Vol.22 No.2

原子力バックエンド研究

研究論文

Demonstrative experiments on the migration of radiocesium from buried soil contaminatedby the accident at Fukushima Daiichi Nuclear Power Station†
Tetsuji YAMAGUCHI＊1 Taro SHIMADA＊1 Makoto ISHIBASHI＊2 Yosuke AKAGI＊2 Mitsuru KUROSAWA＊2
Akiyoshi MATSUBARA＊2 Yuki MATSUDA＊3 Shigeyoshi SATO＊4
福島第一原発事故で汚染された土壌を穴に埋設し，清浄な土壌で覆土すれば，放射性セシウムは汚染土壌から周りの土壌や地下水にほとんど移行しないことは過去の研究から推定できる．本研究では，茨城県美浦村の１つの公園と埼玉
県三郷市の２つの公園において一年にわたって核種移行試験を行って，その推定を実証した．汚染された表層土壌を集めて埋設し，散水によって放射性セシウムの移行を加速した．ボーリングコアの切断分析結果や，土壌水の分析結果か
らは，放射性セシウムの動きは見られなかった．また，実験室におけるカラム移行試験および収着試験によって，放射性セシウムが汚染土壌からほとんど溶出しないことや，たとえ溶出しても周囲の土壌に収着されてほとんど移行しない
ことを示すデータを得た．試験は１年間で終了したが，移流拡散モデルによるシミュレーション解析を 100 年間について行ったところ，セシウム-137 はほとんど移行せずにその場で減衰することが示された．
Keywords: 福島第一原発事故，汚染土壌，放射性セシウム，移行，埋設，収着It is predictable from previous studies that radiocesium hardly migrates into surrounding soils and groundwater from soils
contaminated by the accident at Fukushima Daiichi Nuclear Power Station if they are buried and covered with clean local soils. This
study demonstrated the prediction by performing in-situ migration experiments over a year in a public park in Miho, Ibaraki
prefecture and in two public parks in Misato, Saitama prefecture. Contaminated surface soils were gathered and buried at a depth
range of 0.3 ~ 1.0 m or at 0.3 ~ 1.3 m and covered with clean local soil layer of 0.3 m, and were sprinkled with water to accelerate
the radiocesium migration. Migration of radiocesium was not observed from radiometric analyses of boring cores and soil water
samples. Laboratory column and sorption experiments revealed that the radiocesium hardly leaches out of the soil and even if itleaches out from the contaminated soil, radiocesium is sorbed on surrounding soils and hardly migrates through the soil layer.
Simulation of Cs-137 migration for 100 years by an advection-diffusion model showed that Cs-137 migrates slightly and decays out
in the contaminated soil.
Keywords: Fukushima Daiichi NPS accident, contaminated soil, radiocesium, migration, burial, sorption

1

Introduction

not migrate from the contaminated soils buried on site.

Ground surface was contaminated in Kanto and Tohoku

mobility because of sorption onto soils or sands. Kamiyama et al.

regions by radiocesium released from the accident at Fukushima(1994) [1] performed field tests on migration of H-3, Co-60,

Daiichi Nuclear Power Station after the great earthquake in

Cs-134 and Sr-85 over two years at the field site of loess layer ineastern Japan on March 11 in 2011. It is necessary to quickly

Shanxi, China and showed that most of the Cs-134 did not move.

reduce the effect of the contamination on human health and to

Sakamoto et al. (1999) [2] studied migration behavior of Sr-90

living environments. On-site burial, to remove the contaminated

and Cs-137 in a sand aquifer at Chalk River Laboratories,

surface soils from schoolyards and parks, to accumulate them on

Canada over 30 years and found that Cs-137 was fixed in thesite in a trench and to backfill the trench with clean local soils is

sand. Such demonstrations, however, have never been performed

a candidate for disposing measure of the contaminated soil. It is

in Japan. In this study, demonstrative experiments on the

expected that removing the contaminated surface soils andmigration of radiocesium from buried contaminated soil wereburying them on site will decrease the dose rate on the groundperformed at public parks in Kanto region, eastern Japan.

Previous studies suggested that radiocesium exhibits low

surface. It is, however, necessary to ensure that radiocesium does2
福島第一原発事故で汚染された土壌の埋設場所からの放射性セシウムの移行に関する実証試験 山口徹治(yamaguchi.tetsuji@jaea.go.jp)，島田太郎，石橋純，赤木洋介，黒沢満，松原諒宜，松田祐紀，佐藤滋芳＊1 Japan Atomic Energy Agency
日本原子力研究開発機構
2-4 Shirakata, Tokai, Ibaraki 319-1195, Japan〒319-1195 茨城県那珂郡東海村白方 2-4＊2 Mitsubishi Materials Corporation
三菱マテリアル株式会社
1-297 Kitabukuro, Omiya, Saitama, 330-8508, Japan〒330-8508 さいたま市大宮区北袋町 1-297＊3 Mitsubishi Materials Techno Corporation
三菱マテリアルテクノ株式会社
1-297 Kitabukuro, Omiya, Saitama, 330-0835, Japan〒330-0835 さいたま市大宮区北袋町 1-297＊4 Ministry of the Environment of Japan
環境省
1-2-2 Kasumigaseki, Chiyoda, Tokyo 100-8975, Japan〒100-8975 東京都千代田区霞が関 1-2-2† This project was conducted by Ministry of the Environment of Japan withtechnical support from Japan Atomic energy Agency and from Mitsubishi
Materials Corporation.
(Received 16 January 2015; accepted 16 July 2015)

Experimental

2.1

Field experiments

Contaminated surface soil was gathered and buried in a publicpark A (site A) in Miho village, Ibaraki prefecture and in two
public parks B and C (sites B and C) in Misato city, Saitama
prefecture in March, 2013. Periodical boring of the soil coresand sampling of the soil water were performed for nearly 12months to investigate the radiocesium migration.
2.1.1

Site A in Miho village, Ibaraki prefecture

A 3-cm thick contaminated surface soil was stripped from
relatively highly contaminated areas, 1200 m2, in the park. The
surface soil was clayey fine sand (Table 1) with sparsevegetation. Mineralogical compositions were analyzed by XRD
and shown in Table 2. Dose rate at 50 cm above the ground was
typically 0.25 μSv/h before the stripping and 0.13 μSv/h
21

December 2015

原子力バックエンド研究
afterwards, which suggested the effectiveness of this measure. A
trench with an area of 6 m × 6 m and a depth of 1.3 m was dug
at an edge of the park as shown in Fig. 1. The dug soil was
thoroughly mixed up and used in the field experiment as clean
local soil. The contaminated soil with a volume of 36 m3 wasburied in the trench at a depth range between 1.3 and 0.3 m andwas covered with the clean local soils over 0.3 m. The depth, 1.3m, was chosen considering the groundwater level and rationalityof the construction. A 2 m × 2 m area in the buried area wasseparated as an investigation area by a water impermeable steel
frame over a depth of 1.8 m. This investigation area was dug
down to a depth of 1.8 m in advance to install a soil watercollecting device and combination sensors (Hydra Probe II,

Fig. 1 A trench with an area of 6 m × 6 m and a waterSDI-12, Stevens Water Monitoring Systems, Inc., Portland,

impermeable steel frame installed at site A in Miho,

USA) at depths of 1.7, 1.4, 1.1, 0.8, 0.5 and 0.2 m to measure

Ibaraki prefecture.

temperature, water content and electric conductivity. The setupof the field experiment is shown in Fig. 2.
The hydraulic conductivity had been between 3.510-9 and1.310-7 m/s before digging. Contaminated soil was buried insteps by repeating setting the soil with a thickness of 0.3 m orless and ramming mechanically or manually. After burying, avertical boring was performed to identify the initial vertical
distribution of radiocesium. Then, tap water was sprinkled overthe investigation area to accelerate the radiocesium migration.
Table 1 Grain size distribution(wt%) of the soils from thethree depth ranges of the three sites.
Table 1 Grain size distribution (wt%) of the soils from the three depth ranges of the three sites
Grain size
Clay
Silt
Sand
GravelStone(<5μ m)(5～75μ m)(75μ m～2mm)(2～75mm)(75mm<)
Site and depth
0.2～0.4 (m)Site A 1.2～1.4 (m)1.7～1.9 (m)0.2～0.4 (m)Site B 1.2～1.4 (m)1.7～1.9 (m)0.2～0.4 (m)Site C 1.2～1.4 (m)1.7～1.9 (m)

25.9
14.2
13.6
23.5
25.7
33.1
62.5
65.1
49.5

12.7
9.3
12.5
7.0
6.7
10.8
10.2
18.6
31.4

60.5
76.6
70.7
34.8
39.2
37.4
27.4
16.4
19.1

1.0
0.1
3.2
34.7
28.4
18.1
0.1
0.1
0.1

0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1

Fig. 2 Setup of the field experiments.
Water was sprinkled for about 8 h at a rate of 7 ~ 37 mm/h
almost every two weeks to attain an infiltration of 3200 ~ 3900
mm during the experimental period. The infiltration is

Site A

1.2～1.4

・

・

・

・

・

◎

△

○

Site Cequivalent to 8 ~ 10 years of natural infiltration by assuming thatthe amount of the water sprinkled was the same as that
infiltrated. The annual precipitation is 1300 mm, about 70% of
which is estimated to evaporate and 30% infiltrated into the soil.
Acidification of the sprinkled water simulating acid rains was
not performed because the pH of the soil water was 6-8 and wasconsidered reproducible by using neutral tap water. The daily

Depth, m

1.7～1.9Site B

opal○

calciteplagioclase△

magnetite

potassium feldspar◎

quartz・amphibole・Sample *1

kaolin minerals

・

chlorites

・

micas

・

smectite

0.2～0.4

Mineral

Site

*3

＊2

Table 2 Mineralogical composition of soils analyzed by
XRD. ◎, 〇, △ and ･ represent the presence oflarge, medium, small and trace amount,respectively.

average temperature was -3 ºC at lowest (2014/Feb/14) and 33ºC at highest (2013/Aug/10).

・

Vertical borings obtaining soil cores with a diameter of 20 cm

・

・

・

・

◎

△

○

0.2～0.4

・

・

・

・

・

◎

△

△

・

0.9～1.1

・

・

・

・

・

◎

△

△

・

1.4～1.6

・

・

・

・

・

◎

△

○

・

0.2～0.4

・

・

・

・

・

○

△

○

0.9～1.1

・

・

・

・

・

◎

△

△～○

1.4～1.6

・

・

・

・

・

◎

・

△

*1 Diffraction by untreated, ethylene glycol treated, hydrochloric acid treated and heat treatedsamples were measured for identification of clay minerals.
*2 including vermiculite*3 including halloysite

were performed after around 20, 30, 130, 210, 360 days toinvestigate the radiocesium migration. The cores were sliced
every 0.5 cm for radiometric analysis. The soil water was△

sampled monthly to determine radiocesium concentration, pH,
Eh, DO (dissolved oxygen concentration), SS (suspended solid
concentration) and ammonia nitrogen concentration. Microbialactivity was not analyzed because cesium does not help
microbial metabolism and because no acidification of the soil
water suggesting the microbial activities was observed.
22

A demonstrative experiment on the migration of radiocesium from buried soil
contaminated by the accident at Fukushima Daiichi Nuclear Power Station
2.1.2

Site B in Misato city, Saitama Prefecture

mainly as adsorbed state onto soil particles.

A 3-cm thick contaminated surface soil was stripped fromIn order to simulate more severe conditions under which

about 7200-m2 area in the park using a sod cutter because theunderlying soil does not act as a barrier to the radiocesium

surface soil was clayey fine sand (Tables 1 and 2) and was

migration, another column migration experiment was performed

covered with sod. Dose rate at 50 cm above the ground wasthrough a single contaminated soil layer. The soil column was 12

typically 0.25 μSv/h before the stripping and 0.11 μSv/h

cm in diameter, 3 cm in thickness and 1.3 g/cm3 in density.

afterwards. A trench with an area of 10 m × 30 m and a depth of

140-mm water was permeated through the column at a rate of

1.0 m was dug. The contaminated soil with a volume of 210 m3

20 mm/d.

was buried in the trench at a depth range between 1.0 and 0.3 m
and was covered with the clean local soils over 0.3 m. A
2 m × 2 m area in the buried area was separated as aninvestigation area by a water impermeable steel plate over adepth of 1.5 m. This investigation area was dug down to a depthof 1.5 m in advance to install a soil water collecting device andthe combination sensors at every 10 cm depths between 1.4 and
0.1 m. The hydraulic conductivity had been between 1.210-8
and 4.410-8 m/s in the buried area. The backfilling, borings,
water sprinkling and soil water collection were performed in thesame way as those at site A.
2.1.3

Site C in Misato city, Saitama Prefecture

A 3-cm thick contaminated surface soil was stripped from thewhole park, about 350 m2 area. The surface soil was medium

Fig. 3fine sand (Iwase sand) with no vegetation (Tables 1 and 2). Dose
rate at 50 cm above the ground was typically 0.23 μSv/h before

Columns of the laboratory migration experiments.
A column with three soil layers (left) and one with asingle contaminated soil layer (right).

the stripping and 0.15 μSv/h afterwards. A trench with an area of
3 m × 5 m and a depth of 1.0 m was dug at an edge of the park.
3

The contaminated soil with a volume of 10.5 m was buried in
the trench at a depth range between 1.0 and 0.3 m and wascovered with the clean local soils over 0.3 m. An investigation
area was created in the same way as site B. The hydraulicconductivity had been between 2.910-9 and 1.110-8 m/s in theburied area. The backfilling, borings, water sprinkling and soil

Table 3 Density and porosity of the soils determined using
boring core samples taken after 10 days. The
density of the contaminated soil at Site B was
somewhat lower than those at Sites A and C. The
density of the cover soil and the underlying soil areclose because they were originally the same soil
before the trench was dug.

water collection were performed in the same way as those atsites A and B.

Cover soil

2.2

Contaminated
Soil
Underlying
soil

2.2.1

Laboratory experiments
Column migration experiments

Laboratory migration experiments of radiocesium from theDensity (g/cm3) / Porosity (%)
Site A
Site B
Site C
1.35 / 48.5
1.44 / 46.1
1.39 / 49.6
1.40 / 45.9

1.04 / 59.1

1.53 / 42.3

1.45 / 44.9

1.41 / 46.9

1.20 / 53.7

contaminated soils were performed using soil columns. In an
acrylic column with a diameter of 12 cm and a length of 30 cm,

2.2.2

Leaching experiments

the contaminated soil with a thickness of 12 cm was placed

A sequential leaching test was performed in accordance with

between a cover soil layer with a thickness of 8 cm and an

notification No.18 of the Ministry of the Environment [3].

underlying soil layer as shown in Fig. 3. The densities of theRadiocesium dissolved in soil water was extracted withsoils were the same as those in the field experiment as shown indeionized water by shaking reciprocally for 6 hours at a liquid toTable 3. The lower end of the column was supported by asolid ratio of 80 mL / 8 g. After centrifugation, the cation

stainless steel wire mesh to allow suspended soil to flow

exchanged radiocesium in the soil was extracted with 1 mol/Lthrough.

CH3COONH4 solution by 18-hour shaking.

Twenty millimeters of deionized water was supplied from the

Because the period of the sequential leaching test notified by

top of the column every day to permeate 840 mm of water

Ministry of the Environment may be too short to obtain data toaltogether. The down flow was selected for simulating thebe used for assessing behavior of environmental radiocesium,

rainwater through aerated zones. The effluent was analyzed forlong-term leaching tests were performed. Mixtures of soil andCs-137 concentration and turbidity without filtration because

deionized water or 1 mol/L CH3COONH4 solution wereradiocesium was expected to migrate through the soil column

manually shaken daily for 10 months.
23

December 2015

原子力バックエンド研究
2.2.3

Sorption experiments

The concentration of Cs-137 changes not sharply but rather

A core boring was performed at each site before digging thegradually at the interfaces over 5 cm. The concentration

trench to obtain a soil sample from the depth between 30 cm anddistribution was due not to migration of Cs-137 because that was

180 cm. Sorption distribution coefficients of Cs-137 on theseobserved for the boring core just after burying before sprinklingsoils were determined by using the standard method towater. The concentration distribution was due to the coexistence

determine the sorption distribution coefficient [4]. The soil wasof the contaminated soil and the cover soil or the underlying soil

passed through a sieve with a mesh of 2 mm. Three grams of thein 5-mm thick segments. The depth ranges where such

soil was mixed with 30 mL of deionized water in polyethylene

coexistence was observed were shown as coexisting range in Fig.

bottles. After 24 h, the mixture was added with a 1 mL volume

4. The coexistence would occur during the burying and rammingof Cs-137 stock solution and was kept standing for 7 d being

processes. Increase in the concentration of Cs-137 in the covershaken manually once per day. The sorption run was performed

soil and in the underlying soil was not observed beyond theten-fold. The supernatant solution, filtrate through a 0.45 μm

coexisting ranges as shown in Fig. 5.

filter and filtrate through a filter with a molecular weight cut-off

The results of the analyses of the water collected by the soilof 10,000 was analyzed for Cs-137 radioactivity. The sorption

water collecting device are shown in Table 4. Cs-137 was not

distribution coefficient was determined bydetected in all water samples. Lower Eh and higher ammonia

Kd (mL/g ) 

C0  C1 Vaq (mL)C1
Ws (g)

nitrogen concentration were observed at site B than those at(1)other sites. Those would have something to do with the higher
groundwater level at site B; the groundwater level was deeper

Kd ：sorption distribution coefficient (mL/g)

than 3 m at site A, >3 ~ 0.5 m at site B and 2.0 ~ 1.0 m at site C.

C0 ：concentration of Cs-137 before sorption (110 Bq/mL)

No influence of the water sprinkling was observed on the

C1 ： concentration of Cs-137 after sorption equilibrium

groundwater level.

(Bq/mL)Vaq ：volume of water (mL)

No indication of the migration of Cs-137 was observed fromthe field experiments.

Ws ：mass of soil (g)A blank test with deionized water and Cs-137 stock solution

Table 4 Results of soil water analyses.

without the soil was also performed to confirm negligible

Site A

Site B

Site C

adsorption of Cs-137 on the bottle walls. CH3COONH4 solutions,Cs-137

ND

ND

ND

NaCl solutions and KCl solutions of 10-5 ~ 1 mol/L

pH

6~8

6~8

6~8

concentrations were also used in place of deionized water in

Eh (mV vs.NHE)+281-60 ~ +124

+350

Dissolved oxygen1.23 ~ 3.86

0.99 ~ 3.53

1.65 ~ 3.65

5 ~ 261

8 ~ 271

5 ~ 657<0.1 ~ 0.7

1.0 ~ 110.2 ~ 0.5

3<

0.5 ~ 3<

1~2

order to check the effect of the coexisting ions on the~ +464

distribution coefficient. In this sorption experiments, effects of
the acid rain on the sorption distribution coefficient were not(mg/L)

considered.
3

Results and discussion

3.1

Field experiments~ +481

Suspended

solid(mg/L)
Ammonia
nitrogen (mg/L)
Groundwater

Fig. 4 shows the concentration of Cs-137 determined for thelevel (GL- m)

vertical boring core intersecting the interface between the coversoil and the contaminated soil and that between thecontaminated soil and the underlying soil. The concentration of
Cs-137 is 1000 ~ 3000 Bq/kg in the contaminated soil and less

3.2
3.2.1

Cs-137 had been retained within 3 cm from the surface before
the demonstrative experiments and was entirely removed bystripping the 3-cm thick surface soil. At site B on the other hand,small amounts of Cs-137 had existed at the depth range of 3 ~10 cm before the demonstrative experiments, was not removedby the 3-cm stripping and was accordingly transferred to the soil
used as underlying soil and as cover soil. This is the reason why

column migration experiments using the soil sampled from 3
sites were under the detection limit (< 2 Bq/cm3). The result
suggests that soil particles adsorbing Cs-137 were hardly
suspended in water or were re-captured in soil lumps after being
suspended. Results of the radiometric analysis of the soilcolumns after the migration experiments did not indicate any
migration of Cs-137 upward and downward.
3.2.2

Leaching experiments

In the sequential leaching tests using deionized water or 1

the concentration of Cs-137 in the cover soil and in theunderlying soil of 10 ~ 40 Bq/kg is observed at site B.

Column migration experiments

The concentrations of Cs-137 in the effluents of the 2 types ofthan the detection limit (11~13 Bq/kg) in the cover soil and in
the underlying soil for the sites A and C. At sites A and C,

Laboratory experiments

mol/L CH3COONH4 solution, radiocesium was not detected24

A demonstrative experiment on the migration of radiocesium from buried soil
contaminated by the accident at Fukushima Daiichi Nuclear Power Station

Fig. 4

Concentration of Cs-137 determined by radiometric analysis of boring cores. The detection limits were shown by open
marks in the case that the concentration was under the detection limit.

Fig. 5

Change of the concentration of Cs-137 with time in the contaminated soil and in the cover and the underlying soils.
The detection limits were shown by open marks in the case that the concentration was under the detection limit.
25

December 2015

原子力バックエンド研究(detection limit: 10 ~ 15 Bq/L) in any of the leachates. The
long-term leaching tests also

showedno C gw,i x, t C gw,i x, t Rt i  C gw,i x, t   Dx 
 U gw 
2
t
x
x
2

radiocesium,

concentration in all the leachates were under the detection limit

 Rt i  i  C gw,i x, t   Rt i1  i 1  Cgw,i 1 x, t (1 ~ 2 Bq/L). The results suggest that radiocesium in the soils
hardly dissolves in permeated rainwater or in groundwater.
3.2.3

Sorption experiments(2)

where Rti is the retardation factor of Cs migration through the

The sorption distribution coefficients obtained in the sorption

soil [-], Cgw,i(x,t) the concentration of Cs-137 [Bq/m3] at a depth

experiments were shown in Fig. 6 for site A. The ammonium

x [m] and at time t [y], Dx the longitudinal dispersion coefficientconcentration[m2/y], Ugw the permeation rate [m3/m2/y], λi the decay constantdependences

of

the

sorption

distribution

coefficients on the soils from sites B and C were similar to thatof Cs-137 [1/y]. The Rti and Dx were given as:

for site A. The sorption distribution coefficient is as high as 103

Rti  1 

to 104 mL/g under the cation concentrations less than 10-3 mol/L
anticipated in actual environments. The range of sorption
distribution coefficients was the same as those for the sites B and

1 S

S

  S  Kd S ,i

and

(3)

Dx  Dl  U gw  Dm

C. The concentrations of Na+ and K+ in river water are typically(4)

2.9×10-4 and 3.0×10-5 mol/L, respectively [5] and are lower thanwhere εs is the porosity of the soil [-], ρs the density of the soil

the 10-3 mol/L. The concentration of ammonia nitrogen in the[g/cm3], KdS,i the sorption distribution coefficient of Cs onto soil

-4

soil water at the sites was 11 mg/L or 7.9×10 mol/L at highest-3

as shown in Table 4, which is also lower than the 10 mol/L.

[mL/g], Dl the longitudinal dispersion length [m] and Dm thediffusion coefficient [m2/y].

The results ensure that radiocesium is adsorbed on surrounding

Conditions of the calculations are shown in Table 5. The

soil particles and does not migrate even if leached from thesorption distribution coefficient was assumed to be 1000 mL/g,

contaminated soils into soil water. The sorption distribution

which was the lowest value obtained in the laboratory sorption

coefficient of radiocesium is discussed in relation to the clay

experiment using the soils obtained from the sites and deionizedcontent of the soil in some cases and is found less correlated towater. The sorption distribution coefficients obtained in thethe clay contents in other cases [6]. Further study is necessarypresence of cations were not used because they werefor establishing the correlation.

unrealistically low. The infiltration rate of rainwater in Japan [5]was used as the infiltration rate. The porosity and the density
were taken from our measurements. The diffusion coefficient is
the molecular diffusion coefficient of Cs+ in water. Although
irreversible sorption of Cs-137 on soils may occurs in the fields,
only reversible sorption was considered in the simulation inorder not to underestimate the Cs-137 migration.
Table 5 Conditions of the calculation. Values in parenthesis
are the ones obtained in the experiments.

Fig. 6

4

Sorption distribution coefficient of Cs on soil
obtained from the site A as a function of theconcentration of cations in aqueous phase.

Extrapolation beyond the experimental period bymodel simulation
Although migration of radiocesium through the soil layer was

not detected in the field experiments, it might occur over longer
periods. A series of calculations were performed simulating

Parameter

Value

Infiltration rate into soils(m3/m2/y)

0.4 [5]

Sorption distribution coefficientof Cs (mL/g)

1,000(5,400 ~ 8,200)

Porosity (-)

0.5 (0.5)

Density (kg/m3)

1,350 (1,350)

Diffusion coefficient (m2/s)

2×10 [7]Dispersivity (m)0.01 [7]-9vertical migration of Cs-137 over 100 years.
The results of the calculations were shown in Fig. 7. Only a

A computer code, GoldSim (GoldSim Technology Group LLC,USA), capable of mass transport analysis with decay ofradionuclides, was used. A one-dimensional system that consistsof cover soil, contaminated soil and underlying soil was
considered. The basic mass balance equation is as follows:

small amount of Cs-137 was predicted to migrate downward andupward from the initial position via water permeation anddiffusion. At 5 cm deeper from the interface between thecontaminated soil and the underlying soil, for example, theconcentration of Cs-137 was evaluated to be as high as 10% of26

A demonstrative experiment on the migration of radiocesium from buried soil
contaminated by the accident at Fukushima Daiichi Nuclear Power Station
the initial concentration in the contaminated soil after 30 ~ 50

Kato and Ms. S. Shimoda of Mitsubishi Materials Corporation

years. At the same time, the concentration of Cs-137 wasand Mr. N. Kiyanagi and M. Saga of Mitsubishi Materials

evaluated to be 1% of the initial concentration in theTechno Corporation are acknowledged for their technicalcontaminated soil at 10 cm deeper than the interface and 0.001%

contribution. Dr. Logan Barr of Japan Atomic Energy Agency is

at 20 cm. The concentration was evaluated to be 4% at 5 cm, 2%

acknowledged for linguistic amendment.

at 10 cm and 0.1% at 20 cm after 100 years. Almost all theCs-137 is expected to decay out in the contaminated soil layer.

References[1]

Kamiyama, H., Yamamoto, T., Shimooka, K., Takebe, S.,
Ogawa, H., Tanaka, T., Mukai, M., Komiya, T., Li, Shu.,
Wang, Z., Guo, Z., Li, Z., Zhao, Y. and Li, She.: Field Testof Radionuclide Migration – Cooperation Research
between JAERI and CIRP -. JAERI Research 94-009(1994). (in Japanese)[2]

Sakamoto, Y., Nakamura, H., Killey, R. W., Champ, D. R.:
Migration Behavior of Sr-90 and Cs-137 in a sand aquifer:
Results of a 30-years experiment. 10th Pacific Basin
Nuclear Conf., vol.2, Kobe, Japan, October 23-27, 1996,
pp.1343-1350 (1996).

[3]

Ministry of the Environment: Notification of themeasurement method of leaching of soils. Notification No.
18 of the Ministry of the Environment (2003). (inJapanese)[4]

Atomic Energy Society of Japan: Technical Report of“Measurement Method of the Distribution Coefficient on

Fig. 7the Sorption Process - Basic Procedure of Batch Method

Results of the model simulation of migration of
Cs-137 over 100 years.

relevant to the Barrier Materials used for the Shallow Land
Disposal:2002 and Basic Procedure of the Method

5Conclusion

Relevant to the Barrier Materials used for the Deep
GeologicalSoils contaminated by the accident at Fukushima Daiichi

[5]

for

Editorial board of revised handbook of groundwater:
Revised handbook of groundwater. Construction Industry

migration of radiocesium over a year. Migration of radiocesium

Research Committee (1998). (in Japanese)[6]

cores and the soil water samples.

Office of Radiation and Indoor Air, EPA: Understanding
variation in partition coefficient Kd, values. EPA

Laboratory column and sorption experiments revealed that theradiocesium hardly leaches out of the soil and even if they leachCommittee

AESJ-SC-TR001:2006 (2006). (in Japanese)

public parks in Misato, Saitama prefecture in order to examine
was not detected from the radiometric analysis of the boring

2006”.

Standardization in Atomic Energy Society of Japan,

Nuclear Power Station were buried and covered with clean local
soils in a public park in Miho, Ibaraki prefecture and in two

Disposal:

402-R-99-004B (1999).
[7]

Japanese

Associationof

Groundwater

Hydrology:

out from the contaminated soil, radiocesium is sorbed on

Simulation of groundwater flow and solute transport.

surrounding soils and hardly migrates through the soil layer.

Gihodo Shuppan (2010). (in Japanese)

Simulation of the Cs-137 migration for 100 years by anadvection-diffusion model showed that Cs-137 migrates slightly
and decays out in the contaminated soil.
Acknowledgement
Mr. S. Sugano of Miho village office, Mr. S. Akimoto, Mr. J.
Fujimaru, Mr. Y. Saga and Mr. W. Nakamoto of Misato
municipal office are acknowledged for their support to the field
experiments. Mr. R. Tatsuta and Mr. J. Kurosaka of Ministry of
the Environment are acknowledged for their contribution as
secretaries. Mr. M. Mukai and Dr. T. Tanaka of JAEA and Mr. H.
27

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28

December 2015