SUMMARY REPORT(2013 – 2017)

Cooperation between theInternational Atomic Energy Agency
and Fukushima Prefecture
And
Activities undertaken
By Fukushima Prefecture
Radiation Monitoring and Remediation Following the
Fukushima Daiichi Nuclear Power Plant Accident
30 May 2018

Vienna/Fukushima 2018

SUMMARY REPORT(2013 – 2017)

Cooperation between theInternational Atomic Energy Agency
and Fukushima Prefecture
And
Activities undertaken
By Fukushima Prefecture
Radiation Monitoring and Remediation Following the
Fukushima Daiichi Nuclear Power Plant Accident
30 May 2018

Vienna/Fukushima 2018

Contents
1.

Introduction ..................................................................................................................................... 1
1.1. Background .................................................................................................................................. 1
1.2. Objectives and scope of the cooperation ...................................................................................... 1
1.3. Topics of cooperation ................................................................................................................... 1
1.4. Provision of assistance and structure of this report ...................................................................... 22.

Use of Environmental Mapping Technology for Data Gathered by Unmanned Aerial Vehicles
and Walking Surveys........................................................................................................................... 2

3.

Long Term Monitoring of Radioactive Material in Forests and Associated Countermeasures ...... 3
3.1. Background and objectives .......................................................................................................... 3
3.2. Monitoring programmes ............................................................................................................... 4
3.2.1. Air dose rate .......................................................................................................................... 4
3.2.2. Radiocaesium in forest trees.................................................................................................. 6
3.3. Distribution of radiocaesium in forests ........................................................................................ 6
3.4. Effectiveness of forest countermeasures ...................................................................................... 8
3.5. Satoyama Rehabilitation Model Project ....................................................................................... 93.6. Managing the timber industry ...................................................................................................... 9
3.7. Protection of forest workers against radiation ............................................................................ 10
3.8. Forest fires .................................................................................................................................. 10
3.9. Radiocaesium transfer to forest mushrooms and bamboo shoots............................................... 123.10. Section Summary ..................................................................................................................... 12

4.

Use of Radiation Monitoring Data to Develop Maps to be Made Available to the Public ........... 13
4.1. Background and objectives ........................................................................................................ 13
4.2. Development of revised website ................................................................................................ 15
4.3. Final website design ................................................................................................................... 174.4. Section Summary ....................................................................................................................... 19

5.

Off-Site Decontamination and Environmental Monitoring ........................................................... 19
5.1. Background and objectives ........................................................................................................ 19
5.2. Behaviour of radiocaesium in the natural environment.............................................................. 21
5.3. Results of monitoring programmes ............................................................................................ 225.4. Application of simulation models .............................................................................................. 27
5.5. Experience with remediation and decontamination in river and lakes ....................................... 28
5.6. Experience with remediation and decontamination in residential areas..................................... 31
5.7. Section Summary ....................................................................................................................... 33

6.

Management of Waste from Remediation Activities .................................................................... 34
6.1. Background and objectives ........................................................................................................ 34
6.2. Temporary storage sites.............................................................................................................. 35
6.3. Development of technical guidelines for temporary storage sites .............................................. 37
6.4. Development of a safety assessment for temporary storage sites .............................................. 38
6.4.1. Safety Assessment Framework software tool...................................................................... 39
6.4.2. Building capacities of the Prefecture for performing safety assessment of temporary storagesites ................................................................................................................................................ 40
6.4.3. Safety assessment for a “model” temporary storage site ..................................................... 40
6.4.4. Trial safety assessment of temporary storage site in Fukushima Prefecture ....................... 43
6.4.5. Safety assessment for nine representative temporary storage sites ..................................... 43
6.5. Retrieval strategies for waste stored in temporary storage sites and decommissioning of
temporary storage sites ...................................................................................................................... 44
6.6. Section Summary ....................................................................................................................... 44

7.

Report Summary ........................................................................................................................... 46

| 1

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 (hereinafterreferred 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 a Memorandum of Cooperation. Radiation
monitoring, remediation, decontamination and human health 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 Fukushima 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 andscope of future cooperation, was agreed by the IAEA and the Prefecture. The Practical Arrangements
were signed on December 2012 and are valid for a period of five years after signature, and can beextended by the mutual consent of both sides.
The main role of the IAEA in implementation of these projects is the provision of effective technicalassistance and support based on international experience and best practices.

1.2. Objectives and scope of the cooperation
Practical Arrangements and Modification No. 1 to the Practical Arrangements were signed byrepresentatives of the Prefecture and the IAEA in December 2012 and April/May 2016, respectively.
The objective of the Practical 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 on-going protection of people andthe environment from ionizing radiation resulting from the Fukushima Daiichi accident.

1.3. Topics of cooperation
Section 2 of the Practical Arrangements (as revised in 2016) identified the following areas andactivities 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 of radioactive 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 in analyses ofresults of environmental monitoring and exploration of exposure pathways in order to reduceor avoid exposure; and Research and study on the management of radioactive waste including IAEA’s assistance inthe study on management methods of low level radioactive waste from the above-referenced
decontamination activities.
Cooperation under the Practical Arrangements is designed to complement existing Japanese activities
and to provide immediate assistance and support which will be of direct benefit to those living in the
Fukushima Prefecture.

2 |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 the Prefecture, experts from Japaneseinstitutions, 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 theplanning, implementation and evaluation of the results of activities conducted by the Prefecture, which
was based on IAEA Safety Standards and good international practices. During several missions to thePrefecture, site visits were made to various locations such as temporary storage sites, freshwater
demonstration projects, and forest monitoring and management projects. Additionally, softwaredeveloped by the IAEA was modified so that it could be used by the Prefecture to evaluate the safetyof temporary storage sites for radioactive waste.
This 5 Year Summary Report summarizes the current status and progress made in the cooperation
conducted under the Practical Arrangements and activities undertaken by Fukushima Prefecture from2013 through 2017. The body of this report is organized in 5 main sections that correspond to the main
points of Section 2 of the Practical Arrangements.

2. Use of Environmental Mapping Technology for Data Gatheredby Unmanned Aerial Vehicles and Walking Surveys
The Prefecture identified a need to conduct radiation monitoring in areas that are not accessible byother survey methods, such as car-borne surveys. Consequently, the Prefecture developed amethodology for a walking survey and for the use of Unmanned Aerial Vehicles (UAVs) in areas thator not accessible on foot, or where high radiation levels might exist. Significant assistance wasprovided to the Prefecture in both these projects. This included the provision of a UAV capable ofmaking radiation measurements under another IAEA cooperative project “Rapid Environmental
Mapping with UAV”, which is administered by the IAEA Department of Nuclear Applications.
While the use of monitoring data collected from walking surveys and the use of UAVs formed a partof discussions under this project, the design and development aspects of walking surveys and of a
UAV capability falls outside the scope of the project and is not addressed further in this report.

| 3

3. Long Term Monitoring of Radioactive Material in Forests andAssociated Countermeasures
3.1. Background and objectives
Forests cover approximately 70% of the surface area of the Prefecture. They are used extensively forleisure activities and are also an important economic resource as they provide timber used in theconstruction of dwellings. Forests also help to prevent sediment discharge, landslides and other natural
disasters. In contrast to the situation in Europe, many 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 is consequently
thin compared to European forests. However, in comparing European and Japanese forests, the moregeneral movement of both nutrients and radionuclides are expected to be similar.
In Japan, berries, mushrooms and wild meat are not widely consumed by the public as they are inEurope. However, some Japanese forests are a source of “forest vegetables” (sansai) which arecollected for human consumption.
From studies undertaken in the aftermath of the Chernobyl accident it is known that forests have ahigh interception capacity for all air-borne pollutants. From the time when the Practical Arrangements
were signed in 2012, the Prefecture assessed that the most significant radiological hazard to people
was that from external radiation emitted by 137Cs and 134Cs (collectively referred to herein asradiocaesium), which was present in both the terrestrial and aquatic ecosystems. The half-life of 134Cs
is approximately two years; 137Cs decays more slowly with a half-life of approximately 30 years. Both137
Cs and 134Cs were released to the environment in approximately equal amounts following the
Fukushima Daiichi accident. 137Cs was also released into the environment as a result of the aboveground testing of nuclear weapons that took 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. The Prefecture
concluded that radiocaesium levels in the environment, and associated doses to people would 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 sediment profiles.
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 livingorganisms changes with time.
In this area of cooperation, the Practical Arrangements focused on research and study on radiation
monitoring, including application of environmental mapping technology by using unmanned aerial
vehicles; long term monitoring of radioactive materials in the forest areas, and associatedcountermeasures and the IAEA’s assistance in the use of radiation monitoring data to develop maps tobe made available to the public.
As part of the cooperation, the IAEA also provided advice to the Prefecture on the long termmonitoring of radiocaesium in forests and associated countermeasures performed by the Prefecture in
relation to characterizing the distribution of radiocaesium, establishing radiation monitoring
programmes, reviewing the effectiveness of countermeasures, providing advice on the Satoyama
Rehabilitation Model Project, addressing countermeasures for reducing radiation exposures of forest
workers, assessing the radiological effects of forest fires, and assessing the implications ofradiocaesium transfer to forest mushrooms and bamboo shoots.

4 |FIG 3.1: Coniferous forest in Tokiwa district (Image credit: Fukushima Prefecture)

3.2. Monitoring programmes
A long term monitoring programme in forests has been established by the Prefecture to track the rateof reduction of 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 howthat changes with time.

3.2.1. Air dose rate
The number of monitoring locations in forests for air dose rate has been extended each year by thePrefecture since the accident and at the end of 2017 totalled 1,300 (See Table 3.1.). The monitoring
locations are within forests in Fukushima Prefecture including prefectural forest and private owned
forest.

TABLE 3.1. Forest monitoring sites established in the Prefecture (Fukushima Prefecture)
Year
2011
2012
2013
2014
2015
2016
2017

Number of Monitoring
Sites Added
563
81
187
37
20
50

Total Number of
Monitoring Sites
362
925
1,006
1,193
1,230
1,250
1,300

Based on measurements made by the Prefecture, the air dose rate averaged over all survey points forthe reference date of 1 March 2017 was 0.42 µSv/h; the maximum air dose rate from an individual
monitoring site was 4.59 µSv/h and the minimum was 0.03µSv/h. Compared with August 2011, the air
dose rate overall has decreased by about 70%. When only the original 362 monitoring locations thatwere established in 2011 are considered, between August 2011 and March 2017, the number of survey
points with measured air dose rates of less than 0.23 µSv/h increased from 42 to 309; also, the number

| 5of survey points with measured air dose rates of greater than 1 µSv/h decreased from 127 to 61. These
results are broadly in line with the reduction of air dose rate due to radioactive decay of radiocaesium.
See Fig. 3.2, which shows measured air dose rates, estimated air dose rates based on the radioactive
decay of radiocaesium, and estimated air dose rates in the future at 362 monitoring points in forests
within the Prefecture. There are indications that the measured air dose rate is decreasing faster thanwould be predicted due to radioactive decay.

FIG 3.2: Measured air dose rates, estimated air dose rates based on radioactive decay ofradiocaesium, and estimated air dose rates in the future at 362 monitoring points in forests
within the Prefecture (Fukushima Prefecture)
These data can be used to predict air dose rates in the future. Assuming air dose rates continue to fallin line with the radioactive decay of radiocaesium and no remediation work is undertaken, for the
majority of monitoring sites outside the evacuation zone will be below 0.23 µSv/h1 by March 2031,
i.e. 20 years after the Fukushima Daiichi accident.
The combination of mountain terrain and rainfall tends to increase the mobility of radionuclides andthese will quickly move downhill (both physico-chemically and mechanically) and future radiation
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 one or two years following the Fukushima Daiichi accident, but they have slowed down withtime. Monitoring programmes should be continued at least until a stable situation is reached, but it isdifficult to predict when that might be; some fixed sites established after the Chernobyl accident are___________________________________________________________________________
1

An air dose rate of 0.23 µSv/h corresponds to an additional annual effective dose of 1 mSv above the natural
background dose

6 |still being monitored and continue to provide new and important information. The frequency ofmonitoring could be reduced with time, but data should continue to be collected for many more years.

3.2.2. Radiocaesium in forest trees
The sampling programme for radiocaesium in timber conducted by the Prefecture includes separate
measurements of bark, sapwood, heartwood, old leaves and new leaves. At a number of sites, soil isalso collected by the Prefecture and measured for radiocaesium. In Japanese cedar trees, theconcentration of radiocaesium is higher in the heartwood than in the periphery. Over time, the datacollected by the Prefecture indicated that radiocaesium attached to old leaves is gradually shifting to
the forest floor due to leaves falling from trees. The air dose rate that would result from trees having
radiocaesium concentrations exceeding 8,000 Bq/kg was estimated for various species of trees.2 The
value that resulted from this process, measured at a height of 1 m, was 1.33 µSv/h. It should be noted
that, while such estimated values have significant uncertainties associated with them, they provide a
useful and rapid means for making decisions on whether or not trees can be felled and harvested. Thisis discussed further in section 3.6 ‘Managing the timber industry’.

FIG 3.3: Collecting samples of wood for analysis (Image credit: Fukushima Prefecture)
The radiocaesium content of saplings planted in 2013 has been evaluated by the Prefecture. The
saplings were planted 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 these experiments
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 be available for uptake.
(See section 5.2 of this report for further information about the behaviour of radiocaesium in theenvironment.)

3.3. Distribution of radiocaesium in forests
The data collected by the Prefecture indicate that radiocaesium that is present in coniferous anddeciduous forests is distributed mainly among soil and the litter layer and trees. Through ecological___________________________________________________________________________
2National legislation requires any material that exceeds an activity concentration of 8,000 Bq/kg of radiocaesium to be

managed as radioactive waste, and such waste is considered ‘designated waste’. Details on the selection of thethreshold of 8,000 Bq/kg for designated waste and the reasons for targeting radiocaesium are described in Guidelines
for Processing Waste Contaminated by Nuclear Accident-Derived Radioactive Materials, Ministry of the Environment(2013).

| 7

cycling of materials within these forest types, radiocaesium has been redistributed such that by 2016,
approximately 97% of the radiocaesium in the forests of the Prefecture was located in the soil andlitter (fallen needles or leaves) layers, with the remaining approximately 3% distributed among thetrees (see Fig. 3.4). 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 toreduce the air dose rate should be focused on the soil component. Another conclusion that 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 productivity of the forest and could havean overall negative impact; it would also create additional waste that would need to be managed.

Percentage of radiocaesium

Coniferous forests
100%
80%
60%

Trees

40%

Soil

20%
0%

Fallen needles
2011 2012 2013 2014 2015 2016
Year

Percentage of radiocaesium

Deciduous forests
100%
80%
60%

Trees

40%

Soil

20%
0%

Fallen leaves
2011 2012 2013 2014 2015 2016
Year

FIG 3.4: Change in distribution of radiocaesium in the Prefecture’s coniferous forests anddeciduous forests from 2011 to 2016 (Ministry of Agriculture, Forestry and Fisheries, and the
Fukushima Prefectural Forestry Research Centre)
A soil survey undertaken in forests by 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 low transferof radiocaesium from soil to forest plants and animals. However, if there are any parts of thePrefecture where these clay minerals are absent, much higher transfer factors, and consequently higher
concentrations in trees, understory vegetation and animals, would be expected.

8 |Experiments undertaken by the Prefecture have shown that radiocaesium is recycled within the forest
ecosystem and losses of radiocaesiumarea fraction of a percent per year. Measurements have shownthat the quantity of radiocaesium in water flowing into reservoirs with urban catchment areas is fourtimes higher than water from forested catchment areas.
Some outflows do occur through sediment transport, with the radiocaesium being attached to the clay
minerals in these sediments. (Additional information about the behaviour of radiocaesium in theenvironment including the importance of sediment transport is provided in sections 5.2, 5.3 and 5.4.)
Research undertaken by the Prefecture 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 likelihood of
sediment discharge and landslides.

3.4. Effectiveness of forest countermeasures
Various countermeasures concerning radioactive material in forests have been evaluated by thePrefecture 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% to 12%.
The removal of deciduous trees to aid in the regeneration of understorey vegetation in 2012
resulted in a reduction of air dose rates of 11% to 21%.
The addition of 3 cm of uncontaminated soil (in ‘liquid’ form) or wood chips resulted in a
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%.

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 of understory
vegetation. This in turn helps to bind the soil and prevents erosion. In 2011 and 2012, both of thesecountermeasures 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 the ensuing years, whenmost of the radiocaesium content of forests had migrated to the soil and litter layers, this practice wasless effective in reducing air dose rates.

| 9

FIG 3.5: Application of wood chips as a countermeasure to reduce the air dose rate in aforest (Image credit: Fukushima Prefecture)
Based on the findings by the Prefecture, 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 if suchareas are close to inhabited areas.
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 arestill concerned about radiocaesium being transferred to agricultural land and rice paddies. 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 thatsuch measures are effective in preventing soil erosion and run-off, particularly when the slope of theterrain is 30 degrees or greater. Any radiocaesium lost through sedimentation is likely to be associatedwith clay minerals and, as such, may not be available for transfer to agricultural soils. At the sametime, air dose rates may increase in areas where sediment accumulates.
Air dose rates near inhabited areas may be reduced through a combination of litter removal, branchremoval and topsoil removal. While the addition of soil/wood chips has been shown to be an effective
countermeasure, it is presently not in routine use. A priority is to install log fencing on higher groundto prevent soil erosion and subsequent recontamination of decontaminated areas.

3.5. Satoyama Rehabilitation Model Project
Satoyama is the border zone or area between mountain foothills and arable land and usually consists offorests, grasslands, rice paddies, etc. The people who live in or close to these areas are often selfsufficient 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 live in these areas as they did
before the Fukushima Daiichi accident. Ten communities within the evacuation zones andneighbouring municipalities were selected for participation in the project between September andDecember 2016. The project has three main components: forest maintenance and decontamination;
production of radiation dose maps and performance of personal dosimetry surveys; and the provisionof public information. The IAEA team noted that the effectiveness of countermeasures in these areas
may be limited and that consideration should be given to defining how the success of the project will
be evaluated. As of 2017, the project was in the initial stages of implementation.

3.6. Managing the timber industry
National legislation requires any material that exceeds an activity concentration of 8,000 Bq/kg ofradiocaesium to be managed as radioactive 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 is commonly used as afertilizer and as fuel for biomass plants. It is important to ensure the timber industry is effectively
managed as the wood is an important economic resource used for the construction of new housing, as
well as window frames, household furniture, etc.
Measurements have been made by the Prefecture in an attempt to correlate air dose rates with theradioactivity concentration in bark. As would be expected, wide variability in such measurements wasobserved. An air dose rate of 1.33 µSv/h roughly corresponds to 8,000 Bq/kg in bark, but a range ofvalues from 0.65 to 4.59 µSv/h was observed. The Prefecture had adopted the criteria whereby, inareas where the air dose rate is below 0.5 µSv/h, the trees can be felled and processed without
restriction. If the air dose rate exceeds this value, a sample of the bark must be analysed to determine

10 |the actual activity concentration of radiocaesium. This is a conservative approach, but it seems to work
well.
An additional criterion is to restrict the activity concentration of radiocaesium in firewood to 40 Bq/kg,
which would ensure that the radionuclide concentration of the ash does not exceed 8,000 Bq/kg. The
concentration factor between wood and ash is normally 100 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 for existingtrees; however, experts from the Prefecture presented the results of experiments indicating that theradiocaesium content of newly planted saplings was only a few hundred Bq/kg. As the time for trees toreach maturity is around 50 years, any possible increased uptake 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 comewithin the rooting zone of trees, but one would expect that it will be effectively bound to the 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 duration of these changes.
The highest concentration of radiocaesium measured to date in wood by the Prefecture is 5,500 Bq/kg.
Using the methodology outlined in IAEA TECDOC-1376, Assessing radiation doses to the publicfrom radionuclides in timber and wood products, if such wood were used for house construction, theannual dose to occupants is estimated to be 0.132 mSv. Scaling up, at 8,000 Bq/kg, the annual dosewould be about 0.2 mSv. Due to the conservative nature of the models used, any differences inJapanese house design would not be expected to significantly increase these estimated doses.
Therefore, no additional restrictive measures are deemed necessary at this time to allow timber fromthe 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 translocation of radiocaesium
within trees and the transfer to newly-planted saplings are continued.

3.7. Protection of forest workers against radiation
Forest workers are potentially at risk of exposure to radiation doses. Currently these workers areprovided with gloves and face masks to help minimize their exposure. They are not classified 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 thevalue 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 the operator fromradiation. Also, cabins on certain forest machinery that enclose the operator provide shielding that
reduces worker doses by about 35% – 40%.

3.8. Forest fires
IAEA-TECDOC-1240, Present and future environmental impact of the Chernobyl accident, states“There is thought to be some risk of radionuclide dispersion onto the adjacent territories as a result of
forest fires. However, the available data on radionuclide transfer during forest fires are contradictory.”
The report also states “The main problem produced by forest fires is the re-suspension ofcontaminated ash in the atmosphere.”

| 11

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, whichleads to an increase in the amount of material available for combustion. Following a fire, radionuclides
can be transported over several hundred kilometres through the dispersion in the atmosphere of ash towhich radioactive material is attached. The radiation exposure pathways are external radiation andplume inhalation (firefighters and the public); external radiation from deposited radionuclides (public);
ingestion of contaminated food products (public); and inhalation of radionuclides in resuspended ash
at the site of the wildfire (forest workers and the public).
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 ismobilized during a forest fire. Considering that as of 2016, only about 7% of the radiocaesium present
in the Prefecture’s forests was located in the litter, it would be expected that only a very small
percentage of the total radiocaesium inventory would be mobilized in the event 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 a crown fire, this amount could increase to10%. 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 thefire would not be expected. While forest fires may not disperse large amounts of radionuclides, fires
may damage the capability of the forest to retain soil that may be lost through erosion, and fallen
leaves and needles 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 is present,
which could be transported in the atmosphere. The remainder of the radiocaesium will be found in theash. Even if deposited in rivers and streams, the radiocaesium will be quickly fixed to solid matter andthe impact on biota is likely to be minimal. The impact of forest fires is usually evaluated throughmodelling, in part because the collection of real-time data is problematic due to the hazards associatedwith, and the unpredictable nature of, forest fires. A number of different models for this purpose
already exist. It was noted by the IAEA team that most models overestimate the actual impact of forest
fires and therefore it is important to perform sensitivity analyses by varying parameters and associatedassumptions. It was noted that differences in soil type and topography may lead to a forest fire in the
Prefecture having a lower radiological impact than in the areas affected by the Chernobyl accident.
A number of forest fires have occurred in the Prefecture since 2011, which resulted in public anxiety.
Fukushima 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 firenear Minami-soma City that affected about 32 ha and burned during 3 – 4 April 2016; and (3) a firethat occurred inside the Evacuation 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 water andmountain 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 notdetected 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 than that in unaffectedareas.
As of July 2017, the preliminary assessment conducted by the Prefecture of radiation survey resultsfrom the Namie Town fire indicated that the fire did not have a significant radiological impact in that
only slight increases were observed in air dose rates at nearby measuring points. Further work was12 |planned to assess the extent to which ash may have been deposited in the river passing close to theburnt 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 amountof radiocaesium could have been redistributed.

3.9. Radiocaesium transfer to forest mushrooms and bamboo shoots
The Prefecture is the principal producer of Shiitake and Nameko mushrooms in Japan. These
mushrooms are grown on rotting wood and therefore tend to contain lower radiocaesium
concentrations than those that grow in forest soil.
There are presently restrictions in place within the Prefecture on the shipment of Shiitake mushrooms
from 17 municipalities, bamboo shoots from 27 municipalities and wild mushrooms from 55
municipalities. 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.
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, although chemical fixation by clay minerals will also need to beconsidered. Some surveys and verification experiments might be helpful in identifying long termissues of concern.
Issues to be considered in the future are the production and the use of raw wood from the Prefecture’s
forests, and the prediction of the transfer of radiocaesium from oak logs to shitake mushrooms, which
are a valuable economic product of the Prefecture’s forests.

3.10. Section Summary
An extensive work program has been undertaken by the Prefecture to better understand the behaviourof radiocaesium in forests. When comparing the situation with that which occurred following theChernobyl accident, the more general mechanisms of recycling 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.
The key conclusions which the Prefecture derived from this programme to date are:
 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 below.
 Forest maintenance procedures have helped to prevent erosion and soil-loss and are also very
effective at retaining radiocaesium within forests.
 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 same deposition,
based on measurements undertaken by the Prefecture, the activity concentrations ofradiocaesium in plants and animals in the Prefecture’s forests are considerably lower thanthose observed in European forests after the Chernobyl accident.
 Based on experience with radiation monitoring in areas affected by the Chernobyl accident,
radiation monitoring in forests may be necessary for many more years and monitoringprocedures for measuring air dose rates and the radioactive content of trees may need to be| 13adjusted to account for changing conditions such as the movement of radiocaesium in theenvironment and the deposition of radiocaesium in waterlogged areas where the uptake byvegetation would be higher.
 Since 2012, most of the radiocaesium initially deposited in forests has been transferred fromthe trees to the soil and litter layers. The feasibility of removing large amounts of soil in orderto 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.
 Covering the forest floor with soil or wood chips that has no radiocaesium is an effectivemeans of reducing air dose rates. However, such procedures are expensive and their long term
effectiveness should continue to be evaluated. Regardless, it may be justified to apply themover limited areas with high air dose rates, especially if such areas are close to inhabited areas.
 Various issues should be addressed in the early stages of the Satoyama Rehabilitation Model
Project such as the possible generation of radioactive waste, the effectiveness ofcountermeasures, and defining how the success of the project will be evaluated.
 To date there appears to be no need to restrict the production and use of the timber harvested
from forests. However, monitoring of timber should continue, especially as work commencesin areas with higher concentrations of radiocaesium.
 Measures have been implemented to restrict the radiation exposure of forest workers; theseinclude 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.
 Studies of forest fires conducted by 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 when moreof the radiocaesium inventory was in the litter layer and available to be redistributed as aresult of forest fires.
It is important that monitoring programs are maintained by the Prefecture so that any unforeseenchanges in the behaviour of radiocaesium in forests is quickly identified and addressed. If survey data
indicates that air dose rates over time are relatively stable, it may be justified to reduce the number ofsamples collected and monitoring points maintained.

4. Use of Radiation Monitoring Data to Develop Maps to be Made
Available to the Public
4.1. Background and objectives
In this area of cooperation, the Practical Arrangements focused on the IAEA’s assistance in the use ofradiation monitoring data to develop maps to be made available to the public.
As of the commencement of activities under the Practical Arrangements in 2013, the Prefecture
maintained a website that made radiation monitoring data available to the public. The website
provided detailed information on air dose rate measurements and measurements of radioactivity
concentrations in material from several different sources, including: Over 3,500 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.

14 |As of 2014, the number of site visitors was approximately 20 to 50 thousand per month. The
Prefecture gathered a number of recommendations from these users about how the website could be
upgraded to better meet their information needs. The Prefecture also consulted with the public througha survey about ways in which the website could be improved. There was a clear wish for simple, easy
to understand information, compatibility with mobile technology, and an explanation of the healthrisks.
The IAEA team presented information about web maps that have been developed in a number ofcountries and provided various technical advice concerning the mapping of radiation monitoring dataand presenting such information to the public.

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4.2. Development of revised website
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 for these 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 important consideration. Also, other factors
may introduce apparent differences in the results of surveys such as a large variability in the air dose
rates between seasons (e.g. because of 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 arelikely to be within the experimental error of each measurement. It was considered that infographics
might be useful for explaining these differences. It was also noted that a decision should be made on
the frequency with which these datasets are to be updated on the website.
In December 2015, the Japan Atomic Energy Agency (JAEA) presented their mapping project at a
joint meeting of the IAEA team and Fukushima experts. An environmental monitoring database has
been developed by standardizing and integrating data from several different organizations. As of 2015,
the database included over 400 million data points covering air dose rate, soil (activity concentrationand deposition), dust, water, and terrestrial and marine foods.

Discussion on Website Development
The IAEA team made available a review of web maps in Austria, Belarus, Canada, China, European
Union, France, Germany, Russia, Turkey and Ukraine. Most national maps are based exclusively on
data from fixed monitoring locations; while walking surveys might be undertaken, they are typically
only used for detailed monitoring of small areas. These maps are normally not published on publicly
accessible websites or merged with other datasets. The work being undertaken by the Prefecture
therefore seems to be unique.
As part of detailed discussions the following main points were covered: There are two development projects to be considered: an appropriate mapping tool is required
and this is to be used within a redeveloped website. It is important to identify both componentsof 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 thework 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 and infographics.
The promotional role of the website as part of an overall communications strategy is also
important.
 It is preferable to keep the website and maps simple and intuitive. Many people are notfamiliar with radiation protection terminology and concepts, and for them the message is more
important than the numbers. In order to keep the website simple, the value of including air
dose rate data from other prefectures on the map should be considered. Also, administrative
boundaries in the Prefecture could be integrated into the map.
 For those who require more detailed information, such as on units of measurement, radiation
risks, etc., this can be provided through a separate link, or through the use of explanatory
graphics.
 The importance of large scale overview maps was discussed, as was the importance of maps
showing localized/detailed information. One suggestion was to use “clickable” maps where16 |one could access progressively more detailed maps by clicking on an area of interest on a map.
Scalability of grid sizes must be considered.
 It is important to emphasize and make readily available the most important information, which
is usually the most recent information.
 Historical data is valuable in demonstrating how the radiation doses have decreased since
March 2011. Where possible, this data should be retained and used. In particular, air dose rates
prior to the Fukushima Daiichi accident should be made available.
 It would be helpful to include some data from “high natural background” areas in the world,
for comparison with the current air dose rates in the Prefecture.
 The concept of having “key messages” on the website was considered useful and it was notedthat these might need to be regularly updated.
 The Google Application Program Interface (API) currently used may not provide sufficient
flexibility and other APIs (such as java script, Environmental Systems Research Institute(ESRI) or open layers) should be considered.
 All maps should be consistent in the use of data schema, colour codes, ranges, etc. Where
possible, the lower end of the lowest range should be as close to natural background as
possible.
 A time slider is a very useful way to show progressive reduction in air dose rates andincorporating such a feature should be considered.
 Greater public interaction can be encouraged through links to social media.
 It is important to consider the weighting to be assigned to each dataset in developing theoverview maps.
 It might be desirable to provide automatic access to the GPS location from which access ismade, i.e. people can see the exact radiation situation in the location where they are at the time.
 Adding a search parameter of ‘dose rate’ should be considered.
 In the future it might be desirable to map the air dose rates in the forests, which represent 70%of the surface area of the Prefecture. While no permanent fixed monitoring sites are located in
the forests, the data from the network of measurement stations established by the forestry
group might be used.
 There are a number of areas within the Prefecture with relatively high thorium concentrationsin the soil. As a result, the background air dose rate may be highly variable across thePrefecture and the use of one standard value for all air dose rate charts may be misleading.
Data on the potassium, uranium and thorium concentrations in soils are available on thewebsite of the Japan Geological Society – this may allow calculation of the actual air dose rate
at various locations.
 It is essential to provide sufficient background information to support interpretation andunderstanding of the available maps.
 The JAEA and the Prefecture datasets can be used separately (i.e. separate maps), they can bemerged directly, or the raw data can be merged and new maps developed. As the scales andcolour coding of the JAEA and the Prefecture maps are different, it was agreed that the optionof merging the information and creating new maps is probably preferable.
 It is suggested that the Prefecture decides what information will be made available to the
public on its new website, for example whether it will be possible only to download theexisting maps or whether the raw data will be made available to allow individuals to prepare
their own maps. In deciding this issue, a balance must be achieved between the benefits oftransparency versus the risk of misuse of the data. The IAEA team advised that, in theirexperience, data are seldom intentionally misused but accidental misuse and misinterpretation
should be considered and factored into a final decision.



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4.3. Final website design
Following the revision of the website, a presentation on the completed work was made by the
Fukushima experts at the joint meeting held with the IAEA team in June/July 2016. Much of theadvice received from the IAEA team has been applied to the development of the design andfunctionality of the new website. Fukushima experts confirmed that the monitoring data collected aspart of the car-borne surveys has been normalized to 1 m above ground in outdoor air. The new
website 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 associatedwith specific locations and to specify dates of interest. Clickable maps allow users to access data from
specific points on a map (See Fig. 4.1). Air dose rates and the results of environmental samples are
displayed on the same map. The variation of air dose rates with time can be accessed intuitively
through the use of a “time ruler” (See Fig. 4.2). Also, the revised website has the capability to present
the transition of doses over time through the generation of graphs (See Fig. 4.3). In addition to theJapanese, the website is also available in English, Chinese and Korean. The English language portal
for the revised website can be found at this web address: http://fukushima-radioactivity.jp/

FIG. 4.1. Clickable Radiation Measurement Map (Fukushima Prefecture website)

18 |FIG. 4.2. Time ruler from Radiation Measurement Map (Fukushima Prefecture website)

FIG. 4.3. Graph of measurement data from a specific measuring point over a specified
timeframe from Radiation Measurement Map (Fukushima Prefecture website)

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4.4. Section Summary
The Prefecture recognized that 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. Specifically, thePrefecture identified that while overview maps give a general view of how air dose rates are reducing
with time, people also want more localized information regarding the location where they live, work
or are visiting. The Prefecture’s 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 ensuringthat historic data is also available for those who wish to review it.
Radiation data have been collected in a number of different ways, each of which uses different
measurement methodologies. Over 3,000 monitoring stations provide continuous data from fixedlocations 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).
The Prefecture recognized the challenges of presenting different datasets that were collected undervarying conditions that could affect the results. For example, the air dose rate on a road is unlikely tobe identical to that on a nearby footpath and snow cover in winter will reduce the air dose rate, which
will increase when the snow melts. The height above ground at which the measurement is made andthe speed of car travel compared with an individual undertaking a walking survey also needs to betaken into account.
Several steps were necessary so that the public could access radiation monitoring information from thePrefecture 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 and other data. All of these issues
were discussed in detail between the IAEA team and Fukushima experts in IT, public information
strategy and radiation measurement.
The IAEA team noted that the provision of information through a website is only one component of acommunications strategy.
The Prefecture identified the growing demand for the Prefecture to provide information and advice topotential returning evacuees on the expected reduction in air dose rate with time and the associatedhealth risk. The presentation of such information must take account of reductions due to the physicalhalf-life of radiocaesium and also the effectiveness of any applied countermeasures. Such calculations
are site-specific and the uncertainties in the estimates of the future situation must also be provided.
The Prefecture recognized that such information cannot easily be provided through a website and thatfurther consideration will be necessary on how the Prefecture can best meet these requests.

5. Off-Site Decontamination and Environmental Monitoring
5.1. Background and objectives
According to data collected and an assessment conducted by the Prefecture, significant amounts ofradioactive fallout were deposited in the Prefecture as a consequence of TEPCO’s Fukushima Daiichi
accident, especially in the area northwest of the Fukushima Daiichi Nuclear Power Plant. During thetime period in which the Practical Arrangements were active, the Prefecture identified that the mostsignificant radiological hazard to people was from external radiation emitted by radiocaesium. (Seealso section 3.1 for further information about radiocaesium in the environment). Based on data

20 |collected, the Prefecture determined that radiocaesium levels in the aquatic and terrestrial ecosystems,
and associated doses to people have declined because of decontamination activities, radioactive decay,
and the removal of radiocaesium by weathering from surfaces and vertical migration down soil andsediment profiles. Figure 5.1 shows air dose rates in the Prefecture at a height of 1 meter on August 28,
2011 (5 months post-accident) and November 18, 2016 (5 years and 8 months post-accident). These
dose rates were calculated by using data obtained from aircraft monitoring. The Prefecture concluded
that the significant decrease in dose rates was due to decontamination activities, radioactive decay, andthe removal and movement of radiocaesium caused by natural processes.

FIG. 5.1. Air dose rates in the Prefecture at a height of 1 m on August 28, 2011 andNovember 18, 2016 (Image credit: Fukushima Prefecture)
The Prefecture recognizes the need for remediation and decontamination depends to a large extent on
the evolution of doses to members of the public over time. Decisions relating to remediation activities
are based on an assessment of future doses that would be reduced by remedial actions and those thatwould occur without intervention. It is therefore helpful to make predictions regarding changes overtime in air dose rates and doses to people.
Item 2 of the Practical Arrangements focuses on research and study of off-site decontamination
including the IAEA’s assistance in analyses of results of environmental monitoring and exploration of
exposure pathways in order to reduce or avoid exposure. The cooperation addressed the following
topics for which the IAEA provided technical advice: Behaviour of radiocaesium in the terrestrial and aquatic ecosystems in the areas of thePrefecture affected by the Fukushima Daiichi accident; Effectiveness of remediation and decontamination measures for aquatic systems;
 Analysis of monitoring results in order to identify time trends of radiocaesium concentrations
in environmental media (soil, water, sediments) and of the air dose rate;

| 21 Review of experience gained from remediation activities in order to elaborate input for theselection 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.
These topics are addressed in the following sections of this report.

5.2. Behaviour of radiocaesium in the natural environment
Global experience with radiocaesium in the natural environment
Radiocaesium has been released to the natural environment by atmospheric nuclear weapon tests,
operations of nuclear facilities, and as a consequence of accidental releases. In general, in theterrestrial ecosystem, radiocaesium is strongly bound by mineral soil components, which results in its
slow movement in soil and a low uptake by plants from soil. However, in acidic, organic soils withlow potassium content, radiocaesium uptake by plants is much higher. In tropical areas, where soils
are subject to physical and chemical weathering over thousands of years, clay minerals have largely
disintegrated with potassium leaching in acidic conditions and may no longer be present in significant
quantities; therefore, the uptake by plants may be much higher.
In freshwater ecosystems, caesium binds strongly to suspended sediments, which causes a rapid
decline in dissolved radiocaesium, and the ultimate deposition of caesium that is bonded to sedimenton the bottom of bodies of water. The transport of radiocaesium in rivers and lakes is largely causedby the redistribution of sediments. Because radiocaesium in dissolved form is readily taken up by
freshwater biota and readily absorbed by particles and suspended sediments, the amount in freshwater
systems depends on radiocaesium sorption, sedimentation and uptake by biota.

Caesium behaviour under the environmental conditions of the Prefecture
The behaviour of radiocaesium under the environmental conditions in the Prefecture has been thesubject of many studies carried out by the Prefecture since 2011. These studies have addressed thelong term behaviour of radiocaesium in soil including the uptake by crops and the downward
migration in soil profiles. Due to the strong sorption of radiocaesium in soil, in agreement with global
experience, both the downward migration of radiocaesium in soil and the uptake of radiocaesium
through crops from soil are very low. Radiocaesium in soil is gradually bound with soil components,
especially clay particles. This sorption may be reversible, which constitutes the fraction of
exchangeable radiocaesium, or, largely irreversible, which constitutes the fixed fraction.
According to studies conducted by Fukushima University, the proportion of the exchangeable fractionof radiocaesium in soils continuously decreased over time, and the radiocaesium levels in crops havecontemporaneously decreased since 2011. For the prevailing soil types of the Prefecture, theRadiocaesium Interception Potential (RIP), which characterizes the ability of a soil to selectively
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 Chernobyl accident to predict the radiocaesium uptake by crops based on soil
parameters. In soils with a low RIP value, the application of clay can be effective in reducing thetransfer to crops.
The studies of research institutions (e.g. Fukushima University) indicated that very limited amounts of90
Sr were released during the Fukushima Daiichi accident, and that, except for the immediate vicinityof the Fukushima Daiichi Nuclear Power Plant, 90Sr concentrations in farmland and crops were nearly
equal to those resulting from fallout of atmospheric nuclear weapons testing in the 1960s.

22 |The study performed by the institutions, including Fukushima University, estimated internal doses due
to ingestion of agricultural products in Fukushima City and Date City, are on the order of a few tens ofμSv per year, which does not modify the dose estimates for people significantly.
International experience with the behaviour of 137Cs in the environment and environmental
remediation projects was provided by the IAEA team. Following the Chernobyl accident and the
Fukushima Daiichi accident it was observed that natural attenuation processes contributed to the
reduction of radiation levels and to the decline of radioactivity levels in the environment. However,
the wash-off of radiocaesium was observed to be higher in the Prefecture than in areas affected by the
Chernobyl accident due to: Greater rainfall precipitation from the occurrence of typhoons and higher temperatures;
 Greater biological activity;
 Longer frozen periods in Chernobyl;
 Steeper slopes of hill sides.
All these factors significantly affected 137Cs wash-off from the contaminated watersheds in the
Fukushima Prefecture.

5.3. Results of monitoring programmes
Transport processes
The transport of radiocaesium from a catchment area via a river or a river system is illustrated
schematically in Figure 5.2. Radiocaesium is deposited in forests, and 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. The figure also indicates the interaction between theterrestrial and the aquatic ecosystems as well as the possible transfer routes to agricultural products.
The following processes are important: Radiocaesium is removed from forests, residential and agricultural areas through run-off,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, river flooding and turbulent flow can affect previous deposits ofradiocaesium bound to sediments.
 Some amounts of radiocaesium will be transported to the ocean.

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FIG 5.2. Illustration of radiocaesium transport through a catchment area and interactions
with terrestrial elements (Image credit: Fukushima Prefecture)
Caesium in water and sediments
In the Prefecture, river water is widely used as a source of water for the city water consumption, foragricultural activities and other purposes. Therefore, the Prefecture established a comprehensive
programme to monitor radiocaesium in freshwater bodies, which is performed by the Fukushima
Prefectural Centre for Environmental Creation.
The programme of survey includes the measurement of radiocaesium dissolved in water as well asradiocaesium bound to suspended sediments in rivers and lakes. Due to the strong sorption ofradiocaesium by suspended sediments and its deposition on the bottom of water bodies, radiocaesium
levels in river water declined considerably with time and have reached a safety level which allows its
use as drinking water.
Beyond the general surveillance of radiocaesium levels in water, the monitoring programme
conducted by the Prefecture focuses on studying the long term behaviour of radiocaesium in thecatchment areas of the Prefecture, and specifically on two aspects:
 Levels and the behaviour of radiocaesium associated with suspended particles. This includes
the deposition or removal of radiocaesium bound by sediments and floodplain soils during
floods including the effects on air dose rates.

24 | Radiocaesium in its dissolved form, i.e. transfer to agricultural products, wild animals andplants via the accessible ecosystem. Further studies will also be focused on better
understanding of the dynamics of particulate and dissolved radiocaesium.
In addition to the radiocaesium levels in water and sediments, for characterizing the physico-chemical
properties of the water, the concentrations of major ions (potassium, calcium, magnesium, andammonium) are determined.
The measurements made by the Prefecture were focused on the catchment areas that were affected by
the deposition of 137Cs, see Figure 5.3. Emphasis was given to the Hirose River basin, where elevenmonitoring points were set up. The monitoring points were located along the river and its tributaries,
including the Takane River, the Nuno River and the Oguni River, respectively. Beyond the parameters
mentioned above, the measurements included determination of water flow rates, turbidity of water andthe concentration of suspended sediments. As expected, rainfalls coincided – with some delay – withan increase of the flow rate and an increased concentration of suspended sediments. Although there areconsiderable fluctuations with time, the 137Cs levels have decreased continuously since 2011.

FIG 5.3. Distribution of 137Cs-deposition in the Prefecture as determined during the Third
Airborne Monitoring Survey (MEXT, 3 July 2011)
Meanwhile  more than 6 years after the accident  measurements by the Prefecture indicate that
dissolved radiocaesium levels in water are close to or below the detection limit. This can be explainedby the strong sorption of radiocaesium by sediments, in which much higher radiocaesium levels areobserved. There is also a clear decline of the concentration of radiocaesium in suspended sediments,
especially when further erosion from contaminated catchment areas is limited. Radiocaesium
concentrations in sediments tend to increase with decreasing particle size.
Measurements made by the Prefecture showed that radioactivity concentrations in water andsuspended matter in the Abukuma River and its tributaries declined as well. The investigations of thetransport of radiocaesium in rivers within the Prefecture included also the Hamadori and the Nakadori

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districts. Measurements covered more than 30 points; the results for the suspended 137Csconcentrations since 2011 are shown in Figure 5.4. In this figure, solid circles indicate monitoring
points in Kuchibuto River and its tributaries, and open circles indicate monitoring points in Abukuma
River and its tributaries. The suspended radiocaesium levels have decreased continuously since 2011.
During the heavy rainfall event in September 2015, the suspended radiocaesium concentrations
decreased, which was a consequence of the dilution effect caused by the large amounts of sandy
particles in the sediment transport load in the river waters with low adsorption capacities.

FIG5.4. Decline of 137Cs in suspended matter of rivers in the Prefecture from 2011 – 2017
(Fukushima Prefecture)
Since most of the radiocaesium in water bodies is associated with suspended materials in the riverwaters, the measurements allowed  in combination with the data on water flow and sedimenttransport  the estimation of the total flux of radiocaesium from the catchment area to the Pacific
Ocean for the period of 2011 – 2015. The increase of the cumulative loss (i.e. the amount of theradiocaesium transferred into the Pacific Ocean during a certain period) became less and less overtime, and can be observed as a lessening of the slope of the lines presented in Figure 5.5. In this figure,solid circles indicate monitoring points in Kuchibuto River and its tributaries, and open circles indicate
monitoring points in Abukuma River and its tributaries.
An analysis performed by the Prefecture indicated that since 2011, the cumulative loss of 137Cs activity
from the catchments of the Abukuma and the Kuchibuto tributary was about 2.7% (2.5% – 3.0%) and
1% (0.5% – 1.5%), respectively. These small percentages indicate that the reduction of theradiocaesium levels in the natural environment is mainly caused by the radioactive decay ofradiocaesium, and that the run-off of radiocaesium provides only a minor contribution to the reductionof the overall inventory in the catchment (due to wash-off and erosion process affect only the very top
surface layer of the contaminated soils at the water catchments). These results also indicate that theexchange of radiocaesium between different elements of the landscape is limited.

26 |FIG5.5. Cumulative loss of 137Cs from the catchments of rivers in the Prefecture from June
2011 to August 2015 (Fukushima Prefecture)
The measurement campaign by research institutes in Fukushima Prefecture included measurements inreservoirs and the investigation of the 137Cs balance of reservoirs. Measurements performed in 2014
for the Yokokawa dam reservoir included the radiocaesium dissolved in water as well as radiocaesiumin suspended matter. It was observed that the total activity of radiocaesium dissolved in water in the
inflow and in the outflow of a reservoir was very similar. However, the amount of particulate
radiocaesium in the outflow is much less than in the inflow, since the particulate radiocaesium issubject to sedimentation in waters with a very low flow velocity, as is the case in a reservoir. This
example shows that reservoirs act as a kind of sediment trap. This observation is, in principle, also
applicable to lakes.
Since the sorption to suspended matter plays a key role in the behaviour of radiocaesium in the naturalenvironment, efforts were undertaken by the Prefecture to quantify the strength of radiocaesium
sorption to soils and sediments. This is usually characterized by the distribution coefficient (Kd), which
is derived from measurements of radiocaesium in the dissolved and particulate phase. For theinvestigated lake water, Kd-values in the range of 105 to 106 L/kg were measured, reflecting the strong
sorption of caesium to particulates3. The Kd-values increased with decreasing particle size. It was
concluded that, in comparison to the observations of the caesium sorption made after the Chernobyl
accident in Ukraine and the Russian Federation, in general, higher Kd-values for caesium wereobserved in the Prefecture.

Radiocaesium in phytoplankton and zooplankton
The measurements by research institutes in Fukushima Prefecture of radiocaesium in freshwater
bodies of the Hamadori and Nakadori districts included measurements of phyto- and zooplankton and___________________________________________________________________________
3 A distribution coefficient (K ) of, e.g. 1,000,000 L/kg means that the concentration in the sediment is 1,000,000dtimes higher than in water. This indicates a very strong caesium sorption and that the vast majority of the radiocaesium
inventory is bound to sediments.

| 27

their radiocaesium levels. The expected amounts of phyto- and zooplankton were very low. There
were temporal and spatial variations in the amounts of plankton in the water. In the Yokokawa Dam
Reservoir, the concentration of phytoplankton in water was determined to be only on the order of 0.1
mg/L; the concentrations of zooplankton were approximately a factor of 10 less, although theradiocaesium activities for both phyto- and zoo plankton range from tens to tens of thousands of Bq/kg(dry weight). This means that the total radiocaesium activity, which is incorporated into phyto- andzooplankton, did not exceed a small fraction of a percent of the radiocaesium present in the body ofwater.

Caesium in irrigation ponds
The Prefecture determined radiocaesium concentrations in water and sediments for about 3 thousand
irrigation ponds inside and outside the evacuation order zone in 2014.
Since radiocaesium bounds strongly to clay particles, the concentrations of dissolved radiocaesium inthe water of these ponds are orders of magnitude lower than the radiocaesium concentrations in
sediments. This finding agrees very well with the observations made by the Prefecture in rivers andlakes. In 1% of the water samples collected in the irrigation ponds, the concentrations of radiocaesiumin the dissolved phase were above 1 Bq/L, and these ponds are mainly found inside the evacuation
order zone. The number of ponds with dissolved radiocaesium of above 1 Bq/L decreased from 2013
to 2014.
The Fukushima Prefecture government tested technologies to reduce the concentrations of dissolved
radiocaesium in pond water. The technologies were selected through open recruitment in fiscal 2014
and 2015. The methods were as follows: Separation of the sand, gravel and the clay fractions by means of an underwater device, whichtakes advantage of the fact that the caesium activity concentrations in sand and gravel particles
are much lower than in clay materials. 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 andenhances sedimentation. This procedure prevents the outflow of the radiocaesium from thepond.
 Removing water from the pond and fixing the sediment in place by adding cement, whichbinds the sediment together and prevents the outflow of radiocaesium.
The Japanese government developed a manual for countermeasure techniques based on these test
results. In the Prefecture, the countermeasures against radioactive material are implemented inaccordance with this manual.

5.4. Application of simulation models
To facilitate the interpretation of monitoring results, models were applied by the Prefecture to simulate
the transport 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)
developed by Onishi, Y., et al (Development of a Multimedia Radionuclide Exposure Assessment
Methodology for Low-Level Waste Management, PNL-3370, Pacific Northwest National Laboratory,
Richland, Washington, USA (1983)) was applied to simulate the 137Cs flux in the Ukedo-Takase Riverand in the Ogaki Dam Reservoir. This model has been applied previously to several other large,
medium and small rivers all around the world. All previous applications involved assessments,
analysis and evaluation of the transport of radionuclides following releases to the environment

28 |following the Chernobyl accident, and from nuclear facilities in Mayak (Russian Federation), Hanford
and Savannah River (USA).
The TODAM model can estimate the transport of 137Cs with sediments and water in the rivers. Thismodel produces results that take account of the possible influence of water flow, topography and landuse. The model provides valuable information on:
 The possibility of using the water for domestic and agricultural purposes.
 The effectiveness of remediation measures to be applied to rivers can be assessed, which may
support decision making.
 The effect of re-contamination of rivers, which is important for evaluating the permanence ofremediation measures.
 The 137Cs flux from the catchment area to the ocean can be estimated.
The TODAM model was applied by the Prefecture to simulate the movement of 137Cs in the Ogaki
Dam Reservoir and to investigate the role of the dam for the dispersion of radiocaesium. It was foundthat the dam reservoir can retain about 90% of the suspended radiocaesium. This result is similar toobservations made for the Yokokawa Dam reservoir. The very low water flow rate favours thesedimentation of suspended sediments.
During several workshops involving the IAEA and Fukushima Prefecture experts from different
Japanese and other international institutions discussed their experience in the use of different types ofmodels for radiocaesium prediction in aquatic ecosystems.

5.5. Experience with remediation and decontamination in river andlakes
Global experience
In recent decades, a number of areas world-wide have been affected by the deposition of radionuclides.
In many cases, freshwater ecosystems were impacted. Examples are the Chernobyl accident as well as
the releases of radionuclides from nuclear facilities in Mayak (Russian Federation), and from theSavannah River Plant and the Hanford site (USA).
All of these events were unique; they varied in terms of areas affected, level of contamination,
relevance of the exposure pathways, the levels of doses to people, the relevance of the aquatic
pathways with regard to exposure of people living in those areas, and the measures taken in the aquatic
system to mitigate radiological and social consequences. Following these contamination events, twodifferent types of countermeasures were applied: Technical measures, such as:(1) removal of sediments from contaminated water bodies,(2) construction of dams to reduce the further dispersion of radionuclides with water(3) application of substances which increase the pH value of the water body to reduce theuptake by fish, and(4) construction of sediment traps to accelerate sedimentation of particle-boundradionuclides.
 Administrative measures, such as restriction of access to contaminated areas, restrictions forfishing and for withdrawing drinking and irrigation water.
One lesson derived from the analysis of past events is that technical measures have only a limited
potential to control the dispersion of radionuclides in water bodies. Freshwater systems are

| 29characterised by a pronounced time-dependence of water flow rates and water levels, which is
associated with enormous variation in flow velocities and water levels. Transport of radionuclides
occurs predominantly during temporary periods of high water volume flow, usually associated with
re-suspension, displacement and re-deposition 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 through restriction ofaccess and the implementation of recommendations is less complicated. Such measures with regard to
the use of freshwater bodies are easy to implement and have been proven effective in reducing
radiation exposure through aquatic pathways. However, clear instructions and recommendations arenecessary for successful implementation. Experience shows that public must be kept informed aboutsuch 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 (1) to determine time-trends ofactivity levels in water, sediments and biota, (2) to identify new contamination patterns which may becreated through displacement of material and sediment during high waters and floods, and, (3) toverify the success of countermeasures should they have been applied.

Demonstration of test decontamination measures in Fukushima Prefecture
In this project, the Prefecture tested decontamination measures at riverside areas in the Prefecture to
reduce air dose rates. These works continue and are described below.
Demonstration at the Kami-Oguni River
Part of one side of the river (approximately 200 m long) is traversed by children as they walk to andfrom 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 and radiocaesium concentrations in bottom sediments.
Decontamination measures such as weeding, removal of sediments in the low-water bed, and removalof vegetation and soil from the river dykes were implemented in autumn 2014 (See Figure 5.6). The
results of the air dose rate measurements before and after the decontamination campaign are shown in
Figure 5.7. According to the monitoring measurements carried out before and after thedecontamination measures, the air dose rates were reduced by about 50 %.

FIG5.6. River bed before (left) and after (right) the implementation of decontamination
measures (Fukushima Prefecture)30 |Air dose rate 1m AGL(µSv/h)1.0
0.8

50% reduction

0.6

No increase

0.4
0.2
0.0

Sep., 2014

Oct., 2014

PrePostweeding weeding

Oct., 2014

Dike

Oct., 2014

Nov., 2014

Sediment
Decontamination

Dec., 2014

Feb., 2015

Postdecontamination

Sep., 2015

Postflood

FIG5.7. Air dose rate at 1 m height before, during and after the remediation anddecontamination measures at a river in the Prefecture
The area was affected by a severe flood in September 2015, which caused intensive re-suspension,
displacement and sedimentation of radiocaesium associated with suspended particles. Sediments andvegetation in the river were removed and new material containing mainly coarse material and stones
was deposited at this place. The measurements of the air dose rate carried out after the flood by thePrefecture (See Figure 5.7.) did not indicate significant modification of 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/h.
Model simulations performed for this area by the Prefecture indicated that decontamination measures
may reduce the air dose rate in the considered area by about 35% (Table 5.1). Without any
decontamination measures, the air dose rate would decline after one year by about 13% due toradioactive decay.
Further reduction of the predicted annual radiation doses due to decontamination measures wasassessed by the Prefecture as well, taking into account local habits and occupancy times for various
activities, e.g. walking, cleaning/beautification, and playing in or near the water.
Calculations performed by the Prefecture showed that decontamination measures may reduce theannual effective dose to an individual by 1–15 µSv/yr. Results of projected individual doses related tothe use of this part of the Niida River are given in Table 5.1. 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 river bed. Parts of the river banks
were removed, and at higher levels 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 thetransport processes makes the assessment of the sustainability of decontamination measures very
complex. However, even with the impact of flooding in 2015 on the geometry of the river bed,measurements made by the Prefecture after these flooding events indicated that the effects of theremedial actions had not been affected significantly. Even considering this information, due to thelikelihood of flooding in the coming years, monitoring of the effects of decontamination efforts should
continue.

| 31

TABLE 5.1. Estimation of dose reduction at a demonstration site through decontamination(Fukushima Prefecture)
Item

Activity
Recreation

Walking

Water activity

0.38

Cleaning/
beautification
0.39

Dose rate (µSv/h)(derived from air dose
measurements over 15 minutes)

0.53

Occupancy (hours per year)

16

111

48

9

(1 h/d × 48
d/y)(0.5 h/d × 9
d/y)(4 h/d × 4 d/y) (1 h/d × 111
d/y)

0.26

Annual additional dose (mSv/y)
Before decontamination

0.008

0.038

0.017

0.002

After decontamination

0.005

0.023

0.010

0.001

After 1 year without
decontamination

0.007

0.032

0.015

0.002

5.6. Experience with remediation and decontamination in residential
areas
In Fukushima Prefecture, houses, public facilities, farmland, and roads were decontaminated to reduce
the effects of environmental contamination that resulted from the Fukushima Daiichi accident. Someof the most common decontamination techniques that have been employed in the Prefecture are shownin Figure 5.8.

32 |FIG. 5.8. Main decontamination techniques (Photo credit: Fukushima Prefecture)
In Table 5.2, the status of the effort by the Prefecture to decontaminate different categories of facilities
and areas are summarized. For residences (houses), decontamination is the most advanced; as of theend of October 2017, 99.9 % of the planned activities were completed.

TABLE 5.2. Progress of municipality decontamination (as of end of October 2017)
Category

PlannedCompleted

Percentage
completed

Residences (houses)

418,582

418,579

99.9

Public facilities

11,653

11,627

99.8

Roads (km)18,78517,701

94.2

Agricultural land (ha)31,252

31,196

99.8

Forests (in living areas)
(ha)

4,398

4,307

97.9

For assessing the effectiveness of the decontamination activities in residential areas, measurements of
air dose rate were performed by the Prefecture before and after decontamination measures werecarried out. The effectiveness was quantified in terms of reduction of air dose rate in the areas thatwere subject to remediation.
Specific sets of remediation actions were applied to residential areas, public facilities, roads,
agricultural land and forests respectively. Depending on the type of area treated, air dose rates werereduced by approximately 20 – 50% (See Table 5.3); such reduction factors are very similar to thoseachieved by remediation measures in areas affected by the Chernobyl accident.

| 33

TABLE 5.3 is based on measurements performed before and after decontamination work that was
performed from March 2012 to October 2013. (Japanese Government)

TABLE 5.3. Reduction of the air doses rate due to decontamination work

Category

Number of measurements

Residences areas

82,757

Reduction of
air dose rate (%)
36

Public facilities

32,31145

Roads

33,45131

Agricultural land

20,14729

Forests

12,69721

5.7. 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 inslow 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 bodies of water andwhich causes a rapid decline of dissolved radiocaesium in water.
In the freshwater bodies of the Prefecture  more than 6 years after the accident  dissolved
radiocaesium levels in water are close to or below the detection limit of 0.05 Bq/L. This can be
explained by the strong sorption of caesium by sediments in riverbeds, in which much higher
radiocaesium levels are observed. There is also a clear decline of the concentration of radiocaesium insuspended sediments.
The reduction of the radiocaesium levels in the environment is mainly caused by radioactive decay ofradiocaesium, whereas the run-off of radiocaesium provides a further contribution to the reduction.
The cumulative loss of 137Cs activity since 2011 until September 2015 from the catchments of the
Abukuma and the Kuchibuto tributary was about 3 % (2.5% – 3.5%) and 1% (0.7% – 1.5%)
respectively.
Measurements of radiocaesium in the in- and outflow of reservoirs show that the amount of suspended
radiocaesium in the outflow is much less than in the inflow. This shows that reservoirs act as a kind of
sediment trap.
Sorption of caesium to suspended matter plays a key role for its behaviour in the environment.
Measurements by the Prefecture of the sorption of radiocaesium in soils and sediments show that it isin general stronger under the conditions of the Prefecture in comparison to the observations made after
the Chernobyl accident in Ukraine and the Russian Federation.
Measurements performed by the Prefecture indicated that the amount of radiocaesium incorporated
into zoo- and phytoplankton was very low. The radiocaesium activities for both phyto- andzooplankton range from tens to tens of thousands of Bq/kg (dry weight). This means that the total
radiocaesium activity incorporated into phyto- and zooplankton did not exceed a small fraction of apercent of the radiocaesium present in the body of water.

34 |To facilitate the interpretation of monitoring results, models were applied by the Prefecture to simulate
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 assessing the effectiveness ofremediation measures to be applied for rivers. In addition, simulation models allowed the assessmentof the effect of re-contamination of rivers. The Prefecture recognized that if decontamination measures
are necessary, the use of models may help to identify the most appropriate locations within the
freshwater ecosystem to apply such measures.
Since the Fukushima Daiichi accident, the focus of remediation and decontamination activities of thePrefecture were on public areas including routes traversed by children going to and from kindergarten
and schools, and on recreational areas. In addition, the Prefecture has initiated a number of projects
concerning freshwater bodies to demonstrate the effectiveness of such countermeasures. Suchmeasures reduce air dose rates.
The IAEA team described worldwide experience with freshwater remediation activities whichindicates that technical measures have not, for the most part, been able to control the dispersion ofradionuclides in freshwater bodies. The IAEA team indicated that for reducing exposure to the publicfrom radionuclides deposited in freshwater bodies, recommendations and restrictions with regard to
the use of these freshwater bodies are relatively easy to implement and more effective in reducing
exposure than technical measures.
Since 2011, intensive decontamination work has been carried out by the Prefecture in private homes,
public facilities, roads, agricultural land, and forests. For residences (houses), decontamination is themost advanced; as of the end of October 2017, 99.9 % of the planned activities were completed.
The Prefecture applied specific sets of remediation actions to residential areas, public facilities, roads,
agricultural land, and forests. Depending on the type of area, the Prefecture observed that air dose
rates were reduced by approximately 20% – 50%; such a reduction in dose rates are very similar to
those achieved by remediation measures in areas affected by the Chernobyl accident.

6. Management of Waste from Remediation Activities
6.1. Background and objectives
As stated in Technical Volume 5, Post-accident Recovery, of the IAEA’s The Fukushima Daiichi
Accident, “According to the decontamination plan formulated by the MOE (Ministry of theEnvironment), contaminated soil and waste generated from remediation in the Prefecture are to becollected and stored at, or near, the sites undergoing remediation in temporary storage sites.
Afterwards, the material will be placed in the ISF (Interim Storage Facility). After interim storage forup to 30 years, final disposal will be take place outside Fukushima Prefecture.” The ISF is to be
developed and operated by the central government. Temporary Storage Sites (TSS) have been
established in municipalities and the Prefecture based on laws and government guidelines. Since the
Fukushima Daiichi accident, the Prefecture has performed a significant amount of work concerning
remediation activities and the management of the resulting radioactive waste.
Representatives of the Prefecture stated that when activities under the Practical Arrangementscommenced in 2013, the Prefecture was faced with an urgent shortage of TSSs in which to store wastefrom remediation activities. Furthermore, the Prefecture noted concerns that were raised by the public
about the safety of existing TSSs, and prospective TSSs that were to be established to accommodate

| 35

radioactive waste generated by ongoing remediation activities. Also, it became necessary to store
waste in TSSs for greater time periods than was originally intended. TSSs were established with theintention that waste would be stored in these facilities for only three years before being transferred to
the ISF. However, because of delays in the development of the ISF, waste is now being stored in TSSs
for more than three years. Consequently, the safety of the storage of waste in TSSs for more than three
years is an issue that should be evaluated to ensure the safety of these facilities and also to address
public concerns.
Item 3 of the Practical Arrangements refers to research and study on the management of radioactive
waste including IAEA’s assistance in the study on management methods of low level radioactive
waste from the above-referenced decontamination activities.
The activities concerning the management of waste from remediation activities under the Practical
Arrangements consequently focused on providing technical advice to the Prefecture related to: finalizing technical guidelines for the establishment of temporary storage sites; demonstrating the safety of temporary storage sites in different situations for the different
phases of their development; and retrieval strategies for waste stored in TSSs.

6.2. Temporary storage sites
Three main types of TSSs have been established in the Prefecture: aboveground storage, semiunderground storage and underground storage, each of them having advantages and disadvantages
with regard to ease of construction, transfer of waste to the ISF, stability, etc. However, the preferred
option in the Prefecture for storing contaminated materials is the above-ground storage design. FIG 6.1
provides conceptual diagrams of three types of TSS designs.

36 |FIG. 6.1 Conceptual diagrams of three types of TSSs (Image adapted from Technical
Guidelines for Temporary Storage Sites, Fukushima Prefecture)
As of September 2017, 843 TSSs have been established or are planned in municipalities within the
Intensive Contamination Survey Area. As indicated by FIG 6.2, the number of TSSs increased
dramatically from 2013 to 2014 and has increased moderately from 2014 to March 2017.

| 37

FIG.6.2. Number of TSSs in Municipalities from May 2012 to March 2017
Since the emplacement in TSSs of the bags containing waste from remediation activities, in somecases, various phenomena have been observed and concerns have been raised concerning the
temporary storage sites including: Limitation on the number of bags that can be stacked;
 Effect on long term stability and integrity of stored waste bags resulting from lack of rigidityof the bags and voids between the bags;
 Uncertainty of the long term stability of facilities established on sloping land; Potential leaching phenomena; Degradation of the organic matter in storage bags and potential impact on the integrity of thestorage facility;
 Gradual caving in of the waste bags and accumulation of water in the resulting depressions intarps covering the stored waste bags;
 Risks of fires due to auto-combustion of the contents of waste bags.

6.3. Development of technical guidelines for temporary storage sites
When the activities under the Practical Arrangements began in 2013, intensive remediation activities
were being conducted in the Prefecture and many new TSSs were being established to store theresulting waste. In 2013, the Prefecture had been developing a guidance document on theestablishment and operation of TSSs. At this time, as part of the further development of the guidance
document, the IAEA team encouraged the Prefecture to take stock of their experience with thedevelopment and operation of TSSs. Consequently, an analysis was conducted by the Prefecture of theactivities carried out so far regarding the development of TSSs in the different municipalities. This
analysis aimed at identifying the main issues affecting TSSs, identifying good practices implemented,
and comparing the different strategies for developing TSSs in the different municipalities. Such an
approach should serve as a basis for the development of an overall harmonized strategy for thedevelopment of TSSs in the Prefecture and identify potential improvements or corrective actions that
could be applied to the existing temporary storage sites.
The IAEA team provided technical advice and feedback to the Fukushima experts concerning thedevelopment of the guidance document on TSSs including reviewing the draft text and providing

38 |comments on its content. Version 1 of Technical Guidelines for Temporary Storage Sites was
published by the Prefecture in August 2013. Subsequent revisions to this document were issued inJune 2014 (Version 2), March 2015 (Version 3), March 2016 (Version 4), and August 2017 (Version
5). The major issues to be addressed in Version 5 are extension of the storage period, export of stored
waste, and remediation and restoration of TSSs. The following main topics were addressed in Version
2 (the latest version of the document available in English as of August 2017) of the document:
 Site selection, including: information to be gathered about site characteristics, criteria for site
selection and relevant laws and ordinances concerning the establishment of TSSs; Structure and design, including: advantages and disadvantages of the three main types of TSSs
(i.e. aboveground storage, semi-underground storage and underground storage); facility
location, arrangement of waste bags, and use of shielding in order to reduce air dose rates;
various aspects of waste bags; arrangement of waste bags so that integrity of the grouping ofbags is maintained; storage of waste bags containing material that is subject to organic decay;
specifications and information about various components of TSSs such as: liners, rainfall
collection system, leachate collection system, water collecting tanks, gas venting mechanisms,
monitoring equipment for contamination of ground water, ancillary facilities, fences and otherenclosures, notice boards, and access roads;
 Installation, maintenance and management, including: radiation measurement procedures;
prevention of penetration by rainwater; recordkeeping; regular reviews of the condition of
TSSs.
The technical guidelines also provided information about the initial storage of waste material at
locations where remediation activities are being performed.

6.4. Development of a safety assessment for temporary storage sites
When managing waste defined as radioactive waste, a demonstration of the safety of relevant facilities
and activities should be developed by the so-called operator(s) either for authorization/approval by aregulatory authority, or to build its own confidence or the confidence of any other interested party inthe safety of such facilities and activities. The demonstration of safety, in particular, aims at presenting
the various aspects of the site and its design that would allow a regulatory authority to verify andensure that the facility or activity may be operated safely and that people and the environment areprotected from harmful effects of radiation now and for the life of the facilities. In accordance with the
IAEA Safety Standards, the demonstration of safety should be supported by a quantitative evaluationof the radiological impact (safety assessment) of the facility or activity, under normal operating
conditions and accident scenarios.
Confidence in the safety of TSSs would also be increased by showing evidence that existing andprospective TSSs would have minimal radiological impact. The development of a safety assessment
would involve identifying all relevant parameters that could affect safety such as site characteristics,
designed safety features of the site, characteristics of the waste and its containers to quantitatively
assess the impact of the temporary storage for different periods of time, and different scenarios, inparticular, normal operating conditions and accident scenarios. Such an assessment could beestablished for a generic or model storage facility, i.e. generic enough so that its parameters would be
representative of all existing and potential storage facilities in the Prefecture.
Prior to the commencement of the activities under the Practical Arrangements, Fukushima experts had
no experience with the performance of safety assessments as called for by the IAEA Safety Standards.
As such, the development of a safety assessment for the TSSs proceeded in a stepwise fashion
beginning with an educational phase and subsequent phases in which Safety Assessment Framework
software tool (SAFRAN) (See Section 6.4.1) was applied first to a “model” TSS, then on a trial basis

| 39

to the TSS in Fukushima prefecture, and finally to 12 selected TSSs in the Prefecture. The safetyassessment development process is presented schematically in FIG 6.3.

FIG. 6.3 Activity flow of the development of a safety assessment for TSSs in the Prefecture
6.4.1. Safety Assessment Framework software tool
The IAEA methodology for safe predisposal management of radioactive waste is provided in the
Safety Guide GSG–3, The Safety Case and Safety Assessment for the Predisposal Management ofRadioactive Waste (IAEA, 2009), which provides recommendations on meeting the safety
requirements in GSR Part 5, Predisposal Management of Radioactive Waste (IAEA, 2013). In order tofacilitate the application of this methodology, the IAEA developed SAFRAN to guide the user inperforming a systematic and structured safety assessment of facilities and activities related to40 |predisposal radioactive waste management and decommissioning. As such, SAFRAN could be used indeveloping a safety assessment for TSSs 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
according to user needs. The demonstration of safety of TSSs under the Practical Arrangements was
supported by the use of SAFRAN. In some cases, adjustments were made to the software by the IAEA
so that it could be applied to the specific situations in the Prefecture.

6.4.2. Building capacities of the Prefecture for performing safety assessment of
temporary storage sites
In 2014, an IAEA team conducted a training session for Fukushima experts that addressed thedemonstration of safety (safety assessment) and specifically the use of SAFRAN for TSSs.
Information about the IAEA methodology for the evaluation of the safety of predisposal managementof radioactive waste as established in the IAEA Safety Standards was provided. The IAEA team andFukushima experts identified the purpose, scope, approach and endpoints of activities concerned withsafety assessment of TSSs. Key elements of the regulatory framework relevant to the safetyassessment which were identified are dose limits for occupationally 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 and bottom of
the stacked waste bags, and various types of cover and radiation shielding.
The process of development of a safety assessment for TSSs 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 Fukushima experts on the explanation and dissemination of
the results of the safety assessment.

6.4.3. Safety assessment for a “model” temporary storage site
As an educational tool for the Fukushima experts and to assure the applicability of the IAEA safetyassessment methodology including the use of SAFRAN, the IAEA methodology was initially applied
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 FIG 6.4. Three general activities concerning waste bags and the model
TSS were addressed by SAFRAN: emplacement, storage, and retrieval. Normal operating conditions
and accident scenarios were evaluated. Each of these activities requires separate analyses, withspecific conditions under normal operating conditions and accident scenarios taken into account.

FIG 6.4. Typical layout for a TSS. Radiation doses are calculated with respect to the distancefrom stored materials.

| 41

The safety of the model TSS, as with other engineered facilities, depends on robust and proven designand construction. The most important design features are those that provide necessary assurances thatthe 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 uponwhich the design is based are necessary in order to assess the safety of the facility currently and in the
future. Regardless of the fact that a TSS does not represent a complicated civil engineering structure, it
still has several important safety features which have to be properly quantified and understood.
Therefore, the work of the Prefecture started with definition 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 that must be entered into SAFRAN. When available, actual
data were used by the Prefecture. For parameters that could not be established with a high degree of
accuracy, a process for conservatively estimating such information was implemented by the
Fukushima experts. This approach was used throughout the development of the safety assessment.
Information about the radioactive waste to be stored must be gathered, which includes 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 were estimated including
inventories, throughput rates, activity concentrations, etc. that are required for quantitative
assessments in SAFRAN. Other parameters important for the safety assessment, such as the vicinity of
the nearby houses, data about the site, the engineering features, etc. were collected and/or estimated by
the Fukushima experts.
A hazard analysis was performed by the Prefecture based on an in-depth analysis of waste
management activities associated with the model TSS, which addressed the hazards which arise undernormal 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 specific scenarios was performed based on qualitative assessments of the likelihood of
identified events and the significance of possible impacts. An extensive set of hazards during
emplacement, storage and retrieval were analyzed under normal operating conditions and in accident
scenarios through this process.
After defining the parameters needed for analysis, it became necessary to slightly adjust SAFRAN inorder to meet the design aspects of the existing and planned TSSs in Fukushima prefecture. One
specific change was made to SAFRAN so that it can analyse releases of radioactive material to air andto groundwater.
Joint discussion and analysis of data reveals again that results of the safety assessment should be used
to facilitate exchange between interested parties on issues relating to the safety of TSSs. Through thestep by step approach, the Prefecture should engage consultation with the public concerning any
specific decision points.

Normal operating conditions
The assessment of the impact of normal operations by the Prefecture at a model TSS was based on
assessment of annual radiation doses for both, occupationally exposed persons and a resident living in
the vicinity of the facility. An occupationally exposed worker may be exposed under varying
conditions, e.g. during the emplacement of the waste packages, or during their removal, i.e. retrieval
processes. Nearby residents could be exposed due to direct exposure during theemplacement/replacement operations. However, under normal operating conditions these exposuresare very small. Predicted exposures during the storage period area small fraction of allowable radiationdose limits under normal operating conditions.

42 |The doses for normal situations are assessed by the Prefecture for the case when all operations are
performed as planned, assuming an average time needed for specific activities, and assuming average
air dose rates expected during these activities.
The potential exposure depends on the number of waste storage bags and their storage area; therefore,
SAFRAN was used to evaluate TSSs of three different sizes, which would characterize the existingand planned TSSs in the Prefecture. For these three model facilities, various shielding configurations
such as the use of sand bags and soil spread on the top of the facility were also evaluated using
SAFRAN.
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 by the Prefecture based on air dose rates, residence timeand shielding effects. The internal doses were calculated on the basis of the radionuclide dependent
activity concentrations, dose conversion factors, and residence time. The total dose accumulated bymembers of the public was calculated by summing the predicted external and internal exposures.

Accident scenarios
Deviations from planned operating conditions may cause unplanned exposures of workers and the
public. The safety assessment of the model TSS by the Prefecture therefore also included anassessment of hazards resulting from accidents throughout the life of the facility.
The Prefecture performed a comprehensive analysis of different safety aspects and possible impacts on
the TSS using the IAEA methodology. The assessment of impact from accidents required detailed
analysis of the initiating events. These events were analysed by the Prefecture and a list of resulting
potential scenarios was created. As expected, the fact that the engineering structure of the model TSS
is relatively simple, does not exclude scenarios which require further examination and involvement ofcountermeasures.
The hazard screening process conducted by the Prefecture excluded irrelevant exposure pathways (orthose with an extremely low probability of occurrence). Accidental releases into the atmosphere (e.g.
fires at the facility) may cause exposures of the workers at the site and/or the public. Accidental
discharges through the water pathways may be relevant only for the public.
The radiation doses due to the atmospheric releases were calculated as a sum of contributions fromvarious exposure pathways such as inhalation, ingestion and external exposures from a passing plume.
Regarding the choice of the accidental scenarios, and having in mind the layout and structure of a TSS,
various scenarios were considered by the Prefecture such as waste bags falling to the ground, damage
to waste bags due to various means such as high temperature, snow and high winds, and damage to thefacility by various means such as earthquakes and fire.

Conclusions regarding application of SAFRAN to a model temporary storage site
The Prefecture performed a complete representation of all relevant waste management activities andfacilities within the scope of the model TSS using SAFRAN. A complete representation of the
facilities, activities, waste streams and hazards were analyzed through the application of SAFRAN.
This formed the basis for finalizing the safety assessment for application to 12 representative TSSs.
The preliminary analysis performed by the Prefecture for normal operational conditions clearly
showed that shielding in the form of protective walls made of sand bags can significantly reduce theradiation doses to the nearby population. Adding soil on the top of the facility further reduces
predicted radiation doses by an order of magnitude to a level that is significantly less than 1mSv/year.

| 43Regarding operational radiation protection, predicted radiation doses to workers (within the borders of
the facility) for normal operating conditions as assessed by SAFRAN were also below the occupation
radiation dose limits, even using conservative assumptions.
Based on input data developed by the Prefecture and the use of SAFRAN involving many different
numerical simulations, one could conclude that based for normal operational conditions, the model
TSS has been designed properly, without any undue risk to workers at the sites and for nearby
residents.
Predicted doses to occupationally exposed workers resulting from accidents generally do not exceed
1 mSv including extreme cases such as the crushing of twenty waste containers by a falling tree.
When considering radiation doses to the public as a result of accidents, the analysis of most scenarios
predicted doses to the public that would be a small fraction of applicable dose limits. However, certain
scenarios that were analysed by the Prefecture indicated that the public could receive doses in excess
of 0.5 mSv and therefore further analysis of these scenarios should be performed and theimplementation of countermeasures should be considered under these circumstances.
Based on the analysis performed by the Prefecture, the potential for radioactive material leaking fromthe TSSs into groundwater and rivers is very limited, resulting in very low predicted radiation doses
from exposure to groundwater and from the consumption of fish.
Finally, the analysis performed under the Practical Arrangements by the Prefecture demonstrates that
the IAEA methodology including the application of SAFRAN for predisposal safety assessment isfully applicable to TSSs throughout their lifecycle for the all exposure pathways to workers and the
public for both, normal operating conditions and accident scenarios.

6.4.4. Trial safety assessment of temporary storage site in Fukushima Prefecture
Following on the success of the application of SAFRAN to a model TSS, the Fukushima experts
applied the IAEA safety assessment methodology to an existing TSS in Fukushima Prefecture. The
lessons learned and the experience gathered through this activity should facilitate development of thesafety assessments for other TSSs. As with the safety assessment for the model facility, the trial safetyassessment used SAFRAN to evaluate predicted radiation doses to workers and the public from TSSs
under normal operating conditions and as a result of accidents.
The results of the trial safety assessment carried out by the Fukushima experts are similar to the resultsof the model safety assessment, which clearly indicates that the process of developing the safetyassessment is coherent, that the data used as input to the safety assessments are satisfactory and therethat no major safety issues were identified under the conditions that were considered. The process ofdeveloping the safety assessment using more realistic data for the trial safety assessment contributed tothe building of confidence in the Fukushima experts in the safety assessment process.

6.4.5. Safety assessment for nine representative temporary storage sites
In order to complete the safety assessment of TSSs, a decision was reached to apply the IAEA safetyassessment methodology to nine selected TSSs throughout the Prefecture. The selected sites werechosen so that their characteristics would be representative of the existing and prospective TSSs within
the Prefecture. Actual data was acquired for these sites and in situations where data could not be
obtained, data was estimated conservatively as was the case for the model TSS.
During the further development of the safety assessment by the Prefecture for the TSSs, further
initiating events that had not been previously included in the safety assessment were incorporated into
the ongoing safety assessment development process including the impact of, flooding, retrieval of44 |waste bags from TSSs, transport of waste bags, and aging of waste bags and facilities beyond three
years (the storage period originally anticipated for the TSSs). If waste is stored in TSSs for long
periods of time beyond what is currently expected, it will be necessary to revise the safety assessment
to take into account the effects of ageing on the waste bags and on the overall structure of the facilities.
The manufacturers of the waste bags specified working lives of the bags of several years and it
appears that the storage time of the bags in the TSSs will exceed the working life of the bags andtherefore it was deemed necessary that the safety assessment should address this issue.
The results of the safety assessment for the nine representative TSSs in the Prefecture were similar to
those obtained for the model TSS, even with the consideration of additional initiating events. Also,
safety was demonstrated for TSSs under normal operating conditions; however, for large scale
accidents, e.g. fire, countermeasures may be necessary to protect against radiation doses.
Discussions were also held concerning the documentation and dissemination of the results of thesafety assessment. Accordingly, as of September 2017, the Fukushima experts had prepared a draft
document describing the development process for the safety assessment and its conclusions.

6.5. Retrieval strategies for waste stored in temporary storage sites anddecommissioning of temporary storage sites
In the later stage of the cooperation under the Practical Arrangements, the IAEA team and Fukushima
experts discussed a retrieval strategy for waste stored in TSSs. Because of the ageing of waste bags as
discussed in section 6.4.5, it can be anticipated that the degradation of waste bags will lead todifficulty in retrieving these bags from TSSs. The IAEA team suggested that the ongoing review of the
durability of waste bags should be continued, that the results of this review should be entered into a
database, and that this information should be used to inform the development of a prioritization for the
retrieval of waste bags. A significant issue that should be addressed through the safety assessment
process is the transport of waste bags from TSSs to other storage facilities (such as the ISF); the resultsof a safety assessment should specifically inform the development of a prioritization of the specificwaste bags to be transported. As new information arises as a result of the ongoing work concerning theageing of waste bags and the consideration of transport issues, the safety assessment should be revised
to take this information into account. The IAEA team also noted that a substantial increase inradioactive waste options could be achieved, if municipal landfills could be used for the disposal of
remediation waste. It was noted that based on an IAEA project on the derivation of specific clearance
levels for landfill disposal of bulk amounts of waste, in terms of radiation protection principles, there
should be no objections to disposing of waste in landfills containing concentrations of 137Cs withmaximum concentrations up to 8,000 Bq/kg.
The IAEA team noted that decommissioning of TSSs after all waste material has been removed will bea significant undertaking that should be approached in a systematic way in accordance with the IAEA
Safety Standards. Various issues in this regard must be addressed such as techniques for site
restoration including radiation survey procedures and the establishment and implementation ofradiation protection objectives including radiation dose criteria.

6.6. Section Summary
The use of the IAEA’s SAFRAN provided the Prefecture with the ability to use an iterative approachin performing a safety assessment of TSSs. It also provided a means for the Prefecture to go throughthe key steps in developing a safety assessment several times to refine assumptions, add elements, andoptimize the balance between conservatism and realism. Since the safety assessment is updated

| 45

automatically during each of these steps, Fukushima experts noted, the risk that such iterations lead toconfusion, contradictions and the lack of consideration of important aspects is substantially reduced.
During the implementation of the software, a part of the SAFRAN database was changed to fit to thespecific conditions of the TSSs in the Prefecture.
Fukushima experts noted that the development of a safety assessment for the TSSs in the Prefecture
through the application of SAFRAN to, a model TSS, a TSS in Fukushima Prefecture, and nineselected TSSs, 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.
During the development of the safety assessment for TSSs, several technical issues have been
identified whose impact on safety has been evaluated by the Prefecture (e.g. water accumulation indifferent places of the temporary storage, flooding, retrieval of waste bags from TSSs, transport ofwaste bags, collapse of waste packages, and blockages of exhaust piping). On the basis of these
dedicated evaluations of the impact on safety, the Prefecture could establish technical measures toremediate and prevent the problems and could assess their effectiveness.
Fukushima experts concluded that the systematic process carried out using SAFRAN provided
arguments and confidence that no significant issues were disregarded. It also provided a framework
for explaining why certain systems and processes are considered safe and why certain improvementsof safety and countermeasures are necessary.
The results gained through the use of SAFRAN and the analysis conducted by the Prefecture in thedevelopment of a safety assessment for the TSSs in the Prefecture clearly indicated that all radiation
doses (calculated using conservative values) are in most of the cases well below the prescribed dose
limits.
Following discussions with the IAEA team concerning retrieval strategies for waste stored in TSSs
that took account of the ageing of waste bags, Fukushima experts noted that the safety assessment for
TSSs should be revised to account for new information that arises as a result of the ongoing work on
the ageing of waste bags.
Fukushima experts also noted that decommissioning of TSSs after all waste material has been
removed will be a significant undertaking that should be approached in a systematic way.

46 |7. Report SummaryLong Term Monitoring
CountermeasuresofRadioactive

Material

in

Forests

andAssociated

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 of radiocaesium within this ecosystem. While
extensive research on forest ecosystems had been carried out in the years following the Chernobyl
accident in 1986, forests in Europe differ from those in Japan and the results of previous studies may
not be directly applicable. For this reason, an extensive monitoring program has been established in
the Prefecture.
Data gathered by the Prefecture indicate that clay minerals present in the forest soils in the Prefecture
are immobilizing 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 contained in the trees
themselves. The relatively low concentrations measured by the Prefecture in harvested wood to date
support the continued unlimited 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 to areas offorest not currently being managed; this in turn may bring new challenges in terms of continued use of
the timber as well as managing radiation exposure of forest workers.
Another 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 deposited is retained
within the forest and the amount of radiocaesium lost from the system to date seems to be low. Thissuggests that the likelihood of ongoing contamination of nearby agricultural land is low (unlessthrough some unforeseen catastrophic event). At the same time, the reduction in air dose rate within
the forest is likely to be dominated by the half-life of 30 years of 137Cs. Some countermeasures are
currently being evaluated in terms of long term effectiveness but their high cost is likely to limit theirwidespread applicability.
The life cycle of trees from planting to harvesting is normally a number of decades. At the time of the
Fukushima Daiichi accident, the forests that received radioactive fallout were at various stages ofdevelopment, from newly-planted saplings to fully mature trees ready for harvesting. The distribution
and movement of radiocaesium between the forest floor and vegetation will therefore need to bemonitored to ensure that long term cycling mechanisms are fully understood. The knowledge gained
will allow the forests to be managed in an effective manner for the benefit of the people of thePrefecture.

Radiation Monitoring Data for Developing Maps to be Made Available to the Public
The website of Fukushima Prefecture is extensively used by the local population as an authoritative
source of information. The views of those who use the website have been sought to identify the type of
information they require and how the website can be improved to better meet their needs. The need for
the Prefecture to supplement the information available through the website with a broader outreach tothe public was highlighted. In this regard, the information needs of returning evacuees are particularly
important.
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 theuse of interactive maps, were considered. Technical issues such as how to present representative data,

| 47

how to indicate long term trends in air dose rate and how to merge data from fixed monitoring stations
and different types of measurement surveys are not straightforward and different approaches andpractical 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 isfully accessible from both PCs and smartphones. With the revised website, it is now possible to easilybrowse data associated with specific locations and dates. The variation of air dose rates with time canbe accessed graphically and through the use of a “time ruler”. In addition to Japanese, the website isalso available in English, Chinese and Korean.

Off-site Decontamination and Environmental Monitoring
In the freshwater bodies of the Prefecturemore than 6 years after the accidentmeasurements by
the Prefecture indicate that dissolved radiocaesium levels in water are close to or below the detection
limit (of 0.05 Bq/L). This can be explained by the strong sorption of radiocaesium by sediments inriverbeds, in which much higher radiocaesium levels are observed. There is also a clear decline in theconcentration of radiocaesium in suspended sediments.
The reduction of radiocaesium levels in the environment is mainly caused by the radioactive decay ofradiocaesium, whereas the physical removal of radiocaesium through run-off provides a further
contribution to the reduction. The suspended radiocaesium is subject to sedimentation in reservoirs;such waters act as a kind of sediment trap.
Simulation models have been used by the Prefecture to simulate the transport of radiocaesium fromcatchment areas through the river system to the Pacific Ocean. The results facilitate the interpretationof monitoring measurements. Additionally, models provide valuable input, when planning the possible
effects of countermeasures. A number of demonstration projects were initiated by the Prefecture to test
the effectiveness of measures for reducing air dose rates in recreation 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. For reducing
exposure to the public from radionuclides deposited in freshwater bodies, recommendations andrestrictions with regard to the use of these freshwater bodies are relatively easy to implement and more
effective in urgently reducing exposure than technical measures.
Since 2011, intensive decontamination work has been carried out by the Prefecture in private homes,
public areas, agricultural land and forests. For residences (houses), decontamination is the mostadvanced; the Prefecture indicated that as of the end of October 2017, 99.9% of the planned activities
were completed. The Prefecture also indicated that depending on the type of area treated, air dose rates
were reduced by approximately 20% – 50%: such reduction rates are very similar to those achieved byremediation measures in areas affected by the Chernobyl accident.

Management of Waste from Remediation Activities
The development of a safety assessment for the TSSs by the Prefecture through the application of the
IAEA’s SAFRAN to, a model TSS, a TSS in Fukushima Prefecture, and nine selected TSSs, was animportant step toward establishing a safe and reliable way to store the large amount of radioactive
waste accumulated from remediation activities in the Prefecture. 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 the applicability of the methodology. The
implementation process was supported by using SAFRAN, developed by the IAEA, which enabled an
iterative approach to safety assessment of TSSs. It also enabled Fukushima experts to go through the

48 |key steps relevant for safety several times to refine assumptions, add elements, optimize balance
between conservatism and realism, etc.
During the application of the software, a part of the SAFRAN database was changed by the IAEA
team to fit the specific conditions of the TSSs in the Prefecture.
An equally important benefit from the systematic assessment process is to provide a justification forimposing additional safety measures, if necessary. The results of applying SAFRAN to TSSs by thePrefecture indicated that all predicted radiation doses (calculated using conservative values) are in
most of the cases well below prescribed dose limits. A systematic analysis of all relevant hazards
provided a sound justification for imposing the measures, if necessary, to avoid or significantly reduce
any type of undue consequences to people and to the environment.
The development of the safety assessment for the TSSs by the Prefecture is important, but represents
only the first step in finding a safe and reliable solution for storage of large amount of radioactive
waste accumulated from remediation activities. Discussions were held involving the IAEA team andFukushima experts concerning retrieval strategies for waste stored in TSSs that take account of theageing of waste bags. It was noted that the safety assessment for TSSs should be revised to account for
new information that arises as a result of the ongoing work on the ageing of waste bags.
Decommissioning of TSSs after all waste material has been removed will be a significant undertaking
that should be approached in a systematic way in accordance with IAEA Safety Standards.