Project Subjects
Low level Radio Active Waste Disposal
Background and Objective
A sub-surface disposal site constructed about 50〜100m underground is planned for low-level radioactive waste generated from the driving and decommissioning of a nuclear plant. In the safety evaluation of thesub-surface disposal facilities with the pit disposal facilities, a long-term evaluation is needed on the engineered
barrier and natural barrier.
In this project, the engineered barrier and natural barrier in a sub-surface disposal facility decreases theuncertainty by efﬁcient valuation over the long term. In addition to becoming a high valuation technique, wedeveloped barrier material needed for quality inspective system construction.

Main results
1. Proposal of an analytical method for evaluating the effects of gas migration on radioactive waste disposal
facilities
In the current concept of repository for radioactive waste disposal, it is pointed out that hydrogen gas isgenerated inside the engineered barrier by anaerobic corrosion of metals. Thus, it is necessary to evaluate theeffect of gas migration on the function of the engineered barrier. In CRIEPI, on the basis of the experimental
facts obtained through gas migration tests, a gas migration mechanism in highly-compacted bentonite is proposed[N07005]. Furthermore, it is revealed that the results of gas migration tests can be simulated with accuracy byincorporating the gas migration mechanism into existing computer code “GETFLOWS” (Fig.1, Fig.2) [N09003].
2. Construction of a quality inspective system of cement system material at a disposal facility
In the sub-surface disposal facility, a long-term nuclear seed transference control function is needed forcementitious material, so management (quality inspection system) of construction, recuperation after grasping theinﬂuence of change in quality and scattering is important [N08081].
We developed a technique that can judge the quality of construction by non-destruction using a surfacelayer permeability test in addition to grasping the ﬁxed quantity-style relationship of quality, and obtained aforecast of application to a quality inspective system with a concrete recuperation condition in this laboratory(Fig. 3).
3. Effect of highly alkaline solutions leached from cementitious materials on the permeability of the compacted bentonite.
The alteration behavior and change in permeability of compacted bentonite which is one of the engineered
barriers were estimated through the combined experiments of immersing and permeability test using highly alkaline solutions of varying chemical compositions [N09015]. In the results of the combined experiments over one
year, the permeability of the compacted bentonite was almost constant under the assumed chemical environmentsof a low-level radioactive waste disposal facility (Fig.4).
A study of the above results is being reﬂected and has become the basic data for electric companies, a planof a disposal facility in JNFL, and a safety valuation examination of AESJ academic standards formulation thataffects sub-surface disposal and a JCSE academic technique report.
Other reports
18[N09014], [V09029]

Nuclear Technology

1.E-05○ Measured－ Calculated

2.5

1.E-072

1.E-08
1.E-091.5↓Small bubbles appear in discharged water 1.E-10
Discharged gas↑Sudden 1.E-11

1

再現解析結果0.5

increase in 1.E-12
gas flow 1.E-13
rate

Bentonite
Bentonite
ﾍﾞﾝﾄﾅｲﾄ
ｾﾒﾝﾄ系
Cement材料Construction

打継目jointGaspressure

1.E-14020406080100120
3経過時間（日）Elapseddays

Volume of discharged fluid (cm )0Cement mortar blocks
containing construction joints are combined with compacted
bentonite to form acement-bentonite composite specimen.

1.E-06

Discharged water3
3
Gas 透気流量（flow rateNm(Nm/s） /s)

3
Volume of dischargedwater(cm3)
累積排水量 (cm)Back pressure3

Fig.1 Numerical simulation of gas migration tests for thebentonite specimen by the modiﬁed computer code
By modifying the existing computer code “GETFLOWS”, which
was originally developed by Geosphere Environmental Technology Corporation, gas migration test results can be simulated withaccuracy, in particular the time history of volume of discharged
water and gas ﬂow rate, days of small bubbles appearance andsudden increase in gas ﬂow rate.

20Measured
Calculated

15
10
50050

100

150

200250Elapsed days

Fig.2 Numerical simulation of gas migration
tests for the cement-bentonite composite specimen by the modiﬁed computercode
The results of the gas migration test for the cement-bentonite composite specimen, which simulates actual gas
migration path, can be simulated with accuracy.

Carbonation Depth (mm)Accelerate carbonation period

Fig. 3 Non-destruction valuation by a surfacelayer Permeability test related to qualityof cement system material
By implementing recuperation adequately, we showedcarbonation resistance as a valuation index a thing that
long-term durability property of cementitious material
can expect but a making result of such material candetect by a surface-layer permeability feeling coefﬁcient. To conﬁrm whether to be gift with a core seedtransference control function that is supposed to benecessary to sub-surface disposal after construction byapplying a non-destruction test like this is enabled.

A surface-layer Permeability feeling coefficientin 91 days of material age kT(10-6m2)

Permeability（m/s）

10-9

NaOH (pH14)(pH14)NaOH 1.0M
NaOH(pH12)NaOH 0.01M(pH12)
KOH(pH14)(pH14)
KOH 1.0M
KOH(pH12)
KOH 0.01M(pH12)
CaOH22 (pH12)
0.005M
CaOH(pH12)
イオン交換水Deionizedwater
イオン交換水

10-10

Fig.4

10-11
10-12
10-13

0100

200300Evolution in permeability of compacted
bentonite immersed in various types ofhighly alkaline solutions
The permeability increased with time in the case ofalkaline solutions with pH14 as extreme chemical conditions. On the other hand, permeability changed slightly
with time under the assumed chemical environments of
low-level radioactive waste disposal facility.

Time（day）
19