Project Subjects
High-Level Radioactive Waste Management
Background and Objective
Long term durability of underground facility and suppressive function of ultralong term radioactive
nuclide migration are required by considering geological/rock mechanical/hydraullic properties of deep seatedrock mass in the geological disposal of HLW. In this project research, CRIEPI proceeds with the developmentof elementary technology and systematization of these technologies for the PI (preliminary investigation) and theDI (detailed investigation).

Main results
１．Systematization and veriﬁcation of survey technology and estimation method for site selection
In order to conduct ecomic and rational PI, systematic survey and estimation ﬂow diagram of the PI isproposed based on the results of desk simulation to the virtual site and the knowledge accumulated during existing survey [N11]. The geological survey and drilling considering the proposed ﬂow diagram was conducted at
the CRIEPI Yokosuka site as a collaboration work with HLW implementer NUMO, and applicability of the ﬂow
diagram was estimated (Fig. 1). These results contribute to the NUMO activities.
2．Development of advanced element technology for site selection
Following element technologies thought to be important for the PI and the DI are developed.
(i) Ground water dating technology: Simple extraction method of 36Cl from water sample was developed[N09028] and 36Cl method together with 4He method were applied to the Horonobe site in Hokkaido and groundwater at the site can be estimated to be several million years old (Fig. 2) [N09027]. (ii) Controlled drilling
technology: Horizontal drilling from 800m to 900m long and survey and test in the borehole were carried out
and its applicability was demonstrated at the Hornobe site. (iii) Microbe effect assessment to the geochemical
condition: Laboratory test using rock and water sample collected at the Horonobe site was carried out. As a result,a microbial reaction induced the decrease of oxidation-reduction potential (Fig. 3). (iv) Estimation of long termrock mechanical behavior around disposal cavern: World ﬁrst centrifuge which can mount the model of disposal
pit was newly developed and an acceleration test for estimating the ultra long term behavior was started (Fig. 4).
Several monthsʼ operation of the centrifuge makes it possible to estimate rock deformation for several thousandyears.
Research on controlled drilling and ground water dating was done under contracts awarded from METI
(Ministry of Economy, Trade and Industry) and the on-site work was conducted in collaboration with JAEA
(Japan Atomic Energy Agency).
Other reports

16[N09016], [N09020], [N09026]

Nuclear Technology
Colored: water extraction from core sample
White: water sampling from borehole section

Drilling & survey plan

100No【【Borehole wall stability: low】
Mud water conditions

YesCasing cementing

Fresh water conditions

The endFig. 1 Flow diagram of drilling and survey in the PI stage
From the results of a desk simulation based on real data andcooperative research “Yokosuka D&V project” at the CRIEPI
Yokosuka, a systematic survey and estimation ﬂow and operation manual for the PI was constructed.

Oxidation-Reduction Potentials,
mV vs Ag/AgCl

Aeration
Aeration（Under operation）

200
1000-100 0-200-300-400-500-600-700

Air shutoff（After closing a repository）
Sterilized

1020304050

Microbial
Microbialeﬀect
eﬀect

Non-sterilized
Non-sterilized

Aeration
Aeration stopstop

Depth (m)104510Time, dayStirred jar-fermenter

In-situ sampler
1067104He age (y)Attain the target depth?

Reaming
To the next
drilling stage

Pumping-600

Borehole test (hydro, mechanical)【Borehole wall stability: high】

-500

h

Borehole test (hydro)

-400

e pt

Logging (2) (flow-meter, fluid)-300

hdw itBorehole cleaning

Logging (1)(geophysical)

sase

Logging (1) (geophysical)

-200

cre

Caliper log

n inCaliper log

No

Water Core Borehole
HCD-2
HCD-3
HDB-9
HDB-10
HDB-11orati
ent

Borehole wall
stable? under freshwaterYes-100fault crushed zones, etc.

Attain the terminal depth of this stage

Protection (borehole wall)

0ccon

Borehole logging, testHeStart of core drilling
No (Take measures)
Encounter geological factors ofYes
Need to protect
obstacles in drilling? ※1
the borehole※1 Inflow and outflow layers,wall?
unconsolidated layers,
Yes
No

4Fig. 2 He age in Horonobe site
Ground water age calculated by 4He contents and4
He accumulating rate is equivalent to the age of theWakkanai formation (2.9-13 Ma). This indicatesthat the ground water must be stagnant.

Fig. 3 Laboratory simulation of microbially mediated redox changes with
Horonobe rock and groundwater.
Laboratory jar-fermenter experiment was conducted with rock and groundwater samples collected at Horonobe URL (G.L.-140m). As a result,after discontinuation of aeration, redox potentials
decreased to ca. -600mV by microbial activities(i.e., aerobic respiration, iron reducing and fermentation), whereas sterilized slurry maintained
high redox potential (ca. +100mV). This resultshows that microbial activity affects groundwaterevolution.

Fig. 4 Long term behavior of disposal pit
Controlling thermo-hydro-mechanical condition, the 1/30 scale centrifuge model test around deposition hole was started.
Base on the similarity scaling law, it is possible to estimate several thousand years of mechanical behavior through the six
month centrifuge model test.

17