Radiation Monitoring and Remediation Following
theFukushima Daiichi Nuclear Power Plant Accident

Cooperation between
Fukushima Prefecture and the IAEA
INTERIM REPORT(2013 to 2020)【Fukushima Prefecture Initiative Projects】【Detailed version】(Temporary translation)

March 2021
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. Abstract

5

1.2. Purpose

51.3. Content of implementation

6

1.4. Results

8

1.5. Conclusions

15

2. FIP2 Survey of radionuclide movement with wildlife
2.1. Abstract

17

2.2. Purpose

172.3. Content of implementation

18

2.4. Results

19

2.5. Conclusions

26

3. FIP3 Sustainable countermeasures to radioactive materials in freshwater system
3.1. Abstract27

3.2. Purpose

27

3.3. Content of implementation

27

3.4. Results

31

3.5. Conclusions

35

4. FIP4 Development of environmental mapping technology using GPS walking
surveys（ Ended in FY2015）
4.1. Abstract37

4.2. Purpose

37

4.3. Content of implementation

39

4.4. Results

41

4.5. Conclusions48

5. FIP5 Study of proper treatment of waste containing radioactive material
5.1. Abstract49

5.2. Purpose

49

5.3. Content of implementation

51

5.4. Results

55

5.5. Conclusions

69

Report summary

70

Introduction
The Great East Japan Earthquake occurred on 11 March 2011. It was followed by the accidentof Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant 1 , and radioactive
materials have been released into the environment which contaminated the land . Due to thecontamination of the land and other relevant reasons, more than 160,000 prefectural residents wereforced to evacuate. About 38,000 residents have no t been able to return home, as of 2020 July,
about 9 years after the disaster (Fukushima Prefecture’s website “Fukushima Revitalization
Station”; https://www.pref.fukushima.lg. jp/uploaded/attachment/403521.pdf ).
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, it wasnecessary to respond at the aftermath by collecting knowledge and world -wide experience, so theprefecture decided to cooperate with the International Atomic Energy Agency (hereinafter referred
to as the “IAEA”), which owns high -level nuclear-related knowledge. In December 2012, a
memorandum for cooperation was signed between the prefecture and the IAEA.
Based on the memorandum, an agreement relating to the fields of “radiation monitoring” and“decontamination” was signed between the parties on the same day (projects based on thisagreement is referred to as “ FCPs; Fukushima Cooperative Project”).
Subsequently in April and October 2013, agreements were signed for five projects (hereinafterreferred to as “ FIPs; Fukushima Initiative Project”) as described below in a new framework inwhich these projects would be supported by the IAEA for three years, and the FIPs started(hereinafter referred to as “previous Project”). In April and May 2016, they signed agreements forextending the FIP cooperation period (originally set at “until December 2017”) expanding therange of their cooperation 2 .
【 Themes of the FIPs before the extension of cooperation period (From April 2013 to December2017)】
1 Survey of radionuclide movement in river systems
2 Survey of radionuclide movement with wildlife
3 Countermeasures for radioactive materials in rivers and lakes
4 Development of environmental mapping technology using GPS walking surveys
5 Study of the proper treatment of waste c ontaining radioactive materials at municipal
solid waste incinerators
The achievements of the FIPs conducted between April 2013 and December 2017 were compiledin the report on “Cooperation between Fukushima Prefecture and the IAEA – SUMMARYREPORT (2013 to 2017) [Fukushima Prefecture Initiative Projects]” in March 2018 (hereinafterreferred to as "previous report"). The previous report is available in a book form and also in thefollowing website:
https://www.pref.fukushima.lg.jp/sec/298/iaeasummary2017.html

1

1 The owner of the Fukushima Daiichi Nuclear Power Plant was renamed from Tokyo ElectricPower Company to Tokyo Electric Power Company Holdings, Incorporated in April 1, 2016.
2 In accordance with the change of the cooperation range, the names of some FIPs were changed.
However, because remediation of the environment in the Prefecture was halfway through and theaccomplishment of the proposed projects require d further support from the IAEA, th e prefecture
obtained in December 2017 the IAEA ’s agreement and signature for a continued support until
December 2022 (hereinafter referred to as “this Project”). Subsequently, according to the contentsof the projects, some project themes were renamed. This report is an interim report on activities
from Fiscal Year (hereinafter referred to as “FY”) 2013, focusing on activities from FY2018 toFY2019, excluding FIP4. FIP4 was completed in FY2015 and has not been extended, so theprevious report is reprinted with some wordings revised and updated since FY2015.
FIP1: Survey of radionuclide movement in river systems
Survey, and evaluation of the effect, of radiocaesium dynamics in the aquatic
systems based on the continuous monitoring <Renamed>
The purpose of this project is to determine the movements of radionuclides in the river watersin Fukushima Prefecture to foster the sense of safety and security of its residents. From theachievements attained by Fiscal Year 2017 (as described in the previous report), it was
confirmed that the cesium concentrations decreased to about 1/10 during the five years after theaccident and that their decrease rates were different depending on whether decontamination had
been performed. It was decided to further continue this project because it was necessary toobtain the IAEA’s advice and proposals regarding the identification of radionuclide movements
as well as radiocesium movement prediction and impact assessment using numerical models
derived from monitoring results. An impact assessment review was also included in this project,so the project theme was renamed.
FIP2: Survey of radionuclide movement with wildlife (theme name unchanged)
The project is intended to determine the movements of radionuclides among wild animals suchas wild boars, with a view to lifting their shipment restrictions and relieving the concerns of
the residents in the prefecture. Outcomes obtained by Fiscal Year (FY) 2017 revealed that theCs-137 concentrations in the muscles of wild boars tended to be higher than those in the musclesof Asian black bears and that the Cs -137 concentrations in the muscles of both animals
fluctuated seasonally and increased particularly during winter. It was also found t hat the Cs137 concentrations in the muscles of wild boars were positively linked to those contained intheir gastric contents. With regard to birds, the Cs -137 concentrations in the muscles of copper
pheasants were higher than those in the muscles of Japa nese pheasants, mallards, and spot billed ducks. The continuation of the project was decided because of the necessity of the IAEA’s
further advice and proposals in the measurements of radionuclide concentrations in wild animals’
muscle tissues, gastric contents and food, in the analyses of their feeding habits, investigations2

on behavioral patterns and population structures, and in the estimation of factors contributing
to the high radiocesium concentrations in the muscles of some wild animals and the long -term
fluctuations of radiocesium concentrations in the wild animals.
FIP3: Countermeasures for radioactive materials in rivers and lakes
Sustainable countermeasures to radioactive materials in freshwater system<Renamed>
The purpose of this project is to check the effectiveness of measures that have been taken forrivers and lakes to identify effective radioactive material countermeasures. As achievements
attained by FY 2017, radiocesium countermeasures applicable to the f reshwater systems in
Fukushima Prefecture were organized and it was found that topsoil removal according to cesium
concentration distribution is effective in riverside areas and a decontamination effect was foundto be maintained even after flooding.
These findings were made known to the municipalities. On the other hand, the presence of
persistent anxieties regarding the water environment in seriously contaminated regions wasrecognized. It was decided to continue the project further because the IAEA ’s advice andproposals were still necessary to continuously determine the movements of radioactive materials
in the future and clarify causes in case of re -contamination and establish effective
countermeasures. In addition, the project theme was renamed becau se it was decided to takemedium- to long-term measures.
FIP4: Development of environmental mapping technology using GPS walking surveys
The purpose of this project is to improve the efficiency of radiation monitoring by developinga system capable of quickly and precisely measuring radioactivity even in locations whereradioactivity is immeasurable using a vehicle. This system was established by the end of March
2015 and was utilized since FY 2016 while walking surveys were carried out and survey
equipment was lent in response to requests from the municipalities. Because the purpose of the
project was achieved, it ended in FY 2015.
FIP5: Study of the proper treatment of waste containing radioactive materials at
municipal solid waste incinerators
Study of proper treatment of waste containing radioactive material <Renamed>
This project is intended to promote the treatment of incinerated ash generated in general waste
incineration facilities and check the migration of cesium from incinerated ash to fly as hdepending upon incineration conditions. By FY 2017 it was found that the clarification ofcesium migrations between incinerated ash and fly ash is difficult and that the mixture of zeoliteor the like into incinerated ash decreases cesium leaching rate. These findings were made known
to the municipalities. It was decided to further continue the project because it was necessary toobtain the IAEA’s advice and proposals in analyzing the forms of radiocesium present in3

incinerated ash and identify an effecti ve method of making radiocesium hardly soluble and of
its removal technique. The project theme was renamed to cover general waste containing
radioactive materials.

41. FIP1 Survey, and evaluation of the effect, of radiocesium dynamics in theaquatic systems based on the continuous monitoring.
1.1. Abstract
More than nine years after the Fukushima Daiichi Nuclear Power Plant accident, theconcentration of radiocesium in river water has fallen considerably. However, continuous
monitoring of the effects of various social conditions and sudden events on the dynamics ofradiocesium in rivers is still considered necessary. This project is thus an extension of the previous
project that monitored the concentration of radiocesium in several rivers in Fukushima Pr efecture.
In addition, the efficacy of decontamination activities on radiocesium concentrations in river water
were investigated. Model simulations were also performed to assess changes in the suspended anddissolved forms of radiocesium under both base - and high-flow conditions. The estimated results
showed good agreement with measured values, although some improvements are considerednecessary.
1.2. Purpose
As a result of the Fukushima Daiichi Nuclear Power Plant accident in March 2011, large amountsof radioactive materials were released as fallout into the environment. Previous studies showedthat these materials were deposited on the surrounding areas and that they contaminated the soil.
To ensure the safe use of rivers and river waters, which is widely used for drinking, agriculture
and industry, it is important to clarify the actual situation of the dynamics of radioactive materials(especially radiocesium) in rivers. In addition, predictions of future dynamics of these materials
in rivers also need to be performed. Radiocesium in river water occurs as suspended (adsorbed byfine particles) and dissolved (dissolved in water) forms. Since the role of each form of radiocesiumin the environment is likely to be different, it is important to understand th e radiocesium dynamics
of these forms separately.
In the previous project (“Survey of radionuclide movement in river systems ” in the previous
report), we conducted long -term monitoring and clarification of the dynamics of radiocesium
concentrations in rive rs in Fukushima Prefecture. We also used models to predict changes inradionuclide concentrations following advice from the International Atomic Energy Agency. That
project was comprised of two parts; the first was “Wide-area Multipoint Survey”, in which we
conducted long-term monitoring of suspended cesium -137 concentrations in the Abukuma River
Basin and rivers in the Hamadori area. The second was a “Survey of the Hirose River Basin ”, inwhich we predicted the dynamics of radiocesium in the Hirose River, which is a primary tributaryof the Abukuma River, using a numerical model. The results showed that the concentration ofsuspended radiocesium in river water tended to decrease over time, that dams and decontamination
activities in the basin both affect th e transport dynamics of radiocesium along the length of therivers, and that land use in the basin affects the rate of decrease in the concentration of suspended
radiocesium in river water. Some of the findings of the report were published as an academic
1)

paper . In addition, changes in the radiocesium concentration under baseflow conditions in the5Hirose River were reproduced by using the TODAM model

2 ), 3 ).

More than nine years after the accident, the concentration of radiocesium in the rivers inFukushima Prefecture has decreased sufficiently, and levels are now well below the levelrecommended for drinking waters (10 Bq L -1 ). However, changes in social conditions (e.g.,completion of surface decontamination activities, return of residents, and resumption of farming
following the lifting of evacuation orders) or the occurrence of sudden events (e.g., fires in themountains and forests, large -scale high flows due to typhoons, heavy rains, etc.) may change thedynamics of radiocesium in rivers. Thus, it is im portant to continue monitoring and disseminating
information based on the results of monitoring.
In this project, to better understand the trends in radiocesium concentrations over time, we will
monitor radiocesium concentrations in river water, mainly in the Abukuma River system and rivers
in the Hamadori area, as a continuation of the "Wide -area Multipoint Survey". In addition, theeffects of decontamination on the transport of suspended radiocesium in river water and rates oftransport will be analyzed in detail. Furthermore, a small number of the suspended solids (SS)samples collected to date in the Wide -area Multipoint Survey showed much higher radiocesium
concentrations compared with other samples. It is therefore important to elucidate the causes ofthis particular increase in radiocesium concentration in SS samples to understand the transport
dynamics of radiocesium in rivers, as radiocesium concentrations typically decrease over time. In
this project, we hypothesize that the presence of radioactive cesium microparticles (CsMPs) in thesamples are the cause of this phenomenon.
In this project, the Kuchibuto River Basin, which was previously monitored as part of the "Wide area Multipoint Survey", is newly designated as a target basin in the "Single Bas in Survey", andpreparations for the application of the TODAM model to this basin have been undertaken. In the
Hirose River Basin, we will continue monitoring to improve the accuracy of the calculations andto reproduce the changes in radiocesium concentra tions under high-flow conditions using the
TODAM model. To elucidate the dynamics of radiocesium through the river in more detail, we
will estimate the source of suspended radiocesium based on the characteristics of the organic
matter (total carbon and stable carbon isotope composition) in SS.
1.3. Content of implementation
Figure 1 shows the monitoring points used in this project; (a) the Kuchibuto River Basin, (b) themonitoring points used in the Wide -area Multipoint Survey, and (c) the Hirose River Bas in for themodel simulation.
(1) Wide-area Multipoint Survey
In the Wide area Multipoint Survey, monitoring has been continued by maintaining the devices
used in the 2013-17 project (including an SS sampler, turbidity meter, and water level meter).
Suspended solids were collected by samplers at 1 - to 2-month intervals, dried in a vacuum freeze dryer, and cesium-137 concentrations were measured using a germanium semiconductor detector.
Turbidity and water level data were obtained at 10-minute intervals, and the concentration ofsuspended sediment (mg L - 1 ) and flow rate (m 3 s -1 ) were calculated using the conversion equations
6

employed in the previous study. The suspended cesium-137 flux was estimated by multiplying theconcentration of SS, the river flow rate, and the cesium-137 concentrations in the SS.
In addition, the concentration of suspended and dissolved forms radiocesium in river water wasquantified by collecting 40 to 80 L of river water approximately twice a year and then collecting
radiocesium using a multi-stage filtration system (Fig. 2(a)). To clarify the actual effect of CsMPs
on suspended cesium-137 concentrations in river water, we used SS samples collected by the SS
sampler that showed much higher radiocesium concentrations compared with other samples. Usinga germanium semiconductor detector, an imaging plate (IP), and other techniques, highly
concentrated radioactive particles in SS samples were identified.

Figure 1. Monitoring points used in this study; (a) Kuchibuto River Basin, (b)Wide-are Multipoint Survey, (c) Hirose River Basin.

Figure 2. Radiocesium collecting devices; (a) multi -stage filtration system,(b)radiocesium monitoring device.

7

(2) Single basin survey
In this study, we maintained the monitoring network established in the Hirose River basin during
the previous project. In addition, an additional monitoring point was established along th e mainriver channel of the Hirose River in 2019 (St. 4). As for the Kuchibuto River Basin, we havestarted monitoring at five monitoring points, mainly those that were already i ncluded in the Widearea Multipoint Survey.
Approximately 100 L of river water was collected at each monitoring point at base -flow levels(every 2 to 3 months) and the 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
radiocesium were collected from river water samples in a cartridge filter for cesium monitoring
using a radiocesium monitoring device (Fig. 2 (b)). Each form of radiocesium was then measured
with a germanium semiconductor detector. In addition, a survey of the riverbed morphology(cross-section) and soil sampling (riverbed and river bed soil) were carried out. Based on these
data, we estimated radiocesium concentrations and their changes in the river under base -flow andhigh-flow conditions using the TODAM model.
To estimate the loading source of suspended radiocesium in river water, each subsample (500mL to 1 L) was collected and filtrated using glass fiber filter paper (pore size 0.7 μm), which had
been heated at 450ºC for 4 hours to remove organic matter.
The filters were then dried (105ºC, >48 hours), weighed and ground. The total carbon
concentration and stable carbon isotope composition of the SS were then measured by elemental
analyzer coupled to a stable isotope ratio mass spectrometer.
1.4. Results(1) Wide-area Multipoint Survey
Figures 3(a) and 3(b) show the results of the changes in suspended a nd dissolved cesium-137
concentrations over time (as of December 2018) obtained from the Wide -area Multipoint Survey.
The data include results from the University of Tsukuba until the end of FY2014 and in theprevious report. Although the change was not as rapid as that observed immediately after theaccident, the concentration of suspended cesium -137 at each monitoring point showed a tendency
to decrease over time after the start of this project. As of December 2018, the concentration was
generally less than 1/10 of that observed immediately after the accident (Fig. 3(a)). The
concentration of dissolved cesium-137 exhibited an identical decreasing tendency as that of thesuspended form of cesium-137 (Fig. 3(b)), although there was a period of missing data,
indicating that the concentration of radiocesium in the rivers of Fukushima Prefecture gradually
decreased over time and that this tendency continues at present.
In addition, the effective environmental half -lives of suspended and dissolved cesium -137 were
estimated to be approximately 2.8 and 3.6 years, respectively (Fig. 4), based on data obtained
from 2012 to 2018.

8

Comparing Chernobyl and Fukushima, the values of effective environmental half -lives ofcesium-137 were similar just after the accident (0.24 year in Abukuma River vs 0.31 year in
Pripyat River) 1 ) . In the second year and beyond, the decreasing rate of the concentration ofsuspended cesium-137 has lowered to about 1/10 of the initial rate in Fukushima. However,like just after the accident, the values of effective environmental half -lives are similar still(values of Fukushima are within the same range of values of European rivers; 1 to 4 years 4 ) ).

(a)

(b)

Year s from th e acc iden t (yea r)

Figure 3. Cesium-137 concentrations in river water.
(a) Suspended Cs-137,(b) Dissolved Cs-137.

9

Susp ended
Diss olved

Figure 4. Effective environmental half -life of cesium-137 concentrations in riverwater in each region (data from 2012–2018). The asterisk indicates the range
in the effective environmental half -life reported for European rivers after
the Chernobyl Nuclear Power Plant Accident).

Figure 5. Progress in farmland decontamination
Next, the data for the Kuchibuto River basin were analyzed to examine the effect of thedecontamination on the suspended of radiocesium in river water. These data mainly focused onchanges in the concentrations of the suspended radiocesium as decontamination activities
progressed. The basin was fully designated as a special decontamination area; work in the basin
was planned in August 2012, began in March 2013, and was completed in December 2015
(Ministry of the Environment Decontamination Information Site,
http://josen.env.go.jp/area/details/kawamata.html ).Figure 5 shows the changes in the area of
decontaminated farmland over time. Decontamination started in March 2013 but did not makemuch progress until March 2014. However, intensive farmland decontamination was carried out
from April 2014 and decontamination was completed in December 2015. Thus, the interval
before February 2013 was defined as “Pre-decontamination”, that during which very slow
10

progress was made, from March 2013 to March 2014, was defined as “Decontamination inprogress① ”, and the interval during which rapid progress was made, from April 2014 toDecember 2015, was defined as “Decontamination in progress ② ”. Finally, after January 2016
when decontamination was completed, the interval was defined as “Post decontamination”.
The changes in suspended cesium-137 concentrations at three monitoring points (upstream,
midstream, and downstream; Fig. 1 (a)) are shown in Fig. 6. The effective environmental half lives for each period are shown in Table 1. Importantly, the results show an increase in the rateof the decrease in suspended cesium-137 concentration in the upstream and midstream sites ofthe special decontamination area during “Decontamination in progress ② ”. Also, the rate ofdecrease decreased consistently in the downstream sites and slowed down in the second half of
the “Decontamination in progress ② ”period (after about 4 years since the accident). In
addition, the amount of sediment in 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 “postdecontamination” period, the amount of sediment in runoff decreased, but it was still higher
than in the “pre-decontamination” period (Fig. 7).

Figure 6.Change in suspended Cs–137 concentration over the course of
decontamination.

11

Table 1. Effective environmental half-life for each period (years)
Monitoring

Pre-

point

In progress In progress Post-decontami①②

nation① Upstream

0.77

n.s.

0.98

n.s.

② Midstream

1.2

n.s.

1.6

n.s.

③ Downstream

0.86

0.59

4.2

4.8

n.s. indicates that suspended cesium -137 concentration did not change significantly during each period.

Figure 7. Relationship between decontamination progress and the amount of sediment
runoff.
Figure 8 shows the changes in suspended cesium -137 concentration over time at a monitoring
point in the Hamadori area included in the Wide -area Multi-point Survey. Since the start ofmonitoring, the concentration of suspended
cesium-137 at the same monitoring point
has been gradually decreasing. However,the sample collected at the monitoring
point in October 2018 showed extremelyhighcesium-137

significant

concentrations,deviation

from

this

a

trend.

Thereafter, the concentration returned tonormal levels and trended downward overtime. Therefore, a hypothesis for
detection

of

this

specificthecesium-137

concentration is that a component with ahigh cesium-137 concentration might bepresent in the sample only. Previous studies
have reported the presence in the environmentofradioactive

cesiumenriched

particles(CsMPs) derived from nuclear power plant
12

Figure 8. Temporal changes suspended
Cs-137 concentrations

accidents 5), 6), 7) . Therefore, in this project, we hypothesize d that the increase of cesium-137
concentration in the SS sample was caused by the inclusion of CsMPs in the sample, andconducted some experiments to investigate the presence of CsMPs in the sample. In addition, if
the presence of CsMPs was found, we trie d to characterize them by imaging and elemental
analyses. Two CsMPs particles were found in the sample using IP (image processing) andgermanium semiconductor detectors. The radioacitivity of cesium -137 in those two particles wasestimated to be about 13 % of the total radioactivity. In the future, we establish the method todetermine the presence of CsMPs in SS samples with very high conetration of cesium -137.
(2) Single basin survey
Figure 9 shows the calculated and measured concentrations of suspended and dissolved
cesium-137 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 of the Hirose River. The measured values include the results obtained during theprevious project undertaken from 2013 to 2017 . In the previous report, we were able toreproduce the data obtained at five monitoring points along the main stream of the Hirose River
using the TODAM model. At monitoring point St. 4 established in FY2019, the results obtainedby the model simulation were in relatively good agreement with the measured values.
A simulation of the change in the concen tration of cesium-137 in river water at the time of high water flows from August 16 to 19, 2016 (total precipitation 67 mm; Japan Meteorological Agency,
Yanagawa, Fukushima Prefecture) is shown in Figure 10. The results also showed a good
agreement between measured and calculated values at the four monitoring points (St. 3, 7, 9, and
10) under high-water flow conditions. However, some deviations were observed and it will be
important to resolve these discrepancies by refining the model and to conduct trials for different
scales of water discharge in the future.
In this project we have started the monitoring in the Kuchibuto River basin (Fig. 1 (a)) for thesimulation of the suspended and dissolved cesium -137 concentrations in river waters by TODAM
model. In the Kuchibuto River basin, the water level and turbidity have been monitored at the 4monitoring point (① Upstream, ② Midstream、③ Downstream、and ⑤ Mizusakai River. Fig1(a)).
In this survey, we have started monitoring of the concentrations of suspended and disso lved
cesium-137 in river water at both base - and high-water flows at a total of five monitoring points,
including those points and a new point in a tributary river ④ AdachiOhta River. We willcontinuethis monitoring in this basin and plan to conduct simulat ions by TODAM model in the
future.

13

Figure 9. Simulation results of changes of cesium -137 concentration atbase-flow levels water estimated using the TODAM model

Figure 10. Simulation results of changes in cesium -137 concentrations
during flood events estimated using the TODAM mode l. [Upper rows:
Suspended cesium-137 concentration, lower rows: Dissolved cesium 137 concentration] (high-water flow events from 16 August 2016 to
19 August 2016)

14

The

concentration

of

SS

in

river

water

increases

substantially during high water flows compared to that inbase water. In the Hirose River Basin, significantly higher
SS concentrations were also observed under high -flow
conditions than under base -flow conditions (Fig. 11). Thislarge amount of SS is transported by the river and carries
with it large amounts of radioactive cesium to the ocean.
In this project, to clarify the source of the SS loads (asupply source), we focused on SS that is added to the riverunder high-flow conditions. For this purpose, we estimatedthe load source of the SS based on the qualitative
information of the organic matter (carbon, nitrogen, etc.)
in the SS.
13

12

The stable isotope ratios ( C/ C and

15

14

Figure 11. Concentrations of SS

N/ N), which

represent the qualitative information of the organic matter,in river water under base and high-flow conditions.

were also analyzed. In future, the relative contribution ofeach load source will be estimated by mixing the values of the potential load sources (riverbank
soil, riverbed sediments, organic matter from upstream forests, etc.) and the changes in therelative contributions of each load source with the increase in the SS concentratio n will beverified.
1.5. Conclusions
In this project, continuous monitoring of the radiocesium concentrations in river water inFukushima Prefecture is reported. The findings of the present study indicate that the decreasing
trend observed in radiocesium concentrations reported previously has been maintained. In addition,
the decontamination activities carried out in the basin have had a noticeable effect on theconcentrations of suspended cesium-137 in the river runoff in the region. The simulations results
were refined under base -flow condition. In addition, the simulation was carried out under high-flow
condition. Finally, preparations for new surveys and monitoring have been started in another basin.
References
1) Taniguchi, K., Onda, Y., Smith, H, G., Blake, W, H., Yoshimura, K., Yamashiki, Y.,
Kuramoto, T., Saito, K. 2019. Transport and redistribution of radiocaesium inFukushima fallout through rivers. 2019. Environ. Sci. Technol. 53, 12339–12347.
2) Onishi, Y., and Perkins, W.A. 1994. TODAM One–dimentional Sediment andContaminant Transport Model with Multiply Connected Networks. Theory and
Numerical Methods, vol. 1, Pacific Northwest National

Laboratory, Richland,

Washington.
3) Perkins, W., and Onishi, Y. 1994. TODAM One–dimentional Sediment andContaminant Transport Model with Multiply Connected Networks User ’s Guide, vol. 2,
15

Pacific Northwest National Laboratory, Richland, Washington.
4) Smith, J.T., Voitsekhovitch, O. V., Konoplev,

A. V., Kudelsky,

A. V. 2005.

Radioactivity in aquatic systems, in: Smith, J.T., Beresford, N.A. (Eds.), Chernobyl Catastrophe and Consequences. Praxis Publishing, 139 –190.
5) Hikaru Miura, Yuichi Kurihara, Aya Sakaguchi, Kazuya Tanaka, Noriko Yamaguchi,
Shogo Higaki, Yoshio Takahashi. Discovery o f radiocesium-bearing microparticles inriver water and their influence on the solid -water distribution coefficient (Kd) ofradiocesium in the Kuchibuto River in Fukushima. 2018. Geochem. J. 52. (2). 145–
154.
6) Yukihiko Satou, Keisuke Sueki, Kimikazu Sasa, Hideki Yoshikawa, Shigeo Nakama,
Haruka Minowa, Yoshinari Abe, Izumi Nakai, Takahiro Ono, Kouji Adachi, Yasuhito
Igarashi. Analysis of two forms of radioactive particles emitted during the earlystages of the Fukushima Dai-ichi Nuclear Power Station accident. 2018. Geochem. J.
52. (2). 137–143.
7) Yasuhito

Igarashi, Toshihiro Kogure, Yuichi

Kurihara, Hikaru Miura, Taiga

Okumura, Yukihito Satou, Yoshito Takahashi, Noriko Yamaguchi. 2019. A review of Csbearing microparticles in the environment emitted by the Fukushima Dai-ichi Nuclear
Power Plant accident. J. Environ. Radioact. 205–206.101–118.

16

2. FIP2 Survey of Radionuclide Movements in Wildlife
2.1. Abstract
Fukushima Prefecture is conducting surveys and studies 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 investigated fluctuation s in the concentration of radiocesium containedin the bodies of wild animals over time. Because of a possibility that wild animals with highradiocesium concentrations in their body have been moving into areas where wild animals withrelatively low radiocesium concentrations, 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. Radionu clides have been detected in many wild animals
inhabiting the natural environment there because they ingested radioactive materials from theenvironment through food.
In order to ensure the safety and security of environment that citizens of Fukushima pref ecture
are living, the Prefectural government, since immediately after the accident in 2011, has beenmonitoring radionuclide concentrations in the muscles of game animals whose meat is generally
consumed by people. As a result of monitoring, mainly cesium -134 and 137, which are gamma ray emitting nuclides, have been detected from the muscles of wild animals. This led to thelaunching of surveys and studies on radiocesium movements in the ecosystem. The migration ofcesium-137 from the environment to the wild animals seems to be strongly affected by theirecology such as food habits and behavioral patterns. From 2013 to 2017, radiocesium
concentrations in the bodies of wild animals were measured and their fluctuations with time anddifferences by animal species were investigated. In addition, wild animals ’ food habits andbehavioral patterns deemed to be closely related to radionuclide movements into their bodies werealso investigated. There is a positive relationship betw een the cesium-137 concentrations in themuscle and the stomach contents 1 ) . The relationship between radiocesium and the existing form
fraction 2 ) was clarified by the survey from 2013 to 2017. Presently, a food habit survey by the
DNA analysis of stomach contents has started, and radiocesium migration to the bodies of wild
animals according to food habits have been investigated in detail. A behavioral survey regarding
the home ranges of wild boars and Asian black bears using GPS collar has been also carried out,
however, the number of surveying has been inadequate. To show their behavioral characteristics,
the behavioral survey is being continued concurrently with the food habit survey.
In addition, the survey starting from 2018, analyses using linear models were performed to clarify
the long-term fluctuations of cesium-137 concentrations in the muscles of wild animals withseasonal fluctuations taken into account. DNA analyses were carried out in order to show thestructure of wild animal populations, which of the populations are increasing and which are17

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. Content of implementation
Just as in the 2013 to 2017 period, the present survey has mainly targeted wild boars, whoseradiocesium concentrations have been higher than those of other wild animals, and Asian blackbears inhabiting the same forestry ecosystem as wild boars.
(1) Measurement of radionuclide concentrations in the muscles of wild animals
Regarding radionuclide concentrations in the muscles of wild animals inhabiting the prefecture,
the Nature Conservation Division is monitoring game species such as wild boars, As ian blackbears, copper pheasants, Japanese pheasants, spot -billed ducks and mallards captured for theculling by management program or for hunting, thereby identifying the cesium -134 and 137
concentrations in their muscles. Using the measurement results, the variations of cesium-137 in
the muscles of wild boars and other animals and the fluctuations over time after the accident
were also investigated.
(2) Long-term fluctuations of cesium -137 concentrations in the muscles of wildboars and Asian black bears
The survey conducted from 2013 to 2017 clarified seasonal fluctuations in cesium -137
concentration in the muscles of wild animals (Figure 1) 3 ) . Based on the seasonal fluctuation
patterns, the data were divided into the low -concentration period of April to August and the high concentration period of December to March for wild boars and the low -concentration period ofJuly to September and the high -concentration period of November to January for Asian blackbears. The long-term fluctuations of cesium-137 concentrations in the muscle after the accident
was analyzed with a linear model that used the log 1 0 conversion of the cesium-137 concentrationsin their muscles as objective variable and the dates when they were captured and the log 1 0
conversion of cesium-137 deposition density on soils at the locations where they were captured
as explanatory variables. The linear model was applied in each of the low-concentration periods,
high-concentration periods and the entire period.

18

Figure 1. Seasonal fluctuations of Cs -137 concentrations in the muscles of(a) wild boars and (b) Asian black bears(3) Population Structure of wild boar s
We surveyed the population structure of wild boar s in Fukusuhima prefecture using by 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 treated as an out -group
population. Single-nucleotide polymorphisms (SNPs) were obtained from genome -wide regions
by MIG-seq method 2 ) for clarifying genetic structures of wild boars. We conducted
STRUCTURE 3 ) and cluster analysis using the derived SNPs information.

Incidentally, thissurvey was conducted in collaboration with the Fukushima Prefectural Center for Environment
Creation and the National Institute for Environmental Studies.
2.4. Results(1) Measurement of radionuclide concentrations in the muscles of wild animals
Figure 2 shows the cesium-137 concentrations in the muscles of wild boars and Asian blackbears captured in Fukushima Prefecture in May 2011 to March 2020.

19

Figure 2. Results of measuring the Cs -137 concentrations in the musclesof(a) wild boars and (b) Asian black bears* Black dot indicates the measured value of wild animal. The geometricaverage of Cs-137 concentrations in each fiscal year is indicated by abar graph, the 1st quartile (25%) and the 3rd quartile (75%) areindicated by the upper and lower ends of each box respectively, andmaximum and minimum values are indicated by bars (those less than lower
detection limit excluded).
The cesium-137 concentrations in the muscles of wild boars showed large variation amongindividuals. Some of them showed concentrations lower than the detectio n limit although thoseshowing concentrations close to 10,000 Bq/kg were observed even in recent years. Asian blackbears showed cesium-137 concentrations exceeding 100 Bq/kg *1 , which is the limit for general
foodstuffs in Japan, were also found in FY 2019 ( *1 Sum of cesium-134 and -137).
20

Figure 3 shows the color-coded results of monitoring cesium-137 concentrations in the musclesof wild boars and Asian black bears by the regions of Fukushima prefecture.

Figure 3. Cs-137 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.

21

The survey conducted from 2013 until 2017
revealed that the cesium-137 concentrations in
the muscles of wild boars and Asian black bears
were positively affected by the cesium -137
deposition density on the soils of locations
where they were captured (Figure 4). 1 ) In Soso
District,

Ken-poku

District

District,wherecesium-137

the

and

Ken -chu
deposition

density on soils was relatively high, many wildboars and Asian black bears with high cesium 137 concentrations were captured. In Aizu
District and Minami-Aizu District, where thecesium-137 deposition density on soils was
relatively low, many wild boars and Asian blackbears with low cesium-137 concentrations were

Figure 4. Relationship between theCs-137 concentrations in thecaptured. In Ken-chu District, those whose

musclesofwild

cesium-137 concentrations in their muscles wereAsianlower than the detection limit were captured,Cs-137 deposition density on

however, even in FY 2018, those whose cesium-

soils

137 concentrations in their muscles were close tothey were captured

black

of

boars

bears

and

locations

and
the

where

10,000 Bq/kg were also captured, thus suggesting
the wide range of cesium-137 concentrations in their muscles.
(2) Long-term fluctuations of cesium-137 concentrations in the muscles of wildboars and Asian black bears
Figure 5 shows the results of analyzing the long -term fluctuations of cesium-137
concentrations in the muscles of wild boars and Asian black bears.
With regard to cesium-137 concentrations in the muscles of wild boars, a decreasing trend
was observed during the entire period, low -concentration period (April to August) and high concentration period (December to March). However, the decreasing rate was small, and thecesium-137 concentrations estimated from a regre ssion line showed a wide range in the high concentration period. The wide cesium -137 concentration range during the high -concentration
period and inadequate data are likely to have resulted in the imprecise estimation of a long term fluctuation.
As for cesium-137 concentrations in the muscles of Asian black bears, a decreasing trend wasobserved during the entire period and the low -concentration period (July to September), but therange of estimated values widened over time during the high -concentration period (November
to January).

22

These results suggest the necessity of the abundance of data and reconsidering the models inorder to precisely estimate the long -term fluctuations of cesium-137 concentrations in bothanimals particularly during the high-concentration periods.

Figure 5. Long-term fluctuations of Cs-137 concentrations in
the muscles of (a) wild boars and (b) Asian black bears(3) Population structure of wild boar s
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. For confirming thegeographical trends of population structure, the wild boars captured in Fukushima prefecture
were classified into seven groups based on their captured locations and those captured in
Kumamoto Prefecture into one group (e ight groups in total) (Figure 6). A STRUCTURE 3 ) 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 that they were divided
into two genetic lineages (Figure 7). 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 we stern group
inhabiting Ken-poku District, Ken-chu District and Aizu District of Fukushima Prefecture and23

Kumamoto Prefecture (Figure 8). ( *The meat specimens obtained in Kumamoto Prefecture areprovided by Munemasa Kousan, a stock company.)

Figure 6. Grouping of specimens after their MIG -seq analyses and the number ofanalyses

Figure .7. Results of STRUCTURE analysis based on wild boar s DNA data
2 colors (red and green) represent genetic lineages suggested by the results of
STRUCTURE analysis. Ratio o f the colors are of the lineages in each sample shownby vertical column (0.00-1.00)

24

Figure 8. Results of cluster analysis based on wild boars’ DNA data
Figure 9 shows the results of the detection rates of two genetic lineages in each city, town andvillage. These results suggested that two genetic lineages divided by the east and west area alongwith Abukuma river as the boundary that restricted the movement to east and west.

Figure 9. Geographical distribution of wild boars of two genetic lineages
Ratio of genetic lineages shown by the STRUCTURE analysis (SeeFigure 7) in each municipality. Size of the circle represents theamount of samples.

25

2.5. Conclusions
High cesium-137 concentrations of muscle were observed in wild boars and Asian black bears
captured in areas where the cesium -137 deposition density were high, but the concentrations
significantly varied among individuals in the areas. Even in recent years, those showing
concentrations exceeding the limit for general foodstuffs in Japan were captured sometimes.
Regarding long-term fluctuations of cesium-137 concentrations in the muscles of wild boars andAsian black bears, it decreased over time during the entire period and low -concentration periods .
But during the high-concentration periods, the range of estimated values increased over time.
Wild boars in Fukushima Prefecture were suggested that they were divided into two lineages andthese populations divided by east and west area along with Abukuma River and around as theboundary that restricted the movement to east and west.
Cesium-137 concentrations in muscles of wild boars and Asian black bears were on a decreasing
trend, but they varied among individuals and fluctuated seasonally. Therefore, in o rder to precisely
estimate their long-term fluctuations, further data expansion is necessary. Moreover, themovement and dispersion of the wild animals seem to be a factor contributing to the variation ofcesium-137 concentrations observed even among those captured in the same region.
In the future, the monitoring of radiocesium concentrations in the bodies of wild boars and others
will be continued, the factors contributing to the high radiocesium concentrations in some wild
animals will be investigated, and survey methods to the conservation and management of wild
animals will be studied.
References
1) Nemoto, Y., Oomachi, H., Saito, R., Kumada, R., Sasaki, M., Takatsuki, S. Effects of 1 3 7 Cs
contamination after the TEPCO Fukushima Dai -ichi Nuclear Power Station accident on food andhabitat of wild boar in Fukushima Prefecture. J. Environ. Radioact. (in press)
2) Saito, R., Nemoto, Y., Tsukada, H. Relationship between radiocaesium in muscle andphysicochemical fractions of radiocaesium in the stomach of wi ld boar. 2020. Sci. Rep. 10, 6796.
3) Nemoto, Y., Saito, R., Oomachi, H. Seasonal variation of Cesium -137 concentration in Asian
black bear (Ursus thibetanus) and wild boar (Sus scrofa) in Fukushima Prefecture, Japan. PLoS
ONE. 2018. 13, e0200797.
4) Suyama, Y., Matsuki, Y. MIG -seq: an effective PCR-based method for genome -wide singlenucleotide polymorphism genotyping using the next -generation sequencing platform. 2015. Sci.
Rep. 5, 16963.
5) Evanno, G., Regnaut, S., Goudet, J. Detecting the number of clusters of individuals using thesoftware STRUCTURE: a simulation study. 2005. Mol. Eco. 14, 2611–2620.

263. FIP3 Sustainable countermeasures to radioactive materials in freshwater system
3.1. Abstract
In order to clarify the sustainability of the decon tamination effect and natural radiation
attenuation effect resulting from the large -scale flooding in riverside areas, field surveys wereconducted targeting the decontaminated riverside areas and parks. As a result, it was found that
decontamination is still in effect for five years after the test were conducted in the target riverside
areas, even under the vegetation growth. It was also found that air dose rates tend to decrease atriverside parks after large flooding. It was confirmed that the effect was large near a river, andgenerally no re-contamination was found.
3.2. Purpose
Radioactive materials (mainly radiocesium) spreading in the environment due to the accident at
the Fukushima Daiichi Nuclear Power Plant had contaminated the water environment. As a
response, monitoring surveys on water, deposited materials and aquatic products were conducted
to clarify the behavior of radioactive materials, and decontamination and some other measures
were taken by administrative agencies and researc h institutions. In this project that lasted until
December 2017, applicable radioactive material countermeasures were organized based on theexisting knowledge accumulated domestically and abroad. A decontamination test was also
performed at a river where limited decontamination measures were taken, thereby clarifying theeffectiveness of sustainability of decontamination. In addition, contamination situations weresurveyed targeting public riverside areas in Fukushima Prefecture. Above survey results wereshown in previous report. However, flood can cause the erosion and deposition of sediments
containing radioactive materials and change the contamination situation at the river. This could
raise the concern of re -contamination of these public areas . For this reason, in 2018 and onward,
the sustainability of decontamination effect on riverside areas where the decontamination test
had been performed was continuously checked, and the contamination situations and changes in
air dose rate at riverside parks due t o large flooding caused by typhoon No. 19 (Hagibis) in 2019were investigated.
3.3. Content of implementations(1) Verification of the sustainability of decontamination effect on riverside
areas under the vegetation(a) Purpose
As a measure against external exposure at riverside areas, a decontamination test was
performed in 2014 by removing deposited materials based on radiocesium distribution to checkthe reduction effect of the radiation dose. In most cases, however, rivers ha ve a nondecontaminated forest area in their upstream catchments, from which earth and sandcontaminated by radiocesium are supplied to the rivers when floods occur. Although theparticulate radiocesium concentrations in the river water are decreasing over time, the27

deposition of sediment contaminated by radiocesium raises the concern of river area re contamination. Particularly in the case of a riverside area with a vegetation growth, fine -grained
sediments with a relatively high radiocesium concentration may deposit because plants easily
capture the fine sediments, which can lead to re-contamination. Therefore, in areas where
decontamination tests were carried out, re -contamination due to vegetation growth was checked
by a continuous monitoring of air dose rates and sediment deposition while keeping thevegetation growth unchanged.
(b) Method
The test site was set at the downstream end of the Kami -Oguni River, which is a tertiary branchof the Abukuma River, and is located 55 km northwest from the Fukushima Daiichi Nuclear
Power Plant (Figure 1). The deposition amount of radiocesium (Cs -134 and Cs-137) is 300 to
600 kBq/m 2 1 ) . Most of the river basin is covered by a forest, with farmlands and residential
areas existing along the river (Figure 1 (b)). The decontaminated zone ’s total length is 170
meters, width is 15 meters on average, and the width of river channel at the base flow level is
two to six meters (Figure 1 (c), 1 (d)). The river’s left bank area had been used for an elementary
school and access routes to the school. The right bank area had been used for an orchard, andthe flood channel had been used for the elementary school ’s outdoor education. The elementary
school and its access routes were decontaminated before the test. In the decontami nation test
conducted in 2014 for the riverside area, the depth distribution of radiocesium concentrations
in sediments was measured first. According to the distribution, the depths of sediment removal(scraping) were set at 15 to 35 cm, and then decontami nation was conducted. As a result, theaverage air dose rate at the decontaminated zone decreased from 0.66 µSv/h to 0.34 µSv/h. The
details of the test are described in Nishikiori and Suzuki (2017) 2 ) . During the period after thedecontamination test until the end of 2016, all the flood channel vegetation was cut down andthen observations were made. On the other hand, since 2017, observations were made without
cutting down the vegetation. In 2018, an embankment construction was carried out as disaster relief work at the upstream side of the right bank.
The air dose rates 1 meter above the ground surface of the test zone were measured during abase flow period. Newly-deposited sediments that accumulated during an observation interval
and previously-deposited materials that had accumulated earlier were distinguished based on
the ring method (erosion pins), and then samples of deposited materials were taken from sevenpoints in the riverside area. Radiocesium concentrations in the deposited materials were
measured after removing gravels and pebbles. The ratio of mud (silt and clay) in the entire
sample mass was also calculated. Vegetation was cut down partially in the test zone, and plantbiomass on the flood channel was measured. Because plant biomass before th e decontamination
test had not been measured, plant biomass on the flood channel without any artificial
disturbance was measured in 2019 to compare the plant biomass before and after thedecontamination test in 2014.

28

Figure 1. Outline of the Kami -Oguni River Survey Area
Note: The amounts of radiocesium deposition were derived based on
the results of the 3rd aircraft monitoring (converted on July2, 2011) 1 ) .
(2) Changes in contamination situation in riverside area due to large flooding(a) Purpose
In a riverside area, the deposition of sediment can lead to the accumulation of radioactive
materials. Surveys conducted by December 2017 also indicated that radiocesium had
accumulated at river vicinities, with air dose rate increasing. In a riverside are a, the erosion
and the new deposition of sediments caused by large flooding due to typhoons can change thedepth distribution of radiocesium concentrations (Konoplev et al., 2017 3 ) ; Nakanishi et al.,2019 4 ) ). Such a phenomenon reportedly lowers the air dos e rate in a riverside area and iscalled natural attenuation.
The impact of Typhoon No. 19 (Hagibis) in October 2019 caused river dike breaches andoverflows in Fukushima Prefecture, resulting in submergence of the riverside areas andcausing significant damage. To clarify the presence or absence of re -contamination due topreviously reported flood -caused erosion and deposition or a decrease in air dose rate due tonatural attenuation, changes in air dose rate and contamination situations in the riverside a rea
and parks after the passage of typhoon No. 19 were surveyed.
(b) Method
Surveys were carried out at two riverside parks (Figure 4) located in Hamadori area in29

Fukushima Prefecture and the decontamination test site at the Kami -Oguni River (Figure 1).
Park A is located along the Niida River ’s mainstream and Park B is located along the
Mizunashi River, which is the primary branch river of the Niida River. The amount ofradiocesium deposition (Cs -134 and Cs-137) at the watershed exceeded 1000 kBq/m 2 in the
upstream area but was below 100 kBq/m 2 at the lowest point downstream 1 ) . The amount ofradiocesium deposition was 490 kBq/m 2 at Park A and 210 kBq/m 2 at Park B 5 ) . The areas ofPark A and Park B are 2.7 ha and 1.6 ha, respectively.

Figure 2. Survey areas in riverside parks
Note: The amounts of radiocesium deposition were derived based on the
results of the 3rd aircraft monitoring (converted on July 2, 2011). 1 )Typhoon No. 19 Hagibis passed through Fukushima Prefecture on October 12 to 13, 2019. At
the meteorological observatory (in Hara -machi) nearest to Parks A and B, a precipitation of
274.5 mm was observed as a result of a series of rainfalls 6 ) . Dike breaches and flooding damage
occurred at the major river, namely Abukuma River, and other rivers in t he prefecture. River
dike breaches and overtopping occurred also at the survey area.
Using a portable gamma -ray-measuring device (gamma plotter H, Japan Radiation Engineering
Co., Ltd.), the air dose rates one meter above the ground surfaces were measured in the survey
area. Measurements were carried out on January 31, 2018 (before the typhoon) and October 17,
2019 (after the typhoon). After the passage of the typhoon, a field observation was performed
to check the sediment erosion and deposition situation s in the riverside areas and parks.

30

3.4. Results(1) Verification of the sustainability of decontamination effect on riverside
areas under the vegetation
Figure 2 shows changes in air dose rate until the end of 2018. In the test zone, the air dose ratecontinued to decrease from 2017 when the cutting down of vegetation was stopped. In thedecontaminated zone, a decontamination test revealed that the air dose rate generally halved andthen decreased slightly faster than the pace of physical decay.
Also regarding the non-decontamination zone, the air dose rate decreased at a pace faster thanphysical decay, and the environmental half -life obtained by applying an exponential function was
5.9 years, which was shorter than 8.1 years for the decontaminated zo ne. The largest air dose
rate decrease was observed after the passage of a typhoon in September 2015. It is likely that thedecrease was caused by large flooding of the area. The measuring of air dose rates after thedecontamination test confirmed no re -contamination.

Figure 3. Changes in air dose rate at the Kami -Oguni River
Note: The physical dacay of radiocesium 134 and 137 was calculatedwith the initial deposition ratio being 1:1. Initial values
were fitted to the values measured on November 16, 2014 after
the completion of the decontamination test.
From the end of 2016 until August 2017, the radiocesium concentrations in newly -depositedmaterials that accumulated on the flood channel with vegetati on were higher than those without
vegetation sampled until the end of 2016 and were higher than those in previously-depositedmaterials sampled in August 2017 (Figure 4). These sediments contained relatively high ratiosof clay and silt, and it is understo od that the vegetation trapped the fine -grained sediment.
However, compared with deposited materials in the riverside area before the decontamination
test, radiocesium concentration and mud ratio were smaller in these sediments. It is likely that,
because the amount of their deposition was not high, the measurement in August 2017 did not31

show an increase in air dose rate.
On the other hand, after typhoon No. 21 (Lan) in 2017, a 20 cm thick sediment deposited in
the riverside area (Figure 3). However, their radiocesium concentration was lower than that of
surface soil after the decontamination test, and their mud ratio was low. Biomass quantity inthe riverside area in the summer of 2017 was 40 % of the pre -decontamination-test reference
value measured in 2019. After one-year vegetation recovery , a normal rainfall can cause thedeposition of fine-grained sediment whose cesium concentrations are high, but the trapping
effect of the fine-grained sediments is deemed to have been small in large -scale flooding
caused by typhoons. In 2018, large -scale rainfalls that involved the deposition of sediments
were few and the radiocesium concentrations and mud ratios in deposited materials were also
low.

Figure 4. An example of depth distribution of radiocesium concentrations indeposited materials in a riverside area (center of the survey area)(2) Changes in contamination situation in riverside area due to large flooding
The results of air dose rate measurement in Park A are shown in Figure 5. The average air dose
rates before the typhoon Hagibis (January 31, 2018) and after the typhoon (October 17, 2019)were 0.30 µSv/h and 0.20 µSv/h, respectively. The air dose rate decreased by 13% during theinterval between two measurements because of physical decay. With this taken into account, thetyphoon and rainfall effect decreased the air dose rate by 23% compared with that before thetyphoon. In comparison, the air dose rate after the passage of Typhoon No. 15 (Etau) in September
2015 decreased to 14% of that before its passage. It was obvious that the effect of typhoon
Hagibis was stronger than typhoon Etau. This difference in effect resulted from differences in32the scales of erosion and deposition. As shown in the aerial photographs (Figure 5), Typhoon
Hagibis also eroded a significant amount of sediments along the Niida River. Portions that had
shown the highest radiation level during the pre -typhoon measurement flowed away, and the bankprotections of the parks were exposed (Figure 6 (a)).
In this area, highly-concentrated radiocesium was present at first, but the passage of Typhoon
Etau in 2015 also resulted in less contaminated sediment depositing on the surface and shielded
the highly-contaminated portions, thus lowering the air dose rate as shown in the previous report.
However, as Figure 6 (b) shows, sediment remained deposited and vegetation was growing on
the bank protections. A decrease in air dose rate after the passage of Typhoon Hagibis was causedby the removalof radiation sources by the typhoon, so the typhoon’s effect seems to have been
larger than the shielding effect that occurred after Typhoon Etau. On the other hand, because thedeposition of a large amount of sand was observed at the Niida River flowing in the park and thebranch river north of the park (Figure 6 (c) and (d)), a decrease in air dose rate inside the park
seems to have resulted from a shielding effect.
As for Park B, the average air dose rates before and after the passage of Typhoon Hagibis were0.21 µSv/h and 0.16 µSv/h, respectively. After the correction of physical decay, the average after
the passage of the typhoon decreased by 12% of that before its passage because of the effect of
typhoon Hagibis (Figure 7). In comparison with the effect of Typhoon Etau in 2015 decreasing
the air dose rate by 5% of that before its passage, Typhoon Hagibis in 2019 significantly
decreased the air dose rate in Park B in the same way as in Park A. The passage of Typhoon Etau
caused almost no erosion or deposition in Park B, but the passage of Typhoon Hagibis flooded
the entire park, changed the river channels at the park ’s upstream, and deposited a large amountof sand, gravel and pebble particularly at the upstream area in the park. Decrease in the air dose
rate was also larger in the upstream side of the park . This would imply that the shielding effectby deposited sediments decreased the air dose rate.
In the Kami-Oguni River survey area, air dose rate decreased not only in the river channel but
also on the river bank. Althoug h most of sediments in the river channel had been removed by the
excavation work immediately before the survey, a large amount of sediments such as sand, pebble
and gravel were re-deposited.
This survey revealed that Typhoon No. 19 Hagibis in 2019 did not cause re-contamination in all
survey sites generally; rather, it was confirmed that natural attenuation has caused the decreased
air dose rate.

33

Figure 5. Air dose rate distribution in Park A [(a) after the passage of Typhoon
No. 19, (b) before its passage]
Note: Background photograph (a) is a satellite image taken by the Cabinet
Intelligence and Research Office 7 ) on October 17, 2019. Background photograph(b) was obtained from Google Earth Pro 8 ) (date of the photo: October 21, 2018).

Figure 6. Photos showing the situations of riverside areas(a) River revetment exposed due to river bank erosion caused by thepassage of Typhoon No. 19, (b) The same river revetment before being
eroded (a photo taken from the opposite side on September 28, 2015),(c) Sediments deposited along the Niida River, (d) Sediment depositedalong the branch river north of the park34

Figure 7. Air dose rate distribution in Park B(a) After the passage of Typhoon No. 19, (b) Before its passage
Note: The background photographs were obtained from Google Earth
Pro 8 ) (date of the photos: October 21, 2018).
3.5. Conclusions
In this project, we contined to confirm the persistence of the decontamination test in 2014. In
the decontaminated riverside site , air dose rate decreased with time even on the vegetated flood
channel after 2017 following typhoons. An increase in radiocesium accumulation on the flood
channel was not observed. These results show the persistence of the deconatamination test. In
addition, we surveyed the change in the air dose rate in the riverside parks after typhoon No, 19,
Hagibis, which caused significant damage in Fukushima Prefecture in 2019. After the passage oftyphoon Hagibis, air dose rate in the riverside parks generally decreased. Recontamination by thedeposition of the sediments with high radiocesium concentration was not observed, rather naturalattenuation during the flooding occured.
In the future, we continue to monitor the riversides and the riverside parks to confirm thepersistence of the impact of the decontamination test as well as to understand the recontaminationand the change in the air dose rate after the large flooding by typhoons.

35

References
1)

Ministry of Education, Culture, Sports, Science and Technology. 2011. The
Results of Measuring Radiocesium Deposition by the 3rd Aircraft Monitoring
https://radioactivity.nsr.go.jp/ja/contents/5000/4858/24/1305819_0708.pdf

2)

Nishikiori, T., Suzuki, S. 2017. Radiocesium decontamination of a riverside in
Fukushima, Japan. Journal of Environmental Radioactivity 177, 58 -64.

3)

Konoplev A., Golosov V., Wakiyama Y., Takase T., Yoschenko V., Yoshihara T.,
Parenyuk O., Cresswell A., Ivanov M., Carradine M., Nanba K., Onda Y. 2017.
Natural attenuation of Fukushima -derived radiocesium in soils due to its verticaland lateral migration. Journal of Environmental Radioactivity.
doi:10.1016/j.jenvrad.2017.06.019.

4)

Nakanishi T., Sato S., Matsumoto T. 2019. Temporal changes in radiocesium
deposition on the Fukushima Floodplain. Radiation Protection Dosimetry, 1 –4.
doi:10.1093/rpd/ncz086

5)

Nuclear Regulatory Authority. 2017. Radiation Distribution Map Website.
http://ramap.jmc.or.jp/map/

6)

Japan Meteorological Agency. 2020. Data and documents
http://www.jma.go.jp/jma/menu/menureport.html

7)

Cabinet Intellignece and Research Office. 2019. Processed Images of Areas
Damaged by Typhoon No. 19 in 2019https://www.cas.go.jp/jp/houdou/191017csice.html

8)Google Earth Pro aerial photograph36

4.FIP4 Development of environmental mapping t echnology 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 dose 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 device 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 -timedose-rate measurement system)(b): Example of a car-borne survey (KURAMA-II installed on theback of a local bus)

37

(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 areas, 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 a lleys 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 more detailed and effective.

38

Figure 3. Measurement ranges of conventional measurement methods
4.3. Content of implementation(1) Development of equipment
We used the KURAMA -II, which was developed by Kyoto University, for walking surveys,
and assembled five pieces of equipment in a way suited to walking surveys (Figure 4). Theorange 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 atransverse course while merging dose rate data from the low -dose CsI detector and position
information from the high -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 interval 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 displayed on the computer screen.
39

Measurers can look at the screen to check the measurement position and dose rate while
conducting detailed measurements.

Figure 5. Display screen on a personal computer(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 s hown in Figure 6.

Result ofwalking survey

GIS tool

Result of airborne survey by a
UAVCombined 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 dos e
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).

40

Figure 8. Map data and dose rate plottin g

Figure 9. Interpolated dose map(3) Walking survey implementation
We collected parameters necessary for walking surveys, and carried out the survey in several
areas.
(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(1) Gathering parameters necessary for walking surveys
We conducted a field test of walking surveys, andgathereddata for evaluation and analysis (Figure10). Data were gathered to check the direction
characteristics and appropriate measurement density, as
well as to determine correction factors.
A Checking direction characteristics
Shielding from the measurers themselves affects

Figure 10. View of a walking

the contribution from the radiation source depending

surveyon 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 theradiation 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
the same during forward and reverse passes (Figure 12). We also confirmed that reducing thewalking 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 valueof a walk survey was considered small at a constant walking speed.

41

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

B Determination of correction factors in a comparison test with survey meters
We 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,
we faced north, south, east, and west and made meas urements five times in each direction to
mitigate direction characteristics. We then took the average value for all directions as themeasurement for that point. We next plotted the measurements of walking surveys against thesurvey meter to determine the correction factor.

42

(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
the measurements of walking surveys and the survey meter below a survey metermeasurement of 1 μSv/h, whereas the linearity deteriorated above approximately 1 μSv/h.
This phenomenon is due to count loss caused by exc essive radiation incidence on the lowdose CsI detector.
In light of the above results, we changed the detector to a high -dose-rate CsI detector(Figure 17) and compared the results obtained using the survey meter with measurement
results of walking surve ys again. The results are shown in Figure 16(b). We confirmed thatas 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 thanthe 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 changed detectors at the samegeographic point. Th e maximum indicated value is higher for the high -dose-rate CsI
detector than for the low -dose-rate CsI detector, and the high -dose-rate area represented
by red markers appears, indicating that measurements are made without counting loss ofradiation.

43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 (Cs-137, 662keV measuring ra nge: 0.001 to 10 μ Sv/h)and NaI survey meter.
● Comparison of the measurements of the high -dose-rate CsI
detector (Cs-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 -dosefrom the measurement detector, with the intercept being zero.

44

Figure 17. High-dose CsI detector (Hamamatsu Photonics C12137)
According to the above comparisons, we set the correction factor s 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.

(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.
C 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.

45

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 low dose-rate CsI detector but 42.7% for the high-dose-rate detector. Error in measurements madewith the low-dose-rate detector was
0.12

rate achieved with the large crystal

0.10

with the high-dose-rate detector
was large because of the small
counting rate achieved with thesmall crystal.
On this basis, we decided to use

dose rate

while error in measurements made[µSv/h]small because of the high counting

KURAMA for
low dose rate
KURAMA forhigh dose rate

0.08
0.06
0.04
0.02
0.00
3

the low-dose-rate CsI detector,

18

33

48

63
time

78

93

108

123

[sec.]

which has a small variation at low
dose rates, at geographic points

Figure 19. Measured value dispersion checkwith a dose rate less than 1 µSv/h, and to use the high-dose-rate CsI detector at geographic
points with a dose rate greater than 1 µSv/h.
(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 walki ng surveys
are described below.
A Walking survey in western Fukushima City
We conducted a walking survey on a trial basis in western Fukushima City. At the center ofthis geographic 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 andsurrounded by 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 comparedwith 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 a ddition, theradiation dose in the vicinity of the ditch was higher than that of the surroundings. This isprobably because there was an inflow of radioactive material from the surrounding area.
We conducted a high-density walking survey and tested interpo lation with a GIS tool (Figure21). Interpolation was conducted with IDW. The interpolated radiation dose rate in the paved
area was low, and the dose rate in the vicinity of the ditch was high.

46

Paved area

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

Figure 21. Results ofinterpolation with IDW

B Walking survey in the periphery of a temporary storage area
We conducted a walking survey in a
temporary storage area and its periphery intheNakadori

regionofFukushima

Prefecture (Figure 22). The area inside thered frame in the figure is the temporarystorage

area.

The

dose

rate

near

the

temporary storage area was equal to or lessthan the dose rate in the periphery, and noeffect of external decontaminated waste on
the outside area was seen in this temporary
Figure 22. Dose map(with the temporary storage area
indicated by the red frame.)storage area.

C 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.

47

Figure 23. Dose map

Figure 24. IDW interpolation result

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

Figure 25. Dose map

Figure 26. Results ofinterpolation by IDW

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 Project) .

48

5. FIP5 Examination of Proper Treatment of Waste Containing Radioactive Materials
5.1. Abstract
Using incineration ash (bottom ash and fly ash) containing radiocesium generated in Fukushima
Prefecture, laboratory tests were conducted to investigate radiocesium elution and the suppressionof radiocesium elution by acid clay and zeolite. Based on the r esults, experiments regarding the
suppression of radiocesium elution from fly ash using two different addition methods were carriedout at actual municipal waste incineration facilities.
Moreover, each status of the landfill disposal sites was investigated regarding incineration ash
and radiocesium elution. While a study on landfill disposal sites was included in this project fromFY 2018, Fukushima Prefecture had launched the same study on its own before that, so this report
also includes the contents of the study conducted by FY 2017.
5.2. Purposes
The incineration of municipal waste containing radiocesium scattered due to the accident at
Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Plant Station
resulted in the migration of radiocesium to incineration ash and its concentration. Some
incineration ash generated in this way cannot be subjected to landfill disposal even when its
radioactive concentration is below 8,000 Bq/kg, a standard value provided by law, and so, someare forced to be stored.
Although the concentrations ofradioactive materials
significantly decreased after nine
years from the accident,
incineration ash containing
radioactive materials is daily
generated from the incinerationof municipal waste, and its
proper disposal is an urgent task.
Thus, as described in the final
report for the previous project,
the distribution of radiocesium
between bottom ash and fly ash,

Figure 1. The contents of the past studies

the proper treatment of bag -filter waste cloths and the suppression of radiocesium elution fromfly ash were studied until FY 2017.
(1) Distribution of radiocesium between bottom ash and fly ash
It is generally known that radiocesium volatilizes upon its combustion and tends to migrate to
fly ash rather than to bottom ash. The factors that influence the migration of radiocesium wereclassified into five, i.e. combustion temperature, air ratio, waste quality, chemical addition and49ash particle diameter. Among these factors, the correlation between “combustion temperature andchemical addition,” which are relatively easy to control and “radiocesium migration behavior ”
were investigated through verification tests at actual facilities. As a result, it was found that itis difficult to change th e combustion temperature in an operating incinerator because
maintenance and management standards stipulating an allowable combustion temperature range
have been established by laws relating to Waste Manegement and Public Cleaning Act . As for achemical addition method, the addition of hydrated lime to incinerated waste somewhat promoted
radiocesium migration to fly ash at some facilities, but the reproducibility of such a phenomenon
was scarce.
(2) Tests on the proper treatment of bag -filter waste cloths
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 anotheroperation with the co -combustion of radiocesium-containing waste filter cloths and municipal
waste by changing the input ratio and input time interval of the radiocesium -containing waste
filter cloths were carried out. The results revealed tha t 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.
(3) A study on the suppression of radiocesium elution from fly ash
Radiocesium elution tests were conducted for fly ash and bottom ash (64 samples in total) at 15
facilities in Fukushima Prefecture to obtain cesium elution data. At facility K, zeolite or
bentonite, both of which are expected to be effective in cesium elution suppression, was a dded
to and kneaded with incineration ash and then a radiocesium elution test was performed. The
results showed the excellent effects of zeolite and bentonite in the suppression of radiocesium
elution from the fly ash, and the effect of zeolite was particu larly remarkable.
For this interim report, as a development from (3) above, verification tests were performed atincineration facilities when in operation to investigate the effectiveness of techniques forremoving radiocesium or suppressing the elution of radiocesium from incineration ash based on
the understanding of radiocesium elution property, for the purpose of safely and properly
disposing of incineration ash (bottom ash and fly ash).
In order to assess the future safety of landfill disposal sites where radiocesium-containing
incineration ash is subjected to landfill disposal, landfill disposal sites having started burying
radiocesium-containing incineration ash were investigated in terms of their status of incineration
ash landfill and a correlatio n between a disposal site structure and radiocesium elution50

5.3. Content of implementation(1) Tests on radiocesium elution suppression
A Tactical agitation tests using a germanium semiconductor detector
Using a germanium semiconductor detector, radiocesium 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
property of radiocesium was performed using 2.5 L of ultrapure water for about 250 g ofincineration ash, in accordance with JIS K 0058 -1. A radiocesium elution rate (%) was
determined by the following:[radiocesium concentration (Bq/kg) in the eluate] x [the weight of ultrapure water used in theelution test (kg)] ÷ [radiocesium concentration in incineration ash (Bq/kg)] x [the weight ofincineration ash used in as-is agitation test (kg)] x 100.
B A test on radiocesium elution suppression (long -term as-is agitation test)
In order to find a method of suppressing radiocesium elution from incineration ash having
been exposed to rain water during its s torage or after a landfill (elution -suppressing method),an acid clay was added to an incineration ash by 5% in weight, they were mixed with water
until the water content reached 30% and then were subjected to a radiocesium measurement
using a germanium semiconductor detector and a long -term as-is agitation test. The durationsof agitation were set at 6 hours, 24 hours, 7 days, 14 days, and 30 days. Radiocesium elution
rates were determined and the radiocesium elution -suppressing effect of an acid clay wasinvestigated by mixing or not mixing it into the incineration ash.
C A test on radiocesium elution suppression (MP -AES / ion chromatography test)
In order to investigate the effect of mixing acid clay into incineration ash on the 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 device.
(2) Tests on radiocesium elution suppression in incineration ash at municipal
waste incineration facilities
Regarding zeolite, which was found to be effective in the suppression of radiocesium elution
as described in 5.2.(3), zeolite addition tests were performed a t two systems of an actual
municipal waste incineration facility to verify the feasibility of a radiocesium elution
countermeasure using zeolite at an incineration facility.
A 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 radiocesium concentrations and elution properties.
51

(a) Germanium semiconductor detector test, a JIS K 0058 -1 elution test and theEnvironment Agency’ s Notice No. 13 elution test

Using the methods shown in Table 1, tests were conducted to investigate the radiocesium
concentration of each sample and the elution properties of radiocesium and heavy metals.
(b) Repetitive elution tests (JIS K 0058 -1)
In order to investigate the quantities of repetitive elution of radiocesium and heavy metals,
the JIS K 0058-1 elution test shown in Table 1 was repeated four times (each sample used for
an elution test was subjected to another elution test by putting it i nto a new solvent) using
bottom ash and treated fly ash
time

zone

when

the

radiocesium concentrationin fly ash was the highest
during a normal operation
period. An eluate obtained
from

each

test

was

examined for radiocesium
concentration, heavy metal

Table 1. Test Conditions and Others
SampleRadiocesium
Concentration

sampled during the sameContainElution
pH
EC
Hg
Cd
Pb
As
Se
Cr
Cl-

Test Methods
Gamma-raySpectrometry byGermanium
Semiconductor
Detector, Radioactivity
Measurement Method
Series No. 7 by MEXT

JIS K 0058-1
JIS K 0058-1
orEnvironment Agency’s
Notice No. 13 (NoticeNo. 13)

Used Equipment

Germanium Semiconductor Detector(ORTEC GEM20P4-70)

GST-5741C, DKK-TOA CORPORATION
CM-30R, DKK-TOA CORPORATION
RA-3A, Nippon Instruments Corporation
Agilent Technologies 7500ce ICP-MS
or
7800 ICP-MS
Thermofisher Scientific ICS-1100

Minimum Determination Limit
Fill U8 container up to a height of
5 cm and measure for 3,600
seconds

Fill a 2L Marinelli container up toa height of 12 cm and measurefor 20,000 seconds
0.0005mg/L
0.009mg/L
0.03mg/L
0.01mg/L
0.02mg/L
0.1mg/Lconcentrations, pH and EC.
(c) Zeolite addition test in laboratory
To study zeolite addition ratios in zeolite addition tests at actual facilities, zeolite was addedby 5 to 20% (in 5% increments) to the fly ash and treated fly ash that were sampled during anormal operation test period and that showed the highest radiocesium concentrations, and thenwater was mixed with the fly ash and treated fly ash until their water content reached 30%.
The test shown in table 1 was performed on each mixed sample to check the presence orabsence of a radiocesium elution suppression effect and an effect on heavy metals and others.
B Tests on zeolite addition to an exhaust gas treatment agent at actual
facilities

At the municipal waste facilities mentioned in A, exhaust gas treatment using an exhaustgas 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
to determine radiocesium concentrations and elution property.
(a) 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 addit ion test period, using methods
described in the Waste Management Division ’s Notification No. 95, Exhibit 3, II and theMinistry of the Environment’s 2011 Notification, No. 111.

52

(b) Germanium semiconductor detector test, JIS K 0058 -1 elution test and theEnvironment Agency’ s Notice No. 13 elution test
To investigate radiocesium concentrations and the elution properties of radiocesium andheavy metals in treated fly ash sampled during the chemical mixture addition test period, tests
were performed using the methods shown in Table 1.
(c) Repetitive elution tests (JIS K 0058 -1)
The average of radiocesium concentrations in the treated fly ash sampled during the chemical
mixture addition test period was calculated. A sample that indicated a radiocesium
concentration closest to the average value was subjected to four JIS K 0058 -1 repetitive elution
tests (a sample having been subjected to an elution test was immersed into a new solvent andthis operation was repeated four times) shown in Table 1. An eluate obtaine d from each test
was examined for radiocesium concentration, heavy metal concentrations, pH and EC. Tests
using artificial seawater as a solvent were also carried out.
C Tests on zeolite addition to the mixture of fly ash and chelate agent by
kneading at actual facilities
At the municipal waste incineration facilities mentioned in A, heavy metal elution suppression
treatment in which zeolite was added to a chelate agent kneader for suppressing heavy metalelution from incineration ash was performed for fiv e consecutive days. During the heavy metalelution suppression treatment period, the treated fly ash was sampled at 14:00 each day andtested to determine radiocesium concentrations and elution property.
(a) Germanium semiconductor detector test, JIS K 005 8-1 elution test and theEnvironment Agency’ s Notice No. 13 elution test

Tests were conducted using the method shown in Table 1 to examine the radiocesium
concentrations and the elution properties of radiocesium and heavy metals in the treated
fly ash sampled during the mixing addition test period.
(b) Repetitive elution tests (JIS K 0058 -1)
The average of radiocesium concentrations in the treated fly ash sampled during the mixing
addition test period was calculated. A sample that showed a radiocesium concentration closest
to the average value was subjected to four JIS K 0058 -1 repetitive elution tests (a sample
having been subjected to an elution test was immersed into a new solvent, and this operation
was repeated four times). An eluate obtained from each test was examined for radiocesium
concentration, heavy metal concentrations, pH and EC. Tests using artificial seawater as asolvent were also carried out.

53

(3) Situations of landfill and radiocesium elution
A 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

Table 2. Situations of the landfill of incinerationwater), discharged water, watertreatedsludgeandashnearbyunderground water were sampled
once a month at the sites. Then
their radiocesium concentrations
were measured to investigate a correlation between landfill situation and radiocesium elution.
In addition, radiocesium concentrations in leach ate and discharged water were compared tocheck the radiocesium treatment situations at leachate treatment facilities. The situations ofincineration ash landfill at the seven landfill disposal sites are shown in Table 2. Their
incineration ash landfill si tuations 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 the sandbags.
B FY 2016
In November and February, leachate (seeping water), discharged water, water -treated sludge,
and nearby underground water were sampled from six landfill disposal sites in total (Table 3,
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 was buried in the same method used
before the accident, and landfill disposa l site I where only bottom ash was buried), and theirradiocesium was analyzed.
Table 3. The list of landfill disposal sites(4) Correlation between the annual elution situation of radiocesium and otherelements
In FYs 2017 and 2018, leachate (seeping water), discharged water, water-treated sludge, andnearby underground water were sampled from four landfill disposal sites A, B, D and H,
whereby their radiocesium concentrations were measured. Water-treated sludge was sampled
only in FY 2017. Among the four landfill disposal sites, three landfill disposal sites A, B and
H were burying fly ash in the same methods they used before the nuclear power station accident,
54and landfill disposal site D was burying fly ash after putting it in large sandbags. However ,during a certain period immediately after the accident, site D buried part of fly ash without
putting it in large sandbags (Table 4). In FY 2017, elements and others shown in Table 5 inaddition to radiocesium were measured for their concentrations.
Table 4. Situations of incineration ash landfill at fourdisposal sites

Disp osa lDisp osa lDisp osa lDisp osa l

Sit e A

Sit e BSit e D

Sit e H

Bottom Ash

○

○

○

○

Fly Ash

○

○

△

○

○ : Landfilling is done in the same way as before the accident.
△ : Landfilling is conducted so as not to contact rainwater.
Table 5. Analyzed elements and others
Elements to be analyzed
Sodium, magnesium, sulfur, potassium, calcium,rubidium, barium, antimony, nickel, cobalt,
molybdenum, selenium, cesium, strontium, chloride ion,
nitrous acid, nitric acid5.4. Results(1) Radiocesium elution suppression test
A Germanium semiconductor detector and as -is agitation tests
Table 6 summarizes test results regarding solid phase radiocesium concentrations, liquid
phase radiocesium concentrations (as -is agitation test), radiocesium elution rates and others.
The results of radiocesium concentrations in solid phase sample showed a tendency inwhich radiocesium concentrations were higher in fly ash and treated fly ash than in the bottom
ash and treated bottom ash.
Regarding solid phase samples in the same facility, radiocesium concentrations were lower intreated fly ash than in fly ash. This is probably because of the effect of water added duri ng
chelate agent treatment to suppress heavy metal elution from fly ash. Similarly to the test
results of the solid phase samples, the test results of radiocesium concentrations in liquid
phase samples suggested that radiocesium concentrations tend to be h igher in fly ash andtreated fly ash than in bottom ash and treated bottom ash. The comparison of radiocesium
concentrations in bottom ash and treated bottom ash indicated a tendency in which theradiocesium concentrations in treated bottom ash were lower in general, whereas thecomparison of those in fly ash and treated fly ash did not show a similar tendency. The resultsof calculating radiocesium elution rates indicated a tendency in which those of fly ash andtreated fly ash were generally higher than t hose of bottom ash and treated bottom ash.
55

Table 6. Results of germanium semiconductor detector
and as-is agitation tests

B A test on radiocesium elution suppression (long -term as-is agitation test)

Figure 2 summarizes the results (radiocesium elution rates) of radiocesium 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% in weight suppresses radiocesium elution rate to 30% or lower, in other words, an acidclay is effective in the suppression of radiocesium elution. This is probably because a clay
mineral, which is the major component of a clay, captures radiocesium into its structure andsuppresses its elution. The maximum duration of these tests were 30 days, during which noradiocesium elution rate exceeded 30%.

56

40

%

20
0
0

40 80 120 160 200 240 280 320 360

Radiocesium Elution Rate (%)

80● Facility 5 Treated Fly Ash▲ Facility 5 Treated Fly Ash + Acid Clay 5%

40
20
0
0

60

40 80 120 160 200 240 280 320 360

Agitation time (h)● Facility 3 Treated Fly Ash▲ Facility 3 Treated Fly Ash + Acid Clay 5%

40

20
0
0

Agitation time (h)

100

60

80

40 80 120 160 200 240 280 320 360

Agitation time (h)Radiocesium Elution Rate (%)● Facility 1 Treated Fly Ash▲ Facility 1 Treated Fly Ash + Acid Clay 5%

80

60

20
0
0

100

80

80

60

● Facility 6 Treated Fly Ash▲ Facility 6 Treated Fly Ash + Acid Clay 5%

40

20
0
0

40 80 120 160 200 240 280 320 360

Agitation time (h)● Facility 4 Treated Fly Ash▲ Facility 4 Treated Fly Ash + Acid Clay 5%

40

100

Radiocesium Elution Rate (%)

60

100

Radiocesium Elution Rate (%)

80

100

Radiocesium Elution Rate (%)

Radiocesium Elution Rate (%)

100

60

40 80 120 160 200 240 280 320 360

Agitation time (h)● Facility 7 Treated Fly Ash▲ Facility 7 Treated Fly Ash + Acid Clay 5%

40
20
0
0

40 80 120 160 200 240 280 320 360

Agitation time (h)Figure 2. Results of radiocesium elution suppression tests (radiocesium elution rates)

C Radiocesium elution suppression tests (MP -AES / ion chromatography test)
Table 7 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 othe rs. As a result of comparing 30 -day agitation without mixing
an acid clay and 30-day agitation after mixing an acid clay, some cases were observed in whichacid clay mixture resulted in low concentrations, but generally the obtained concentrations
showed a similar tendency and suggested that the mixing of an acid clay does not block theeffect of chelate.
Table 7. Results of radiocesium elution suppression test
(concentrations of metals and others in eluates) * mg/L

57

**g/L

(2) Tests on radiocesium elution suppression in incineration ash at municipal
waste incineration facilities
A Tests during a normal operation(a) Germanium semiconductor detector test, JIS K 0058 -1 elution test and theEnvironment Agency’ s Notice No. 13 elution test
Figures 3 to 5 show the daily fluctuations of radiocesium concentrations (contained or elution
concentrations) and elution rates in the bottom ash, fly 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 radiocesium contents, elution quantities and elution rates.

Figure 3. Daily fluctuations ofradiocesium concentrations inbottom ash (normal operation)

Figure 4. Daily fluctuations ofradiocesium concentrations in fly ash(normal operation)

Figure 5. Daily fluctuations ofradiocesium concentrations inchelated fly ash (normal operation)

Radiocesium 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 radiocesium 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.
Radiocesium 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.
(b) Repetitive elution tests (JIS K 0058 -1)
Table 7 (bottom ash) and Table 8 (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. Radiocesium
elution property indicated by each sa mple and also the results of the repetitive elution tests
showed a tendency in which radiocesium elution rates were higher in the case of treated fly
ash than bottom ash. The cumulative rate of radiocesium 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 and rate of radiocesium elution, which gradually decreased as the number58

of tests increased.
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.
Table

8.

Results of repetitive
tests using bottom ash
operation)

elution(normalTable

9.

Results of repetitive elution
tests using treated fly ash(normal operation)

From the results of the test described in 2.A(a) and the repetitive elution tests, it was
found that the radiocesium concentrations (of contained or eluted radiocesium) in treated
fly ash and the rates of radiocesium elution from it were higher compared with bottom ash
and that the suppression of radiocesium elution by means of chelate agent treatment isdifficult as the elution rate was high even before the earthquake. Therefore, it isparticularly important to study the methods of suppressing radiocesium elution from thetreated fly ash in municipal waste incineration ash.
(c) Zeolite addition test in laboratory
Tables 10 (fly ash) and 11 (treated fly ash) show test results. In order to investigate thepresence or absence of a zeolite addition effect on heavy metals and others in the test of adding
zeolite to fly ash, zeolite was added by different ratios (5%, 10%, 15%, 20%) to the treated
fly ash (chelate agent addition ratio: 2% across the board) before the test.

59

Table 10. Results of adding zeolite to fly

Table

11.

Resultsofaddingzeolitechelated ash in laboratory

ash in laboratory

The comparison of the test results indicated that the addition of zeolite to fly ash andtreated fly ash suppresses radiocesium elution. A tendency in which an increase in zeolite
addition ratio increased a radiocesium elution suppression effect was also observed. The
test results concerning heavy metal elution indicated that the addition of zeolite does notblock the effect of chelate agent.
In chemical mixture addition and mixing addition tests at actual facilities, a goal of
suppressing the total ratio of Cs 134 and 137 elution 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 theresults of daily radiocesium concentration fluctuations, each addition test at actual
facilities was performed by mixing (kneading) zeolite and the chemical mix ture so thatzeolite is added by about 20%.
B Tests on zeolite addition to an exhaust gas treatment agent at actual
facilities(a) Exhaust gas composition analysis tests

Table 12 shows the results of exhaust gas composition analysis tests. A comparison wi th
the results obtained during normal operation revealed that the injection of a chemical
mixture (containing zeolite) did not result in any anomalous values of the basic items, withthe standard values satisfied.

60

toTable 12. Results of analyzing exhaust gas Composition(b) Germanium semiconductor detector test, JIS K 0058 -1 elution test and theEnvironment Agency’ s Notice No. 13 elution test

Table 13 shows the concentrations of radiocesium, heavy metals and others in sampled
treated fly ash. Figure 6 shows the daily fluctuations of radiocesium concentrations (ofcontained or eluted radiocesium) and the summarized radiocesium elution rates based on
the results of Table 13. First, radiocesium contents were 2,200 to 4,100 Bq/kg (2.800
Bq/kg on average), the quantities of radiocesium elution were 8 to 16 Bq/L (11 Bq/L on
average) and radiocesium elution rates were 3.1 to 5.5% (4.1% on average).
The comparison of each average value of radiocesium in treated ash obtained from normal
operation tests and each average value of radiocesium obtained from chemical mixture
addition tests performed this time indicated that the injection of zeolite significantl yreduced quantities of radiocesium elution (normal operation: 121 Bq/L → after chemical
mixture addition: 11 Bq/L) and radiocesium elution rate (normal operation: 73.0% → after
chemical mixture addition: 4.1%). The results of the Environment Agency’s Notice No.
13 elution test indicated that, as with the resultsof zeolite addition test in laboratory, the blow
injection of the mixture of hydrated lime andzeolite at an actual facility also did not block theeffect of a chelate agent.

Figure 6. Daily fluctuations of chelated fly
ash concentrations (after blow injection)

61

Table 13. Results regarding chelated fly ash (blow injection)(c) Repetitive elution tests (JIS K 0058 -1)

Tables 14 (solvent: ultrapure water)and 15 (solvent: artificial seawater)

Table 14. Results of repetitive elution tests onshow the results of repetitive elution

chelated fly ash (solvent: ultrapure water)

tests.

This

sampled

on

time,
the

treated
third

fly

day,

ash

whose

radiocesium concentration was closest
to the average value of treated fly ash
sampledduringchemicalmixtureaddition test period, was used.
With regard to radiocesium elution
properties,

when

four

tests

were

performed using ultrapure water as asolvent, 14% of radiocesium eluted in
total. When this was compared with the results of treated fly ash not added with zeolite
shown in Table 9, zeolite was found to significantly suppress radioc esium elution (totalelution rate of the four-time tests:

Table 15. Results of repetitive elution tests

81.9% → four-time total elution rateon the elution of chelated fly ash

after(solvent: artificial seawater)

chemicalmixtureaddition:

14%).
However, when artificial seawater
was used as a solvent, the total
radiocesium elutionrateincreased (total elution rate using
ultrapure water 4 times: 14% →artificial seawater 4 times: 56.1%).
It was found that regardless of theuse of the either solvent, treated fly
ash added with zeolite showed a62certain radiocesium elution suppression effect compared with treated fly ash not addedwith it. The heavy metal elution when ultrapure water or artificial seawater was used also
did not result in any anomalous values.
C Tests regarding zeolite addition to the mixture of fly ash and chelate agent(mixture using a kneader) at actual facilities(a) Germanium semiconductor detector test, JIS K 0058 -1 elution test and theEnvironment Agency’ s Notice No. 13 elution test
Table 16 shows the results of the concentrations of radiocesium, heavy metals and others insampled treated fly ash. Figure 7 shows the daily fluctuations of radiocesium concentrations(contained and eluted radiocesium) and radiocesium elution rates based on the results of Table
16. First, radiocesium contents were 1,200 to 1,400 Bq/kg (1,280 Bq/kg on average), qu antities
of radiocesium elution were 6 to 11 Bq/L (8 Bq/L on average) and radiocesium elution rates
were 4.6 to 7.9% (5.9% on average).
The comparison of radiocesium average values in treated fly ash sampled in chemical
mixture addition tests and mixing ad dition tests indicated that the quantities of radiocesium
elution were similar in both cases (11 Bq/L for chemical mixture addition, 8 Bq/L for mixing
addition, and 121 Bq/L for normal operation) and radiocesium elution rates (4.1% forchemical mixture addition, 5.9% for mixing addition, and 73% for normal operation). Thus it
was concluded that, regardless of zeolite addition method (the blow injection or mixing ofzeolite), its addition itself has the effect of suppressing the elution of radiocesium. The
results of the Environment Agency’s Notice No. 13 elution tests indicate that similar to theresults obtained from zeolite addition tests and chemical mixture addition tests in thelaboratory, the simultaneous mixing of fly ash, a chelate agent and zeolite at actual facilities
did not block the effect of the chelate agent.

Table 16. Results regarding chelated flyash (mixed with zeolite)

Figure 7. Daily fluctuation of chelated flyash (mixed with zeolite)

63

(b) Repetitive elution tests (JIS K 0058-1)
Tables 17 (solvent: ultrapure water) and 18 (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 radiocesium concentration was closest to the average value, was
used.
Table

17. Results of repetitive elution
tests on elution from chelated flyash (ultrapure water)

Table

18.

Results of repetitive elution
tests on elution from chelated flyash (artificial seawater)

First, regarding radiocesium elution properties, when four tests were carried out using
ultrapure water as a solvent, radiocesium eluted by 10.3% in total. The results (81.9%
radiocesium elution in total in four tests during normal o peration → 14% radiocesium
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 14.
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
and 43.1% 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 water or artificial seawater was used as a solvent.
Given the effect of zeolite in suppressing radiocesium elution sho wn in the zeolite mixing
addition tests and the results of laboratory tests on zeolite addition to treated fly ash, before
the repacking of ash whose treatment is difficult because of its high radiocesium
concentration to a new container, the addition and mixing of zeolite into the treated fly ash
seems to be one of effective means of enhancing safety.
While both the zeolite addition methods (the method using the chemical mixture and thezeolite mixing method) were found effective in suppressing radiocesiu m elution, when it
comes to the burial 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 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
addition of zeolite, the modification of the facility may be necessary.
64

In the case of the chemical mixture addition method, an existing hydrated lime silo canbe used and all of the hydrated lime needs are to be replaced with the chemical mixture forradiocesium elution suppression. However, unlike the blow addition of hydrated lime alone
during a periodical inspection, this method may cause pipe abrasion or may clog the bag
filter, so careful measures in details may have to be taken.
In the case of adopting a mixing addition method, a silo equipped with a chelate agent
kneading machine and a mechanism capable of adding zeolite may need to be newly built,
and in such a case, periodical inspections may be needed to carefully check the abrasionof such a machine. Therefore, optimal addition method and quantity should be selectedaccording to the characteristics of disposal facility to ensure applicability to it.
(3) Status of landfills and radiocesium elution
Table 19 shows radiocesium analysis results in FY 2015. Radiocesium was detected inleachate (seeping water) and discharged water from disposal sites A and B, where incineration
ash was buried, and from disposal site D, where fly ash was buried without contact withrainwater. On the other hand, radiocesium in leachate and discharged water was below thelower 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 radiocesium concentration in
nearby underground water.
Table 19. Results of analyzing radiocesium 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 20 shows radiocesium analysis results in FY 20 16. Radiocesium was detected inleachate (seeping water) and discharged water from the disposal site H only, where fly ash
had been buried as it is. Radiocesium concentrations in underground water at all the landfill
disposal sites shown in Table 20 were below the lower detection limit (0.1 Bq/L).
T able 20. Results of analyzing radiocesium in leachate and others in FY 2016

Lower detection limit: 1 Bq/kg or Bq/.L

Based on the results in FYs 2015 and 2016, it was likely that radiocesium was detected65

in leachate and discharged water only at landfill disposal sites having buried radiocesium containing fly ash without preventing its contact with rainwater. Regarding disposal siteD, where radiocesium 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 a part of the fly ash had been buried without a rainwater contact
prevention measure during a period immediately after the Fukushim a accident, namelyfrom the period of reconstructing the incineration facility until the Ministry of theEnvironment’s notice ordering the halt of incineration ash burial. It is likely thatradiocesium continuously eluted from the incineration fly ash in q uestion and leached fromthe disposal site D through discharged water.
(4) Correlation between the annual elution of radiocesium and other elements
Tables 21 and 22 show measurement results in FYs 2017 and 2018. Figures 8 and 9 are thegraphs of measured results in the same years, intended to clarify the presence or absence of aseasonality (seasonal factor) common among the disposal sites. These results did not indicate
a seasonality common among them.
Figures 10 to 13 are graphs using the two years ’ results, intended to clarify the presence orabsence of a seasonality in terms of radiocesium elution at each disposal site
Table 21. Results of analyzing radiocesium inleachate and others in FY 2017
Units: Bq/L for leachate and discharged water and Bq/kg for sludge
Lower detection limit: 1 Bq/kg or Bq/kg

Table 22. Results of analyzing radiocesiumin leachate and others in FY 2018
Units: Bq/L for leachate and discharged
water
Lower detection limit: 1 Bq/kg

Figure 9. Measured results in FY 2018
Figure 8. Measured results in FY 201766

A Disposal site A
The highest radiocesium concentration in leachate
at disposal site A was about 5 Bq/L. In FY 2017,
radiocesium concentrations in April were low but
increased toward March next year. In FY 2018,
radiocesium concentrations in April to June werehigh but decreased in winter. In comparison, these
do not suggest a seasonality in radiocesium elution.

Figure 10. Radiocesium concentrations inleachate at disposal site A

B Disposal site B
The highest radiocesium concentration in leachate at
disposal site B was about 13 Bq/L. In FY 2017,
radiocesium

concentrations

were

high

in

July,

November, and March but low in May and December to
February

next

year.

In

FY

2018,

radiocesium

concentrations from July to September, and December
were low, but were high in April, May, October,
November, and January to March the next year. This Figure 11. Radiocesium concentrations incomparison

suggested

a

trend

of

radiocesium

leachate at disposal site B

concentration increasing in winter but does notwarrant a conclusion that seasonality is inherent to
the landfill disposal site exists.
C Disposal site D
The highest radiocesium 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.
D Disposal site H
The highest radiocesium concentration in leachate at

Figure 12. Radiocesium concentrations inleachate at disposal site D

disposal site H was about 8 Bq/L. In FY 2017,
radiocesium concentrations from June to November
were below the lower detection limit, and in FY
201X, they were about 1 Bq/L throughout the fiscal
year.

While

radiocesiumafluctuation

concentration

was
in

FY

observed

in

2017,

no

commonality with data in FY 2018 was confirmed,
thus indicating the absence of a seasonality inradiocesium elution.

Figure 13. Radiocesium concentrations inleachate at disposal site H

67

Table 23 shows the results of analyzing elements in leachate at landfill disposal sites in FY
2017, namely radiocesium and chloride ion concentrations. A possibility was suggested thatthe higher the chloride ion concentration, the higher the radiocesium concentration becomes.
A correlation diagram (Figure 14) was developed by plotting radiocesium concentrations on
the vertical axis and chloride ion concentrations on the horizontal axis. The diagram indicateda positive correlation between them.
Table 23. Radiocesium and chloride ion concentrations

Figure 14. Correlation between radiocesium and chloride ion concentrations

685.5. 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 ofradiocesium. 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 radiocesium concentration and chloride ion concentrationsuggested a possibility that chloride ions in incineration ash are affecting radiocesium elution.
As a result of testing radiocesium elution from incinerati on ash (bottom ash, treated bottom ash,
fly ash and treated fly ash) , which seems to be the cause of radiocesium detected from leachate(seeping water) at the landfill disposal sites, radiocesium concentrations in and radiocesium
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 radiocesium elution property, the radiocesium elution decreased and the acidclay 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, whoseradiocesium elution suppression effect had been recognized in the final report of the pr evious
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 radiocesiu m elution and does not block the heavy
metal elution prevention effect of the chelate agent. Based on these results combined withlaboratory results, these methods are effective in suppressing radiocesium 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 land fill disposal site,
including condideration of an increase in the amount of landfill disposal due to zeolite addition
as well as facility structure and capacity.

69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
We are continuing to observe the concentration of suspended and dissolved radioactive cesiumin river water in Fukushima Prefecture. As a result, for both forms of radiocesium, the tendency
to decrease with the passage of time, which had been observed immediately after the accident,
was maintained. Furthermore, it was confirmed that decontamination in river basins has a strong
effect on the concentration of suspended cesium -137 in river water. For the simulation for future
prediction of the concentration of radioactive cesium in river water, the calculation was refinedfor normal flow conditions, and a trial calculation was carried out under high flow flood
conditions.
FIP2: Survey of radionuclide movement with wildlife
As a result of confirming the seasonal change of cesium-137 concentrations in the muscles ofwild boar and Asian black bear, even in recent years, individuals with high concentrations that
greatly exceeded the standard value of radioactive cesium concentration in general foods were
captured. The long-term fluctuation of cesium -137 concentration in the muscles of wild boar andAsian black bear showed a decrease over time during the entire period, both the low
concentration period and the high concentration period. The model now needs to be reconsidered
to provide a better estimate of the long -term fluctuations of radiocesium in the animals ,particularly during the high concentration period . 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 and around as the boundary.
FIP3: Sustainable countermeasures to radioactive materials in freshwater system
The sustainability of the decontamination effect was continuously verified at the riverside area
where the decontamination demonstration test was conducted in 2014. Even under the conditionof overgrown vegetation on the riverbed, the air dose rate continued to decrease. No significant
accumulation of radiocesium was observed, confirming that the effect of the decontamination
was maintained.
In addition, in order to verify the presence or absence of recontamination around the river due
to the passage of Typhoon No. 19 in 2019, the air dose rate was measured and fieldreconnaissance was conducted at river side areas and parks. An increase in the air dose rate was
not generally confirmed, but rather the air dose rate decreased significantly near the river, andthe effect of the natural attenuation associated with flooding was confirmed.
70

FIP4: Development of environmental mapping technology using GPS walking surveys
A GPS-linked dose rate measurement device, KURAMA from Kyoto University, was used 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 analysi s ofthe obtained 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 formeasurement such as directional characteristics and calibration constant s. 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 eveninexperienced people can use the system. Since fiscal 2016, it has been used for conducting
walking surveys and has been rented 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 radioactive material
Surveys and tests were conducted at landfill sites and waste incinerators to examine treatment,
disposal and management methods for waste containing radiocesium generated in the prefecture.
A survey of leachate at the landfill site confirmed that when the incinerated fly ash was buriedin contact with rainwater, radiocesium was eluted from the incinerated fly ash and was detectedin the leachate. In order to supp ress the elution of radiocesium from this incinerated fly ash,various incineration ash elution tests and incineration ash sparingly soluble tests were conductedin laboratories and facilities. As a result, it was found that the addition of zeolite into th e
incineration ash has a remarkable effect of suppressing the elution of radiocesium 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 theamount of zeolite added.

71