FINAL SUMMARY REPORT(2013–2022)
Cooperation between theInternational Atomic Energy Agency
and Fukushima Prefecture
Radiation Monitoring and Remediation

Vienna/Fukushima May 2023
(Approved)

CONTENTS
1.

INTRODUCTION ................................................................................................... 1
1.1.
1.2.
1.3.
1.4.

2.

LONG TERM MONITORING OF RADIOACTIVE MATERIAL IN
FORESTS AND ASSOCIATED COUNTERMEASURES.................................... 3
2.1.
2.2.

2.3.

2.4.
2.5.
2.6.
3.

BACKGROUND ....................................................................................... 1
OBJECTIVES AND SCOPE OF THE COOPERATION ........................ 1
TOPICS OF COOPERATION .................................................................. 1
PROVISION OF ASSISTANCE AND STRUCTURE OF THISREPORT .................................................................................................... 2

BACKGROUND AND OBJECTIVES ..................................................... 3
MONITORING PROGRAMMES ............................................................ 4
2.2.1. Air dose rate ................................................................................... 4
2.2.2. Distribution of radiocaesium in forests .......................................... 6
2.2.3. Radiocaesium in forest trees .......................................................... 7
2.2.4. Future monitoring of forests .......................................................... 8
SPECIFIC STUDIES ................................................................................. 9
2.3.1. Radiocaesium transfer to wild mushrooms .................................... 9
2.3.2. Radiocaesium in bamboo shoots.................................................. 10
2.3.3. Radiocaesium in freshwater fish .................................................. 11
2.3.4. Radiocaesium in wild vegetables ................................................. 11
2.3.5. Effectiveness of forest countermeasures ...................................... 12
2.3.6. Managing the timber industry ...................................................... 13
2.3.7. Protection of forest workers against radiation ............................. 14
2.3.8. Forest fires ................................................................................... 14
SATOYAMA REHABILITATION MODEL PROJECT ....................... 16
MANAGEMENT OF WILD FOODS ..................................................... 17
SECTION SUMMARY ........................................................................... 19

MONITORING OF RADIOACTIVE MATERIAL AND ASSOCIATED
REMEDIATION AND DECONTAMINATION IN TERRESTRIAL AND
AQUATIC ENVIRONMENTS ............................................................................. 22
3.1.
3.2.

3.3.

BACKGROUND AND OBJECTIVES ................................................... 22
BEHAVIOUR OF RADIOCAESIUM IN TERRESTRIAL AND
AQUATIC ECOSYSTEMS .................................................................... 23
3.2.1. Global experience on radiocaesium in the natural environment .. 23
3.2.2. Radiocaesium behaviour under the environmental conditionsof the Prefecture ........................................................................... 23
3.2.3. Transport processes in catchments .............................................. 24
ANALYSIS OF RESULTS OF MONITORING PROGRAMMES ....... 24
3.3.1. Monitoring of radiocaesium in water and sediments ................... 24
3.3.2. Effective half-life of caesium-137 in Prefecture rivers ............... 29
3.3.3. Radiocaesium in phytoplankton and zooplankton ....................... 34
3.3.4. Occurrence and characterization of radiocaesium-bearing
radioactive particles (CsMPs) ...................................................... 34
3.3.5. Redistribution of radiocaesium in surface water catchments ...... 37
3.3.6. Flux of caesium-137 with suspended sediments.......................... 38
3.3.7. Influence of land use on surface runoff ....................................... 41

3.4.
3.5.

3.6.
3.7.
4.

MANAGEMENT OF WASTE FROM REMEDIATION ACTIVITIES.............. 56
4.1.
4.2.
4.3.
4.4.

4.5.

4.6.
4.7.
5.

BACKGROUND AND OBJECTIVES ................................................... 56
TEMPORARY STORAGE SITES ......................................................... 56
DEVELOPMENT OF TECHNICAL GUIDELINES FORTEMPORARY STORAGE SITES ......................................................... 59
DEVELOPMENT OF A SAFETY ASSESSMENT FOR TEMPORARYSTORAGE SITES ................................................................................... 60
4.4.1. Safety Assessment Framework software tool .............................. 60
4.4.2. Building capacities of the Prefecture for performing safetyassessment of temporary storage sites ......................................... 62
4.4.3. Safety assessment for a ‘model’ temporary storage site .............. 62
4.4.4. Trial safety assessment of a real temporary storage site in the
Prefecture ..................................................................................... 65
4.4.5. Safety assessment for several representative temporary storagesites in the Prefecture ................................................................... 66
RETRIEVAL STRATEGIES FOR WASTE STORED IN
TEMPORARY STORAGE SITES AND DECOMMISSIONING OF
TEMPORARY STORAGE SITES ......................................................... 66
LONG TERM SAFETY OF FORMER TEMPORARY STORAGESITES....................................................................................................... 67
SECTION SUMMARY ........................................................................... 68

APPLICATION OF ENVIRONMENTAL MAPPING TECHNOLOGYUSING UNMANNED AERIAL VEHICLES ....................................................... 70
5.1.
5.2.
5.3.
5.4.
5.5.

6.

3.3.8. The carbon-13/carbon-12 ratio as tracer for identifying theorigin of suspended matter in rivers ............................................ 41
APPLICATION OF SIMULATION MODELS...................................... 43
EXPERIENCE WITH REMEDIATION AND DECONTAMINATIONIN RIVER AND LAKES ........................................................................ 44
3.5.1. Global experience ........................................................................ 44
3.5.2. Countermeasures to reduce radiocaesium in irrigation ponds ..... 45
3.5.3. Decontamination measures in riverside areas in the Prefecture .. 46
EXPERIENCE WITH REMEDIATION AND DECONTAMINATIONIN RESIDENTIAL AREAS .................................................................... 51
SECTION SUMMARY ........................................................................... 54

BACKGROUND AND OBJECTIVES ................................................... 70
DEVELOPMENT AND DELIVERY OF UAV-BASED SYSTEM ...... 70
IN SITU CALIBRATION OF EQUIPMENT AND VALIDATIONOF METHODOLOGY ............................................................................ 70
TRIAL MEASUREMENTS AT TEMPORARY STORAGE SITES ..... 72
SECTION SUMMARY ........................................................................... 72

INFORMATION DISSEMINATION FOR THE PUBLIC IN
FUKUSHIMA PREFECTURE.............................................................................. 74
6.1.
6.2.

BACKGROUND AND OBJECTIVES ................................................... 74
DEVELOPMENT OF REVISED WEBSITE, 2013–2016 ..................... 74
6.2.1. General mapping considerations .................................................. 74
6.2.2. Discussion on website development ............................................ 75
6.2.3. Final website design..................................................................... 76

6.3.
6.4.

6.5.
7.

FUKUSHIMA REVITALIZATION STATION WEBSITE ................... 76
INFORMATION DISSEMINATION ..................................................... 80
6.4.1. Outreach materials ....................................................................... 81
6.4.2. Brochure for local hunters and wild mushrooms ......................... 82
6.4.3. Information Dissemination Seminar ............................................ 85
SECTION SUMMARY ........................................................................... 86

REPORT SUMMARY .......................................................................................... 88
7.1.
7.2.

7.3.
7.4.

LONG TERM MONITORING OF RADIOACTIVE MATERIAL IN
FORESTS AND ASSOCIATED COUNTERMEASURES ................... 88
MONITORING OF RADIOACTIVE MATERIAL AND ASSOCIATED
REMEDIATION AND DECONTAMINATION IN TERRESTRIAL
AND AQUATIC ENVIRONMENTS ..................................................... 89
MANAGEMENT OF WASTE FROM REMEDIATIONACTIVITIES ........................................................................................... 90
INFORMATION DISSEMINATION FOR THE PUBLIC IN
FUKUSHIMA PREFECTURE ............................................................... 90

REFERENCES ................................................................................................................ 93
ANNEX: OUTCOMES FROM WORK UNDERTAKEN UNDER THE
FUKUSHIMA COOPERATIVE PROJECTS ....................................................... 99

1.

INTRODUCTION

1.1. BACKGROUND
The 11 March 2011 earthquake off the Pacific coast of Tohoku and the subsequent tsunami andaccident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant(hereinafter referred to as ‘Fukushima Daiichi accident’) resulted in radioactive contamination
deposited in various areas of Japan, including Fukushima Prefecture (hereinafter referred to as‘the Prefecture’). Following the accident, the Prefecture and the IAEA concluded aMemorandum of Cooperation. Radiation monitoring, remediation, decontamination and humanhealth were identified as areas for cooperation. Concrete projects, as well as ways and means
to implement them, were discussed between the IAEA and the Prefecture.
A memorandum titled, Practical Arrangements between the Prefecture and the International
Atomic Energy Agency on Cooperation in the Area of Radiation Monitoring and Remediation(hereinafter referred to as ‘Practical Arrangements’), which elaborated further on the objectives
and scope of future cooperation, was agreed by the IAEA and the Prefecture. Practical
Arrangements were signed on December 2012 and were valid for a period of five years after
signature and were extended and modified by the mutual consent of both sides in April 2016
and December 2017 and continued until 2022.
The main role of the IAEA in implementation of these projects is the provision of effective
technical assistance and support to the Prefecture based on international experience and bestpractices.
1.2. OBJECTIVES AND SCOPE OF THE COOPERATION
Practical Arrangements and Modification No. 1 and Modification No. 2 to the Practical
Arrangements were signed by representatives of the Prefecture and the IAEA in
December 2012, April/May 2016, and December 2017, respectively. The objective of thePractical Arrangements is to set forth the framework for cooperation between the Prefecture
and the IAEA, and to provide broad and extensive assistance in the Prefecture in areas related
to radiation monitoring and remediation in order to ensure ongoing protection of people and theenvironment from ionizing radiation resulting from the Fukushima Daiichi accident.
1.3. TOPICS OF COOPERATION
Section 2 of the Practical Arrangements (as revised in Modification No. 1 in 2016) identified
the following areas and activities in which cooperation may be pursued:Research and study on radiation monitoring to include: application of environmental
mapping technology by using unmanned aerial vehicles; long term monitoring ofradioactive material in the forest and associated countermeasures and the IAEA’s
assistance in the use of radiation monitoring data to develop maps to be made available
to the public;
Research and study on off-site decontamination including the IAEA’s assistance inanalyses of results of environmental monitoring and exploration of exposure pathways inorder to reduce or avoid exposure; andResearch and study on the management of radioactive waste including IAEA’s assistancein the study on management methods of low level radioactive waste from the abovereferenced decontamination activities.

1Section 2 of the Practical Arrangements was further revised in December 2017 (Modification
No. 2 to the Practical Arrangements) identifying further areas and activities in which
cooperation may be pursued:Research and study on remediation of environment in the Prefecture;
Research and study on management of radioactive waste from decontamination activities;
andResearch and study on radiation monitoring, including application of environmental
mapping technology by using unmanned aerial vehicles, long term monitoring ofradioactive materials in the forest areas, and associated countermeasures.

Information dissemination interlinks with and is in line with all the areas and activities ofcooperation under the Practical Arrangements. To strengthen efforts in information
dissemination, the IAEA and the Prefecture have organized several activities under the scopeof each of the topics of cooperation. These were based on international examples of bestpractices in informing the public about the effects of radiation.
Cooperation under the Practical Arrangements is designed to complement existing Japaneseactivities and to provide immediate assistance and support which will be of direct benefit toresidents of the Prefecture as well as visitors to the Prefecture.
1.4. PROVISION OF ASSISTANCE AND STRUCTURE OF THIS REPORT
After signature of the Practical Arrangements, work on the cooperative projects has been
implemented primarily through a series of bilateral meetings  two meetings held in the
Prefecture and one in Vienna annually. During each meeting, the representative of thePrefecture, experts from Japanese institutions, international experts identified by the IAEA, and
IAEA staff members gathered together for discussions related to the subjects under the Practical
Arrangements. International experts and IAEA staff members (herein referred to as the ‘IAEA
team’) provided technical advice related to the planning, implementation and evaluation of theresults of activities conducted by the Prefecture, which was based on the IAEA Safety Standards
and good international practices. During several missions to the Prefecture, site visits weremade to various locations such as temporary storage facilities, freshwater demonstration
projects, and forest monitoring and management projects. Additionally, software developed by
the IAEA was modified so that it could be used by the Prefecture to evaluate the safety of
temporary storage sites for radioactive waste.
This Final Summary Report summarizes the current status and progress made in the activities
conducted under the Practical Arrangements from 2013 through 2022. The Final Summary
Report updates and replaces ‘Mid Term Summary Report (2013–2020)’ and the ‘SUMMARYREPORT (2013–2017); Cooperation between the International Atomic Agency and Fukushima
Prefecture and activities undertaken by Fukushima Prefecture’. The body of this report isorganized in 5 main sections that correspond to the main points of Section 2 of the Practical
Arrangements (as revised in 2016). Sections 2, 5 and 6 cover activities in area 1, Section 3
covers activities under area 2 and Section 4 covers activities under area 3. The work undertakenon the further areas and activities identified in Modification No. 2 to the Practical Arrangements
in 2017 are included in the respective Sections of the report.
In January 2023, a workshop was held in the Prefecture to present a summary of the activities
and the key outcomes of the cooperation during 2013–2022 under the Practical Arrangements.
A brief summary of the key outcomes is given in an Annex to this report.
2

2.

LONG TERM MONITORING OF RADIOACTIVE MATERIAL IN
FORESTS AND ASSOCIATED COUNTERMEASURES

2.1. BACKGROUND AND OBJECTIVES
Forests cover approximately 70% of the surface area of the Prefecture; an example of aconiferous forest is shown in Figure 2.1. They are used extensively for leisure activities and arealso an important economic resource as they provide timber used in the construction of
dwellings. Forests also help to prevent sediment discharge, landslides and other natural
disasters. Many Japanese families live within or on the immediate outskirts of forests, which
gives rise to specific challenges in terms of countermeasures to reduce external dose rates due
to gamma radiation (hereinafter referred to as ‘air dose rate’). The forests in the Prefecture differ
from European forests in terms of annual rainfall, temperature and topography. These
differences result in faster decomposition of the litter layer in the Prefecture, which isconsequently thin compared to European forests. However, in comparing European andJapanese forests, the more general movement of both nutrients and radionuclides are expected
to be similar.
In Japan, berries, wild mushrooms and wild meat are not as widely consumed by the public asthey are in Europe. However, some Japanese forests are a source of ‘forest vegetables’ (sansai)
which are collected for human consumption.
From studies undertaken in the aftermath of the Chornobyl accident it is known that forests
have a high interception capacity for all airborne pollutants. From the time when the Practical
Arrangements were established in 2012, the most important exposure pathway for people isexternal radiation emitted by caesium-137 (137Cs) and caesium-134 (134Cs) (collectively
referred to herein as radiocaesium), which is present in both the terrestrial and aquatic
ecosystems. The half-life of 134Cs is approximately two years; 137Cs decays more slowly with ahalf-life of approximately 30 years. Both 137Cs and 134Cs were released to the environment inapproximately equal amounts following the Fukushima Daiichi accident. 137Cs was also
released into the environment as a result of the above ground testing of nuclear weapons thattook place in the 1950s and 1960s. Due to 137Cs having a much longer half-life than 134Cs, in
December 2017 the ratio of 137Cs/134Cs was about 8:1 and by December 2019 this had changed
to 16:1. Radiocaesium levels in the environment, and associated doses to people will decline
without intervention as a result of the radioactive decay of radiocaesium, and the removal ofradiocaesium by weathering from surfaces and vertical migration down soil and sedimentprofiles. Once deposited within forests, radiocaesium is retained and recycled within the forest
ecosystem. The distribution of radiocaesium within the different components of the forest floor,
vegetation and living organisms changes with time.
The Practical Arrangements have allowed the IAEA team to share international experience with
the Prefecture on longer term monitoring of radiocaesium in forests and associatedcountermeasures. Issues discussed since 2012 included characterizing the distribution and longterm accumulation of radiocaesium in various components of the forest ecosystem, establishingeffective radiation monitoring programmes, reviewing the effectiveness of countermeasuresand assessment of the Satoyama Rehabilitation Model Project. Other topics considered werecountermeasures for reducing radiation exposures of forest workers and assessing theradiological impact of forest fires. International experience in the management of radiation
doses from wild foods was reviewed and discussed in detail during a number of meetings.

3

FIG. 2.1: Coniferous forest in Tokiwa District, Tamura City (Image credit: Fukushima Prefecture).

2.2. MONITORING PROGRAMMES
A long term monitoring programme in forests has been established to track the rate of reductionof the air dose rate from radiocaesium and to better understand radiocaesium movement
between the different components of the forest. The monitoring programme is also evaluating
the distribution of radiocaesium within different components of trees (wood, bark and leaves),
and how that changes with time.
2.2.1.

Air dose rate

The number of monitoring points in forests for air dose rate has been extended each year since
the accident and at the end of 2017 totalled 1300 (see Table 2.1). Air dose rate is measured at
all monitoring points and, at 80 of these, sampling of soil and the leaves and wood of trees iscarried out annually. The monitoring locations are within forests administered by the Prefecture
including Prefecture and privately owned forests.
The air dose rate in the forest continues to fall in line with the physical half-life of radiocaesium.
Considering only the 362 monitoring points established in the first year, the average dose rate
has fallen from 0.91 μSv/h in August 2011 to 0.17 μSv/h at the end of 2021 i.e. a reduction of
81%, entirely by natural processes (see Figure 2.2). While a significant proportion of theprefecture’s total area is now showing air dose rates less than the target value fordecontamination in residential areas (0.23 μSv/h), there are still a small number of sites close
to the evacuated area which exhibit higher air dose rates is >2.5 μSv/h. The data suggest that
forests with air dose rates exceeding 0.23 μSv/h will still remain in 2036, 25 years after theaccident.
In March 2011 the ratio between 137Cs and 134Cs was 1:1. By December 2019, that had changed
to approximately 16:1, primarily due to the radioactive decay of 134Cs, which has a half-life of
2.06 years compared to the much longer half-life of 30.07 years for 137Cs. This means that therate of reduction of air dose rate due to natural processes will slow considerably in future years
and year to year reductions will be much more difficult to quantify.

4

Table 2.1. Forest monitoring sites established by Fukushima Prefecture
Number of Monitoring
Sites Added

Fiscal Year

Total Number of
Monitoring Sites

2011

362

2012

563

925

2013

81

1006

2014

187

1193

2015

37

1230

2016

20

1250

2017

50

1300

2018

–

1300

2019

–

1300

2020

–

1300

2021

–

1300

Measuredvalue(average of 362 points)
測定値（362カ所の平均）

Estimated value from radioactive decay
自然減衰による線量予測

Air dose rate (µSv/h)

2.0

1.5

1.0

0.91
0.79
0.62

0.5

0.44

0.39

0.32

0.27

0.23

0.23

0.20

0.18

0.17

2022/12021/1

2020/1

2019/1

2018/1

2017/1

2016/1

2015/1

2014/1

2013/1

2012/1

2011/1

0.0

FIG. 2.2: Measured air dose rates at 362 monitoring points in forests within the Prefecture andestimated air dose rates based on radioactive decay of radiocaesium, (Image: based on data from
Fukushima Prefecture).

5

The combination of mountain terrain and rainfall tends to increase the mobility of radionuclides
and these will quickly move downhill (both physico-chemically and mechanically) and futureradiation monitoring efforts may need to be adjusted for such processes.
Dynamic processes affecting the movement of radionuclides in the environment were relatively
rapid in the initial years following the Fukushima Daiichi accident, but they have slowed downwith time. Monitoring programmes should be continued at least until a stable situation isreached, but it is difficult to predict when that might be; some fixed sites established after the
Chornobyl accident are still being monitored and continue to provide new and important
information.
The IAEA team advised that, due to expected lower rate of decrease in air dose rate, a reductionin the frequency of monitoring to once every two, three or even five years, in particular at thosesites furthest inland from the coast, would be justified from a technical viewpoint. The
monitoring programme could be designed to ensure that measurements are carried out in eachmunicipality, but not at every monitoring location, every year.
2.2.2.

Distribution of radiocaesium in forests

Radiocaesium that is present in coniferous and deciduous forests is distributed mainly between
among soil and the litter layer and trees. Through ecological cycling of materials within forests,
radiocaesium has been redistributed such that by 2016, approximately 97% of the radiocaesiumin the forests of the Prefecture was located in the soil and litter (fallen needles or leaves) layers,(see Figure 2.3). This observation still applies at the end of 2021. The results of the study haveshown the positive effect of the removal of fallen leaves in 2012 on the radioacaesium
concentration in young trees, as well as confirming that the litter and 0–5 cm of topsoil are themain sources of 137Cs in trees. By 2021, the data collected suggest that the activity concentrationof 137Cs in the forest environment is approaching a quasi-equilibrium between the source (litterand soil) and trees. The percentage of the total inventory of radiocaesium present in understory
vegetation, mushrooms and wild animals is less than 1% of the total. Therefore, any measures
to reduce the air dose rate is best focused on managing the soil component. Another conclusionthat can be drawn is that the harvesting of trees is unlikely to significantly reduce the ambient
air dose rate. Large scale removal of soil would be expected to reduce the overall productivityof the forest and could have an overall negative impact; it would also create additional wastethat would need to be managed.
A soil survey undertaken in forests in the Prefecture has identified the presence of illite andvermiculite in all samples collected. Both are clay minerals that are known to strongly bindradiocaesium in a non-reversible form. This observation probably explains the relatively lowtransfer of radiocaesium from soil to forest plants and animals. However, if there are any partsof the Prefecture where these clay minerals are absent, much higher transfer factors, andconsequently higher concentrations in trees, understory vegetation and animals, would be
expected.
Experiments undertaken by the Prefecture have shown that radiocaesium is recycled within theforest ecosystem and losses of radiocaesium are a fraction of a percent per year. Measurements
have shown that the quantity of radiocaesium in water flowing into reservoirs with urban
catchment areas is four times higher than water from forested catchment areas.

6

FIG. 2.3: Change in distribution of radiocaesium in the Prefecture’s coniferous forests and deciduous
forests from 2011 to 2019 (Adapted from cooperation with the Ministry of Agriculture, Forestry and
Fisheries, and the Fukushima Prefectural Forestry Research Centre).

Some outflows do occur through sediment transport, with the radiocaesium being attached tothe clay minerals in these sediments. (Additional information about the behaviour ofradiocaesium in the environment including the importance of sediment transport is provided in
Sections 3.2 and 3.3). Research has also shown that the greater the vegetation cover, the lower
the outflow of sediment. This underlines the importance of forest management, whereby regularthinning encourages the growth of understory vegetation, which in turn reduces the likelihoodof sediment outflow and landslides.
2.2.3.

Radiocaesium in forest trees

The sampling programme for radiocaesium in timber includes separate measurements of bark,sapwood, heartwood, old leaves and new leaves. At a number of sites, soil is also collected andmeasured for radiocaesium. An example of collecting samples of wood for analysis is shownin Figure 2.4.
For the various species of trees in both coniferous and deciduous forests, the highest
radiocaesium concentrations are found in bark, followed by wood and branches/leaves. In somespecies the activity concentration is higher in sapwood than in heartwood, and the reverse inothers, for example Japanese cedar. This difference is believed to be linked with the processesof potassium uptake and its (re)distribution within the trees.
Over time, radiocaesium attached to old leaves is gradually shifting to the forest floor due toleaves falling from trees. The air dose rate that would result from trees having radiocaesium
concentrations exceeding 8000 Bq/kg was estimated1. The value that resulted from this process,measured at a height of 1 m, was 1.57 µSv/h. It should be noted that these estimated values
have significant uncertainties associated with them. This is discussed further in Section 2.3.5‘Managing the timber industry’.

1 Japanese National legislation requires any material that exceeds an activity concentration of 8000 Bq/kg of radiocaesium to

be managed as radioactive waste, and such waste is considered ‘designated waste’.

7

FIG. 2.4: Collecting samples of wood for analysis (Image: Fukushima Prefecture).

The radiocaesium content of saplings planted in 2013 has been evaluated. The saplings wereplanted at a depth of about 10 cm. Until 2015, no correlation was observed between theradiocaesium content of the wood and the air dose rate in the planting area. As the root systemdevelops, the transfer of radiocaesium to the wood may increase in future years, so theseexperiments should be continued. While it is believed that much of the radiocaesium may be
attached to clay minerals in the soil, some percentage of the radiocaesium is always likely to beavailable for uptake. (See Section 3.2 of this report for further information about the behaviourof radiocaesium in the environment.)
At the request of the Prefecture, IAEA experts gave an overview of different models available
for predicting future activity concentrations of 137Cs in forest trees and wild mushrooms. Six
models were presented that can be applied for different situations and ranging in different levelsof complexity and parameterization. The presented models and the data requirements for theirapplication indicated that long term monitoring data will still be needed to compliment andvalidate the model predictions but the frequency and extent of monitoring could be reduced (seeSection 2.2.4).
2.2.4.

Future monitoring of forests

There are uncertainties (estimated at several orders of magnitude) on measurements ofradiocaesium concentrations in trees and important forest products, including Shitake logs andedible mushrooms, which add the uncertainty on the requirements and decisions on future
monitoring of forests. The Prefecture’s experts have identified that future monitoring needs tobe able to evaluate the activity The Prefecture scientists discussed with the IAEA experts ways
in which further analysis and evaluation of existing data could be used to establish relationships
between forest compartments and trends that can then be used to inform future monitoring. The
topics of how best to monitor standing trees to provide respresentative concentrations, thespatial and temporal scales of monitoring and the focus of monitoring in areas where evacuation
is to be lifted in the near future, as well as collecting data for research, were discussed. The
advice of the experts was that a good first step would be to specify well formulated and traceable
new questions that need to be answered by the forest monitoring programme before defining afuture monitoring programme, especially if the initial objectives have already been met. The
support of statisticians in this task would be beneficial.

8

2.3. SPECIFIC STUDIES
2.3.1.

Radiocaesium transfer to wild mushrooms

The Prefecture is the principal producer of Shiitake and Nameko mushrooms in Japan. These
mushrooms are saprophytes and artificial cultivation is carried out using rotting wood, enabling
radiocaesium concentrations to be controlled.
Shiitake mushrooms
There are presently restrictions in place in the Prefecture on the distribution of open-field
Shiitake mushrooms from 17 municipalities, bamboo shoots from 27 municipalities and wildmushrooms from 55 municipalities.
Prior to 2011, the Prefecture was the main producer of oak logs for growing shitake and othertypes of mushrooms. Many of the main production areas were close to the reactor site and highconcentrations of radiocaesium were present in the logs, making it impossible to growmushrooms that complied with the 100 Bq/kg distribution limit for radiocaesium in food to be
sold commercially.
In an effort to regain market share, research has been undertaken to predict the activity
concentration in the tree trunk by either measuring the exchangeable potassium in the soil orthe radiocaesium concentration in fresh growth (leaves and twigs). Both approaches haveshown some promise. However, most of the scientific knowledge on the relationship between
potassium and caesium comes from plants and agricultural crops, with considerably less datafrom forests. The IAEA experts recommended that further research be undertaken to better
quantify the relationship under different circumstances.
The IAEA experts also proposed to investigate if aggregated transfer factors would be a usefulpredictive tool. The experts suggested that large areas of Aizu province might be suitable forlog production. It was noted that the scientific literature suggests a 1:1 ratio between the activity
in the wood and that in the mushrooms grown on it. The index value of 50 Bq/kg forradiocaesium in oak logs destined for mushroom production therefore appears to beconservative.
Wild mushrooms
Prior to the Fukushima Daiichi NPP accident, forest mushrooms were collected and sold in
local markets and roadside stalls to the local population and to visitors, some of whom travelled
to the Prefecture specifically to purchase this local produce. At the end of 2019, there is still afull restriction on ‘distribution’ (i.e. sale) of forest mushrooms in place in 55 of the 59
municipalities. In three municipalities there is a ban on the collection of wild mushrooms while
in some of the other municipalities, people are asked to refrain from collection.
The restrictions in place apply to all species of mushrooms. To lift a restriction on one species
in any given municipality, 60 samples (700g or more for each sample) must be collected within
the municipality for at least 3 years and all of the activity concentrations need to be below
50 Bq/kg. Once a species is de-restricted, samples must be collected at the beginning of eachseason, and all activity concentrations must be below the 100 Bq/kg limit. If one of the samples
exceeds 100 Bq/kg, the restriction is again imposed for all mushroom species in thatmunicipality.

9Currently the range of radiocaesium activity concentrations in forest mushrooms is 10 to
82 000 Bq/kg fresh weight — the highest levels are observed in mycorrhizal species and theactivity concentrations reduce with distance as you move inland from the coast. Large
variability is also observed within the same species. The samples analyzed so far have been
provided by the local population and therefore represent the most popular edible species. The
IAEA team noted that higher concentrations are often found in poisonous (to man) species
which may be a food source for wild animals, and that some saprobic species also have very
high concentrations.
Between 2017 and 2019, no reductions have been observed in the concentrations of 137Cs inwild mushrooms. The IAEA team commented that in the first eight years after the Chornobyl
accident, concentrations in wild mushrooms in some European countries were reasonably
constant, but subsequently fell will an effective half-life of six to eight years. For this reason, it
is important that monitoring programmes should be maintained. As the forest soils andmushroom species are different between Europe and Japan, it cannot be assumed that theobservations in Europe will apply in Japan and some comparative studies on the same speciesof mushroom were recommended by the IAEA team. By the end of 2021, the frequency ofmonitoring for fungus bed grooving mushrooms is being reduced through the time, due to stable
results of the monitoring being demonstrated. However, there has been no change for log-grownmushrooms or wild mushrooms.
The current policy of the Prefecture is to de-restrict ‘distribution’ (i.e. sale) on a
species/municipality basis. It was agreed that a restriction for some species in somemunicipalities is likely to be in place for many years. The IAEA team underlined the importanceof providing advice and information to the general public on the likely concentrations ofradiocaesium in different mushroom species across the Prefecture.
Following on from the conclusion presented by the Prefecture that radiocaesium concentrationsof 137Cs in wild mushrooms will remain above 100 Bq/kg for many years, an overview ofseveral studies conducted in Russian Federation on mushrooms after the Chornobyl accident
were presented by an IAEA expert. Based on the study in 2020 in several different regions of
the country, even 35 years after the accident, there were several types of mushrooms measuring
over 600 Bq/kg (wet weight) of 137Cs. It was discussed that consumption of privately collectedmushrooms is not forbidden in Russia; instead, the population is advised to measure thesampled products in the local sanitary hygiene laboratories, apply different cooking methods toreduce 137Cs concentration in products and decide on consumption themselves (self-support
actions). This is further discussed in Section 2.5.
2.3.2.

Radiocaesium in bamboo shoots

A year on year reduction in the radiocaesium concentration in bamboo shoots has been observed
but this reduction does not appear to be related to the activity concentration of the soil.
The IAEA team commented that older bamboo plants may have deep roots that are therefore
located in soil with low radiocaesium content. The radionuclide content in bamboo might be
expected to increase with time as radiocaesium diffuses into the rooting zone, althoughchemical fixation by clay minerals will also need to be considered. Some surveys andverification experiments might be helpful in identifying long term issues of concern.

102.3.3.

Radiocaesium in freshwater fish

For the vast majority of river systems, radiocaesium concentrations in fish are below 100 Bq/kg.
However, there are still some restrictions on some fish species in some areas and distributionof fish and recreational fishing are not allowed. As of the end of 2022 some restrictions werestill in place in four rivers for five species.
In selected river systems in the Hamadori region (along the east coast of the Prefecture where
the Fukushima Daiichi Nuclear Power Plant is located) some species continue to show
exceptionally high concentrations. For example, activity concentrations of 137Cs up to
16 000 Bq/kg were measured in Masu salmon in the Ukedo river system north west of the
Fukushima Daiichi NPP. A relationship of increasing activity concentration with fish size wasestablished.
Laboratory experiments with dace carried out by the Fukushima University have established aconcentration ratio (CR) for 137Cs transfer from water to fish of ~10. By contrast, the CR values
observed in the field are 1240 to 12 900, clearly demonstrating that the 137Cs in the water is not
the source of the 137Cs in the flesh. Analysis of the gut content of fish caught in the wild showedthat the diet includes both terrestrial insects and aquatic insects. Further work showed muchhigher concentrations of 137Cs in the forest insects, correlated with the much higher
concentrations of 137Cs in the flesh of fish inhabiting forest streams. These insects are known
to feed on forest litter and on mushrooms.
Some fish have a diet of algae rather than insects. The algae have 137Cs concentrations similar
to those observed in forest insects, but much lower concentrations are present in the flesh of
those fish that consume large amounts of algae. This has been shown to be because the 137Cs inalgae and attached silts is much less bioavailable than that from digested insects and hence there
is a lower transfer from the gut to the flesh. The Prefecture has indicated that it wishes to lift
the remaining restrictions as quickly as possible but the currently available information suggeststhat some restrictions may need to be retained for a long time in some areas. The IAEA teamprovided information on the situation regarding freshwater fish in the Ukraine where, as a resultof the Chornobyl accident, the concentrations of both 137Cs and strontium-90 (90Sr) remain very
high in some water bodies and in many species of fish.
Information has also been provided by the IAEA team on restrictions on fishing in parts of theUnited States because of concerns about mercury contamination. Fishing is still allowed, but
consumption is forbidden. The experience is that, once the fishermen understand the basis forthe decision, it is accepted. However, where such fishing is for commercial purposes, there is acontinuing economic impact of the restrictions. The Prefecture has a large aquaculture (fishfarming) industry for freshwater fish. In order to ensure compliance with the distribution limit
for radiocaesium of 100 Bq/kg, a limit of 40 Bq/kg has been established for the concentrationof radiocaesium in fish feed. This value, relating the activity concentration in the feed with thatin the edible portion of the fish, were developed through research at Japanese government
research institutions. The IAEA team noted the conservative nature of the value used.
2.3.4.

Radiocaesium in wild vegetables

Fukushima Prefecture scientists have carried out studies to measure the radiocaesium
concentrations in wild vegetables. Samples of different wild growing vegetables and plants inseveral different municipalities of the Prefecture have been analyzed. Most of the plants
demonstrate a decreasing trend in radiocaesium concentrations. In a study to investigate ways
to reduce 137Cs concentrations in cultivated bracken, the use of reversed tillage combined withfertilization with potassium has proven most effective. Further discussions on ways to manage
wild vegetables and mushrooms exceeding the standard value of 100 Bq/kg were requested by
the Prefecture and are summarized in Section 2.5.
11

2.3.5.

Effectiveness of forest countermeasures

Various countermeasures to reduce the exposure due to radiocaesium in forests have been
evaluated to determine their effectiveness and potential applicability, with the following results:
(1)
(2)
(3)

(4)

The thinning of coniferous trees in 2011 resulted in a reduction of air dose rates of
9–12%.
The removal of deciduous trees to aid in the regeneration of understorey vegetation in2012 resulted in a reduction of air dose rates of 11–21%.
The addition of 3 cm of uncontaminated soil (in ‘liquid’ form) or wood chips resulted ina reduction of air dose rates of approximately 20% that was observed at 24 months after
application. However, the introduction of an additional 3 cm of wood chips had very
limited additional impact.
The removal of fallen leaves resulted in a reduction of air dose rates on the order of 10%,
but there was a negative impact of increased erosion.

Countermeasures (1) and (2) are normal forest management practices; the thinning of trees
increases the amount of sunlight reaching the forest floor, thereby encouraging the growth ofunderstory vegetation. This in turn helps to bind the soil and prevents erosion. In 2011 and 2012,both of these countermeasures were shown to be highly effective in reducing air dose rates
when a significant percentage of the deposited radiocaesium was still located in the trees. In theensuing years, when most of the radiocaesium content of forests had migrated to the soil andlitter layers, this practice was less effective in reducing air dose rates.
The experiment involving the addition of uncontaminated wood chips (countermeasure (3)above), and illustrated in Figure 2.5, was continued after the initial two year period and annual
measurements of dose rate were made. At the end of 2019, the Prefecture reported that theinitial reduction in air dose rate had been maintained for a fifth consecutive year. The IAEA
team noted that the uncertainty estimates for each of the measurement points overlapped withthe technical calculation of dose rate due to radioactive decay and therefore it was not possible
to say with certainty that there is any effect. They also questioned why the addition of fallen
leaves on top of the wood chips in each of the five years had apparently made no contribution
to increasing the dose rate. Finally, it was commented that, over a period of five years, one
might reasonably expect some form of disturbance by animals or decomposition of the woodchips, but that seems not to be the case.
The Prefecture concluded that the implementation of countermeasures involving the additionof liquid soil or wood chips is expensive and unlikely to be justified for widespread application.
However, it is realistic to apply them over smaller areas with high air dose rates, especially ifsuch areas are close to inhabited areas. Presently, these countermeasures are not in routine use.
The Prefecture is investigating the movement of radiocaesium from the forest ecosystem before,
during and after the thinning of trees. While the overall losses are believed to be low, local
farmers are still concerned about radiocaesium being transferred to agricultural land and ricepaddies. The Prefecture is also investigating the effectiveness of log fencing and sandbags in
reducing sedimentation rates and losses of radiocaesium from the ecosystem. Preliminary
results indicate that such measures are effective in preventing soil erosion and runoff,
particularly when the slope of the terrain is 30 degrees or greater. Any radiocaesium lost throughsedimentation is likely to be bound with clay minerals and, as such, may not be available fortransfer to agricultural soils. At the same time, air dose rates may increase in areas wheresediment accumulates.

12

FIG. 2.5: Application of wood chips as a countermeasure to reduce the air dose rate in a forest (Image:
Fukushima Prefecture).

Air dose rates near inhabited areas may be reduced through a combination of litter removal,
branch removal and topsoil removal. A priority is to install log fencing on higher ground toprevent soil erosion and subsequent recontamination of decontaminated areas.
2.3.6.

Managing the timber industry

National legislation requires any material that exceeds an activity concentration of 8000 Bq/kg
of radiocaesium to be managed as ‘designated waste’. This is a concern in relation to forest
management. An initial step in the processing of felled trees is the removal of bark, which iscommonly used as a fertilizer and as a fuel for biomass plants. It is important to ensure that thetimber industry is effectively managed as the wood is an important economic resource used forthe construction of new housing, as well as window frames, household furniture, etc.
Measurements have been made in an attempt to correlate air dose rates with the radioactivity
concentration in bark. As would be expected, wide variability in such measurements wasobserved. An air dose rate of 1.69 µSv/h roughly corresponds to a radiocaesium concentrationof 8000 Bq/kg in bark. The Prefecture has adopted a rule whereby, in areas where the air dose
rate is below 0.5 µSv/h, the measurement of activity concentrations in bark is not required andlogging and transportation of trees can be performed without restriction. .If the air dose rate
exceeds this value, a sample of the bark must be analyzed to determine the actual activity
concentration of radiocaesium. This is a conservative approach, but it seems to work well.
An index value has been set of 40 Bq/kg for the activity concentration of radiocaesium infirewood to ensure that the radionuclide concentration of the ash does not exceed 8000 Bq/kg.
The concentration factor between wood and ash is normally 100 Bq/kg or less so this is again
a relatively conservative approach.
For newly planted trees, the uptake of radiocaesium would be expected to be greater than forexisting trees; however, experts from the Prefecture presented the results of experiments
indicating that the radiocaesium content of newly planted saplings was only a few hundred
Bq/kg. As the time for trees to reach maturity is around 50 years, any possible increased uptake
13will be more than compensated for by reductions due to the radioactive decay of radiocaesium
over that time period.
As the radiocaesium in forests in the soil and litter layers migrates deeper into the soil, it will
come within the rooting zone of trees, but one would expect that it will be effectively bound tothe clay minerals present. This downward movement will result in changes in the
uptake/transfer factor, but it is difficult to be specific at this stage about the onset and durationof these changes.
The highest concentration of radiocaesium measured to date in wood is 5500 Bq/kg. Using themethodology outlined in IAEA-TECDOC-1376 [1], if such wood were used for house
construction, the annual dose to occupants is estimated to be 0.132 mSv. Scaling up, at
8000 Bq/kg, the annual dose would be about 0.2 mSv. Due to the conservative nature of themodels used, any differences in Japanese house design would not be expected to significantly
increase these estimated doses. Therefore, no additional restrictive measures are deemednecessary at this time to allow timber from the forests of the Prefecture to be used for house
construction.
While radiocaesium concentrations in timber are currently low and well within international
standards, it is important that the research studies which have commenced on the translocationof radiocaesium within trees and the transfer to newly planted saplings are continued.
2.3.7.

Protection of forest workers against radiation

Forest workers are potentially at risk of exposure to radiation doses. Currently these workers
are provided with gloves and face masks to help minimize their exposure. They are notclassified as occupationally exposed workers and their work is restricted to those areas in which
the air dose rate does not exceed 2.5 µSv/h. This corresponds to an annual dose on the order of
5 mSv, which is the value adopted by the Prefecture for protection of forest workers. The annual
dose limit for workers that are occupationally exposed to radiation is 20 mSv.
In order to reduce doses to workers, tree harvesting machines are being introduced to replace
manual cutting; the operator is higher above the ground and the machine further shields theoperator from radiation. Also, cabins on certain forest machinery that enclose the operator
provide shielding that reduces worker doses by about 35–40%.
2.3.8.

Forest fires

According to IAEA-TECDOC-1240 [2] “There is thought to be some risk of radionuclide
dispersion onto the adjacent territories as a result of forest fires. However, the available data onradionuclide transfer during forest fires are contradictory.” The TECDOC also states “The main
problem produced by forest fires is the resuspension of contaminated ash in the atmosphere.”
While elevated radiation levels do not increase the likelihood of forest fires, they often
contribute to reduced forest management activities so that the regular thinning of trees is not
performed, which leads to an increase in the amount of material available for combustion.
Following a fire, radionuclides can be transported over several hundred kilometres through thedispersion in the atmosphere of ash to which radioactive material is attached. The radiation
exposure pathways are external radiation and plume inhalation (firefighters and the public);
external radiation from deposited radionuclides (public); ingestion of contaminated foodproducts (public): and inhalation of radionuclides in resuspended ash at the site of the wildfire(forest workers and the public).
14

The amount of radionuclides available for transportation as a result of a forest fire is relatively
low. Experimental studies have shown that only a few percent of the radiocaesium in the litter
layer is mobilized during a forest fire. Considering that as of 2016, only about 7% of theradiocaesium present in the Prefecture’s forests was located in the litter, it would be expectedthat only a very small percentage of the total radiocaesium inventory would be mobilized in theevent of a forest fire. For example, following a fire involving vegetation and litter only, about
0.1 to 0.5% of the radionuclides that are present could be mobilized; however, in the case of acrown fire, this amount could increase to 10%. Most of the radiocaesium that would be
mobilized would be expected to be deposited within a few hundred metres of the location of
the fire, so increases in air dose rates at large distances from the fire would not be expected.
While forest fires may not disperse large amounts of radionuclides, fires may damage thecapability of the forest to retain soil that may be lost through erosion and fallen leaves andneedles that may be more readily washed away in the absence of understorey vegetation.
High temperatures resulting from forest fires may vaporize some of the radiocaesium that ispresent, which could be transported in the atmosphere. The remainder of the radiocaesium will
be found in the ash. Even if deposited in rivers and streams, the radiocaesium will be quickly
fixed to solid matter and the impact on biota is likely to be minimal. The impact of forest fires
is usually evaluated through modelling, in part because the collection of real time data is
problematic due to the hazards associated with, and the unpredictable nature of, forest fires. A
number of different models for this purpose already exist. It was noted by the IAEA team thatmost models overestimate the actual impact of forest fires and therefore it is important toperform sensitivity analyses by varying parameters and associated assumptions. It was notedthat differences in soil type and topography may lead to a forest fire in the Prefecture having alower radiological impact than in the areas affected by the Chornobyl accident.
A number of forest fires have occurred in the Prefecture since 2011, which resulted in publicanxiety. Prefecture experts presented information about three forest fires that took place in 2016
and 2017: (1) a fire near Date City that affected about 38 ha that burned during 30 March–
1 April 2016; (2) a fire near Minami-soma City that affected about 32 ha and burned during 3–
4 April 2016; and (3) a fire that occurred inside the Evacuation Designated Zone near Namie
Town that affected about 75 ha and burned during 29 April–10 May 2017.
To examine the radiological impact of the 2016 fires, the Prefecture established a monitoring
programme that measured air dose rates and the radiocaesium content of surface stream waterand mountain stream water. An increase in air dose rates was not observed. A minor amount ofradiocaesium was detected in surface stream water in the Minami-soma District. Radiocaesium
was not detected in mountain stream water downstream of the areas affected by the fires. The
amount of sediment outflow from the area affected by fire was three to five times greater thanthat in unaffected areas.
As of July 2017, the preliminary assessment of radiation survey results from the Namie Town
fire indicated that the fire did not have a significant radiological impact in that only slightincreases were observed in air dose rates at nearby measuring points. Further work was planned
to assess the extent to which ash may have been deposited in the river passing close to the burnt
area and the transportation of radiocaesium downstream.
The IAEA team noted that had the fires in 2016 and 2017 taken place soon after the Fukushima
Daiichi accident when a larger percentage of the radiocaesium was in the litter layer, a greater
amount of radiocaesium could have been redistributed.

15

2.4. SATOYAMA REHABILITATION MODEL PROJECT
Satoyama is the border zone or area between mountain foothills and arable land and usuallyconsists of forests, grasslands, rice paddies, etc. The people who live in or close to these areas
are often self-sufficient and may cultivate mushrooms in the forest. The aim of the Satoyama
Rehabilitation Model Project, which was initiated in 2016, is to allow people to return to livein these areas as they did before the Fukushima Daiichi accident. Communities within theevacuation zones and neighbouring municipalities were selected for participation in the project
between September and December 2016. At this time, people were starting to return or wereconsidering returning to the identified municipalities. This is a joint project between a numberof local and relevant Government of Japan Ministries and 14 of the 17 municipalities in the
Hamadori and Nakadori Regions are participating.
The project has three main components: forest maintenance; decontamination; production ofradiation dose maps; and performance of personal dosimetry surveys.
The project is driven primarily by the need for public reassurance and once completed, thePrefecture intends to share results from all 14 sites with local communities.
In 2017, the IAEA assistance in the following activities became the part of the modified
Practical Arrangements:Creation of radiation dose maps;
Decontamination of forests and surrounding areas used on a daily basis;
Forest maintenance.

After the formal agreement was in place, the implementing staff of the Prefecture described the
project to the IAEA team, who were impressed with the attention to detail of the work and notedthat all necessary information to undertake a cost effectiveness study are available. For example,
the radiation doses received by workers have been recorded and the dose reduction achieved
takes account of what would be expected in any case due to radioactive decay alone. The IAEA
team also noted that the effectiveness of countermeasures in the selected areas may be limited
and that consideration should be given to defining how the success of the project would be
evaluated.
In order to familiarize the IAEA team with the local environment and the nature of theremediation work, in July 2019 a site visit was organized to Iitate Village. In February 2020,
another site visit was organized to Okuma Town and Kawauchi Village.
At both Okuma Town and Kawauchi Village, tree thinning and selective cutting of trees has
been undertaken. In Okuma, which is a relatively high dose rate area (up to 2 μSv/h), theobserved reduction in dose rate was an average of 8% above that due to radioactive decay. In
Kawauchi, where the annual dose rate is only marginally above background levels, no reduction
above that due to radioactive decay was observed. Figure 2.6 shows the results of maintenancework on trails in Kawauchi Village and Okuma Town.

16

FIG. 2.6: Examples of remediation work in the Satoyama Rehabilitation Model Project at Kawauchi
Village (top) and Okuma Town (bottom) (Image: Fukushima Prefecture).

In Kawauchi Village, an area where the dose rate was 0.26 μSv/h (just above the ‘target’ valueof 0.23 μSv/h), 9 cm of litter and topsoil was removed, resulting in a reduction in the dose rate
to 0.19 μSv/h. The experts commented that in a few months the dose rate would have reduced
in any case to 0.23 μSv/h and questioned whether or not this work was justified in terms ofradiation protection.
The IAEA team underlined the importance of providing information on the results of the project
to former evacuees to help inform their decision on whether or not to return.
At Ainosawa, Itate Village, it was reported in 2022 that, after the remediation work, a small
number of the general public have visited Satoyama for recreational purposes. Combinationsof remedial actions have been used: decontamination by litter removal; forest maintenance; anddose measurements/assessment. A major reason for the success of these projects has been thereassurance that they provide to the public through the establishment of a safer environment for
local residents and visitors.
2.5. MANAGEMENT OF WILD FOODSThe IAEA team has provided information on the approach and philosophy in setting limits forradiocaesium in agricultural and wild foods in Belarus, Czech Republic, Norway and Sweden
following the Chornobyl accident. In all cases, a considerably higher limit was applied to wild
foods compared to agricultural foods. This is because wild foods are normally consumed inrelatively small amounts and the associated radiation doses to consumers are not high, eventhough the activity concentrations may be much higher than is observed in agriculturally
produced foods. National authorities also considered the societal implications, including17

disruption of lifestyle, that would result if the consumption of wild foods was severely restricted
and concluded that the associated radiation doses did not warrant such action.
A representative of the Prefecture has explained that the current limit of 100 Bq/kg forradiocaesium in wild foods that are sold into the marketplace is unlikely to be revised for two
main reasons: firstly, it is a national limit and not within the control of the Prefecture to change
and, secondly, an increase in the limit so many years after the accident would probably not be
accepted by the public. Another important consideration is that the restrictions currently in place
apply only to foods that are sold: those who wish to harvest wild foods for their own personal
consumption are free to do so.
Given that the 100 Bq/kg distribution limit is likely to continue to apply to wild foods for atleast the foreseeable future, in spring 2020, the IAEA team advised that greater focus needs tobe given to reducing the doses to those who source wild foods — wild boar, mushrooms, sansei
and freshwater fish — in the forest for their own consumption and to whom the distribution
restriction does not apply. While there is a measurement service in place whereby people canhave their foods measured for radiocaesium, it is mainly used more for checking locally
produced agricultural foods such as cereals and vegetables but not game meat; people need to
be encouraged to use this service also for wild foods. A list of plants and mushrooms is provided
for the Fukushima Prefecture inhabitants, explaining which species are restricted in different
municipalities (see also Section 6).
In the case of forest products such as wild boar, the IAEA team suggested to develop the ‘invivo’ technology used widely after the Chornobyl accident. Such a measurement would provide
a quick estimate of the radiocaesium content of the meat and allow the hunter to make an
informed decision on whether or not to consume it or have it destroyed. The IAEA team gave
two presentations as input to the discussions on this topic. The first was on ‘Monitoring
programme of wild species in Fukushima Prefecture’, and the second was on ‘In vivo
measurement of Cs in animals in Norway’. A description was given, based on the experiencein Sweden, on how the Prefecture could build up a monitoring programme of the wild animals,
including a representative sampling strategy, to ensure that measurement data sufficient forlifting the restrictions for hunters are available. It was also advised that, having undertaken a
preliminary statistical evaluation of the measurement data in the Prefecture for wild boar, there
will never be 100% certainty that concentrations of Cs will be <100Bq/kg in the near future andso dialogue with municipalities and hunters will be needed in order to lift restrictions and allow
for taking personal decisions. The second presentation described how to perform monitoring ofradionuclides in animals in vivo and the methods developed in Norway in the first few years
after the Chornobyl accident in order to determine the Cs concentrations in sheep/cattle andreindeer and the experience of communication of the measurement results to interested groups
based on the experience in Norway. Following the discussions on the two presentations, it wasnoted that the high concentrations of radiocaesium in the flesh of wild boar mean that
restrictions are unlikely to be lifted in many of the Prefecture municipalities in the near future.
However, relatively low concentrations are being observed in a small number of municipalities
in Aizu district.
The experiences of monitoring game and wild mushrooms in Sweden were presented by an
IAEA expert in the February 2022 meeting. The Swedish programme was designed in the late1980s to provide the general public on the information about 137Cs contamination of food. There
have never been any restrictions on the consumption of game meat and mushrooms in Sweden
based on the Cs concentrations; the measurement service available for the hunters allows themto make a decision on their personal consumption of hunted game meat and wild mushrooms.
18

To provide the population with the measurement results, a network of measurement laboratories
was established in the countries and the measurements are subsidised by the government.
The Swedish Food Safety Authority provides a recommendation on the consumption of foodcontaining 137Cs [3]. The approach used is based on the combination of concentration of the137
Cs in an individual product and the volume of the product that can result in doses above 1
mSv/a. The recommendations are:


300–1 500 Bq/kg: not more than a few times per week;
1 500–3 000 Bq/kg: not more than a few times per month;>10 000 Bq/kg: not recommended for consumption.

The limit for selling the meat and wild mushrooms is set at 1500 Bq/kg.
A new method that can be used for the non-destructive analysis (NDA) of the matsutake
mushroom was presented by the Prefecture during the February 2022 meeting. The objective is
to not destroy this valuable forest product after measurement so that it can be distributed andconsumed, if the result of NDA allows it. The Prefecture plans to continue discussion withcentral governmental bodies regarding the extension of the NDA for matsutake mushroom andother species. If NDA can be applied to other wild mushroom species, this would allow theconsumption and distribution of wild mushrooms collected in Prefecture municipalities andalso, importantly, allow the population to return to traditional collecting and consumption of
the wild plants and mushrooms.
The IAEA team noted that restrictions are likely to be necessary for certain wild foods in someparts of the Prefecture for many years or even decades. The IAEA team also noted thatmonitoring programmes will need to be maintained and it is essential to keep providing
information on the trends of radicaesium concentrations in wild foods to the population,
including hunters.
2.6. SECTION SUMMARY
The Prefecture has implemented an extensive monitoring and research programme to better
understand and follow the behaviour of radiocaesium in forests. When comparing the situation
with that which occurred following the Chornobyl accident, the more general mechanisms ofrecycling of both nutrients and radionuclides are expected to be similar. However, differences
between the forests in the Prefecture and European forests in terms of annual rainfall,temperature, topography and soil characteristics have been shown to be important in influencing
the movement and cycling of radiocaesium.
Some of the key conclusions from the work undertaken by the Prefecture are as follows:
Radiocaesium movement and cycling(1)

Radionuclides deposited in the forests of the Prefecture are effectively retained within theecosystem and the likelihood of transfers of radiocaesium to agricultural land appears to
be low.

(2)

Forest maintenance procedures have helped to prevent erosion and soil loss and are also
very effective at retaining radiocaesium within forests.

(3)

The presence of clay minerals in the underlying forest soils will chemically bind theradiocaesium and limit its transfer to vegetation. The result is that, for the same19

deposition, the activity concentrations of radiocaesium in plants and animals in the forestsin the Prefecture are considerably lower than those observed in European forests after the
Chornobyl accident.
(4)

Based on experience with radiation monitoring in areas affected by the Chornobyl
accident, radiation monitoring in forests may be necessary for many more years.
Monitoring procedures for measuring air dose rates and the radiocaesium content of trees
may need to be adjusted to account for changing conditions such as the movement ofradiocaesium in the environment and the deposition of radiocaesium in waterlogged
areas, where the uptake by vegetation would be expected to be higher. Based on themonitoring survey in forests up to 2022, the results indicate that ‘background’ dose rates
have now been observed over serval monitoring campaigns at a number of sites. The
Prefecture is now considering the decrease in frequency and density of monitoring to
reduce the number of measuremetns made based on clear objectives. However, it isrecognised that some continued monitoring into the future will continue to be requested
for public reassurance, even at sites where doses are very low.

(5)

All components of the forest ecosystem are interdependent: the forest insects eat
mushrooms, which are in turn eaten by both wild boar and some freshwater fish. While
not a part of this report, wild boar are believed to eat mushrooms directly. There do notappear to be any realistic remediation options that are cost effective and can be applied
without causing damage to the environment. The available data suggests that restrictions
will be in place in parts of the Prefecture for certain foods for many years, probably
decades. In the meantime, monitoring programmes with high associated costs will be
required.

(6)

Because future reductions in dose rates will be dominated by the radioactive decay of
137
Cs, the annual reductions will be low and, as such, the situation can be regarded as
being more stable. In such circumstances, it may be justified, from a technical viewpoint,
to reduce the frequency of monitoring without the loss of valuable information.

Possible countermeasures(7)

Since 2012, most of the radiocaesium initially deposited in forests has been transferredfrom the trees to the soil and litter layers. The feasibility of removing large amounts ofsoil in order to reduce the air dose rate is not practical; it is expensive, produces additional
waste material that must be managed, and has the potential to reduce the productivity of
the forest.

(8)

Covering the forest floor with soil or wood chips that has studied as a potential measure
to reduce air dose rates. A number of questions regarding the long term effectiveness ofthese measures remain. In the meantime, the Prefecture has already concluded that,
because of the associated high costs, the application of such measures may be justified
only over limited areas with high air dose rates, especially if such areas are close to
inhabited areas.

(9)

To date there appears to be no need to restrict the production and use of the timber
harvested from forests. However, monitoring of timber needs to continue, especially as
logging work commences in areas which were affected by higher deposition ofradiocaesium.

20Protection of workers(10) Measures have been implemented to restrict the radiation exposure of forest workers;
these include the use of harvesting machines and limitations on working hours. Overall,a conservative approach has been taken in order to reduce the radiation doses of these
individuals.
Forest fires(11) Studies of forest fires in the Prefecture have not identified a significant radiologicalimpact that resulted from these events. However, forest fires may have had a greater
radiological impact if they had occurred soon after the Fukushima Daiichi accident whenmore of the radiocaesium inventory was in the litter layer and available to be redistributed
as a result of forest fires.
Public information(12) The Satoyama Rehabilitation Model Project was concluded in fiscal year 2019. It is
intended to publish the results obtained and make them widely available to the generalpublic. This information is particular important for former evacuees to help inform theirdecision on whether or not to return.
(13) There are many similarities between the three monitoring programmes for wild foods.
Apart from being interdependent, the data for wild mushrooms, freshwater fish and wild
animals all show high concentrations of radiocaesium, many outlier values and a very
slow reduction in levels. The activity concentrations in many of these foods well exceed
the limit of 100 Bq/kg for general foods sold commercially that was established in April
2012 for the foreseeable future. A non-destructive analysis (NDA) has been developed
for the matsutake mushroom to be able to distribute this valuable forest product for further
consumption after the measurement. If NDA can be applied to other wild mushroom
species, this would allow the consumption and distribution of the products collected inany municipality of the prefecture and allow the population to return to traditional
collecting and consumption of the wild plants and mushrooms.
(14) Ongoing attention needs to be given to providing more and better information on levelsof radiation in the environment so that people can make informed choices on the radiationdose they are prepared to accept.
(15) Also related to public information, as time progresses, monitoring programmes will
identify more and more ‘less than’ or ‘not detectable’ results. These can be an important
communication tool to show that the situation is improving, even if restrictions remain inplace. A standard approach should be agreed and applied uniformly across all monitoring
programmes.

21

3.

MONITORING OF RADIOACTIVE MATERIAL AND ASSOCIATED
REMEDIATION AND DECONTAMINATION IN TERRESTRIAL AND
AQUATIC ENVIRONMENTS

3.1. BACKGROUND AND OBJECTIVES
Based on the data collected and an assessment conducted by the Prefecture, during the periodof the Practical Arrangements, the most important exposure pathway for people is externalradiation emitted by radiocaesium (see also Section 2.1 for further information on radiocaesiumin the forest environment). Furthermore, the Prefecture has determined that radiocaesium levelsin the terrestrial and aquatic environments and associated doses to people have declined due todecontamination activities, radioactive decay, the removal of radiocaesium by weathering fromsurfaces (including during extreme weather events, see Section 3.5) and vertical migration
down soil and sediment profiles.
The need for remediation and decontamination depends to a large extent on the evolution ofdoses to members of the public over time. Decisions relating to remediation activities are basedon an assessment of current doses, as well as future doses that would be achieved throughremedial actions relative to those that would occur without intervention. It is, therefore, helpful
to make predictions regarding temporal changes over time in air dose rates and doses to people
with and without intervention.
The Practical Arrangements refer to the provision of assistance to the Prefecture on issues
related to off-site decontamination, analyses of the results of environmental monitoring, andexploration of exposure pathways in order to reduce or avoid exposure. Under this activity, thecooperation has addressed the following topics:










Behaviour of radiocaesium in the terrestrial and aquatic ecosystems, excluding forests(See Section 2), in the areas of the Prefecture affected by the Fukushima Daiichi accident;
Effectiveness of remediation and decontamination measures in aquatic systems;
Analysis of monitoring results to identify temporal trends in radiocaesium concentrations
in environmental media (soil, water, sediments), and of air dose rate;
Review of experience gained from remediation activities in order to elaborate input forthe selection of appropriate and technically feasible remedial actions;Application of models to simulate radiocaesium flux in aquatic systems;
Effectiveness of decontamination measures implemented in residential areas;
Impacts of severe weather events, such as typhoons, on radiocaesium dynamics infreshwater environments;
Dissemination of information on effectiveness of decontamination and remediation, doses
to members of the public in the Prefecture, monitoring results and engagement ofinterested parties (this topic is covered in Section 6).

These topics are addressed in the following sections of this report.

22

3.2. BEHAVIOUR OF RADIOCAESIUM IN TERRESTRIAL AND AQUATICECOSYSTEMS
3.2.1.

Global experience on radiocaesium in the natural environment

Radiocaesium has been released to the natural environment by atmospheric nuclear weapon
tests, operations of nuclear facilities, and by accidental releases. In general, in the terrestrial
environment, radiocaesium is strongly bound by mineral soil components, resulting in its slow
migration and low uptake by plants from soil. Radiocaesium in soil is gradually bound to soil
components, especially clay particles. This sorption may be reversible, constituting the fractionof exchangeable radiocaesium, or, largely irreversible, constituting the fixed fraction. However,in acidic, organic soils with low potassium content, radiocaesium uptake by plants is muchhigher. In tropical areas, where soils are subject to physical and chemical weathering overthousands of years, clay minerals have largely broken down and potassium has been depleted
by leaching under acidic conditions; therefore, the uptake by plants may be much higher.
In freshwater ecosystems, radiocaesium binds strongly to suspended and bottom sediments,
which causes a rapid decline in dissolved radiocaesium, and ultimately, deposition ofradiocaesium in bottom sediments of surface waters. The transport of radiocaesium in rivers
and lakes is largely due to the redistribution of sediments [4]. An increase in dissolved
potassium concentration in fresh surface waters will result in a decrease in accumulation ofradiocaesium by freshwater organisms due to competitive uptake between these two elements.
In addition, following uptake, differences in the relative loss rates of caesium and potassiumfrom freshwater organisms can lead to bioaccumulation of radiocaesium resulting in an increasein the activity concentration between each trophic level [5, 6]. Therefore, the physicochemical
conditions in a water body that affect transport of particles and/or radiocaesium dynamics (e.g.
pH, basin bathymetry, depth, concentrations of suspended sediments and potassium), as well as
the length of the aquatic food chain, will influence the activity concentration of radiocaesium
at the top of the aquatic food chain. Monitoring of radiocaesium in wild fish is described in
more detail in Section 2.3.3 of this report.
3.2.2.

Radiocaesium behaviour under the environmental conditions of the Prefecture

The behaviour of radiocaesium under the environmental conditions in the Prefecture has been
the subject of many studies since 2011. Consistent with experience made after the Chornobyl
accident and other contamination events [7, 8], these studies have shown that both the
downward migration of radiocaesium in soil and the uptake of radiocaesium through crops fromsoil are very low due to the strong sorption of radiocaesium by soil.
According to studies conducted by Fukushima University, the proportion of exchangeableradiocaesium in soils and radiocaesium levels in crops in the Prefecture havecontemporaneously decreased since 2011. For the prevailing soil types of the Prefecture, theRadiocaesium Interception Potential (RIP), which characterizes the ability of a soil toselectively adsorb radiocaesium, has been determined. Soils and sediments with a high RIP
value strongly adsorb radiocaesium and, therefore, radiocaesium transfer from the soils to crops
is small. This concept was widely applied after the Chornobyl accident to predict theradiocaesium uptake by crops based on soil parameters. In soils with a low RIP value, theapplication of clay can be effective in reducing radiocaesium transfer to crops.
Limited amounts of 90Sr were released during the Fukushima Daiichi accident [9]. The
deposition density of 90Sr was 3–4 orders of magnitude less than for 137Cs. In the immediate
vicinity of the Fukushima Daiichi Nuclear Power Plant, 90Sr deposition to the ground were23

nearly equal to those resulting from fallout of atmospheric nuclear weapons testing in the 1960s.
Resulting 90Sr activities in foods were low as well; e.g. in 2012, 90Sr was measured in foodstuffs
in municipalities at a distance of 20–30 km from the FDNPP; in all cases the 90Sr levels were
below the level of detection [10]. In UNSCEAR (2013) [11] doses to the population outside theevacuated areas arising from 90Sr are not explicitly estimated because they were considered as
insignificant.
International experience on the behaviour of radiocaesium in the environment andenvironmental remediation projects was provided by the IAEA team. Following both the
Chornobyl and Fukushima Daiichi accidents, it was observed that natural attenuation processes
contributed to the reduction of radioactivity in the environment. However, the washoff ofradiocaesium was found to be higher in the Prefecture than in areas affected by the Chornobyl
accident due to:






Greater rainfall precipitation from the occurrence of typhoons and higher temperatures;Greater biological activity due to higher precipitation and higher temperatures;
Longer frozen periods in Chornobyl;
Steeper slopes of hill sides.

These factors affected radiocaesium transport processes, as described in the following section.
3.2.3.

Transport processes in catchments

The transport of radiocaesium from a catchment area via a river or river system is illustrated
schematically in Figure 3.1. Radiocaesium is deposited in forests, agricultural and residential
areas. Since radiocaesium is strongly adsorbed by mineral components in soil, it is transported
via river flow and the associated redistribution of sediments. Figure 3.1 also depicts theinteraction between terrestrial and aquatic ecosystems, including the possible transfer pathways
to agricultural products. The following processes are important:






Radiocaesium is removed from forests, residential and agricultural areas through runoff,
which depends on the intensity of rainfall, the slope of the terrain and its surface
characteristics (vegetated, paved, bare soil);River systems are connected to ponds, lakes and reservoirs, which might be used as
drinking water or for irrigation purposes during the growing season;
Following intensive rainfall or extreme weather events (e.g. typhoons), river flooding andturbulent flow can affect previous deposits of radiocaesium bound to sediments;
Some radiocaesium will be transported to the ocean.

3.3. ANALYSIS OF RESULTS OF MONITORING PROGRAMMES
3.3.1.

Monitoring of radiocaesium in water and sediments

In the Prefecture, river water is widely used as a source of water for the city water consumption,
for agricultural activities and other purposes. Therefore, the Prefecture started monitoring
radiocaesium in fresh surface waters and the campaign is conducted by the Fukushima
Prefectural Centre for Environmental Creation (see Figure 3.2 and Table 3.1).

24

FIG. 3.1: Illustration of radiocaesium transport through a catchment area and interactions withterrestrial elements (Image: Fukushima Prefecture).

FIG. 3.2: Distribution of 137Cs deposition in the Prefecture as determined during the Third Airborne
Monitoring Survey (MEXT, 2 July 2011).

25

Table 3.1. Catchment area and average 137Cs inventory in the wide area river survey [12]Catchment
Area
(km2)

Average 137Cs
Inventory(kBq/m2)

Kuchibuto River

8

587

Kuchibuto River

21

408

Abukuma River

Kuchibuto River

63

304

Kuchibuto River Downstream

Abukuma River

Kuchibuto River

135

248

Fushiguro

Abukuma River

Abukuma River

3645

102

6

Iwanuma

Abukuma River

Abukuma River

5313

96

7
8

Mano
Ojimadazeki

Mano River
Mano River

Mano River
Mano River

76
111

521
418

9

Matsubara

Same River

Same River

871

46

10

OnahamaFujiwara River

Fujiwara River

70

45

11

Tsukidate

Abukuma River

Hirose River

84

222

12

Nihonmatsu

Abukuma River

Abukuma River

2380

88

13

MiyodaAbukuma River

Abukuma River

1287

77

14

Nishikawa

Abukuma River

Shakado River

289

137

15

Kitamachi

Niida River

Mizunashi River

36

537

16

Kawamata

Abukuma River

Hirose River

57

226

17

Marumori

Abukuma River

Abukuma River

4124

113

18
19

Funaoka Ohashi
SenoueAbukuma River
Abukuma River

Shiroishi River
Surikami River

775
313

27
51

20

YagitaAbukuma River

Ara River

185

63

21

Kuroiwa

Abukuma River

Abukuma River

2921

109

22

TomitaAbukuma River

Ouse River

73

117

23

Ota

Ota River

Ota River

50

1638

24

Odaka

Odaka River

Odaka River

50

750

25

Asami

Asami River

Asami River

26

197

26

Tsushima

Ukedo River

Ukedo River

25

813

27

Ukedo

Ukedo River

Ukedo River

153

2329

28

TakaseUkedo River

Takase River

264

696

29
30

Haramachi
Akanuma

Niida River
Abukuma River

Niida River
Otakine River

200
243

858
57

31

Watari

Abukuma River

Abukuma River

5313

96

Site Name

Catchment
drainage
SystemRiver Name

1

Mizusakai River

Abukuma River

2

Kuchibuto River Upstream

Abukuma River

3

Kuchibuto River Midstream

45Site No.

*The Watari Point (31) is on the bank opposite the Iwanuma Point (6) and was setup as a backup monitoring point.

The monitoring programme includes the measurement of radiocaesium dissolved in water, as
well as radiocaesium bound to suspended sediments in rivers and lakes. In addition, samples
are screened for highly enriched radiocaesium bearing microparticles (CsMPs) (seeSection 3.3.4).
Due to the strong sorption of radiocaesium by suspended sediments and its deposition in thebottom sediments of water bodies, radiocaesium levels in river water have declined
considerably with time, and within less than 7 years of the accident, were close to or below
0.05 Bq/L [13] for the measurement technique used (a level far below the criterion of 10 Bq/L
for drinking water quality recommended by the World Health Organization (WHO) [14].
There was also a clear decline in the activity concentration of radiocaesium in suspended
sediments, especially when further erosion from contaminated catchment areas is limited.
26

Consistent with the international literature, radiocaesium activity concentrations in sediments
have tended to increase with decreasing particle size.
The Prefecture monitoring programme has focused on studying the long term behaviour ofradiocaesium in the catchment areas of the Prefecture, and specifically on three aspects:Levels and the behaviour of radiocaesium associated with suspended particles, including
the deposition or removal of radiocaesium bound by sediments and floodplain soils during
floods and extreme weather events (e.g. typhoons), and the corresponding effects on air
dose rates;
Radiocaesium in its dissolved form, i.e. transfer to agricultural products, wild animals andplants via the accessible ecosystem;
The dynamics of particulate and dissolved radiocaesium in river catchments.

Concentrations of major ions (potassium, calcium, magnesium, and ammonium) are alsomeasured to characterize the physicochemical properties of the water, which affects
radiocaesium dynamics in aquatic systems (see Section 3.2). Tracer techniques are being
applied in the Prefecture to gain further understanding of radiocaesium transfer between
terrestrial catchment areas and surface water environments (see Section 3.3.5).
The measurements made by the Prefecture have focused on the catchment areas affected by thedeposition of 137Cs, see Figure 3.2 and Table 3.1. This included general surveys at monitoring
points in multiple rivers to monitor temporal and spatial changes in radiocaesium activity
concentrations and the influence of basin characteristics on radiocaesium dynamics. In addition,
detailed surveys and studies were carried out in the basins of the Hirose and Kuchibuto Rivers
to estimate radiocaesium transport and to compare measured data with estimates generatedusing a simulation model (see Section 3.4). Emphasis was placed on the Hirose River basin,
where twelve monitoring points were established along the river and its tributaries, including
the Takane River, the Nuno River and the Oguni River. In addition to the physicochemical
attributes of the surface waters, the measurements included determination of water flow rates,
turbidity of water and concentration of suspended sediments. As expected, rainfall events
coincided — with some delay — with increases in the flow rate and concentration of suspended
sediments. Although there are considerable fluctuations with time, the 137Cs levels havedecreased continuously in dissolved form and suspended sediments since 2011. Similar trends
were observed in studies of radiocaesium transport in rivers within the Hamadori and the
Nakadori Districts; the results for the suspended 137Cs activity concentrations since 2011 at
more than 30 points are shown in Figure 3.3. During a heavy rainfall event in September 2015
(Typhoon 15 Etau), suspended radiocaesium concentrations temporarily decreased.
These results are in accordance with a study conducted by Ueda, et al. [15] who measured theconcentration of particulate and dissolved 137Cs in the Hiso and Wariki River (two small rivers
in the Soma District, Fukushima Prefecture) from 2011 to 2021. There is a continuous,
relatively smooth decline during the whole observation period. The time dependence of the137
Cs concentrations is shown in Figure 3.4. A fast component immediately after the deposition
is followed by a slower component starting a few months after deposition.
The IAEA team and Prefecture experts have agreed that, in conducting monitoring to assessradiocaesium dynamics, it is important to apply standardized sample collection and storage
procedures, and where relevant, standardized expression of monitoring results, to facilitate
intercomparison between aquatic systems, which allows the results to be compared withinternational literature.
27

FIG. 3.3: Decline of 137Cs in suspended matter (top) of dissolved 137Cs (bottom) in water of rivers in the
Prefecture from 2011 to 2021 (Image credit: Fukushima Prefecture) [16, 17].
The numbers represent the following rivers: 1 Mizusakai River, 2 Kuchibuto River, Upstream,
3 Kuchibuto River Midstream, 4 Kuchibuto River Downstream, 5 Fushiguro, 6 Iwanuma, 7 Mano,
8 Ojimadazeki, 9 Matsubara, 10 Onahama, 11 Tsukidate, 12 Nihonmatsu, 13 Miyoda, 14 Nishikawa,
15 Kitamachi, 16 Kawamata, 17 Marumori, 18 Funaoka Ohashi, 19 Senoue, 20 Yagita, 21 Kuroiwa,
22 Tomita, 23 Ota, 24 Odaka, 25 Asami, 26 Tsushima, 27 Ukedo, 28 Takase, 29 Haramachi,
30 Akanuma, 31 Watari (see Table 3.1).

28

FIG. 3.4: Activity concentration of particulate and dissolved 137Cs from 2011 to 2021 in the Hiso andthe Wariki River (reproduced from Ref. [15]. (Please note: Some circles are on top of each other, so it
looks like there are black circles, but there are only open circles).

3.3.2.

Effective half-life of caesium-137 in Prefecture rivers

Since 2011, freshwater bodies have been monitored to study the dynamics of 137Cs in water andin suspended and bottom sediments. The 137Cs activity concentrations in water bodies and theirtime dependence are the results of an interaction of deposition density, catchment area, size of
the water body, precipitation, rainfall intensity, slope, and land use.
Data obtained from monitoring of particulate and dissolved 137Cs in water over time have beenused to estimate the effective half-life (Teff) of 137Cs in each of these forms1. Monitoring of 137Cs
in river water was also conducted in Europe after the accident in the Chornobyl nuclear power
plant. To facilitate the comparison of the behaviour of 137Cs in freshwater systems, the timedependence of radionuclides in sediments, suspended sediments or water is approximated byexponential functions with one to three components [18].
In long term studies, starting immediately after the Chornobyl deposition, a typical pattern of
the long term decline of radiocaesium in water is characterized by 3 phases [18]:The first phase reflects the rapid decrease of activity due to dilution processes in the firstweeks after deposition.
The second phase is the result of fixation of radiocaesium to fine particles.

1 The effective half-life (Teff) is the time interval needed for the radioactivity of a certain amount of radioactive substance (inthis case,137Cs in suspended and dissolved forms) to decrease to half its original value due to radioactive decay and other loss
processes.

29

The third phase represents the long term decline of radiocaesium in rivers due to thegradually reduction of radiocaesium runoff from the catchments.

However, in some cases, the observations started too late after the deposition, and as a result,the initial activity concentration in water could not be determined. In such cases, the rapid
decline immediately after the deposition was not covered by the observation period. In othercases, the observation period was not long enough to identify the long term component of thedecline. Therefore, in both Japanese and the European studies, the number of components ofthe exponential functions identified varies, depending on the observation period and the start ofthe observation period after the contamination event.
Data on half-lives on 137Cs in water of Japanese and European rivers are summarized inTable 3.2 and Table 3.3, respectively. The half-lives are given for the short term, theintermediate and the long term component of the decline. If more than one component is given,
the weighting factors for these components are given in brackets.
Most of the data are for suspended sediments. However, the effective half-lives observed forparticulate and dissolved 137Cs are in the same range. By and large, the temporal trends observedin Japan and other parts of the world agree quite well. From the results summarized inTables 3.2 and 3.3, the following conclusions can be drawn:
Following both accidents, initially, activity concentrations in water decrease rapidly. The
effective half-lives determined depend on the beginning of the measurement series after thedeposition event, whereby:







In water of European rivers, immediately after deposition, a decline of the 137Cs wasobserved following an effective half-life of 5 days during a period of about 2–3 weeks.
For measurements of 137Cs in water, starting several days after deposition, effective
half-lives in the range of 20–50 days were observed.
In some cases, the measurements started later (in 1987 following the Chornobyl accident,
in 2012 following the accident in FDNPP). In such cases, the very rapid immediate
decline of concentrations is no longer reflected in the first component, and effective
half-lives of 70–270 days were found; in one case, an effective half−life of 1.6 years wasobserved.
The results achieved in Japan agree well with the global experience.

Many data sets do not include the initial phase with the fast decline, and instead, most data are
available for the second component, which covers observation periods of 5–15 years starting
several months after radionuclide deposition, as follows:




30

For the Fukushima Prefecture, data on effective half-lives for 48 (data sets) are available,
ranging from 0.7 to 16 years. Three values are below 1 year, and three values are above
5 years. Forty-two values are in the range of 1.1–4.6 years.
These results agree very well with the effective half-lives observed in Ukraine,
Russia, and Finland. For Ukrainian rivers, the effective half-lives found are in the rangeof 2.0–6.5 years. In two Finnish rivers, effective half-lives of 3.5 and 6 years wereobserved. In the Iput River (Russia), an effective half-life of 1.3 years was observed in
the period 1987–1991.

Table 3.2. Summary of effective half-lives (Teff) of 137Cs in Japanese rivers affected by the
FDNPP accident, half-lives are given — as available) for the short term, the intermediate andthe long term component of the decline. If more than one component is given, the weighting
factors for these components are given in brackets.
Effective half-lives(Weighting factors of components)
River or site name

Observation
periodMediumTeff,1(short
term)
–
–
–
–
–
–
–

Ukedo

2015–2018

Ota

2015–2018

Koutaishi
Iboishi
Ishidaira

2011–20132011–20132011–2013

Dissolved
Particulate
Dissolved
Particulate
Dissolved
Dissolved
Dissolved

Fukushima Rrivers

2012–2014

Dissolved

Odaka River

2012–2016

Sediment
River water
Sediment
River water
Sediment
River water
Sediment
River water

Ota
Niida
Mano
Mizusakai

2011–2016

Particulate

Kuchibuto_Upper

2011–2016

Particulate

Kuchibuto_Middle

2011–2016

Particulate

Kuchibuto_Down

2011–2016

Particulate

Fushiguro

2011–2016

Particulate

Iwanuma

2011–2016

Particulate

ManoOjimadazeki
Matsubara
Onahama
Tsukidate
Nihonmatsu
MiyotaNishikawa
Kitamachi
Kawamata
Marumori
SenoueYagitaKuroiwa
Tomita
Ota
Odaka
Asami
Tsushima
Ukedo
TakaseHaramachi
Akanuma

2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016
2012–2016

Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
Particulate
ParticulateTeff,2

Teff,3

Reference

3.7 y
2.3 y
2.4 y
1.6 y
0.69 y0.69 y
1.5 y

(long
term)
–
–
–
–
–
–
–

–

1.8±0.5 y

–

[20]

–
–
–
–
–
–
–
–
1.6 y
(0.64)
135 d(0.79)
120 d(0.74)
274 d(0.64)
66 d(0.96)
80 d(0.92)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

4.7±1.3 y
3.7±0.6 y
1.5±0.4 y
2.1±0.6 y
1.8±0.6 y
1.0±0.2 y
2.1±0.2 y
0.9±0.1 y
2.7 y
0.36)
2.0 y
(0.21)
1.6 y(0.26)
1.4 y(0.36)
1.8 y(0.04)
1.5 y(0.08)
8.2 y
4.6 y
3.7 y
2.1 y
1.1 y
1.6 y
2.9 y
2.9 y
1.5 y
1.1 y
1.8 y
2.4 y
16 y
1.3 y
1.5 y
3.8 y
11 y
2.1 y
1.7 y
2.8 y
1.7 y
3.0 y
2.0 y

–
–
–
–
–
–
–
–

[21]

(intermediate)

[14]

[19]

–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

[22]

[22]

31

Effective half-lives(Weighting factors of components)
River or site name

Abukuma River

Observation
periodMedium

2011–2017

Particulate

2011–2017

Particulate

2011–2017

Dissolved

Hiso River

2011–2021

Particulate

Hiso River

2011–2021

Dissolved

Wariki River

2011–2021

Particulate

Wariki River

2011–2021

Dissolved

Rivers coastal region of
Fukushima Prefecture
Abukuma and rivers of coastal
region32

Teff,1(shortterm)
0.14 y(0.96)
0.12 y(0.93)
0.14 y(0.94)
0.068 y(0.97)
0.20 y(0.914)0.071 y(0.975)0.24 y(0.82)

Teff,2

Teff,3(intermediate)

(long
term)

1.5 y
(0.04)
2.6 y(0.07)
2.6 y(0.06)
1.7 y(0.03)
1.8 y(0.086)19y(0.025)
1.7 y(0.18)

Reference

–
–

[23]

–
–
–
[15]
–
–

Table 3.3. Summary of half-lives of 137Cs in European rivers affected by the Chornobyl accident.
Effective half-lives
River or site name

Observation period

Pripyat (Ukraine)
Dnieper (Ukraine)
Glatt (Switzerland)
Elbe (Germany)
Po (Italy)
European rivers
9 Ukrainian rivers
5 Finnish rivers
5 Belarussian rivers
Dora Baltea (Italy)
Rhine (Germany)
Rhine (Germany)
Pripyat (Ukraine)
Pripyat (Ukraine)
Dnieper (Ukraine)
Desna (Ukraine)
5 Finnish rivers
5 Belarussian rivers
Pripyat (Ukraine)
Dnieper (Ukraine)
Desna (Ukraine)

20 May to July 86
1–15 May 1986
1987–1991
1987–1991
1987–1991
1987–1991
1987–1991
1987–1991
1987–1991
1995–1998
1995–1998
1995–1998
1995–2002
1994–1998
1995–1998
1995–1998
1995–1998

Pripyat (Ukraine)

1987–2001

Pripyat (Chornobyl)

1987–2001

Dnieper (Ukraine)

1987–2001

Uzh (Ukraine)

1987–2001

Teterev (Ukraine)

1987–2001

Irpen (Ukraine)

1987–2001

Braginka (Ukraine)

1987–2001

Ilya (Ukraine)

1987–2001

Sakhan (Ukraine)

1987–2001

Glinitsa (Ukraine)

1987–2001

Pripyat (Ukraine)
Dnieper (Ukraine)
Ukrainian rivers
25 rivers in Asia andEuropeIput River (Russia)
Kymijoki (Finland)
Kokemäenjoki (Finland)

1988–2018
1989–2012
1987–2001

May 1986,
Week 1–3 after
deposition

1987–2001
1987–1991
1990–1996
1990–1996

MediumDissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Particulate
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Dissolved
Particulate
Particulate
Particulate
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfiltered
water
Unfilteredwater
Particulate
Particulate
Dissolved
Unfilteredwater

Teff,1(short
term)
11 d
9.0 d
19 d
18 d
35 d
5d
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

Teff,2

Teff,3(intermediate)

(long
term)

Reference

[24]
[25]
[26]
1.0–2.1 y
1.7–4.3 y
1.0–1.4 y
1.9 y
1.3 y
1.9 y
1.6 y
3.8 y
3.6 y
9.9 y
5.2–7.5 y2.1–4.5 y
8.2 y
7.5 y
2.6 y

–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

–

3.0 y *

14 y *–

2.5 y *

15 y *–

1.9 y *

8.3 y *–

2.6 y *

6.2 y *

–

3.1 y

–

–

2.8 y

–

–

5.3 y *

6.0 y *

–

3.2 y

–

–

2.7 y *

16 y*–

2.0 y *

21 y *–––
20 d(0.905)–––

1.1 y *
3.6 y *
2.0–6.5 y

10 y*
7.6 y*–
16 y(0.005)–––

1.6 y (0.09)
1.3 y
6.0 y
3.5 y

[24]

[27]

[27]
[18]
[28]
[29]

* The data indicate that the decrease of 137Cs in these rivers follows an exponential function with two components.
However, the weighting factors for the 2 components are not given by the authors, since the uncertainty of thelong term component is very high, and it was not considered reasonable to assign a specific value for the weighting
factors. The values should therefore be considered as a first estimation of the long term component. The highuncertainty of the long term component is due to the short observation period compared to its ecological half-life.

If the observation period is long enough, in some cases a third phase can be identified. However,quantifying a third decline component requires observation times of at least 15 years, since the33overall contribution of a third exponential term is very small. So far, in the studies carried out
in the Fukushima Prefecture, such long observation periods are not possible since only 12 years
have passed since the accident in FDNPP. In an analysis of the time dependence of 137Cs inwater of 25 rivers in Europe and West Asia, a third component with an effective half-life of
16 years was identified. The contribution to the overall decline of this component was only
0.5 percent and the relevance in practice is of minor importance. Finally, it is important to notethat the effective half-life of a radionuclide (in this case, for 137Cs) can change over timereflecting timing aspects, as well as changes in both particle and radiocaesium dynamics in ariver basin. For example, monitoring of 137Cs in suspended sediments over time in areas in the
Kuchibuto River basin have indicated that in areas where extensive decontamination wasundertaken during spring 2014 (details on this observation are given in Figure 3.11 located in
Section 3.5.3 below), 137Cs in suspended sediments rapidly declined, with a corresponding
decrease in the effective half-life (see Table 3.2).
3.3.3.

Radiocaesium in phytoplankton and zooplanktonRadiocaesium levels in phytoplankton and zooplankton (‘plankton’) populations were
investigated in the Yokogawa reservoir [30]. Measurements were performed at three sites of
the reservoir. The contribution of plankton species to the total plankton (sum of phyto- andzooplankton) varied both temporally and spatially. The 137Cs activity concentration in phytoand zooplankton is approximately in the same range. Only a small fraction of the 137Cs in thereservoir is bound to plankton. The ratio of 137Cs bound to phytoplankton and 137Cs in thereservoir water varies from 0.016% to 0.83%. The ratio for zooplankton is about a factor of 10
lower and varies between 0.0018% and 0.011%. This means that the total radiocaesium activity
in phytoplankton and zooplankton represents only a small fraction of a percent of theradiocaesium present in a given water body [30].
3.3.4.

Occurrence and characterization of radiocaesium-bearing radioactive particles(CsMPs)In several investigations carried out in the Fukushima Prefecture, glassy particles containing
radiocaesium were found by autoradiography methods in various materials as air filters, house
dust, soils, plant leaves near the accident site, agriculture materials, feather of birds, and riverwater (e.g. see Refs [31–34]). The particles are usually called CsMPs and these particles werereleased from the reactors and dispersed in the atmosphere. So far, most CsMPs were foundrelatively close to the reactors.
Studies were carried out to investigate the chemical and isotopic compositions of the CsMPs,
to identify the likely sources of the CsMPs and the processes generating CsMPs during theaccident. The particles are classified into two categories, called Type A and Type B particles[33, 35]:





34

Type A particles are usually nearly spherical and have a diameter of less than 5 µm.
Typically, 137Cs activities are on the order of a few Bq of 137Cs per particle. However,
Igarashi et al. [33] described a type A particle with a total 137Cs activity of nearly 400 Bq.
The 134Cs/137Cs ratio is above 1, reflecting the fuel burnup at the time of the accident inUnits 2 and 3 of the FDNPP. Therefore, Type A particles are associated to the Units 2
and 3. Type A particles consist of silicate glass in which Cl, K, Rb, Cs, Mn, Fe, Zn, andSn are dissolved.
Type B particles have various shapes, with diameters of a few to up to 400 µm. Due totheir larger size, they are predominantly found close to the FDNPP. These particles

appear to originate from fibre silicate, which is an insulation material used in thereactor. Activities are in general higher than for type A particles, activities are in the rangeof 30–19 000 Bq. The 134Cs/137Cs ratio is lower than 1. Type B particles are associatedwith Unit 1 of FDNPP.
During a monitoring campaign in October 2018, an elevated 137Cs activity concentration was
detected in one of the suspended sediment samples from a river in the Hamadori Region of thePrefecture (see Figure 3.5). It was determined that insoluble highly enriched radiocaesium
microparticles (CsMPs) may have been entrained into the sample.
Kd values of 137Cs and CsMPs
Since the sorption to suspended sediment plays a key role in the behaviour of radiocaesium inthe natural environment, efforts were undertaken by the Prefecture to quantify the strength ofradiocaesium sorption to soils and sediments. This is often characterized by the distribution
coefficient (Kd), which is derived from measurements of radiocaesium in the particulate relative
to the dissolved phase. For the investigated rivers, Kd values in the range of 105 to 107 L/kg dry
sediment were measured, reflecting the strong sorption of caesium to particulates 1 (seeFigure 3.6). The apparent distribution coefficient (Kd) normalized by particle size did not show
any significant change throughout the first 4 years [22].

FIG. 3.5: Temporal changes in activity concentrations of 137Cs in suspended sediment (SS) samples
collected from a river in the Hamadori Region, Fukushima Prefecture) (Image: Fukushima Prefecture).

1 An apparent distribution coefficient (K ) of for example 1 000 000 L/kg means that the concentration in the sediment is
d

1 000 000 times higher than in water. This indicates a very strong caesium sorption and that the vast majority of theradiocaesium inventory is bound to sediments.

35

FIG. 3.6: Apparent1 distribution coefficients Kd in dry suspended sediment samples collected from 2011
to 2014 at six river sites of the Fukushima Prefecture [22]. The different colours represent samples atdifferent river sites.

Miura et al. [36] compiled the characteristics of CsMPs found in the Kuchibuto River during
campaigns carried out from 2011 to 2016 (Table 3.4). The distribution coefficients Kd for 137Cs
in the suspended sediment samples were calculated based on the 137Cs activity in the sample,
both excluding and including the activity of the CsMPs. In all cases, the Kd values based on the
total activity (including the 137Cs activity of the CsMPs) are higher than those based the activity
excluding the 137Cs activity of the CsMPs, indicating the low solubility of the CsMPs. However,in both cases, the Kd values indicate strong sorption of 137Cs to the suspended sediments.
The characteristics of 5 CsMPs deposited on a non-fabric cloth 50 km west of the FDNPP were
investigated [34]. Diameters varied from 1.6 to 2.7 µm, the total 137Cs activity ranged from
0.7 to 1.9 Bq, and 134Cs/137Cs ratios between 0.96 and 1.17 were found. Based on theseproperties, and the on ratios of 235U/238U, all these CsMPs were classified as Type A originatingfrom Unit 2.
The investigations of CsMPs in soil and suspended sediment samples [33, 36] indicate that only
a minor fraction of the 137Cs in the environment is associated with Cs-microparticles. CsMPs
are slowly degraded. In solubility experiments using a CsMP with a radius of approximately
1 µm a lifetime for this particle of less than 10 years in seawater has been estimated. In purewater, the dissolution rate was estimated to be 10 times slower than in seawater, which indicatesa low solubility and a slow degradation. The low solubility in the freshwater system indicates
low bioavailability [37].

1 The calculation of the Kd value requires equilibrium conditions. Since it is not known whether equilibrium conditions exist
in the samples, the term apparent distribution coefficient is used in this context.

36

Table 3.4. Concentrations of 137Cs in CsMPs collected in the Kuchibuto River; the number of
CsMPs, and Kd values without and with consideration of the CsMP in the solid phase [36].
Sampling dat
31 July 2011
3 Aug 2012
3 May 2014
22 November 2014
22 November 2015
1 April 2016

Number of
CsMPs
17
1
6
4
5
3

Caesium-137
in CsMPs
(Bq)
4.3
0.11
4.1
0.77
2.3
0.48

Fraction of
CsMPs on filter
(%)
15
1.3
36
67
66
36

Kd excluding
CsMPs
(L/g)
1400
1910
1100
4600
3200
850

Kd including
CsMPs
(L/g)
1700
1950
1700
14 0009300
1300

Following both accidents in Fukushima and in Chornobyl, particles with enhanced levels ofradionuclides were detected. International experience on CsMPs, their occurrence andcharacterization was provided by the IAEA team. The Chornobyl hot particles are fuelfragments, and they are very different from the CsMPs which are found in the Fukushima
deposited material. CsMPs are smaller and contain much lower activities than those released
from the Chornobyl reactor.
The total number of CsMPs found so far is relatively small. In most cases, their total activity isa few becquerel per particle. So, they do not contribute significantly to the total environmental
radiocaesium. Nevertheless, it was recognized that screening for such particles as part ofexisting monitoring programmes in freshwaters is important to provide reassurance that thesituation does not change.
The CsMPs are generally very small and contain only a few becquerels per particle, so a large
radioanalytical effort is required for their full characterization. Therefore, a screening method
has been developed for easy detection and rapid radioanalytical characterization of CsMPs,
which is bases on Photo Stimulated Luminescence (PSL). Should a sample be suspected ofcontaining a CsMP, the sample is spread on a plate with a material sensitive to high energies,
producing an image showing the areas with enhanced radioactivity. The total activity of a CsMP
is determined based on a calibration curve that links the PSL-signal to the amount ofradioactivity in the CsMP.
3.3.5.

Redistribution of radiocaesium in surface water catchments

Redistribution of radiocaesium can occur due to natural processes and/or anthropogenic
disturbances that impact transport of particles and/or radiocaesium in catchments. Naturalprocesses can include typical or extreme weather events, such as rainfall events, snowmelt,storms, or typhoons. Such events can cause increased runoff, flooding and radiocaesium
washoff into downstream surface waters and/or erosion. This can lead to redistribution of soil
and/or sediment particles onto which radiocaesium is bound or transport processes, such as
senescence of vegetation and subsequent decomposition and remobilization of radiocaesiumthat has accumulated in plant tissues. Anthropogenic activities can include work resulting inphysical disturbances in a catchment that alter exposure pathways and/or facilitate
remobilization of radiocaesium through processes, such as runoff, erosion and/or washoff (seeFigure 3.1 above).
When such events or disturbances occur, it is important to understand the sources andredistribution of material, such as suspended sediments, their influence on radiocaesium
dynamics, and ultimately, on exposure. The application of environmental tracers, such as stable37

isotopes, was discussed by the IAEA team, as they can provide important insight regarding thesources of suspended sediments (including organic matter and inorganic substances) and theirinfluence on radiocaesium transport dynamics, for example, between forested catchments andsurface waters. For example, stable carbon isotopic signatures (δ13C)1 [38] are distinctive in
different environmental media, as well as for different types of plants. Therefore,characterization of δ13C signatures, in addition to 137Cs activity concentrations in forest litter,
forest soil as well as river sediments, an of total organic carbon (TOC) can serve as tools to gaina better understanding of radiocaesium dynamics in catchments.
3.3.6.

Flux of caesium-137 with suspended sediments

Since most of the radiocaesium in water bodies is associated with suspended sediments in riverwater, the measurements of radiocaesium in rivers allowed the estimation of the total flux ofradiocaesium from the catchment areas.
For the monitoring stations in Table 3.1, the transport of 137Cs from the catchment withsuspended sediments was estimated for the period June 2011 to March 2017 [22, 39]. The lossof 137Cs from catchments via surface runoff was calculated from the average initial depositionin the catchment areas as of June 2011, the 137Cs activity concentrations in suspended sediment,
the concentration of suspended sediment in water, the flow rate of the river, the precipitation,and the topographical data (including elevation and land use data).
The total losses of 137Cs from the different catchments are shown in Figure 3.7. The observation
periods vary for the different monitoring points. In general, the losses of 137Cs activity from thecatchments due to runoff and river transport are low.



Six monitoring points (stations 1–6, red columns) cover the whole observation period
from June 2011 to March 2017, and their total 137Cs fluxes vary from 0.4 to 3.3%;
The blue stations cover the observation from October 2012 to March 2017. The total flux
varied from 0.04 to 4.4%. Most values are well below 1% and there is no obvious reason
for the relatively high values for station 22. Excluding the value for station 22, the range
is from 0.4 to 1.1%;
The observation period for station 20 (grey) is from October 2012 to March 2016, forstation 26 (violet) from October 2012 to August 2015, and for station 12 (black)
September 2015 to March 2017. The total flux during for the station 20, 26, and 12 during
these observation periods are 1.1%, 0.1% and 0.08% respectively.

Due to radioactive decay, 137Cs activity in the watershed was reduced by 12.4% and 9.7%
during the periods from June 2011 to March 2017 and October 2012 to March 2017,
respectively.

1 Carbon-13 is a natural stable carbon isotope, about 1.1% of the global carbon is C-13. The 3C signature quantifies thedeviation of the C-13/C-12 ratio from Vienna PeeDee Belemnite (VPDB) standard [38] in an environmental sample in permille;
it is also called the 13C-signature. The 3C level is calculated from the concentrations of 13C and 12C in the samples and in
the VPDB standard according to:13C = [(13Csample/12Csample - 13Cstandard/12Cstandard)/ 13Cstandard/12Cstandard)] x 1000.
The depletion of C-13 in organic material is due to the higher atomic mass of C-13 compared to C-12, this facilitates the uptakeof 12CO2 by plants during the photosynthesis, and it causes the depletion of C-13 in plant material.

38

FIG. 3.7: Flux of 137Cs in catchments of the Fukushima Prefecture.

These small percentages indicate that the reduction of the radiocaesium levels in the naturalenvironment is mainly due to radioactive decay, and that runoff is only a minor contributor to
the reduction of the overall radiocaesium inventory in these catchments (since washoff anderosion process affect only the very top surface layer of the contaminated soils in the water
catchments). These results also indicate that the exchange of radiocaesium between different
elements of the landscape is limited.
The increase of the cumulative loss of 137Cs as function of time from the catchments to the
Pacific Ocean for the period of 2011 to 2016 is shown in Figure 3.8. The increase in the
cumulative loss (i.e. the amount of the radiocaesium transferred into the Pacific Ocean duringa certain period) became less and less over time, as reflected by the decreasing slopes of thelines presented in Figure 3.8).
Assessment of the relative amounts of 137Cs outflow from the Abukuma River in the suspended
versus the dissolved forms indicated that 96.5% was in suspended form during the five year
period after the Fukushima Daiichi accident [22] (Figure 3.9).

39

FIG. 3.8: Cumulative loss as function of time from the watersheds of sites 1–6 (Table 3.1) during theperiod 2011–2016.

FIG. 3.9: Relative 137Cs fluxes from forested areas relative areas of human activities (paddy fields,
farmlands and urban, ‘PFU’, areas) of the Abukuma River during the five year period following the
Fukushima Daiichi accident [22].

403.3.7.

Influence of land use on surface runoff

The relationship between the activity concentration and flux of suspended 137Cs and the land
coverage ratio was evaluated for different land uses in the Imanuma catchment with a total 137Cs
inventory of 470 TBq. From 2011 to 2015, in total 12 TBq 137Cs were lost from the catchmentwith surface runoff. The study considered forest areas and areas with high human activities(e.g. paddies, farmland, urban areas, ‘PFU’) (Figure 3.9) It was concluded that the reduction
rate for the 137Cs activity concentration and the outflow rate were low in forested areas, butwere high in areas of human activities (e.g. paddies, farmland, urban areas) (see Figure 3.9).
Areas with human activities contributed a total of 85% of the 12 TBq 137Cs flux from thewatershed and forested areas contributed the remaining 15%. These results were reported in apeer reviewed scientific paper in the Journal of Environmental Science and Technology [22].
The flux of 137Cs flux from forest and PFU areas in different time periods was studied as well.
The flux in the 9 month period from June 2011 to February 2012 was compared against the
3.5 year period from March 2012 to August 2015 [22]:In the first period (i.e. the 9 month period), 0.38% of 137Cs in forests was lost with surface
runoff, whereas 4.3% was lost with surface runoff from PFU areas. These results areequivalent to annual fluxes of 137Cs of 0.51%/year and 5.7%/year for forests and PFU
areas, respectively.
In the second period (i.e. the 3.5 year period), the 137Cs flux from forests is like that in thefirst period. However, the 137Cs flux from PFU areas is lower than in the first period by afactor of 2. The annual fluxes for this period are 0.1%/year and 0.6%/year for forest andPFU areas, respectively.

The data show that the 137Cs flux with surface runoff declines with time. In total, during thewhole observation period from 2011 to 2015, approximately 2.5% of the total 137Cs inventoryof the catchment was transported out of the catchment with surface runoff from both forests
and PFU areas; so, there is significant movement of 137Cs with sediments in the riverbed.
However, compared to the total 137Cs inventory of the catchment, runoff is of minor importancein reducing the total 137Cs inventory in the catchment. During the observation period from 2011
to 2015, the 137Cs inventory decreased by approximately 10% due to radioactive decay.
Dissolved and suspended radiocaesium were measured in the Yokokawa dam reservoir in 2014
by the Japan Atomic Energy Agency (JAEA) and National Institute for Environmental Studies(NIES) in the Prefecture in 2014 [40]. The total activity of dissolved radiocaesium in the inflow
relative to the outflow of the reservoir were very similar. However, the amount of particulate
radiocaesium in the outflow was much less than in the inflow, since the particulate radiocaesium
is subject to sedimentation in waters with a very low flow velocity, as is the case for reservoirs
and lakes. In this way, reservoirs act as a kind of sediment trap.
3.3.8.

The carbon-13/carbon-12 ratio as tracer for identifying the origin of suspended
matter in rivers

Since the deposition of radiocaesium in March 2011, dissolved and particulate 137Cs levels havesteadily declined as the amounts of radiocaesium entering rivers via surface runoff fromwatersheds have also been decreasing. However, due to the variations of rainfall, surface runoff
is not a continuous process. For a better understanding of the 137Cs transport with surface runoff,
the relationships between water level, concentration of suspended sediments and the 137Cs
levels in suspended sediments were investigated in the catchment of the Hirose River [41] from41

September 2017 to October 2019. Water samples were also taken during and after typhoons tocover both base flow and high flow conditions1; the following quantities were determined:









Particulate 137Cs in river water (activity concentation per unit volume)
Particulate 137Cs in suspended sediments (activity concentration per unit mass of
sediment);
Concentration of suspended sediments (sediment load in the river water);
Total organic carbon (TOC) in water and in suspended sediments;
Caesium-137 and TOC levels in adjacent forest soil, forest litter, riverbank soil and river
sediments;
The ratio of carbon-13 (13C) to carbon-12 (12C) in forest soil, forest litter, riverbank soil
and river sediments. This ratio is quantified by the 13C-signature1;
In addition, the fractions of forest soils, forest litter, forest soils, and river sediments insuspended sediments were determined based on the concentrations of 137Cs, TOC, and13C-signature in these media. The fractions were estimated by means of a mixing model
for base flow and high flow conditions.

Comparison of 137Cs activity concentrations in suspended sediments between base flow versus
high flow conditions indicated that 137Cs levels were higher during base flow periods. This isconsistent with results of work conducted in the Prefecture, which indicated that a dilution
effect had occurred when large amounts of sandy particles became suspended in rivers of thePrefecture during a heavy rainfall event in September 2015, resulting in reduced activity
concentrations of 137Cs in suspended sediments. Additionally, it was found that with increasing
concentration of suspended sediments in river water:







the concentration of particulate 137Cs in river water increased;
the concentration of organic matter in water increased;
the concentration of particulate 137Cs in suspended sediment declined;
the total organic carbon in suspended sediments decreased; andthe 13C-level in suspended sediments decreased.

The 13C-signatures, the TOC concentration in water and the 137Cs activity concentration insuspended sediments were used to determine the source of carbon in a sample. The
13C-signatures in different media and forest soil samples indicate the origin of the increased
amounts of suspended matter in river water. Table 3.5 summarizes the 13C-signatures, the 137Csconcentrations and the TOC concentrations in various samples in the study site. There is a clear
difference of the 13C-signatures among river sediments, riverbank soil, forest soil, and forest
litter The 13C-signatures for material from the river vary from ˗25.4 to ˗26.4‰, whereas the13C-signatures in forest soil and litter vary from ˗26.4 to ˗30.0‰.

1 Base flow conditions are defined, if the sampling of water was carried out at least 2 days after the last precipitation, TSS

concentration varied from 1.5 to 4.2 mg/L.
Sampling under high flow conditions was carried out during and after typhoons, SS concentrations varied from 5 to 930 mg/L.

42

Table 3.5: 13C-signatures, 137Cs activity concentration, total organic carbon and for river andforest samples [41].
Material

13C signature (‰)

Caesium-137 activity
concentration (Bq/kg)

Total organic carbon(mgC/mg)

Forest soil

˗26.9
˗30.0
˗26.4
˗25.4

5400

0.11

Forest litterRiverbank soil
River sediment

240

0.47

470

0.018

110

0.001

The decline of the 13C signature with increasing concentrations of SS in water — and with atendency to increasing flow velocities — indicates that the relative contribution of forest soil
and forest litter declines. At the same time, the relative contribution of riverbank soils and river
sediments to SS increases with increasing concentrations of SS in river water. A simulation of
the different contributors to SS confirms this hypothesis:

Under base flow conditions forest soil contributes nearly 70% to the SS. Riverbank soil
and river sediments together contributed approximately 7%.
At high flow, the TOC concentration in river water increased. However, the relative
contribution of forest soil to SS decreased to 48%, while the input of both riverbank soil
and river sediments to SS in total increased to about 50%.

3.4. APPLICATION OF SIMULATION MODELS
To facilitate the interpretation of monitoring results, models were applied to simulate thetransport of radiocaesium from catchment areas through the river system to the Pacific Ocean.
For this purpose, the TODAM model (Time dependent, One dimensional Degradation And
Migration) [42] was applied to simulate the 137Cs flux in the Ukedo-Takase River and in the
Ogaki Dam reservoir. This model has been applied previously to several other large, medium
and small rivers around the world. Previous applications of the TODAM model involved
assessments, analysis and evaluation of the transport of radionuclides following releases to theenvironment as a result of the Chornobyl accident, and from nuclear facilities in Mayak
(Russian Federation), Hanford and Savannah River (USA).
The TODAM model can be used to estimate the transport of 137Cs with sediments and water inrivers, taking account of the possible influence of water flow, topography, land use and otherfactors on radiocaesium dynamics, for example, in the evaluation of the:






Possibility of using the water for domestic and agricultural purposes;
Effectiveness of remediation measures to be applied in rivers in support of decision
making;Effect of recontamination of rivers, which is important for evaluating the persistence ofremediation measures;
137
Cs flux from the catchment area to the ocean.

The TODAM model was applied by the Japan Atomic Energy Agency (JAEA) to simulate thetransport of 137Cs in the Ogaki Dam Reservoir and to investigate the role of the dam in thedispersion of radiocaesium. It was determined that the dam reservoir can retain about 90% of
the suspended radiocaesium. This result is similar to observations made for the Yokokawa Dam
reservoir. The very low water flow rate in such reservoirs favours the sedimentation ofsuspended sediments.
43

FIG. 3.10: Comparison of 137Cs activity concentration measurements in dissolved andparticulate forms over time relative to TODAM model predictions at the lowest downstream
monitoring station in the Hirose River during conditions of high water level (Image: Fukushima
Prefecture).

In addition, measured 137Cs activity concentrations were compared to those estimated using the
TODAM model in the Hirose River basin under conditions of normal and high water levels (seeFigure 3.10). In general, there was reasonable consistency between measured and modelledvalues.
Several workshops involving the IAEA and the Prefecture experts from different Japanese andother international institutions were held, during which experts discussed their experiences in
the use of different types of models for radiocaesium prediction in aquatic ecosystems.
3.5. EXPERIENCE WITH REMEDIATION AND DECONTAMINATION IN RIVER
AND LAKES
3.5.1.

Global experience

In recent decades, a number of areas worldwide have been affected by the deposition ofradionuclides. In many cases, freshwater ecosystems were impacted. Examples include theChornobyl accident, as well as the releases of radionuclides from nuclear facilities in Mayak
(Russian Federation), and from the Savannah River Plant and the Hanford site (USA). These
global experiences were presented by the IAEA team.
All of these cases were unique; they varied in terms of the areas affected, level of contamination,
relevance of different exposure pathways (including aquatic pathways) with regard to exposureof people living in those areas, the magnitudes of doses to people, and the measures taken in
the aquatic system to mitigate radiological and social consequences. Following the release ofcontamination, the IAEA team identified two types of countermeasures that were applied:

44

(1)

Technical measures, such as: removal of sediments from contaminated water bodies; construction of dams to reduce the further dispersion of radionuclides with wate; application of substances to increase pH of a water body to reduce bioaccumulation;and construction of sediment traps to accelerate sedimentation of particle boundradionuclides.

(2)

Administrative measures, such as:
 restriction of access to contaminated areas; restrictions for fishing and for withdrawing drinking water and irrigation water and;
 guidance to the public.

One lesson derived from the analysis of past releases of contamination is that technicalmeasures have only a limited potential to control the dispersion of radionuclides in water bodies
and the potential to have significant adverse effects on aquatic habitat. Freshwater systems areoften characterized by a pronounced time dependence of water flow rates, mixing dynamics
and water levels, which can be associated with significant variation in flow velocities andtransport of radionuclides occurs predominantly during temporary periods of high water flow,usually associated with resuspension, displacement and redeposition of contaminated sediments.
Such processes are difficult to control; therefore, the sustainability of technical measures often
remains limited.
The control of exposures to the public arising from the use of rivers and lakes throughadministrative measures, such as restriction of access and the implementation of guidance isless complicated. Such measures can be relatively easy to implement and have been proveneffective in reducing radiation exposure through aquatic pathways; however, clear instructions
and guidance are necessary for successful implementation. Experience shows that the publicmust be kept informed about such administrative measures as long as they are in place.
Due to the dynamic nature of freshwater systems, once radioactive contamination has occurred,monitoring of radionuclides may be a long term commitment in order to: (1) determine timetrends of radiocaesium in water, sediments and as relevant, biota; (2) identify newcontamination patterns, which may be created through displacement of material and sediment
during high flow and floods; and (3) verify the effectiveness of any applied remediation
measures.
3.5.2.

Countermeasures to reduce radiocaesium in irrigation ponds

The Prefecture determined radiocaesium activity concentrations in water and sediments inabout three thousand irrigation ponds inside and outside the evacuation designed zones in 2014.
Since radiocaesium binds strongly to clay particles, the activity concentrations of dissolved
radiocaesium in the water of these ponds are orders of magnitude lower than those in sediments.
This finding agrees very well with the observations made by the Prefecture for rivers and lakes.
In 1% of the water samples collected from irrigation ponds, the activity concentrations ofradiocaesium in the dissolved phase were above 1 Bq/L, and these ponds are mainly foundinside the evacuation designated zones. The number of ponds with dissolved radiocaesium
exceeding 1 Bq/L decreased between 2013 and 2014.

45

The Prefecture government tested technologies to reduce the activity concentrations of
dissolved radiocaesium in pond water. The technologies were selected through open
recruitment in 2014 and 2015 and were as follows:







Separation of the sand, gravel and the clay fractions by means of an underwater device,
which takes advantage of the fact that the radiocaesium activity concentrations in sandand gravel particles are much lower than in clay minerals. The sand and gravel fractions
remain in the pond, whereas the clay fraction is removed;
Removal of sediments from ponds and storage in bags, where the material is dehydrated,which reduces the volume of the waste material;
Installation of silt fences in ponds, which reduces the flow velocities in irrigation ponds
and enhances sedimentation. This procedure prevents the outflow of the radiocaesium
from the pond;
Removal of water from the pond and fixation of the sediment in place by adding cement,
which binds the sediment together and prevents the outflow of radiocaesium.

The Japanese government developed a manual for countermeasure techniques based on thesetest results. In the Prefecture, the countermeasures have been implemented in accordance withthis manual.
3.5.3.

Decontamination measures in riverside areas in the Prefecture

The Prefecture experts presented work on decontamination measures tested in three riverside
areas in the Prefecture to reduce air dose rates. These projects are described below and areongoing.
Evaluation of effect of decontamination on 137Cs in suspended particles
A wide area, multiple point survey was undertaken in the ‘upstream’ section of the Kuchibuto
River in the Special Decontamination Area (SDA) of the Prefecture where 137Cs activity
concentrations were relatively high, and at ‘midstream’ and ‘downstream’ locations.
Radiocaesium survey data for suspended particles was evaluated during the‘Pre-decontamination’ period prior to February 2013, the ‘Ongoing decontamination 1’ period
from March 2013 to March 2014, the ‘Ongoing decontamination 2’ period from April 2014 toDecember 2015, and the ‘Post-decontamination’ period after January 2016 (see Figure 3.11).
Based on this survey, it was determined that the concentration of 137Cs reduction rate increased
during decontamination at both upstream and midstream locations, whereas no change wasmeasured at the downstream location.
Demonstration at the Kami-Oguni River
Part of one side of the Kami-Oguni River (approximately 200 m long) is traversed by children
as they walk to and from school and is used for recreational purposes by local inhabitants. In
August and September 2014 (prior to decontamination), extensive monitoring was carried out
by the Prefecture in this area, which included the measurement of air dose rates andradiocaesium activity concentrations in bottom sediments. Decontamination measures, such as
weeding, removal of sediments in the low waterbed, and removal of vegetation and soil fromthe river dykes, were implemented in autumn 2014 (see Figure 3.12). Monitoring data collected
before and after implementation of decontamination measures shows that the air dose rates werereduced by about 50% (see Figure 3.13).

46

Predecontamination

Ongoingdecontamination①

Ongoingdecontamination②

Postdecontamination

FIG. 3.11: Temporal changes in activity concentrations of 137Cs in suspended sediments during
pre-decontamination, ongoing decontamination 1, ongoing decontamination 2 andpost-decontamination periods in the Kuchibuto River basin (Image: Fukushima Prefecture).

FIG 3.12: River bed before (left) and after (right) decontamination measures in the Kami-Oguni
River [43].
47FIG 3.13: Air dose rate at 1 m height before, during and after the remediation and decontamination
measures at a river in the Prefecture (Image: Fukushima Prefecture).

FIG. 3.14: Before and after pictures of 2019 excavation work (Sep 2019) and Typhoon No. 19 (12–13
October 2019) in the Kami-Oguni River. Photograph A was taken prior to excavation (27 August 2019)and Photograph B was taken after excavation (30 September 2019). Photograph C (30 September 2019)was taken after the excavation work and before Typhoon No. 19. Photographs D to G were taken after
Typhoon No. 19 (18 October 2019). Photograph D was taken at approximately the same location as
Photograph C (Images: Fukushima Prefecture).

48

The area was affected by a severe flood in September 2015, which caused intensive
resuspension, displacement and sedimentation of radiocaesium associated with suspended
particles. Sediments and vegetation in the river were removed and new material (mainly coarse
material and stones) was deposited at this location. Measurements of air dose rate carried out
after the flood by the Prefecture (see Figure 3.14) did not indicate significant change in the air
dose rate as a result of the flood.
Waterside park at the Niida River
This park is close to a river which is used for leisure and recreational purposes. Air dose rates
measured in 2015 by the Prefecture averaged approximately 0.6 µSv/. By comparison, air dose
rates of 0.20 µSv/h were reported in mid-October 2019.
Model simulations performed for this area by the Prefecture indicated that decontamination
measures may reduce the air dose rate by about 35% (Table 3.6). Without any decontamination
measures, the air dose rate would be expected to decline by about 13% after one year due toradioactive decay. Further reduction of the predicted annual radiation doses due todecontamination measures was assessed by the Prefecture, as well, taking into account local
habits and occupancy times for various activities, e.g. walking, cleaning and beautification, andplaying in or near the water.
Calculations performed by the Prefecture showed that decontamination measures may reduce
the annual effective dose to an individual by 1–15 µSv/yr. Results of projected individual doses
related to the use of this part of the Niida River are given in Table 3.2 above. This analysis
underlines that doses resulting from activities at this particular location are quite low.
Flooding in 2015 had a considerable impact on the geometry of the riverbed. Parts of theriverbanks were removed, and at higher elevations of the riverbanks, where the water velocity
during the floods was reduced, large amounts of coarse material (mainly sand) were deposited.
The dynamic nature of the transport processes makes the assessment of the sustainability ofdecontamination measures very complex; however, even with the impact of flooding in 2015
on the geometry of the riverbed, measurements made by the Prefecture after these flooding
events indicated that the effects of the remedial actions had not been affected significantly.
Nevertheless, due to the likelihood of flooding in the coming years, it is important thatmonitoring of the effects of decontamination efforts are continued.

Table 3.6. Estimation of dose reduction at a demonstration site through decontamination
Activity
Item
Dose rate after decontamination (µSv/h)*
Occupancy (hours per year)
Annual additional dose (mSv/y):
Before decontamination
After decontamination
After 1 y without decontamination

Recreation

Walking

0.53
16(4 h/d × 4 d/y)

0.38
111
(1 h/d × 111 d/y)Cleaning/
beautification
0.39
48(1 h/d × 48 d/y)

0.008
0.005
0.007

0.038
0.023
0.032

0.017
0.010
0.015

Water activity
0.26
9(1 h/d × 9 d/y)
0.002
0.001
0.002

*Derived from air dose measurements over 15 minutes.

49Impacts of anthropogenic disturbances and extreme weather events on the Kami-Oguni River
In 2019, the Kami-Oguni River was impacted by both anthropogenic and natural disturbances.
The anthropogenic disturbance involved excavation work, which was undertaken to remove
sediments and enhance the flow capacity during flooding, as part of routine maintenance (seeFigure 3.14).
In addition to the anthropogenic disturbance due to the planned maintenance work, theKami-Oguni River was also impacted by Typhoon No. 19, which hit Japan 12–13 October 2019and caused collapse of the riverbank, deposition of sediment, cobbles and rocks, and flooding(see Figure 3.14, Photographs D–G).
Monitoring data collected following Typhoon No 19 indicate that air dose rates on riverbanks
impacted by the typhoon have either decreased or remained the same, compared to pre-typhoon
values (see Figure 3.15). Air dose rates (1 m above ground surface) measured on the shorelineof the Kami-Oguni River prior to the typhoon (31 January 2018) were 0.34 µSv/h, compared to
0.18 µSv/h after the typhoon (17 October 2019).
Findings were similar in the areas of Niida River park (0.30 µSv/h before and 0.20 µSv/h after
Typhoon No. 19) and the Mizunashi River (0.214 µSv/h before and 0.156 µSv/h after Typhoon
No. 19). In both cases, increased air dose rates following Typhoon No. 19 were not observed.
At these sites, natural processes have contributed to the reduction of doses and dose rates.
Further work is being done to analyze 137Cs in suspended sediments and river water downstreamof areas impacted by the typhoon.

FIG. 3.15: Maps of air dose rates at 1 m height above the ground after and before Typhoon No. 19(Hagibis) (Image: Fukushima Prefecture).

50

3.6. EXPERIENCE WITH REMEDIATION AND DECONTAMINATION IN
RESIDENTIAL AREAS
In the Prefecture, houses, public facilities, farmland, and roads were decontaminated to reduce
the effects of environmental contamination that resulted from the Fukushima Daiichi accident.
Some of the most common decontamination techniques that have been applied in the Prefecture
are shown in Figure 3.16.
By March 2018, the decontamination activities in the Prefecture (with the exception of the‘Difficult–to–Return–Zones’) were terminated. In Table 3.7, the status of the effort todecontaminate different categories of buildings and areas within the Prefecture is summarized[44]. Remediation and decontamination activities in the Prefecture were focused on public areas,
including routes traversed by children going to and from kindergarten and schools, and on
recreational areas.
For assessing the effectiveness of the decontamination activities in residential areas,measurements of air dose rate were taken before and after decontamination. The effectivenesswas quantified in terms of reduction of air dose rate in the areas that were subject to remediation.
Specific sets of remedial actions were applied to residential areas, public facilities, roads,
agricultural land and forests, respectively. Depending on the type of area treated, air dose rates
were reduced by approximately 20–50% (see Table 3.8); such reduction factors are very similar
to those achieved by remediation measures in areas affected by the Chornobyl accident.
Table 3.8 is based on measurements performed before and after decontamination work that was
performed from June 2011 to February 2016. Further details on countermeasures implemented
in forests are given in Section 2.
The effectiveness of decontamination work is shown in Figure 3.17 for the ‘Special
Decontamination Area’ [45]. Depending on the land use, the average gamma dose rate
immediately after the decontamination work was reduced by 44–60%. Six to twelve months
after the decontamination work, the gamma dose rate was 55–76% lower than before
decontamination; this decrease is due to ongoing attenuation processes relating to migration in
soil, street cleaning, and radioactive decay (especially of the relatively short lived 134Cs).
The distribution of the gamma dose rates before and after the decontamination work for the
SDA is shown Figure 3.18 [44]. The measurements were performed before, immediately after,
and a few months after termination of the decontamination activities. The average value of the
gamma dose rate declined from 1.27 µSv/h (before) to 0.63 µSv/h (immediately after) to
0.44 µSv/h (a few months after), respectively. The ongoing decline of the gamma dose rate after
the termination of the decontamination work confirms the persistence of the measures; theresults indicate that recontamination is a phenomenon of minor importance, if it occurs at all.

51

FIG. 3.16: Main decontamination techniques (Image: Fukushima Prefecture).

Table 3.7. Summary of decontamination completed in the municipalities [44]Category
Residences (total no. of houses)

Decontamination completed
418 579（418 897)

Public facilities (total no.)11 627（12 376)

Roads (km)17 701（20 476)

Agricultural land (ha)31 196（31 061)

Forests (in living areas) (ha)4307（4513)

Table 3.8. Reduction of the air doses rate due to decontamination work
Category
Residences
School Park
Forests

52

Number of measurements
117 949
7 783
11 603

Reduction of air dose rate (%)
42
55
21

FIG. 3.17: Effect of decontamination work for different land uses in the Special Decontamination Area
(redrawn using data in Ref. [45].

FIG. 3.18: Distribution of gamma dose rates in the Special Decontamination Area (SDA) before andafter decontamination work [44].

533.7. SECTION SUMMARY
The behaviour of radiocaesium in ecosystems has been studied for the last several decades. In
general, in the terrestrial environment, caesium is strongly bound by mineral soil components,
which results in slow movement in soil and a low uptake by plants from soil. In freshwater
ecosystems, caesium is in general strongly bound to suspended sediments, which deposits on
the bottom of surface waters and causes a rapid decline of dissolved radiocaesium in the watercolumn. Sorption of caesium to suspended sediments, therefore, plays a key role in its
environmental behaviour.
The physicochemical conditions in surface waters (e.g. pH, basin bathymetry, depth,
concentrations of suspended sediments and potassium) can also affect transport of particles
which bind radiocaesium and radiocaesium dynamics. Such conditions might explain thegenerally stronger radiocaesium sorption onto soils and sediments that was measured under theconditions in the Prefecture compared to Ukraine and Russian Federation after the Chornobyl
accident [46].
The IAEA team and Prefecture experts have agreed that continuation of routine monitoring ofradiocaesium in river catchments of the Prefecture is important to assess temporal and spatialchanges. This includes monitoring within a river drainage basin, where water collects, as wellas in the tributaries that carry radiocaesium from upstream of the basin into larger rivers
downstream. In conducting such monitoring to assess radiocaesium dynamics through time andspace, it was agreed that it is important to apply standardized sample collection and storage
procedures, and where relevant, standardized expression of monitoring results, to facilitate
intercomparison between aquatic systems, which in turn allows the results to be compared withinternational literature.
In the freshwater bodies of the Prefecture (within less than 7 years of the accident dissolved
radiocaesium levels in water were close to or below 0.05 Bq/L, a value far below the World
Health Organization (WHO) [14] recommended quality criterion for 137Cs in drinking water of
10 Bq/L. There also continues to be a clear decline of the concentration of radiocaesium insuspended sediments.
Usually, the time dependence of 137Cs in river water can be described by exponential functions
with one to three components representing different phases after the deposition, as follows:






54

Immediately after deposition, a decline of 137Cs in European rivers according to aneffective half-life of 5 days during a period of about 2–3 weeks was observed. However,many data sets do not include the initial phase with the fast decline.
Most data sets cover an observation period of 5–15 years starting several months afterradionuclide deposition. For rivers in the Fukushima Prefecture, the values for theeffective half-life of 137Cs in rivers for 48 sites are ranging 0.7–16 years. Only 3 values
were below 1 year, and only three values were above 5 years. Forty-two values were in
the range 1.1–4.6 years.
If the observation period is long enough, in some cases a third phase can be identified.
However, quantifying a third decline component requires observation times of at least
15 years. For the studies in the Fukushima Prefecture, such long observation periods are
not possible. In water of 25 rivers in Europe and West Asia, a long term component with
an effective half-life of 16 years was identified. The contribution to the overall decline ofthis component was only 0.5 percent and the relevance, in practice, is of minor
importance.



By and large, the time trends observed in the Prefecture agree reasonably well with thoseobserved in other parts of the world after the Chornobyl accident andthe general patternof the decline is quite similar.

The reduction of the radiocaesium levels in the environment is mainly caused by radioactive
decay, whereas runoff of radiocaesium provides a further contribution to the reduction. The
cumulative losses of 137Cs activity between 2011 and September 2015 from the catchments of
the Abukuma and the Kuchibuto tributary were about 3% (2.5–3.5%) and 1% (0.7–1.5%),
respectively. The loss of 137Cs due to runoff is influenced by the land use. The loss of 137Cs
increases with increasing fractions of rice paddies, farmland, and residential areas.
Decontamination activities in catchment areas cause a higher runoff of soil and of 137Cs sorbed
to soil particles.
Measurements of radiocaesium in reservoirs have shown that the amount of suspended
radiocaesium in the outflow is much less than in the inflow. This indicates that reservoirs act
as a kind of sediment trap.
The density of plankton in freshwater bodies in the Prefecture was very low and the total
radiocaesium activity incorporated into phyto- and zooplankton did not exceed a small fractionof a percent of the radiocaesium present in the water bodies studied.
To facilitate the interpretation of monitoring results, models were applied by the Prefecture tosimulate the transport of radiocaesium from the catchment area through the river system to the
Pacific Ocean. The Prefecture recognized that models were also very useful in selecting
appropriate remedial options and assessing the effectiveness of remediation measures being
applied in rivers. In addition, simulation models allowed the assessment of the effect ofrecontamination of rivers.
International experience shows that decontamination work in rivers is challenging due to the
dynamic nature of flowing waters. Engineering measures are costly and often difficult toimplement. Usually, the experiences shows that the overall impact on public doses remains low.
To reduce exposures to the populations, restrictions on the abstraction of drinking water andfishing were most effective.
Following both the accidents in Fukushima and in Chornobyl, particles with enhanced levels ofradionuclides were detected. The Chornobyl ‘hot particles’ are fuel fragments, and they are
different from the CsMPs which are found in the Fukushima deposited material. CsMPs are
smaller and contain much lower activities than those released from the Chornobyl reactor.
Since 2011, intensive remediation and decontamination work has been carried out by thePrefecture in private homes, public facilities, roads, agricultural land, and parts of the forests
close to inhabited areas, with particular focus on public areas, including routes traversed bychildren going to and from kindergarten and schools, and on recreational areas. Depending on
the type of area, the Prefecture observed that air dose rates were reduced by circa 20–50%,
similar to results achieved by remediation in areas affected by the Chornobyl accident.
Decontamination of residences (houses) in the Prefecture was completed by March 2018.
In addition, the Prefecture has initiated a number of projects in and around freshwater bodies todemonstrate the effectiveness of implementing decontamination measures. These measures
have been found to reduce air dose rates. Based on international experience, the IAEA teamindicated that administrative measures, such as restrictions and guidance to reduce exposure via
freshwater pathways, are relatively easy to implement compared to technical measures (e.g.
sediment removal) and tend to be more effective.
55

4.

MANAGEMENT OF WASTE FROM REMEDIATION ACTIVITIES

4.1. BACKGROUND AND OBJECTIVESAs stated in Technical Volume 5, Post-accident Recovery, of the IAEA’s The Fukushima
Daiichi Accident Report [47]:“According to the decontamination plan formulated by the MOE (Ministry of theEnvironment), contaminated soil and waste generated from remediation in the Prefecture
are to be collected and stored at, or near, the sites undergoing remediation in temporarystorage facilities. Afterwards, the material will be placed in the ISF (Interim Storage
Facility). After interim storage for up to 30 years, final disposal will take place outside
the Prefecture.”
The ISF is to be developed and operated by the central government. Temporary storage sites(TSS) were established in municipalities and the Prefecture based on laws and government
guidelines. After the Fukushima Daiichi accident, the Prefecture performed a significant
amount of work concerning remediation activities and the management of the resulting
radioactive waste.
The radioactive waste that resulted from remediation activities required urgent but also safe andsustainable management. The IAEA team advised that the applicable IAEA Safety Standards
should be used. When activities under the Practical Arrangements commenced in 2013, thePrefecture was faced with an urgent shortage of TSS in which to store waste from remediation
activities. Furthermore, concerns were raised by the public about the safety of existing TSS,
and prospective TSS that were to be established to accommodate radioactive waste generated
by ongoing remediation activities. Later, it became necessary to store waste in TSS for greater
time periods than was originally intended. TSS were established with the intention that waste
would be stored in these facilities for only three years before being transferred to the ISF.
However, it has become necessary to store waste in TSS for more than three years because thetransportation of the waste from the TSS to the ISF has taken longer than expected. It has
therefore become an issue that needed evaluation to ensure the safety of these facilities and toaddress public concerns.
The activities concerning the management of waste from remediation activities under thePractical Arrangements consequently focused initially on providing assistance to the Prefecture
in finalizing technical guidelines for the establishment of temporary storage facilities andassisting the Prefecture in demonstrating the safety of temporary storage facilities. As time has
passed, the provision of assistance shifted gradually to focus more on the safety of the longer
term operation of the TSS, on strategies for the retrieval of waste from the TSS, and on theremediation and long term safety of the former TSS. A key aspect of the assistance provided
by IAEA has been to facilitate the sharing of expertise and experiences of relevant radioactive
waste management practices from outside Japan.
4.2. TEMPORARY STORAGE SITES
Three main types of TSS have been established in the Prefecture: aboveground storage, semiunderground storage and underground storage, each of them having advantages anddisadvantages with regard to ease of construction, transfer of waste to the ISF, stability, etc.
Figure 4.1 provides conceptual diagrams of three types of design for TSS.
As of September 2022, 151 TSS remain in municipalities within the Intensive Contamination
Survey Area. As indicated by Figure 4.2, the number of TSS increased rapidly from 2013 to2014, peaked in 2015 and has since slowly decreased.
56

FIG. 4.1: Conceptual diagrams of three types of TSS (Image: Fukushima Prefecture).

57

FIG. 4.2. Number of TSS in Municipalities from March 2012 to September 2022 (Image: Fukushima Prefecture).

58

After the emplacement in TSS of bags containing waste from remediation activities, various
phenomena were observed and concerns were raised concerning some of the storage facilities
including:









Limitations on the number of waste bags that could be stacked;
Effect on long term stability and integrity of stored waste bags resulting from lack ofrigidity of the bags and voids between the bags;
Uncertainty in the long-term stability of facilities established on sloping land;
Potential leaching phenomena;
Degradation of the organic matter in waste storage bags and potential impact on the
integrity of the storage facility;
Gradual caving in of the waste bags and accumulation of water in the resulting
depressions in tarps covering the stored waste bags;
Risks of fires due to auto-combustion of the contents of waste bags.

4.3. DEVELOPMENT OF TECHNICAL GUIDELINES FOR TEMPORARY STORAGESITESWhen the activities under the Practical Arrangements began in 2013, intensive remediation
activities were being conducted in the Prefecture and many new TSS were being established tostore the resulting waste. In 2013, the Prefecture had been developing a guidance document on
the establishment and operation of TSS. At this time, as part of the further development of theguidance document, the IAEA team encouraged the Prefecture to take stock of their experience
with the development and operation of TSS. Consequently, an analysis was conducted of theactivities carried out so far regarding the development of TSS in the different municipalities.
This analysis aimed at identifying the main issues affecting TSS, identifying good practices
implemented, and comparing the different strategies for developing TSS in the different
municipalities. The aim of this approach was that it would serve as a basis for development ofan overall harmonized strategy for the development and operation of temporary storage sites in
the Prefecture and for the eventual removal of waste from the TSS and the cleanup of the sites.
The IAEA team provided technical advice and feedback to the Prefecture experts concerning
the development of the guidance document on TSS including reviewing the draft text andproviding comments on its content. Version 1 of Technical Guidelines for Temporary Storage
Sites was published in August 2013. Subsequent revisions to this document were issued in June2014 (Version 2), March 2015 (Version 3), March 2016 (Version 4), August 2017 (Version 5)
and September 2019 (Version 6).
Version 6 of the Technical Guidelines were presented, reviewed and discussed at the mission
held in Fukushima during 1–8 February 2020. The IAEA team considered that the 6th Version
was generally sensible and pragmatic and should help to optimize the waste management
process. The IAEA team suggested:The need to further elaborate procedures for dealing with water removed from the wastebags.
The need to further address the issue of whether underground tanks used for the collectionof contaminated water at some of the TSS can be safely left in the ground, or whether thetanks should be removed.
The need to ensure that the number of measurement points used to verify satisfactorycleanup of a restored site is appropriate for the size of the site.
59The need to further address the guidelines for the retention of records and the transfer ofthe sites of former TSS back to the landowners.

The Prefecture has considered these suggestions in the Technical Guidelines for the TSS.
4.4. DEVELOPMENT OF A SAFETY ASSESSMENT FOR TEMPORARY STORAGESITESWhen managing radioactive waste, the operator of relevant facilities and activities (e.g. TSS)
is required to provide a demonstration that the facilities and activities are safe. The IAEA teamadvised that, according to the IAEA Safety Standards, this demonstration of safety should be
used to support the authorization of the facilities and activities by the regulatory body. The
demonstration of safety, in particular, aims at representing the various aspects of the site andthe facility design to allow the regulatory body to have confidence that the facility or activity
may be developed, operated and closed safely so that people and the environment are protectedfrom harmful effects of radiation now and in the future. In accordance with the IAEA Safety
Standards, the demonstration of safety should be supported by quantitative evaluation of theradiological impact (safety assessment) of the facility or activity at each stage, under normal
operating conditions and accident scenarios.
The development of a safety assessment involves identifying all relevant features, event andprocesses that could affect safety, such as site characteristics, the designed safety features ofthe facility, the characteristics of the waste and its containers, and then using this information
together with appropriate models and parameter values to quantitatively assess the impact of
the temporary storage sites.
Prior to the commencement of the activities under the Practical Arrangements, the Prefecture
experts had no experience in the performance of safety assessments as required by the IAEA
Safety Standards. Therefore, training and assistance was provided on the development of safetyassessment for the TSS. This proceeded in a stepwise fashion, beginning with an educational
phase and followed by subsequent phases in which the IAEA Safety Assessment Framework
software tool (SAFRAN)1 was applied first to a ‘model’ site, then on a trial basis to a site in the
Prefecture, and then to several selected TSS in the Prefecture. The safety assessment
development process is presented schematically in Figure 4.3.
4.4.1.

Safety Assessment Framework software tool

The IAEA methodology for safety assessment of the predisposal management of radioactive
waste is provided in the General Safety Guide, GSG-3, The Safety Case and Safety Assessment
for the Predisposal Management of Radioactive Waste [48]. GSG-3 [48] provides
recommendations on meeting the safety requirements in GSR Part 5, Predisposal Managementof Radioactive Waste [49]. In order to facilitate the application of this methodology, the IAEA
developed a Safety Assessment Framework Software Tool, SAFRAN, to guide the user inperforming a systematic and structured safety assessment of facilities and activities for thepredisposal management of radioactive waste. As such, SAFRAN is suitable for used indeveloping a safety assessment for the TSS in the Prefecture. SAFRAN has various modules
concerning site and waste stream characteristics, postulated scenarios, and regulatory
requirements, as well as tools for performing quantitative analyses. The software has its own
databases, which can be adjusted enhanced with further data according to available evidence
and user needs.

1 http://safran.facilia.se/safran/show/HomePage60

FIG. 4.3: Activity flow of the development of a safety assessment for TSS in the Prefecture.

61

The demonstration of the safety of the TSS developed under the Practical Arrangements was
supported by the use of SAFRAN. In some cases, this involved adapting SAFRAN so that it
could be better applied to the specific situations in the Prefecture.
4.4.2.

Building capacities of the Prefecture for performing safety assessment of
temporary storage sites

In 2014, an IAEA team conducted a training session for the Prefecture experts that addressed
the demonstration of safety (including safety assessment) and specifically the use of SAFRAN
for TSS. Information about the IAEA methodology for the evaluation of the safety ofpredisposal management of radioactive waste as established in the IAEA Safety Standards wasprovided. The IAEA team and Prefecture experts identified the purpose, scope, approach andendpoints of activities concerned with safety assessment of TSS. Key elements of the regulatory
framework relevant to the safety assessment which were identified are dose limits foroccupationally exposed individuals and dose limits for the public in accordance with the IAEA
Safety Standards, both for normal operating conditions and accident scenarios; these values
were then entered into SAFRAN.
SAFRAN was adapted by the IAEA to consider the structure of an ‘open type’ TSS with several
layers of bags containing radioactive waste from remediation activities, liners on the top andbottom of the stacked waste bags, and various types of cover and radiation shielding.
During the subsequent period, from 2014 up to and including 2022, further advice has been
given to the Prefecture experts on safety assessment (e.g. on regulatory criteria, on scenarios,
on safety assessment tools, on the possibilities for verification of safety assessment results using
measurements), and relevant experiences in countries outside Japan (e.g. in Brazil, Sweden,
UK, Ukraine, US) have been presented and discussed.
To address specific questions that are becoming more relevant as time passes since the
Fukushima Daiichi Accident, including the potential migration of radiocaesium into
groundwater at TSS and the suggestion from the IAEA team that some materials might not need
to be managed as radioactive waste because they contain extremely low levels of radioactive
contamination, training has been provided on further safety assessment tools, including
ECOLEGO and Normalysa1.
The process of development of a safety assessment for TSS should also include the sharing andexplanation of the results of the assessment the interested stakeholders, such as members of the
public. As such, assistance was provided to the Prefecture experts on the explanation anddissemination of the results of the safety assessments made for each stage of facility
development.
4.4.3.

Safety assessment for a ‘model’ temporary storage site

As an educational tool for the Prefecture experts and to assure the applicability of the safetyassessment methodology including the use of SAFRAN, the IAEA methodology was initiallyapplied to a ‘model’ TSS having generic but conservatively estimated site, facility and waste
characteristics. A schematic depiction showing the distance from stored waste to a location
where radiation doses would be evaluated is shown in Figure 4.4. Three general activities
concerning waste bags and the model TSS were addressed by SAFRAN: waste emplacement,
waste storage, and waste retrieval. Safety assessments for the sites of former TSS from which
the waste has been removed to the ISF are discussed in Section 4.6.

1 http://project.facilia.se/normalysa/software.html

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FIG. 4.4: Typical layout for a TSS. Radiation doses are calculated with respect to the distance fromstored materials (Image: Fukushima Prefecture).

The safety of the TSS, depends on the characteristics (e.g. activity level) of the waste, robust
design and appropriate construction and operation of the facility. The most important design
features are those that provide necessary assurances that the radioactive waste can be handled,stored, retrieved, etc. without undue risk to workers, the public or the environment.
Understanding of detailed facility design and fundamental assumptions upon which the designis based is necessary in order to assess the safety of the facility currently and in the future. Even
though a TSS is not a complicated civil engineering structure, it still has several important safety
features which have to be properly quantified and understood. Therefore, the work started withdefinition of parameters used in assessment models and which describe the range of conditions
under which the facility may operate.
Discussions were held concerning the data to be entered into SAFRAN. When available, actual
data were used. For parameters that could not be established with a high degree of accuracy, a
process for conservatively estimating such information was implemented by the Prefecture
experts. This approach was used throughout the development of the safety assessment.
Information about the radioactive waste to be stored was gathered, including a set of physical,
chemical, biological, radiological and other data, and information about the waste packages, i.e.
characteristics of the waste bags in which the waste is stored. Waste streams, inventories,
throughput rates, and activity concentrations, etc. were estimated as required for quantitative
assessments in SAFRAN. Other parameters important for the safety assessment, such as thevicinity of the nearby houses, data about the site, the engineering features, etc. were collected
and/or estimated by the Prefecture experts.
A hazard analysis was performed based on an in depth analysis of waste management activities
at the model TSS, which addressed the hazards under normal operation conditions and which
could result from accidents. An initial screening of the hazards was performed and hazards
which were not relevant for the model TSS were excluded. A final screening of specificscenarios was performed based on qualitative assessments of the likelihood of identified eventsand the significance of possible impacts.
After defining the parameters needed for safety assessment, it became necessary to slightly
adjust SAFRAN in order to represent the design aspects of the existing and planned TSS in the
Prefecture. One specific change was made to SAFRAN so that it could analyze releases ofradioactive material to air and to groundwater.
Joint discussion and analysis of data emphasized that results of the safety assessment should be
used to facilitate exchange between interested parties on issues relating to the safety of TSS.
Through the step by step approach, the Prefecture could engage with the public concerning any
specific decision points.
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Normal operating conditions
The assessment of the impacts of normal operations at a model temporary storage site included
calculation of annual radiation doses to both occupationally exposed persons and residents
living in the vicinity of the facility. An occupationally exposed worker may receive a radiationdose under varying conditions, e.g. during the emplacement of the waste packages, or during
their removal. Nearby residents could be exposed due to direct exposure during theemplacement/replacement operations. However, under normal operating conditions these
exposures are very small. Under normal operating conditions the assessed exposures during thestorage period were shown to be a small fraction of the radiation dose limits.
The doses for normal situations were assessed for the case in which all operations were
performed as planned, assuming the operators spend an average amount of time to performtasks involving exposure to radiation, and assuming average air dose rates expected during these
activities.
SAFRAN was used to evaluate TSS of three different sizes representing existing and planned
TSS in the Prefecture. For these three model facilities, various shielding configurations wereassessed, such as the use of sand bags and soil spread on the top of the facility.
Calculations were performed with SAFRAN in which the distance from the TSS to the nearest
residential buildings was varied from 1 to 100 meters.
External exposures of people were calculated based on measured air dose rates, average
residence times and taking account of shielding effects. Internal exposures were calculated on
the basis of radionuclide dependent activity concentrations, dose conversion factors, andresidence times. The total dose to members of the public was calculated by summing theexternal and internal exposures.
Accident scenarios
Deviations from planned operating conditions may cause unplanned exposures of workers andthe public. The safety assessment of the model TSS, therefore, also included an assessment of
hazards resulting from accidents throughout the life of the facility.
The Prefecture experts performed a comprehensive analysis of the possible impacts of accidents
on the TSS following the IAEA methodology. The assessment of impacts from accidents
required detailed consideration and analysis of possible initiating events. These events wereanalyzed and a list of resulting potential scenarios was created. As expected, the fact that theengineering structure of the model TSS is relatively simple, does not exclude scenarios which
required further examination and the potential need for countermeasures.
The hazard screening process excluded irrelevant exposure pathways (including those with anextremely low probability of occurrence).
Regarding the choice of the accidental scenarios, and having in mind the layout and structureof a TSS, various scenarios were considered such as waste bags falling to the ground, damage
to waste bags due to various causes such as high temperature, snow and high winds, and damage
to the facility by various means such as earthquakes and fire.

64

Accidental releases into the atmosphere (e.g. as a result of fires at the facility) may cause
exposures of the workers at the site and/or the public. Accidental releases into water pathways(e.g. rivers, groundwater) may be more relevant to exposures to the public than to workers.
Conclusions regarding application of SAFRAN to operations at a model temporary storage site
The use of SAFRAN to represent waste emplacement, waste storage and waste retrieval at themodel TSS formed the basis for applying the safety assessment to several representative TSS.
The assessment for normal operational conditions clearly showed that shielding in the form ofprotective walls made of sand bags can significantly reduce the radiation doses to the nearby
population. Adding soil on the top of the facility further reduces predicted radiation doses byan order of magnitude, to a level that is significantly less than 1mSv/year. Regarding operationalradiation protection, assessed doses to workers for normal operating conditions were also below
the occupation radiation dose limits, even using conservative assumptions.
Based on input data developed by the Prefecture experts and the use of SAFRAN involving
many different numerical simulations, was concluded that for normal operational conditions,the model TSS has been designed properly, and would not cause any undue risk to workers at
the sites or nearby residents.
Calculated potential doses to occupationally exposed workers resulting from accidents
generally do not exceed 1mSv, including in assessed extreme cases.
When considering radiation doses to the public as a result of accidents, the analysis of mostscenarios predicted doses to the public that would be a small fraction of applicable dose limits.
However, certain scenarios that were analyzed indicated that the public could receive doses inexcess of 0.5 mSv and, therefore, that further analysis of these scenarios should be performed
and the possible need for the implementation of countermeasures should be considered underthese circumstances.
Based on the analysis performed, the potential for radioactive material leaking from the TSS
into groundwater and rivers is very limited, resulting in very low potential radiation doses fromexposure to groundwater and from the consumption of fish.
4.4.4.

Trial safety assessment of a real temporary storage site in the Prefecture

Following the successful application of SAFRAN to operations at a model temporary storagesite, the Prefecture experts applied the IAEA safety assessment methodology to an existing
temporary storage site in the Prefecture. The lessons learned and the experience gathered
through this activity were designed to facilitate development of the safety assessments for other
TSS. As with the safety assessment for the model facility, the trial safety assessment involved
the use of SAFRAN to evaluate predicted potential radiation doses to workers and the publicfrom TSS under normal operating conditions and as a result of accidents.
The results of the trial safety assessment carried out by the Prefecture experts were similar to
the results of the model safety assessment, which clearly indicates that the process ofdeveloping the safety assessment was coherent, that the data used as input to the safetyassessments were satisfactory and no major safety issues were identified under the conditions
that were considered. The process of developing the safety assessment using more realistic data
for the trial safety assessment contributed to the further building of confidence in the Prefecture
experts.
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4.4.5.

Safety assessment for several representative temporary storage sites in the
Prefecture

A decision was reached to apply the safety assessment methodology to nine selected TSS
throughout the Prefecture. The selected sites were chosen so that their characteristics would be
representative of the TSS within the Prefecture. Actual data were acquired for these sites andin situations where data could not be obtained, data were estimated conservatively as was thecase for the model TSS.
During the further development of the safety assessment for the TSS, further initiating events
that had not been previously included in the safety assessment were incorporated into theprocess, including the impact of, flooding, retrieval of waste bags from TSS, transport of wastebags, and aging of waste bags and facilities beyond three years (the storage period originally
anticipated for the TSS).
The results of the safety assessment for the nine representative TSS in the Prefecture weresimilar to those obtained for the model temporary storage site, even with the consideration of
additional initiating events. Safety was demonstrated for TSS under normal operating
conditions but for large scale accidents (e.g. fire), countermeasures were shown to be necessary.
It was noted that where waste is stored in TSS for longer periods of time than originally assumed,
it is necessary to take into account the effects of ageing on the waste bags and on the overall
structure of the facilities. According to the manufacturers of the waste bags, the working lives
for the waste bags could be guaranteed for approximately three years. As the storage time of
the waste bags in the TSS will exceed the working life of the bags, it was deemed necessarythat the safety assessment should address this issue.
Initial results from a detailed study conducted by the Prefecture experts on the durability of
waste bags were presented and discussed with the IAEA at the mission held in Fukushima
during 26 January to 2 February 2019. This study had examined the tensile strengths of thewaste bags and the mechanisms of their degradation. The potential implications of bag
degradation were discussed, including the potential effects on the ability to lift the bags (e.g.
with cranes) during their retrieval from the TSS, and the potential effects of bag degradation on
impacts from scenarios involving dropping of a waste bag.
Throughout the assistance, discussions have been held concerning the documentation anddissemination of the results of the safety assessments.
4.5. RETRIEVAL STRATEGIES FOR WASTE STORED IN TEMPORARY STORAGESITES AND DECOMMISSIONING OF TEMPORARY STORAGE SITESIn the later stages of the cooperation under the Practical Arrangements, the IAEA team and thePrefecture experts discussed the strategy for a retrieval strategy of the for waste stored in TSS
and the decommissioning and cleanup of the sites of the former TSS.
Because of the ageing of waste bags as discussed previously in Section 4.4.5, it was anticipatedthat the degradation of waste bags would lead to difficulty in retrieving these bags from the
TSS. The IAEA team suggested that the study of the durability of waste bags should becontinued, that the results of this review needed to be entered into a database, and that thisinformation should be used in a very practical way to inform the development of a prioritization
for the retrieval of waste bags. A significant issue that needed to be addressed was the transportof waste bags from TSS to other storage facilities (such as the ISF); procedures for managing
transport accidents should be in place; the results of a safety assessment should specificallyinform the development of a prioritization of the specific waste bags to be transported.
66

The IAEA team also noted that it might be possible, from a radiological safety perspective, touse municipal landfills for the disposal of remediation waste. Examples of the disposal ofradioactive waste in landfills in countries outside Japan were presented and discussed during
the missions held during 2018, to 2022. It was noted that based on an IAEA project on thederivation of specific clearance levels for landfill disposal of bulk amounts of waste, in termsof radiation protection principles, there should be no objections to disposing of waste in landfills
containing concentrations of 137Cs with maximum concentrations up to 8000 Bq/kg.
The IAEA team noted that decommissioning of TSS after all waste material has been removed
would be a significant undertaking that should be approached in a systematic way in accordancewith the IAEA Safety Standards. Various issues in this regard needed to be addressed such astechniques for site restoration including radiation survey procedures and the establishment andimplementation of radiation protection objectives including radiation dose criteria.
According to the discussions held, the restoration of sites is progressing well, for example, by
the end of 2022 there anywhere no operating TSS in the Prefecture and by 2024 all sites offormer TSS in the Prefecture will have been restored. In addition, it is not expected that any
further radioactive waste will be generated in the Prefecture.
4.6. LONG TERM SAFETY OF FORMER TEMPORARY STORAGE SITESThe operators of the TSS are working to ensure that after removal of the waste to the ISF andcleanup, as appropriate, any residual contamination is at levels that are not a safety concern.
The approach is aligned to the Guidelines of the MOE and includes verifying the final state of
the sites of former TSS principally using measurements of air dose rate, supported by further
measurements of radionuclide concentrations in soil. The IAEA experts noted that this approach
is appropriate, but that it is important that enough measurements are made.
Correspondingly, in the latter part of the project, the IAEA provided assistance to the Prefectureon the development of a generic safety assessment methodology that could be applied to
specific sites of former TSS from which the waste had been removed.
This generic safety assessment method was designed so that it could be applied to specific sites
with the aim of demonstrating that the sites are safe now and will be safe in future for a wide
range of potential uses, and thus to be useful in building the confidence of landowners and the
local population.
The assistance comprised discussions of issues, including:









the range of potential future land uses at the sites and the scenarios considered in thesafety assessments;
details of the potential exposure pathways and durations;details of models and parameters values;
the number of soil sampling points at the sites and the subdivision of larger sites into
smaller areas for sampling;
the calibration of the method for estimating caesium concentrations in soil from air dose
measurements;
the possibility of localized contamination ‘hot spots’ at the sites;
the presentation and communication of the safety assessments and the results forinterested parties.

67

The potential exposure pathways considered in the generic safety assessment methodology areillustrated in Figure 4.5.
The generic safety assessment methodology was applied by the Prefecture experts in some casestudy calculations to calculate the potential doses for three TSS sites based on measured
caesium concentrations in soil. Further calculations were made using air dose measurements at
TSS to estimate caesium concentrations in soil and to calculate the potential doses at those sites.
For all scenarios considered, the doses calculated by the Prefecture experts were well below
1 mSv/year.
4.7. SECTION SUMMARY
Activities concerning the management of waste from remediation activities under the Practical
Arrangements focused initially on assisting the Prefecture to develop technical guidelines forthe establishment of temporary storage facilities and assess and demonstrate the safety of thetemporary storage facilities.
When managing radioactive waste, the operator of relevant facilities and activities (e.g.
temporary storage sites) is required to demonstrate that the facilities and activities are safe. Prior
to the commencement of the activities under the Practical Arrangements, Prefecture experts had
limited experience in the performance of safety assessments as required by the IAEA Safety
Standards. Therefore, training and assistance was provided on the development of safetyassessments for the TSS. This was done in a stepwise fashion, beginning with an educational
phase and followed by subsequent phases in which the IAEA Safety Assessment Framework
software tool (SAFRAN) was applied.
As time has passed, the provision of assistance has shifted gradually to focus more on the safetyof the longer term operation of the TSS, on strategies for the retrieval of waste from the TSS,
and on the long term safety of the sites of former TSS. A key aspect of the assistance provided
has been the sharing of expertise and experiences of relevant radioactive waste management
practices from outside Japan.
The use of the IAEA’s SAFRAN tool enabled an iterative approach to safety assessment of
TSS. The safety assessment was carried out by the Prefecture experts following the IAEA
methodology for assessing the safety of predisposal radioactive waste management facilities
and activities. It also provided a means to go through the key steps in developing a safetyassessment several times and to refine assumptions, add elements, and optimize the balance
between conservatism and realism.
The safety assessment carried out by the Prefecture using the IAEA methodology for assessing
the safety for predisposal radioactive waste management facilities and activities demonstrated
fully applicability of the methodology itself, including the applicability of the IAEA’s
SAFRAN software. During the implementation of the software, a part of the SAFRAN database
was modified to better represent the specific conditions of the TSS in the Prefecture.
The development of a safety assessment for the TSS in the Prefecture, through the applicationof SAFRAN to a model temporary storage site, one in the Prefecture; and nine selected TSS, isan important step toward establishing a demonstrably safe and reliable way to store the large
amount of radioactive waste accumulated from remediation activities after the Fukushima
Daiichi accident.

68FIG. 4.5. Illustration of potential exposure pathways for sites of former TSS.

During the development of the safety assessment for TSS, several technical issues wereidentified whose impact on safety was evaluated (e.g. localized water accumulation in thetemporary storage facilities, flooding, fires, degradation of waste bags, transport of waste bags,
collapse of waste packages, etc.). On the basis of specific evaluations of the impact of theseissues on safety, technical measures to remediate and prevent the problems were identified andtheir effectiveness estimated.
The systematic process followed using SAFRAN included assessment of all credible hazards
and technical issues and provided arguments and confidence that no significant issues wereomitted or disregarded. It also provided a framework for explaining why certain systems andprocesses are considered safe and why certain improvements of safety and countermeasures arenecessary.
The results gained from the safety assessments for the TSS in the Prefecture clearly indicatedthat as long appropriate operating procedures were followed and appropriate measures are put
in place, all radiation doses should be below the relevant dose limits. The systematic analysisof all relevant hazards also provided a sound justification for imposing control measures asnecessary, to avoid or significantly reduce any possible unacceptable impacts on consequences
to people and to the environment from events including accidents.
Discussions were held involving IAEA and Prefecture experts concerning waste retrieval
strategies for waste stored in TSS, taking account of the ageing of waste bags.
The IAEA also provided assistance to the Prefecture on the development of a generic safetyassessment methodology that could be applied to specific sites of former TSS from which thewaste had been removed.
69

5.

APPLICATION OF ENVIRONMENTAL MAPPING TECHNOLOGYUSING UNMANNED AERIAL VEHICLES

5.1. BACKGROUND AND OBJECTIVESThe Prefecture identified a need to conduct radiation monitoring in areas that are not accessible
by other characterization methods, such as car-borne surveys. Consequently, the Prefecturedeveloped a methodology for the use of Unmanned Aerial Vehicles (UAVs) in areas that are
inaccessible on foot or where high radiation levels might exist. Significant assistance wasprovided to the Prefecture in the two consecutive cooperative projects: ‘Rapid Environmental
Mapping with UAV’ and Rapid Environmental Mapping with UAV Phase II: Operational
Support’, both administered by the IAEA Department of Nuclear Sciences and Applications.
5.2. DEVELOPMENT AND DELIVERY OF UAV-BASED SYSTEM
Under the first project, ‘Rapid Environmental Mapping with UAV’ a complete UAV-based
system was delivered to the Prefecture (see Figure 5.1). The device was specifically customized
for airborne radiological measurements in Japan, i.e. comprised of a versatile detection system,
remote control compliant with Japanese regulations, carbon rotor blades, laser altimeter, andsome other additions.
The project also included training of the Prefecture staff in the use of UAV, its instrumentation
and related software for data taking and analysis. This was achieved by performing numerous
tests in laboratory as well as in situ flights under realistic conditions.
5.3. IN SITU CALIBRATION OF EQUIPMENT AND VALIDATION OF
METHODOLOGY
The follow up project ‘Rapid Environmental Mapping with UAV Phase II: Operational Support’included calibration of equipment and validation of measurement methodology before
performing measurements in the areas not accessible otherwise or where high radiation levels
might exist.
Five sites with different levels of gamma dose rates have been selected to perform calibration
measurements. The respective dose equivalent rates varied from 0.1µSv/h to 8µSv/h. The
different altitude measurements were performed with the UAV-based system equipped with
Geiger–Müller counter. The same area was also characterized by using backpacks, loaded withCsI spectrometers. Finally, reference measurements using NaI detectors also were carried out.
As an example of one of such measurement campaigns is illustrated in Figure 5.2.
As a result of these measurements the following has been systematically confirmed:




70

The altitude dependence of the measurements performed with the UAV-based systemfollows an exponential law, and therefore the gamma dose rates can confidently be
extrapolated to ground level values (see Figure 5.3 on the left);
Ground level values, obtained from the UAV-based system, are systematically higher
than equivalent values reported by the NaI reference measurements; therefore, systematic
correction factor can be applied when reference measurements are not possible (seeFigure 5.3 on the right).

FIG. 5.1: UAV-based system and its instrumentation components delivered to the Prefecture. Image:
IAEA.

FIG. 5.2: Example of in situ measurements (not corrected raw data) performed in the area accessible
both for backpack and UAV techniques: data points obtained with the UAV system (Geiger–Müller
counter) flying at 10m altitude (on the left); data points obtained with backpack system (CsI
spectrometer) walking throughout the area with the detector located at 1m altitude (on the right). Image:
Fukushima Prefecture.

FIG. 5.3: On the left: illustration of exponential dependence of the dose equivalent rates measured by
the UAV-based system and represented as a function of altitude. On the right: illustration of linear
dependence of UAV data obtained with Geiger–Müller counter with respect to reference NaI data (bothmeasurements were performed at 1 m altitude and for different dose equivalent rates). Image:
Fukushima Prefecture.
71

FIG. 5.4: Combination of UAV (marked within red rectangle) and backpack based radiological mapping,carried out at one of the temporary storage sites of the Fukushima Prefecture. Image: Fukushima
Prefecture.

The measurement methodology as well as altitude correction factors, including sensitivity
analysis, were further confirmed using advanced Monte Carlo modelling. The dependence on
different geometry considerations, homogeneous versus heterogenous source distribution,different gamma energy emission, soil type, contamination depth profile, and some othervariables were systematically investigated. Finally, statistical data analysis and interpolation–
extrapolation treatment were developed and tested using R-code, what allows detailed 2-Dradiological mapping based on UAV measurements.
5.4. TRIAL MEASUREMENTS AT TEMPORARY STORAGE SITES
After the measurement methodology was validated, trial measurements were started. Figure 5.4
illustrates clear advantages of performing measurements using the UAV based system. In thiscase the radiological mapping was done at one of the temporary storage sites located in the
Fukushima Prefecture, where a combination of backpack (loaded with CsI spectrometer) andUAV based measurements were performed. The latter was carried out by flying over the above
ground storage site at 10m altitude. Indeed, walking with backpack on the top of piled waste
containers is neither practical nor desirable.
Other similar temporary storage sites have been identified and more trial measurements areplanned, both before and after removal of contaminated soil. One notes separately that the UAV
based measurements might have certain advantages when compared to backpacks in the caseof eventual spill of the soil during manipulation or transportation: quick UAV based survey
would allow remote determination of radiation levels in such situations.
5.5. SECTION SUMMARY
The Prefecture developed a methodology for the use of instrumented UAVs in areas that are
not accessible on foot or where high radiation levels might exist. Significant assistance wasprovided by the IAEA Department of Nuclear Sciences and Applications through twoconsecutive cooperative projects. This included the provision of a complete UAV based72

instrumentation system capable of making radiation measurements together with thepost-measurement analysis and interpretation methodology. These projects also included
training of the Prefecture staff in the use of UAV, its instrumentation and related software fordata taking and analysis.
The first part (validation) of the project consisted of in situ calibration of equipment andvalidation of measurement procedures. Both experimental data from reference NaI surveys,
combined with Monte Carlo modelling, were used to establish altitude dependence of the UAV
based measurements, define correction factors between UAV and NaI results and perform
extensive sensitivity analysis. In most of the cases UAV based data were also compared toequivalent backpack surveys, obtained using CsI spectrometers.
In the second part (application), trial measurements were carried out in areas that are notaccessible on foot or where high radiation levels might exist. The established methodology has
a great potential to be expanded and applied in radiological mapping relevant to contaminatedsites as a result of nuclear accidents, mining activities as well as part of decommissioning andremediation projects.

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6.

INFORMATION DISSEMINATION FOR THE PUBLIC IN
FUKUSHIMA PREFECTURE

6.1. BACKGROUND AND OBJECTIVES
Radiation monitoring undertaken by the Prefecture authorities confirmed that radiation levels
in publicly accessed areas of the Prefecture are within the in Japan. The Prefecture government
sought support, via cooperation under the Practical Arrangements, in disseminating andexplaining these results and achievements to the public in a timely and understandable manner,
based on global experience in dealing with similar situations worldwide.
To strengthen efforts in information dissemination, the IAEA and the Prefecture organized
several activities under the scope of each topic under the Practical Arrangements.
Prior to the start of the activities under the Practical Arrangements in 2013, the Prefecture’s
main activity in information dissemination related to radiation was a website that maderadiation monitoring data available to the public. The website provided detailed information on
air dose rate measurements and measurements of radioactivity concentrations in material fromseveral different sources, including:
(1)
(2)
(3)

About 3500 fixed monitoring locations (only 24 of these existed prior to the accident);
Car-borne surveys;
Radionuclide data for foodstuffs, drinking water and other environmental media.

Since shortly after the accident, the Prefecture government disseminated information about
radiation monitoring results, radiocaesium levels in the environment, decontamination,
remediation and waste related activities in the area, provided explanations of the concepts ofradiation doses to the public. For this purpose, the Prefecture used a dedicated website andnewsletter as its main distribution channels.
As of 2014, the number of site visitors to the website was between 20 000 and 50 000 per
month. Some of these users made a number of recommendations about how the website could
be improved to better meet their information needs. The Prefecture also consulted with the
public through a survey about ways in which the website could be improved. There was a clear
wish for information in easy to understand language, compatibility with mobile technology, andan explanation of the radiation doses.
6.2. DEVELOPMENT OF REVISED WEBSITE, 2013–2016
In the period 2013–2016, the IAEA team supported the Prefecture in the development of arevised website. The IAEA team presented information about web maps that developed in a
number of countries and provided technical advice concerning the mapping of radiation
monitoring data and presenting such information to the public.
6.2.1.

General mapping considerations

In many instances, data collected from separate surveys and using different instrumentation areavailable for the same location; however, as a result of differences in monitoring procedures,
multiple measurements made at the same location may vary and it is important to account forthese differences in information presented to the public. If the available datasets are merged,
the need to apply correction factors to data from different survey types is an importantconsideration. Also, other factors may also introduce apparent differences in the results of74

surveys such as a large variability in the air dose rates between seasons (due to, for instance,snow cover) and between on-road and off-road measurements made at the same location. As
such, the differences in air dose rate between these survey types are likely to be within theexperimental error of each measurement. It was considered that infographics could be usefulfor explaining these differences. It was also noted that a decision should be made on thefrequency with which these datasets are to be updated on the website.
In December 2015, the Japan Atomic Energy Agency (JAEA) presented their mapping projectat a joint meeting of the IAEA team and Prefecture experts. An environmental monitoring
database had been developed by standardizing and integrating data from several different
organizations. As of 2015, the database included over 400 million data points covering air doserate, soil (activity concentration and deposition), dust, water as well as terrestrial and marine
foods.
6.2.2.

Discussion on website development

The IAEA team made available a review of web maps from Austria, Belarus, Canada, theEuropean Union, France, Germany, the Hong Kong SAR of China, Russia, Turkey and Ukraine.
Most of these maps were based exclusively on data from fixed monitoring locations; where
walking surveys could be undertaken, they were typically only used for detailed monitoring of
small areas. These maps are normally not published on publicly accessible websites or mergedwith other datasets. The approach of the Prefecture therefore seemed to be unique.
As part of detailed discussions, the following main points were covered:


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



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

An appropriate mapping tool is required to be used within a redeveloped website. It is
important to identify both components of the project individually as they require different
skills sets.
The website should be considered as both a source of information and a tool to promote
the work that is being carried out.
In considering the changes to be made, the Prefecture is paying particular attention to
making the website more user friendly and to providing information through maps andinfographics.
It is preferable to keep the website and maps simple and intuitive. Most of the target
audience is not familiar with radiation protection terminology and concepts, and for themthe conclusion is more important than the numbers. It is therefore essential to provide
sufficient background information to support interpretation and understanding of theinformation.
For those who require more detailed information, such as units of measurement, radiation
doses, etc., this can be provided through a separate link, or through the use of explanatory
graphics.
The importance of displaying the most recent information first and the large scale
overview maps was discussed, as was the importance of maps showing localized/detailed
information.
Historical data is also valuable, especially for demonstrating how radiation doses
decreased since March 2011. Where possible, this data should be retained and used.
In the future it could be desirable to map the air dose rates in the forests, which represent
70% of the surface area of the Prefecture. The data from the network of measurement
stations established by the forestry group could be used.

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

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6.2.3.

There are a number of areas within the Prefecture where there were relatively highthorium concentrations in the soil. As a result, the background air dose rate may be highlyvariable across the Prefecture and the use of one generic background value for all air dose
rate charts may not provide the correct picture. Data on the potassium, uranium andthorium concentrations in soils are available on the website of the Japan GeologicalSociety — this may allow calculation of the actual air dose rate at various locations.
As the scales and colour coding of the JAEA and the Prefecture maps are different,
merging the raw data and using it to create new maps is the recommended approach.
The Prefecture needs to decide what information to be made available to the public on its
new website, i.e. will it be possible only to download the existing maps or will the raw
data be made available to allow individuals to prepare their own maps? In deciding thisissue, a balance must be achieved between the benefits of transparency versus the risk ofmisuse of the data.
Final website design

Following the revision of the website, a presentation on the completed work was made by thePrefecture experts at the joint meeting held with the IAEA team in June/July 2016. Much of theadvice received from the IAEA team was applied to the development of the design andfunctionality of the new website. Prefecture experts confirmed that the monitoring datacollected as part of the car-borne surveys had been normalized to 1 m above ground in outdoor
air. The new website was more user friendly and faster than the previous version, and optimized
to both computer screens and smartphones. With the revised website, it became possible toeasily browse data associated with specific locations and to specify dates of interest. Clickablemaps allowed users to access data from specific points on a map (see Figure 6.1). Air doselevels and the results of environmental samples were displayed on the same map. The changes
in air dose rates over time could be accessed intuitively through the use of a ‘time ruler’ (seeFigure 6.2). Also, the revised website had the capability to present the transition of doses overtime through the generation of graphs (see Figure 6.3). In addition to the Japanese, the website
was also made available in English1, Chinese and Korean.
6.3. FUKUSHIMA REVITALIZATION STATION WEBSITE
Since 2015, the Prefecture has operated the Fukushima Revitalization Station website as a main
resource of information for people in Japan and abroad. The website integrates information
about the reconstruction work in the Prefecture for visitors and citizens, and information about
air dose rate measurements and measurements of radioactivity concentrations in material. The
website also hosts the radiation monitoring measurement map displaying monitoring data
accessible to the public.
To assist the Prefecture with maintaining and strengthening the website, the IAEA team held
lectures and practical sessions on international examples and best practices in online
communication of radiation related information.

1 The English language portal for the revised website can be found at this web address:

http://fukushima-radioactivity.jp/

76

FIG. 6.1: Clickable Radiation Measurement Map (Fukushima Prefecture website).

77

FIG. 6.2: Time ruler from Radiation Measurement Map (Fukushima Prefecture website).

78

FIG. 6.3: Graph of measurement data from a specific measuring point over a specified timeframe from Radiation Measurement Map (Fukushima Prefecture
website).
79

The IAEA team and the Prefecture concluded that simple and well-structured web content isimportant. The home page should include main points and recent updates, while the moredetailed content should be provided on supporting pages. ‘Push’ information via social media
or newsletters reaching people not actively looking for this information is another engaging
way of targeting the public.
The Prefecture and the IAEA team further discussed the recent communication trends indisplaying monitoring data through visualization tools such as maps, animations andinfographics. As international examples showed, these proved to be effective in conveying data
in an understandable manner to the public in other situations with radiological concerns.
The Fukushima Revitalization Station is available in ten languages (Japanese, English, Chinese(simplified and traditional), Korean, Thai, German, French, Italian, Spanish, and Portuguese).
Analytical tools such as Google Analytics support the understanding of website visibility andfunctionality. Results from April 2019 show that the visits to foreign language webpages
account for 4.8 per cent out of the total number of visits. English pages attract half of the foreign
visitors and the most visited webpage is ‘Radiation levels in the prefecture’.
To further assist the Prefecture, the IAEA team provided written recommendations on how to
optimize information dissemination via the Fukushima Revitalization Station site. This paper
provided recommendations and information to the following:










Tailor website content and layout to audience needs;
Launch a poll on the website on surveying audience needs;
Concentrate on the most visited languages: English, Chinese and Korean;
Translate videos on monitoring available on the Japanese website;
Use the results of Google Analytics for further optimizing website;
Ensure all pages of the website are secure;Work on search engine optimization for better search engine ranking;
Improve web publishing workflow, so that technical divisions can update their content
more regularly according to a plan.

In 2021, the Forestry Promotion Division in the Prefecture successfully published information
on monitoring and restrictions on wild mushrooms on their website, provided information to
the media as well as broadcast information on radio. The Division created maps of distribution
restrictions that were to be updated when restrictions are lifted. The map is colour coded. The
IAEA team advised that, as well as colour coded maps, the data could be presented in a databaseformat that could be filtered by the user. A visitor to the website could, for example, select 1)
the municipality and/or 2) the species of interest; the website would display the corresponding
restrictions.
6.4. INFORMATION DISSEMINATIONThe Prefecture government disseminates information about radiation monitoring results,
radiocaesium levels in the environment, decontamination, remediation and waste related
activities in the area, and explains the effects of radiation to the public and other relevant
stakeholders. For this purpose, the Prefecture uses dedicated websites (see Sections 6.2 and 6.3)
and a newsletter.

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The Fukushima Prefecture public relation magazine on ‘Environmental radiation monitoring’
published in March 202210.
A 2017 public opinion poll targeting Tokyo residents, presented by the Prefecture, showed that
residents still did not have a correct understanding of the current situation in the Prefecture —on average a third would not recommend family members, children, friends, foreign tourists tovisit the Prefecture. This poll and other information presented by the Prefecture indicated that
communicating radiation and associated risks and shifting perceptions from perceived risks toactual risk remains a challenge.
To strengthen efforts in information dissemination, organized activities for the topics under thescope of the Practical Arrangements were carried out between 2018 and 2022. These were basedon international examples of best practices in informing the public about the effects of radiation.
As part of the ‘Long term Monitoring’ Working Group, in 2021, the IAEA team presented
experiences of using informed decision making by the members of public in territories
contaminated by deposited radioactive material from the Chornobyl accident (Ukraine, Belarus).
A system of village radiologists was established in 1989–1990 who were educated and trainedby central government. The candidates to become village radiologists were nominated from thetrusted groups of population (teachers, doctors, agriculture specialists) and were local and sowere trusted and were part of the community. During 1987–2000 over 12 700 specialists weretrained for the agriculture and processing industry in Ukraine. In Belarus centers for practicalradiological culture were established and equipped with modern instrumentation for measuring
radiation in foodstuffs and other environmental samples, as well as for measuring ambient dose
rates. This initiative allowed for developing a better attitude of people to the radiation risk
associated with living in conditions of long term radioactive contamination (i.e. understanding
and knowledge of the current situation, maintaining reasonable vigilance regarding theradiation risks, without exaggerating the danger) and creating conditions for managing possible
risks.
6.4.1.

Outreach materials

To support three main topic areas, radiation monitoring, off-site decontamination andremediation and the management of radioactive waste, the IAEA team and the Prefecture
produced outreach materials targeting the general public.
Outreach materials were created in a form of flyers explaining:






The current radiological trends and overall dose rates;
Steps undertaken by the Prefecture in radiation monitoring and mapping, remediation,
decontamination and management of radioactive waste;
Radiation effects to the public and comparison to other situations;
Results of the IAEA–Fukushima Prefecture cooperation from 2013 until 2017.

10 Available in English at:https://www.iaea.org/sites/default/files/22/06/fuku-moni_march_2022erevised_.pdf

81The flyers included text, images and whenever possible, infographics and engaging graphs andcharts to underline the monitoring data. These data visualizations help the public and otherstakeholders understand the complex information in a plain language.
The flyers were developed under the each of three topics covered in Sections, 2, 3 and 4. They
were presented and discussed at the workshop for officials from the Prefecture governmentorganized from 6 to 8 February 2018 in Japan and later distributed to the municipalities in the
Prefecture. English versions are also available online11.
An illustration of the front page of one of the leaflets and a page with infographics is illustrated
in Figure 6.4.
In February 2020, the IAEA team and the Prefecture discussed creating further outreachmaterials on an ongoing basis during the remainder of the duration of the Practical Arrangement.
Topics that were raised were:







6.4.2.

Develop information on the prevalence and potential health effects of high Cs
microparticles found in river sediments;
To translate the results of decontamination and monitoring activities into English,
Chinese and Korean for web site;
To develop messages and have a communication plan to use in case of natural disasters
like the recent typhoon;
To strongly emphasize the message that radiation levels in most of the prefecture are now
within the range of background radiation globally;
Following safety assessments undertaken for the former TSS’s, communicate that thesites are safe to use, including those on agricultural land (both for both farmers andconsumers of the produce).
Brochure for local hunters and wild mushrooms

The IAEA provided assistance to the Prefecture by designing a brochure for local hunters
containing information and advice on the consumption of meat of wild animals including wildboar captured in the Prefecture12 (see Figure 6.5).
In 2021, the Local Branches in the Prefecture successfully published information on restrictions
for wild mushrooms in their public relations magazine, created and distributed paper version
material and disseminated material in shops. They created brochures and leaflets withvisualization of the restrictions in chart form, as well as specific items concerning the peakseason of mushroom distribution.
The IAEA team advised that the information dissemination products (such as the leaflets andbrochures) contained too much information, which made them hard to understand and advisedthat the information and tables were reduced and simplified, focusing on what is most relevant.

11 https://www.fukushima-kankyosozo.jp//lancelot/common_files/images/public/9_Leaflet(English).pdf
12 https://www.iaea.org/sites/default/files/21/07/fp_brochure_for_hunters.pdf)

82

Municipalities also published information on their websites as well as printed the informationin their magazines. Their websites have been updated with restrictions on wild mushrooms andinformation has been distributed via magazines and local websites.

83

FIG. 6.4: An illustration of the front page of one of the leaflets and a page with infographics in English(Image: Fukushima Prefecture).

FIG. 6.5: An illustration of the front page of the informational brochures on advice and information for
hunter and pickers and distributors of wild mushrooms ‘in English’ (Image: Fukushima Prefecture).

84

The IAEA team proposed to create a more generic information brochure, similar to the brochurecreated for hunters, with reference made to the website for details on actual restrictions andmore up to date information. The proposal was that on a specific web page, individuals could
select their preferred municipality and get more information tailored to their needs. This would
allow users and readers to have a general idea of the information from the brochure but would
also allow ones that need of more specific information to find it easily and readily. The IAEA
team also suggested having interactive maps, which could help to increase the time span people
stay on the website, as well as make information more understandable and visually appealing.
The IAEA team subsequently provided assistance to the Prefecture by designing a genericbrochure on wild mushrooms, similar to the one prepared for hunters. The target audience ofthe brochure was the general public who gather wild mushrooms, as well as distributors tostores and farmers’ markets. The key objective of the brochure is to inform the target audience
about the restrictions on consumption and distribution, commercial and non-commercial, ofdifferent species of wild mushrooms. An online version of the brochure was issued in April
2022 and a printed version was issued in September 2022 (Figure 6.5 – English version). The
Prefecture highlighted that the update of the brochure will take place once a year, in September
before the picking season starts. The English version mentions that the updated information is
only available in Japanese13.
6.4.3.

Information Dissemination Seminar

In July 2019, a seminar was held in Japan which focused on dissemination of information
related to radiation monitoring results, decontamination, remediation and waste related
activities implemented by the Prefecture. The target audience was Prefecture officials withresponsibilities for outreach and engagement with the public in various divisions.
The aim was to exchange knowledge and experience with international experts on effective
communication strategies and best practice communication methods and techniques. The
2.5 day seminar was composed of a plenary style session and interactive sessions. During the
Seminar, Prefecture representatives presented how they dealt with information dissemination
to date and what challenges they were facing.
The IAEA team had experience in risk communication and showed case studies and advised on
the specific situation of the Prefecture. The interactive sessions were led by communication
experts facilitating the discussions in separate working groups.
The Seminar was structured in two parts:(1)

Lectures — these included:
 Presentations on the Prefecture experience, results of their communication strategy
and challenges encountered so far.
 International case studies related to communicating incidents and radiation risks.
 Possible solutions to the points raised by the Prefecture and feedback provided by
IAEA and international experts.

(2)

Interactive sessions — these included:
 Discussions based on information provided during the lectures.

13 The brochure in English can be found at:https://www.iaea.org/topics/radiation-protection/cooperation-fukushima-prefecture85

Practical exercise and skill building through group dialogues and roles plays split
into three parallel groups (web, face to face, events).

One conclusion of the Seminar was that it is important to communicate doses and dose rates in
simple terms and putting them into perspective by providing context to show that the dose levels
in most parts of the Prefecture are comparable to those in other parts of the world.
The IAEA team stressed that when communicating the beauty and diversity of the Prefecture
to potential tourists, it is crucial to communicate that the dose rates are within the normal range
and do not pose risks to tourists. When reaching out to foreign audiences, it is important toclarify that the term ‘Fukushima’ refers not to the Fukushima Daiichi nuclear power plant but
to the entire prefecture.
The most efficient way of getting messages across to stakeholders is to move away from one
way information disseminations to engagement. It was suggested to involve citizens in dose
rate monitoring (‘citizen science’). By identifying community ambassadors (people that are
respected and closer to the community), information on decontamination, risks and waste
storage could be provided directly to their peers. Early engagement of stakeholders is also a key
for building trust as well as connecting with stakeholders at a personal level.
The Prefecture website was also a topic of the Seminar. More information is provided in
Section 6.3.
6.5. SECTION SUMMARY
The availability of accurate and up to date information on the radiation situation in the
Prefecture is important both for the local population and for visitors. While Fukushima
Prefecture radioactivity measurement map large scale maps, available on the Prefecture
website14 give a general view of how air dose rates are reducing over time, people also wantmore localized information regarding the location where they live, work or are visiting. The
revised website that was finalized in 2016 made this information available in a form that is easy
to understand and prioritized the most recent data while also ensuring that historic data is alsoavailable for those who wish to review it.
Radiation data were collected in a number of different ways, each of which uses different
measurement methodologies. Over 3000 monitoring stations provide continuous data fromfixed locations across the Prefecture, and these are augmented by data collected by car-borne
surveys (where radiation monitors are affixed to vehicles that are driven around the streets of
the Prefecture).
Several steps were necessary so that the public could access radiation monitoring informationfrom the Prefecture website in a more organized and understandable way: standardization of
the large volume of available data; development of maps to accurately represent the radiation
situation at different levels of detail; and upgrading the website to allow access to these andother data. All of these issues were discussed in detail between the IAEA team and Prefecture
experts in IT, public information strategy and radiation measurement.

14 http://fukushima-radioactivity.jp/pc/

86

The provision of information through a website is only one component of a communications
strategy. It has been recognized that the Prefecture needs to provide information and advice toresidents of the Prefecture as well as tourists from Japan and abroad on the expected reduction
in air dose rates with time. This has to take into account natural reductions due to the physicalhalf-life of radiocaesium and also the effectiveness of any applied countermeasures. Suchcalculations are site specific and the uncertainties in the estimates of the future situation mustalso be provided. The key takeaways arising from the cooperation with IAEA are:







The most efficient way of getting messages across is to move away from one way
information dissemination to engagement.
An important task to increase trust of the general public in the Prefecture itself, in Japanand abroad, enabling them to form informed opinions. This can be done through active
public engagement and easily understandable communication products.
When reaching out to outside of Japan it is important to clarify that the term ‘Fukushima’
does not refer to the Fukushima Daiichi nuclear power plant but to an entire Prefecture.
Channels such as well structured website are keys in reaching out to the target audiencein a timely manner.
Given the importance of traditional media in Japan, and even more so in the prefecture,communicating through mass media is important.

The results of the activities highlighted the importance of sharing international examples andbenefits of worldwide assistance.
The IAEA team assisted the Prefecture in developing a brochure for local hunters and anotherone for the general public who gather wild mushrooms, as well as distributors to stores andfarmers’ markets. The key objective of the brochures is to inform the target audience about the
restrictions on consumption and distribution, commercial and non-commercial, of wild gameand different species of wild mushrooms.

87

7.

REPORT SUMMARY

From the time when Practical Arrangements was established in 2012, the most important
exposure pathway for people is external radiation emitted by radiocaesium, which is present inboth the terrestrial and aquatic ecosystems. Radiocaesium levels in the environment, andassociated doses to people will decline without intervention as a result of the radioactive decayof radiocaesium, and the removal of radiocaesium by weathering from surfaces and verticalmigration down soil and sediment profiles. Furthermore, the Prefecture has determined thatradiocaesium levels in the terrestrial aquatic ecosystems and associated doses to people havedeclined due to remediation activities. Since the Fukushima Daiichi accident, the Prefecture has
performed a significant amount of work concerning remediation activities and the managementof the resulting radioactive waste. This report covers the work undertaken under the Practical
Arrangements from 2013 to early 2020.
7.1. LONG TERM MONITORING OF RADIOACTIVE MATERIAL IN FORESTS AND
ASSOCIATED COUNTERMEASURES
The importance of forests in the economy of the Prefecture and in the life of its inhabitants
underlines the need to understand the mechanisms of movement and accumulation ofradiocaesium within this ecosystem. While extensive research on forest ecosystems was carriedout in the years following the Chornobyl accident in 1986, forests in Europe differ from thosein Japan and the results of previous studies may not be directly applicable. For this reason, an
extensive monitoring and research programme has been established by the Prefecture.
There are clear indications that clay minerals present in the forest soils in the Prefecture areimmobilizing radiocaesium in a manner that reduces its uptake to understory vegetation and totrees. As a result, only approximately 0.2% of the radiocaesium in forests is now contained in
the trees themselves. The relatively low concentrations measured in harvested wood to date
support the continued use of timber from the forests in the Prefecture. It is important, however,to assess whether this trend continues, as well as any differences in uptake by newly planted
saplings. With time, the reduction in air dose rates due to natural decay will allow access toareas of forest not currently being managed; this in turn may bring new challenges in terms ofcontinued use of the timber as well as managing radiation exposure of forest workers.
An important observation is that the overwhelming majority of the radiocaesium initiallydeposited in the forests of the Prefecture has now been transferred to the soil and litter layer,
where it continues to contribute to the air dose rate. Most of the radiocaesium initially depositedis retained within the forest and the amount of radiocaesium lost from the system to date seems
to be low. This suggests that the likelihood of ongoing contamination of nearby agriculturalland is low (unless through some unforeseen catastrophic event).
Forests are also an important source of foods such as mushrooms, sansei and the meat of wildboar. Additionally, freshwater fish are caught in rivers and streams, some of which partly
transverse forests. While these can be considered as minority foods — compared to agricultural
foods — they tend to concentrate radiocaesium; there are many outlier values and a very slow
reduction in levels is observed to date. The activity concentrations in many of these wild foods
well exceed the limit for radiocaesium of 100 Bq/kg for general foods sold commercially. For
all these reasons, ongoing attention needs to be given to providing more and better information,
including measurement data, to those who collect wild foods for their own personal
consumption.

88

Looking to the future, the reduction in air dose rate within the forest will be dominated by thehalf-life of 30 years of 137Cs. While monitoring programmes will need to be maintained formany years, those that have been established in earlier years need to be reviewed regularly todetermine if, from a technical point of view, the frequency of monitoring can be reduced
without the loss of necessary information.
The knowledge gained will allow the forests to be managed in an effective manner for the
benefit of the people of the Prefecture. This knowledge should be disseminated widely so thatthe public has a clear understanding of the levels of radiation to which they are exposed.
7.2. MONITORING OF RADIOACTIVE MATERIAL AND ASSOCIATED
REMEDIATION AND DECONTAMINATION IN TERRESTRIAL AND AQUATICENVIRONMENTS
In the freshwater bodies of the Prefecture, dissolved radiocaesium levels in water are close toor below the detection limit (of 0.05 Bq/L). This can be explained by the strong sorption ofradiocaesium by sediments in riverbeds, in which much higher radiocaesium levels areobserved. There is also a clear decline in the concentration of radiocaesium in suspended
sediments.
The reduction of radiocaesium levels in the environment is mainly caused by the radioactive
decay, whereas runoff and washoff provide further reduction. Suspended radiocaesium issubject to sedimentation in reservoirs, which act as a kind of sediment trap.
Simulation models have been used to assess the transport of radiocaesium from catchment areas
through the river system to the Pacific Ocean. The results facilitate the interpretation ofmonitoring measurements and support decisions that can lead to reducing exposure to the public.
Additionally, models provide valuable input when identifying appropriate countermeasures(including those related to decontamination and remediation) and evaluating their effectiveness.
For example, several demonstration projects have been initiated to test the effectiveness ofmeasures for reducing air dose rates in recreational areas near rivers.
Worldwide experience with freshwater remediation activities indicates that technical measures
have only a limited potential to control the dispersion of radionuclides in freshwater bodies.
Instead, administrative measures, such as restrictions on the use of freshwaters, are relatively
easy to implement and more effective in reducing exposure to the public from radionuclides
deposited in freshwater bodies.
Since 2011, intensive decontamination work has been carried out in private homes, public areas,
agricultural land and parts of the forests close to inhabited areas. For residences (houses),decontamination is the most advanced the planned activities were completed by March 2018.
Following decontamination, air dose rates were reduced by 20–50%, similar to those achievedby remediation in areas affected by the Chornobyl accident.
Monitoring of dissolved and suspended radiocaesium in rivers of the Prefecture continues,
along with complementary studies applying tracer techniques, to gain a better understanding oftransport processes and dynamics in river catchments, and the influence natural andanthropogenic activities on exposure. Such data can be used to respond to questions raised by
local communities and publishing results of studies in peer-reviewed journals serves as
independent verification of findings. The work being done provides an important body ofliterature for local residents and the international community.

897.3. MANAGEMENT OF WASTE FROM REMEDIATION ACTIVITIES
Activities concerning the management of waste from remediation activities under the Practical
Arrangements focused initially on assisting the Prefecture to develop technical guidelines forthe establishment of temporary storage facilities and on assisting the Prefecture to assess anddemonstrate the safety of the temporary storage facilities.
When managing radioactive waste, the operator of relevant facilities and activities (e.g.
temporary storage sites) is required to demonstrate that the facilities and activities are safe. Prior
to the commencement of the activities under the Practical Arrangements, Prefecture experts had
limited experience in the performance of safety assessments as required by the IAEA Safety
Standards. Therefore, training and assistance was provided on the development of safetyassessments for the TSS. This was done in a stepwise fashion, beginning with an educational
phase and followed by subsequent phases in which the IAEA Safety Assessment Framework
software tool (SAFRAN) was applied.
As time has passed, the provision of assistance has shifted gradually to focus more on the safetyof the longer term operation of the TSS, on strategies for the retrieval of waste from the TSS,
and on the decommissioning and cleanup of the former TSS sites. A key aspect of the assistanceprovided has been the sharing of expertise and experiences of relevant radioactive waste
management practices from outside Japan.
The development of a safety assessment for the TSS in the Prefecture is an important step
toward establishing a safe and reliable way to store the large amount of radioactive waste
accumulated from remediation activities after the Fukushima Daiichi accident.
The results gained through the use of SAFRAN for the development of safety assessments for
the TSS in the Prefecture indicate that as long appropriate operating procedures are followed
and appropriate measures are put in place, radiation doses should be well below the relevant
dose limits. A systematic analysis of the relevant hazards provided a sound justification forimposing measures where necessary to avoid or significantly reduce any possible unacceptable
impacts to people and to the environment.
Discussions were held involving the IAEA team and Prefecture experts concerning retrieval
strategies for waste stored in TSS that takes account of the ageing of waste bags.
Decommissioning of TSS and any remediation of the sites after all the waste has been removed
will be a significant undertaking and this should be approached in a systematic way and the
IAEA team advised that the applicable IAEA Safety Standards are used.
The IAEA team provided assistance to the Prefecture on the development of a generic safetyassessment methodology that could be applied to specific sites of former TSS from which thewaste had been removed.
7.4. INFORMATION DISSEMINATION FOR THE PUBLIC IN FUKUSHIMAPREFECTURE
Since shortly after the accident, the Prefecture government has disseminated information 15
about radiation monitoring results, radiocaesium levels in the environment, decontamination,
remediation and waste related activities in the area to the public and other relevant stakeholders.

15 http://www.pref.fukushima.lg.jp/site/portal/90

For this purpose, the Prefecture has used dedicated websites and a newsletter as its main
distribution channels.
International experience in providing radiation data to the public was reviewed by radiation
protection, public information and IT experts. A wide range of options regarding data
presentation, including the use of interactive maps, were considered. Technical issues such as
how to present representative data, how to indicate long term trends in air dose rate and how tomerge data from fixed monitoring stations and different types of measurement surveys are notstraightforward and different approaches and practical solutions were discussed.
The revised website, the development of which was informed by the advice provided by the
IAEA team was completed in 2016; it is more user friendly and faster than the previous version,and it is fully accessible from both PCs and smartphones. With the revised website, it is now
possible to easily browse data associated with specific locations and dates.
Advice, based on international advice and best practices, was also provided for information
dissemination via face to face meetings and events, as well as on the new Fukushima
Revitalization Website. The importance of engagement and the involvement of citizens in dose
measurements was underlined. Several concrete suggestions on making the Revitalization
website more targeted to the different audiences, including from abroad, were provided.
The IAEA team assisted the Prefecture in developing a set of flyers for the general public aswell as specific brochures for local hunters and those who gather wild mushrooms in the forest,
as well as distributors to stores and farmers’ markets. The key objective of the flyers was toinform about the results of the cooperation and the decrease in radiation levels, while thebrochure informed the specific target audiences about the restrictions on consumption anddistribution, commercial and non-commercial, of wild game and different species of wildmushrooms.

91

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ANNEX:OUTCOMES FROM WORK UNDERTAKEN UNDER THE FUKUSHIMACOOPERATIVE PROJECTSThe key outcomes as a result of the 10 years cooperation under the Fukushima Cooperative
Projects were summarized at the end of the Summary Workshop held between 31 January and3 February 2023.
The outcomes were presented by the IAEA Technical Leader of the IAEA–Fukushima Project
are given below.
Monitoring of Radioactive Material in the Environment Associated Countermeasures
Monitoring: forests
Radiocaesium in forests

Radionuclides deposited in the forests of the Prefecture are effectively retained within theforest ecosystem and the likelihood of transfers of radiocaesium to agricultural land
appears to be low.

Forest maintenance procedures are very effective at retaining radiocaesium within forests.

The presence of clay minerals in the underlying forest soils has chemically bind theradiocaesium and limit its transfer to vegetation.

Measures have been implemented to restrict the radiation exposure of forest workers.

Monitoring in forests

Radiation monitoring in forest may be necessary for many more years.



Optimization of forest monitoring is needed moving forward due to available resources.

Monitoring of wild foods

Activity concentrations in wild foods are variable but there are high concentrations still
being measured in 2022 that are >100 Bq/kg.

Decline in Cs concentrations in wild mushrooms and other wild foods is slow andrestrictions may be required for many years for some species and in some areas.
Therefore, monitoring will need to continue in the long term to provide surveillance andreassurance and to remain vigilant to changes in forest systems.



A non-destructive analysis method has been tested for matsutake mushrooms to avoid
destroying expensive mushroom species.



Although significant progress has been made over the past decade in lifting distribution
restriction for inland fish, there are still restrictions on some fish species in some areas,
where recreational fishing is not allowed to resume.

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Monitoring of Radioactive Material in the Environment Associated Countermeasures
Monitoring: terrestrial and aquatic environments
Behaviour of caesium in aquatic systems

Environmental and climatic conditions in the Fukushima and Chornobyl regions are quite
different but the behaviour of radiocaesium in the environment is similar. In particular,
strong sorption of caesium to solids is observed and, in fresh waters, most of the 137Cs isfound in suspended or bottom sediments.



Survey data indicate a continuous decline in radiocaesium concentrations in rivers since2011. Decline observed in the Prefecture and in other parts of the world agree reasonably
well.



Predictions using a simulation model for dynamics in rivers (TODAM) show agreementwith measurements under base- and high-river flow conditions.



In the Prefecture, loss of 137Cs due to runoff depends on the land use. The loss is low —about 1% in the year of deposition and well below 1% per year thereafter. This is in
general agreement with the experience in other countries.

A small number of caesium microparticles (CsMPs) have been found with low levels ofradiocaesium bound to them. Caesium bioavailability is likely to be low and no significant
impacts are likely.

Remediation of the terrestrial environmentCountermeasures that control release of 137Cs into surface waters (e.g. decontaminationof upstream environments) can be an effective approach to prevent accumulation in
sediments in aquatic systems.

Gamma dose rates in forests, on agricultural lands and residential areas after
decontamination are reduced by about 20–50%, both after the Chornobyl and Fukushima
accidents.



For reducing 137Cs levels in crops, a similar range of techniques was applied after the
Chornobyl and Fukushima accidents. Where comparable, reduction factors are similar.

Control of dispersion in dynamic aquatic systems: engineering measures

Aquatic systems are complex and very site specific.

Large scale engineering measures are costly and often difficult to implement.



Natural sediment traps have been demonstrated to work well e.g. at the Yokokawa dam
and at the Kiev reservoir in Ukraine due to calm waters with low water flows leading tohigh sedimentation.

Removal of bottom sediments is an effective and globally applied measure for
remediation of water bodies (including demonstration test in the Fukushima Prefecture).

Removal of riverside sediments and vegetation (demonstration test in Kam-Oguni River)reduced gamma dose rates by a factor of about 2: this reduction persisted and was notaffected by typhoons and flooding.

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Management of Waste from Remediation Activities

After the 2011 Fukushima Daiichi accident, enormous amounts of materials weremanaged as radioactive waste.



A cumulative total of over 1000 Temporary Storage Sites (TSS) were established in the
Prefecture based on “Technical Guidelines”.

The waste was later moved to Interim Storage Facilities



IAEA assisted the Prefecture by:
 Explaining IAEA Safety Standards;
 Reviewing the Technical Guidelines; Sharing expertise and experiences from outside Japan;
 Training the Prefecture on assessing the safety of TSS; Advising on the presentation and communication of information.



The Prefectures’ capabilities on radioactive waste management were significantly
enhanced over the period of the project.

The Prefecture has Technical Guidelines for procedures for safe waste management.
IAEA provided comments to the Prefecture on all the versions of the Technical
Guidelines.

Support was provided by the IAEA to the Prefecture for the safety assessment of
Temporary Storage Sites (TSS) for normal and accidental situations and for all phases of
their development.



Assessed doses during operation of TSS and after waste removal are well below relevant
dose limits and long term goals.

Information Dissemination to the Public

IAEA’ s assistance on information dissemination interlinks with all the areas andactivities of cooperation.



IAEA’s assistance was provided on effective ways to communicate information to the
public in a timely and understandable manner.



Methodologies and expertise provided by IAEA were based on global experience indealing with accidental releases.

The most efficient way of getting messages across to the public and other interested
parties is to move away from one way information dissemination to engagement with
them.



Concrete communication products were developed in order to better inform audiences
about radiation levels, risks and the radiation levels in the Prefecture.



The Prefecture websites was revised in line with IAEA recommendations, to provide a
better user experience, higher search engine optimization and therefore a higher impact.

The Google Analytics tool was used to obtain quantitative data on visitor rate, retention,
revisiting rates, drill down and bounce rates.

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

An important task is to increase trust of the general public in the Prefecture itself, in Japanand abroad, enabling them to make informed opinions. This requires the definition oftarget audiences, appropriate communication goals and tools and messages.



It is essential to communicate accurate messages to the target audience without using too
specific scientific concepts.

To make outreach products easily understandable, it was recommended to simplify
language and to use infographics, graphs, animations, videos, etc.

Lesson learned were: to simplify information presented on the page of the website, tobuild information architecture/taxonomy, include more actionable items on main page
(surveys, videos…), to focus on fresh news on regular basis.

Radiation Safety Navigator was introduced as the new IAEA’s online tool for effective
communication about radiation safety. This tool can be utilized by the Prefecture, forexample, in conveying messages about radiation doses.

102