｂ）
(ｂ)
(c)
2
2
立
体
角 ステラジアン
sr
1
m /m
周
波
数 ヘルツ（ｄ）
Hz
s-1
力
ニュートン
N
m kg s-2
圧力
応
力 パスカル,Pa
N/m2
m-1 kg s-2
エ ネ ル ギ ー , 仕 事 , 熱 量 ジュールJNm
m2 kg s-2
仕 事 率 ， 工 率 ， 放 射 束 ワット
WJ/s
m2 kg s-3
電
荷
電気量 クーロン,
CsA
電 位 差 （ 電 圧 ） , 起 電 力 ボルト
VW/A
m2 kg s-3 A-1
静電
容量 ファラドF
C/V
m-2 kg-1 s4 A2
電
気
抵
抗 オーム
Ω
V/A
m2 kg s-3 A-2
コ ン ダ ク タ ン ス ジーメンス
S
A/V
m-2 kg-1 s3 A2
磁
束 ウエーバWb
Vs
m2 kg s-2 A-1
磁
束
密
度 テスラ
T
Wb/m2
kg s-2 A-1
イ ン ダ ク タ ン ス ヘンリーH
Wb/A
m2 kg s-2 A-2
セ ル シ ウ ス 温 度 セルシウス度(ｅ)℃K
光
束 ルーメンlm
cd
cd sr(c)照度 ルクスlx
m-2 cdlm/m2
Bqs-1
放 射 性 核 種 の 放 射 能 （ ｆ ） ベクレル（ｄ）
吸収線量, 比エネルギー分与,
グレイ
Gy
J/kg
m2 s-2カーマ
線量当量, 周辺線量当量,Sv
J/kg
m2 s-2シーベルト（ｇ）
方向性線量当量, 個人線量当量酸素
活性 カタールkat
s-1 mol

1 d=24 h=86 400 s
1°=(π/180) rad1’=(1/60)°=(π/10 800) rad”1”=(1/60)’=(π/648 000) radha 1 ha=1 hm 2=104m2
L，l 1 L=1 l=1 dm3=103cm3=10-3m3t
1 t=103 kg

秒
ヘクタール
リットル
トン

表７．SIに属さないが、SIと併用される単位で、SI単位で表される数値が実験的に得られるもの
名称
記号
SI 単位で表される数値
電 子 ボ ル ト
ダ ル ト ン
統一原子質量単位

eV
Da
u

天

ua

文

単

位

1 eV=1.602 176 53(14)×10 -19J

1 Da=1.660 538 86(28)×10-27kg
1 u=1 Da

1 ua=1.495 978 706 91(6)×1011m

表８．SIに属さないが、SIと併用されるその他の単位
名称
記号
SI 単位で表される数値
バー
ル bar １bar=0.1MPa=100 kPa=10 5Pa
水銀柱ミリメートル mmHg １mmHg≈133.322Pa(a)SI接頭語は固有の名称と記号を持つ組立単位と組み合わせても使用できる。しかし接頭語を付した単位はもはや
コヒーレントではない。
(b)ラジアンとステラジアンは数字の１に対する単位の特別な名称で、量についての情報をつたえるために使われる。
実際には、使用する時には記号rad及びsrが用いられるが、習慣として組立単位としての記号である数字の１は明示されない。
(c)測光学ではステラジアンという名称と記号srを単位の表し方の中に、そのまま維持している。
(d)ヘルツは周期現象についてのみ、ベクレルは放射性核種の統計的過程についてのみ使用される。
(e)セルシウス度はケルビンの特別な名称で、セルシウス温度を表すために使用される。セルシウス度とケルビンの単位の大きさは同一である。したがって、温度差や温度間隔を表す数値はどちらの単位で表しても同じである。
(f)放射性核種の放射能（activity referred to a radionuclide）は、しばしば誤った用語で”radioactivity”と記される。
(g)単位シーベルト（PV,2002,70,205）についてはCIPM勧告2（CI-2002）を参照。

表４．単位の中に固有の名称と記号を含むSI組立単位の例
SI 組立単位
組立量
SI 基本単位による
名称
記号
表し方
-1
粘
度 パスカル秒
Pa s
m kg s-1
力 の モ ー メ ン ト ニュートンメートル
Nm
m2 kg s-2
表面
張力 ニュートン毎メートル
N/m
kg s-2角
速度 ラジアン毎秒
rad/s
m m-1 s-1=s-1
角
加速度 ラジアン毎秒毎秒
rad/s2
m m-1 s-2=s-2
熱 流 密 度 , 放 射 照 度 ワット毎平方メートル
W/m2
kg s-3
熱 容 量 , エ ン ト ロ ピ ー ジュール毎ケルビン
J/K
m2 kg s-2 K-1
比 熱 容 量 ， 比 エ ン ト ロ ピ ー ジュール毎キログラム毎ケルビン J/(kg K)
m2 s-2 K-1
比 エ ネ ルギ ー ジュール毎キログラム
J/kg
m2 s-2
熱伝
導率 ワット毎メートル毎ケルビン W/(m K) m kg s-3 K-1
体 積 エ ネ ル ギ ー ジュール毎立方メートル J/m3
m-1 kg s-2
電界の強さ ボルト毎メートル
V/m
m kg s-3 A-1
電荷密
度 クーロン毎立方メートル C/m3
m-3 s A
表面
電
荷 クーロン毎平方メートル C/m2
m-2 s A電 束 密 度 ， 電 気 変 位 クーロン毎平方メートル C/m2
m-2 s A誘
電率 ファラド毎メートル
F/m
m-3 kg-1 s4 A2
透磁率 ヘンリー毎メートル
H/m
m kg s-2 A-2
モ ル エ ネ ル ギ ー ジュール毎モル
J/mol
m2 kg s-2 mol-1
モルエントロピー, モル熱容量 ジュール毎モル毎ケルビン J/(mol K) m2 kg s-2 K-1 mol-1
照 射 線 量 （ Ｘ 線 及 び γ 線 ） クーロン毎キログラム
C/kg
kg-1 s A
吸収線
量率 グレイ毎秒
Gy/s
m2 s-3放射
強度 ワット毎ステラジアン
W/srm4 m-2 kg s-3=m2 kg s-3
放射輝
度 ワット毎平方メートル毎ステラジアン W/(m2 sr) m2 m-2 kg s-3=kg s-3
酵 素 活 性濃 度 カタール毎立方メートル kat/m3
m-3 s-1 mol

名称

オングストローム
海
里
バ
ー
ン

Å
Ｍ

１Å=0.1nm=100pm=10-10m
１M=1852m

b

ノ
ネ
ベ

ト
パ
ル

kn
Np
Ｂ

１b=100fm2=(10-12cm) 2 =10-28m2
１kn=(1852/3600)m/s

ル

dB

ッ
ー

デ

シ

ベ

SI単位との数値的な関係は、対数量の定義に依存。

エ

表９．固有の名称をもつCGS組立単位
名称
記号
SI 単位で表される数値
ル
グ erg 1 erg=10-7 J

ダ
ポ

イ
ア

ス
ス

ト ー ク
チ
ル

フ
ガ

ォ

ン dyn 1 dyn=10-5N
ズ P 1 P=1 dyn s cm-2=0.1Pa s
ス St 1 St =1cm2 s-1=10-4m2 s-1
ブ sb 1 sb =1cd cm-2=104cd m-2
ト ph 1 ph=1cd sr cm-2 =10 4lx
ル Gal 1 Gal =1cm s-2=10-2ms-2

マ ク ス ウ エ ルガ
ウス
エルステッド（ ａ）

Mx
G
Oe

1 Mx = 1G cm2=10-8Wb
1 G =1Mx cm-2 =10-4T
1 Oe (103/4π)A m-1（a）３元系のCGS単位系とSIでは直接比較できないため、等号「は対応関係を示すものである。

キ
レ
ラ

名称
ュ
リ
ン

レ
ガ

ト

表10．SIに属さないその他の単位の例
記号
SI 単位で表される数値
ー Ci 1 Ci=3.7×1010Bq

ゲ

ン

ン R
ド rad
ム rem
マ γ

フ
ェ
ル
ミ
メートル系カラット

1 R = 2.58×10-4C/kg

1 rad=1cGy=10-2Gy
1 rem=1 cSv=10-2Sv
1 γ=1 nT=10-9T
1 フェルミ=1 fm=10-15m

ト
標

準

気

1 メートル系カラット = 0.2 g = 2×10-4kg
ル Torr 1 Torr = (101 325/760) Pa
圧 atm 1 atm = 101 325 Pa

カ

ロ

リ

ー

cal

ミ

ク

ロ

ン

µ

大

」

1 cal=4.1858J（｢15℃｣カロリー），4.1868J（｢IT｣カロリー），4.184J（｢熱化学｣カロリー）

1 µ =1µm=10-6m（第8版，2006年）