ABSTRACT A number of studies concerning a cavern type disposal facility have been carried out for disposal of low level radioactive waste mainly generated by power plant decommissioning in Japan 1) . The disposal facility is composed of an engineered barrier system with concrete pit and bentonite buffer, and planed to be constructed in sub-surface 50 -100 meters depth. Though the previous studies have mainly used laboratory and mock-up tests, we conducted a demonstration test in a full-size cavern. The main objectives of the test were to study the construction methodology and to confirm the quality of the engineered barrier system. The demonstration test was planned as the construction of full scale mock-up. It was focused on a buffer construction test to evaluate the construction methodology and quality control in this paper. Bentonite material was compacted to 1.6 Mg/m 3 in-site by large vibrating roller in this test. Through the construction of the buffer part, a 1.6 Mg/m 3 of the density was accomplished, and the data of workability and quality is collected

Katsuhide Matsumura

Kazuhiro Onuma

Kenji Terada

Tadafumi Fujiwara

Takahiro Nakajima

Takao Tsuboya

Yoshihiro Akiyama

CiteSeerX

WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Buffer Construction Methodology in Demonstration Test  
For Cavern Type Disposal Facility -9182 
 
Yoshihiro Akiyama, Takahiro Nakajima, Katsuhide Matsumura, Kenji Terada, Takao Tsuboya 
Radioactive Waste Management Funding and Research Center 
1-15-7, Tsukishima, Chuo-ku, Tokyo, 104-0052, Japan 
 
Kazuhiro Onuma 
Hazama Corporation 
2-2-5, Toranomon, Minato-ku, Tokyo, 105-8479, Japan 
 
Tadafumi Fujiwara 
Taisei Corporation 
344-1, Nase-cho, Totsuka-ku, Yokohama-shi, Kanagawa, 245-0051, Japan 
 
ABSTRACT 
A number of studies concerning a cavern type disposal facility have been carried out for disposal of 
low level radioactive waste mainly generated by power plant decommissioning in Japan1). The disposal 
facility is composed of an engineered barrier system with concrete pit and bentonite buffer, and planed 
to be constructed in sub-surface 50 – 100 meters depth. Though the previous studies have mainly used 
laboratory and mock-up tests, we conducted a demonstration test in a full-size cavern. The main 
objectives of the test were to study the construction methodology and to confirm the quality of the 
engineered barrier system. The demonstration test was planned as the construction of full scale 
mock-up. 
It was focused on a buffer construction test to evaluate the construction methodology and quality 
control in this paper. Bentonite material was compacted to 1.6 Mg/m3 in-site by large vibrating roller in 
this test. Through the construction of the buffer part, a 1.6 Mg/m3 of the density was accomplished, and 
the data of workability and quality is collected.  
INTRODUCTION 
The cavern type disposal facilities for disposal of low level radioactive waste will be constructed in 
sub-surface 50 – 100 meters depth, and employs an engineered barrier system with a concrete pit and 
bentonite buffer. 
The model of the sub-surface disposal with engineered barriers is shown in Figure 1. The engineered 
barrier system works to reduce migration of nuclide from disposal facilities through groundwater flow. 
The main engineered barriers are as follows2): 
1) A buffer layer of bentonite material which reduces groundwater inflow through facilities 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
2)    A low diffusion layer of cement material inside the low permeable layer, and which contains 
any groundwater that seeps from the inner diffusion area. 
 
(Bentonite material) 
Filler 
Low diffusion layer 
Concrete pit 
(Cement material) 
Waste 
Buffer Tunnel support 
Backfill 
Figure 1 Model of sub-surface disposal facility2) 
 
A basic test data has been mainly obtained by laboratory scale tests in preliminary studies for 
sub-surface disposal with engineered barriers. But construction methodology for cavern type disposal 
facility has not been validated. The performance of an engineered barrier system depends on 
construction methodology, so a demonstration test for sub-surface disposal facilities is required to 
choose and validate the construction methodology for the engineered barrier system. 
Demonstration test for cavern type disposal facility has been commissioned by Ministry of Economy, 
Trade and Industry of Japan (METI) to be carried out by Radioactive Waste Management Funding and 
Research Center (RWMC) since FY2005. And this demonstration test has been carried out at a cavern in 
Rokkasho site with the support of Japan Nuclear Fuel Limited (JNFL). The construction test in-situ 
began in FY2007, and will be continued for a few years. 
The buffer is located outside in an engineered barrier system, and compacted bentonite to 1.6Mg/m3 at 
the drying effective clay density to ensure 5×10-13m/s at permeability. The dispersion of density and 
smoothness of compacted plane is different by construction methodology. So the buffer quality depends 
on the construction methodology. On other hand, the construction methodology is limited for 
construction space in cavern. Therefore it is important to confirm characteristics of the construction 
methodology to establish the buffer quality in the test cavern3). 
The bottom part of the buffer is located lower in the engineered barrier system, and is constructed after 
the construction test of backfill concrete at the bottom and side. Bentonite material is compacted on-site 
by vibrating roller. And the scales of bottom area are width 13.55m, length 16.10m, thickness 1.00m.  
The methodology of construction test for the bottom part of the buffer is reported in this paper and the 
characteristics about density are shown. 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
BUFFER CONSTRUCTION TEST 
Construction methodology for buffer 
Each part of buffer has unique condition for construction, so the test case at each part is selected. The 
test case for the buffer is shown in figure 2. 
In the construction test for the buffer, the common bentonite material Kunigel GX is used. This is 
screening raw material of Kunigel V1 which is used in construction materials by 10mm diameter, 
produced in north east Japan the mean density value for the buffer is set at 1.6Mg/m3 to obtain the 
required buffer permeability.  
In the test case, each construction methodology for buffer can be roughly classified into two groups. 
One is construction by vibrating roller, and the other is by using bentonite blocks. The weight of 
vibrating roller or size of bentonite block is selected by conditions of construction area. 
The bottom area is a relatively large construction, so large machine was adapted for the construction 
test. The side parts and upper area is narrow, and small vibrating roller was adapted to avoid damage in 
the nearby concrete pit4). 
 
 
 
Buffer construction test at bottom area 
We were able to construct the bottom buffer area using large vibrating roller to compact efficiently, as 
the construction area is large and there is no diffusion layer for radioactive waste. The buffer thickness is 
1.00m, and the thickness of bentonite layer is 0.10m, with 10 layers constructed.  
Figure 2 Construction methodology of buffer 
振動ローラ
振動 ーラロ
大型ブロック
振動ローラ
現場締固め
振動ローラ
振動ローラ
小型ブロックSmall bentonite block 
In-site compaction by compactor 
In-site compaction by small vibrating roller 
In-site compaction by large vibrating roller 
Large bentonite block 
In-site compaction by small vibrating roller 
(a) Section 
(b) Profile 
In-site compaction by large vibrating roller 
In-site compaction by small vibrating roller 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Construction procedures related to spreading and compaction are repeated in the construction test. 
Therefore, it is important to confirm that the construction methodology included quality control through 
the construction cycle. 
After the test plan of the bottom area buffer construction test was studied in FY2006, a buffer 
construction test at the lowest layer was carried out in FY2007 to validate construction methodology in 
the test. After the construction procedure is determined by the results at first layer the rest of layers are 
compacted. And the quality is measured by performance test at all layers. Based on the results of 
construction test and performance test, the quality of buffer will be evaluated for construction 
methodology and quality control4). 
 
 
Det er minat ion of 
Const ruct ion 
Select ion of 
Const ruction Pr ocedure
Const ruct ion Test  
Dry Dens ity is 
1.6±0.1 Mg/m 3?
YES 
NO 
Change of Const ruction 
Procedur e 
Const ruct ion Test   
F inal Layer ? 
YES 
NO 
Performance Test
Evalution
First layer 
Second layer ~ 
Test  P lan
Measurement of Buffer  
Dr y Density
 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Figure 3 Flow Chart of Buffer Construction test 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Testing condition of buffer construction test at bottom area 
Construction methodology is selected in each area by construction conditions like the construction 
space, the size of machine for construction, the procedure for construction. At the bottom area, bentonite 
is mainly compacted on-site by using a large vibrating roller. Because of a narrow side area, bentonite is 
compacted in-site with a small vibrating roller. The construction areas are shown in figure 4. The 
construction machines used at each area are shown in table 1. 
 
N
ear en
d
 area
Side area 
Side area 
Main area 
F
ar en
d
 area 
Test area 
Figure 4. Construction area 
 Table 1. Construction machine 
Area Machine Step 
 Type Size (mm) Weight (ton)
Spread Except far end Asphalt finisher 6,425*2,550,*3,100 21.0 
Side, Near end, Far 
end 
Small vibrating 
roller 
1,770*1,200*850 1.5 
Small vibrating 
roller 
2,625*1,290*1,570 2.5 
Compaction 
Main 
Large vibrating 
roller 
6,250*2,530*2,975 19.7 
 
Construction procedure 
Bentonite (Kunigel GX) is added to water, with the target value of water content set from 19 % to 23 % 
(mean 21 %). The property of Kunigel GX is shown in table 2. 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
 Table 2. Standard value of buffer material 
Test item Standard value 
Grain size Maximum 10mm 
Water content Under 10% 
Plastic limit test Under 30% 
Methylene blue test Over 63mmol/100g (45%) 
Swelling test Over 10 ml/2g 
 
The construction procedure is as follows: 
① At far end area (width approximately 2m), the bentonite is spread by manpower and mainly 
compacted by small vibrating roller. Manpower compaction using tamping rammer or vibrating 
compactor is tested in a few parts. 
② At main area and side areas, the bentonite is spread by asphalt finisher. The width of spreading 
lane is approximately 4.5m. 
③ At the near end area, the temporary bar is set to control horizontal movement. 
④ Preliminary compaction by non-vibrating roller (weight is 2.5 ton) to get in the loose bentonite 
by large vibrating roller. 
⑤ At the side and near end areas (width is approximately 2m each), compaction by small vibrating 
roller. 
⑥ Primary compaction by large vibrating roller. At this step, the compaction without vibrating is 
carried out in order to avoid destruction by strong vibration. The number of primary compaction 
is 8 times. 
⑦ Main compaction by vibrating roller. The tentative number of main compaction is 6 times, and 
the main compaction is going to add by the result of measurement of dry density. 
The spreading by asphalt finisher is shown in figure 5. Construction by large vibrating roller at main 
area is shown in figure 6. Construction by small vibrating roller at side areas is shown in figure 75). 
 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Figure 5. Spreading by Asphalt Finisher 
 
 
Figure 6. Compaction by large vibrating roller at main area 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Figure 7. Compaction by small vibrating roller at side areas 
 
 
Construction test results 
After the construction test for the first buffer layer, the buffer density has been confirmed by core 
sampling. The density has been calculated by weight and length of the core. The positions of sampling 
are shown in figure 8 below. These positions of sampling are divided into main area, side area, far end 
area, near end area and its boundary. 
The density of the layer on-site compaction includes the difference between the upper and lower parts. 
Therefore some sampling cores are divided three parts, and each part has been measured in density to 
grasp the dispersion. The positions of sampling cores divided three parts were six points called s1-s3 
and s7-s9. 
 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
Figure 8. Positions at core sampling for dry density 
 
 
The results of dry density by sampling core are studied all data. A dry density histogram for all 
sampling cores is shown in figure 9(a). The target value of dry density is set from 1.5 Mg/m3 to 1.7 
Mg/m3. The mean is set 1.6 Mg/m3. The results on 39 samples are as fellows. 
 Average value of dry density is 1.669 Mg/m3. 
 Maximum value of dry density is 1.714 Mg/m3. 
 Minimum value of dry density is 1.567 Mg/m3. 
 Number of core exceeding the upper limit is 4 (10% of cores). 
 Number of core exceeding the lower limit is 0 (0% of cores) 
Therefore 90% of the samples have been within the density target value. This result will be useful for 
quality control at future construction processes. 
It is thought that the dry density is different at boundary and the others. So sampling core is divided 
into two groups. The histogram on dry density of cores, except samples at boundary, is shown in figure 
9(b). The histogram on dry density of cores on samples at boundary is shown in figure 9(c). The results 
are as follows. 
 For cores, except samples at boundary, the average value of dry density is 1.674 Mg/m3 and the 
difference for all samples is 0.005 Mg/m3 (0.3%). 
 For cores of samples at boundary, the average value of dry density is 1.658 Mg/m3 and the 
difference for all samples is -0.011 Mg/m3 (-0.7%). 
Because the difference of dry density has been minimal, the effect it has is negligible on construction 
methodology at the boundary. 
On the other hand, the relation between water content and dry density of cores, except samples at 
boundary, is shown in figure 10(a). The relation between water content and dry density of cores of 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
samples at boundary is shown in figure 10(b). Moisture content has been calculated by dry and wet 
weight of the cores. In these figures, the curve at no porosity is added. Most cores have been compacted 
in high density. 
Regarding the variation of dry density by depth, the relation between depth and density of cores is 
shown in figure 12. It has been proven that the dry density at the upper part is bigger than lower one. 
But every dry density was within range of target value6) . 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
 
0
10
20
30
1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8
例
数
乾燥密度（Mg/m3）
全コア試料（10cm）
平均値　： 1.669
標準偏差： 0.032
最大値　： 1.714
最小値　： 1.567
試料数　： 39
0
5
10
15
20
1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8
例
数
乾燥密度（Mg/m3）
一般部（奥部，側部，端部含む）
平均値　： 1.674
標準偏差： 0.029
最大値　： 1.714
最小値　： 1.579
試料数　： 27
0
5
10
15
20
1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8
例
数
乾燥密度（Mg/m3）
境界部 平均値　： 1.658
標準偏差： 0.038
最大値　： 1.699
最小値　： 1.567
試料数　： 12
 
 
 
1.5
1.6
1.7
1.8
1.9
16 18 20 22 24
一般部
奥部
側部
端部
乾
燥
密
度
（
Mg
/m
3 ）
含水比 (%)
一般部
 
1.5
1.6
1.7
1.8
1.9
16 18 20 22 24
奥部
側部
端部
乾
燥
密
度
（
Mg
/m
3 ）
含水比 (%)
一般部との境界
 
 
 
(a) All cores 
(N=39) 
Figure 9. Dry density histogram 
(b) Cores except boundary 
(N=27) 
(c) Cores at boundary 
(N=12) 
(a) Cores except boundary 
(N=27) 
Figure 10. Relation between water content and dry density 
(a) Cores at boundary 
(N=12) 
Cores
except boundary 
Number: 27 
Average: 1.674 
Deviation: 0.029 
Maximum: 1.714 
Minimum: 1.579 
All cores 
Number: 39 
Average: 1.669 
Cores at boundary 
Number: 12 
Average: 1.658 
Deviation: 0.032 Deviation: 0.038 
Maximum: 1.714 Maximum: 1.699 
Minimum: 1.567 Minimum: 1.567 
Dry density (Mg/m3) Dry density (Mg/m3) Dry density (Mg/m3)
N
um
be
r 
N
um
be
r 
N
um
be
r 
D
ry
 d
en
si
ty
 (
M
g/
m
3 )
 
D
ry
 d
en
si
ty
 (
M
g/
m
3 )
 
Water content (%) Water content (%) 
○Main area
△Far end area 
▽Side area 
□Near end area 
Cores except boundary Cores at boundary △Far end area 
▽Side area 
□Near end area 
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
1.5 1.6 1.7 1.8
0
2
4
6
8
10
乾燥密度（Mg/m3）    
1.5 1.6 1.7 1.
0
2
4
6
8
10
高
さ
（
cm
）
一般部
平均値
＋σ
－σ
8
乾燥密度（Mg/m3）
高
さ
（
cm
）
境界部
平均値
＋σ
－σ
 
 
 
CONCLUSION 
The buffer construction test has been conducted since FY2007 to validate construction methodology 
and quality control. Additionally, the buffer construction test has been carried out at first layer to 
confirm the procedure. At the result, the construction methodology that spread bentonite by asphalt 
finisher and compact on-site by large vibrating roller has been confirmed. On the other hand, the dry 
density of buffer after construction has ranged in 1.6±0.1 Mg/m3 set for target value. 
Now that the plan of buffer construction test has been reviewed, the remaining buffer construction tests 
will be continued from this time. After the buffer construction tests, laboratory tests will be carried out 
to investigate mechanical and hydrogical characteristics, and the evaluation for construction 
methodology and quality will be carried out. These results will enable the use of the confirmation of 
construction methodology and quality control in future. 
 
ACKNOWLEDGEMENT 
This report is one part of the report on demonstration test for cavern type disposal facility at the 
consignment of the Ministry of Economy, Trade and Industry of Japan. This study received the guidance 
of the committee of the Demonstration Test for Cavern Type Disposal Facility. The authors wish to 
express their appreciation and thanks to the committee. 
(a) Cores except boundary 
Figure 11. Relation between depth and dry density 
(a) Cores at boundary 
H
ei
gh
t (
cm
) 
Cores except boundary Cores at boundary
H
ei
gh
t (
cm
) 
Average Average 
Dry density ( g/ 3) Dry density (Mg/m3)
WM2009 Conference, March 1-5, 2009, Phoenix, AZ 
 
REFERENCES 
 
[1] A. Yamato, “The current status of JNFL sub-surface disposal plan for relatively higher LLW”, 
Proceeding of International Conference on the Safety of Radioactive Waste Disposal, IAEA, Japan, 
(2005) 
[2] K. Onuma, K. Terada, S. Kubota, K. Matsumura and T. Tsuboya, "Demonstration test outline for 
underground cavern type disposal facilities", Proceeding of 2007 International Symposium on Radiation 
Safety Management, Korea, (2007) 
[3] T. Tsuboya, K. Terada, K. Matsumura, K. Onuma, S. Kubota, " Outline of demonstration test of 
underground cavern type disposal facilities", Proceedings of the 62nd JSCE Annual Meeting, CS5-73, 
(2007), in Japanese 
[4] K. Onuma, K.Ishibashi, K. Matsumura, K. Terada, "Outline of buffer construction test in 
demonstration test of cavern type disposal facility", Proceedings of the 63rd JSCE Annual Meeting, 
CS5-01, (2008), in Japanese 
[5] T. Ishihara, T. Fujiwara, T. Yamamoto, K. Onuma, K. Ishibashi, K. Terada, M. Chijimatsu, I. 
Yoshikoshi, "Construction methodology for buffer in demonstration test of cavern type disposal facility 
", Proceedings of the 63rd JSCE Annual Meeting, CS5-02, (2008), in Japanese 
[6] T. Yamamoto, T. Fujiwara, K. Yamashita, M. Chijimatsu, I. Yoshikoshi, K. Onuma, K. Ishibashi, K. 
Terada, "Density on buffer at bottom part in demonstration test of underground cavern type disposal 
facilities", Proceedings of the 63rd JSCE Annual Meeting, CS5-03, (2008), in Japanese 
 


Buffer Construction Methodology in Demonstration Test For Cavern Type Disposal Facility -9182

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=D3F93780CDB24A2609A0244B226368E1?doi=10.1.1.1054.7062&rep=rep1&type=pdf

Buffer Construction Methodology in Demonstration Test For Cavern Type Disposal Facility -9182

Abstract

Similar works

Full text

Available Versions

CiteSeerX