Radiation Monitoring and Remediation Following
the Fukushima Daiichi Nuclear Power Plant Accident

Cooperation between
Fukushima Prefecture and the IAEA
FINAL REPORT(2013 to 2022)【Fukushima Prefecture Initiative Projects】(Temporary translation)

March 2023
Fukushima PrefectureIndexIntroduction

1

1. FIP1: Survey, and evaluation of the effect, of radiocaesium dynamics in the aquatic
systems based on the continuous monitoring
1.1. Abstract3

1.2. Purpose

3

1.3. Content of implementation

4

1.4. Results

10

1.5. Conclusions

24

2. FIP2: Survey of Radionuclide Movements in Wildlife
2.1. Abstract

27

2.2. Purpose

27

2.3. Investigation results made from 2013 to 201728

2.4. Investigation results made from 2018 to 2022

41

2.5. Conclusions73

3. FIP3: Sustainable countermeasures for radioactive materials in terrestrial andaquatic areas
3.1. Abstract77

3.2. Purpose

77

3.3. Content of implementation

77

3.4. Results

83

3.5. Conclusions96

4. FIP4: Development of environmental mapping technology using GPS walking
surveys（ Ended in FY2015）
4.1. Abstract99

4.2. Purpose

99

4.3. Content of implementation

101

4.4. Results

103

4.5. Conclusions

110

5. FIP5: Study of proper treatment of waste containing radioactive material
5.1. Abstract111

5.2. Purpose

111

5.3. Radiocaesium distribution between bottom ash and fly ash

111

5.4. Radiocaesium elution tests from ashes

127

5.5. Situations of landfill and radiocaesium elution

147

5.6. Radiation safety assessment using landfill assessment tool155

5.7. Landfill site management after the completi on of landfill of waste

170

5.8. Conclusions

172

Report summary

174

Introduction
The Great East Japan Earthquake occurred on 11 March 2011. It was followed by the accident ofTokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant 1 , leaving a lot ofdamage to the Fukushima Prefecture. R adioactive materials have been released into theenvironment which contaminated the land. Due to the contamination of the land and other relevant
reasons, more than 160,000 prefectural residents were forced to evacuate. About 29,000 residents
have not been able to return home, as of 202 2 September, about 11 years after the disaster 2 .
In order for Fukushima Prefecture to recover from the severe and unprecedented nuclear disasterand create an environment where the residents can live with peace of mind in the future, theprefecture decided to cooperate with the International Atomic Energy Agency (hereinaf ter referred
to as the “IAEA”), which owns high -level nuclear-related knowledge and world-wide experience.
In December 2012, a memorandum for cooperation was signed between the prefecture and the
IAEA.
Based on the memorandum, the Practical Arrangements (hereafter referred to as the “PA”)
relating to the fields of “radiation monitoring” and “decontamination” was signed between theparties on the same day (projects based on this PA are referred to as “FCPs; Fukushima
Cooperative Project”).
Subsequently in April and October 2013, PA were signed for five projects (hereinafter referred
to as “FIPs; Fukushima Initiative Project”) as described below in a new framework in which theseprojects would be supported by the IAEA for three years, and the FIPs started. In April 2016, they
signed PAs for revising 3 the scope of cooperation and extending the duration of the FIPs. It
continued until December 2017 (hereinafter referred to as “previous Project”).
【 Scope of cooperation for the previous Project (From April 2013 to December 2017)】
FIP1 Survey of radionuclide movement in river systems
FIP2 Survey of radionuclide movement with wildlife
FIP3 Countermeasures for radioactive materials in rivers and lakes
FIP4 Development of environmental mapping technology using GPS walking surveys
FIP5 Study of the proper treatment of waste containing radioactive materials at municipal
solid waste incinerators
The outcomes of the previous Project were summarized in the report on “Cooperation between
Fukushima Prefecture and the IAE A – SUMMARY REPORT (2013 to 2017) [Fukushima Prefecture

The o wner of the Fukushima Daiichi Nuclear Power Plant was renamed from Tokyo Electric Po wer
Company to Tokyo Electric Po wer Company Holdings, Incorporated in April 1, 2016.
1

2

Steps for Revitalization in Fukushima (ver.31.2; December 27, 2022).
(https://www.pref.fukushima.lg.jp/uploaded/attachment/547379.pdf)

3

Revision of the scope of cooperation for FIP1~3, 5 and completion of FIP4.

1

Initiative Projects] 4 ” in March 2018.
However, remediation of the environment in the Prefecture was halfway and the accomplishmentof the proposed projects required further support from the IAEA, the prefecture agreed with the
IAEA to extend the PA 5 in December 2017 until December 2022 (hereinafter referred to as “thisProject”).
【 Scope of cooperation for this Project (From January 2018 to December 2022)】
FIP1 Survey, and evaluation of the effect, of radocaesium dynamics in the aquatic systems
based on the continuous monitoring
FIP2 Survey of radionuclide movement with wildlife
FIP3 Sustainable countermeasures to radioactive materials in freshwater system
FIP5 Study of proper treatment of waste containing radioactive material
The outcomes of the previous Project and this Project are summarized in this report.

4

The previous report is available as printed material and also in the following website;(https://www.pref.fukushima.lg.jp /sec/298/iaeasummary2017.html)

5

Revise the scope of cooperation for FIP1~3, 5.

2

1. FIP1: Survey, and evaluation of the effect, of radio caesium dynamics in theaquatic systems based on the continuous monitoring
1.1. Abstract
As a result of the Fukushima Daiichi Nuclear Power Plant accident in March 2011, radioactive
materials were released and deposited in the Fukushima Prefecture. It is important to provide
information for the safe use of river water in the Prefecture. To inv estigate the dynamics ofradioactive materials in river systems and to estimate the changes in radio caesium concentrations
in rivers over time by the model simulations, studies were conducted in the rivers of the Fukushima
Prefecture. Surveys of the dynamics in suspended and dissolved radio caesium were conducted in
the Abukuma River system and in major rivers of the Hamadori area. The results obtained in March
2021 showed that the suspended and dissolved radio caesium concentrations continue decreasing,even beyond ten years after the accident. In addition, it was shown that the migration ofradiocaesium was affected by the presence of dams and decontamination activities in thecatchment. Even though the radio caesium concentrations tends to decrease over time , somesuspended sediment samples showing an extremely high concentration were found. The
investigation was carried out, and the presence of radio caesium-bearing microparticles (CsMPs)
was confirmed, however their contribution was suggested to be small. Mo del simulations werealso performed to assess changes in the suspended and dissolved forms of radio caesium under bothbase- and high-flow conditions. The estimated results showed good agreement with measured
values, although some improvements are considere d necessary. It was presumed that the load ofsuspended sediments due to riverbank erosion and resuspension of river sediment under high flow
conditions contributed greatly to the increase in suspended radio caesium transport.
1.2. Purpose
As a result of the accident in the Tokyo Electric Power ’s Fukushima Daiichi Nuclear Power Plant
in March 2011, large amounts of radioactive materials were released into the environment, andtheir fallout anddeposition in Fukushima Prefecture were confirmed.

Therefore, it has been

important to clarify the actual situation of radioactive materials (especially radio caesium) in rivers
and to provide the necessary information for future predictions and safe use of rivers and riverwater, considering that they are widely used for drinking water, agriculture, and industry.
Radiocaesium in river water is found in suspended (adsorbed on fine particles) and dissolved(dissolved in water) forms. It is assumed that the dynamics in the environment differs dependingon the difference in the form. Therefore, it is essential to understand the concentration ofradiocaesium in the different forms, in order to comprehensively clarify the dynamics of bothforms of radiocaesium in rivers. As there are many forested areas without decontaminatio n in theupper catchment of rivers in Fukushima Prefecture, it is necessary to pay attention to the
influences of these on the dynamics of radio caesium in rivers in the surrounding area. Changes insocial conditions (e.g. completion of the decontamination works, return of residents andresumption of farming following the lifting of evacuation orders) and the occurrence of3

unexpected events (e.g. forest fires, large -scale floodings due to typhoons, heavy rainfalls, etc.)
should be considered.
In this project, a long-term observation survey was conducted on the concentration ofradiocaesium in rivers in Fukushima Prefecture, considering its different forms. The state of
decline in the concentration of radio caesium in rivers was assessed. The amount of radio caesium
fluxes in rivers were estimated from the monitoring results. The factors that could contribute tochanges in the concentration and amount of flux in radio caesium (e.g. decontamination works andthe presence of CsMPs) were investigated.
In addition, to elucidate the dynamics of radio caesium through rivers in more detail and be able
to predict its future, model simulations reproduce the changes in the radio caesium concentrations
were carried out. And the source of suspended radio caesium using characteristics of organic matter(total organic carbon and stable isotope composition) in suspended sediment was also estimated.

Figure 1. Schematic diagram describing
dynamics of radio caesium in a river basin.

1.3. Content of implementation
Figure 2 shows the monitoring points considered in this project. The background colour of the
map indicates the deposition amount of radio caesium on the ground surface as of July 2, 2011,
which is assumed to be the initial deposition in this document. The m onitoring points in the
Abukuma River and major rivers in Hamadori area for the Wide -area Multipoint Survey are shownin Figure 2(b). The monitoring points in the Kuchibuto River Basin and the Hirose River Basin
which are tributaries of the Abukuma River f or a single basin survey, are shown in Figure 2(a)and 2(c), respectively.

4

(a)

(b)

(c)

Figure 2. Monitoring points used in this study; (a) Single Basin Survey (Kuchibuto
River Basin), (b) Wide-area Multipoint Survey, (c) Single Basin Survey (Hirose
River Basin)
1.3.1. Wide-area Multipoint Survey
1.3.1.1. Wide-area Multipoint Survey
1.3.1.1.1. Purpose
From the fiscal year 2015, a Wide -area Multipoint Survey of the Abukuma River Basin and eightwater systems in the Hamadori area was performed. Figure 2(b) shows the caesium-137-depositionin the study area and the positions of the monitoring points. Samples were taken regularly following the same procedure - to explore the time-dependence of the caesium-137 activity
concentration and to identify relationships with the basin characteristics. This survey was acontinuation of a survey carried out by the University of Tsukuba from fiscal year 2011 to 2014as a project on behalf of the Ministry of Education, Culture, Sports, Science and Technology and
the Nuclear Regulation Authority. The results including the past survey conducted by the
University of Tsukuba are also provided.
1.3.1.1.2. Method
At each monitoring point, the monitoring has been continued by installing and operating theequipment (including a suspended sediment (SS) sampler, a turbidity meter, and a water level
gauge). The suspended sediments were collected with samplers at intervals of 1 to 3 -month, driedin a vacuum freeze-dryer, and caesium-137 concentrations were measured using a germanium
semiconductor detector. Turbidity and water level data were obtained at 10-minute intervals, andthe concentration of suspended sediment (mg L - 1 ) and the flow rate (m 3 s -1 ) were calculated
applying the equations elaborated in the FIP Summary Report (2013 -2017). The flux of suspended5caesium-137 was estimated by multiplying the concentration of suspended sediments, the river flow
rate, and the caesium-137 concentrations in the suspended sediments.
To quantify the concentration of suspended and dissolved forms of radiocaesium, 40 to 100 L ofriver water were collected approximately twice a year. Dissolved and suspended radio caesium
forms were separated using a multi-stage filtration system (Figure 3). The samples were measured
with a germanium semiconductor detector, and the sus pended and dissolved caesium-137
concentrations in the river water were evaluated.

Figure 3. Radiocaesium collecting devices; Multi-stage Filtration System.

1.3.1.2. Survey of radiocaesium-bearing microparticles in suspended sediment
samples
1.3.1.2.1. Purpose
In the SS samples collected during the Wide -area Multipoint Surveys, several samples withextremely higher than normal radio caesium concentrations were found. An example is shown in
Figure 4. While the concentration of radio caesium tends to decrease with time, it is important toclarify the factors that specifically increased the concentration of radio caesium in SS samples inorder to understand the dynamics of radio caesium transport through rivers.
Previous studies have reported the presence of radio caesium-bearing microparticles (CsMPs),
released during nuclear power plant accident 1 ), 2 ) , 3 ) . In this study, it was hypothesized that thismay be due to the inflow of CsMPs into the river and their subsequent mixing with the SS.

6

Figure 4. Temporal changes of suspended caesium-137 concentrations at one of
the monitoring points of the Wide -area Multipoint Survey in Hamadori area
(In the sample collected in October 2018, a higher concentration of caesium137 was detected, significantly deviating from the trend of gradual decreasein concentration.)

1.3.1.2.2. Method
To clarify the influence of CsMPs on the suspended caesium-137 concentrations, the SS samples
collected by the SS sampler that showed much higher radio caesium concentrations compared toother samples were used. The radioactive particles in SS samples with high caesium-137
concentrations were investigated. The radioactivity of the particles was measured by germanium
semiconductor detectors and imaging plate (IP) autoradiographic techniques, and the particle sizeand elemental analysis of the particles were measured by Scanning Electron Microscopy -energy
dispersive X-ray spectroscopy (SEM) and Electron Probe Micro Analyzer (EPMA). In addition, a
simple method for determining the presence or absence of CsMPs in the presence of such samples
was investigated.
1.3.2. Single basin survey
1.3.2.1. Simulation of radio caesium dynamics in river by TODAM 1 model
1.3.2.1.1. Purpose
The purpose of this study is to examine the future effects of radioactive caesium migration andredeposition via rivers. In this study, a numerical model was applied for the Hirose River and theKuchibuto River, tributaries of the Abukuma River, and simulations of the dynamics ofradiocaesium were performed. In the areas near the southeast boundary of the Hirose River Basin,
Time-dependent One-dimensional Degradation And Migration Model 4 , 5 ) , The TODAM model
was provided by Prof. Yasuo Onishi, an IAEA specialist, in fiscal year 2015. For this simulation,technical support from Prof. Onishi was received.
17

a relatively large amount of radio caesium was deposited (Figure 2(c)). The depositions were alsohigh in the catchments of the tributaries, the Nuno River and the Oguni River (Table 1).
Table 1. Catchment area and initial caesium-137 deposition within
the Hirose River Basin.
River basin area

Average Cs-137 deposition[km 2 ]

[kBq m - 2 ]Hirose River

267.9

231

Takane River

19.2

270

Nuno River

18.6

343

Ishida River

30.1

290

Oguni River

40.4

343

To simulate the dynamics of radio caesium in river water in these catchments, monitoring was
carried out at twelve sites, as shown in Fig ure 2(c), from 2013 to 2021.An additional monitoring
point was established along th e main river channel of the Hirose River in 2019 (St. 4). For the
Kuchibuto River Basin, the monitoring was carried out at five monitoring points, from 2017 to
2021, mainly those that were already included in the Wide -area Multipoint Survey. The initialdeposition of radiocaesium in the catchment at each monitoring point was calculated and shown in
Table 2.
Table 2. Catchment area and initial caesium-137 deposition within the
Kuchibuto River Basin

Mizusakai River
Kuchibuto River

River basin area

Average Cs-137deposition[km 2 ]

[kBq m - 2 ]

7.52

587

21.4

408

62.8

304

17.6

235

135.2

247

Upstream
Kuchibuto River
Midstream
Adachiota River
Kuchibuto River
Downstream

1.3.2.1.2. Method
At each monitoring point, approximately 100 L of river water were collected at base -flow levels(every 2 to 3 months) and at high -flow levels (7 samples/1 high -flow event, for 24 hours). Water
quality (pH, electrical conductivity (EC), oxidation–reduction potential (ORP)) and SS
concentrations were measured at the time of collection. Suspended and dissolved forms ofradiocaesium were collected from river water samples in a cartridge filter
86)

for caesiummonitoring using a radiocaesium monitoring device (Figue 5) 7 ) . Each form of radiocaesium wasthen measured with a germanium semiconductor detector. In addition, investigations of activity
concentrations in the cross -section of the riverbed, and samplings of riverbank soil and sedimentwere carried out. Based on these data, the radiocaesium concentrations and their changes in theriver were estimated under base flow and high flow conditions using the TODAM model. The
TODAM model can simulate temporal changes of radionuclide concentrations in waters andsediments. For example, the TODAM model makes it possible to estimate the amount ofradionuclides transported to the Pacific Ocean in rivers, to predict the l ocations in rivers wheresediments are preferentially deposited, and to evaluate the influence of decontamination measureson the dislocation of sediments in rivers. In this survey, the TODAM model was used to estimate
the radiocaesium activity and their changes under base flow and high flow conditions.

Figure 5. Radiocaesium monitoring device 7 ) .

1.3.2.2. Estimation of the source of SS loads
1.3.2.2.1. Purpose
Suspended sediments (SS) play a significant role in the transition of caesium-137 as a particulate
form through rivers. The concentration of SS in river water generally increases during high -flow
events, resulting in quite a lot of caesium-137 transportation even in a single high -flow event. In
order to clarify the relative contrib utions of the potential SS sources in a watershed to the amountand concentrations of fluvial SS both under high - and base-flow conditions, caesium-137
radioactivities, total organic carbon (TOC) concentrations, and stable carbon isotope composition( 1 3 C) in SS were employed for a simulation using a Bayesian isotopic mixing model, Stable
Isotope Analysis in R (SIAR ver. 4.2).
1.3.2.2.2. Method
For measurements of TOC and 13C in SS, about 0.5 or 1.0 L river waters sampled at the same time as for
caesium-137 measurements were filtrated by glass fiber filters (GF/F) which had been precombusted at 450 ℃
for 4 hours. Four potential SS sources were determined in this project (forest soils and litters, riverbank soils,
and river sediments). Forest soils and litters were sampled in adjacent forests at the headwater region of theHirose River. Riverbank soils and river sediments were sampled along the mainstream and tributaries of the9Hirose River. These source materials were air-dried at 40℃ for more than 48 hours. The samples were
measured using an elemental analyzer coupled to an isotope ratio mass spectrometer using an interface. The
detail procedures were shown in a study of Arai et al. (2021) 8).
1.4. Results
1.4.1. Wide-area Multipoint Survey
1.4.1.1. Wide-area Multipoint Survey
Figures 6(a) and 6(b) show the variations in suspended and dissolved caesium-137 concentrations
over time (as of March 2021) obtained from the Wide -area Multipoint Survey. The data include
results from the University of Tsukuba until the end of FY2014. The concentration of suspended
caesium-137 at each monitoring point showed a tendency to decrease over time after the start ofthis project, but the decline observed immediately after the accident was the fastest 9 ), 1 0 ) .

As ofMarch 2021, the concentration of dissolved and suspended caesium-137 was generally less than
1/10 of the value observed immediately after the accident (Figure 6(a)). The concentration ofdissolved and suspended caesium-137 showed a similar time -dependence (Figure 6(b)). T here wasa period of missing data for dissolved caesium-137, h o w e v e r, t h e o v e r a l l p a t t e r n s u g g e s t sthat the concentration of dissolved caesium-137 in the rivers of Fukushima Prefecture gradually
decreased over time.
Based on data obtained from 2012 -2021, the effective half -lives of suspended and dissolved
caesium-137 were estimated to be approximately 3.2 and 2.8 years, respectively (Fig ure 7).
Comparing Chornobyl and Fukushima, the of effective half -lives of caesium-137 in river water
were similar just after the accident (0.24 year in Abukuma River vs 0.31 year in Pripyat River) 11 ) .
In the second year and beyond, the effective half -lives of the concentration of suspended caesium137 in rivers of the Fukushima prefectu re are in the range of 1 to 4 years; similar observations
were made for European rivers. 11 ) .

10

(a)

(b)

Years from the accident [y]Figure 6. Caesium-137 concentrations in river water.
(a) Suspended caesium-137, (b) Dissolved caesium-137.

※

Figure 7. Effective environmental half -life of caesium-137 concentrations in riverwater in each region (data from 2012 –2021). The asterisk indicates the range inthe effective environmental half-life reported for European rivers after the
Chornobyl Nuclear Power Plant Accident).

11

Figure 8 shows the average monthly flux of suspended caesium-137 at six monitoring points from2011 to December 2018. The caesium-137 fluxes do not show a clear tren d due to the strong
temporal fluctuations of the flow rate of the river and the caesium-137 concentrations of suspended
sediments. At the two monitoring points along the Abukuma River, 3.0 -4.0% of the caesium-137inventory of the catchment was displaced an d located with suspended sediments, while at the fourmonitoring points along its tributaries the flux was 0.6 -2.2% of the catchment’s caesium-137
inventories.
The upper part of Figure 9 shows the flux of suspended caesium-137 integrated from October
2012 to October 2014. The lower part of Figure 9 shows the ratio of the area of a reservoir to thetotal catchment area (excluding No.12, 17, 18 due to several problems during the monitoring
period - lower graph). Low caesium-137 fluxes were observed at the poi nts where the area of the

1.E+13
1.E+12
1.E+11
1.E+10

1.E+09
1.E+081.E+07
1.E+06

2011/03
2011/06
2011/092011/122012/032012/06
2012/09
2012/122013/032013/06
2013/09
2013/12
2014/03
2014/06
2014/09
2014/122015/03
2015/06
2015/09
2015/122016/03
2016/06
2016/09
2016/122017/032017/06
2017/092017/122018/032018/06
2018/092018/12Monthly migration of the suspended
Cs-137 flux [Bq]dam covers a large area of the catchment (red hatched part in the graph).

Years from the accident
No.1

No.2

No.3

No.4

No.5

No.6

Figure 8. Monthly migration of the suspended caesium-137 atmonitoring points (No.1-6) from May 2011 to December 2018.

12

Figure 9. Total flux of suspended caesium-137 from Oct.
2012 to Oct. 2014. Red hatched bars indicate the monitoring
point with higher proportion of the watershed area for dams
to the total catchment area.

In addition, the impact of the surface decontamination measures implemented by the national
government and the municipalities on the caesium-137 concentrations in river waters was assessed.
The observed decreases in caesium-137 concentrations were similar to the trends observed inEuropean rivers after the Chornobyl accident (Fig ure 6). However, it is difficult to determine theeffect of surface decontamination measures on the caesium-137 concentrations in rivers because
the area decontaminated is very sma ll in relation to the area of the catchment. Therefore, it isassumed that the decrease observed in areas where decontamination measures were implemented
is largely caused by natural attenuation processes 11 )Subsequently, the data for the Kuchibuto River Basin were analyzed to investigate the effect of
decontamination on suspended radio caesium in river water. The data focused on the variations of
the caesium-137 concentrations in suspended sediments during the decontamination works. The
basin to decontaminate farmland was fully designated as a special decontamination area; work inthe basin was planned in August 2012, it started in March 2013, and it was completed in December
2015 2 . Figure 10 shows the progress of the decontamination of farmland. Decontamination started

Decontamination Information website, Ministry of the Environment,
http://josen.env.go.jp/area/details/kawamata.html
213

in March 2013, but only little progress was made until March 2014. Intensive farmland
decontamination was carried out from April 2014 and decontamination was complet ed in December
2015. Thus, the period before February 2013 was defined as “Pre-decontamination”, the period
from March 2013 to March 2014, when progress was very slow, was defined as “Decontaminationin progress① ”, and the period from April 2014 to Decemb er 2015, w h e n rapid progress was

made, was defined as “Decontamination in progress ② ”. Finally, the interval after January 2016,

Deconta minated a rea of fa rm la ndwhen decontamination was completed, was defined as “Post decontamination”.

Figure 10. Progress in farmland decontamination
The time-dependence of caesium-137 concentrations in suspended sediments at three monitoring
points (upstream, midstream, and downstream; Fig ure 2(a)) is shown in Figure 11. The effective
half-lives for these periods are shown in Table 3. The results showed a faster decrease in suspended
caesium-137 concentration in the upstream and midstream sites of the special decontamination
area during “Decontamination in progress ② ”. However, the decrease was slower in thedownstream sites, and i t slowed down in the second half of the “Decontamination in progress ② ”
period (about 4 years after the accident). In addition, the amount of suspended sediment in surface
water runoff as a function of precipitation and catchment area showed a tendency to increase after
the start of farmland decontamination, and a significant increase was observed during the“decontamination in progress ② ” period. In the “post-decontamination” period, the amount of
sediment in runoff decreased, but it was still higher than in the “pre-decontamination” period(Figure 12). This shows the same trend as the results of the analysis in the Niida River flowing
through the Hamadori area, following decontamination, reported in the previous study 1 2 ) .

14

Figure 11. Change in suspended caesium–137 concentration
over the course of decontamination.
Table 3. Effective environmental half -life for each period (years)
MonitoringPre-

In progress

In progress

Post-

point

decontamination①②

decontamination① Upstream

0.77

n.s.

0.98

n.s.

② Midstream

1.2

n.s.

1.6

n.s.

③ Do wnstream

0.86

0.59

4.2

4.8

n.s. indicates that suspended caesium-137 concentration did not change significantly during eachperiod.

Figure12.

Relationshipbetweendecontamination

sediment runoff.

15

progressandtheamountof1.4.1.2. Survey of CsMPs in SS samples
Two spherical CsMP particles (A and B) were found in the suspended sediment samples (Table4). The radioactivity of caesium-137 in those two particles was estimated to be approximately
13% of the total radioactivity of the sample.
Table 4.
SampleCharacteristics of CsMPs identified in SS samples

Particle size (μm)

Cs-137 (Bq)A

4.2

14±0.1B

1.0

0.25±0.01

nameDetected Element
O, Si, Cl, Fe, Zn, Sn, Cs
O, Si, Cl, Fe, Zn, Cs

When suspended sediments with extremely high caesium-137 concentration were found, asimple method to determine the presence or absence of CsMPs was investigated. Dry methods 2 ),3 ) and wet methods 1 ) have been reported as methods for searching and separating a single CsMP

from a sample. On the other hand, a simple method for determining the radioactivity and numberof CsMPs without separating a single particle from the sample has been reported 1 ), 1 3 ) . Applying
this simple method to CsMPs with known radioactivity, we developed an equation relating
radioactivity and IP brightness and attempted to determine the presence or absence of CsMPs insuspended sediment samples. The threshold of radioactivity for CsMP was set as the maximum
radioactivity value of a particle different from CsMP (0.189 Bq) 1 4 ) , and particles above thisradioactivity were classified CsMPs. Table 5 shows the results obtained: the presence of CsMPsin five suspended sediment samples collected in 2018 -2019 was investigated and nine CsMPs
were estimated to be present. The results indicated the presence of CsMPs in suspended sediment
samples, but their contribution was very small.

Table 5. IP measurement results and radioactivity contribution of the
SS samples

Samp lenameCs-137conc entrati onin the sa mple
(Bq/g)

Wei ghtof S S(g)

Cs-137in thesample(Bq)

Th enumber of
CsMPs

1-NZ1910

3.2±0.07

2.7

8.7

0

2-S U1910

18±0.3

1.4

23

2

3-S D1910

23±0.3

1.4

32

6

4-NR1810

2.1±0.03

3.2

6.7

0

5-TR1907

4.9±0.12

3.0

15

1

Cs-137 in
CsMPs
in tota l(%)

Cs-137 in CsMP
(Bq)

N/ A
3.0

0.48

0.22

0.41

0.36

0.32

0.30

0.23

0.19

5.7
N/ A

0.46

3.1

1.4.2. Single basin survey
1.4.2.1. Simulation of radio caesium dynamics in river by TODAM model
Figure 13 shows riverbed cross sections at the monitoring points of St.3 and St.10 of the Hirose
River (Figure 2a). Both points are about 24 km apart. Although the water depth was similar, the16

river width at St.10, including the floodplains, was about twice as large as that at the St.3. During
the monitoring, high flow events caused the riverbed and bank t o be eroded, and fresh sedimentdeposited on the riverbed, but the riverbed cross -section at each monitoring point did not change
significantly.
(a) St. 3
Elevation [m]

188
184
180
0

10
20
30
Distance from the left bank [m](b) St. 10
Elevation [m]

56
52
48
0

10

20
30
40
Distance from the left bank [m]5060

Figure 13. The cross sections at the monitoring points in the
Hirose River Basin (St. 3 and St. 10).
Figure 14 shows the variations in suspended caesium-137 and suspended sediment concentrations
in water at each monitoring point along the Hirose River in April 2016 at base flow levels. The
concentration of suspended caesium-137 was high in the some of the tributaries. The caesium-137
concentrations are strongly influenced by the initial deposition in the catchment. The results
varied between monitoring points, irrespective of the monitoring points and items (suspended
caesium-137 and suspended sediment concentrations).

17

Figure 14. Suspended caesium-137, and SS concentrations at
each monitoring point in April 2016

Figure 15 shows a scheme of the monitoring network considered in the application of the TODAM
model to the Hirose River. The distance from the confluence of the Hirose River with the Abukuma
River to the confluence of the Takane River with the Hirose River is 31,732 m. In the simulation,
the inflows were considered from the Takane River, Nuno River, Ishida River, and Oguni River,main tributaries of the Hirose River. For the Hirose River, the simulation was performed every
200 m in the direction of the flow channel, and 150 calculation points were set in the Hirose River
Basin. The dynamics of radiocaesium were simulated in the Hirose River based on the monitoring
data.

18

Figure 15. A schematic representation of the monitoring
network in the Hirose River Basin.
Figure 16 shows the calculated and measured concentrations of suspended and dissolved caesium137 concentrations along the Hirose River using the TODAM model under base flow conditions.
The solid line represents the values estimated by the TODAM model, and the boxplot represents
the actual measurement values obtained at six monitoring points along the main river channel ofthe Hirose River. It was possible to reproduce the data obtained at six monitoring points along themainstream of the Hirose River using the TODAM model. The results obtained by the model
simulation were in relatively good agreement with the measured values.

Figure 16. Simulation results of changes of caesium-137 concentration atbase flow levels water estimated using the TODAM model (Hirose River).

19

A simulation of the concentration of caesium-137 in river water during the high flows from
August 16 to 19, 2016 (total precipitation 67 mm; Japan Meteorological Agency, Yanagawa,
Fukushima Prefecture) 1 5 ) is shown in Figure 17. The results also show a good agreement between
measured and calculated values at the four monitoring points (St. 3, 6, 8, and 10) under high flow
conditions.

St.3

St.6

St.8

St.10

Figure 17. Simulation results of changes in caesium-137 concentrations
during high flow events estimated using the TODAM model (Hirose River).
[Upper rows: Suspended caesium-137 concentration, lower rows: Dissolved
caesium-137 concentration] (High flow events from 16 August 2016 to 19
August 2016)

Monitoring data collected from 2017 at the Kuchibuto River Basin (Fig ure 2(a)) was used tosimulate of the suspended and dissolved caesium-137 concentrations in river waters by the
TODAM model. The results of the model simulation of the Kuchibuto River Basin ar e shown in
Figure 18 and 19. In the results of the application along the flow path during base flow conditions,the characteristics of low caesium-137 concentrations in both dissolved and suspended forms in② Midstream were generally reproduced (Figure 18). The simulation results at ③ Downstream
based on the data from the outflow on 5 -6 July 2018 (total precipitation 36 mm; Japan
Meteorological Agency, Tsushima, Fukushima Prefecture) 1 5 ) , were also able to reproduce temporalchanges in suspended sediment and both suspended and dissolved caesium-137 concentrations.
Through this cooperative project, it was possible to simulate the dynamics of caesium-137 using
20

the TODAM model for two rivers. In addition to predicting the dynamics of caesium-137 in theserivers, future applications to other rivers and to the dynamics of other contaminants are possible.
The accuracy of the simulation predictions can be improved through the calibration with site specific information and data. In particular, hydrological data are required, such as therelationships between water level and flow rate in the target river, and between the flow rate andsuspended sediment concentrations with particle size distributions. It is c onsidered necessary toobtain these data in advance when performing preliminary impact assessments in preparation foran eventual nuclear disaster.

6000
5000
4000
3000
2000
1000
0

(a )

40000

35000

30000

25000

20000

15000

10000

5000

0

Dist ance from the confluen ce with t he Abukuma River [m]
SAND

10

Silt-2Silt-1

Particulate Cs137

Observation

(b )

7.5
5
2.5

0

40000

35000

30000

25000

20000

15000

10000

5000

0

Dist ance from the confluen ce with t he Abukuma River [m]DissovedCs137

Dissolved

AVE

Figure 18. Simulation results of changes of caesium-137 concentration
at base flow levels water estimated using the TODAM model (Kuchibuto
River).
(a) Suspended caesium-137 concentration, (b) Dissolved caesium-137
concentration.

21

0.4

8

0.3

6

0.2

4

0.1

2

Q [m3 s-1]

1000
9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00
7/5

7/6

Time

SSC-sand

SSC-Silt2

SSC-Silt1

実測SSC

SSC-total
SSC-observed

Q

SSC-measured

8000

4

6000

3

4000

2

2000

1

0

0
9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00
7/5

7/6

Cs137-sandSuspended-measured
Cs137-dissolved

Dissolved Cs-137
concentration [mBq L-1]

Suspended sedimentconcentration [g L-1]
Suspended Cs-137
concentration [Bq kg-1]

0.5

Time
Cs137-Si2
Cs137-Si1
Dissolved-measured

Cs137-si2
Cs-137-suspended

Figure 19. Simulation results of changes in caesium-137 concentrations duringhigh flow events estimated using the TODAM model (Kuchibuto River). [Upper rows:
Suspended

caesium-137

concentration,

lower

rows:

Dissolved

caesium-137

concentration] (High flow events from 5 July 2018 to 6 July 2018)
1.4.2.2. Estimation of the source of SS loads
It was found that contents of caesium-137 and organic carbon in river water were i ncreased withincreasing SS concentration in river water (Fig ure 20). These results confirmed that both caesium137 and organic carbon were move together with SS. On the other hand, there were no significant
relationships between SS concentrations and both caesium-137 and TOC concentrations in SS(Figure 20). However, the average values of both caesium-137 and TOC concentrations in SS at
the base-flow condition tended to be larger than those at the high -flow condition, indicating thatthe additional SS supp lied during high-flow events had lower concentrations of caesium-137 and
TOC than SS at the base -flow condition. In other words, during high -flow events, caesium-137
and TOC in SS were diluted by an input of mineral materials with low caesium-137 concentrations.
The  1 3 C values in SS showed a gradual decreasing trend with increasing SS concentration (Fig ure20), which suggested a gradual change of organic carbon source in SS with increasing SS
concentration in river water.
22

Figure 20. Changes of both contents in river water ((a) particulate
caesium-137 and (b) particulate organic carbon) and properties in SS((c) caesium-137, (d) TOC, and (e)  1 3 C) with SS concentrations areshown. Blue squares indicate the data at base -flow, while red circles
indicate the data at high-flow river.

The results of caesium-137, TOC, and  1 3 C in four potential sources of SS are shown in Table 6.
As expected, forest soils showed the highest caesium-137 concentrations due to the lack of
decontamination practices. Forest litters showed the highest TOC concentration and the mostdepleted  1 3 C value, and riverbank soils and river sediments showed relatively low caesium-137
and TOC concentrations. The result of simulation by SIAR using these data revealed that forest
soil is the predominant source of fluvial SS during base -flow condition, and the contributions ofother sources remained at low levels (Fig ure 20). At the high-flow condition, on the other hand,the contribution of forest soils reduced significantly, although the contribution was still high.
These results led to the conclusion that erosion of riverbank and resuspension of river sediments
at high-flow events promoted additional inputs of SS m aterials with low caesium-137
concentrations, resulting in dilution effects of total SS in high -flow river water. It is suggested
that it is better to clarify the formation process of SS during high -flow events and to assess thesimulation results, using additional tracers and fingerprinting properties in future works.
23

Table 6. Properties of four potential SS sources. Averages are shown with thestandard deviations (S.D.).
Type

137

Cs

n

Bq kg − 1

δ13C

n

TOC

n

mgC mg − 1‰

Forest Soils

5400 ± 1600

12

−26.9 ± 0.6

120.105 ± 0.021

12

Forest litters

240 ± 15016−30.0 ± 0.5

160.468 ± 0.011

16Riverbank soils

470 ± 53046

−26.4 ± 0.8

150.018 ± 0.015

15River sediments

110 ± 110175

−25.4 ± 0.8

210.001 ± 0.001

21

p value *<0.001<0.001<0.001*Results of the Kruskal−Wallis H test.

Figure 21. Simulation results for the relative contributions of each four
potential source to SS under base - and high-flow conditions. The data wereshown as the credible interval.

1.5. Conclusions
In the Wide-area Multipoint Survey of the Abukuma River system and major rivers in the
Hamadori area, it was confirmed the presence of both suspended and dissolved radio caesium
concentrations, with a decreasing trend over time just after the accident in 2011. It was clarified
that the amount of suspended radio caesium fluxes decreased at the monitoring point with dams in
the catchment area, and the decontamination works in the catchment clearly impacted on
suspended radiocaesium-137 concentrations. The presence an d the contribution of CsMPs were
investigated for suspended sediment samples with greater radio caesium concentrations. Although24the presence of CsMPs was confirmed in the samples, it was suggested that their contribution to
the radioactivity in these samples was small.
TODAM model simulations were carried out for two rivers during base and high flow conditions,and the results were well reproduced the monitoring analysis results. In addition, riverbank erosion
and resuspension of river sediments play signi ficant roles in the increase of SS concentrations inriver waters under high flow conditions.
References
1) Hikaru Miura, Yuichi Kurihara, Aya Sakaguchi, Kazuya Tanaka, Noriko Yamaguchi, Shogo
Higaki, Yoshio Takahashi. 2018. Discovery of radiocesium -bearing microparticles in riverwater and their influence on the solid -water distribution coefficient (Kd) of radiocesium in the
Kuchibuto River in Fukushima. 2018. Geochem. J. 52. (2). 145–154.
2) Yukihiko Satou, Keisuke Sueki, Kimikazu Sasa, Hideki Yoshikawa, Shige o Nakama, Haruka
Minowa, Yoshinari Abe, Izumi Nakai, Takahiro Ono, Kouji Adachi, Yasuhito Igarashi. 2018.
Analysis of two forms of radioactive particles emitted during the early stages of the Fukushima
Dai-ichi Nuclear Power Station accident. 2018. Geochem . J. 52. (2). 137–143.
3) Yasuhito Igarashi, Toshihiro Kogure, Yuichi Kurihara, Hikaru Miura, Taiga Okumura, Yukihito
Satou, Yoshito Takahashi, Noriko Yamaguchi. 2019. A review of Cs -bearing microparticles inthe environment emitted by the Fukushima Dai -ichi Nuclear Power Plant accident. J. Environ.
Radioact. 205–206.101–118.
4) Onishi, Y., and Perkins, W.A. 1994. TODAM One –dimentional Sediment and Contaminant
Transport Model with Multiply Connected Networks. Theory and Numerical Methods, vol. 1,
Pacific Northwest National Laboratory, Richland, Washington.
5) Perkins, W., and Onishi, Y. 1994. TODAM One –dimentional Sediment and Contaminant
Transport Model with Multiply Connected Networks User ’s Guide, vol. 2, Pacific Northwest
National Laboratory, Richland, Washington .
6) Tsuji, H., Kondo, Y., and Suzuki, Y., Yasutaka,T., 2014. Development of a method for rapid
and simultaneous monitoring of particulate and dissolved radiocesium in water with nonwoven
fabric cartridge filters, Journal of Radioanalytical and Nuclear Chemis try, Volume 299, Issue
1, 139-147.
7) Radioactive Caesium Monitoring Consortium for Environmental water Technical Report
Revision WG. 2021. Technical Report: A Comparison of the Radio Caesium Pretreatment andanalytical methods in Environmental Water (2nd edi tion) February 2021.
https://staff.aist.go.jp/t.yasutaka/MoniCons/MoniCons_index.html
8) Arai, H., Fujita, K., Yoshita, H., Taniguchi, K., Differences in the Proportional Contributions ofParticulate Radiocesium Sources under Base- and High-Flow River Conditions: A Case Study in
the Central Region of Fukushima, Water 2021, 13(21), 3021.
9) Taniguchi, K., Onda, Y., Smith, H, G., Blake, W, H., Yoshimura, K., Yamashiki, Y., Kuramoto,T., Saito, K. 2019. Transport and r edistribution of radiocaesium in Fukushima fallout throughrivers. 2019. Environ. Sci. Technol. 53, 12339–12347.
2510) The Nuclear Regulatory Agency (2015), Fiscal 2014 Project Report about Integration ofRadioactive Material Distribution Data and Development of Migration Model Accompanying
Disaster at Tokyo Electric Power's Fukushima Daiichi Nuclear Power Plant - Part 2"Radiocaesium migration status survey on river water systems" at
http://radioactivity.nsr.go.jp/ja/list/560/list -1.html
11) Smith, J.T., Voitsekhovitch, O. V., Konoplev, A. V., Kudelsky, A. V. 2005. Radioactivity inaquatic systems, in: Smith, J.T., Beresford, N.A. (Eds.), Chernobyl - Catastrophe andConsequences. Praxis Publishing, 139–190.
12) Feng, B., Onda, Y., Wakiyama, Y., Taniguchi, K., Hashimoto, A. and Yupan Zhang, 2022.
Persistent impact of Fukushima decontamination on soil erosion and suspended sediment. Nat
Sustain (2022). 1-11.
13) Ryohei Ikehara, Mizuki Suetake, Tatsuki Komiya, Genki Furuki, Asumi Ochiai, Shinya
Yamasaki,William R. Bower, Gareth T. W. Law, Toshihiko Ohnuki, Bernd Grambow, Rodney

C. Ewing, and Satoshi Utsunomiya. 2018. Novel Method of Quantifying Radioactive Cesium Rich Microparticles (CsMPs) in the Environment from the Fukushima Daiichi Nuclear Power
Plant, Environ. Sci. Technol. 2018, 52, 6390−6398.
14) Taiga Okumura, Noriko Yamaguchi, and Toshihiro Kogure. 2019. Finding Radiocesium bearing Microparticles More Minute than Previously Reported, Emitted by the Fukushima
Nuclear Accident, Chemistry Letters,

2019, 48, 1336–1338.

15) Japan Meteorological Agency: Meteorological data (in Japanese)
http://www.jma.go.jp/jma/menu/menureport.html. (Retrieved on 29th of July, 2022).

26

2. FIP2： Survey of Radionuclide Movements in Wildlife
2.1. Abstract
Fukushima Prefecture is conducting surveys and s tudies on the migrations of radionuclides towild animals that constitute a part of the ecosystem to understand the movements of radionuclides
in the ecosystem.
The present survey has measured the activity concentration of radio caesium contained in thebodies of wild animals, and investigated its fluctuation over time and differences among species.
As the activity concentration is deeply related to wild animals ’ behaviour. For example, there is apossibility that wild animals with high radi o caesium activity concentrations in their body havebeen moving into areas where wild animals with relatively low radio caesium activity
concentration s inhabit. Therefore, the movements and dispersion of animal populations were
investigated.
2.2. Purpose
The accident at the Fukushima Daiichi Nuclear Power Plant caused a widespread environmental
contamination by radioactive materials. Radionuclides have been detected in many wild animals
inhabiting the natural environment there because they ingested radioactive ma terials from theenvironment through food and water.
In order to ensure the safety and security of environment that citizens of Fukushima prefecture
live, the Prefectural government, since immediately after the accident in 2011, has beenmonitoring radionuclide activity concentrations in the muscles of game animals whose meat is
generally consumed by people. As a result of monitoring, mainly caesium -134 and 137, which are
gamma-ray emitting nuclides, have been detected from the muscles of wild animals. How ever, it
hasn’t been studied enough how the radio caesium has been accumulated from the environment
into their flesh. So in order to lift the distribution and consumption restrictions of the meat, andto ensure the local people’s safety and security, surve ys and studies on radio caesium movementsin the ecosystem have been launched.
The migration of caesium-137 from the environment to the wild animals seems to be strongly
affected by their ecology such as food habits and behavioral patterns. From 2013 to 2 017, radio
caesium activity concentrations in the bodies of wild animals were measured and their fluctuations
with time and differences by animal species were investigated. In addition, wild animals ’ food
habits and behavioral patterns deemed to be closely related to radionuclide movements into theirbodies were also investigated. There is a positive relationship between the caesium-137 activity
concentrations in the muscle and the stomach contents 1 ) .
The relationship between radio caesium and the existing form fraction 2 ) was clarified by thesurvey from 2013 to 2017. Presently, a food habit survey by the deoxyribonucleic acid (DNA)analysis of stomach contents has started, and radio caesium accumulation in the bodies of wild
animals according to their food habits has been investigated in detail. A behavioral survey
regarding the home ranges of wild boars and Asian black bears using global positioning system
27

(GPS) collars has been also carried out, however, the amount of surveying has been i nadequate to
draw any firm conclusions. To show their behavioral characteristics, the behavioral survey using
GPS collars was carried out concurrently with the food habit survey.
In addition, using the survey results starting from 2018, analyses using line ar models were
performed to clarify the long -term fluctuations of caesium-137 activity concentrations in themuscles of wild animals which took account of the seasonal fluctuations in the diet.
DNA analyses were carried out in order to show the structure of wild animal populations, whichof the populations are increasing and which are moving into other areas as a result of the long term abandonment of humans in the evacuation zones (zones where the evacuees still cannot
return) and in the residence -restricted zones.
2.3. Investigation results made from 2013 to 2017
2.3.1. Content of implementation
We selected wild boars which inhabit wide areas of the prefecture as the main subjects of thisresearch, because even studies assessing the impact of the Chernob yl disaster did not show any
clear tendency of decrease in the time -series changes of radio caesium taken into animals.
2.3.1.1. Radionuclide dynamics in wild animals
2.3.1.1.1. Measurement of gamma -ray emitting radionuclide activity concentrations
in wild animals
We measured gamma-ray emitting nuclides (wet weight) contained in the muscles of gamespecies (wild boars, Asian black bear, copper pheasant, green pheasant, spot -billed duck, andmallard) captured by nuisance kill or by hunting. Figure 1 show s the measuring procedure. By
using the measurement results, we investigated the variation of caesium -137 contained in themuscles of wild boars and other animals between individuals, and the tendency of fluctuation withthe passage of time after the accid ent. We also measured gamma -ray emitting radionuclide activity
concentrations in stomach contents and of various organs in the same way to check radionuclide
distributions in wild boars.
We checked the caesium-137 soil ground deposition at the capture points of target wild animals
from their capture information, and analyzed relationships between caesium -137 soil grounddeposition and caesium-137 activity concentration in muscle. As to the soil ground deposition, weused the results of UAV surveys carried out by the Japan Atomic Energy Agency.

Mea sureme nt o f rad ionuc lid e a ct ivity conce ntr at ion

Example of sample (Muscle)

Cell U-8(Germa niu m sem ico nduct or detect or)

Figure 1. Measurement of radionuclides in wild animals

28

2.3.1.1.2. Radionuclide migration from the environment into wild animals
To investigate the effect of diet on caesium -137 activity concentrations in the muscles of wild
animals, we measured caesium-137 activity concentrations in the stomach contents of wild boars
captured in Nihonmatsu Cityfrom fiscal 2013 to 2015. Then, we investigated relationships between
caesium-137 activity concentrations in stomach contents and in the muscles of the same
individuals.
2.3.1.1.3. Physicochemical fractions of radiocaesium in stomach contents
There are three physicochemical fractions of radiocaesium in soil (Figure 2). In the case of plants,
they mainly absorb radiocaesium of exchangeable fractions. However, for plants, radiocaesium ofstrongly bound fraction, for example strongly bound clay ores is difficult to absorb. In the case ofwild boar, it is thought that they take in soil when eating foods or gaining minerals intentionally.
Because of soil intake and the influence of physicochemic al fractions of radiocaesium in soil,
there is also possibility that caesium -137 activity concentration in the muscles of boars is higher
than those in other wildlife. However, it remains unknown about the amounts of absorption andmigration of caesium-137 from soil and foods eaten by boar into their bodies.

Soil
Figure 2. Physicochemical fractions of radiocaesium in soil
Exchangeable fraction: Comparatively, easily to elute.
Organic matter bound fraction: Coupled with organic matter.
Strongly bound fraction: Exist in soil particle.
In this study, we focus on about activity concentrations and ratios of physicochemical fractionsofcaesium-137

instomachcontents,

andresearch

about

the

relationships

betweenphysicochemical fractions of caesium -137 in stomach contents and migration into their body.
The physicochemical fractions of radio caesium is related to the absorption of the radio caesium
from soil to plants. In collaboration with the Institute of Environmental Radioactivity at
Fukushima University, we are verifying the possibility that the physicochemical fractions of radio
caesium in stomach contents affects radio caesium migration into wild boars.
2.3.1.2. Investigating the home ranges of wild animals
We attached GPS data loggers (hereinafter, GPS collars) (Figure 3) to wild boars and investigatedtheir behaviors. We set the GPS fix schedule of GPS collars as 1 GPS fix / 15 minutes, and recorded
wild boar behaviors for more than one month. We investigat ed wild boar behaviors inside andoutside the evacuation order zone (Figure 4).

29

Figure 3. GPS collar.

Figure 4. Attaching a GPS collar to an anethesizedwild boar captured with the cooperation of aharmful bird and animal capture team.

2.3.2. Results
2.3.2.1. Dynamics of radionuclides in wild animals
2.3.2.1.1.

Resultsofmeasuring

gamma -rayemitting

radionuclide

activity

concentrations in wild animals
Figure 5 shows the caesium-137 activity concentration in the muscles of wild boars captured
throughout Fukushima Prefecture from May 2011 until March 2017.

Figure 5. Results of monitoring caesium -137 activity concentration in wildboar muscles.
The X-axis indicates wild boar capture timing, and the Y -axis indicateslogarithmically transformed caesium-137 activity concentration. The black
dots indicate the measured values for individuals. The bar graph shows thegeometric mean value of caesium -137 activity concentration in each year.
Each box indicates the reliability section from 75% at the top and 25% at
the bottom. The bars indicate the maximum and minimum values (May 2011 toMarch 2017).
From figure 5, any clear tendency was not shown because the varia tion in activity concentrations
between individuals was great.
30

Figure 6. Temporal trends of caesium-137 in the muscle of boars(Regensburg, Southern Germany) 1 ) .
For comparison with wild boars captured in Fukushima Prefecture, we investigated the annualchanges of radio caesium activity concentrations in wild boars captured in Europe after the
Chernobyl disaster. Figure 6 shows the case of Regensburg in South Germany 1 ) . Also in the caseof Regensburg, caesium-137 activity concentration varied greatly between individuals and did notshow any clear tendency of decrease. Since wild boars in Fukush ima Prefecture also showed asimilar tendency, we should continue to monitor the contamination trends in wild boars captured
in Fukushima Prefecture.
Figure 7 shows caesium-137 activity concentrations in the muscles of Asian black bears that
inhabit the forest ecosystem like wild boars. In Asian black bears, caesium -137 activity
concentrations decreased with the passage of years confirmed by a statistical analysis of the data.
This indicates that the annual change of caesium -137 activity concentration in mu scles differs
depending on the animal species.

31Cs-137 activity concentration [Bq/kg wet weight]

FY: p<0.0001

Figure 7. Results of monitorin g caesium-137 activity concentration in Asian
black bear muscles.
The X-axis indicates Asian black bear capture timing, and the Y -axis
indicates logarithmically transformed caesium -137 activity concentration.
The black dots indicate the measured values for individuals. The bar graphshows the geometric mean value of caesium -137 activity concentration ineach year. Each box indicates the reliability section from 75% at the top
and 25% at the bottom. The bars indicate the maximum and minimum values(May 2011 to March 2017).
Figure 8 shows relationships between caesium -137 soil ground deposition at the wild boar andAsian black bear capture points, and caesium-137 activity concentrations in muscles. Both wildboars and Asian black bears showed positive relationships between caesium -137 soil grounddeposition at the capture points and caesium -137 activity concentrations in muscles. Wild boars
and Asian black bears captured at points of greater caesium -137 in-soil deposition amounts showed
higher caesium-137 activity concentrations in muscles. From the regression line in the figure, wildboars showed higher activity concentrations in muscles than Asian black bears captured at points
with the same soil ground deposition.

32

Figure 8. Relationships between caesium -137 activity
concentrations in Asian black bear and wild boar muscles,
and the amount of caesium-137 deposition to soil at thecapture points.
Figure 9 shows wild boar and Asian black bear monitoring results by coloring depending on thearea of capture. Individuals with high caesium -137 activity concentrations in muscles were
frequently captured in the Hamadori region where the caesium -137 soil ground deposition iscomparatively high. Individuals with low caesium -137 activity concentrations in muscles were
frequently captured in the Aizu region where the caesium -137 soil ground deposition iscomparatively low.
It has also been confirmed with birds that caesium-137 activity concentration in muscles of birds
differs between species.

33

Cs-137 activity concentration [Bq/kg wet weight]
Cs-137 activity concentration [Bq/kg wet weight]

Figure 9. Monitoring results of caesium-137 activity concentration in themuscles of wild boars and Asian black bear (by the captured area).
The X-axis indicate the capture timing of wild boar and black bear and the
Y-axisindicates
logarithmicallytransformed
caesium -137
activity
concentration. The dots indicate the measured value for individuals that
captured Hamadori (red dot), Nakadori (yel low dot), and Aizu (green dot).
(May 2011 to March 2017)
Figure 10 shows caesium-137 activity concentrations in the muscles of copper pheasant, green
pheasant, spot-billed duck, and mallard captured in the period from October 2011 until February
2017. When including N.D. values, the caesium -137 activity concentration in the copper
pheasant muscles was higher than in the other species. The copper pheasant is not a migratory
bird and inhabits a forest ecosystem. 2 )34

Cs-137 activity concentration in muscles[log10 Bq/kg, wet weight]

Copper pheasantGreen pheasant

Spot-billedduck Mallard

Figure 10. Monitoring results of caesiu m-137 activity concentrations in themuscle for copper pheasants, green pheasants, spot -billed ducks and mallards(data period: October 2011 - November 2017)
The activity concentration of caesium-137 in an individual that was below thedetection limit was set at 4 Bq/kg (wet weight) 2 ) .
Figure 11 shows the temporal change of caesium -137 activity concentration in muscle of copper
pheasant and green pheasant. Caesium-137 activity concentration in muscle decreased graduallyin the green pheasant, but no clear trend was observed in the copper pheasant where a large
variation between individual birds was observed, similarly to the situation seen for wild boars.
The reason for the difference between bird species is probably because of difference of food
habitat and/or the condition of the accumulation of radionuclides in their environmental habitat;
copper pheasant mainly inhabits forests, while green pheasant mainly i nhabits the Satoyama
ecosystem. 2 )35

［ Bq/kg, wet weight］

Cs-137 activity concentration in m uscles

Copper pheasantGreen PheasantReferenc e Va lu es for Radi oact ive Cs in Gen era l Food s(Combined va lu e of C s -134 an d Cs-137)

Number of days since disaster ［ Base date； March 11, 2011 ］

Figure 11. Monitoring results of caesium -137 activity concentration in the muscle
of copper pheasants and green pheasants (October 2011 - November 2017)
The activity concentration of caesium -137 in individuals that was below thedetection limit is set as 4 Bq/kg (wet weight) 2 )2.3.2.1.2. Radionuclide migration from the environment into wild animals
Figure 12 shows relationships between caesium-137 activity concentrations in the muscles andstomach contents of the same wild boars. The caesium -137 activity concentrations in the muscles
and stomach contents showed positive relationships. These relationships indicate the strong effectof intake of caesium-137 such as food items and soil on caesium -137 activity concentrations inwild boars.

Figure 12. Relationship between caesium -137 activity concentration inmuscle and in stomach contents of wild boar.
According to research on the impact of the Chernobyl disaster, caesium -137 activity
36concentrations in the muscles of wild animals vary with the seasons because of such biologicalfactors as food habits and habitat use. Thus, we analyzed relationships betwe en caesium-137
activity concentrations in the muscles of wild boars and Asian black bears, and the months inwhich the animals were captured. Figure 13 shows the results.
Both species of wild boar and Asian black bear showed seasonal variation of caesium -137 activity
concentration in muscles.

Figure 13. Seasonal variation of caesium -137 activity concentration inwild boar and Asian black bear muscles.
However, the variation pattern differs between the species. Caesium-137 activity concentrationsin the muscles of wild boars were low in May to August, and high in November to March. Caesium137 activity concentrations in the muscles of Asian black bears decreased from May to September,then increased until January.
2.3.2.1.3.

Physicochemical

fractions

of

radio

caesium

contained

instomachcontents
Figure 14 shows correlations between caesium -137 activity concentrations in muscles of wildboars captured in the prefecture in 2015, and caesium -137 activity concentrations of each fraction
in stomach contents. Caesium-137 activity concentrations in muscl es showed significant
correlations with activity concentrations in exchangeable fractions, and activity concentrations
summed of exchangeable fractions and organic matter -bound fractions in the stomach contents.
However, caesium-137 activity concentrations in muscles did not show significant correlations
with activity concentrations of strongly bound fractions. Therefore, there is a possibility thatexchangeable fractions and organic matter -bound fractions contained in (partially) ingested food
item and soil are strongly related to caesium-137 migration into the bodies of wild boars. 3 , 4 )37

Figure 14. Correlation of the physicochemical fractions of caesium -137 activity
concentrations between muscle tissue and stomach contents of wild boars
2.3.2.2. Investigating the home ranges of wild animals
We tracked boar behaviors by using a GPS collar, and could define the spat ial range covered by
the boar (home range) from 2013 to 2016 as shown in Figure 15. The home range was separated
into a core area of a high activity concentration of measurement points (area containing almost
95% of points by activity concentration analysis) i.e. where the boar spent most of their time, anda larger roaming area containing all points (outermost area). The results of the analysis showedthat the boars have two residential zones, the core area is approximately 37 ha, and the total areaof their home range is 244 ha.

38

Figure 15. Example of sample structure of home range area.
We carried out wild boar home range surveys in Fukushima City (2 boars tracked for 50 and 99days) and Tazawa, Iwashiro -chiku, Nihonmatsu City (4 boars, tracked for 9 to 110 days) outside
the evacuation order zone. Figure 16 shows the survey results on the same scale (one -kilometer
mesh in the figure). Fukushima City has urban and suburban environments, while Tazawa,
Iwashiro-chiku, Nihonmatsu City is located between plains and mountains. The wild boars
surveyed on this occasion had a core area of about 20 to 50 ha and home ranges of about 100 to
250 ha.

Figure 16. Size of wild boar home range outside the evacuation order zone.
We investigated wild boar home ranges in Tomioka -town, inside the evacuation order zone, tosee how the ranges would change in the situation where there were fewer human activ ities. Figure
17 shows the core area and home range areas of 7 individuals tracked inside and outside theevacuation order zone. No. 50, 85, and 208 are in the evacuation order zone. No. 52 and 58 are in
an environment around cities outside the evacuation order zone. No. 66 and 67 are in mountainous
areas outside the evacuation order zone.
In the current survey, the number of animals that have been tracked is small and the sex, weightand duration of GPS collar attachment differ between individuals (Table 1). However, from theavailable data, the increase of human presence appears to be reducing the home ranges of wild
boar.

39

Figure 17. Comparison of home range and core area.
Table 1. Sexes, weights, and numbers of days with GPS collar

ID

No.50

No.85

No.208

No.52

No.58

No.66

No.67

Sex

M

F

F

M

M

F

F

Weight (kg)

37

48

51

44

70

35

37

81

99

117

99

50

110

34

Numbers ofdays withGPS collar
Wild boar home ranges may change depending on the timing of survey. Therefore, we compared
the home range sizes of eight individuals (the inside of the evacuation order zone: three females
and two males, the outside of the evacuation order zone: one male and two fem ales) whose data
could be acquired for one month or longer in November to December (winter), and January to
February (the breeding season) in 2013 and 2014. Although the number of samples was small, thehome ranges tended to be larger inside the evacuation order zone than outside (Figure 18).

Figure 18. Average of home range size of wild boars inside and outside theevacuation zone. The error bars indicate the minimum and maximum values.
We investigated habitat type in the home ranges of individuals. In home ranges of individuals
inside the evacuation order zone, farmland occupied a high percentage of the area and the results
suggest that the home ranges of individuals inside the evacuation order zone includes roaming on
farmland (Figure 19).
40

Figure 19. Ratio of land use in the home ranges of wild boars insideand outside the evacuation order zone (each bar indicates the value
for an individual). Study areas showed the city where the wild boars
were captured (Outside the evacuation order zone: Fukus hima city and
Nihonmatsu city, inside the evacuation order zone: Tomioka town).
2.4. Investigation results made from 2018 to 2022
Just as in the 2013 to 2017 period, the present survey has mainly targeted wild boars, whoseradio caesium activity concentrations have been higher than those of other wild animals, and Asian
black bears inhabiting the same forestry ecosystem as wild boars.
2.4.1. Content of implementation
2.4.1.1. Fluctuation of radiocaesium activity concentrations in wild a nimal’ s
flesh
Regarding radionuclide activity concentration s in the muscles of wild animals inhabiting theprefecture, the Nature Conservation Division is monitoring game species such as wild boars, Asian
black bears, copper pheasants, Japanese pheasants, spot-billed ducks and mallards captured forthe culling by management program or for hunting, thereby identifying the caesium-134 and 137
activity concentrations in their muscles. Using the measurement results, the variations of caesium137 in the muscles of wild boars and other animals and the fluctuations over time after the accident
were also investigated.
The survey conducted from 2013 to 2017 clarified seasonal fluctuations in caesium-137 activity
concentration in the muscles of wild animals (see 2.3.2.1.2. Figure 13) 5 ) . Based on the seasonal
fluctuation patterns, the data were divided into the low -activity concentration period of April toAugust and the high -activity concentration period of December to March for wild boars and the41

low-activity concentration period of July to September and the high -activity concentration periodof November to January for Asian black bears. The long -term fluctuations of caesium-137 activity
concentrations in the muscle after the accident was analyzed with a linear model that used thelog 1 0 conversion of the caesium-137 activity concentrations in their muscles as objective variable
and the dates when they were captured and the log 1 0 conversion of caesium-137 deposition density
on soils at the locations where they were captured as explanatory variables. The linear model wasapplied in each of the low-activity concentration periods, high -activity concentration periods andthe entire period.
2.4.1.1.1. Relationship with the animals’ feeding habit
Previous studies (see Section 2.3.2.1.2. ) showed a positive relationship between caesium-137
activity concentrations in boar muscle tissue and stomach contents, suggesting that caesium-137
activity concentrations in boar bodies are strongly influenced by ingestion of c aesium-137 in foodand soil (Figure 12). Therefore, with the aim of investigating factors that cause the extremely
wide variations in measured values among individual wild boars and the factors that cause seasonal
fluctuations and migration of high caesium -137 activity concentrations, we attempted toinvestigate the relationship between wild boar feeding habits and caesium -137 activity
concentrations in their muscle tissues. This was carried out by (i) analyzing feeding habits basedon metabarcoding methods (DNA analysis) and (ii) measuring caesium -137 activity concentrationsin their main foods. DNA extracted from thoroughly agitated and crushed wild boar stomach
contents was used to analyze wild boar feeding habits and the nuclear DNA ITS -2 region was
analyzed to estimate herbivorous feeding habits 6 ) .
In addition to food, wild boars are thought to ingest a large amount of soil from digging up andeating roots and stems that grow underground, but the transfer of caesium -137 into the bodies ofwild boars through soil ingestion and its levels were unknown. Therefore, we considered a survey
methodology to investigate the transfer of caesium -137 by soil ingestion.
Samples of main food species were collected in Nihonmatsu City and in the Adatara and Azuma
Mountain ranges from 2016 to 2019. Samples of herbaceous plants (e.g., white clover, tsukushi hagi, etc.), nuts (e.g., konara oak, Japanese oak, chestnuts, etc.), and Berry fruits (e.g., Padus
grayana, etc.) were collected and measured for caesium -137.
2.4.1.1.2. Relationship with the animals’ habitat
It has been reported that caesium-137 activity concentrations in the muscle tissues of wild
animals are positively correlated with caesium-137 activity concentrations in food, and that these
activity concentrations are positively correlated with caesium-137 soil deposition in theenvironment 7 ) . One possible reason for the seasonal variation in muscle caesium-137 activity
concentrations could be seasonal use of locations for foraging with varying levels of caesium-137
contamination. In this study, therefore, we used behavioral data of Asian black bears wearing GPS
collars in Fukushima Prefecture to examine the relationship between seasonal cha nges in habitat
use and levels of caesium-137 contamination in these locations.
42

To assess the exposure dose rates of Asian black bears and wild boars in the study site, theactivity concentration of caesium-137 in muscle (Bq/kg in wet weight) of Asian blac k bears andwild boars in the aforementioned Radiation Monitoring Survey for Wild Birds and Animals
conducted by Fukushima Prefecture and caesium-137 soil deposition (Bq/m 2 ) at the capture
location of each sample animal 8 ) were used to estimate the exposure dose rate (µGy/h) by ERICA
tool 9 ) .
2.4.1.2. Management of wild animals in the area contaminated by radionuclides
2.4.1.2.1. Monitoring
Caesium-134 and caesium-137 activity concentrations were measured in the muscle of pheasantscaptured throughout Fukushima Prefecture between October 2011 and March 2022.
2.4.1.2.2. Investigations of wild animals around the Evacuation -Designated Zone
(EDZ)
We surveyed the population structure of wild boars in Fukusuhima prefecture using by
multiplexed ISSR Genotyping by sequencing (MIG -seq) analysis. DNA extracted from the muscle
tissue of wild boars captured widely in Fukushima prefecture and those captured in part areas in
Kumamoto Prefecture that were treated as an ou t-group population. Single -nucleotide
polymorphisms (SNPs) were obtained from genome -wide regions by MIG -seq method 1 0 ) for
clarifying genetic structures of wild boars. We conducted STRUCTURE 11 ) and cluster analysis
using the derived SNPs information. This survey was conducted in collaboration with the
Fukushima Prefectural Center for Environment Creation and the National Institute forEnvironmental Studies.
2.4.1.2.3. Strategy to lift restrictions for distribution and consumption
History of consumption and distribution restrictions since the incident①

History of restrictions on consumption and distribution due to the nuclear incident
In response to the spread of radioactive materials from the nuclear power plant incident

following the Great East Japan Earth quake on March 11, 2011, the government establishedon April 4, 2011 provisional regulation values for radioactive materials based on the Food
Sanitation Act, and compiled the "Concepts of Inspection Planning and the Establishment andCancellation of Items and Areas to which Restriction of Distribution and/or Consumption ofFoods Concerned Applies." (hereinafter referred to as “guidelines”)
Subsequently, on April 1, 2012, the national government set the standard value forradioactive caesium in general foods at 100 becquerels/kg based on the results of previous
inspections and other factors.
In this prefecture, a private research institute conducted a private survey on activity
concentrations of radionuclides in muscle tissue in conjunction w ith the survey commissionedby the Ministry of the Environment. Since the results of the private survey were provided tothe prefecture, they were made public. Since some samples from meat were found to exceed
43

the provisional regulation value of 500 becque rels per kilogram for radioactive materials, wereached out to prefectural residents through hunting groups and municipalities to refrain fromprivate consumption.
Since October of the same year, the prefecture has announced and conducted surveys tomeasure activity concentrations of radionuclides in the meat of edible wild game in theprefecture, including wild boars, black bears, Japanese deer, pheasants, copper pheasants,
and mallard ducks in seven areas of the prefecture to ensure the safety and securi ty of theliving environment.
As a result of this investigation, radioactive caesium exceeding 5,000 Bq/kg was found inwild boars in Soma City in November of the same year. Based on this, the national government(Nuclear Emergency Response Headquarters) i ssued a temporary order to refrain fromconsumption and distribution of wild boar meat originating in the Soso district, in accordancewith Article 20, paragraph 3 of the Act on Special Measures concerning Nuclear Emergency
Preparedness.
Subsequently, samples exceeding the standard values were detected in other areas of theprefecture, so distribution restrictions were placed on wild game including wild boars in all
prefectures in July 2013. In the Kenpoku and Soso districts, the consumption restrictions st ill
continue.
Changes in populations of wild game (wild boars) caught in Fukushima Prefecture②

Changes in numbers of wild boars caught in the prefecture since 2010 are shown in Figure
20.

Numbers of captured wild boar
35,69829,727 30,738
26,13020,603

11,087
3,736 3,021

2010

15,467

5,824

2011

Figure 20.

③

13,094

2012

2013

2014

2015

2016

2017

2018

2019

2020

Numbers of captured wild boar (2010 FY～ )Changes in the amount of damage caused by wild boar in Fukushima Prefecture
Changes in the amount of agricultural damage caused by wild boar in the prefecture since

FY 2010 expressed in terms of monetary costs, are shown below in Figure 21.

44

Damage cost caused by wild boar
(tens of thousand JPY)
12,00010,000
8,000
6,000
4,000
2,000
0
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Figure 21.

Damage cost caused by wild boar (2010FY ～ )Management framework of radioactive material after the accident①

Issues arising from consumption and distribution restrictions
Due to national consumption and distribution restrictions, the meat of wild birds andbeasts captured in Fukushima Prefecture was no longer available, limiting their capture forprivate consumption and sale. This made it impossible to apply sufficient trapping pressure,and the wild boar population was expected to increase and their habitat to expand , which
would also cause serious damage to agricultural crops.
Therefore, Fukushima Prefecture greatly increased the number of wild boars captured toprevent an increase in the wild boar population and expansion of their habitat area, and tocontrol damage to crops.

②

The need to consider lifting the distribution restrictions for addressing challenges
Since the earthquake, in order to reduce damage caused by wild game to the living
environment and agriculture, forestry and fishery industries in the prefe cture, theprefecture has continued to implement measures such as habitat management and damage
control by installing electric fences, etc. Direct captures were done by the prefecture
workers and experts dispatched to local communities to conduct environme ntal researchaccording to local conditions.
However, where the government has imposed consumption and distribution restrictions
on meat from wild game, it is not possible to utilize them captured for Gibier, etc., andthis has led to a decline in hunters ’ motivation to hunt wild animals .

45

③Requirements for lifting distribution restrictions set by the government (partial excerpts
from the guidelines)【Lifting】
Area
In principle, the whole prefecture shall be covered. However, if some areas in
the prefecture meet the conditions for restriction lifting and can be managed by
the prefecture, municipalities, etc. so that only game caught in those areas are
distributed, easing of restrictions may be made in units that clearly define thegeographical range (i.e., municipalities).
Conditions for lifting restrictions
In areas where the restrictions will be lifted, inspections shall be conducted while
ensuring a sufficient number of samples in consideration of the mobility,
individual differences, seasonal va riations, and the period of capture of wild game,and the results shall be below the standard values.
【Partial lifting】
If a system is in place to properly control and inspect the meat of wild gameaccording to the distribution and inspection policy establ ished by the prefecture,meat testing below the standard value may be distributed.
※Excerpt from the guidelines.

④

Current prefectural initiatives against national requirement
The prefectural government conducts radiation monitoring surveys of wild game meat forthe safety and security of prefectural residents, and publishes the survey results.
The wild game covered in this survey are wild boars, black bears, pheasants, copper
pheasants, spot-billed ducks, mallard ducks, common teals, Japanese deer, and h ares.
An overview of the survey results (wild boars) to date is shown below.

46

Figure 22.

Monitoring result of caesium-134 + caesium-137 activity concentrationin the flesh of wild animal (wild boar; 2011FY ～ 2020FY)
In response to the situation, with the cooperation of the IAEA, we discussed, among otherthings, what methods should be used to meet the requirements indicated by the national
government to lift consumption and distribution restrictions for wild game meat.
As the requirements for lifting restrictions are indicated in the guidelines, “ensuring asufficient number of samples ” is required. However, there is no specific number of samples
nor relationship between the location where the samples were captured and the area where
the restrictions will be lifted.
2.4.2. Results
2.4.2.1. Fluctuation and its reasons of radionuclides’ activity concentration inwild animal’ s flesh
Figure 23 shows the caesium-134+137 activity concentrations in the muscles of wild boars andAsian black bears captured in Fukushima Prefecture in May 2011 to March 2022.

47

a)

b)

Figure23.

Resultsofmeasuringthecaesium-134+137

activity

concentrations in the muscles of (a) wild boars and (b) Asian blackbears* The 1st quartile (25%) and the 3rd quartile (75%) are indicated by
the upper and lower ends of each box respectively, and maximum andminimum values are indicated by bars (those less than lower detection
limit excluded).
The caesium-134+137 activity concentrations in the muscles of wild boars showed larg e variation
among individuals. Some of them showed activity concentrations lower than the detection limit
48

although others shown higher activity concentration s than 10 times of the standard value ofactivity concentration. Asian black bears showed caesium-134+137 activity concentrations
exceeding 100 Bq/kg *1 , which is the limit for general foodstuffs in Japan, were also found in FY
2021 ( *1 Sum of caesium-134 and -137).
Figure 24 shows the color-coded results of monitoring caesium-137 activity concentrations in
the muscles of wild boars and Asian black bears in the regions of Fukushima prefecture.
a)b)

Figure 24. Caesium-137 activity concentrations in the muscles of (a)wild boars and (b) Asian black bears (in regions where they were
captured)* Each dot indicates the measured value for each wild animal.
49

The survey conducted from 2013 until 2017 revealed that the caesium-137 activity concentrationsin the muscles of wild boars and Asian black bears were positively affected by the caesium-137
deposition density on the soils of locations where they were c aptured (see 2.3.2.1.1. Fig.8) 7 ) . In
the Soso District, Ken -poku District and Ken -chu District, where the caesium-137 deposition
density on soils was relatively high, many wild boars and Asian black bears with high caesium137 activity concentration s were captured. In the Aizu District and Minami -Aizu District, where
the caesium-137 deposition density on soils was relatively low, many wild boars and Asian blackbears with low caesium-137 activity concentrations were captured.

Long-term variations in radio caesium activity concentrations in Asian black bear and wild boar
muscle tissues
To understand long-term variations in the activity concentration of radionuclides in Asian black
bear and wild boar muscle tissues, we analyzed the long -term variations of caesium-137 activity
concentrations in the muscle of both species. Data collected fr om May 2011 to March 2016 fromthe Radiation Monitoring Survey for Wild Birds and Animals conducted by Fukushima Prefecture
were used. Since seasonal variations were already known for A sian black bears and wild boars 5 ) ,based on that report, both data were used with divisions between low activity concentration
periods (Asian black bear: July -September, wild boar: April -August) and high activity
concentration periods (Asian black bear: November-January, wild boar: December-March). Using
data from the low-activity concentration periods, the high-activity concentration periods, and all
periods combined, a linear model was estimated with log10-transformed caesium-137 activity
concentrations in muscle tissues (Bq/kg wet weight) as the objective variable and the c apture dateof each individual and log10 -transformed caesium-137 soil deposition (Bq/m 2 ) 8 ) as explanatory
variables. The estimated linear model was selected by Akaike ’s information criterion (AIC).
As a result, a model that included capture dates and log10 -transformed caesium-137 soil
depositions as explanatory variables was selected for Asian black bears in the low -activity
concentration period, the high -activity concentration period, and all periods combined (Table 2).
The long-term variation showed a decreasing trend in each period, while the 95 % confidence
interval of the estimated value tended to increase with time in the high activity concentration
period (Figure 25). This is attributed to a limited amount of data.

50

Table 2. Model of long-term variation of caesium-137 activity concentration inmuscle of Asian black bears
PeriodAIC

Delta AICIntercept

Explanatory variables
Capture date

log10 (Cs-137
soildeposition)

Entire period

151.6

0.00*

7.729

(n=271)

168.6

16.92

-1.057319.7

168.0313.930337.6

186.001.768

Low activity

57.2

0.00*

6.819

concentration

68.8

11.59

-1.497

period222.7

165.47

12.520(n=191)230.5

173.251.706High activity

20.9

0.00*

-0.4854

concentration

22.8

1.90*

1.2520-4.036*10 - 5-2.486*10 - 4

period

35.5

14.52

12.3400(n=28)

36.0

15.07

2.0570*: Valid model（ Delta AIC<2.0）51-0.0002

0.61890.6394-0.0002-0.00020.71110.7226-0.00020.57850.5631

Figure 25. Long-term variation of caesium-137 activity concentration in muscle of
Asian black bears
52

For wild boars, a model which included capture date and log10 -transformed caesium-137 soil
deposition as explanatory variables for the low -activity concentration period, the high -activity
concentration period, and the entire period was also selected (Table 3). In each period, adecreasing trend was observed over time, but the d egree of the decrease was small. This trend was
similar to that observed in wild boars in Europe 1 2 ) .
Table 3. Model of long-term variation of caesium-137 activity concentration inmuscle of wild boars
PeriodAIC

Delta AICIntercept

Explanatory variables
Capture date

log10 (Cs137soil
deposition)

Entire period

1514.0

0.00*

7.656

(n=1031)1578.937.87-1.2001865.6324.6210.9601890.5349.53

2.444

Low activity

338.6

0.00*

14.140concentration

367.6

28.98

-1.425

period438.9

100.3017.660(n=285)458.7

120.102.168

High activity

720.9

0.00*

2.738

concentration

722.1

1.12*

-1.033

period838.1

117.186.631(n=456)838.9

117.92

2.612*: Valid model（ Delta AIC<2.0）53-0.00020.74090.7377-0.0002-0.0004

0.73530.7342-0.0004-9.061*10 - 5

0.73080.7320-9.671*10 - 5

Figure 26. Long-term variation of caesium-137 activity concentration in muscle ofwild boars
54

Differences in radio caesium activity concentration s in muscle tissues of Asian black bears andwild boars based on sex
To clarify the differences in the degree of radionuclide transfers from the environment to thebodies of Asian black bears and wild boars (depending on sex), we conducted analyses using
monitoring data from the Radiation Monitoring Survey for Wild Birds and Animals by Fukushima
Prefecture, in the same as 1) Long -term variation of radio caesium activity concentration in muscle
tissues of Asian black bears and wild boars (hereinafter referred to as 1). Data used were divided
into low and high activity concentration periods as in 1). In the low and high activity concentration
periods, a linear mixed model was estimated with log10 -transformed caesium-137 activity
concentration s in muscle tissues (Bq/kg wet weight) as the objective variable, log10 -transformed
caesium-137 soil deposition (Bq/m 2 ) 8 ) at the capture location of each sample animal as the
explanatory variable, sex as the interaction term for the explanatory variable, and the capture yearof each animal as a random effect, to examine the effect of sex on the relationship betwee n
caesium-137 activity concentrations in muscle tissues and caesium-137 activity concentration s at
capture locations. Subsequently the model selection was performed by AIC.
As result, for both Asian black bears and wild boars, only log10 -transformed caesium-137 soil
deposition (Bq/m 2 ) was included as an explanatory var iable in the models selected for each period,
but not sex (Tables 4 and 5). This result indicates that there is no difference between sexes in theextent of radionuclide transfer from the environment to the body for both species (Figures 27 and
28). Sexual dimorphism (i.e., body size) has been reported to be an important variable inecological factors in wild animals 1 3 , 1 4 ) . It is known that there are regional differences of Asian
black bears and wild boars regarding sexual dimorphism in home range size, ha bitat selection, andbehavioral patterns 1 5 - 1 8 ) . In this study, it is possible that there are no differences in sexual
dimorphism and associated ecological factors in Asian black bears and wild boars in the region
compared to other regions. Future studies of ecological factors such as behavior and sexual
dimorphism, such as in body size, may shed light on these factors.

55

Table 4. Linear mixed model estimating the effect of sex on the relationship of
caesium-137 activity concentration between in muscle and a t the capture locationof Asian black bears
PeriodAIC

Delta AICIntercept

Explanatory variables

Low activity

69.1

0.0*

-1.3720.7076*log10 (Cs-137soil
deposition)

concentration
period78.5

9.4-1.370(n=191)log10 (Cs-137soil deposition) *Sex
Female: 0.7064
Male: 0.7076

High activity

229.3

160.2

-1.80429.1

0.0*-0.485

deposition)

concentration
period

0.5785*log10 (Cs-137soil

34.5

5.4

-0.275(n=28)

log10 (Cs-137 soil deposition) *Sex
Female: 0.5535
Male: 0.5146

41.2

12.1

2.057

*: Valid model（ Delta AIC<2.0）56

Table 5. Linear mixed model estimating the effect of sex on the relationship of
caesium-137 activity concentration between in muscle and at the capture locationof wild boars
PeriodAIC

Delta AICIntercept

Explanatory variables

Low activity

350.2

0.0*

-1.3000.7192*log10 (Cs-137soil
deposition)

concentration
period356.9

6.7-1.344(n=285)log10 (Cs-137soil deposition) *Sex
Female: 0.7178
Male: 0.7349

High activity

442.4

92.2

2.211

650.7

0.0*

-0.776

deposition)

concentration
period

0.5785*log10 (Cs-137soil

659.0

8.3

-0.794(n=456)log10 (Cs-137soil deposition) *Sex
Female: 0.5535
Male: 0.5146

762.6

111.9

2.561

*: Valid model（ Delta AIC<2.0）

High activity concentration period

Low activity concentration period

MaleFema leMale
Fema leFigure 27. Relationship of caesium-137 activity concentration between in muscle
and at the capture location by each sex of Asian black bears

57

Low activity concentration periodHigh activity concentration period

MaleFema leMale
Fema leFigure 28. Relationship of caesium-137 activity concentration between in muscle
and at the capture location by each sex of wild boars
2.4.2.1.1. Relationship with the animals’ feeding habit
In the results of feeding habits analysis for wild boars captured in Nihonmatsu City in FY 2017,
many individuals that fed on nuts (e.g., Japanese oaks and chestnuts) were found during theactivity concentration increasing period (September to November) and the high activity
concentration

period (December to March). The results of caesium-137 activity concentrations

in food are shown in Figure 29. Nuts tended to have highe r caesium-137 activity concentration sthan herbaceous and berry fruits. The relationship between the feeding habits of wild boars andthe activity concentration of caesium-137 in their muscle tissues will be investigated in the futureusing DNA analysis and other methods, with researchers taking the lead in cooperative studies.

Figure 29. Caesium-137 activity concentrations in herbaceous plants, nuts andberry fruits

58

Figure 30. Experimental methodology for leaching of radio caesium from soil in thestomach and small intestine of wild boar
In evaluating the transfer of caesium-137 by soil ingestion of wild boars, we devised a method
for soil radio caesium leaching in the stomach and small intestine of wild boars (Figure 30), basedon the "artificial digestion test method mimicking digestion in the stomach and small intestine ofpigs 1 9 ) " as shown below. Data collection by this method, using soil collected in Fukushima
Prefecture, will be conducted in the future with researchers taking the lead in the cooperative
study.
2.4.2.1.2. Relationship with the animals’ habitat
Changes in wildlife habitat use and radio caesium contamination of use locations
It has been reported that caesium-137 activity concentration s in the muscle tissues of wild
animals are positively correlated with caesium-137 activity concentrations in food, and thatcaesium-137 these activity concentration s are positively correlated with caesium-137 soil
deposition in the environment 7 ) . One possible reason for the seasonal variation in muscl e caesium137 activity concentration s could be seasonal use of locations for foraging with varying degrees
of caesium-137 contamination. In this study, therefore, we used behavioral data of Asian blackbears wearing GPS collars in Fukushima Prefecture to examine the relationship between seasonal59

changes in habitat use and degrees of caesium-137 contamination in these locations.
In 2018, bear traps were set in national forests in Otama Village (Figure 31) and three sample
animals that were captured in the forests of Koriyama City by the Koriyama Ci ty Hunting Club
were anesthetized, fitted with GPS collars and released. Date on the captured bears are shown in
Table 6. Age estimates were taken by sectioning extracted the first premolars and counting theannual growth rings at the roots in cross sectio n. The home ranges shown in Table 5 were estimatedusing the 100% Minimum Convex Polygon (hereafter referred to as 100 % MCP) (Figure 32). The
GPS collars worn were set to record one GPS location point every hour.

Nihonmatsu City

Otama Village

Lake Inawashiro

Koriyama City

Bear trap
Figure 31. Capture locations: Traps for bears were set up in the national forests
enclosed by light blue lines.

60

Table 6. Information on captured individuals which are obtained by behavioral
data from GPS collars
Individuals’

Sex

Age

Weight (kg)Data period

Home range
size (km 2 ;ID

100% MCP)
AM01

Male

9

74

2018/7/23-

74

2019/8/30
AM02

Male

10

114

2018/8/14-

104

2019/7/30
AM03

Male

4

53

2018/10/28-

269

2019/7/30

AM01

AM02

AM03

Figure 32. Home ranges of each individual estimated by 100% MCP
Using the behavioral data from these GPS collars, we first analyzed seasonal changes in caesium137 soil deposition (Bq/m 2 ) 8 ) at the use location. As use locations, the 95 % Brownian Bridge
Movement Model 2 0 ) (hereafter referred to as BBMM) and 50 % BBMM were used for each sample
animal and each month using the obtained GPS points to estimate its home range and intensive
use area. Random points were then created at a density of 100 points/km 2 in each home range andintensive use area. Caesium-137 soil deposition (Bq/m 2 ) at each random point was obtained fr om
a caesium-137 soil deposition map 8 ) . A generalized Additive Mixed Model (hereinafter referred toas GAMM) assuming gamma distribution was estimated to estimate the seasonal variation of
caesium-137 soil deposition within the home ranges and intensive use area by using the caesium61

137 soil deposition at the obtained random points as the objective variable, months in the homeranges and intensive use areas where the random points were generated as ex planatory variables,
and individual IDs as random variables. The estimate models were selected by AIC.
Next, to analyze relationships between caesium-137 soil depositions and environmental factors,
we created an outer contour of GPS points for all individu als and generated 100 random points/km 2
within the contour.
Then, environmental factors (i.e., elevation, distance from urban land, distance from farmland,
vegetation [beech (Fagus crenata) forest, Japanese oak (Quercus crispula) forest, berried fruit(e.g. Malus toringo and Cerasus sp.) forest, planted forest, conifer forest, broadleaf forest, mixed
forest, shrub forest, grassland, naked land]) and the caesium-137 soil deposition at each random
point were obtained. Linear models were estimated using caesium-137 the soil deposition at eachrandom point as the objective variable and each environmental factor as explanatory variables.
The estimated models were selected by AIC.
In addition, to clarify the seasonal variation pattern of each environmental factor at its use
location, we obtained environmental factors at random points generated in the home ranges andintensive use area as described above, and then estimated its GAMM with each environmental
factor as the objective variable, the month in which the ho me ranges and intensive use area wereused as explanatory variables, and individual IDs as random variables.
To further clarify habitat selection for each month, the Generalized Linear Mixed Model(hereafter referred to as GLMM) assuming a binomial distrib ution was estimated using
environmental factors obtained at random points generated in each of the above -mentioned homeranges and intensive use areas, with the binary variable set to 0 if each random point was in thehome ranges and 1 if it was in the int ensive use area as the objective variable, each environmental
factor as the explanatory variable, and individual IDs as random variables. The estimated models
were selected by AIC.
The results showed that caesium-137 soil deposition within the home ranges did not change
seasonally, while caesium-137 soil deposition within the intensive use area did. However, such aseasonal variation pattern differed from the radio caesium activity concentration patterns inmuscle tissues which decreases from spring to summ er and then increases during winter 5 ) , showing
a decrease from April to June, and a sharp increase in July, and then a decrease during winter.

62

Table 7. GAMM which estimated monthly variation of caesium-137 soil deposition
within the home ranges and intensive use area
Use location

AIC

Delta AICIntercept

Explanatory
variables

Home ranges

Intensiveuse-316853.3

0*

2.29*10 - 5-316631.4

221.892.30*10 - 5

Month-32344.50*

2.55*10 - 5

Month-32240.4

104.16

2.55*10 - 5

areasoil(Bq/m2)

137Cs deposition to*: Valid model（ Delta AIC<2.0）

MonthFigure 33. Seasonal variation of caesium-137 soil deposition within the intensive
use area
The center horizontal line indicates the mean, the box indicates 75 % of the data,
and the bar indicates 95% of the data.
The blue line shows the regression curve estimated by GAMM.
The results of the relationship between caesium-137 soil deposition and environmental factors
in the study site are shown in Table 8. Locations closer to the farm and urban lands as well as
lower elevations, caesium-137 soil deposition tended to be higher. Caesium-137 soil depositions
tended to be higher in the locations proportionate t o higher activity concentration s of beech forests,
broadleaf forests, coniferous forests, planted f orests, mixed forests, scrub forests, grassland, or
naked land. On the other hand, caesium-137 soil depositions tended to be lower in locations witha higher proportion of Japanese oak and Berry fruit forests.
Seasonal variations of environmental factors in the home ranges and intensive use areas aredescribed in Figures 34 -37 (based on the above results of the relationship between caesium-137
soil deposition and environmental factors in the study site), which are divided into negative andpositive relationships with caesium-137 soil deposition. Regarding the environmental factors thatwere negatively related to caesium-137 soil deposition, a similar pattern of seasonal variations inmuscle tissue caesium-137 activity concentrations was observed for all environmental factors
63except for berry fruit forests in both the home ranges and intensive use areas. This seasonal use
pattern of environmental factors may be account for the inconsistency of seasonal pattern of
caesium-137 soil depositions within the home r anges and why the seasonal pattern of caesium-137
soil deposition within the intensive use area does not follow the seasonal pattern of caesium-137
activity concentration in muscle tissue. On the other hand, environmental factors that werepositively related to caesium-137 soil deposition showed a pattern of seasonal variation similarly
to the seasonal variation of caesium-137 activity concentration s in muscle tissues in beech forests,
both in the home ranges and in the intensive use area. Therefore, it is likely that seasonal variations
in beech forest use affects seasonal variations in caesium-137 activity concentrations in muscle.
The seasonal variation in use locations pattern revealed that the Asian black bears in the study
area gradually increase their use of broadleaf forests, planted forests, and berry fruit forests atlower elevations from spring to summer, (resulting in closer proximity to farm and urban lands),
while gradually increasing their use of Japanese oak forests and beech forests at higher elevations
from autumn to winter.
Table 8. Relationship between

caesium-137 soil deposition and environmental

factors in the study site
Environmental factor

Regression

Standard

coefficienterror-1533.49

t value

Pr (>|t|)

93.85-16.34<2e-16-1820.86

87.26-20.87<2e-16

Elevation-5415.76

102.71-52.73<2e-16Beech forests

22147.57

185.73119.25<2e-16

Japanese oak forests-9347.18

171.6-54.47<2e-16

Berry fruits forests-8170.12

111.73-73.12<2e-16

Broadleaf forests

10521.41

94.93

110.83<2e-16

Coniferous forests

1514.94

81.96

18.48

<2e-16

Planted forests

9818.76103.8894.52<2e-16

Mixed forests

1573.31

82.4

19.09

<2e-16

Scrub forests

1901.4182.66

23<2e-164363.89

88.4

49.37

<2e-16

Distance

from

the

from

the

farmlandDistance
urban land

Grassland
land

or

naked

64

Distance from urban landDistance (m)Distance (m)Distance from farmlands

Month

Month
Elevation (m)Proportion

Elevation (m)Japanese oak forests

Month

Month

Proportion

Berry fruit forests

Month
Figure 34. Seasonal variation of environmental factors negatively related tocaesium-137 soil deposition within the home ranges

65Coniferous forests

Broadleaf forests

Month

Month

Month

Planted forests

Mixed forests

Scrub forests

Month

Month

Month

Proportion

Proportion

Beech forests

Proportion

Grassland or naked landMonthFigure 35. Seasonal variation of environmental factors positively related tocaesium-137 soil in home range

66

Distance from farmlands

Proportion
Distance (m)Distance (m)Distance from urban land

Month

Month

Elevation

Proportion

Elevation (m)Japanese oak forests

Month

Month

Proportion

Berry fruit forests

Month
Figure 36. Seasonal variation of environmental factors negatively related tocaesium-137 soil deposition within the intensive use area

67

Beech forests

Broadleaf forests

Month

Month

Planted forests

Mixed forests

Scrub forests

Month

Month

Month

Proportion
Proportion

Coniferous forests

Proportion

Month

Proportion

Grassland or naked landMonthFigure 37. Seasonal variation of environmental factors positively related tocaesium-137 soil deposition within the intensive use area
For the results of the habitat selection analysis, each environmental factor is noted in Figure 38
for environmental factors negatively related to caesium-137 soil deposition, and in Figure 39 forenvironmental factors positively related to caesium-137 soil deposition, based on the results of
the relationship between caesium-137 soil deposition and environmental factors described above.
For the negatively related environmental factors, locations far from farmlands were selected in
October and December; in A ugust, September, and December, locations far from urban lands wereselected. The lower elevations were selected in April, June to October and December, while thehigher elevations were selected in November. Japanese oak forests were selected in June, Octo ber,and December, but avoided in May and July. Berry fruit forests were selected in June and October,but avoided in December. For environmental factors positively related to caesium-137 soil
deposition, a variety of vegetation types were selected in Apri l, June, and July, i.e., beech forests,
broadleaf forests, planted forests, mixed forests, and scrub forests. The lack of a clear pattern of68seasonal variation in caesium-137 activity concentrations in muscle tissue for any of theenvironmental factors suggests that seasonal variation in caesium-137 activity concentration s may
be affected by seasonal variations in habitat use, particularly the frequency of use of beech forests,
as opposed to habitat selection.

Forest of Japanese oak

Prefer target vegetation, distant place and high location

Avoid

Figure 38. Habitat selectivity of environmental factors negatively related tocaesium-137 soil deposition

Prefer target vegetation, distant place and highlocation

Avoid

Figure 39. Habitat selectivity of environmental factors positively related tocaesium-137 soil deposition
2.4.2.2. Management of wild animals in the area contaminated by radionuclides
2.4.2.2.1. Monitoring
Figure 40 shows the activity concentration of caesium 134+137 in the muscle of green pheasantscaptured throughout Fukushima Prefecture from October 2011 to March 2022. Since then, no
individuals have been detected with caesium activity concentrations exceeding the food standard
values. In recent years, caesium activity concentrations have remained below the detection limit
in many individuals.

69

Figure 40. Monitoring results of caesium-137 concentrations in the musclesof pheasants2.4.2.2.2. Investigations of wild animals around the Evacuation-Designated Zone
(EDZ)
Genomic DNA of wild boars was extracted from 179 specim ens in Fukushima Prefecture and 9
specimens in Kumamoto Prefecture*, and subjecting them to a MIG -seq analysis. As a result, in a
total of 688 Single-nucleotide polymorphisms (SNPs) were extracted 2 4 ) . For confirming thegeographical trends of population structure, the wild boars captured in Fukushima Prefecture wereclassified into seven groups based on their captured locations and those captured in Kumamoto
Prefecture into one group (eight groups in total) (Figure 41).
A STRUCTURE 11 ) analysis and cluster analysis using the SNPs information was then carried out.
According to ΔK value under STRUCTURE analysis data, the results for wild boars suggested thatthey were divided into two genetic lineages (Figure 42). Moreover, the results of cluster analysis
revealed two clusters that can be divided into an eastern group inhabiting northern Soso District,southern Soso District, Iwaki District and Ken -nan District of Fukushima Prefecture, and a westerngroup inhabiting Ken-poku District, Ken-chu District and Aizu District of Fukushima Prefecture
and Kumamoto Prefecture (Figure 43). (*The meat specimens obtained in Kumamoto Prefecture
are provided by Munemasa Kousan, a stock company.) BayesAss 2 5 ) estimated gene flow for thewild boar population distributed on the east side of the Abukuma River and the population on thewest side. The results showed that the gene flow from the eastern population to the western70population (10.3%) was greater than that from the western population to the east population (3.3%).
The results also indicated that gene exchange within the east and west populations was moresignificant than between the east and west populations (within the east populati on: 96.7%, within
the west population: 89.7%). It was expected that the east and west populations would bemaintained as separate populations across the Abukuma River and the urban area and that there
would be little back and forth between each other's pop ulations (Figure 44).

Figure 41. Grouping of specimens after their MIG -seq analyses and the number ofanalyses

Figure 42. Results of STRUCTURE analysis based on wild boars DNA data
2 colors (red and green) represent genetic lineages suggested by the
results of STRUCTURE analysis. Ratio of the colors are of the lineages ineach sample shown by vertical column (0.00 -1.00)

71

Figure 43. Results of cluster analysis based on wild boars’ DNA data

Figure 44. Geographical distribution of wild boars of two genetic lineages
Ratio of genetic lineages shown by the S TRUCTURE analysis (See Figure 42 ) ineach municipality. Size of the circle represents the amount of samples.
2.4.2.2.3. Strategy to lift restrictions for distribution and consumption
IAEA’s recommendations
Therefore, the Prefecture made a request to the IAEA ’s knowledge and received thefollowing recommendations.
72

【Prior cases in overseas】
・Based on prior cases in overseas, it would likely be difficult deciding to lift distribution
restrictions, etc, only when the monitoring result of samples in areas where lifted
restrictions are found below the standard values. Rather, establishing a system to allow
residents to directly monitor and self -consume or distribute only those samples that are
below the standard values should be considered.
Considerations in response to recommendations
At present, the prefectural government, in cooperation with the Consumer Affairs Agency
and the National Consumer Affairs Center of Japan, lends or transfers radioactive material
inspection equipment to municipalities with which prefecture residents can in spect theirvegetables and other food products for radioactive materials in their neighborhoods, and is
working to enhance and strengthen the inspection system. However, the foods underconsumption and distribution restrictions are not covered by such insp ections.
On the other hand, regarding the distribution of wild game as commercial products, although
the national government (Ministry of Agriculture, Forestry and Fisheries) has a system inplace to subsidize municipalities for the construction of meat p rocessing facilities to promote
the utilization of wild game as Gibier, no municipalities in the prefecture have constructed
or currently operate meat processing facilities because the government subsidizes only halfof construction costs, the municipaliti es must bear the remaining costs and is thus unlikely
to be commercially profitable.
In view of this, the prefecture continues to request the national government to prepare
requirements for lifting restrictions in accordance with the actual conditions of t he regions
due to the considerable difficulties of conducting continuous monitoring and ensuring
sufficient samples of wild game.

Creation of a brochure aimed at fostering understanding among hunters
To convey the importance of monitoring and ensuring su fficient sample numbers, a brochurefor hunters was prepared in cooperation with the IAEA and 4,000 copies were distributed tohunters in the prefecture in October 2021.
2.5. Conclusions
Comparisons of the activity concentration s of caesium-137 in the muscle tissues of wild boars
and Asian black bears reveale d higher activity concentration s in wild boars, while comparisons
between copper pheasant and green pheasants revealed higher levels in copper pheasant, revealingthat trends differed depending on the species.
The activity concentrations of caesium-137 in the muscle tissues of wild boars were confirmed
to be strongly affected by diet. Seasonal variations were also observed in both wild boars andAsian black bears (which were higher in win ter season), although the patterns differed.
73

High caesium-137 activity concentration s of muscle were observed in wild boars and Asian blackbears captured in areas where the caesium-137 deposition density was high, but the activity
concentrations significantly varied among individuals in the areas. Even in recent years, thoseshowing activity concentration s exceeding 10 times the standard limit for general foods in Japan
have sometimes been captured. Regarding long -term fluctuations of caesium-137 activity
concentrations in the muscles of wild boars and Asian black bears, they have decreased over time
during the entire period and during times of the year with low-activity concentrations in muscle
tissues observed. However, during times of the year where high -activity concentrations in muscle
tissue are observed, the range of estimated values increased over time.
Compared to wild boars living outside the areas under evacuation orders, those living in the areas
under evacuation orders tended to have wider ho me ranges that tended to shift to farmlands. In
addition, the results of the studies suggested that the wild boars in Fukushima Prefecture are
divided into two lineages, and these populations are situated in the east and west areas around the
Abukuma River, with the river acting as the boundary that restricts the movement fr om east to
west and vice versa.
Caesium-137 activity concentrations in muscles of wild boars and Asian black bears are on adecreasing trend, but they vary among individuals and are obse rved to fluctuate seasonally.
Therefore, in order to precisely estimate their long -term fluctuations, further data expansion isnecessary. Moreover, the movement and spatial range covered by the wild animals seems to be afactor contributing to the variation of caesium-137 activity concentrations observed even among
those animals captured in the same region.
In the future, the monitoring of radio caesium activity concentrations in the bodies of wild boars
and other wild animals and birds will be continued. The factors contributing to the high radi ocaesium activity concentrations in some wild animals will be investigated, and survey methods
for the conservation and management of wild animals will be studied.
References
1)

Semizhon, T., et al., Time -dependency of the 137Cs contamination of wild boar from a region
in Southern Germany in the years 1998 to 2008. Journal of environmental radioactivity, 2009.
100 11: p. 988-92.

2)

Saito, R., et al., Monitoring 137Cs activity concentrations in bird species occupying di fferent
ecological niches; game birds and raptors in Fukushima Prefecture. Journal of environmental
radioactivity, 2019. 197: p. 67 -73.

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Saito, R., Y. Nemoto, and H. Tsukada, Relationship between radiocaesium in muscle andphysicochemical fractions of radio caesium in the stomach of wild boar. Sci Rep, 2020. 10(1):p. 6796.

4)

Saito, R. and H. Tsukada, Physicochemical Fractions of Radiocesium in the Stomach Contentsof Wild Boar and Its Transfer to Muscle Tissue, in Behavior of Radionuclides in theEnvironment III. 2022, Springer. p. 495 -505.

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Nemoto, Y., R. Saito, and H. Oomachi, Seasonal variation of Ce sium-137 concentration in74

Asian black bear (Ursus thibetanus) and wild boar (Sus scrofa) in Fukushima Prefecture, Japan.
PLoS One, 2018. 13(7): p. e0200797.
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SAITO, R., et al., The use of DNA metabarcoding to analyse wild boar diets: Reproducibilityof plant diet analyses and effective blocking of boar DNA amplification when evalua tinganimal dietary components .Japanese Journal of Ecology, 2020. 70(3): p. 163.

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Nemoto, Y., et al., Effects of (137)Cs contamination after the TEPCO Fukushima Dai -ichi
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JAEA, Results of Deposition of Radioa ctive Cesium of the Fifth Airborne Monitoring Survey
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9)Brown, J.E., et al., A new version of the ERICA tool to facilitate impact assessments ofradioactivity on wild plants and animals. Journal of environmental radioactivity, 2016. 153:
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10) Suyama, Y. and Y. Matsuki, MIG -seq: an effective PCR-based method for genome -wide singlenucleotide polymorphism genotyping using the next -generation sequencing platform. S ci Rep,
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11) Evanno, G., S. Regnaut, and J. Goudet, Detecting the number of clusters of individuals using
the software STRUCTURE: a simulation study. Mol Ecol, 2005. 14(8): p. 2611 -20.
12) Strebl, F. and F. Tataruch, Time trends (1986–2003) of radiocesium transfer to roe deer andwild boar in two Austrian forest regions. Journal of environmental radioactivity, 2007. 98(1 2): p. 137-152.
13) Rode, K.D., S.D. Farley, and C.T. Robbins, Sexual dimorphism, reproductive strategy, andhuman activities determine resource use by brown bears. Ecology, 2006. 87(10): p. 2636 -2646.
14) Ciarniello, L.M., et al., Grizzly bear habitat selection is scale dependent. Ecol Appl, 2007.
17(5): p. 1424-1440.
15) Massei, G., et al., Factors influencing home range and activity of wild boar (Sus scrofa) in a
Mediterranean coastal area. Journal of Zoology, 1997. 242(3): p. 411 -423.
16) Morelle, K., et al., Towards understanding wild boar Sus scrofa movement: a synthetic
movement ecology approach. Mammal Review, 2014. 45: p. 15 -29.
17) Takahata, C., et al., Habitat selection of a large carnivore along human -wildlife boundaries ina highly modified landscape. PloS one, 2014. 9(1): p. e86181.
18) Nemoto, Y.K., C. ;Yamazaki, K. ;Koike, S. ;Masaki, T. ;Kaji, K., Individual andsexual variation in the selection of hard mast forests and artificial land by Asian black bears
in fall. Mammalian Science (Honyuryu Kagaku) 2018. 58(2): p. 205 -219.
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76

3. FIP3 ： Sustainable countermeasures for radioactive materials in terrestrial
and aquatic areas
3.1. Abstract
Decontamination methods were developed and tested in rivers designated for radio caesium
removal measures. Their effectiveness and sustainability were studied. The contamination
situation in riverside areas used by the public in Fukushima Prefecture and the measures taken to
deal with it were also considered. In addition, the contamination of riverbanks and changes in air
dose rates following heavy rains were investigated.
3.2. Purpose
Radioactive substances, including radioactive caesium, were released into the environment
following the accident in the Fukushima Daiichi Nuclear Power Plant. The aquatic environment
was contaminated and this potentially affected the use and management of rivers, lakes and otherfreshwater bodies. In response, monitoring of water, sediments and aquatic products was
conducted to understand the behaviour of radioa ctive substances in the aquatic environment,
mainly by government authorities and research institutions. Decontamination measures were also
promoted. In this project, countermeasures for radio caesium applicable for use in Fukushima
Prefecture were planned and implemented based on national and international knowledge. Tests
were conducted for demonstrating the decontamination of rivers and to study the resulting
reduction of external exposures in such areas. The persistence of the decontamination measures
implemented was also tested. In addition, the contamination situation at riverside parks in the
Fukushima Prefecture was investigated and the impact of the flood caused by Typhoon No.19 in2019 (Hagibis) on the air dose rates at the studied sites was assesse d.
3.3. Content of implementation
3.3.1. Identification of radiocaesium countermeasures considered applic able to
Fukushima Prefecture
Among the measures taken against the diffusion of radioactive substances in the environment
after the accident at the Fuk ushima Daiichi Nuclear Power Plant of the Tokyo Electric Power
Company, the measures for radioactive substances deposited on inland water bodies (rivers, lakes,etc.) and their effectiveness have not been clarified. Therefore, at the start of this project, thefocus was on studying measures that would enable the use of rivers, lakes and other freshwater
bodies affected by the accident. The effectiveness of decontamination measures consideredapplicable in Fukushima Prefecture to reduce activity levels in ri vers was studied.
3.3.2. Decontamination tests at riverside parks and sustainability of theireffectiveness3.3.2.1. Purpose
There are only few examples for countermeasures to reduce external exposure caused by the77contamination of riverbeds, riverbanks a nd flood plains of rivers. In the Fukushima Prefecture, as
there are in many cases where non -decontaminated forested areas exist upstream, surface run -offwater transports radiocaesium bearing material downstream into rivers. As a result, there may be
thick deposits of soil and sediment containing radio caesium in areas outside the embankments ofrivers. Soil decontamination methods applied to agricultural land, forests, and residential areas
assume that radiocaesium usually has accumulated in the surface la yer of a few centimetres.
However, it is not clear whether these methods are appropriate for flood plains outside theembankments of rivers where sediments may continuously deposit during floods, for example
following typhoons.
Even after decontamination o f the outside of the embankment, there is a concern that re contamination may occur in these areas, due to the continuous input of surface run -off watercontaining contaminated suspended sediments. In particular, if vegetation thrives in the outerareas of the embankment, fine -grained sediment with a relatively high caesium-137-concentration
may be retained by vegetation leading to a local increase of radio caesium concentrations.
Therefore, an effective decontamination method for the outer areas of the emb ankment was
expected to be sediment removal and this was carried out to investigate its effectiveness in
reducing air dose rate. The thickness of the removed layer was defined by the depth distributionof radiocaesium in the sediments on the embankments. T he sustainability of the decontamination
effect was also investigated. The same species of vegetation continued to grow where thedecontamination demonstration tests were carried out as had been growing before sedimentremoval. The air dose rate and the de position of sediments were continuously monitored toinvestigate whether or not there was re -contamination due to the growth of the vegetation.
3.3.2.2. Method
The study site is located 55 km north -west of the Fukushima Daiichi Nuclear Power Plant of theTokyo Electric Power Company Holdings, Inc., in the lowest reach of the Kami -Oguni River, atertiary tributary of the Abukuma River (Figures 1(a) and 1(b)). The deposition of radio caesium(caesium-134 and caesium-137) as of July 2011 ranged from 300 to 600 kBq/m 2 . 1 ) Most of thecatchment is covered by forest, with farmland and residential areas located along the river (Fig ure
1(b)). The total decontamination area was 170 m long, with an average bank width of 15 m on
both banks and a river channel width of 2 -6 m during normal water (Figures 1(c) and 1(d)). The
left bank of the river was used as school route to the primary schoo l, the right bank was used by
the arboretum, and the flood channel was used by the primary school for teaching and otherpurposes. The primary school and the school route were decontaminated before the test.

78

Study site

Figure 1. Outline of the study site
Radiocaesium deposition is based on the results of the third round of aircraft
monitoring 1 ) (converted to 2 July 2011).
The decontamination demonstration of the outer embankment area was carried out in 2014
according to the procedure shown in Figure 2. First, the depth distribution of the radio caesium
concentration in the sediments outside the embankment was measured. The depth of sedimentremoval was set according to the radio caesium distribution, and decontamination was carried out
accordingly. Air dose rates were continuously measured after decontamination. From thedecontamination in 2014 to the end of 2016, all vegetation in the outer bank area was mowed, andfrom 2017, vegetation was not mowed. In 2018, embankment works were carried out on the
upstream side of the right bank for flood protection.

79

Figure 2. Photographs of the decontamination test procedures
Air dose rates at 1 m above the surface of the decontaminated area were measured during
baseflow using a NaI scintillation survey meters. High waterbed and riverbed sediments were
sampled from before the decontamination demonstration test (in 2014) up to 2016. Sediment
samples in the high waterbed were divided into sediments that were newly deposited since the lastmeasurement (new sediments ) and sediments that had been deposited before (old sediments) atseven sites in 2017-2018 using the ring method (A method in which rings are placed on the groundsurface in advance and the old and new sediments are separated according to their top and bot tom.
See Figure 7.). The sediments were measured for radio caesium concentrations; gravel was removed
before the measurement. The ratio of the mud fraction (silt and clay, particle size < 63 µm) to thetotal mass of the samples was determined.
The annual dose due to external exposure before and after decontamination was calculated in thefollowing way. It was assumed that the time of use was 35 hours per year (10 minutes per day, 210
days per year) for walking to school on the left bank and 24 hours per year (2 hours per day, 12days per year) for teaching and other activities on the high waterbed. This was multiplied by theaverage air dose rate at the study site minus the air dose rate before the nuclear accident (0.04µSv/h). 2 )80

3.3.3. Investigation of the distribution of radiocaesium in river parks andtesting remedial measures
3.3.3.1. Purpose
As mentioned above, radiocaesium may deposit outside the embankment as a result of
sedimentation during floods. In the Coastal region, the eastern part of the Fukush ima Prefecture,
there is a relatively high deposition in the upstream area, and it is very likely that downstream
areas near the river outside the embankment are more contaminated than areas farther away fromthe riverbed. Therefore, the contamination situ ation was studied and countermeasures for riverparks on high water beds in the Coastal region were investigated.
3.3.3.2. Method
The survey was conducted at two sites downstream of the Niida River, which flows through thecoastal region (Figure 3). Park A is located along the mainstream of the Niida River and Park B
is located along the Mizunashi River, a primary tributary of the Niida River. A dam is located 5
km upstream of Park B. Deposition of radio caesium (caesium-134 and caesium-137) in thecatchment as of July 2011 exceeds 1000 kBq/m 2 in the upper reaches, but it is less than 100 kBq/m 2
in the lowest reach. Deposition of radio caesium in Park A is 490 kBq/m 2 and 210 kBq/m 2 in Park
B. 3 ) The area of Park A is 2.7 ha and that of Park B is 1.6 ha.

Figure 3. Location of study sites
The map of the radio caesium deposition is based on the results of the third roundof aircraft monitoring 1 ) (converted to 2 July 2011).

Air dose rates were measured in August 2015 in the study area at 1 m height above the groundusing a portable gamma -dose rate meter (GAMMA Plotter H, Japan Radiation Engineering Co.,
Ltd.). Based on the data obtained, a map of the spatial distribution of radio caesium was created81using the decontamination activity support system (RESET) 1 developed by Japan Atomic Energy
Agency. Air dose rates were measured again on 28 September 2015, as a flood event occurred from
6-11 September 2015 (total precipitation during the period at the AMeDAS Haramachi station (6km southeast of Park A) was 385 mm 5 ) ), when nearly half of the park was flooded. Soil cores werecollected in December 2015 and the depth distribution of radio caesium in soil in the study area
was investigated.
External exposures for the parts of the parks, used for recreation, walking a nd maintenance, were
estimated using a dosimeter that provides the integrated air dose rate over the measurement period(DOSE e nano, Fuji Electric Co., Ltd.). Based on a dosimeter reading for about 1 hour, external
exposures were estimated assuming that b oth parks were used for 36 hours per year 2 .
3.3.4. Exploring public concerns on the safety of freshwater bodies
3.3.4.1. Purpose
When considering future medium- and long-term measures to mitigate the consequences of theaccident in the Fukushima Daiichi Nuclear Power Plant, it is important to understand the issues
and trends related to the use of freshwater resources by various stakeholders in the Fukushima
Prefecture. The aim of this study was to identify concerns related to the management of freshwater
resources through interviews with relevant stakeholders, and to identify changes over time in theprefectural residents' views on the safety of the aquatic environment.
3.3.4.2. Method
From May to June 2016, administrative officials responsible for implem enting measures to ensure
the safe uses of water were interviewed to learn about the challenges they faced caused byradioactive substances in the aquatic environment. From the results of the interviews, the relevant
issues were extracted and addressed. In addition, raw data from the prefectural public opinion
survey conducted by Fukushima Prefecture 6 ) every fiscal year from 2010 to 2015 was provided by
the Public Consultation Unit of the Fukushima Prefectural Government. From this data, we focusedon the question “Do you feel safe from pollution including water and air pollution in your living
environment? ” Trends and changes in the responses to this question over time by gender, age, andplace of residence were examined, and an analysis was conducted to de termine whether there wasa relationship between this question and the question “Is your living space safe from radiation? ”(radiation risk).

Restoration Support System for Environment (RESET). The system can be use d to simulate thepercentage reduction in air dose rates due to decontamination and the changes in air dose rates
after decontamination. 4 )2 Park A: 12 hours per year for recreation (2 hours per day, 6 days per year), 12 hours per year
for walking (1 hour per day, 12 days per year), 12 hours per year for park maintenance such as
flowerbeds (1 hour per day, 12 days per year)
Park B: 24 hours per year for recreation or playground equipment use (2 hours per day, 12 days
per year); 12 hours per year for walking (1 hour per day, 12 days per year))182

3.3.5. Changes of radiocaesium concentration in riverbanks during large-scale
flooding
3.3.5.1. Purpose
Radioactive materials may accumulate in riverbanks as a result of sediment deposition.
Resuspension of riverbank sediments and additional dep osition of suspended sediments onriverbanks can also occur, especially during flood events caused by typhoons or heavy
precipitation. These processes result in changes of the depth distribution of radio caesium
concentrations in bottom sediments . 7 , 8 ) These processes can reduce air dose rates from riverbanks,
and are generally referred to as natural attenuation.
Typhoon Hagibis, which passed through Fukushima Prefecture in October 2019, caused riverbank
breaches and overflows in various rivers of the Fukushima Prefecture, causing significant damage
along the rivers. To clarify whether there was recontamination due to erosion an d sedimentation
during the water run -off, and whether air dose rates decreased due to these processes, changes in
air dose rates and contamination levels in riverbanks and river parks following the passage ofTyphoon Hagibis were investigated.
3.3.5.2. Method
Surveys were conducted in two river parks in the Niida River catchment (Figure 3) and at thedemonstration site on the Kami -Oguni River (Figure 1), as described in section 3.3.3. and 3.3.2 ..
Typhoon Hagibis passed through Fukushima Prefecture on 12 -13 October 2019. At the AMeDAS
Haramachi station, which is closest to Parks A and B, 274 mm of precipitation was observed as aresult of a series of rainstorms. 5 ) In the Fukushima Prefecture, rivers in various areas, including
the Abukuma River, a major river in the prefecture, suffered dike breaches and flood damage, andriver dikes in the surveyed areas were overflowed. Air dose rates at a height of 1 m above theground were measured using a portab le gamma-dose rate meter in January 2018 before the typhoon
and in October 2019 after the typhoon. In addition, the erosion and deposition of sediment in theriverbank and park were confirmed when walking at the site after the passage of the typhoon.
3.4. Results
3.4.1. Indentification of radiocaesium countermeasures considered app licable to
Fukushima Prefecture
The exposure pathways and transfer processes and potential measures that can be implemented
that are related to the use of rivers, lakes, etc. are addressed in the guidelines of the relevant
ministries 9 , 1 0 ) and in the report on the experience of the Chornobyl nuclear accident. 11 ) The mostimportant contents are briefly summarised in Table 1.

83

Table 1. Issues and measures for specif ic purposes in rivers and lakes
Issue (Exposure pathways

Related media

MeasuresRivers and lakes

Changing water sources

Rivers and lakes

Reducing sediment inflow using silt

and environmental transfer)
Internal exposure due to use
as drinking waterTransfer from irrigationwater to agricultural
products and external

fencesIrrigation ponds

Reducing sediment outflow using silt

exposure during farming

fencesRemoval of bottom sediment
Agricultural products

Application of enhanced levels of
potassium fertilizer to reduce Csuptake from soilInternal exposure fromRivers and lakes

Shipping restrictions

consuming freshwater fish

Application of potassium (effective only
in closed lakes)

External exposure fromRivers and lakes

Restricting access, soil decontamination

using watersides

Removing riverbed sediments to reduce(Parks, roads, residences,sediment deposition onto riverbanks

etc.)

Building embankments for inundation
control
Irrigation ponds

Use restriction, removal of sediments,(at drainage)

and covering of exposed bottom
sediments

Common to all issues

Decontamination of sources andprevention of sediment discharge
Risk communication to reduce anxieties

3.4.2. Decontamination tests at riverside parks and sustainability of theireffectivenessThe depth distribution of radio caesium concentrations in the sediments of the high waterbed
before decontamination is shown in Figure 4. The samples were collected 3.5 years after theaccident in the Fukushima Daiichi Nuclear Power Plant at 5 points as sho wn in Figure 4. The
caesium-134 concentration was a few kBq/kg, but the caesium-137 concentration at points 1 and2 exceeded 10 kBq/kg at depths greater than 10 cm. These layers had a relatively high mud fractionof 39-56% (Figure 4). As radiocaesium is strongly adsorbed by clay and silt, 1 2 ) it is unlikely thatradiocaesium would penetrate downwards below the mud -rich layers. Therefore, these layers are
considered to be the results of sediment deposition. On the other hand, points 3 to 5 had relatively
low caesium-137 concentrations. Due to this heterogeneous distribution of radio caesium, both in
the vertical and planar direction, the depth to which sediments were removed in the84decontamination demonstration test was set at 15 -35 cm. Similar depth distributions have beenreported for flood beds, 7 ), 1 3 ) so it is considered important to know the depth distribution inadvance for decontamination of the areas outside the embankment.

Figure 4. Depth profile of radiocaesium concentrations and the mud fractions i npercent in high waterbed sediments before decontamination
The spatial distribution of air dose rates at 1 m above the ground surface before and after thedecontamination demonstration test is shown in Figure 5. The mean value before decontamination
was 0.66 µSv/h (standard deviation: 0.22 µSv/h), which was approximately halved to 0.34 µSv/h(standard deviation: 0.11 µSv/h) when decontamination by removing sediment was completed,confirming the effectiveness of this decontamination measure. The concentrat ion of caesium-137
in the upper 5 cm layer of the sediment in the high waterbed (5 sites, Fig ure 4) was less than 3
kBq/kg in all cases after decontamination.

Figure 5. Distribution of air dose rates at 1 m above the ground surface b efore
and after decontamination

85

The temporal changes in air dose rates at 1 m above the ground from 2014 (before
decontamination) to the end of 2018 are shown in Figure 6. The figure also shows the measured
values in the non-decontaminated section located 20 m upstream of th e upstream edge of thedecontaminated area. At the AMeDAS Yanagawa station (9 km north of the decontamination area),
rainfall of 50 mm per day or more was observed four times during the two years after
decontamination. 5 ) Therefore, it is assumed that the high waterbed was flooded several times, but
the air dose rate there decreased as slowly as in the non -decontaminated area.
In the decontaminated sections, after the initial reduction of the air dose rate by about a factorof 2 following the decontamination test, the air dose rate decreased slightly faster than the physicaldecay of radiocaesium (considering caesium-134 and caesium-137). For the non-decontaminatedsections, the air dose rate also decreased faster than physical decay only. The effective
environmental half-life obtained by fitting an exponential function was shorter for the non decontaminated section (5.9 years) t han for the decontaminated section (8.1 years). The largest
decrease in air dose rate occurred when Typhoon Etau passed in September 2015, which isconsidered to have been significantly affected by large -scale flooding.
After 2017, when the vegetation in t he decontaminated sections was no longer cleared, the trendof declining air dose rates continued, and no re -contamination after the decontamination
demonstration test has been observed.

Figure 6. Changes over time in air dose rates at 1 m above the ground surface
The physical decay of caesium-134 and caesium-137 was calculated with the initialdeposition ratio being 1:1. Initial values were fitted to the values measured on
November 16, 2014 after the completion of the decontamination test.
Based on the assumption for the occupancy times of these areas, the annual additional external
dose due to the school walk and the use of the flood bed was estimated to be 0.029 mSv per year
before decontamination and 0.016 mSv per year after decontamination in 2014. In the vicinity of86

the study site, based on measurements for adults using glass badges 3 from July 2013 to June 2014,
the annual additional dose from external exposure was estimated to be 1.23 mSv per year. 1 4 )Therefore, it was concluded that the doses due to external exposure received from the study sites
represent a small proportion of the overall doses from external exposure in daily life (before
decontamination: 2.3%, after decontamination: 1.3%).
Between the end of 2016 and August 2017, new sediments de posited on riverbanks where there
was thriving vegetation showed higher radio caesium concentrations than new sediments depositedon riverbanks without vegetation at the end of 2016 or the old sediments collected in August 2017
(Figure 7). These new sedimen ts also had a relatively high clay and silt content, suggesting thatvegetation facilitated trapping of fine -grained sediment. However, the radio caesium concentrationof this material was lower than that of the riverbank sediments before the decontaminatio n test,
and the mud content was smaller. It should be mentioned that the air dose rate did not increaseduring the August 2017 measurements because the overall amount of sediment was not large.
On the other hand, after the passage of Typhoon Lan in 2017, a sediment layer with a thicknessof about 20 cm was deposited on the riverbank (Fig ure 7). However, the radio caesium
concentration of this material was lower than that of the riverbank sediments after thedecontamination demonstration test, and the mud fra ction was low. The amount of vegetation
biomass on the riverbank as of summer 2017 was only 40 % of that near the decontamination area
(measured in 2019). During the recovery and re -growth of the vegetation during the year after
heavy flooding such as typhoons, the retention effect of fine -grained sediment is likely to havebeen small. In 2018, there were fewer heavy rainfall events that could have resulted in sedimentdeposition, and the sediments had lower radio caesium concentrations and a smaller mud content.

A type of integrated dosimeter that uses a special glass that emits fluorescence when exposed
to ultraviolet light after irradiation. The dosimeter is attached to the chest of the human body andmeasures 1 cm dose equivalent.
387Figure 7. An example of depth distribution of radio caesium concentrations in post decontamination materials deposited in a riverside area (center of the survey
area)
3.4.3. Investigation of the distribution of radiocaesium in river parks andtesting remedial measures
Air dose rates at 1 m above the ground of Park A measured in August and September 2015 (before
and after flooding following the passage of Typhoon Etau) are shown in Figure 8. Before the flood,the dose rates above 1.0 µSv/h were found along the river and in the north -eastern area. However,after the flood, at many of these sites gamma dose rate dropped to values of less than 1.0 µSv/h.
In Park B, on the other hand, no notable changes were observed before and after the flood (Figur e
9).

88Figure 8. Distribution of air dose rates at 1 m above ground surface in Park A
The park is marked by white lines.

Figure 9. Distribution of air dose rates at 1 m above ground surface in Park B
The park is marked by white lines.
The deposition of caesium-137 in soil of Park A is shown in Figure 10. The total inventory of
caesium-137 in the sampling depth ranged from 200 to 400 kBq/m 2 in lawns and flower beds,
whereas the maximum caesium-137-inventory of up to 2400 kBq/m 2 was observed along theriverbanks, which was almost ten times higher. The high air dose rates along the riverbanks before
the floods reflected this observation. In the lawn area, the caesium-137 concentration was highest
in the surface layer (a few centim etres), while in the deeper layers the concentration was uniform
and much lower than in the surface layer. In the flower beds, the distribution is quite uniform up
to a depth of 15 cm due to homogenisation by cultivation. On the other hand, in the riversid e area,
low-concentrations were found to a depth of about 25 -30 cm and the caesium-137 concentration
peaked at a depth of about 40 -50 cm. Observation of soil cross -sections at site 3 showed a clear
89difference in colour tone and sediment grain size at a dep th of around 30 cm, indicating that the
30 cm thick surface layer along the part of the riverbank is likely to consist of deposits from theSeptember 2015 flood. Due to the formation of this low concentration layer and the erosion in thenorth-eastern part of the river bend (Figure 8), it was observed that the air dose rate decreased
after the flood and so natural decontamination had occurred due to the flood. In the Niida Riverbasin, it has been reported that significant erosion in the upper reach and dep osition of sedimentswith low caesium-137 concentrations in the lower reach of this major flood have resulted in natural
decontamination action along the riverbanks in various parts of the catchment. 1 5 ) The findings forPark A are consistent with this.
The situation was different in Park B, where the total inventory of caesium-137 up to the sampling
depth of 20 cm was in the range of 130 -220 kBq/m 2 in both flooded and unflooded areas. In bothcases the high concentration layer remained within the surface l ayer of 10 cm. (Figure 11).
Therefore, it can be assumed that only little sediment deposition occurred and this is why the air
dose rates did not change noticeably (see Figure 9). These differences between the two sites interms of sediment deposition and the tendency to accumulate caesium-137 are likely to be assumed
for the following reasons based on the observations and measurements made.
The riverbank of Park B is grassland, while in Park A there is thick vegetation of about 1
m height along the riverbank, which easily retains sediment;

Upstream of Park B, sediment is retained in the reservoir, therefore, the sediment transport
to Park B is low;The highly contaminated area (> 1000 kBq/m 2 ) is located upstream of the dam (Figure 3);
therefore it is unlikely that sediments with high radio caesium concentrations will reach
Park B.

90

Figure 10. Depth distribution of radiocaesium in soil of Park A
Samples were collected after the extreme flood in September 2015.

Figure 11. Depth distribution of radiocaesium in soil of Park B
Samples were collected after the extreme flood in September 2015.
The annual external doses due to the use of Parks A and B was estimated to be 0.018 mSv/year
and 0.009 mSv/year respectively. The annual external dose estimated from measurements using
glass badges in Minamisoma City where the parks are located, is 0.44 mS v/year (measurement
period: July-September 2015; measured values were extrapolated to one year), 1 6 ) and the exposure91

associated with park use is equivalent to 2 -4% of this value. Therefore, the overall effect in termsof exposure reduction by decontaminat ion of these parks is limited. Taking into account the results
for the Kami-Oguni River in section 3.4 (2), it is considered that the importance of implementing
decontamination measures along the riverbank is not high, as the time that people spend on theriverbank is generally limited and the radiation levels along the river decline due to naturalprocesses 4 .
3.4.4. Exploring public concerns on the safety of freshwater bodies
Five years after the accident, it was found that the challenges facing the admin istrative bodies
in Fukushima Prefecture with regard to the aquatic environment due to radioactive substances andother factors are "hindrance to activities carried out before the accident ", "future impact ofradioactive substances" and "continuation and maintenance of post-accident measures". The
results of the Fukushima Prefecture Public Opinion Survey also showed that there are regional
differences in the change of Fukushima residents' views on safety for water, air and theenvironment. The change of vie w tends to be slower in the Central and Coastal Region than in
Aizu Region (Figure 12). It was also found that perceptions of water and air and environment
safety were significantly associated with the perception of radiation risks.

Such processes include in particular i) migration of radionuclides to deeper layers =>radionuclides in deeper layers are shielded by the overlying material, ii) deposition of sedimentwith lower radiocaesium activity on top of sediment with higher radiocaesium activity =>shielding of the sediment with a high activity, iii) dislocation of sediment containing
radionuclides due to erosion, iv) shielding effect due to vegetation
4

92

Figure 12. Changes over time in responses to question "Do you feel that yourliving environment is safe from environmental pollution incl uding water and air
pollution?"
EOAs represents Evacuation Order Areas.
3.4.5. Changes of radiocaesium concentration in riverbanks during large-scale
flooding
The results of air dose rate measurements in Park A are shown in Figure 13: the average air dose
rate before (31 January 2018) and after (17 October 2019) the passage of Typhoon Hagibis in 2019
was 0.30 µSv/h and 0.20 µSv /h respectively. Taking into account the 13% decrease in air dose
rates due to physical decay between the measurements, this means that air dose rates havedecreased by 23% due to erosion caused by rainfall events as typhoons. The impact of Typhoon
Hagibis was stronger than that of previous typhoons, e.g., the air dose rate decreased by 14 % after
the passage of Typhoon Etau in September 2015. This difference in impact may be due to thedifferent extent of erosion and sedimentation. After the passage of Typh oon Hagibis, a large
amount of riverbank sediment was eroded along the Niida River as shown in the aerial photograph93

of the park (Figure 13), e.g., the area with the highest air dose rate measured before the typhoon
was washed away, exposing the park revet ment (Figures 14(a) and 14(b)).
High radiocaesium inventories were observed in this area, but during the passage of Typhoon Etau
in 2015, sediments with relatively low radio caesium concentrations were deposited on the surface
which caused a shielding effec t, reducing the air dose rate (from the results in section 3.4 .3.).
However, as shown in Figure 14(b), sediment was deposited on the dike and vegetation continued
to thrive after the passage of Typhoon Etau.
The main impact of Typhoon Hagibis on the reduct ion of air dose rates was caused by the loss ofradiocaesium due to erosion of riverbank sediment. Therefore the effect of Typhoon Hagibis on
the reduction of air dose rates was probably greater than the shielding effect due to deposition of
sediments with low caesium activities that occurred during Typhoon Etau. On the other hand, thelarge amount of sand deposited around the Niida River inside the park and the branch river to thenorth of the park (Figures 14(c) and 14(d)) suggests that the reduction in a ir dose rates inside thepark was due to shielding.

Figure 13. Air dose rate distribution at 1 m above ground surf ace in Park A(a) after the passage of Typhoon Hagibis, (b) before its passage
Background photographs (a) and (b) were obtained from Google Earth Pro 1 7 ) (date of
the photo: October 21, 2018).

94

Figure 14. Photos showing the situations of riverside areas(a) River revetment exposed due to river bank erosion caused by the passage ofTyphoon Hagibis, (b) The same river revetment before being eroded (a photo takenfrom the opposite side on September 28, 2015), (c) Sediments deposited along theNiida River, (d) Sediment deposited along the branch river north of the park
For Park B, the mean air dose rate before and after the passage of Typhoon Hagibis in 2019 was
0.21 µSv/h and 0.16 µSv/h, respectively. When corrected for physical decay, this corresponds toa decrease of 12% due to erosion caused by events such as Typhoon Hagibis (Figure 15). Compared
to a 5% decrease caused by Typhoon Etau in 2 015, as in Park A, Typhoon Hagibis led to a larger
decrease of air dose rates.
For Park B, only little erosion and sedimentation occurred during the passage of Typhoon Etau,
but with the passage of Typhoon Hagibis, the entire park was flooded, causing cha nges in the river
channel in the upstream area of the park. Large amounts of sand and gravel were deposited in thepark, especially on upstream sides of the river channel. Considering the significant decrease of
air dose rates in upstream areas, it is assu med that the reason that the air dose rates decreased was
mainly due to shielding by deposited sediment.

95

Figure 15. Spatial distribution of air dose rate at 1 m above ground surface inPark B(a) After the passage of Typhoon Hagibis, (b) Before its passage
The background photographs were obtained from Google Earth Pro 1 7 ) (date of thephotos: October 21, 2018).
In the Kami-Oguni River study site, air dose rates decreased not only in the river channel but
also on the embankment around the river. Most of the sediment in the river channel had been
removed due to the channel excavation work carried out immediately before the survey, but large
amounts of newly deposited sediments (in particular sand and gravel) had accumulated in the river
channel due to Typhoon Hagibis.
The results of this study confirm that Typhoon Hagibis in 2019 did not generally cause re contamination at all sites investigated in this study, but rather reduced air dose rates throughnatural attenuation processes, such as removal of mat erial with relatively high radio caesium
activities and sedimentation of material with low radio caesium concentrations.
3.5. Conclusions
Firstly, the project tested countermeasures applicable for terrestrial and aquatic areas of the
Fukushima Prefecture to mitigate the effects of radiocaesium deposition, based on existingknowledge. In addition, the effectiveness of decontamination methods based on the spatial
distribution of radiocaesium was demonstrated at a study site set up in a riverbank, and thesustainability of the effectiveness after the decontamination test was verified. In addition, it was
found that – although radiocaesium may accumulate in the riverbeds downstream – in the case oflarge-scale floods such as Typhoon Etau in 2015 and Typhoon Hagib is in 2019, there was no re contamination due to sediment deposition, but rather that the natural ‘decontamination’ processes
worked to reduce the air dose rate. External exposure at the riverbanks was therefore found to below.
96In addition, analysis of the results of public awareness surveys confirmed that there is still
persistent concern about the safety of the aquatic environment in severely contaminated areas.
The results of this study were successively communicated to the relevant departments inFukushima Prefecture. The methods for decontamination of the riverbeds were subsequently
utilised as river maintenance measures.
References
1)

Ministry of Education, Culture, Sports, Science and Technology (2011) Results of the 3rdround of aircraft monitoring measurements by the Ministry of Education, Culture, Sports,
Science and Technology. (Japanese)
https://radioactivity.nsr.go.jp/ja/contents/5000/4858/24/1305819_0708.pdf

2)Minato S. (2006) Distribution of Terrestrial Gamma Ray Dose Rates in Japan. Journal of
Geography, 115, 87-95 (Japanese)

3)

Japan Atomic Energy Agency, Database for Radioactive Substance Monitoring Data.
https://emdb.jaea.go.jp/emdb/

4)Japan Atomic Energy Agency, Overview of Operations at Fukushima Environmental Safety
Center (Advancement of Deconta mination and Volume Reduction Technology) (Japanese),https://fukushima.jaea.go.jp/fukushima/work/work3.html

5)Japan Meteorological Agency, Data and Materials (Japanese),
http://www.jma.go.jp/jma/menu/menureport.html.

6)

Fukushima Prefecture, the prefectural pu blic opinion survey (Japanese),https://www.pref.fukushima.lg.jp/sec/01010e/koucho1 -439.html

7)

Konoplev A., Golosov V., Wakiyama Y., Takase T., Yoschenko V., Yoshihara T., Parenyuk O.,
Cresswell A., Ivanov M., Carradine M., Nanba K., Onda Y. (2018) Natural a ttenuation of
Fukushima-derived radiocesium in soils due to its vertical and lateral migration. Journal ofEnvironmental Radioactivity, 186, 23 -33.

8)

Nakanishi T., Sato S., Matsumoto T. (2019) Temporal changes in radiocesium deposition on
the Fukushima Floodplain. Radiation Protection Dosimetry, 184, 311 -314.

9)

Ministry of the Environment (2013) Decontamination Guidelines 2nd Edition (Japanese)
http://josen.env.go.jp/material/pdf/josen -gl-full_ver2_supplement_1803.pdf,(Tentative Translation)
http://josen.env.go.jp/en/policy_document/pdf/decontamination_guidelines_2nd.pdf10) Ministry of Agriculture, Forestry and Fisheries (2016) Technical Manual for
Countermeasures against Radioactive Materials in Reservoirs (Japanese),https://www.maff.go.jp/j/nousin/saigai/attach/pdf/tamemanu_zentai -3.pdf11) IAEA (2006) Environmental consequences of the Chernobyl accident and their remediation:
Twenty years of experience report of the Chernobyl forum expert group ‘environment’.
Vienna.

9712) Nakao, A., Funakawa, S., Tsukada, H., Kosaki, T. (2012) The fate of caesium -137 in a soil
environment controlled by immobilization on clay minerals. SANSAI Environ. An
Environmental Journal for the Global Community, 6, 17 -29.
13) Tanaka, K., Kondo, H., Sakaguchi, A., Takahashi, Y. (2015) Cumulative history recorded in
the depth distribution of radiocesium in sediments deposited on a sandbar. Journal ofEnvironmental Radioactivity, 150, 213 -219.
14) Date City, Fukushima Prefecture (2015) Date Recovery and Revitalizatio n News (Vol. 22)(Japanese), https://www.city.fukushima -date.lg.jp/uploaded/attachment/16650.pdf15) Konoplev, A., Golosov, V., Laptev, G., Nanba, K., Onda, Y., Takase, T., Wakiyama Y.,
Yoshimura, K. (2016) Behavior of accidentally released radiocesium in soil –water
environment: Looking at Fukushima from a Chernobyl perspective. Journal of environmental
radioactivity, 151, 568 -578.
16) Minamisoma City, Fukushima Prefecture (2016) Results of the Indivisual Cumulative Dose
Measurement (July – September 2015) (Japanese),https://www.city.minamisoma.lg.jp/portal/health/hoshasen_hibaku/3/1/3/4954.html
17) Google Earth Pro aerial photograph. https://www.google.co.jp/earth/984. FIP4： Development of environmental mapping technology using GPS walking
surveys(Note: Reprint of the previous report with some wordings revised and update added since
the theme ended in FY2015)
4.1. Abstract
Fukushima Prefecture developed environmental mapping technology with GPS walking
surveys as a tool for surveying the regional distribution of air dose rates.
This report covers the results of parameter verification necessary for the development of thistechnology and the history of development.
4.2. Purpose
To understand the air dose rate (hereinafter simply referred to as the d ose rate) in Fukushima
Prefecture after the accident at the Fukushima Daiichi Nuclear Power Plant, we haveconducted fixed-point measurements with monitoring posts and dose rate measurements in
car-borne surveys using the GPS-linked dose rate measurement d evice KURAMA (Kyoto
University RAdiation MApping System)-II, and have provided information to prefecture
residents on the prefecture homepage (Figure 1 and 2).

(b)

(a)

Figure 1. Example of current monitoring(a): Example of a fixed-point measurement (using a real-time doserate measurement system)(b): Example of a car-borne survey (KURAMA-II installed on theback of a local bus)

99

(a)

(b)

Figure 2. Fukushima Prefecture radiation measurement map(http://fukushima-radioactivity.jp/pc/)(a): Example of a fixed-point measurement(b): Example of a traveling survey
As of March 2016, measurements are being made at 3500 fixed points with monitoring posts inFukushima Prefecture. Car-borne surveys using local buses are also being conducted with the
purpose of interpolating the fixed -point measurements.
It is, however, difficult to conduct fixed -point measurements or car-borne surveys in some places,
including parks, forests, and alleys near residential ar eas, and dose rates sometimes differ between
fixed measuring points at the same facility or site (Figure 3). For these reasons, in addition to
fixed-point measurements and car-borne surveys, we require measurement technology with which
to understand a more detailed distribution of dose rates, and we need to present the measurement
results in a format that is easy to understand.
Therefore, to employ interpolation to obtain dose rates for parks, forests, and alleys nearresidential areas where fixed -point measurements and car-borne surveys are difficult, wedeveloped environmental mapping technology using GPS walking surveys together with unmanned
aerial vehicles (UAVs) developed by the IAEA.
The prefecture and IAEA have shared the development of environmental mapping technology
with GPS walking surveys (FIP4) and environmental mapping technology with unmanned aerial
vehicles (FCP3), and by combining these technologies and visualizing measurement results, wewere able to create dose distribution maps that are m ore detailed and effective.

100

Survey Met er

Monitoring Post etc.

Travelin g Su rvey
Range wh ere d os e rat e can b e u nderstood with tra velin g su rveys and fi xed
point m easu rem ent
Range subj ect t o wa lkin g su rveys

Figure 3. Measurement ranges of conventional measurement methods
4.3. Content of implementation
4.3.1. Development of equipment
We used the KURAMA -II, which was developed by Kyoto University, for walking surveys, andassembled five pieces of equipment in a way suited to walking surveys (Figure 4). The orange
backpack contains a CsI (T1) scintillation detector, which is a low -dose-rate detector, and a high precision GPS unit. The back packer measures the dose rate by walking on a transverse course
while merging dose rate data from the low -dose CsI detector and position information from thehigh-precision GPS device.
(a

(b

)

)

Figure 4. Walking survey equipment(a): Appearance of the devices(b): Low-dose-rate CsI detector (Hamamatsu Photonics K.K.
C12137-01) and high-precision GPS unit (SOKKIA GIR1600)
The measurement screen is shown in Figure 5. The measurement interv al may be selected as 3
seconds, 5 seconds, and so on. At the start of the measurement, information such as the current
position and dose rate are recorded to a notebook computer, and the position information, doserate, trends, and mapping results are dis played on the computer screen.
Measurers can look at the screen to check the measurement position and dose rate while101conducting detailed measurements.

Figure 5. Display screen on a personal computer
4.3.2. Development of mapping technology using Geographic Information System (GIS)
We conducted a specification study and developed a GIS tool for capturing, combining, andmapping the dose rate and position information gained from walking surveys and UAVs. An
overview of the tool is shown in Figure 6.

Result ofwalking survey

GIS tool

Result of airborne survey by a
UAV

年月日
時間
緯度
経度
標高
速度
方位
線量率 検出器温度
2015/3/15 12:17:05 37.47682 140.9572
25.8
0.5
98.95
1.71
15.51
2015/3/15 12:17:08 37.47679 140.9572
26.7
8.5
165.71
1.78
15.51
2015/3/15 12:17:11 37.47676 140.9572
27.5
8.5
193.67
1.83
15.53
2015/3/15 12:17:14 37.47672 140.9572
28.2
7.8
168.791.73
15.53
2015/3/15 12:17:17 37.47669 140.9572
28.6
9.6
187.571.76
15.53
2015/3/15 12:17:20 37.47666 140.9572
28.9
8.9
224.37
1.78
15.54
2015/3/15 12:17:23 37.47663 140.9571
29.2
11.4
229.71
2.01
15.54
2015/3/15 12:17:26 37.47661 140.9571
29.2
10.4
221.91
1.98
15.54
2015/3/15 12:17:29 37.47657 140.9571
29.2
9.2
196.46
1.91
15.56
2015/3/15 12:17:32 37.47654 140.9571
29.3
9.1
190.881.96
15.56
2015/3/15 12:17:35 37.4765 140.9571
29.3
11.6
183.682.03
15.56
2015/3/15 12:17:38 37.47646 140.9571
29.3
9.2
186.22
2.14
15.56
2015/3/15 12:17:41 37.47643 140.9571
29.3
10.5
186.58
2.14
15.58
2015/3/15 12:17:44 37.47639 140.9571
29.2
7.7
151.32
2.16
15.58
2015/3/15 12:17:47 37.47636 140.9571
29.3
7.8
174.76
2.09
15.58

Combined map

Figure 6. Overview of the GIS tool

Figure 7. Data including the dose rate

It is possible to produce a contour map using the GIS tool. Data in comma-separated-value
format recorded in walking surveys are converted to Microsoft Excel file format (Figure 7), andpoint data with dose rate information are created from the latitudinal and longitudinal
information contained in the data (Figure 8). With the GIS tool, it is possible to estimate the dose
rate at unmeasured positions and to produce contour maps from the point data created using any
interpolation algorithm, such as Inverse Distance Weighting (IDW) algorithm (Figure 9).

102

Figure 8. Map data and dose rate plotting

Figure 9. Interpolated dose map

4.3.3. Walking survey implementation
We collected parameters necessary for walking surveys, and carried out the survey in several
areas.
4.3.4. Manual preparation
We created a manual surveying the walking survey method. Photos and sentences are combinedin this manual for easy understanding.
4.4. Results
4.4.1. Gathering parameters necessary for walking surveys
We conducted a field test of walking surveys, and gathered data for evaluation and analysis(Figure 10). Data were gathered to check the direction characteristics and appropriate
measurement density, as well as to determine correction factors.

Figure 10. View of a walking survey

4.4.1.1. Checking direction characteristics
Shielding from the measurers themselves affects the contribution from the radiation source
depending on the walking direction in walking surveys (Figure 11). Walking surveys were
therefore conducted by changing the walking speed and by walking back and forth so as to straddle
the radiation source and check the effect of direction characteristics.
As a result, while shifts occurred in places where peaks appeared, they fell within a range ofabout 2 meters, and measurements showed that the maximum value of the dose rate was nearly thesame during forward and reverse passes (Figure 12). We also confir med that reducing the walking
103speed caused the peaks of the dose rate distribution to grow sharply (Figures 13 and 14).Judging
from the above result, the impact of direction characteristics on a measured value of a walk survey
was considered small at a con stant walking speed.
3

Direction A (slow)
Direction A (ordinary)dose rate [μSv/h]Direction A (fast)
Direction B (slow)

2

Direction B (ordinary)
Direction B (fast)

1

0
-20

-10

0

10

20

distance from radiation hotspot [m]Figure 11. Measurement of
direction characteristics

Figure 12. Measurements after changing
speed and direction

dose rate [μSv/h]4

survey metervery slow
slow
ordinary
fast

3
2
1
0
-20

-10

0

10

20

distance from radiation hotspot [m]Figure 13. Change in walking speed

Figure 14. Change in measurements due towalking speed

4.4.1.2. Determination of correction factors in a comparison test with survey
metersWe assumed measurements made with a NaI (Tl) scintillation survey meter (TCS -172B) at aheight of 1m to be the most reliable, and the survey meter was calibrated with traceability. We
compared measurements made using a survey meter with those obtained in a walking survey(Figure 15). A comparison was made at several points with differing dose rates. At each point, wefaced north, south, east, and west and made measurements five tim es in each direction to mitigate
direction characteristics. We then took the average value for all directions as the measurement forthat point. We next plotted the measurements of walking surveys against the survey meter todetermine the correction factor.

104

(a)

(b)

Figure 15. Images of measuring(a): Measurement with a survey meter(b): Measurement with a walking survey
Both measurements were made facing four directions.
The results of the comparison are shown in Figure 16(a). There was good linearity between themeasurements of walking surveys and the survey meter below a survey meter measurement of 1
μSv/h, whereas the linearity deteriorated above approximately 1 μSv/h. This phenomenon is due
to count loss caused by excessive radiation incidence on the low -dose CsI detector.
In light of the above results, we changed the detector to a high -dose-rate CsI detector (Figure17) and compared the results obtained using the surve y meter with measurement results of walking
surveys again. The results are shown in Figure 16(b). We confirmed that as a result of changing
the detector, the linearity of walking survey measurements against survey meter measurements is
obtained even in the high dose range.
We also confirmed that the high -dose CsI detector can make better measurements than the low dose rate CsI detector in the high dose range in field tests. This is also confirmed in Figure 18,
which shows the walking survey results having c hanged detectors at the same geographic point.
The maximum indicated value is higher for the high -dose-rate CsI detector than for the low -doserate CsI detector, and the high -dose-rate area represented by red markers appears, indicating thatmeasurements are made without counting loss of radiation.

105y = 1.3287x

0.8

R² = 0.9957
y = 0.9888x

0.6[μSv/h](a)

NaI(Tl) Scintillation Survey meter

1.0

R² = 0.9931
0.4

0.2

0.0
0.0

0.2

0.4

0.6

0.8

1.0

Walking Survey [μSv/h]y = 0.2553x2 + 1.0814x
R² = 0.9963
15[μSv/h](b)

NaI(Tl) Scintillation Survey meter20

y = 1.1285x
10

R² = 0.9984

5

0
0

5

10

15

20

Walking Survey [μSv/h]

Figure 16. Comparison of measurements of the survey meter and walking
survey(a): Chart plotting data below 1 μ Sv/h(b): Chart plotting all data
● Comparison of the measurements of the low -dose-rate CsI detector(caesium-137, 662keV measuring range: 0.001 to 10 μ Sv/h) and NaI survey
meter.
● Comparison of the measurements of the high -dose-rate CsI detector(caesium-137, 662keV measuring range: 0.01 to 100 μ Sv/h) and NaI survey
meter.
Note that the approximate curve is not affected by the self -dose fromthe measurement detector, with the intercept being zero.

Figure 17. High-dose CsI detector (Hamamatsu Photonics C12137)
106

(b)
(a)
Figure 18. Walking surveys having changed the detector(a): Walking survey with the low -dose-rate CsI detector.
The indicated value range is 2.77 to 5.99 μ Sv/h.
(b): Walking survey with the high -dose-rate CsI detector.
The indicated value range is 5.00 to 29.5 μ Sv/h.
According to the above comparisons, we set the correction factors of walking surveys to 1.3
when using the low-dose-rate CsI detector at points with a dose rate less than 1 µSv /h and 1.1
when using the high-dose-rate CsI detector.
4.4.1.3. Confirming variations in measurements
We conducted-fixed point measurements to confirm variations in measurements for ameasurement time of 3 seconds in the low dose rate range. Fixed -point measurements were madewith both the low-dose-rate CsI detector and the high -dose-rate CsI detector.
Results showed that the variation in measurement results was larger for the high -dose-rate CsI
detector at points with a low dose rate (Figure 19). The variation coefficient obtained from
dividing the standard deviation of measurements by the average value was 19.7% for the lowdose-rate CsI detector but 42.7% for the high -dose-rate detector. Error in measurements made withthe low-dose-rate detector was small because of the high counting rate achieved with the large
crystal while error in measurement s made with the high -dose-rate detector was large because of
the small counting rate achieved with the small crystal.
0.12

KURAMA for
low dose rate
KURAMA forhigh dose rate

dose rate[µSv/h]

0.10
0.08
0.06
0.04
0.02
0.00
3

18

33

48

63
time

78

93

108

123

[sec.]

Figure 19. Measured value dispersion check107

On this basis, we decided to use the low-dose-rate CsI detector, which has a small variation at
low dose rates, at geographic points with a dose rate less than 1 µSv/h, and to use the high -doserate CsI detector at geographic points with a dose rate greater than 1 µSv/h.
4.4.2. Conducting walking surveys
With the purpose of studying the operation of walking surveys and acquiring basic data, weconducted walking surveys at places with differing conditions. Examples of such walking surveys
are described below.
4.4.2.1. Walking survey in western Fukushima City
We conducted a walking survey on a trial basis in western Fukushima City. At the center of thisgeographic area is a surface paved with asphalt, with ditches along the edges. There were no
obstructions on the outside of the asphalt surface, leaving the surface wide open and surroundedby grass.
Results of a walking survey conducted at this geographic point are shown in Figure 20. The paved
surface at the center of the range of the walking survey had a low dose rate compared with that of
the surroundings. It is considered that this low dose rate is due to the easy decontamination of the
paved surface and the strong effect of weathering. In addition, the radiation dose in the vicinityof the ditch was higher than that of the surroundings. This is probably because there was an inflow
of radioactive material from the surrounding area.
We conducted a high-density walking survey and tested interpolation with a GIS tool (Figure 21).
Interpolation was conducted with IDW. The interpolated radiation dose rate in the paved area waslow, and the dose rate in the vicinity of the ditch was high.
Paved area

Figure 20. Results of a walking
survey in western Fukushima
City

Figure 21. Results ofinterpolation with IDW

108

4.4.2.2. Walking survey in the periphery of a temporary storage site
We conducted a walking survey in a temporary storage site and its periphery in the Nakadori
region of Fukushima Prefecture (Figure 22). The area inside the red frame in the figure is the
temporary storage site. The dose rate near the temporary storage site was equal to or less than thedose rate in the periphery, and no effect on the outside on the outer side was seen in this temporarystorage site.

Figure 22. Dose map(with the temporarystoragesite

theindicatedbyredframe.)
4.4.2.3. Walking survey in the Hamadori region (outside the evacuation zone)
We conducted a walking survey around rivers in the Hamadori region of Fukushima Prefecture(outside the evacuation zone) ( Figures 23 and 24). There is a paved surface on the left side of the
figure, with the rest of the study area being gravel or grassland. The dose rate was low on the
paved surface and nearly uniform in other areas.

Figure 23. Dose map

Figure 24. IDW interpolation result

4.4.2.4. Walking survey in a difficult -to-return evacuation zone
We conducted a walking survey in a difficult -to-return evacuation zone in Fukushima
Prefecture (Figures 25 and 26). The area where the walking survey was conducted was nearly109

uniform grassland. The dose rate was nearly uniform in the area, with no large de viation
observed.

Figure 26. Results ofinterpolation by IDW

Figure 25. Dose map

4.5. Conclusions
Results were obtained in developing walking surveys by 2015.
In terms of developed equipment, the walking survey system adopted KURAMA, which was
designed by Kyoto University and has a structure suitable for a walking survey. Additionally, toanalyze the obtained data or to work with other monitoring methods, such a s a UAV survey, we
prepared a GIS data processing system. Furthermore, by collecting data for the determination of
direction characteristics and calibration constants, it has become possible to measure the dose rate
in a walking survey.
We conducted walking surveys at several points and confirmed that it is possible to measure theair dose rate and to create a contour map with a GIS processing system.
We published a manual for walking surveys and made the manual available to the general public.
In fiscal 2016, we conducted walking surveys or lent the necessary equipment at the request ofmunicipalities. In recent years, walking surveys have been utilized in the public projects formonitoring of the air dose rates (e.g., Satoyama Restration Model Projec t).

110

5. FIP5： Study of proper treatment of waste containing radioactive material
5.1. Abstract
Using incineration ash (bottom ash and fly ash) containing radio caesium generated in Fukushima
Prefecture, laboratory tests were conducted to investigate radiocaesium elution and the
suppression of radiocaesium elution by acid clay and zeolite. Based on the results, experiments
regarding the suppression of radio caesium elution from fly ash using two different addition
methods were carried out at actual muni cipal waste incineration facilities.
Moreover, each status of the landfill disposal sites was investigated , including the method of
landfilling incineration ash and the concentration of radioactive caesium in leachate. While a study
on landfill disposal sites was included in this project from FY 2018, Fukushima Prefecture hadlaunched the same study on its own before that, so this report also includes the content of thestudy conducted by FY 2017.
5.2. Purpose
When municipal waste containing radioactive caesium scattered by the incident at TEPCO's
Fukushima Daiichi Nuclear Power Station is incinerated, radioactive caesium moves andconcentrates in the incineration ash. Although 10 years have passed since the accident andconcentrations of radioact ive caesium have decreased considerably, ash from the incineration ofmunicipal waste contaminated with radioactive materials is still continuously produced, making
the proper treatment and disposal of this ash a challenge. In particular, landfill sites, which are
the final destination of waste containing radioactive caesium, are required to continue to provide
safe (i.e., non-leaking) storage of radioactive caesium until it decays to an acceptable level.
Therefore, Fukushima Prefecture has decided to compile actual cases on methods to prevent
leakage of radioactive caesium from incineration fly ash (which contains particularly high levelsof radioactive caesium), investigate leakage behavior of radioactive caesium from landfill sites,
assess the safety of individual disposal sites and their management of monitoring after completionof landfill disposal, etc..
5.3. Radiocaesium distribution between bottom ash and fly ash
Incineration of waste generates two types of incineration ash: fly ash generated during theexhaust fumes treatment process and bottom ash discharged from the bottom of the furnace.
Radiocaesium in fly ash has a high concentration and is easily dissolved in water, while
radiocaesium in the bottom ash has a low concentration and is difficult to dissolve in water.
Therefore, two methods to control the distribution of radio caesium in fly ash or bottom ash were
explored for the purpose of separation of radiocaesium; washing or the safe storage of bottom ash
containing radiocaesium.
In addition, to confirm the safety of incinerating the waste filter cloth in the incineration facility,
which was generated during the exchange of bag filters of equipme nt to collect fly ash in theexhaust fumes treatment process, incineration tests of waste filter cloth were conducted, and an111

investigation of the exhaust fumes and incineration ash emitted during the incineration was
conducted.
5.3.1. Investigations
5.3.1.1. Radiocaesium distribution between bottom ash and fly ash
Radiocaesium generally tends to evaporate during incineration and to transfer to fly ash rather
than remaining in bottom ash. The distribution of radiocaesium in bottom ash and fly ash atincineration facilities in Fukushima Prefecture are given in Table 1. Approximately 60% of total
radiocaesium is transferred to fly ash.
Table 1. Radiocaesium distribution between bottom ash (BA) and fly ash (FA) at
MSW incineration facilities in Fukushima Prefecture.

Facilty

Capacity

Dustcollection[t/d]Annualinicineration(2011FY)

Ash generation

Radiocaesium
concentration

Radiocaesium
distribution

BA

BA

BA

FA
[t/y]

[t/y]

FA

[Bq/kg]

FA
[％]

A

105

BF

16,035

2,053

632

12,22049,400

45

55

B

120

BF

28,964

4,019

747

3,910

34,900

38

62

F

80

BF

20,230

2,190

1,076

16,64033,900

50

50

G

100

EP

30,111

2,912

737

3,920

36,300

30

70

H

90

BF

16,948

1,392

681

1,494

6,640

31

69

J

60

BF

10,181

1,342

336

639

4,650

35

65

N

50

BF

837

93

41

3,140

13,110

35

65

P

50

BF

8,906

720

422

2,269

5,690

40

60

Q

150

EP

35,612

4,797

724

7,540

45,500

52

48

R

40

BF

12,401

2,190

262

2,200

17,360

51

49

S

30

BF

4,574

381

86

1,706

12,26038

62Note 1 V alues in this table are not corrected for the amount of water and materials added.
Note 2 incinerators at all facilities are of the stoker furnace.
Note 3 Radiocaesium concentrations were measured in July 2011.
Note 4 Dust collection method, BF:bag filter; EP:electrostatic precipitator

We identified the following five main factors that have the potential to govern the transfer ofradiocaesium: (a) combustion temperature, (b) air ratio, (c) waste composition, (d) addition ofchemicals, and (e) particle size of ash.
Among these factors, (b) air ratio (air volume) affects various system parameters, including theflue gas velocity, which potentially disturbs the combustion balance and affects proper
incineration, (c) waste composition cannot be con trolled, and (e) ash particle size is technicallydifficult to control. We thus focused on the relationships between the migration behavior ofradiocaesium and (a) combustion temperature and (d) addition of chemicals.

1125.3.1.1.1. Effect of combustion tempe rature
Of the 16 municipally owned municipal solid waste incineration facilities in Fukushima
Prefecture, we performed tests in cooperation with 4 incineration Facilities A to D. All facilities
were equipped with stoker furnaces.
We compared the distribution of radiocaesium in bottom ash and fly ash when the temperature at
the incineration chamber outlet was increased (or decreased) 50°C from the normal operating
temperature range during normal operation.
To obtain a combustion chamber outlet temperat ure of 50°C higher or lower than that in normal
operation, we changed the temperature of combustion air supplied to the combustion chamber (i.e.,
primary air) by approximately 50°C from the temperature maintained during normal operation.
The amount of combustion air (i.e., primary air) was not changed which prevented changes in the
production of bottom ash and fly ash due to ash blow up. Other operating conditions, such as thoserelated to the furnace water spray and the amount of secondary air, differ among facilities.
The true combustion temperature (combustion temperature range in the incinerator) could not bemeasured directly. Therefore, we used the combustion chamber outlet temperature measured by
the facility as an index of the combustion temperat ure and evaluated the impact of the chamber
outlet temperature changes on radio caesium migration. At Facility C, however, we inserted athermocouple into the incineration chamber to measure the internal temperature as an index of the
combustion temperature because the automatic control of secondary air flow could not be
disengaged, and changes in the combustion chamber outlet temperature might not correspond toactual changes in the incinerator internal temperature.
The test operation was continued for 1 da y (i.e., 24 h) under the same conditions based on thetime needed to stabilize the combustion state and the long retention time of the bottom ash in thesystem.
We sampled fly ash and flue gas at least 1 h after the establishment of the test conditions.
For bottom ash, owing to the facility -specific retention time inside the incinerator and ash
discharger, we predetermined for each facility a sampling time based on the retention times
estimated in a simple model and a tracer test (where metal cans were thr own into the waste hopper
and their arrival was observed at a planned sampling point).
Figure 1 shows sampling points for bottom ash, fly ash, and exhaust gas, and estimated retention
times of bottom ash inside the system for Facility A. Incinerator ashes was collected every hour,
but the start of bottom ash collection was delayed by two hours from the start of fly ash collection
because the discharge of bottom ash is considered to be two hours later than fly ash due todifferences in discharge routes.

113

Figure 1. Sampling positions of bottom ash, fly ash, and exhaust gas and estimatedresidence times for bottom ash at incinerator Facility A.

The measurements and analysis procedures are shown in Table 2 for the bottom ash, fly ash, andflue gas sampled as described above.
Table 2. Samples and measurement items.

Waste Composition
Bottom Ash

Moisture content, Ash content, Combust content, Material
composition, heating value、elemental analysis（C、H、N、O、
S、Cl）
Radiocaesium concentration(Note 1), ignition loss(Note 2)
elemental analysis（Cs、Na、K、Ca、Mg、Al、Si、P、Fe）

Fly AshRadiocaesium concentration(Note 1), elemental analysis（Cs、Na、K、Ca、Mg、Al、Si、P、Fe）

Flue Gas

Radiocaesium concentration(Note 3), Dioxins(Note 2)

Note 1 :4 samples of bottom ash and fly ash were collected every hour. Four were mixed
and distributed for the analysis. Radiocaesium concentration of 4 samples before
mixing were also subject to NaI gamma ray spectrometer.
Note 2 :Conducted to check that there is no incomplete combustion under low temperature
operation.
Note 3 :Conducted to check that there is not increased radiocaesium under hightemperature operation and operation with radiocaesium evaporation promotoin
agents added.

114

Analytical results for the waste composition are given in Table 3 and constitute the most basic
information about waste. Compositional differences are thought to define the behavior ofradiocaesium in the combustion process.
Table 3. Waste composition analysis.

We did not observe a clear relation between the composition of waste and the area or season inwhich the waste was generated. The waste incinerated at Facilities A and B had calorific valuesof 8,330 to 9,920 kJ/kg, while all values exceed ed 10,000 kJ/kg at Facility C, which had higher
caloric value for waste in summer. Meanwhile, although Facility D received autumn waste at theend of November, it had the lowest calorific value.
5.3.1.1.2. Continuous sampling test
We conducted a tests in order to understand the relations hip between combustion temperatureand radiocaesium distribution during normal furnace operation. Stoker furnace equipped facilities(B and F) had bottom and fly ash sampling every two hours continuously for 5 days. Ash samples
were subject to radiocaesium concentration measurement by NaI spectroscopy.
The first four samples obtained each day were mixed together, divided and distributed for Ge
measurements and an elemental (Cs, Na, K, Ca, Mg, Al, Si, P, and Fe) a nalysis. These data wereused to examine the relationship between the combustion temperature during normal operationand migration behavior (distribution of bottom ash/fly ash) of radio caesium.
Sampling points and times were determined according to the m ethods employed in subsection115

5.3.1.1.1..
5.3.1.1.3. Effects of a radio caesium evaporation accelerator and inhibitor
We examined the effects of adding hydrated lime (Ca(OH) 2 ), which is expected to promote theevaporation of radiocaesium, and bentonite (clay), which is expected to inhibit the evaporation ofradiocaesium.
① Test of hydrated lime (2.4%) and bentonite (2.2%) addition at Facility A② Test of hydrated lime (2.6%, 5.5%) addition at Facility A to determine the reproducibilityof the effect observed in test ① .
③ Test of hydrated lime (2.2%) addition at Facility D to determine whether the results
obtained in tests ① and ② are facility-specific.
④ The materials were sprayed on the surface of each crane of waste thrown into the hopper.
5.3.1.2. Proper treatment of used filter cloths of bag filters
We conducted three test runs at both Facility B using glass -fiber made filter cloths and at Fac ility
E using Tefaire ® filter cloths. In one run, ordinary incineration was performed without used filter
cloths co-incineration (Run-1). In the other two runs, co -incineration of used filter cloths with
MSW was performed, but the used filter cloth throw -in amount and interval differed between Run2 and Run-3 (Table 4). At Facility B, two used filter cloth throw -in ratios were set according to aquestionnaire survey of facilities having with actual experience with co -incineration treatment.
These had a mean value of 0.20% and the maximum value of 0.40%. At Facility E, the throw -inratio was set to 0.03% according to ‘Cleaning Technical Report, No. 8’ issued by the Clean
Authority of Tokyo (2008) and other data. The incinerators at both facilities are st oker-type
incinerators.

116

Table 4. Details of the used bag filter cloth co -incineration test.
Fa c il it y n a me
F ilt e r c lo t h ma te r ia lRun
C o - in c i n e ra t io n ra t io
F ilt e r c lo t h in p u t a mo u n t
I n p u t a mo u n t a n d t i me i n t e r v a l, t ime
continued
U s e d fi lt e r
c lo t h

F lu e ga s
Measure ment
it e mB o tt o mash
F ly a s h

B ( 6 0 t / fu r n a c e ⋅d a y )G l a s s fi b e r
RUN 1
N o r ma loperation

R a d io c a e s iu m

E ( 7 5 t / fu r n a c e ⋅ d a y )Te fa i r e ®

RUN 2
0.2%
6.4 kg/H

RUN 3
0.4%
12.8 kg/H(1 . 5 / 0 . 5 H ) ,6 h

3 / 0 . 5 H, 6
H

RUN 1
N o r ma loperatio
n

RUN 2

RUN 3
0.03%
0.90 kg/H

0 . 5 / 1 H, 6
H○

1 . 5 / 3 H, 6
H○

R a d io c a e s iu m

○

○

○

○

–

○

Hydrogenc h lo r id e

–

○

○

–

○

○

S u lp h u r o x id e

–

○

○

–

○

○

N it ro g e n
o x id e
D io x i n s ( *2 )

–

○

○

–

○

○

–

–

○

–

–

○

F lu o r i n e
c o mp o u n d s

–

–

–

○

○ ( fo u r
t i me s )○ ( fo u r
t i me s )R a d io c a e s iu m
( *1 )

○

○

○

○

○

○

I g n it io n lo s s( *2 )
R a d io c a e s iu m
( *1 )

–

–

○

–

–

○

○

○

○

○

○

○

*1 ) R a d io c a e s iu m s a mp le s w e re c o lle c t e do n c e p e r h o u r fo r N a I me a s u r e me n ts , fo r a
to ta l o f f i v e s a mp le s , fo u r o f w h ic h w e r e
mi x e d in t o o n e s a mp le a n d t h e n d iv id e dfo r G e me a s u r e me n ts .
*2 ) C o n d u c te d in t h e R U N u n d e r t h e mo s t
s e ve r e c o n d it io n s .

F ilt e r c l o t h d i me n s i o n s : φ1 6 4 m m ⋅5 2 5 0 m m ( L) .
T h e ma n u fa c t u r e r ’ s s t a n d a r d v a l u e
w a s u s e d fo r w e i g h t : 2 . 3 8 k g e a c h ,c a lc u l a t e d fr o m a d e n s i t y o f 8 8 0 g / m 2 .

F i l t e r c l o t h d i me n s i o n s : φ 1 4 0 m m ⋅6 0 0 0 m m ( L) .
T h e ma n u fa c t u r e r ’ s s t a n d a r d v a l u e
fo r w e i g h t w a s u s e d : 2 . 0 k g e a c hme a s u re d v a l u e a t t h e fa c i l i t y.

The effects of co-incineration on the migration behavior of radio caesium due to fly ash that
contains radiocaesium adhering to the filter cloth was studied. For used cloths with glass fiber,
combustion is difficult in the established conditions, and for the cloths made of Tefaire, there isan increase in the concentration of fluorine compounds due to the ir combustion. We collected andanalyzed bottom ash, fly ash, and flue gas before and during the test or collected measurements
obtained by the facility. For these items, we then compared the data obtained before inputting thefilter cloth and during the test and surveyed the effects on the migration of radiocaesium. Sampling
points and times were set according to the methods described in subsec tion 5.3.1.1.1..
5.3.2. Results
5.3.2.1. Radiocaesium distribution between bottom ash and fly ash
5.3.2.1.1. Effect of combustion temperature
Data on the migration and distribution of radio caesium are given in Table 5.
Ordinary untouched operation is re garded as a standard test.
The tests were conducted at four facilities, but we were unable to obtain a combustion chamber
outlet temperature that was higher than that of standard operation during high -temperature
operation at Facility C. Additionally, at Facility D, we were unable to obtain a combustion chamber
outlet temperature that was lower than that of standard operation in low -temperature operation.

117

Table 5. Combustion temperature and migration of radio caesium for each facility
and each test.

At Facilities A and B, where high -temperature runs produced high combustion chamber outlet
temperatures, the distribution of radiocaesiumin fly ash increased on the second day of the high -temperature run. We obtained a rise of 2.6% in the distribu tion rates at Facility A and a rise of
0.8% at Facility B per 10°C combustion temperature by linear approximation, excluding dataobtained on the first day ( Figures 2 and 3).

118

Bentonite
Standard 2
Standard 1
High Temp 1(Facility B)

High Temp 2(%)

High Temp 2

Radiocaesium distribution to fly ash

Hydrated Lime 2.4%(%)

Radiocaesium distribution to fly ash(Facility A)

Low Temp 1

Low Temp 2

High Temp 1

Figure 2. Rate of the

Figure 3. Rate of the

distribution of radiocaesium

distribution of radiocaesium toto fly ash versus the

fly ash versus the combustion

combustion chamber outlet

chamber outlet temperaturetemperature (Facility A).

(Facility B).

To examine variation in the temperature and migration status of radio caesium before and after
changing the combustion temperature conditions from standard to high -temperature operation, we
sampled bottom ash and fly ash every 2 h for 2 days at Facility B, and measured by a NaI detector.
In response to the change in operation mode from low -temperature operation to high -temperature
operation, the combustion chamber outlet temperature increased approximately 100°C, from
850°C to 950°C, and the ratio of fly ash/bottom ash radio caesium concentration increased alongwith the increasing temperature (Figure 4).

Figure 4. Combustionchamber outlet temperature andradiocaesium concentration ratio (Facility B).

119

5.3.2.1.2. Continuous sampling test
Figure 5 (Facility B) and 6 (Facility F) show the combustion chamber outlet temperature, NaI detector-based radiocaesium concentration in bottom ash and fly ash, the radio caesium
distribution to fly ash based on NaI measurements, and the radio caesium distribution ratio to fly
ash based on Ge measurements.

Figure 5. Radiocaesium concentrations in bottom ash and fly ash, radio caesium
distribution based on NaI and Ge measurements, and combustion chamber outlet
temperature (dry ash at Facility B).

Figure 6. Radiocaesium concentrations in bottom ash and fly ash, radio caesium
distribution based on NaI and Ge measurements, and combustion chamber outlet
temperature (dry ash at Facility F).
120

It is difficult to detect a clear relationship between the combust ion chamber outlet temperatureand the distribution of radio caesium to fly ash.
As shown in the plots of the temperature against the radio caesium distribution to fly ash basedon NaI measurements (Figures 7 and 8), the increase in the combustion chambe r outlet temperature
at Facility B was accompanied by an increase in the ratio of the radio caesium distribution to fly
ash. Sudden drops in temperature may correspond to the inputs of sewage sludge, and it should be
noted that the waste composition also ch anged substantially. The range of outlet temperatures forthe combustion chamber of Facility F was small, and no clear relationship between theradiocaesium distribution ratio and combustion chamber outlet temperature was observed.

Figure 7. Combustion chamber outlet temperature and radio caesium distribution to
fly ash (Facility B); the radio caesium concentration was measured by NaI.

Figure 8. Combustion chamber outlet temperature and radio caesium distribution to
fly ash (Facility F); radiocaesium concentration was measured by NaI.

Regarding the relationship between basicity and radio caesium distribution, at Facilities F, wedetected positive correlations between the basicity of the waste calculated from the chemicalcomposition of ash sampled during the 5 -day continuous sampling test and the radio caesium
121

distribution to fly ash (Figure 10). However, we found no positive correlations at the Facility B(Figure 9).

Figure 9. Basicity and radiocaesium distribution to fly ash calculated from theash composition (Facility B).

Figure 10. Basicity and radiocaesium distribution to fly ash calculated from theash composition (Facility F).

5.3.2.1.3. Effects of a radiocaesium evaporation accelerator and inhibitor
The addition of hydrated lime Ca(OH) 2 , (subsection 5.3.1.1.3. ① ) at Facility A increased the ratioof radiocaesium distribution to fly ash remarkably (9.3% increase per 1% addition). However, theinhibitory effect of bentonite could not be confirmed (Figure 11).

122

Figure 11. Effect of additives on the radio caesium distribution to fly ash(Facility A).
We conducted additional tests to determine the general effects of hydrated lime; an effect was
confirmed at Facility A, but it was weaker than that observed in the first test. Additionally,
hydrated lime had no effect at Facility D (Figure 12).

Figure 12. Effect of hydrated lime on the radio caesium distribution to fly ash(Facility D).

The higher basicity of incinerated waste of Facility D is expected to accelerate the evaporationof radiocaesium 1 ) . The basicity of the waste, based on the chemical analysis of bottom ash and fly
ash conducted at Facilities A to D, is given in Table 6. The basicity of waste at Facility A waslower than that at other facilities. It is probable that the obvious effect observed at Facility A was123due to the addition of the basicity-increasing material, hydrated lime, to low -basicity waste. In
the case of Facility D, it is possible that the basicity -increasing material was added to waste whosebasicity was already somewhat high, and the hydrated lime thus did not promote the evaporationof radiocaesium.
Table 6. Basicity of waste calculated from the chemical compositions of BA andFA.
Facility
Ash samplingdate(2014)
Hydrated lime
added[%]
CaO/SiO2

A
6/23 6/26--

10/14 10/16 10/17

2.4

0.44 0.55
0.49

7/2

1.03※1(CaO+MgO+Al2O3) 0.81 0.97
1.43※1/SiO2
0.88
Radiocaesium
distribution to
60
61
84
FA[%]

B

-

2.6

5.5

0.65 1.02※2 1.42※2
1.07 1.46※2 1.89※2
76

83

84

7/8

C

D

7/10 7/28 7/29 11/25 11/26

-

-

-

-

0.82 1.11 0.96 0.62
0.95
1.56
68

64

0.75

0.71
1.11

1.33
71

-

0.67

0.77

1.38 1.79 1.58 1.13

68

-

11/29

1.22

1.16
54

2.2
1.42※3
1.89※352

53

Calculation of basisity for days that hydrated lime was added: We used the average of analyzed chemical composition values andadded hydrated lime quantity of 6/24 and 7/2(※1), the analyzed value of 10/14 for 10/16 and 10/17(※2), and the average ofanalyzed value and added hydrated lime quantity of 11/25 and 11/26 for 11/29(※3）.

In this test, strict operating conditions were used that differ from typical op erating conditions,and it was thought that these conditions increased the radio caesium concentration in flue gas. We
therefore conducted measurements of flue gas and dioxins. We did not detect radio caesium in theflue gas. Furthermore, the dioxin concentr ation in the flue gas and ignition loss values of bottom
ash met relevant regulations (Table 7).
Table 7. DXNs concentration in flue gas and ignition loss of bottom ash.

Operating
Facility
Measurement datecondition
B
C

Low-T
Low-T
Low-T
Low-T

2014
2014

DXNs in flue[ng-TEQ/m3N]

IL of BA [%]Measured Criteria Measured Criteria

July 8July 8
Nov. 26
Nov. 27

0.032
0.019
0.00040.00038

5
0.1

5.9
6.0
<0.1
0.2

10
10

5.3.2.2. Proper treatment of used filter cloths of bag filters
The co-incineration of used filter cloth with MSW was confirmed to be safe and feasible under
the proper management of the co -incineration amount.
Based on many measurements, used filter cloth co -incineration did not affect the measurements,
but increased the concentration of radiocaesium in bottom and fly ash (Table 8).
124

Table 8. Radiocaesium concentration in bottom ash and fly ash.

Facility

B

Test RUN No.

RUN 1

Used filter cloths input(pieces)Radiocaesium Used filter
clothsconcentration（Cs-134＋Cs-137） Bottom ash[Bq/kg]Fly ash

-

E

RUN 2

RUN 3

1.5/0.5H 3.0/0.5H

RUN 1
-

RUN 2

RUN 3

0.5/1.0H 1.5/3.0H

600

1,260

318

400

800

266

157

105

2,400

3,260

3,640

1,400

1,210

1,220

An increase was observed at Facility B and no increase was observed at Facility E. The increaseis thought to be caused by a change in the radio caesium concentration in co -incinerated MSW,
rather than the input of used filter cloth. This is supported by tw o pieces of evidence. First, theincrease was higher than the value calculated from the radio caesium concentration of the input
filter cloth. Second, the increased values remained within the range of variation of themeasurements obtained by the facility i n 2015. No radiocaesium was detected in flue gas and noeffects of co-incineration on flue gas were observed. Table 9 prese nts the results for Facility E.
Table 9. Radiocaesium concentration in flue gas during bag filter cloth co incineration tests.
Facility

B

E

Sampling point

Bag Filter outlet

Bag filter outlet

Sampling date(2015)

7/28

RUN no. and used filter cloth input
rate(pieces)

RUN1
-

7/29

7/30

10/26

10/27

10/28

RUN2

RUN3

RUN 1

RUN 2

RUN 3

-

0.5/H

1.5/H

1.5/0.5H 3.0/0.5H

Cs-134

<0.3

<0.3

<0.3

<0.3

<0.3

<0.3

Cs-137

<0.3

<0.3

<0.3

<0.3

<0.3

<0.3

Cs-134

<0.3

<0.3

<0.3

<0.3

<0.3

<0.3

Cs-137

<0.3

<0.3

<0.3

<0.3

<0.3

<0.3

Wet flue gas

3[m N/h]56,00063,90064,60037,60038,50035,300Dry flue gas

344,40054,70052,20026,10027,10025,600

20.8

14.5

19.1

30.2

29.6

27.1

Radiocaesium
concentration in fluegas
3

[Bq/m N]

Filter
Drain

Moisture content
Gas
composition[m N/h]
[%]

CO2

[%]

2.9

2.5

3.2

5.6

6.7

6.3

O2

[%]

17.6

17.9

17.1

14.7

13.5

13.8

CO

[%]

<0.1

<0.1

<0.1

<0.01

<0.01

<0.01

N2

[%]

79.5

79.6

79.7

79.7

79.8

79.9

Regarding concerned fluorine gas when Tefaire cloths were co -incinerated (Facilities B and E),
measured values of HF were less than approximately 1 mg/m 3 N (Table 10).
There were no changes in the ignition loss of bottom ash, harmful acidic substances, and dioxins
in flue gas at either facility. These p arameters are conceivably changed when combustion
125

conditions deteriorate (Table 10).
Table 10. Harmful acidic substances and dioxins in flue gas, and ignition loss ofbottom ash.
FacilityB

RUN No.

Flue gas

RUN2

RUN3

SOx

[m N/h]

3

<5

<5

NOx

[ppm]

140

160

HCl

[mg/m N]

3

<10

<10

HF

[mg/m3N]

-

-

3

-

0.01

[%]

-

5.1

Dioxins[ng-TEQ/m N]

Bottom Ignition
ash
loss

E
Past figure

RUN2

RUN3

<10
(2015)
140～150(2015)
27～32(2015)

<5

<5

150

170

120

150

-

<1.1

<1

-

0.0028-5.1

0.046～0.072(2015)
5.0～8.1(2015)

Past figure<3.5～80(2015)
99～180(2015)<5～310(2015)<1（2015）
0.060～0.099(2015)
1.3～6.2(2015)

5.3.3. Conclusions
It is generally known that radio caesium volatilizes upon its combustion and tends to migrate to
fly ash rather than to bottom ash. Five factors that influence the migration of radio caesium wereclassified, i.e. combustion temperature, air ratio, waste qu ality, chemical addition and ash particle
diameter. Among these factors, the correlation between “combustion temperature and chemical
addition,” which are relatively easy to control and “radiocaesium migration behavior” were
investigated through verification tests at actual facilities. As a result, it was found that it isdifficult to change the combustion temperature in an operating incinerator because maintenanceand management standards stipulating an allowable combustion temperature range have been
established by laws relating to Waste Management and Public Cleaning Act. As for a chemical
addition method, the addition of hydrated lime to incinerated waste somewhat promoted
radiocaesium migration to fly ash at some facilities, but the reproducibility of s uch a phenomenon
was scarce.
At each of the facilities B (filter cloth: glass fiber) and E (filter cloth: Teflon), a normal operation
without the co-combustion of waste filter cloths and municipal waste and another operation withthe co-combustion of radiocaesium-containing waste filter cloths and municipal waste by changing
the input ratio and input time interval of the radio caesium-containing waste filter cloths werecarried out. The results revealed that the co -combustion of bag-filter waste cloths with municipal
waste at the facilities is safe and appropriate as long as the co -combustion ratio is managed
properly.

126

5.4. Radiocaesium elution tests from ashes
Incineration ash generated at a municipal waste incineration facility in Fukushima Prefecture
was collected and elution tests of radio caesium were conducted. At the same time, laboratory
experiments were conducted to test m ethods to reduce the elution rate of radio caesium by using
zeolite and other materials. The effect of radiocaesium on the rate of insolubility and heavy metal
efflux inhibitors was also investigated.
In addition, a zeolite addition test was conducted a t a waste incineration facility actually in use
in Fukushima Prefecture. In two systems (exhaust treatment system and chelate adding system)of an actual municipal waste incineration facility, investigations were carried out on the ability ofzeolite to suppress radioactive caesium elution, the effect on exhaust gas treatment, and the effecton heavy metal insolubilization.
5.4.1. Investigations
5.4.1.1. Radiocaesium elution tests from ashes
5.4.1.1.1. Data acquisition of radio caesium leaching characteristics
We sampled bottom ash, fly ash and limited number of boiler ash from 15 incineration facilities
in Fukushima Prefecture and performed radio caesium leaching tests for a total of 64 samples toacquire radiocaesium leaching data. For some facilities, we sampled and tested summer and winterash to evaluate seasonal changes in radio caesium leaching properties. Leaching tests were
performed in accordance with ’JIS K0058-1, As-is Agitation Test’; each sample was placed in acontainer as is, pure water was added at a volume that was 10 times greater than the amount ofash (L/kg), and the top liquid phase was agitated with a propeller.
5.4.1.1.2. Laboratory radio caesium immobilisation test
As zeolite, bentonite, and sewa ge sludge are expected to reduce radio caesium leaching fromincineration ash, we used these three materials as additives to the sampled incineration ash. The
test procedure simulates the actual fly ash kneading process. We added the materials to bottom
ash, fly ash, and treated fly ash obtained from Facility K at various amount (20% and 5% of dry
ash weight) and added water (30%). The water -supplemented samples were thoroughly mixed andkept at various temperatures (25°C and 80°C) for different periods (o ne week and one month).
Then, each sample was subjected to leaching tests.
5.4.1.2. Tests on radiocaesium elution suppression
5.4.1.2.1. Tactical agitation tests using a germanium semiconductor detector
Using a germanium semiconductor detector, radio caesium concentrations in bottom ash,humidified bottom ash (treated bottom ash), fly ash, and fly ash provided with a heavy metalelution prevention treatment (treated fly ash) sampled from municipal waste incineration facilities
in Fukushima Prefecture were measured. Next, an elution test to investigate the elution propertyof radiocaesium was performed using 2.5 L of ultrapure water for about 250 g of incineration ash,in accordance with JIS K 0058 -1. A radiocaesium elution rate (%) was determined by the127following:[radiocaesium concentration (Bq/kg) in the eluate] x [the weight of ultrapure water used in theelution test (kg)] ÷ [radiocaesium concentration in incineration ash (Bq/kg)] x [the weight ofincineration ash used in as -is agitation test (kg)] x 100.
5.4.1.2.2. A test on radiocaesium elution suppression (long-term as-is agitation
test)
In order to find a method of suppressing radio caesium elution from incineration ash having been
exposed to rain water during its storage or after a landfill (elution -suppressing method), an acidclay was added to an incineration ash by 5% in weight, they were mixed with water until the watercontent reached 30% and then were subjected to a radio caesium measurement using a germanium
semiconductor detector as a long-term as-is agitation test. The durations of agitation were set at
6 hours, 24 hours, 7 days, 14 days, and 30 days. Radio caesium elution rates were determined andthe radiocaesium elution-suppressing effect of an acid clay was investigated by mixing or not
mixing it into the incineration ash.
5.4.1.2.3. A test on radiocaesium elution suppression (MP-AES / ion chromatography
test)
In order to investigate the effect of mixing acid clay into incineration ash on th e metal elution
from the ash, an elution test was carried out using incineration ash mixed with acid clay and one
not mixed with it. Concentrations of elements in the eluates were measured using an MP -AEA
spectroscopic analyzer and an ion chromatography de vice.
5.4.1.3.

Tests

on

radiocaesium

elutionsuppression

inincineration

ash

at

municipal waste incineration facilities
Regarding zeolite, which was found to be effective in the suppression of radio caesium elution as
described in 5.4.1.1.2., zeolite addit ion tests were performed at two systems of an actual municipal
waste incineration facility to verify the feasibility of a radio caesium elution countermeasure using
zeolite at an incineration facility.
5.4.1.3.1. A test during normal operation
This test was performed for three days in total during a normal operation period. Bottom ash,
fly ash and treated fly ash were sampled at 11:00 and 14:00 each day, and tests were performed
to determine radiocaesium concentrations and elution properties.
5.4.1.3.1.1. Germanium semiconductor detector test, a JIS K 0058 -1 elution test
and the Environment Agency’ s Notice No. 13 elution test
Using the methods shown in Table 11, tests were conducted to investigate the radio caesium
concentration of each sample and the elutio n properties of radiocaesium and heavy metals.

128

Table 11. Test Conditions and Others

5.4.1.3.1.2. Repetitive elution tests (JIS K 0058 -1)
In order to investigate the quantities of repetitive elution of radio caesium and heavy metals, theJIS K 0058-1 elution test shown in Table 11 was repeated four times (each sample used for an
elution test was subjected to another elution test by putting it into a new solvent) using bottom
ash and treated fly ash sampled at the same time when the radiocaesium concentration in fly ash
was the highest during a normal operation period. An eluate obtained from each test was examined
for radiocaesium concentration, heavy metal concentrations, pH and EC.
5.4.1.3.1.3. Zeolite addition test in laboratory
To study zeolite addition ratios in zeolite addition tests at actual facilities, zeolite was addedfrom 5 to 20% (in 5% increments) to the fly ash and treated fly ash that that contained the highest
radiocaesium concentrationsampled during a normal operation test period, and then water was
mixed with the fly ash and treated fly ash until their water content reached 30%. The test shownin table 11 was performed on each mixed sample to check the presence or absence of aradiocaesium elution suppression effect and an effect on heavy metals and others.
5.4.1.3.2. Tests on zeolite addition to an exhaust gas treatment agent at actual
facilities
At the municipal waste facilities mentioned in 5.4.1.3.1., exhaust gas treatment using an exhau st
gas treatment agent mixed with zeolite was performed for five consecutive days. During thetreatment period, the treated fly ash was sampled at 14:00 each day. The samples were tested todetermine radiocaesium concentrations and elution property.
5.4.1.3.2.1. Exhaust gas composition analysis tests
To investigate the effect of the blow injection of chemical mixture on exhaust gas, a test was
performed only for one day during the chemical mixture addition test period, using methods
described in the Waste Management Division’s Notification No. 95, Exhibit 3, II and the Ministry129

of the Environment’s 2011 Notification, No. 111.
5.4.1.3.2.2. Germanium semiconductor detector test, JIS K 0058 -1 elution test andthe Environment Agency’ s Notice No. 13 elution te st
To investigate radiocaesium concentrations and the elution properties of radio caesium and heavy
metals in treated fly ash sampled during the chemical mixture addition test period, tests were
performed using the methods shown in Table 11.
5.4.1.3.2.3. Repetitive elution tests (JIS K 0058 -1)
The average of radiocaesium concentrations in the treated fly ash sampled during the chemical
mixture addition test period was calculated. A sample that indicated a radio caesium concentration
closest to the average value was subjected to four JIS K 0058 -1 repetitive elution tests, shown in
Table 11, (a sample having been subjected to an elution test was immersed into a new solvent andthis operation was repeated four times). An eluate obtained from each test was ex amined forradiocaesium concentration, heavy metal concentrations, pH and EC. Tests using artificial
seawater as a solvent were also carried out.
5.4.1.3.3. Tests on zeolite addition to the mixture of fly ash and chelate agent
by kneading at actual facili ties
At the municipal waste incineration facilities mentioned in 5.4.1.3.1., heavy metal elution
suppression treatment in which zeolite was added to a chelate agent kneader for suppressing heavy
metal elution from incineration ash was performed for five co nsecutive days. During the heavy
metal elution suppression treatment period, the treated fly ash was sampled at 14:00 each day andtested to determine radiocaesium concentrations and elution property.
5.4.1.3.3.1. Germanium semiconductor detector test, JI S K 0058-1 elution test andthe Environment Agency’ s Notice No. 13 elution test
Tests were conducted using the method shown in Table 11 to examine the radiocaesium
concentrations and the elution properties of radio caesium and heavy metals in the treated fl y ash
sampled during the mixing addition test period.
5.4.1.3.3.2. Repetitive elution tests (JIS K 0058 -1)
The average of radiocaesium concentrations in the treated fly ash sampled during the mixing
addition test period was calculated. A sample that showed a radio caesium concentration closest to
the average value was subjected to four JIS K 0058 -1 repetitive elution tests (a sample havin g
been subjected to an elution test was immersed into a new solvent, and this operation was repeatedfour times). An eluate obtained from each test was examined for radio caesium concentration,
heavy metal concentrations, pH and EC. Tests using artificial s eawater as a solvent were also
carried out.

130

5.4.2. Results
5.4.2.1. Radiocaesium elution tests from ashes
5.4.2.1.1. Data acquisition of radiocaesium leaching characteristics
We sampled bottom ash and fly ash from 15 MSW incineration facilities in Fuku shima Prefecture
and performed radiocaesium leaching tests using these samples. The test results indicate thatradiocaesium leaching from bottom ash was limited (below 1% to 16%), but leaching from fly ash
was extremely high (35% to 94%), as is generally expected (Tables 12-1, 2, 3, and 4). Please notethat ‘BA’ and ‘FA’ in the tables are the abbreviations of ‘bottom ash’ and ‘fly ash’ respectively.
Table 12-1. Radiocaesium leaching test results (1).

Table 12-2. Radiocaesium leaching test results (2).

Table 12-3. Radiocaesium leaching test results (3).

131

Table 12-4. Radiocaesium leaching test results (4).

In contrast to most Facilities, for ash from Facilities D and M, we should note that theradiocaesium leaching rate was low for fly ash but high for bottom ash. In addition, theradiocaesium concentration in incinerated ash may differ greatly among facilities. We saw no clear
seasonal trends in the radiocaesium leaching rates when comparing summer and win ter (Figures
13 and 14).

Figure 13. Facility-by-facility

Figure 14. Facility-by-facility

radiocaesium concentration inradiocaesium leaching rate fromsummer and winter samples.

summer and winter incineration
ash.

In Figures 13 and 14, fly ash refers to crude ash captured by a bag filter not yet treated bychelating agent addition or other methods. Treated fly ash is described as FA -t. If possible, we
also sampled and measured boiler ash whose generation is small and is indicated as “BoA”.
Radiocaesium concentration of BoA is closer to FA and radio caesium leaching rate shows anintermediate value between BA and FA.
5.4.2.1.2. Laboratory radio caesium immobilisation test
Table 13 and Figure 15 show relationships between test specimen conditions (ash type, additive
material type, addition rate, curing temperature and curing time) and the radio caesium leaching
rate.
132

Table 13. Laboratory radiocaesium immobilisation test.

Black numerals indicate elution rates calculated from caesium-134 and caesium-137, and red andblue numerals indicate elution rates calculated from caesium-137 (Red indicates the mostimmobilized case).

Figure 15. Relationship between leaching rate and additive, rate of addition,
cure temperature and cure duration (Fly ash).

133

A very obvious reduction of radio caesium leaching rate was observed for fly ash. The additionof 20% zeolite and 1 week of curing at 25°C res ulted in the greatest reduction in the radio caesium
leaching rate, from 79.1% to less than 5% .
The materials added to fly ash showed leaching rate reduction in decreasing order as follows:zeolite, bentonite and sewage sludge. Both zeolite and bentonite showed 1/3 lower leaching rates
for the addition of 20% than for 5%. Zeolite was not effective at a higher cure temperature (80°C)
compared with bentonite. For both zeolite and bentonite, longer (one month) curing duration had
slightly adverse effects on t he leaching rate reduction
5.4.2.2. Radiocaesium elution suppression test
5.4.2.2.1. Germanium semiconductor detector and as -is agitation tests
Table 14 summarizes test results regarding solid phase radio caesium concentrations, liquid phaseradiocaesium concentrations (as-is agitation test), radio caesium elution rates and others.
The results of radiocaesium concentrations in solid phase sample showed a tendency in whichradiocaesium concentrations were higher in fly ash and treated fly ash than in the bo ttom ash andtreated bottom ash.

Table 14. Results of germanium semiconductor detector and as -is agitation tests
Regarding solid phase samples in the same facility, radio caesium concentrations were lower intreated fly ash than in fly ash. This is probably because of the effect of water added during chelate134agent treatment to suppress heavy metal elution from fly ash. Similarly to the test results of thesolid phase samples, the test results of radiocaesium concentrations in liquid phase samples
suggested that radiocaesium concentrations tend to be higher in fly ash and treated fly ash than inbottom ash and treated bottom ash. The comparison of radio caesium concentrations in bottom ash
and treated bottom ash indicated a tendency in which the radio caesium concentrations in treatedbottom ash were lower in general, whereas the comparison of those in fly ash and treated fly ash
did not show a similar tendency. The results of calculat ing radiocaesium elution rates indicated atendency in which those of fly ash and treated fly ash were generally higher than those of bottom
ash and treated bottom ash.
5.4.2.2.2. A test on radiocaesium elution suppression (long-term as-is agitation
test)
Figure 16 summarizes the results (radio caesium elution rates) of radiocaesium elution
suppression tests by mixing an acid clay into treated fly ash by 5% in weight at facilities 1, 3, 4,
5, 6 and 7.
These results have confirmed that the mixture of an acid clay into any treated fly ash by 5% inweight suppresses radio caesium elution rate to 30% or lower, in other words, an acid clay iseffective in the suppression of radio caesium elution. This is probably because a clay mineral,
which is the major component of a clay, captures radiocaesium into its structure and suppresses
its elution. The maximum duration of these tests were 30 days, during which no radio caesium
elution rate exceeded 30%.

Figure 16. Results of radiocaesium elution suppression tests (radio caesium elution
rates)

135

5.4.2.2.3. Radiocaesium elution suppression tests (MP-AES / ion chromatography
test)
Table 15 summarizes the concentrations of metals and others in the eluate. As a result of mixing
an acid clay into treated fly ash by 5% in weight and agitating the mixture for six hours or 30
days, it was found that the long-term agitation did not result in significant differences in theconcentrations of metals and others. As a result of comparing 30 -day agitation without mixing anacid clay and 30-day agitation after mixing an acid clay, some cases were obs erved in which acidclay mixture resulted in low concentrations, but generally the obtained concentrations showed asimilar tendency and suggested that the mixing of an acid clay does not block the effect of chelate.
Table 15. Results of radiocaesium elution suppression test
(concentrations of metals and others in eluates) * mg/L **g/L

136

5.4.2.3.

Tests

on

radiocaesium

elutionsuppression

inincineration

ash

at

municipal waste incineration facilities
5.4.2.3.1. Tests during a normal operation
5.4.2.3.1.1. Germanium semiconductor detector test, JIS K 0058 -1 elution test andthe Environment Agency’ s Notice No. 13 elution test

Figure 17. Daily fluctuations of radiocaesium concentrations in bottom ash(normal operation)
Figures 17 to 19 show the daily fluctuations of radio caesium concentrations (contained or
elution radiocaesium) and elution rates in the bottom ash, fl y ash and treated fly ash sampled innormal operation tests. These results indicate a tendency in which fly ash and treated fly ash rather
than bottom ash showed higher radio caesium contents, elution quantities and elution rates.
Radiocaesium contents were 200 to 280 Bq/kg (248 Bq/kg on average) for bottom ash, 2,300 to
5,200 Bq/kg (3,517 Bq/kg on average) for fly ash, and 1,500 to 2,000 Bq/kg (1,650 Bq/kg on
average) for treated fly ash. The quantities of radio caesium elution were 0.3 to 0.8 Bq/L (0.6 Bq/L
on average) for bottom ash, 150 to 360 Bq/L (240 Bq/L on average) for fly ash, and 97 to 160
Bq/L (121 Bq/L on average) for treated fly ash.
Radiocaesium elution rates were 1.2 to 3.3% (2.5% on average) for bottom ash, 64.3 to 73.9%(68.2% on average) for fly ash, and 64.7 to 81.3% (73.0% on average) for treated fly ash, andtherefore the results of the Environment Agency ’s Notice No. 13 elution test generally satisfied
the basic requirements for heavy metals and others.

137

Figure 18. Daily fluctuations of radiocae sium concentrations in fly ash (normal
operation)

Figure 19. Daily fluctuations of radiocae sium concentrations in chelated fly ash(normal operation)
5.4.2.3.1.2. Repetitive elution tests (JIS K 0058 -1)
Table 16 (bottom ash) and Table 17 (treated fly ash) show the results of repetitive elution tests.
This time, samples taken in the afternoon (14:00) of the first day were used. Radio caesium elution
property indicated by each sample and also the results of the repetitive elut ion tests showed atendency in which radiocaesium elution rates were higher in the case of treated fly ash than bottom
ash. The cumulative rate of radio caesium elution from bottom ash was 3.2% and that from treated
fly ash was 81.9% in the four tests. The samples of the first test showed the highest amount andrate of radiocaesium elution, which gradually decreased as the number of tests increased.

138

Table 16. Results of repetitive elution tests using bottom ash (normal operation)

Table 17. Radiocaesium concentration in flue gas during bag filter cloth co incineration tests

The values of EC also tended to decrease as the number of elution tests increased. Results
regarding heavy metals and others did not show any anomalous value and suggested a trend inwhich their values decreased as the number of elution tests increased similarly to the EC results.
From the results of the test described in 5.4.2.3.1.1. and the repetitive elution tests, it was foundthat the radiocaesium concentrations (of contained or eluted radiocaesium) in treated fly ash andthe rates of radiocaesium elution from it were higher compared with bottom ash . The suppressionof radiocaesium elution by means of chelate agent treatment is difficult to achieve, as the elution
rate was high even before the earthquake and FDNPP accident. Therefore, it is particularly
important to study the methods of suppressing radio caesium elution from the treated fly ash inmunicipal waste incineration ash.
5.4.2.3.1.3. Zeolite addition test in labo ratory
In order to investigate the presence or absence of a zeolite addition effect on heavy metals andothers in the test of adding zeolite to fly ash, zeolite was added by different amount (5%, 10%,15%, 20%) to the treated fly ash (chelate agent addit ion: 2% across the board) before the test.
139

Tables 18 (fly ash) and 19 (treated fly ash) show test results.
Table 18. Results of adding zeolite to fly ash in laboratory

Table 19. Results of adding zeolite to chelated ash in laboratory

The comparison of the test results indicated that the addition of zeolite to fly ash and treated fly
ash suppresses radiocaesium elution. A tendency in which an increase in zeolite addition increaseda radiocaesium elution suppression effect was also obser ved. The test results concerning heavy
metal elution indicated that the addition of zeolite does not block the effect of chelate agent.
In chemical mixture addition and mixing addition tests at actual facilities, a goal of suppressing
the total elution of caesium 134 and 137 from the finally generated treated ash to 10 Bq/L was set,
and the test results revealed that zeolite must be added by at least 15% with each method to achieve
the goal. Therefore, while taking into account the results of daily radio caesium concentration
fluctuations, each addition test at actual facilities was performed by mixing (kneading) zeolite
and the chemical mixture so that zeolite is added by about 20%.
5.4.2.3.2. Tests on zeolite addition to an exhaust gas treatment agent at actual
facilities
5.4.2.3.2.1. Exhaust gas composition analysis tests
Table 20 shows the results of exhaust gas composition analysis tests. A comparison with theresults obtained during normal operation revealed that the injection of a chemical mixture140

(containing zeolite) did not result in any anomalous values of the basic items, with the standard
values satisfied.
Table 20. Results of analyzing exhaust gas Composition

5.4.2.3.2.2. Germanium semiconductor detector test, JIS K 0058 -1 elution test andthe Environment Agency’ s Notice No. 13 elution test
Table 21 shows the concentrations of radio caesium, heavy metals and others in sampled treated
fly ash. Figure 20 shows the daily fluctuations of radio caesium concentrations (of contained oreluted radiocaesium) and the summarized radio caesium elution rates based on the results of Table
21. First, radiocaesium contents were 2,200 to 4,100 Bq/kg (2, 800 Bq/kg on average), thequantities of radiocaesium elution were 8 to 16 Bq/L (11 Bq/L on average) and radi ocaesium
elution rates were 3.1 to 5.5% (4.1% on average).
Table 21. Results regarding chelated fly ash (blow injection)

141

Figure 20. Daily fluctuations of chelated fly ash concentrations (after blow
injection)
The comparison of each average value of radio caesium in treated ash obtained from normal
operation tests and each average value of radio caesium obtained from chemical mixture addition
tests performed this time indicated that the injection of zeolite signif icantly reduced quantities ofradiocaesium elution (normal operation: 121 Bq/L → after chemical mixture addition: 11 Bq/L)
and radiocaesium elution rate (normal operation: 73.0% → after chemical mixture addition: 4.1%).
The results of the Environment Agenc y’s Notice No. 13 elution test indicated that, as with theresults of zeolite addition test in laboratory, the blow injection of the mixture of hydrated limeand zeolite at an actual facility also did not block the effect of a chelate agent.
5.4.2.3.2.3. Repetitive elution tests (JIS K 0058 -1)
Tables 22 (solvent: ultrapure water) and 23 (solvent: artificial seawater) show the results ofrepetitive elution tests. This time, treated fly ash sampled on the third day, whose radio caesium
concentration was clo sest to the average value of treated fly ash sampled during chemical mixture
addition test period, was used.

142

Table 22. Results of repetitive elution tests on chelated fly ash (solvent:ultrapure water)

Table 23. Results of repetitive elution tests on th e elution of chelated fly ash(solvent: artificial seawater)With regard to radiocaesium elution properties, when four tests were performed using ultrapure
water as a solvent, 14% of radio caesium eluted in total. When this was compared with the resultsof treated fly ash not added with zeolite shown in Table 17 , zeolite was found to significantly
suppress radiocaesium elution (total elution rate of the four-time tests: 81.9% → four-time totalelution rate after chemical mixture addition: 14%).
However, when artificial seawater was used as a solvent, the total radiocaesium elution rateincreased (total elution rate using ultrapure water 4 times: 14% → artificial seawater 4 times:
56.1%). It was found that regardless of the use of the either solve nt, treated fly ash added withzeolite showed a certain radio caesium elution suppression effect compared with not adding zeolite
to treated fly ash. The heavy metal elution when ultrapure water or artificial seawater was usedalso did not result in any anomalous values.

1435.4.2.3.3. Tests regarding zeolite addition to the mixture of fly ash and chelate
agent (mixture using a kneader) at actual facilities
5.4.2.3.3.1. Germanium semiconductor detector test, JIS K 0058 -1 elution test andthe Environment Agency’ s Notice No. 13 elution test
Table 24 shows the results of the concentrations of radio caesium, heavy metals and others insampled treated fly ash. Figure 21 shows the daily fluctuations of radio caesium concentrations(contained and eluted radiocaesium) and radiocaesium elution rates based on the results of Table
24. First, radiocaesium contents were 1,200 to 1,400 Bq/kg (1,280 Bq/kg on average), quantities
of radiocaesium elution were 6 to 11 Bq/L (8 Bq/L on average) and radio caesium elution rates
were 4.6 to 7.9% (5.9% on average).
The comparison of radio caesium average values in treated fly ash sampled in chemical mixture
addition tests and mixing addition tests indicated that the quantities of radio caesium elution weresimilar in both cases (11 B q/L for chemical mixture addition, 8 Bq/L for mixing addition, and 121
Bq/L for normal operation) and radio caesium elution rates (4.1% for chemical mixture addition,
5.9% for mixing addition, and 73% for normal operation). Thus, it was concluded that, rega rdlessof zeolite addition method (the blow injection or mixing of zeolite), its addition itself has theeffect of suppressing the elution of radio caesium. The results of the Environment Agency’s NoticeNo. 13 elution tests indicate that similar to the res ults obtained from zeolite addition tests andchemical mixture addition tests in the laboratory, the simultaneous mixing of fly ash, a chelate
agent and zeolite at actual facilities did not block the effect of the chelate agent.
Table 24. Results regarding chelated fly ash (mixed with zeolite)

144

Figure 21. Daily fluctuation of chelated fly ash (mixed with zeolite)
5.4.2.3.3.2. Repetitive elution tests (JIS K 0058 -1)
Tables 25 (solvent: ultrapure water) and 26 (solvent: artificial seawater) show the results ofrepetitive elution tests. This time, treated fly ash sampled on the fourth day of the zeolite -mixing
test period, whose radio caesium concentration was closest to the average value, was used.
Table 25. Results of repetitive elution tests on elution from chelated fly ash(ultrapure water)

145

Table 26. Results of repetitive elution tests on elution from chelated fly ash(artificial seawater)

First, regarding radiocaesium elution properties, when four tests were carried out using ultrapure
water as a solvent, radiocaesium was eluted by 10.3% in total. The results (81.9% radio caesium
elution in total in four tests during normal operation → 14% radiocaesium elution in total in four
tests with the addition of chemical mixture, and 10.3% elution in total in four tests using a mixing
method) were broadly similar to the results of treated fly ash sampled in the chemical mixture
addition tests shown in Table 22.
Secondly, when four tests were carried out using artificial seawater as a solvent, similar results
were obtained (56.1% elution in total for artificial seawater added with chemical mixture and43.1% elution in total for artificial seawater mixed with chemical mixture). Results regarding
heavy metal elution also did not show any anomalous value regardless of whether ultrapure wateror artificial seawater was used as a solvent.
Given the effect of zeolite in suppressing radio caesium elution shown in the zeolite mixing
addition tests and the results of laboratory tests on zeolite addition to treated fly ash, the addition
and mixing of zeolite into the treated fly ash before the repacking of ash (whose treatment isdifficult because of its high radio caesium concentration) to a new container, seems to be one ofeffective means of enhancing safety.
While both the zeolite addition methods (the method using the chemical mixture and the zeolite
mixing method) were found effective in suppressing radio caesium elution, when it comes to theburial of ash at a landfill disposal site, the excessive addition of zeolite to the ash may increase
the total landfill volume, so the addition of zeolite by a maximum of 20% of total volume at a
maximum is deemed appropriate.
In applying a zeolite addition method, either by using chemical mixture or by the mixing additionof zeolite, the modification of the facility may be necessary.
In the case of the chemical mixture addition method, an existing hydrated lime silo can b e used
and all of the hydrated lime needs can be replaced with the chemical mixture for radio caesium
elution suppression. However, unlike the blow addition of hydrated lime alone during a periodical
146

inspection, this method may cause pipe abrasion or may clog the bag filter, so careful measuresin details may have to be taken.
In the case of adopting a mixing addition method, a silo equipped with a chelate agent kneadingmachine and a mechanism capable of adding zeolite may need to be newly built, and in such acase, periodical inspections may be needed to carefully check the abrasion of such a machine.
Therefore, an optimal addition method and quantity of zeolite should be selected according to thecharacteristics of disposal facility to ensure appli cability to it.
5.4.3. Conclusions
Radiocaesium elution tests were conducted for fly ash and bottom ash (64 samples in total) at 15
facilities in Fukushima Prefecture to obtain caesium elution data. At facility K, zeolite or bentonite,both of which are expected to be effective in caesium elution suppression, was added to andkneaded with incineration ash and then a radio caesium elution test was performed. The results
showed the excellent effects of zeolite and bentonite in the suppression of radio caesium elution
from the fly ash, and the effect of zeolite was particularly remarkable.
As a result of testing radiocaesium elution from incineration ash (bottom ash, treated bottom ash,
fly ash and treated fly ash), which seems to be the cause of radio caesium detected from leachate(seeping water) at the landfill disposal sites, radio caesium concentrations in and radiocaesium
elution from the fly ash (including treated fly ash) were higher compared with bottom ash(including treated bottom ash) at each site. When an acid clay was added to and mixed with treated
fly ash having a high radiocaesium elution property, the radiocaesium elution decreased and theacid clay did not block the heavy metal elution prevention effect of chelate.
Tests were performed at actual facilities in which fly ash was added with zeolite, whoseradiocaesium elution suppression effect had been recognized in the final report of the previous
project. The results of the tests confirmed that both the methods of mixing zeolite into a blow -in
chemical such as hydrated lime and the method of adding zeolite immediately before adding andmixing a chelate agent significantly suppress radio caesium elution and does not block the heavy
metal elution prevention effect of the chelate agent. Based on these r esults combined withlaboratory results, these methods are effective in suppressing radio caesium elution not only for
fly ash to be generated at incineration facilities in the future but also for incineration ash
temporarily stored at present. However, the application of these methods to actual disposal
facilities requires the consideration of the characteristics of each incineration facility and landfill
disposal site, including consideration of an increase in the amount of landfill disposal due tozeolite addition as well as facility structure and capacity.
5.5. Situations of landfill and radio caesium elution
The relationship between the landfill status of incineration ash and the concentration ofradiocaesium in leachate was investigated on the waste landfill sites in Fukushima Prefecture
where incinerated waste ash was landfilled after the nuclear power plant accident. As a result,periodic water sampling of leachate at a repository where radio caesium was detected in leachate147

was conducted, and the concentration of radio caesium in the leachate and the relationship between
various elements in the leachate and the status of radio caesium leaching were investigated.
5.5.1. Investigations
5.5.1.1. Situations of landfill and radiocaesium elution
5.5.1.1.1. FY 2015
The investigations regarding the landfill situation of incineration ash (bottom ash and fly ash)were conducted at seven landfill disposal sites in Fukushima Prefecture. From January until March
2016, leachate (seeping water), discharged water, water -treated sludge and nearby undergroundwater were sampled once a month at the sites. Then their radio caesium concentrations were
measured to investigate a correlation between landfill situation and radio caesium elution. In
addition, radiocaesium concentrations in leachate and discharged water were compared to checkthe radiocaesium treatment situations at leachate treatment facilities. The situations ofincineration ash landfill at the seven landfill disposal sites are shown in Table 27. Their
incineration ash landfill situations fell under the following four types: “landfill in the same way
as before the accident, ” “landfill of only fly ash without contact with rainwater, ” “landfill of only
bottom ash,” and “no landfill of incineration ash. ” Landfill disposal sites D and E prevent contact
between fly ash and rainwater by burying fly ash in sandbags.
Table 27. Situations of the landfill of incineration ash

5.5.1.1.2. FY 2016
In November and February, leachate (seeping water), discharged water, water -treated sludge, andnearby underground water were sampled from six landfill disposal sites in total (Table 28, namely
four landfill disposal sites C, E, F and G among seven landfill disposal sites surveyed in FY 2015,
landfill disposal site H where incineration ash w as buried in the same method used before theaccident, and landfill disposal site I where only bottom ash was buried), and their radio caesium
was analyzed.

148

Table 28. The list of landfill disposal sites

5.5.1.2. Correlation between the annual elution situation of radio caesium andother elements
In four landfills (A, B, D, and H) from FY2017 to FY2021 and in five landfills including landfill
J from FY2019, leachate, effluent, water treatment sludge and surrounding groundwater were
sampled and radiocaesium concentrations were measured. Water-treated sludge was sampled only
in FY 2017. Among the five landfill disposal sites, four landfill disposal sites A, B, H and J wereburying fly ash in the same methods they used before the nuclear power station accident, andlandfill disposal site D was burying fly ash after putting it in large sandbags. However, during acertain period immediately after the accident, site D buried part of fly ash without putting it inlarge sandbags (Table 29). In FY 2017, concentrations of elements and others shown in Table 3 0in addition to radiocaesium were measured. Furthermore, with regard to the two landfill sites B
and J, an interview was conducted with two landfill site managers on self -measured data ofradiocaesium concentrations in leachate since FY2011.
Table 29. Situations of incineration ash landfill at five disposal sites
Disp osa lDisp osa lDisp osa lDisp osa lDisp osa l

Sit e A

Sit e BSit e D

Sit e HSit e J

Bottom Ash

○

○

○

○

○

Fly Ash

○

○

△

○

○

○ : Landfi llin g is d on e in the sam e wa y as b efore th e accid ent.
△ : Landfi llin g is c onducted so a s not t o c ontact rain wat er.

Table 30. Analyzed elements and others
Elements to be analyzed
sodium,magnesium,rubidium,barium,sulfur,potassium,

antimony,nickel,calcium,cobalt,molybdenum, selenium, caesium, strontium, chloride ion,
nitrous acid, nitric acid149

5.5.2. Results
5.5.2.1. Situations of landfill and radiocaesium elution
Table 31 shows radiocaesium analysis results in FY 2015. Radio caesium was detected in leachate(seeping water) and discharged water from disposal sites A and B, where incineration ash wasburied, and from disposal site D, where fly ash was buried without contact with rainwater. On theother hand, radiocaesium in leachate and discharged water was below the lower detection limit(about 1 Bq/L) for disposal site C, where no incineration ash was buried, disposal site E, where
incineration ash was buried by preventing its contact with rainwater, and disposal sites F and G,
where only bottom ash was buried. None of these disposal sites exceeded the lower detection limit(about 1 Bq/L) in terms of radio caesium concentration in nearby underground water.
Table 31. Results of analyzing radiocaesium in leachate and others in FY 2015
Units: Bq/L for leachate and discharged water, Bq/kg for sludge
Lower detection limit: 1 Bq/L or Bq/kg

Table 32 shows radiocaesium analysis results in FY 2016. Radio caesium was detected in leachate(seeping water) and discharged water from the disposal site H only, where fly ash had been buried
as it is. Radiocaesium concentrations in underground water at all the landfill disposal sites shownin Table 32 were below the lower detection limit (0.1 Bq/L).
Table 32. Results of analyzing radiocaesium in leachate and others in FY 2016
Units: Bq/L for leachate and discharged water, Bq/kg for sludge
Lower detection limit: 1 Bq/L or Bq/kg

Based on the results in FYs 2015 and 2016, it was likely that radio caesium was detected inleachate and discharged water only at landfill disposal sites having buried radio caesiumcontaining fly ash without preventing its contact with rainwater. Regarding disposal site D, whereradiocaesium was detected in leachate although the site had buried fly ash while preventing its
contact with rainwater, a detailed on -site hearing concerning the landfill situation revealed that apart of the fly ash had been buried without a rainwater contact prevention measure during a period
immediately after the Fukushima accident, namely from the period of reconstructing theincineration facility until the Ministry of the Environment ’s notice ordering the halt of150

incineration ash burial. It is likely that radio caesium continuously eluted from the incin eration fly
ash in question and leached from the disposal site D through discharged water.

5.5.2.2. Correlation between the annual elution situation of radio caesium andother elements
Figures 22 through 26 show concentration of radiocaesium in leachate that have been measured
so far, as well as that in leachate measured voluntarily at B and J disposal sites by each disposal
site.
5.5.2.2.1. Disposal site A
The maximum concentration of radio caesium in the leachate of disposal site A was about 5 Bq/L.
No seasonal trend was observed in leaching conditions, and radio caesium concentrations aregradually decreasing. Because radio caesium concentrations in landfill waste, especially inincineration ash, are also low, that in leachate is also e xpected to be less than the detection limit.

Figure 22. Radiocaesium concentrations in leachate at disposal site A
5.5.2.2.2. Disposal site B
The maximum concentration of radio caesium in the leachate from the disposal site B was about
15 Bq/L. No seasonal trend was observed in changes of radio caesium concentrations in theleachate. Radiocaesium concentrations increased from 2011 to March 2015 and gradually
decreased until January 2018, but they began to increase again, peaking in October 201 9 and began
to decrease again. It is thought that the construction work to raise the height of the disposal site
underway at that time may have had an impact on the results.

151

Figure 23. Radiocaesium concentrations in leachate at disposal site B
5.5.2.2.3. Disposal site D
The highest radiocaesium concentration in leachate at disposal site D was about 3 Bq/L. The
concentrations were generally low, often below the lower detection limit, thus a seasonality was
not confirmed. This is thought to be bec ause the fly ash was placed in large sandbags and landfilled,
preventing them from coming into contact with water.

Figure 24. Radiocaesium concentrations in leachate at disposal site D
5.5.2.2.4. Disposal site H
The maximum concentration of radio caesium in the leachate from disposal site H
was about 8 Bq/L. Although there were some increases and decreases in radiocaesium
concentrations, no seasonal trend was observed. The concentration of radio caesium in theincinerated fly ash that had been l andfilled was similar to that of B disposal site, but since theconcentration of radioactive caesium in leachate was low, it is necessary to compare the structureof the disposal site and the caesium adsorption capacity of the soil lining material with tho se of152

disposal site B to understand the differences .

Figure 25. Radiocaesium concentrations in leachate at disposal site H
5.5.2.2.5. Disposal site J
The maximum concentration of radio caesium in the leachate from disposal site J was about 11
Bq/L. As of 2018, the concentration of radio caesium in the leachate was the second highest
following disposal site B. It was expected to maintain a concentration of about 5 Bq/L, but theconcentration of radiocaesium has decreased since the final covering of the soil in July 2019. It
is thought that the cause may be the reduction in volume of infiltration water due to the final soil
cover, and so continued investigation and research on the cause are necessary.

Figure 26. Radiocaesium concentrations in leachate at disposal site J
Table 33 shows the results of analyzing elements in leachate at landfill disposal sites in FY 2017,
namely radiocaesium and chloride ion concentrations. A possibility was suggested that the higher
the chloride ion concentration, the higher the radio caesium concentration becomes. A correlation
diagram (Figure 27) was developed by plotting radio caesium concentrations on the vertical axis
153

and chloride ion concentrations on the horizontal axis. The diagram indicated a positive
correlation between them.
Table 33. Radiocaesium and chloride ion concentrations

Figure 27. Correlation between radiocaesium and chloride ion concentrations
5.5.3. Conclusions
The surveys conducted this time have confirmed that the burial of fly ash at landfill disposalsites without elution -preventing measures such as water shielding results in the elution ofradiocaesium. Regarding elution situations at the disposal sites, it is presumed that neither
seasonality is common to them nor seasonality at each of them is present. Moreover, a positive
correlation was observed between radio caesium concentration and chloride ion co ncentrationsuggested a possibility that chloride ions in incineration ash are affecting radio caesium elution.

154

It is thought that the concentration of radio caesium in the leachate can be reduced by the structureof the disposal site, the soil cover and t he condition of the soil cover, and so it is necessary tokeep on investigating this topic moving forward.

5.6. Radiation safety assessment using landfill assessment tool
As stated earlier, municipal waste landfills in the Fukushima Prefecture have accepted wastes
containing radioactive caesium since the Fukushima Daiichi Nuclear Power Plant Accident. Even
though the concentration of the radioactive caesium is below the governmental limit (8000 Bq/kg),
the Prefecture as well as the citizens, had certain concerns on the long -term safety of the disposal.
The Prefecture therefore started to develop its own safety assessment of these municipal landfills.
IAEA has developed a landfill clearance tool which supports the assessment of safety by
calculating the radionuclide concentrations in materials that can safely be disposed of in a landfill.
The clearance tool implements a methodology for derivation of specific clearance levels ( Bq/g)
for disposal of different contaminated materials in different types of landfills. The methodology
includes definition of exposure scenarios, assessment models and required input data for themodels.
For the current project, the Prefecture, with the support of the IAEA, modified the IAEA
clearance tool into an assessment tool for use in this safety assessment, that reflects the situationin Fukushima Prefecture. The modification included the use of scenarios that are representativeof the situation and environment in Fukushima Prefecture, and parameters measured at, or suitable
for, the actual disposal site.
The assessment model was calibrated using measured radio caesium concentrations in the seepage(leachate) water from one of the landfills (landfil l B). Landfill B was selected because this site
has long-term data on radiocaesium concentrations in both waste and seepage water. Deterministic
and probabilistic estimates of the radiation doses that the residents could potentially receive were
calculated, and compared with the relevant dose criteria.
5.6.1. Safety assessment approach
The safety assessment approach adopted in this study was based on the IAEA recommendations
for development of a safety case and safety assessment for disposal of radioactive waste (IAEA
2012) 1 ) . It consists of the following main steps:(1)

Assessment context(2)

System description(3)

Description of scenarios(4)

Description of the models(5)

Dose assessment and analysis of compliance

These different steps are described in the sections below.
5.6.1.1. Assessment context
155

5.6.1.1.1. Purpose and scope
For landfills that accept waste containing radio caesium, a reference level of 8,000 Bq/kg has
been established under the "Assessment of the Effects of Radioactive Substances o n the Treatment
and Disposal of Disaster Waste in the Hamadori and Nakadori Areas of Fukushima Prefecture(excluding evacuation zones and planned evacuation zones)" conducted by the JAEA. However,the safety assessment by JAEA was conducted for an inert wa ste disposal site and did not consider
the leaching of radiocaesium from the waste. In fact, the leachability of radio caesium in fly ash
was found to be high, and waste -related guidelines have started to require fly ash to be buried to
avoid contact with water. Nevertheless, there can be situations where radio caesium is leached(including from the properly buried fly ash) by rainwater in the actual landfills. Therefore,
Fukushima Prefecture has started to develop, using the modified IAEA clearance tool a sa fety
assessment of the municipal landfills in the Prefecture considering the leaching and elution ofradiocaesium from the waste.
The purpose of the safety assessment was to evaluate the safety of disposal of fly ash containing
radiocaesium, originating from the nuclear accident at the Fukushima Daichi NPP, in conventional
municipal landfills of Fukushima Prefecture.
In this study, the scope has been limited to an assessment for one municipal landfill (Landfill B).
Future studies may extend the scope to other municipal landfills existing in Fukushima Prefecture.
5.6.1.1.2. Regulatory criteria
The radiological criteria that have been used in this study are those applied in GSR Part 3 (IAEA
2014) 2 ) as basis for calculation of Specific Clearan ce Levels (SCLs) for recycling and landfill
disposal of radioactive materials:
For scenarios likely to occur, the assessed annual potential effective doses to members of the
public shall not exceed 10 µSv/year, when using realistic parameter values in the calculations.
Additionally, in IAEA (2005 and 2021) 3 ) 4 ) it is required that doses calculated for unlikely
scenarios or using conservative low -probability parameter values should not exceed 1 mSv/year.
A scenario unlikely to occur is defined by two cases: 1) The event causing the exposure to non radiation workers and/or the population occurs with a low probability, 2) the values assigned to
one or more parameters are conservative and unlikely to be observed.
A summary of the radiological criteria to derive the SCLs is given in Table 34.
Table 34. Radiological criteria for the public and landfill non-radiation
workers for scenarios likely to occur and for scenarios unlikely to occur.
Scenario likely to

Scenario unlikely to

occur

occur

Dose less than

Dose less thani.e., adults and infants)

10 µSv/year

1 mSv/year

Non-radiation worker

Dose less than

Dose less than

10 µSv/year

1 mSv/year

Group considered
Public (both age groups,

156

These criteria are the same that has been used in the IAEA Basic Safety Standards GSR Part 3(IAEA, 2014) 2 ) and IAEA SRS-44 (IAEA, 2005) 3 ) to derive General Clearance Levels (GCLs).
They are considered “sufficiently low as not to warrant regulatory control ” (IAEA 2014) 2 ) , sincesuch control of the cleared material would yield no net benefit.
5.6.1.1.3. Assessment endpoints
Consistent with the approach used for the derivation of GCLs (IAEA 2005) 3 ) , doses were
calculated for two age groups: adults >17 years old) and infant children (1 -2 years old).
5.6.1.1.4. Assessment timeframes
The assessment considered three main phases of the landfill evolution in time :

The Operational period – when materials are being disposed of in the landfill.

The period of active institutional control – from the moment when the disposal operation s
have ended until the end of the institutional control period, assumed to be 30 years.

The period after the end of the active institutional control period.

5.6.1.1.5. Treatment of uncertainties
The assessment of doses arising during disposal of waste is associated with several sources of
uncertainties. One type of uncertainty is associated with the lack of knowledge about future
exposure pathways. This type of uncertainty has been addressed by co nsidering several exposure
scenarios in the assessments. The mathematical models used in the assessment also have anassociated uncertainty - this has been addressed in this study by applying models from the IAEA
assessment tool which are considered fit fo r this specific assessment purpose. Another type of
uncertainty comes from the limited data available on the parameter values that are used whenestimating the dose. In this work, a probabilistic approach (IAEA 2003a, b) 5 )6 ) has been adopted
for evaluation of parameter uncertainties.
In the probabilistic approach, a Probability Distribution Function (PDF) is assigned to uncertain
parameters. PDFs were either obtained from published data, for parameters with existing statistical
data, or they were assigned by expert judgement, taking care that they were consistent with thevalues selected for the deterministic approach. The Monte Carlo method (Vose, 1996) 7 ) was thenused to propagate the uncertainties through the model, allowing us to obtain different statis tics ofthe calculated doses. This method provides a more holistic consideration of the uncertainties, as
it explores all possible combinations of parameter values, balanced by their relative likelihoods.
It also comes with the added advantage that it also enables parameter sensitivity analyses.
5.6.1.2. System description
Landfill B is a controlled type landfill which has accepted incineration ash containing
radiocaesium (at concentrations less than 8,000 Bq/ kg). The caesium in this incineration ash
derives from the Fukushima Daiichi Nuclear Power Plant accident and was deposited from theatmosphere on various environmental media some of which were managed by incineration.
157

Disposal of radiocaesium-containing ash was conducted in the period following the accident.
Landfill B is a mountain -area landfill and, along with the incineration ash, sludge containing someorganic matter was also landfilled. Information on the characteristics of leachate from the landfill
is given in section 5.5.2..
5.6.1.3. Description of the scenarios
An important step in the assessment was the identification of exposure scenarios. These scenarios
include all relevant activities and potential exposure situations related to the landfill disposal of
the contaminated ash that may cause rad iation exposure to the public.
The exposure scenarios in IAEA (2021) 4 ) have been adopted in this study. The scenarios in IAEA
(2021) 4 ) were the basis of the calculations performed for the derivation of the GCLs recommended
in the IAEA Basic Safety Standards GSR Part 3 (2014) 2 ) and IAEA SRS-44 (2005) 3 ) . Also, other
IAEA work on disposal of radioactive waste in near surface disposal facili ties has been considered(IAEA 2003b) 6 ) .
The scenarios consider exposures to members of the public that may be directly or indirectly
exposed to radionuclides in the disposed radioactive waste. The exposure of members of the public
may occur at or near th e landfill sites.
Some of the exposure scenarios are expected to occur (likely exposure scenarios), while others
may occur only with a small probability (exposure scenarios unlikely to occur). A schematic view
depicting the scenario is given in Figure 28.

Figure 28. A schematic view depicting the scenarios considered in the safetyassessment
158

The scenarios that were used for evaluating doses to the public in the safety assessment arepresented in Table 35. The assessment model used includes generic value s for some parameters,such as the half-life of radioactive nuclides, and dose conversion factors. For other parameterssite-specific values for landfill B were selected by the Prefecture and used in the simulations. The
results of the simulations such as radiocaesium concentrations in seepage water (leachate) werecompared with measured values (calibration step). The doses calculated for residents under
different scenarios were compared with relevant regulatory criteria (evaluation step).
Table 35. Safety assessment scenarios assuming leaching of radiocaesium from fly
ash
Short
na me
RL_OP

Na me of the
scenario
Resident near thelandfill

Landfill phase
Operational
PeriodExposed groups
Resident near thelandfill(adult and child)

Exposure pathways
·
·

·
RL_PO

Resident near theLandfill

ActiveInstitutional
Control Period

Resident near thelandfill(adult and child)

·
·

·
RL_IC

Resident near thelandfill

Period after the
End of Active
Institutional
Control

Resident near thelandfill(adult and child)

·
·

·
RO

Resident On thelandfill

Period after the
End of Active
Institutional
Control

Resident on thelandfill(adult and child)

·

·

·
·
·
SE

Small excavationon the landfill

Period after the
End of Active
Institutional
ControlWorker doing the
excavation(adult and child)··Ingestion of riverwater
Ingestion ofvegetables irrigatedwith river water
Ingestion of riverfish
Ingestion of riverwater
Ingestion ofvegetables irrigatedwith river water
Ingestion of riverfish
Ingestion of well
water
Ingestion ofvegetables irrigatedwith well water
Ingestion of riverfish
Ingestion of
seepage water(leachate)
Ingestion ofvegetables gro wn
onsiteExternal irradiationfrom the ground
Inhalation ofresuspended dust
Inadvertent soil
ingestion (forchildren only)
External irradiationfrom the excavatedmaterial
Inhalation ofresuspended dust

The scenarios RL-OP, RL-PO, RL-IC and SE are classified as high probability, since the exposure
situations covered by these scenarios are likely to occur. For these scenarios the dose criteria of
10 µSv/year applies.
159

Long term exposure situations may result from a loss of knowledge at some point in the future
about the previous use of the site as a landfill. After the end of active institutional control, thesite may be used for purposes that cause exposure to the public. If knowledge about the site is
lost, buildings (e.g., residential houses) may be constructed on top of the covered landfill. During
the construction of houses, the cover would be disturbed, and waste material would be comeaccessible to a limited extent on the surface. Such situations are addressed by the RO scenario. A
complete loss of knowledge about the site is considered not very likely; therefore, it is assumed
that during major construction activities the special nature of the site would be re -discovered, andthe residential use of the site is considered as an unlikely scenario (IAEA 2005, 2021) 3 ) 4 ) . In thiscase, the dose criterion of 1 mSv/y applies.
The construction of a road through the landfill and the subsequ ent use of this road is also possible
in the long term. However, previous studies (IAEA 2003b) 6 ) have shown that this scenario causes
lower doses than residence on site scenario due to considerably shorter exposure times. The
consequences of this scenario are thus covered by the scenario estimating doses to residents on
the site.
The classification of scenarios by their likelihood in this study is consistent with the one adopted
in IAEA (2005, 2021) 3 ) 4 ) for derivation of General and Specific Clearance Lev els.
5.6.1.4. Description of the models
5.6.1.4.1. Models
Mathematical models were used for calculating the annual doses (Sv/y) arising from the different
scenarios for a given radiocaesium concentration (Bq/g) in the disposed waste.
The IAEA assessment tool that has been used consists of models implemented in the modellingand simulation software Ecolego (www.ecolego.se). The models are either identical to thosedescribed in IAEA SRS -44 (2005) 3 ) or have been derived by modifying some of t he SRS-44 models.
The purpose of the original clearance tool was to use it for generic assessment, and to determine
limits for radionuclide concentrations in the waste that can be landfilled while satisfying the dosecriteria. The clearance tool consists o f a set of models of radionuclide transport from landfills toand in the environment, as well as dosimetric models to calculate doses to the public (Figure 29).
The tool includes a database of input parameters required by the models, such as groundwater
flow, food consumption, and solid -liquid distribution coefficients (K d hereafter) for radionuclides.
Since the default values for model parameters used in this tool are generic, the Prefecture applied
modifications to those values to reflect the site -specific conditions in Fukushima Prefecture.

160

Figure 29. The assessment tool as implemented in Ecolego

Figure 30. Influence diagram of the processes corresponding to the total dose toa child for the RO scenario
Radionuclide transport is expressed as transfers between components; an example influence
diagram representing components is shown in Figure 30. The major components of the biosphere,161such as surface soil and river water, are included. Figure 30 shows how the components interact
with each other in the calculation of total doses to a child by different exposure pathways(ingestion of water, ingestion of vegetables, external irradiation, inhalation and inadvertent soil
ingestion) for the RO scenario.
5.6.1.4.2. Model parameters
Key parameters used in the simulation are tabulated in Table 36. For other model parameters,
default values in the IAEA clearance tool were used.
Exposure pathways are defined according to assumptions about how radio caesium may lead toexternal exposure of humans and/or may migrate in water from the landfill and move throughvarious biosphere media. Human characteristics and behaviors, such as jobs and lifestyles, aredetermined to identify how humans may interact with these biosphere media. The model thePrefecture used considers features and processes concerning radio caesium transport in the landfill,aquifer and other surface water systems (river and water wells), together with radio caesiumtransport into environmental components that are accessible to human beings.
Waste disposed of in the landfill B principally consists of incineration ash, inert waste, soil, andsludge. The radiocaesium concentration in incineration ashes were obtained from the datacollected monthly after July 2011. The radiocaesium concentrations in seepage water are governedby the radiocaesium concentration in the disposed waste, K d values, the weight and density of thewaste, the height of the landfill, and the infiltration rate of water into the la ndfill. Data on
groundwater hydraulic gradients after the landfill was constructed at landfill B were scarce, butdata from before landfill construction was available. The Prefecture decided to estimate hydraulicgradients using the data from before the co nstruction. The bulk density of waste was estimated by
dividing the total amount of waste in the landfill by the volume of the landfill. Databases of K dvalues derived from batch sorption experiments and column experiments have been developed
from literature studies. Databases were also developed for transfer factors between soil andvarious agricultural products, as well as for transfer factors between water and aquatic organisms.
The databases were used in probabilistic simulations made the assessment too l.
The final stage of safety assessment concerns radionuclide transport in the biosphere and theexposure pathways giving rise to radiation doses to humans. Though future change are probablee.g. in lifestyles, climate, and farming and fishing practices, the present lifestyle was assumed in
the safety assessment.
Potentially exposed groups (e.g. farming, freshwater fishing) were defined based on their habits
and expected intakes of local products (crops, livestock, and freshwater fishes). Parameters
deemed specific for Japan, such as food consumption, were determined based on average Japaneseconditions, using statistics provided by the Japanese government.

162

Table 36. Values for key parameters used in the simulations

Parameter

Units (FW: Fresh Weight,
DW: Dry Weight,)

Arithmetic
Mean

Arithmetic
Standard Deviation

Radiocaesium
concentration in the
waste

Bq/g

1

n.a.

Groundwater flow
velocity

m/year112.2

125

K d of waste *1

cm 3 /g50

n.a.

K d of soil *1

cm 3 /g370

n.a.

Ingestion rate of ricekg FW/year

108.6 (69.5) *2

64 (33) *2

Ingestion rate of
freshwater fish

kg FW/year

1.97 (1.68) *2

7.85 (5.66) *2

Ingestion rate ofcabbagekg FW/year

11.9 (4.38) *2

19.4 (7.99) *2

Ingestion rate ofonion

kg FW/year

11.6 (7.77) *2

15 (7.63) *2

Institutional control
period

years

30

n.a.

Operational period

years

13

n.a.

Transfer factor fromsoil to ricekg FW/kg DW

0.03 *30.006 *3

Transfer factor fromsoil to cabbage

Kg FW/kg DW

0.3 *3

1.5 *3

Transfer factor fromsoil to onion

kg FW/kg DW

0.05 *30.14 *3

Transfer factor from
fresh water to fish

L/kg FW

3667 *33937 *3*1 Optimized in the calibration step
*2 Values in parentheses are for the children of age 1 to 6. The values for adults are forages above 20 years. These values are the most representative of available statistical data
for the age groups considered in the dose calculations: >17 years old adu lt and 1-2 years
old child.
*3 Values of the mean E[X] and variance V[X] of the log normal distribution from IAEA
database are given. Relationships between geometric mean μ and standard deviation σ are222

E[X]= e ( μ + 2 σ ) and V[X]= (e σ −1) e ( 2 μ + σ ) .
5.6.2. Dose assessment and analysis of compliance
The dose assessment was carried out by performing simulations with the assessment tool for eachscenario. Two types of simulations were performed: deterministic and probabilistic. The
163

deterministic approach consisted of performing one simulation using realistic expected values for
all model parameters. When statistical data was available for a parameter, the mean was used asrealistic value. When statistical data was not available the realistic values were selected by expert
judgement.
In the probabilistic approach, a Probability Distribution Function (PDF) was assigned to
uncertain parameters, whereas for certain parameters realistic estimates were used. The Monte
Carlo method (Vose, 1996) 7 ) was then used by performing 3000 iterations of the model simulationand the results were used to obtain different statistics of the calculated doses.
5.6.2.1. Results of the calibration stepK d values for the waste were optimized in the calibration step using a trial -and-error approach
to fit the measured radiocaesium concentration in the seepage from landfill B (8.7 Bq/L in average).
The optimum K d value was 50 cm 3 /g. This K d value was used throughout the deterministic
simulations in the evaluation step.
After 10,000 runs assuming that the K d for waste had a log-normal distribution, the concentrationof radiocaesium in seepage water was obtained as shown in the histogram below (Figure 31). The
figure shows that the radiocaesium concentration can vary between 1 Bq/L to 40 Bq/L, indicatingthat the K d for waste is one of the important parameters governing the elution o f radiocaesium
from the landfill.

Figure 31. Histogram of radiocaesium concentration in seepage water whenK d values were varied in the simulations with the model
5.6.2.2. Results of the evaluation step
Doses to residents under different scenarios were calculated with the assessment tool. For eachscenario, probabilistic as well as deterministic results of the dose calculations are presented in164

Table 37. For the probabilistic simulations 3000 runs were co nducted and mean, standard deviation,
5th percentile, and 95 th percentile of the dose estimates were tabulated, along with thedeterministic estimate of the dose (Table 37). The results are also shown in Figures 32 and 33.
As shown in the results summarize d in Table 37, the highest dose estimate was obtained for the
RO scenario, which assumes that the potentially exposed group resides on the landfill lacking acover soil (unlikely scenario, low probability scenario). Detailed inspection of the simulation
results for the RO scenario, shown in Table 37(d), revealed that the highest doses were caused byingestion of seepage water (leachate) and external exposure from the waste.
estimates for other scenarios were in the order of RL_OP

The potential dose

≅ RL_IC > RL_PO for the mean dose

obtained in the probabilistic simulation and for the dose estimates obtained in the deterministic
simulations.
Table 37. Dose estimate under each scenario(a) RL_OP: Resident near the Landfill during the Operational Period
Std.
Exposure
Age
Mean
5%
MedianDeviation
pathway
group
µSv/y
µSv/y
µSv/y
µSv/y
Ingestion of fish
adult
2.9E-03
2.1E-02 1.1E-05 3.2E-04

95%
µSv/y

DeterministicµSv/y

9.2E-03

1.6E-03

Ingestion of river water

adult

8.2E-04

6.3E-04

1.1E-04

6.6E-04

2.1E-03

4.4E-04

Ingestion of vegetables

adult

3.7E-05

4.0E-05

3.4E-06

2.4E-05

1.1E-04

2.0E-05

All pathways

adult

3.7E-03

2.1E-02

1.8E-04

1.2E-03

1.1E-02

2.1E-03

Ingestion of fishchild

2.1E-03

7.8E-03

8.9E-06

3.2E-04

8.2E-03

1.3E-03

Ingestion of river waterchild

3.0E-04

2.3E-04

4.0E-05

2.4E-04

7.6E-04

1.6E-04

Ingestion of vegetables

child

2.0E-05

2.1E-05

1.8E-06

1.3E-05

6.1E-05

1.1E-05

All pathwayschild

2.4E-03

7.8E-03

8.3E-05

6.7E-04

8.7E-03

1.4E-03(b) RL_PO: Resident near the Landfill during the Active Institutional Control period
Std.
Exposure
Age
Mean
5%
MedianDeviation
pathway
group
µSv/y
µSv/y
µSv/y
µSv/y
Ingestion of fishadult
1.7E-03
1.3E-02 5.7E-06 1.9E-04

95%
µSv/y

DeterministicµSv/y

5.4E-03

9.5E-04

Ingestion of river water

adult

4.8E-04

3.8E-04

6.6E-05

3.9E-04

1.2E-03

2.6E-04

Ingestion of vegetables

adult

2.2E-05

2.5E-05

1.9E-06

1.5E-05

6.6E-05

1.2E-05

All pathways

adult

2.2E-03

1.3E-02

1.1E-04

7.4E-04

6.3E-03

1.2E-03

Ingestion of fishchild

1.2E-03

4.4E-03

5.3E-06

1.9E-04

4.9E-03

7.5E-04

Ingestion of river waterchild

1.8E-04

1.4E-04

2.4E-05

1.4E-04

4.4E-04

9.6E-05

Ingestion of vegetables

child

1.2E-05

1.3E-05

1.1E-06

7.8E-06

3.5E-05

6.3E-06

All pathwayschild

1.4E-03

4.5E-03

4.9E-05

4.1E-04

5.1E-03

8.5E-04165

(c) RL_IC: Resident near the Landfill during the Period after the End of Active Institutional Control
Std.
Exposure
Age
Mean
5%
Median95%
Deterministic
Deviation
pathway
group
µSv/y
µSv/y
µSv/y
µSv/y
µSv/y
µSv/y
Ingestion of fish
adult
5.0E-07
1.1E-05 <1.0E-10 <1.0E-10 4.3E-08<1.0E-10
Ingestion of well wateradult

3.2E-038.0E-02<1.0E-10<1.0E-10

5.6E-04<1.0E-10

Ingestion of vegetables

adult

2.0E-04

3.7E-03<1.0E-10<1.0E-10

4.7E-05<1.0E-10

All pathways

adult

3.4E-03

8.3E-02<1.0E-10<1.0E-10

6.1E-04<1.0E-10

Ingestion of fishchild

6.3E-07

1.4E-05<1.0E-10<1.0E-10

4.0E-08<1.0E-10

Ingestion of well waterchild

1.2E-033.0E-02<1.0E-10<1.0E-10

2.1E-04<1.0E-10

Ingestion of vegetables

child

1.0E-04

1.7E-03<1.0E-10<1.0E-10

2.7E-05<1.0E-10

All pathwayschild

1.3E-03

3.1E-02<1.0E-10<1.0E-10

2.4E-04<1.0E-10(d) RO: Resident On the landfill during the Period after the End of Active Institutional Control
Std.
Exposure
Age
Mean
5%
Median95%
Deviation
pathway
group
µSv/y
µSv/y
µSv/y
µSv/y
µSv/y
External irradiation
adult 1.1E+01
4.3E+00 5.7E+00 1.0E+01 2.0E+01

DeterministicµSv/y
1.1E+01

Inhalation
Ingestion of seepage
water
Ingestion of vegetables

adult

1.3E-04

1.3E-04

2.5E-05

9.6E-05

3.6E-04

1.3E-04

adult

3.5E+01

2.9E+01

4.2E+00

2.7E+01

9.4E+01

1.9E+01adult

1.2E+00

7.1E+00

3.6E-02

2.5E-01

3.5E+00

9.2E-01

All pathways

adult

4.7E+01

3.0E+01

1.4E+01

3.9E+01

1.1E+02

3.1E+01

External irradiationchild

1.3E+01

5.2E+00

6.8E+00

1.2E+01

2.4E+01

1.3E+01

Inhalation
Ingestion of seepage
water
Ingestion of vegetables

child

2.9E-05

2.7E-05

5.4E-06

2.1E-05

7.8E-05

2.8E-05child

1.3E+01

1.1E+01

1.5E+00

1.0E+01

3.5E+01

7.1E+00child

4.5E-01

2.5E+00

1.8E-02

1.2E-01

1.2E+00

3.6E-01

Ingestion of soilchild

1.1E-01

4.1E-02

5.5E-02

9.9E-02

1.9E-01

1.0E-01

All pathwayschild

2.7E+01

1.2E+01

1.2E+01

2.4E+01

5.1E+01

2.0E+01(e) SE: Small Excavation on the landfill during the Period after the End of Active Institutional Control
Std.
Exposure
Age
Mean
5%
Median95%
Deterministic
Deviation
pathway
group
µSv/y
µSv/y
µSv/y
µSv/y
µSv/y
µSv/y
External irradiation
adult
8.3E-02
3.8E-02
3.4E-02 7.4E-02 1.6E-01
8.3E-02
Inhalation

adult

4.0E-05

2.6E-05

1.2E-05

3.3E-05

9.3E-05

4.1E-05

All pathways

adult

8.3E-02

3.8E-02

3.4E-02

7.4E-02

1.6E-01

8.3E-02

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Figure 32. Histogram of individual dose in RO scenario when a combination of theparameters was varied

Figure 33. Probabilistic and deterministic estimate of the dose
167

The dots in the graph show the doses given by each run, though the runs giving similar results
are overlapped in the Figure. The box in the graph shows the 25th percentile and 75th percentile
values of the dose estimate in the runs .
5.6.2.3. Sensitivity analysis
The results of the probabilistic simulations were used for performing parameter sensitivity
analyses. The parameter sensitivity analysis allows apportioning of the relative effect, of theparameters on the uncertainty of the simulation endpoints.
The effect of the model parameters on a simulation endpoint ( for example the total annual dose)can be positive (i.e., when a model parameter increases or decreases, the dose also increases ordecreases, respectively) or negative (i.e., when the parameter increases the dose decreases andwhen the parameter decreases the dose increases). To illustrate this, Standardized Rank Regression
Coefficients (SRRC) were calculated. The SRRCs are a measure of the effect of varying eachparameter on the value of a model output. The S RRC is obtained by fitting the model predictions
for the output to a linear first order polynomial dependency with the studied input para meters(Saltelli et al. 2004) 8 ) .
The SRRCs can be presented as tornado plots, such as those in Figure 34, showing the parameterswith the highest absolute SRRCs values for the RO scenario.

Figure 34. Importance of the parameters to the final dose estimate

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5.6.2.4. Analysis of compliance with the radiological criteria
For the high probability scenarios (RL-OP, RL-PO, RL-IC and SE), the results of thedeterministic and probabilistic simulations (the mean and even the 95 th percentile) are well below
the applicable regulatory criterion (10 µSv/year). This is true even if the concentrations in thewaste are increased from 1 Bq/g (estimated value for Landfill B) to 8 Bq/g (current landfill
standard).
For the low probability scenario (RO), the results of the deterministic and probabilistic
simulations (the mean and even the 95th percentile) are also well below the applicable regulatory
criterion (1 mSv/year). This is also true even if the concentrations in the waste are increased from
1 Bq/g (estimated value for Landfill B) to 8 Bq/g (current landfill standard).
5.6.3. Conclusions
A safety assessment was conducted for a lan dfill site containing a proportion of Radio caesiumcontaminated incineration ash using a safety assessment tool provided by the IAEA withmodifications to reflect the actual situation in Fukushima Prefecture. The results of the safetyassessment using this modified tool for landfill site B, taking account of the amount of ash
disposed of in the landfill, indicate that the additional exposure dose for residents living near thefacilities in the future is very low for the scenarios considered, the models deve loped, and theparameters used. Furthermore, even for the unlikely scenario of people living on the landfill siteand drinking landfill water (leachate) more than 30 years after the disposal facilities are closed,
the estimated dose was found to be less th an 1 mSv/y. In the future, the scope of the safetyassessment should be expanded to include additional landfill sites in Fukushima Prefecture. If
necessary, the assessment tool should be modified according to each site and scenario, moredetailed dynamic simulations of radiocaesium flow should be performed, and observations should
be continued to confirm that the behavior of radio caesium in the landfill is consistent with thesimulation results.

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5.7. Landfill site management after the completion of landfi ll of waste
In order to consider future maintenance and management standards, including monitoring oflandfill sites where waste containing radioactive caesium has been landfilled in the Fukushima
Prefecture, the IAEA shared information on cases of radioac tive waste being landfilled atindustrial waste sites overseas. We compared the monitoring items and frequency for the overseas
landfill sites with the monitoring standards imposed on landfill sites for waste containing
radioactive caesium in Japan.
5.7.1. Implementation of monitoring plan
Landfill disposal locations in Japan have been managed under the Waste Disposal and Public
Cleansing Law (hereinafter referred to as “Waste Disposal Law”), in addition to related laws andregulations. Those laws and regulations relate to non -radioactive materials and so were based on
the assumption that radioactive materials would not be present in the waste. Additional standards
by national government were imposed for the management of waste containing radioactive
materials under the Act on Special Measure s Concerning Handling of Radioactive Pollution after
the Fukushima accident. These laws mostly stipulate matters related to the management of waste
containing radiocaesium during operational period, and there is no description regarding theconfirmation of radioactive materials during the post operational period and the post Institutional
Control period. Therefore, in order to examine the method of management regarding disposal
locations by the time of decommissioning and the method of confirmation regard ing radiocaesium
at the time of decommissioning, information was provided by the IAEA on examples of landfill
for radiocaesium in foreign industrial waste disposal locations, which will be referenced in order
to investigate to which extent experience in ot her countries could be applied to waste disposal in
Japan.
5.7.2. Results
Guidelines provided by the Ministry of the Environment include additional standards for the
management and monitoring of waste containing radio caesium after landfill under the Act on
Special Measures Concerning Handling of Radioactive Pollution, as shown in the table below.
However, there are no national decommissioning standards for radio caesium concentrations (as ofDecember, 2022), although there are national maintenance management standards at the time oflandfill and by the time of decommissioning (when landfill is completed), as shown in the table
38 below.

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Table 38. Additional criteria for landfill maintenance and management according
to waste-related guidelines
Items
MaintenanceManagement
Standards
Ground water
Measurement

Discharged
Water
Measurement

Waste Disposal Law
Inspection items (such as
groundwater, etc.) and dioxins
should be measured before
starting landfill and at least
once a year during landfill.
The rate of electricalconductivity, or chloride ion
should be measured before
starting landfill and at least
once a month during landfill.
Items included in the discharge
standards and dioxins shouldbe measured at least once a
year.
pH, BOD, COD, SS and T-Nshould be measured at least
once a month.

Additional Standards

Radiocaesium concentrations
should be measured before starting
landfill and at least once a month
during landfill.

Radiocaesium concentrations
should be measured at least once amonth.

－

Radiation doses at the boundary of
the landfill site should bemeasured at least once every 7
days.

RecordThe type and amount oflandfill materials, the content
of inspections under the
maintenance management, anddetails of tests andimplementation should berecorded.
(If municipal waste containing
asbestos is reclaimed,drawings of the landfill
locations should be recorded
as well.)

The type and amount of landfill
materials, the date of the landfill
disposal, the content of inspections
under the maintenancemanagement, details of tests andimplementation, and drawings oflandfill locations should berecorded.

RecordKeeping

Keep until deco mmissioning.

Keep until deco mmissioning.

Spatial Dose
Rate
Measurement

On the other hand, at foreign industrial waste disposal locations where waste containing
radiocaesium is reclaimed, safety cases (safety management standards) for radioactive waste havebeen developed and managed in addition to the original method of disposal location management.
One example of such disposal location is the ENRMF (East Northants Resource Management
Facility) operated by Augean PLC. This disposal location is subject to standards for approval of
disposal locations concerning low level polluted waste known as GRA. In order to meet thosestandards, the ENRMF accepts radioactive waste under spe cific methods and standards for
management in addition to the original standards for management. These standards are not uniform
standards for any and all cases, but detailed standards which are tailored to each disposal location,
taking into consideration the location, structure, landfill methods, and waste which has been
reclaimed in the past. In particular, a detailed monitoring program has been established for safety,
and the measurement locations and frequency of ambient dose rates, gases, leachate, du stconcentrations, surrounding rivers, and observation pits are described in the ESCs. The
measurement frequency for each item is defined as follows: air dose rates are measured constantly,
171the volume of gases generated, leachate, dust concentration and wa ter from observation wells aremeasured once a month, and water from the surrounding rivers is measured once a year.

Figure 35. ENRMF (East Northants Resource Management Facility)
Waste to managed in those foreign disposal facilities is generally con tained in drums or double packed, since the waste is generated from experimental facilities and the vicinity of nuclear power
plants. Waste containing radioactive caesium generated in Fukushima Prefecture is not bagged andtherefore differs from these treatment. With this in mind, while the guidelines stipulate that
landfill methods that prevent water intrusion should be applied, water would likely eventually
intrude when taking caesium half-life into account. This implies that appropriate monitoring an dcountermeasures be anticipated.
5.7.3. Conclusions
The IAEA shared examples of monitoring and management methods of radioactive waste after
disposal in landfill facilities in different countries in the world. In foreign cases, the same
monitoring approaches as those stipulated in the Waste Disposal Law in Japan, such as peripheral
groundwater and discharged water, are implemented. Therefore, the monitoring standards oflegislation in Japan were confirmed to be adequate. On the other hand, in foreign case s, themonitoring frequency and the method of management up to decommissioning were determinedprior to the acceptance of radioactive waste in the facility, taking into account the structure of theindividual disposal locations and its past management, as well as its future handling. In light of
this, in the case of the Fukushima Prefecture, it is considered necessary to consider the method ofhandling and monitoring frequency up to decommissioning for each characteristic of the disposal
facilities.
5.8. Conclusions
Fukushima Prefecture, with advice from the IAEA, has conducted studies and tests on waste
incineration, especially on radioactive caesium in incineration ash, and found (1) that it is difficult
to control the distribution of radioactive caesium in bottom ash/fly ash during waste incineration,(2) that radioactive caesium in fly ash emitted from municipal waste incineration facilities inFukushima Prefecture is soluble in water, and (3) that the elution of radio caesium from fly ash
172can be suppressed by adding zeolite and other materials, which demonstrates satisfactory resultsin actual waste incineration facilities.
The study was also conducted on landfill disposal of waste, and showed (1) that when incineration
fly ash is landfilled while in contact with water, radiocaesium leaches out, but the concentration
is sufficiently low compared to the standard concentration of radio caesium in public waters, (2)that there is no seasonal regularity in the leached concentration, and (3) that there is a positive
correlation between radiocaesium concentration and chloride ion concentration.
The IAEA provided us with a safety assessment tool for landfill disposal, the scenarios in theassessment tool were modified to suit the situation in Fukushima Prefe cture, and a safetyassessment was conducted by using actual data from landfill sites in the prefecture, which clarified
that the current landfill standards are sufficiently on the safe side.
In addition, the monitoring items and frequency related to the a dditional standards formaintenance and management at landfill sites, which are indicated by the Ministry of theEnvironment of Japan, it was confirmed that it is necessary to consider the monitoring items andfrequency according to the disposal site in ad vance for the abolition of landfill disposal sites in
the future by comparing with landfill sites overseas where radioactive waste are buried.
References
1) IAEA (2012). The Safety Case and Safety Assessment for the Disposal of Radioactive Waste.
IAEA Specific Safety Guide SGG -23, Vienna 2012.
2) IAEA (2014). Radiation Protection and Safety of Radiation Sources: International Basic Safety
Standards, General Safety Requirements Part 3, GSR Part 3, Vienna, Austria
3) IAEA (2005). Derivation of activity concentr ation values for exclusion, exemption andclearance. IAEA Safety Reports Series No 44. International Atomic Energy Agency, Vienna,
Austria4) IAEA (2021). Derivation of specific clearance levels in materials being suitable for recycling,reuse, or for disposal in landfills. IAEA Safety Report Series, (IN PRESS)
5)

IAEA (2003a) Evaluating the reliability of predictions made using environmental transfer

models, Safety Series No. 100, IAEA, Vienna (1989)
6)

IAEA (2003b). Derivation of activity limits for the disposa l of radioactive waste in nearsurface disposal facilities. TECDOC -1380. International Atomic Energy Agency, Vienna, Austria
7) Vose, D. (1996). Quantitative Risk Analysis – A guide to Monte Carlo Simulation Modelling,
John Wiley and Sons, New York
8) Saltelli, A, Tarantola, E, Campolongo, F and Ratto, M. (2004). Sensitivity analysis in practice– A guide to assessing scientific models. John Wiley & Sons Ltd., Chichester

173

Report summary
Except for FIP4, this report covers activities from FY2013, focusing on activities from FY2018
and FY2019. Since FIP4 was completed in FY2015, we report on the activities from FY2013 toFY2015 with some wordings revised and update added since the theme ended in FY2015 . The
reports on each theme are summarized as follows.
FIP1: Survey, and evaluation of the effect of radiocaesium dynamics in the aquatic systems
Monitoring of suspended and dissolved radio caesium concentrations in river water in Fukushima
Prefecture were carried out. The resul ts showed that the trends to decrease with time wasmaintained regardless of the forms. Simulations of radio caesium concentrations in river water
during base and high water flow were carried out and generally reproduced the measured values.
FIP2: Survey of radionuclide movement with wildlife
Comparisons of the activity concentration s of caesium -137 in the muscle tissues of wild boars
and Asian black bears revealed higher activity concentration s in wild boars, while c omparisons
between copper pheasant and green pheasants revealed higher levels in copper pheasant, revealingthat trends differed depending on the species.
The activity concentration of caesium -137 in the muscle tissues of wild boars was confirmed to
be strongly affected by diet. As a result of confirming the seasonal change of caesium-137 activity
concentration s in the muscles of wild boar and Asian black bear, even in recent years, individuals
with high activity concentration s that exceeded 10 times the standard limit of radioactive caesium
activity concentration in general foods were captured. The long -term fluctuation of caesium-137
activity concentration in the muscles of wild boar and Asian black bear showed a decrease overtime during the entire period, both the low activity concentratio n period and the high activity
concentration period. The model now needs to be reconsidered to provide a better estimate of thelong-term fluctuations of radio caesium in the animals, particularly during the high activity
concentration period.
Compared to wild boars living outside the areas under evacuation orders, those living in the areas
under evacuation orders tended to have wider home ranges that tended to shift to farmlands. In
addition, wild boars in Fukushima Prefecture are genetically divided into two strain groups,
suggesting that their movement may be restricted from east to west with the Abukuma River andaround as the boundary.
FIP3: Sustainable countermeasures for radioactive materials in terrestrial and aquatic areas
In this project, decontam ination demonstration tests were carried out on riverbanks to investigate
the effectiveness of decontamination methods based on the spatial distribution of radiocaesium.
Continuous measurements of gamma dose rates and activity levels in sediments were cond uctedon the riverbanks after decontamination; the results showed that the air dose rate continuously
decreased and the decontamination effect persisted. In addition, investigations in river parks and174other areas before and after the floods caused by the p assage of Typhoon Hagibis in 2019 showedthat air dose rates in general did not increase and re -contamination due to the flooding was notdetected. The results of these studies were provided to the relevant sections in Fukushima
Prefecture, and the methods for the decontamination of riverbeds were subsequently utilised as
river maintenance measures.
FIP4: Development of environmental mapping technology using GPS walking surveys
A GPS-linked dose rate measurement device, KURAMA from Kyoto University, was us ed as abasis and the configuration was made more suitable for walking surveys. Then, the GIS dataprocessing system was prepared on the assumption that it would be linked with the analysis of theobtained data and the monitoring of aircraft surveys by UAV. In addition, it has become possible
to measure the dose rate in a walking survey by collecting data necessary for measurement suchas directional characteristics and calibration constants. We conducted walking surveys at several
points and confirmed that it was possible to measure dose rates and create contour maps using a
GIS data processing system. A manual was prepared so that even inexperienced people can use thesystem. Since fiscal 2016, it has been used for conducting walking surveys and has been r ented
out at the request of municipalities. In recent years, walking surveys have been utilized in the
public projects for monitoring of the air dose rates (e.g., Satoyama Restration Model Project).
FIP5: Study of proper treatment of waste containing radi oactive material
Surveys and tests were conducted at landfill sites and waste incinerators to examine treatment,
disposal and management methods for waste containing radio caesium generated in the prefecture.
A survey of leachate at the landfill site confir med that when the incinerated fly ash was buried incontact with rainwater, radio caesium was eluted from the incinerated fly ash and was detected in
the leachate. In order to suppress the elution of radio caesium from this incinerated fly ash, various
incineration ash elution tests and incineration ash sparingly soluble tests were conducted inlaboratories and facilities. As a result, it was found that the addition of zeolite into the incineration
ash has a remarkable effect of suppressing the elution of rad iocaesium However, in the application
to the implementation facility, it is added according to the target incineration facility or landfill
site, and so it is considered necessary to further study the method and the amount of zeolite a dded.
In addition, the safety assessment tool provided by the IAEA was modified to suit the conditions
in Fukushima Prefecture, and a safety assessment of the actual deposit location in Fukushima
Prefecture was conducted. As a result of the safety assessment, it was confirmed that currently
landfilling of the landfill site B is a fairly safe value, and future confirmations will be conducted
so that this assessment tool can be applied to other disposal locations in the future. Also, as areference for the future management of disposal locations in Fukushima Prefecture, information
was provided on the management of disposal locations overseas where radioactive waste will beburied. In overseas cases, the waste conditions and dose control methods were defined in adva nce,
and not all disposal locations could be used as a reference. However, information from theseoverseas disposal locations that can be utilized in the management of individual disposal locations
175

in Fukushima Prefecture was obtained, including methods of management depending on the
structure of disposal locations and the frequency of monitoring after the end of landfill operations.

176