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

Cooperation between
Fukushima Prefecture and the IAEA

SUMMARY REPORT(2013 to 2017)[Fukushima Prefecture Initiative Projects]
Outline(temporary translation)

March 2018
Fukushima Prefecture

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1. FIP1: Survey of radionuclide movement in river systems
1.1. Purpose
The accident at Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Plant in2011 resulted in wide contamination of the prefectural area with radioactive materials. Since river water iscommonly used for drinking water and farming, it is important to clarify the dynamics of radioactive
materials in rivers, and provide necessary information for the safe use of river water. If radiocaesium
adsorbed by suspended particulate matters and flows downstream in a suspended form, re-deposition after
events, such as floods, may affect the ambient air dose rates. Accordingly, the migration of dissolved
radiocaesium through the ecosystem should be considered (Figure 1). Thus, we evaluated the dynamics ofradiocaesium depending on its form. The purpose of this survey is to investigate the dynamics ofradiocaesium transport with river flow down in Fukushima prefecture and to verify it by model simulation
based on the monitoring data.

1.2. Content of implementation
The monitoring network was established in
Hirose River basin. The survery was started
from fiscal year 2013 at each monitoring point
established in the mainstream of Hirose Riverand its tributaries (Figure 1 (a)). The widearea survey was conducted at many points of
the Abukuma River basin and eight water
rivers in Hamadori area (Figure 1 (b)). At eachmonitoring point, we have monitored theturbidity and water level continuously andcollected suspended sediments by suspended
sediment samplers.

1.3. Results

Figure 1: Monitoring points in this survey and the initialamounts of Cs-137 in these area (as of 2 July, 2011).
(a) The Hirose River basin. The numbers in the figure werecorresponded to those in Table 3.
(b) The subjected area in the wide area river survey. MEXT
(2011). Regarding the Results of the Third Airborne
Monitoring.

As water flows down the Hirose River,both dissolved and suspended radiocaesium
concentrations changed. We verified thesechanges by the TODAM model. Figure 2 shows
an example of the results. For this simulation,
the ordinary water level and flow rate were set
as base conditions, and the actual radiocaesium
concentrations at the upstream end of Hirose
River main stream and major tributaries were

Figure 2: A result of simulation by TODAM model.

used as the boundary conditions The TODAM model could roughly reproduce the radioactive caesium

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concentrations at each monitoring point in the Hirose River.
In the wide-area survey, the suspended caesium-137 concentrations collected at Abukuma River and rivers
in Hamadori area until May 2017 are shown in Figure 3. The values were varied because of the difference in
the initial amounts of caesium-137 deposition among the basins. However, it was commonly observed thatcaesium-137 concentrations decreased in all points during about one year from the accident significantly.
This rate of decrease was slightly slowed down, but such trend has still continued until now. This continuous
decline was seemed to result from the surface decontamination practices in the terrestrial area, which was
widely conducted in the object basins. However, the similar trend was observed in European rivers after the
Chernobyl nuclear plant accident (without the surface decontamination). Thus, it can conclude that the naturalattenuation caused the decreasing trend observed in this survey.

Figure 3: The changes of the suspended Cs-137
concentrations in river waters.
(a)Abukuma River basin,(b) Rivers in Hamadori area

Figure 4: Suspended Cs-137 concentrations
at upstream points of the Mizusakai (No.1)
and Kuchibuto River (No.2).
Blue bar: Progress of surface decontamination(agricultural land) in the area.

In addition, the effects of the surface decontamination on the suspended caesium-137 concentrations were
investigated at the two monitoring points (No.1 (Mizusakai River) and No.2 (upper stream of Kuchibuto
River) in Fig. 1(b)). The effects would be pronounced at the points because the basin including those points
was totally assigned as the special decontamination area. Figure 4 showed the relationship between thesuspended caesium-137 concentrations and the progression rate of the surface decontamination of the
agricultural lands within the basin. It was shown that the intensive efforts were conducted from April 2014
to December 2015 in the object area. During the period, the drastic decrease in the suspended caesium-137
concentrations coincided with the advance in the surface decontamination.

1.4. Conclusions
We established the monitoring network in the Hirose River basin and investigated the dynamics ofradiocaesium with river flow. The simulation by the TODAM model using the monitoring data could roughly
reproduce the change in radiocaesium with the river flow in the Hirose River. Further works are needed to
improve the prediction accuracy by the continuous monitoring and the reevaluation of the effects by Oguni
River basin due to its high initial radiocaesium level. On the other hand, the suspended radiocaesium

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concentrations showed the decreasing trend with time at the Abukuma River basin and major rivers in
Hamadori area as the wide-area multipoint survey. In addition, the effects of the surface decontamination
were detected at some monitoring points. It can conclude that the continuous monitoring and the subsequentassessment was important because of the possible changes in radiocaesium concentrations in river waters bysuch as the recovery of vegetation and resumption of agricultural practices.

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2. FIP2: Survey of radionuclide movement with wild life
2.1. Purpose

After the accident at Tokyo Electric Power
Company

Holdings'

Fukushima

DaiichiNuclear Power Plant, radiocaesium and otherradionuclides have been detected in manywild

animals

inhabiting

thenaturalenvironment. Therefore, we carried out
survey and research on the dynamics ofradiocaesium in the ecosystem to understandthe implications for the lifting of restrictions,and make prefectural residents feel safe.

2.2. Content of implementation(1) Investigating dynamics of radionuclide inwild animals
We measured and analyzed caesium-137
concentrations in the muscles of wild boars,
Asian black bears, and other wild animals,
and also in the stomach contents of wild boars.
(2) Investigating the home ranges of wild

Figure 1: Annual changes of caesium-137
concentrations in (a)wild boar and (b)Asian black
bear muscles (Period: May 2011 to March 2017).

animals
We investigated behavior of wild boar byusing GPS collars.

2.3. Results(1) Dynamics of radionuclide in wild animals
A. Measurement of radionuclide
concentrations in wild animals
Caesium-137 concentrations in themuscles of wild boars and Asian blackbears were compared. Wild boars showed
great dispersion between individuals andno clear tendency, but Asian black bears
showed tendency of decrease. Tendency
differed between species of wild animals

Figure 2: Relationship between caesium-137
concentration in muscle and in stomach contents ofwild boar.

(Figure 1). Birds also showed different
tendencies depending on the species. When we compared wild boars and Asian black bears captured

5|where the caesium-137 soil ground deposition is the same, caesium-137 concentrations in muscles
was higher in wild boars. In addition, caesium-137 concentration in muscle of Asian black bear andwild boar varied with the seasons.

B. Radionuclide migration from the environment into wild animals
We investigated relationships between caesium-137 concentrations in muscles and in thestomach contents in wild boar. Individuals having higher caesium-137 concentrations in stomach
contents showed higher caesium-137 concentrations in muscles (Figure 2). This confirmed thestrong effect of intake of caesium-137 such as food item and soil.
(2) Investigating the home ranges of wild animals
We investigated the behavior of wild boars byusing GPS collars. The wild boars living outside
the evacuation order zone showed larger homeranges than the individuals living inside the zone
where the human pressure is weak (Figure 3).
Forcomparison,

wesampledeight

individuals whose data could be acquired forone month or longer in the periods from
November to December (winter) and fromJanuarytoFebruary(breedingFigure 3: Comparison of home range and core area.

season).

Although the number of samples was small,home ranges tended to be greater in theevacuation order zone than outside (Figure 4).
We also investigated habitat type in the homeranges of individuals. In home ranges ofindividuals at the evacuation order zone,
farmland occupied a high percentage. It
suggested that the home ranges of individuals in
the evacuation order zone tended to extend to
farmland (Figure 5).

Figure 4: Average of home range size of wild boars
inside and outside the evacuation zone. Error bar
indicates minimum and maximum value.

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Figure 5: Ratio of land use in the home ranges of wild boars inside and outside
the evacuation order zone (each bar indicates the value for an individual).

2.4. Conclusions① When caesium-137 concentrations in muscles were compared between wild boars and Asian blackbears, wild boars showed greater values. The tendency differed between species.
② Caesium-137 concentrations in the muscles of wild boars were found to have been strongly affectedby food habits. Both wild boars and Asian black bear showed seasonal variation.
③ Compared with wild boars outside the evacuation order zone, individuals inhabiting the zone tend tohave larger home ranges and shifted to farmland.

To find out the cause of high caesium-137 concentrations in wild boars, we are investigating food
habits in detail by using cameras and performing DNA analysis on stomach contents while comparing
with Asian black bears and other species. It is considered necessary to monitor the transition ofradiocaesium concentrations in wild boars and predict future tendencies.

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3. FIP3: Countermeasures for radioactive materials in rivers and lakes
3.1. Purpose
As a result of the Fukushima nuclear disaster, radioactive caesium was released into the environment.
This disturbed the use and management of rivers and lakes and caused public concern. Therefore, we
evaluated measures to counteract environmental caesium based on the findings of previous studies and our
researches.

3.2. Content of implementation(1) Selection of suitable measures against radiocaesium in Fukushima Prefecture(2) Riverside decontamination and the sustainability of its effect(3) Investigation of contamination in riverside parks and the selection of countermeasures(4) Interview survey on issues related to the water environment and investigation of temporal trends

3.3. Results(1) Selection of suitable measures against radiocaesium in Fukushima Prefecture
Issue

Related media

MeasuresInternal exposure by drinking

Rivers and lakes

Changing water sources

Transfer from irrigation water toRivers and lakes

Reducing sediment inflow using silt fences

agricultural products and external
exposure during farming

Sediment deposition in dams
Irrigation ponds

Reducing sediment outflow using silt fences
Decontamination of bottom sediments

Internal exposure by the

Agricultural products

Potassium fertilisation to suppress uptake

Rivers and lakes

Shipping restrictions

consumption of fishery products
External exposure by the use of

Potassium input (effective only in closed lakes)
Rivers and lakes

Use restriction and soil decontaminationwatersides

Removing riverbed sediments to reduce sediment(parks, roads, residences, etc.)

deposition onto riversides
Embankment for inundation control

Common to all issues

Irrigation ponds (atUse restriction, decontamination, and covering ofdrainage)

exposed bottom sediments
Source decontamination and sediment discharge
prevention
Risk communication to reduce anxiety about use(2) Riverside decontamination and the sustainability of its effectRadiocaesium is distributed in topsoil in farmland and residential areas, whereas it is frequently
observed at greater depths in riverside sediments. Sediment removal that considers the spatial

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distribution of radiocaesium is important for effective riverside decontamination. Althoughrecontamination associated with floods has been negligible, it may be dependent on the condition of theriverside, including the recovery of plant communities. Accordingly, it is necessary to devise suitablecountermeasures against recontamination.

Figure 1: Temporal changes in the air dose rate at 1 meter above the ground.
Values are presented as means and standard deviation.
(lower part of the Kami-Oguni River, a tributary of the Abukuma River in Fukushima).
(3) Investigation of contamination in riverside parks and the selection of countermeasures
We investigated the contamination state at riverside parks of the lower part of the Niida River, which
is one of the main rivers in the coastal region of Fukushima Prefecture and is heavily contaminated in
the upstream area. On the riverside, the radiocaesium inventory was increased by a factor of ten and theair dose rate was several times higher. However, an extreme flood caused soil erosion and the depositionof a low radiocaesium concentration in the sediment, resulting in a significant attenuation of the air dose
rate. Additional external exposure dose during activities at the parks was estimated to be below 0.1 mSv
per year, indicating that these activities are safe.

(4) Interview survey on issues related to the water environment and investigation of temporal trends
We investigated issues related to the water environment in Fukushima Prefecture after the Fukushima
Daiichi nuclear power plant disaster and evaluated temporal tends. At 5 years after the disaster, theFukushima prefectural government indicated the following issues: ‘difficulty in continuing activities
that were conducted before the disaster’, ‘the impact of radioactive materials in the future’ and‘continuing countermeasures against the disaster’. In Fukushima Prefecture, the perception of therecovery of safety with respect to the water and air environments differed among regions. The recovery
was slower in the central (Nakadori) and coastal (Hamadori) regions than in the western (Aizu) region.
The view of safety was related to the perception of the radiation risk.

3.4. Conclusions
We reviewed countermeasures against radiocaesium according to local activity and evaluated a9|decontamination measure to reduce external exposure at riversides. Considering the contamination
condition of riverside parks, the selection of countermeasures should comprehensively account for the
spatial distribution of radiocaesium, exposure dose rate, and user anxiety.

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4. FIP4 Developing of environmental mapping technology using GPS walking surveys
4.1. Purpose
To grasp 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, wehave measured the dose rate employing avariety of methods, and we provide thisinformation on our homepage.
However, it is difficult to conduct fixedpoint measurements or car-borne surveys in
the alleys of residential areas, parks, orforests.
We
therefore
developed
environmental mapping technology that uses
GPS walking surveys (hereinafter, simply
referred to as walking surveys) to supplement
other forms of monitoring.

Figure 1: Measurement range of walking surveys.

4.2. Content of implementation(1) Development of equipment
We used KURAMA-II, which was developed by Kyoto
University, for walking surveys. KURAMA-II is a systemthat can combine data obtained from a radiation detector
and GPS device to map dose rates. We used a highprecision GPS device and stored the equipment in a
backpack as a configuration that is appropriate forwalking surveys.
(2) Gathering parameters necessary for walking surveys
Because the contribution of radiation sources varies
Picture 1: Image of a walking survey.
depending on the direction in walking surveys, owing to
obstruction by the measurer himself or herself, we
confirmed the direction characteristics.
To decide the correction factor employing comparative tests with survey meters, we used the dose
rate measured 1 m above ground by a NaI (Tl) survey meter, whose traceability has been established as
the most certain, and compared that dose rate with the measurement obtained in walking surveys.
4.3. Results
Results for the direction characteristics indicate that the effect of direction characteristics on
measurements of walking surveys is weak. Additionally, in our comparison with NaI (Tl) survey meters,
we found that it is necessary to use different detectors for low and high dose rates with 1 µSv/h as thedividing line.
In light of this, we set the correction factor as 1.3 when using a low-dose-rate detector and 1.1 whenusing a high-dose-rate detector.

11 |4.4. Conclusions
Certain results have been achieved in the development of walking surveys by 2015, making it possible
to measure the dose rate in a walking survey.
In fiscal 2016, we are conducting walk surveys or lending necessary equipment at the request ofmunicipalities.

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5. FIP5: Study of the proper treatment of waste containing radioactive materials at
municipal solid waste incinerators
5.1. Purpose
We thus conducted tests to confirm the effectiveness of methods to control the migration ofradiocaesium to bottom ash and fly ash. After understanding general aspects of the radiocaesium leaching
characteristics of incineration ash generated in Fukushima Prefecture, we examined technologies andmethods to make radiocaesium in bottom ash and fly ash less soluble.
We evaluated the radiocaesium distribution in bottom ash and fly ash, damage to equipment at themunicipal solid waste (MSW) incinerator and impact on the environment when bag filter cloths were coincinerated together with MSW.

Figure 1: Waste incineration processes and research issues.
5.2. Content of implementation(1) Radiocaesium distribution between bottom ash and fly ash
・ Effects of combustion temperature
We raised and lowered the combustion chamber exit temperature by about 50℃, and compared theradiocaesium distribution in bottom ash and fly ash with the usual distribution to investigate theimpact of temperature changes on migration.
・ Continuous sampling test
We sampled bottom ash and fly ash continuously during ordinary operation and investigated therelationships between combustion temperature and radiocaesium migration to bottom ash and fly ash.
・ Effects of a radiocaesium evaporation accelerator and inhibitor
We added a caesium evaporation accelerator (hydrated lime) and inhibitor (bentonite) at the waste

13 |hopper and investigated their effects.
(2) Proper treatment of used filter cloths of bag filters
At two MSW incineration facilities that use filter cloths of different materials were compared. We
co-incinerated used filter cloths with MSW by changing input ratio and interval to check the impact on
the combustion status.
(3) Study of the reduction of radiocaesium leaching from fly ash
・ Data acquisition of radiocaesium leaching characteristics
We carried out leaching tests for bottom ash and fly ash in the prefecture to investigate the leaching
characteristics of radiocaesium.
・ Laboratory radiocaesium immobilisation test
We investigated the capability of zeolite and other materials to reduce radiocaesium leaching fromfly ash.

5.3. Results(1) Radiocaesium distribution between bottom ash and fly ash
The addition of an evaporation promoter caused radiocaesium to migrate to fly ash. However,reproducibility could not be confirmed. We did not detect clear relationships between combustion
temperature and radiocaesium behaviour.
(2) Proper treatment of used filter cloths of bag filters
We co-incinerated used bag filter cloths with MSW at their original incineration facilities. There was
no impact on the combustion status when the cloths mixing rate was appropriate.
(3) Study on the reduction of radiocaesium leaching from fly ash
・ Date acquisition of radiocaesium leaching characteristics
We conducted tests of radiocaesium leaching from bottom ash and fly ash generated at fifteen
MSW incineration facilities in Fukushima Prefecture. Despite a very low leaching rate from bottom
ash, as expected (less than 1% to 16%), we confirmed a very high rate of leaching from fly ash (35%
to 94%).
・ Laboratory radiocaesium immobilisation tests
We investigated changes in the radiocaesium leaching rate in response to the addition of zeolite,
bentonite, and sewage sludge in bottom ash and fly ash. Zeolite showed a remarkable reducing effecton radiocaesium leaching (from 79.1% to 4.3%).

5.4. Conclusions
Regarding relationships between radiocaesium distribution to fly ash and combustion temperature andchemicals, observations showed but poor reproducibility. We will conduct laboratory tests to understandwhat the differences in waste composition causes the cesium distribution to fly ash. We co-incinerated
used bag filter cloths with MSW at their original incineration facilities. There was no impact on the
combustion status when the cloths imput ratio was appropriate.
Adding and mixing of zeolite to incineration ash was proved effective for reduction of radiocaesium

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leaching from fly ash. We will continue the study to pursue more effective additives and mixing methods
and identify materials with greater immobilisation capability.

15 |Contents of main support received from IAEA
1. FIP1 Survey of radionuclide movement in river systems
・Provision of the TODAM model, a numerical simulation of contaminant migration in a river network,for the quantitative estimation of radionuclides deposited in rivers.
・Technical guidance on the selection of monitoring points and monitoring items, with an emphasis on
the importance of continuous monitoring at each monitoring point, based on previous studies ofChernobyl and Mayak.
・Advice about the operation of TODAM model using the monitoring data by the prefecture, that is, theimportance of measuring the Kd value (solid-liquid distribution coefficient) and sediment particle size
distribution at each observation point, as well as ion concentrations in rivers.
・Advice about the effectiveness of combining wide-area monitoring and simulation models, and theimportance of including small lakes as research subjects for improving our understanding of the
dynamics of radioactive materials in rivers.
・Advice about the need to assess the impact of decontamination and analyzing data excluding artificial
effects.
・Support for on-site inspections concerning radionuclides monitoring in Ukraine, Germany, Slovakia,
and so on.

2. FIP2: Survey of radionuclide movement with wild life
・Provision of foreign literature describing the relationship between wild animals and radionuclides, suchas radionuclide migration to wild animals, including boars and deer, in various regions following theChernobyl nuclear disaster and changes in radiocaesium levels in the bodies of birds, such as theAmerican gallinule and American wood duck, at the Savannah River Ecology Laboratory.
・Provision of information about recent scientific results concerning the bioaccumulation of radiocaesium
and in vivo radiocaesium concentration measurement technology.
・Discussions of study results and data analysis methods, such as the potential for mushrooms to explaina higher radiocaesium concentration in wild boars than those in other taxa in Fukushima Prefecture,
based on observation that mushrooms (deer truffles) cause a high radiocaesium concentration in themuscle tissues of wild boars in Europe.
・Explanation of the impact of the Chernobyl disaster on wildlife animal groups in surrounding areas, thedynamics of wolves and other animals and survey methods to clarify these impacts.

3. FIP3: Countermeasures for radioactive materials in rivers and lakes
・Provision of information related to the environmental dynamics of radioactive materials in rivers andlakes.
・Provision of information related to global environmental remediation activities in rivers and lakes,
including the removal of radioactive materials (countermeasures against the discharge of radioactive
material from the heavily contaminated floodplain in the vicinity of the Chernobyl nuclear power

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plant, and countermeasures against the inflow of radioactive materials into the Kiev Reservoir).
・Facilitation of a visit to the Chernobyl accident site.
・Recommendation regarding the evaluation of a radiocaesium decontamination test in a riverside (e.g.,
selection of the study site, simulation before decontamination, particle size of sediment, and density ofthe plant community).
・Advice on the study of countermeasures against radiocaesium in riverside parks (investigation of thehistory of floods, dikes and dredging to prevent recontamination).
・Recommendations about the study of Fukushima prefectural residents' anxiety and issues related to thewater environment (including the age and sex of residents as factors).
・Support related to the preparation of published materials (papers).

4. FIP4: Developing of environmental mapping technology using GPS walking surveys
・ Provision of information about efforts made by various institutions, such as the United States
Environmental Protection Agency and Lawrence Berkeley National Laboratory, to perform local
radiation dose mapping.
・Suggestion that inverse-distance weighting (IDW) is more appropriate than Kriging as a means ofinterpolation for walking surveys using GIS and that the shielding effect of buildings and the like must
be considered.
・Advice to judge measurement conditions of walking surveys according to the conditions at eachmeasurement point, as uniform measuring conditions are not always necessary.

5. FIP5: Study of proper treatment of waste containing radioactive materials at municipal solid waste
incinerators
・Provision of information related to treatment methods employed in other countries for fly ash, treatment
methods employed in other countries for low-level radioactive waste (i.e., incineration, melting
treatment of metal, and plasma melting) and instruments for measuring the concentrations of radioactive
substances in waste.
・Technical advice about the incineration of general waste, such as the need for studies conducted fromthe perspective of the radiocaesium balance of payments, the importance of comparative analyses ofactual test data and model analysis results, and the need to optimize test conditions and assess wastequality.
・Advice about the importance of countermeasures against the generation of hydrogen fluoride in themixed incineration of bag filters (made from Teflon).
・Advice regarding the safety (e.g. exposure protection and management) of facility workers.
・Suggestion that reducing radiocaesium elution from fly ash is important for the margin of safety whenlandfilling fly ash.