SCIENTIFIC BASIS FOR NATIONWIDE SCREENING OFGEOLOGICAL DISPOSAL SITES IN JAPAN
Takehiro Matsumoto1, Hideaki Hyodo1, Hiromitsu Saegusa1, Akira Deguchi1, Hiroyuki Umeki1
1

Nuclear Waste Management Organization of Japan (NUMO)
4-1-23, Shiba, Minato-ku, Tokyo, 108-0014 Japan

Key words; geological disposal, site selection process, nationwide screening

Abstract
In Japan, the legal system (Final Disposal Act) was established for geological disposal of high level radioactive waste in
2000, which specifies three steps of siting process as literature survey, preliminary investigation and detail investigation to
be conducted by the Nuclear Waste Management Organization of Japan (NUMO). Although NUMO has been promoting
the siting process by a volunteering approach, no volunteer so far has appeared and selection of geological disposal sites
in Japan has not advanced significantly over 15 years. Taking such situation into consideration, the government reinforced
measures for achieving solutions and promoting geological disposal in the “Strategic Energy Plan” published in April
2014. In association with the reinforcement, a new process for selecting repository sites, which is the nationwide
screening by the government before initiating legally defined siting process, has been added by the revision of the Basic
Policy in May 2015. The nationwide screening is aiming at deepen public understanding of geological disposal.

1. Introduction
Discussion for the nationwide screening for stepping
into the literature survey was initiated in December 2014
at Geological Disposal Technology Working Group(Technology WG), which is a geological disposal
advisory committee for the Ministry of Economy, Tradeand Industry (METI). Technology WG developed
requirements and criteria for the screening, andsummarized them in the report which was published in
April 2017 (Technology WG, 2017). In July 28, 2017,
METI published “Nationwide Map of “ScientificFeatures” relevant for Geological Disposal” (METI,
2017(http://www.enecho.meti.go.jp/category/electricity_a
nd_gas/nuclear/rw/kagakutekitokuseimap/maps/kagakutekitokuseimap.pdf (in Japanese)), which was drawn up
based on the report.
NUMO has been developing the nationwide informationbase on the geological environment to be utilized for its
siting process by reflecting the state-of-the-art knowledge.
The information base contributed to the discussion atTechnology WG.
This paper presents the scientific and technical basis for
identification of requirements and criteria for nationwide
screening by Technology WG.
2. The Map for the nationwide screening
The nationwide screening by “Nationwide Map of“Scientific Features” relevant for Geological Disposal”
does not directly indicate specific areas which havesuitable scientific features for developing a geologicalrepository. Stepwise investigation and careful evaluationof candidate sites according to the Final Disposal Act are

essential for selecting a final repository site; this takes into
account various other important factors that are not taken
into account in the Map. Publication of the Map is thefirst step on a long way toward completion of geologicaldisposal.
Areas in the Map are classified by four features“Assumed to be unfavorable from the viewpoint oflong-term stability of the deep geological environment”,“Assumed to be unfavorable from the viewpoint of therisk of future inadvertent human intrusion”, “Assumed to
be favorable” and “Assumed to be preferable also fromthe viewpoint of safe waste transportation”. The
requirements and criteria by Technology WG which areapplied to identify the feature of nationwide areas inJapan are shown in Table 1. The applicability of thecriteria to the four features is shown in Fig. 1.
3. Scientific and technical basis for developing therequirements and criteria
3.1 Basic approach
Technology WG discussed the requirements and criteria
from the viewpoints of 1) geological environment
characteristics and their long-term stability favorable togeological disposal; 2) safety of construction andoperation of facilities; and 3) safety and security of wastetransportation.
Reliable literatures or data, which cover nationwide
areas and are widely available, are selected for developing
the requirements and criteria. In the case when there does
not exist available nationwide data directly used for acriterion, the corresponding requirement is not consideredor alternative criterion is applied if this alternative is

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanrelevant to the corresponding requirement and nationwide
data is available.
For coastal areas which include islands and underseabed, a special study group (Study Group) was
organized to discuss their distinctive features from theview points above mentioned. These features include
favorable characteristics for geological disposal, whichare 1) very low driving force for groundwater flow andmass transport is highly expected and 2) low uplift rate isobserved many places. It is also pointed out for coastal
areas that special attention should be paid to long-term
hydraulic and geochemical changes associated withsea-level changes. The Study Group concluded thatdevelopment of repository at coastal areas is generally
feasible based on the existing technology although R&Ds
are required further to provide geological environment

data and demonstrate investigation techniques specific tothese areas (Study Group, 2016).
NUMO information base for nationwide geologicalenvironments based on open literature was used for the
discussion at Technology WG to provide clear evidence
and arguments for development of requirements andcriteria. The discussion at Technology WG were widely
opened to ask comments, and to be reviewed by technicalexperts in the relevant academic societies and OECD
NEA international review team (NEA, 2016). The review
comments were then discussed at Technology WG further
to modify the requirements and criteria if needed.

Table 1, The requirements and criteria for classification of areas corresponding to specific features (METI, 2017)

Fig. 1, Relationship between the criteria and classification of areas (METI, 2017)

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

3.2 Long-term stability of favorable geologicalenvironments
3.2.1 Requirements and criteria for THMC conditions
Preferable Thermal, Hydrological Mechanical andChemical (THMC) conditions for geological disposal,
from the viewpoint of containment safety function,
characteristics and properties of geological environment
are identified as follows; “low ambient rock temperature”
for restricting temperatures in the Engineered Barrier
System (EBS), “small rock deformation” for themechanical stability of the EBS, “slow groundwater
movement” mainly for the natural barrier function and“Neither high nor low groundwater pH”, “reducing
groundwater” and “low dissolved inorganic carbon in
groundwater” for preventing or restricting dissolution or
migration of radionuclides from the EBS (Table 2).
The THMC conditions should however evaluatedcomprehensively by taking into account interactions
between each conditions at a specific site, which needs
detailed characterizations through site specificinvestigations. These conditions were therefore notapplied for the Map as requirements and criteria.
3.2.2 Requirements and criteria for disruptive natural
events and process
Natural disruptive events and processes thatsignificantly affect the long-term safety of a geologicaldisposal system were identified at Technology WG, forwhich requirements and criteria were discussed forproviding the Map.
As a result, the relevant events and processes with theirconsequence/impact on safety function of containment
and isolation in this regard are 1) volcanic/igneous activity,
2) fault movement, 3) uplift/erosion, 4) geothermal
activity, and 5) volcanic thermal fluids and deep-seatedfluids (see Table 1). The scientific basis to provide criteria
for these events and processes are summarized in thefollowing sections.
3.2.2.1 Volcanic/igneous activity
The locations where volcanic activity occurred in theJapanese archipelago during the Late Miocene to the
Pliocene are limited to distinct regions, only within the

East Japan Volcanic Belt and the West Japan Volcanic
Belt; changes in the location of volcanism during the past
hundreds of thousands of years occurred within somevolcanic regions, including expansion, shrinkage or
movement of active volcanic regions. However, there has
been no prominent shift in the location of volcanic fronts
on the scale of the island arc.
A volcanic front has also developed in Hokkaido. In
southwest Japan, a volcanic front has not clearly
developed in the region extending from San'in to north
Kyushu (Fig.2).
The individual volcanic bodies of each Quaternary
volcano are distributed within 15 km from a
representative location of the volcano in all but some
exceptional cases (Fig.3).
As a nationwide documentation, “Volcanoes of Japan(3rd Edition)” (Geological Survey of Japan, AIST, 2013)
was used for the basis to define the center of each volcano
identified available.
3.2.2.2 Fault movement
Fault movement reaching the repository would break
the repository and damage the barrier performance. In
addition, fault has fracture zone (damage zone) that has
high fracture density, in which has potential to cause
water conducting. Active faults in vicinity of disposalsites are thus to be avoided. In Japan, same tendency ofearthquakes and fault movements of known active faults
have continued approximately past several 100,000 years(JNC, 2000a). From this reason, it can be considered that
present tendency of active fault movements will continue
for future about 100,000 years (JNC, 2000a).
In addition, some papers are shown relationships
between the length of existing faults and the width ofcrush zones (e.g. about 1/350 to 1/150 of fault length(Ogata and Honsho, 1981)).
As a nationwide documentation, “Active Fault Databaseof Japan” (website of Geological Survey of Japan, AIST)
was used for the basis to define the location and length ofactive fault.
3.2.2.3 Uplift/erosion
The mode and rate of crustal movement that have beenstable since the Middle Pleistocene will quite likely

Table 2, Favorable geological environment characteristics for geological disposal (NEA, 2016)

Source : Technology WG (2014), Table 1

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanremain unchanged for future at least about 100,000 years
or so (Umeda et al., 2013). The present understanding is,therefore, that the current mode and rate of crustal
movement will very likely continue for the next hundred
thousand years or so.
Particularly in coastal areas, it is necessary to take into
account that sea-level changes which the maximum
sea-level drop of 150 m during a glacial stage erosion rate
(Clark et al., 2009).
“Japanese Island-arc and Geosphere Stability”(Committee for Geosphere Stability Research, 2011) was
selected to use for the criteria because it shows average
uplift rates of recent 100,000 years as approximately

20km×20km square areas based on the investigations of
sea terraces and river terraces.
However, the legend of the literature designates areas
where the recent uplift rate exceeds 300m/100,000 years
as ‘uplift amounting to >90m during the last 100,000
years’, hence the recent uplift rate exceeds past
300m/100,000 years couldn’t be settled as the criteria. On
the other hand, in coastal areas, the largest estimation of
Quaternary sea level fall is 150m below the current levelfrom mainly the investigations about oxygen isotopes of
ice sheet or fissile (e.g. Huybrechts, 2000). This figure
could account for an eroded thickness of 150m of
overburden. Take this into consideration, coastal areas
where designated as ‘uplift amounting to >90m during thelast 100,000 years’ is likely to excess erosion of 300 m
in next 100,000 years.
3.2.2.4 Geothermal activity
If ground temperature exceeds 130°C for 10,000 years
or exceeds 170°C for 10,000 years, montmorillonite inbuffer would be altered by 50% and performance of thebuffer will be reduced (JNC, 2000b). On the other hand,
JNC (2000b) shows that montmorillonite alteration which
losses ability of the buffer would not be caused in thetemperature of under 100°C from many references.
Considering the repository size (6~10km2), themaximum occupied area of the waste in the repository is
86.6m2 (JNC, 2000b). From thermal analysis, rising intemperature of the buffer in the occupancy isapproximately 40°C not depends on rocks or waste
emplacement style (JNC, 2000b). Assuming theshallowest depth of 300m and surface temperature of
15°C, geothermal gradient of greater than 15°C /100m
may lead to the excess 100°C of the buffer temperature.
As a nationwide database, “Geothermal potential Map
in Japan” (in Japanese) (Geological Survey of Japan,
AIST, 2009) was used for applying the criteria.

Fig. 2, Distribution of Quaternary volcanoes andvolcanic front in Japan (Based on Geological
Survey of Japan, AIST, 2013))

Fig. 3, Maximum distance and frequency between
the center of Quaternary volcanoes and individual
volcanic bodies (Based on Committee for catalogof Quaternary volcanoes in Japan, 1999 and
NUMO, 2004 )3.2.2.5 Volcanic thermal fluids and deep-seated fluids
Existence of low pH groundwater, which derives fromvolcanic thermal fluids or deep-seated water, would
accelerate dissolution of the waste (ex. Wicks et al., 1982,
Inagaki et al., 2012). In addition, carbonate concentration
higher than 0.5mol/dm3, which derives from deep seatedwater, would cause passivation and local corrosion of
overpack due to the passivation (Taniguchi et al., 1999).
However, there is none nationwide literature or data inwhich show existence of hydrothermal convection/deepseated water. For this reason, groundwater with pH lessthan 4.8 that is actual acid region in which has no HCO3(Noda and Takahashi, 1992), or carbonate concentration
higher than 0.5mol/dm3 are considered as the criteria
instead of.
As a nationwide database, same database for geothermal
activity was used for applying the criteria.
3.2.3 Requirements and criteria for human intrusion
Existences of mineral resources of current or potential
economic values are in potential conflict with therepository. After closure and the potential loss of

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanknowledge and memory about the repository, resource
exploration or mining activities might cause an
inadvertent human intrusion into the repository. This
would cause a loss of containment function of therepository.
For nationwide screening of areas with the use ofhydrothermal convection, hot springs and groundwater as
resources, into difficult to set a uniform criteria about theimportance as natural resources. In addition, groundwaterin the depth of less than 300m is normally used as water
resources. As a result, only the mineral mines which areregistered by the mining law and have some quantity
were defined as a requirement to be excluded.
Since there is none of nationwide literature or datasatisfying the requirement, only fields of oil or gas
showed in Geological Survey of Japan (1976), coal
showed in Geological Survey of Japan (1973), and metal
deposits showed in Naito (2017) were used for applying
the criteria.
3.3 Requirements and criteria for engineering
feasibility and safety
Examples of technical bases for identifying the criteria
to them are as follows.
3.3.1 Construction of facilities
For the safety of the underground facilities, it isimportant to provide safe condition for workers whenconstructing shafts and disposal galleries. Since there isalready much experience in similar construction works
such as tunnel excavation et al, and the Japan Society of
Civil Engineers presents a general concept and guidelines
for the assurance of safe work. These guideline indicatedthe specific risk factors to be considered: unconsolidated
geological formation, swelling rock, rock bursts, highground temperature and hot springs, harmful gas
emissions, flooding, and mud eruptions. There have beendeveloped a range of engineering countermeasures forindividual factors which can be applied flexibly,
depending on the specific conditions. It is thus generally
inappropriate to set criteria for these factors applied fornationwide screening.
If there is unconsolidated geological formation deep
underground, however, it is highly likely to collapse
during tunnel excavation because such formation is not
self-supporting, it is desirable to avoid the formation toensure working safes. Specifically, there is no nationwide
database directly showing the existence of unconsolidated
sediments at depths of 300 m or more. Instead, the factthat the geological formations younger than the Middle
Pleistocene are often unconsolidated (e.g. Yorita et al.,2009) was used as an alternative criteria (see Table 1).
For this criteria, nationwide documentation“Three-dimensional Model on the Boundary Depth andThickness of Sediments for Estimation of Groundwater
Storage in the Japanese Islands –first edition” (Koshigai
and Marui, 2012), which summarized the geological ages
and distribution of geological formations, was applied asavailable scientific basis.

3.3.2 Facility operation
The surface facilities include directly handlingradioactive waste, such as the plant encapsulating vitrified
wastes into overpacks. These facilities are required toassure safety operation, in order to minimize the risk ofradiation exposure resulting even at the accident. Since
there exist already similar facilities to handle and store
storing high-level radioactive waste, it was decided toconsider prevention of damage by collapse of the ground,earthquakes, tsunami and external impacts, by reference
to appropriate regulation criteria.
As these issues can be assessed only based on detailed
information obtained through field investigations at
individual sites, it is considered inappropriate to generally
set criteria for nationwide screening.
However, it is desirable to avoid any area where there isa possibility of an impact by volcanic eruptions (e.g.
pyroclastic flows) (see Table 1) that cannot be handled
during operational period. For this purpose, nationwide
database, “Seamless Digital Geological Map of Japan(1/200,000)” (website of Geological Survey of Japan,
AIST) was identified for applying the criteria.
3.4. Safe transportation and security
As the Japanese archipelago extends over 1,000 km
from north to south, consideration of the requirements interms of safe transportation for long-distance is needed.
Assuming restrictions set by the current legal system fortransportation of radioactive materials, marinetransportation is considered to be more preferable method
for long distance transportation than land transportation
by railway or vehicle in terms of expected radiologicalrisk and security.
Even for long-distance marine transportation, landtransportation is needed from the nearest harbor to thefinal disposal facilities. In that case, it is consideredappropriate to set a requirement of sufficiently shortdistance from a harbor to identify “preferable area”. Thisrequirement should be considered both safety (public
exposure) and nuclear security (short transportation time,etc.), when assuming the restrictions in the current legal
system and also limitations of transportation infrastructure(restrictions on the gradient, need for constructing
dedicated roads, etc.).
As an indication for the requirements, it is consideredappropriate to apply to areas within about 20 km from thecoast, based on past experience of land transportation of
vitrified waste over about 10 km.
4. Conclusions
In July 28, 2017, METI published “Nationwide Map of“Scientific Features” relevant for Geological Disposal”,
which was drawn up applying the requirements andcriteria to identify features of areas nationwide provided
by Technology WG. Scientific and technical bases for therequirements and criteria for the Map were provided by
NUMO.
Publication of the Map is the first step on a long way
toward completion of geological disposal. NUMO will

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

continue to hold public dialogues to ensure a deeper
public understanding of geological disposal by utilizing
the Map.
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6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan