Res. 24 : 83-282(2020)Vol.

24 No.2/2020

Progress in Environmental Emergency Research
after the Great East Japan Earthquake andFukushima Nuclear DisasterVol.24 No.2/2020

Progress in Environmental Emergency
Research after the Great East Japan
Earthquake and Fukushima Nuclear DisasterCONTENTS
Progress in Environmental Emergency Research after
the Great East Japan Earthquake and Fukushima Nuclear Disaster
083 Preface ………………………………………………… Toshimasa OHARA, Seiji HAYASHI and Kazuki IIJIMA

Ⅰ．Environmental assessment085	Overview of Environmental Impact Assessment Studies on Radioactive Contamination
after the Fukushima Daiichi Nuclear Power Plant Accident… ……………………………………………… Kazuki IIJIMA, Seiji HAYASHI and Masanori TAMAOKI
095	Overview of Open Biodiversity Data around the Fukushima Disaster Area andthe Nuclear Power Plants in Japan… … Akira YOSHIOKA, Nao KUMADA, Yui OGAWA and Keita FUKASAWA
105	Role and Effect of a Dam on Migration of Radioactive Cesium in a River Catchment
after the Fukushima Daiichi Nuclear Power Plant Accident… …………… Seiji HAYASHI and Hideki TSUJI
115	Dynamics of 137Cs in Water and Phyto- and Zooplankton in a Reservoir Affected by
the Fukushima Daiichi Nuclear Power Plant Accident… ……………………………… Hideki TSUJI, Megumi NAKAGAWA, Kazuki IIJIMA, Hironori FUNAKI,
Kazuya YOSHIMURA, Kazuyuki SAKUMA and Seiji HAYASHI
137
129	Cs Outflow from Forest Floor Adjacent to a Residential Area:
Comparison of Decontaminated and Non-decontaminated Forest Floor… ……………………………………………………… Tadafumi NIIZATO and Takayoshi WATANABE

Ⅱ．Waste management and removed soil
137	Summary of Radioactive Cs Dynamics Studies in Coastal Areas and Assessment of River Impacts… …………… Toshiharu MISONOU, Tadahiko TSURUTA, Takahiro NAKANISHI and Yukihisa SANADA
145	Case History: Decontamination Challenge of Iitate Village… ………………………… Yuuzou MAMPUKU
159	Experimental Study on the Mechanism of Cs Removal from Contaminated Soil andIncineration Ash by Pyroprocessing………… Kazuo YAMADA, Kazuhiko TOKOYODA, and Masahiro OSAKO
173	Insolubilization of Cesium Contained in Fly Ash by Co-heating with Potassium Feldspar… ………………………………………………………………………………………Yasumasa TOJO
181	A Study on the Durability of Covering Sheets Used at Temporary Storage Sites in Fukushima Prefecture… …………………………………………………………… Yusuke TAKAHASHI and Masahiro KOISO

Ⅲ．Environmental renovation
191	Promoting Local Revitalization to Solve Issues on Degraded Forests in Japan:
A Case Study in Oku-Aizu, Fukushima… …………Makoto OOBA, Shogo NAKAMURA and Takuya TOGAWA
199	Smart Community Recovering from the Tsunami-Disaster:Case Study of the Community Energy Supply Project in Shinchi Town, Fukushima… ……… Yujiro HIRANO, Shogo NAKAMURA, Takuya TOGAWA, Tsuyoshi FUJITA and Kenichi ADACHI

207	Longitudinal Evaluation of Energy-saving Effects and Their Implication Using
Electricity Monitoring Data in Shinchi Town, Fukushima… ……… Ayami OTSUKA, Yujiro HIRANO, Shogo NAKAMURA, Tsuyoshi FUJITA and Daisuke NARUMI
217	Impact of TEPCO Nuclear Accident and Associated Evacuation to the Demography in Fukushima… …………………………………………………………………………………………… Kei GOMI
227	A Study on Sustainable Energy Systems for Small Villages in Fukushima… ………………………………… Takuya TOGAWA, Yi DOU, Shogo NAKAMURA and Makoto OOBA
237	Survey on Household Wood Biomass Use and Energy Consumption in the Oku-Aizu Region… …………………………………………………………… Shogo NAKAMURA and Takuya TOGAWA
243	Community Governance in Decontamination Policy after the Fukushima Nuclear Accident:
Two Case Studies from the Naka-dori Region, Fukushima, Japan… ……………………………………………… Takashi TSUJI, Shogo NAKAMURA and Makoto OOBA

Ⅳ．Environmental management253	Overview of the Environmental Emergency Management Studies in National Institutefor Environmental Studies (NIES)… …………………………………… Ryo TAJIMA and Masahiro OSAKO
261	Systematic Analysis of Environmental Release Process and Emergency Response in
Chemical Accident… ………………………… Yosuke KOYAMA, Yoshitaka IMAIZUMI and Noriyuki SUZUKI
267 Strategy to Promote Residents’ Behaviors for Appropriate Disaster Waste Management… …………………………………………………………………… Tomoko MORI and Ryo TAJIMA
275	Expanding the Scope of Environmental Emergency Research towards Disaster-resilience andEnvironmental Sustainability… ……………… Toshimasa OHARA, Ryo TAJIMA, Yujiro HIRANO, Shigenori IINO and Seiji HAYASHI

83

Preface
Just ten years ago, the world witnessed the Great East Japan Earthquake (GEJE), the subsequent Fukushima
Daiichi nuclear power plant (FDNPP) accident and the severe impacts these had on the society and environmentof eastern Japan. A wide range of research related to the nuclear accident has been conducted, with the results
already released in many cases regarding the environmental impacts of the large amounts of radioactive
substances emitted into the environment during that event. In addition, research is being carried out onsustainable community development, including the establishment of sustainable regional environments,
reconstruction according to environmentally conscious principles and creation of disaster resilient regions. Suchenvironmental emergency research has contributed greatly to environmental recovery in areas affected by the
GEJE and nuclear accident and also to environmental emergency management for natural disasters after the
GEJE.
This special issue focuses on the progress in environmental emergency research after the GEJE and nuclear
accident, and provides an integrated body of relevant scientific knowledge. The articles in this issue cover awide range of studies addressing environmental emergency aspects such as post-disaster environmental impactsof pollutants, environmental recovery and management of disaster waste. Many articles have been provided byresearchers of the National Institute for Environmental Studies, Japan Atomic Energy Agency, and otherorganizations. We are profoundly grateful for their contribution of valuable scientific knowledge and technicalexpertise toward environmental restoration, and strongly hope that this information will be utilized in efforts
towards disaster-resilience and environmental sustainability worldwide.
Guest Editors
Toshimasa OHARA
Seiji HAYASHI
Kazuki IIJIMA

85

Overview of Environmental Impact Assessment Studies onRadioactive Contamination after the Fukushima Daiichi
Nuclear Power Plant Accident
Kazuki IIJIMA1, Seiji HAYASHI 2* and Masanori TAMAOKI 2
Fukushima Environmental Evaluation Research Division, Japan Atomic Energy Agency
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: shayashi@nies.go.jp

1

Abstract
The radioactive environmental contamination that resulted from the Fukushima Daiichi nuclear power
plant accident has clearly been declining during the nearly 10 years that have passed since the accident. Many
studies, however, have indicated prolongation of radioactive contamination in natural ecosystems, probably
arising from non-decontaminated forested areas, so a more detailed examination is needed on theenvironmental dynamics of bioavailable radiocesium and its transfer to ecosystems. Also, regarding theinfluences of radiation on organisms, the effects on wild organisms of the evacuation of humans have been
more pronounced than the direct effects from radiation, especially in the Fukushima evacuation zones.
Key words :	dissolved Cs, radiation effect, transfer to ecosystem, wild organism

1. Introduction
As shown by the time change in radiation air dose
rates measured by airborne surveys (Nuclear Regulation
Authority, 2020), serious environmental radioactive
contamination occurred widely as a result of the
Fukushima Daiichi nuclear power plant (FDNPP)
accident. The air dose rate has clearly been declining
during the nearly 10 years that have passed since theaccident thanks to decontamination operations in theliving sphere of the affected areas as well as the natural
decay of Cs-134, the half-life of which is 2.0 years, andweathering of radiocesium.
On the other hand, the forested areas that cover over
80% of the evacuated zones remain mostly nondecontaminated. Considering the reported behavioral
properties of radiocesium in forests such as its highadsorption in clay particles in the soil (Takahashi et al.,2019) and limited runoff ratios even during rain events(Tsuji et al., 2016; Iwagami et al., 2017a), it is assumed
that large amounts of the deposited radiocesium will be
retained in the surface soil layer over a long period oftime. Serious radioactive contamination of forested areasand subsequent long-term contamination of natural
ecosystems were reported after the Chernobyl nuclear
power plant (CNPP) accident in 1986 in the former
Soviet Union (Belli & Tikhomirov, 1996; Bulgakov et al.,Global Environmental Research
24/2020: 085-093
printed in Japan

2002). The same situation is of increasing concern in thearea affected by the FDNPP accident. Additionally, since
long-term retention of radiocesium in the forest floor
means prolonged conditions of high dose rates in the partof the forest environment near the ground, we cannot
overlook the effects of radiation doses on organisms overthe mid to long term.
In this paper, we focus especially on radiocesiumtransfer to natural ecosystems and the various effects ofradiation on organisms in an attempt to assess theenvironmental effects of the FDNPP accident through theaccumulated scientific knowledge from previous research
papers. Concretely, we first give an overview of the
behavioral properties of dissolved radiocesium with highbio-availability, which plays an important role in its
transfer to natural ecosystems in forests and river
systems. Then we describe the state of radiocesiumtransference to forest trees, freshwater fish and wild
animals. In addition, the actual state of radiation doses’
influence on organisms and the influence on biota of theabsence of humans due to evacuation are described
respectively as direct and indirect effects of serious
environmental radioactive contamination.

©2020 AIRES

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2. Migration Behavior of Dissolved Cs in
Terrestrial Areas
In a previous review (Hayashi, 2016), the following
points were indicated as future issues regarding the
behavior of Cs in the environment around Fukushima:- Organization of scientific knowledge on managing
radiocesium runoff from forests based on many casestudies,- Detailed investigations of dissolved radiocesium inriver systems in terms of generation mechanisms,
particularly the contribution of highly contaminatedorganic matter (leaf litter) and seasonal fluctuations
in concentrations,- Investigations on the behavior of sediments with highconcentrations of radiocesium through direct
deposition and initial inflow to clarify the actual
state of bottom sediment contamination in dam
reservoirs, and- Investigations on the possibility of dam reservoirs
acting as a source of dissolved radiocesium.
		 In this chapter, we review recent investigations
on the behavior of dissolved radiocesium in river
systems and forests, which are considered to be twosources.
2.1 Sources of Dissolved Cs in River Systems
Highly contaminated organic litter, such as leaf litter,is considered one of the possible sources of dissolved
radiocesium in river systems. This possibility is supported
by both seasonal fluctuation, with high levels in summer
and low in winter (Tsuji et al., 2016; Nakanishi &Sakuma, 2019), and a rapid but extremely temporary
increase in concentration immediately after rainfall starts(Tsuji et al., 2016; Iwagami et al., 2017b; Sakuma et al.,2019). According to phenomenological model
calculations, these trends in dissolved radiocesium
concentration cannot be expressed by traditional
adsorption-desorption distribution models, so it is thoughtthat the kinetically controlled dissolution of radiocesium
during the decomposition of organic matter might
contribute (Sakuma et al., 2019). Dissolved radiocesium
concentrations are correlated with water temperature(Nakanishi & Sakuma, 2019), dissolved organic carbon+(DOC) and potassium (K ) concentrations (Tsuji et al.,2016), also suggesting contribution of organic matterdecomposition. However, since the width of fluctuation
decreases with time (Nakanishi & Sakuma, 2019), thecontribution of this process might be decreasing.
Desorption from forest soil or river sediments is
another possible source. In the case of forest streams, thedeclining trend of dissolved radiocesium in stream water
is similar to that in groundwater (Iwagami et al., 2017b).
The level of radiocesium dissolved in water contained insoil layers was found to be quite high in July 2011 anddeclined after that, and could be fit with a two-component

exponential model (Iwagami et al., 2017c). The faster
decline rate showed a good correlation with theradiocesium interception potential (RIP), suggesting that
desorption from clay minerals contributed to generationof dissolved radiocesium in forest soil. In the case of river
sediments, the cation exchange capacity (CEC) is
influenced by both clay minerals and organic matter
content (Tachi et al., 2020a). The adsorption behavior at-9
10 M of the initial concentration of radiocesium can be
expressed by a first-order reaction, but the rate constantdecreases with an increase in organic matter content,
indicating that organic matter inhibits radiocesium accessto frayed edge sites (FESs) (Tachi et al., 2020b). In
particular, the dissolved radiocesium concentration in
output water from one of the dam reservoirs inFukushima has shown slightly higher concentrations andslower decline than that of the input water (Funaki et al.,2020). It is thought that radiocesium that has accumulated
in the reservoir sediments may partly be desorbed byammonium ions, dissolving into the reservoir’s water.
The conditions in the reservoir sediment are likely toremain in a reducing condition under which ammonium
ions are easily generated and can desorb cesium ions.
2.2 Behavior of Cs in the Forest Floor
Most of the radiocesium deposited in forests has
moved from the canopy to the forest floor. Throughfall isthe dominant pathway of radiocesium transfer in the firstyear, and the contribution of litterfall gradually increases
with time (Kato et al., 2017). The trend of radiocesium
decreasing in the canopy is expressed by a double
exponential field-loss model. In the six months after theaccident, 82% of the initially deposited radiocesium waspresent on the forest floor in mixed forests and broadleaved forests, and 78-56% in the case of cedar forests(Komatsu et al., 2016). The ratio of radiocesium on thecedar forest floors to the initially deposited amount wasalso reported to be 80% three years after the accident(Gonze et al., 2017) and 94% four years after it(Yoschenko, 2017).
On the forest floor, radiocesium in the litter layer
migrates to the lower mineral layer, and is strongly
adsorbed by the minerals. It has been reported that theradiocesium concentration in the mineral layer located a
few centimeters below the surface gradually increased
and became higher than that in the litter layer after two or
three years (Takahashi et al., 2019). The exchangeable
fraction of radiocesium was of 10% in the organic layer
and 6% in mineral layer after five months, and constant at
2 – 4% in two to four years in both layers, showing thatradiocesium could not easily move to deeper parts(Manaka et al., 2019). Throughfall dominates as thesource of radiocesium migrating downward from thelitter layer in the case of cedar forests, while
decomposition of litter dominates in the case of broadleaved forests (Kurihara et al., 2018).

Overview of environmental impact assessment studies
Litter from forests and elution from the litter/organic
soil layer are likely contributors to the dissolved
radiocesium concentrations in river systems. Based on acompartment model analysis Kurikami et al. (2019)
reported that the origination of dissolved radiocesium
concentration in river water and freshwater fish could be
explained by a combination of these three sources.
Further investigations to clarify the dissolution
mechanism and behavior of radiocesium in forests aredesired, which would enable the establishment of models
for estimating future concentrations.

3. Radiocesium Transfer to Natural Ecosystems
Most of the radiocesium emitted in large quantities
into the environment by the FDNPP accident was
deposited in the mountainous forested areas of
Fukushima Prefecture and its surroundings. Many studies
after the accident suggest that although most of thedeposited radiocesium remains in the surface soil layer
because it is strongly bound with clay particles in the soil,
the runoff ratio from forest catchments is limited to lessthan 1.0% annually even when large storms occur (Tsuji
et al., 2016; Iwagami et al., 2017a). Therefore, forested
areas would not be involved with re-contamination in thedownstream catchment area as the source of radiocesium
migration. However, this situation implies thatradiocesium deposited on the forest floor, especially Cs137 with a long half-life (30.1 yrs.) stays nearly retainable
in the surface soil layer, which is biologically active(Takahashi et al., 2019). Therefore, understanding
radiocesium transfer in natural ecosystems is essential for
inferring future trends.
In this chapter, we outline the current state ofradiocesium distribution and properties of its transfer in
the natural ecosystems of forested areas, freshwater
bodies and wild animals, based on reports from previous
studies after the FDNPP accident.
3.1 Forest Ecosystems
As for the state of radiocesium transfer into forest
products, which is of most concern regarding radioactive
contamination of forest ecosystems, the main researchthat has been conducted has targeted evergreen needleleaved trees like Japanese cedar and cypress which havebeen utilized as timber products (Kanasashi et al., 2015;
Kajimoto et al,. 2015; Kato et al., 2017; Nishikiori et al.,2019). Since uptake followed by translocation from theabove-ground parts, mainly foliage, where it was
deposited soon after the accident, and root uptake areassumed as the transfer processes of radiocesium towood, this is of most interest. Several attempts have been
made to quantitatively evaluate the respective
contributions (Mahara et al., 2014; Nishikiori et al., 2015;
Yoschenko et al., 2018). Imamura et al. (2020) conducteda source analysis utilizing the ratio of Cs-137 activity

87

concentration to stable cesium (Cs-133) concentration inseveral components of Japanese cedar and soil porewater. They estimated that root uptake had contributed toabout 50% of the increment in Cs-137 in the stemwoodof a 40-year-old tree from Jul. 2011 to Aug. 2017 at a
maximum, although the size of this contribution was
highly uncertain. Thiry et al. (2020) applied of theircomprehensive modeling of radiocesium cycling inforests to pine trees in Belarus and Ukraine after the
CNPP accident using the observed data. They proved thatroot uptake contributed to the transfer of Cs-137 to wood
more strongly than uptake from foliage since 10 years
after the accident. Even in Fukushima, continuous
observation will be needed to see if the contribution ofroot uptake to the Cs -137 transfer to the wood ofJapanese cedar and Japanese cypress increases in the
future, although it will depend on how much bioavailable Cs-137 is generated in the soil, corresponding
to forest environment conditions.
Based on a five-year study starting from Aug. 2011,
five months after the FDNPP accident, Imamura et al.
(2017) estimated the initial deposition of Cs-137 onto theabove-ground parts of konara oak to be less than onethird of those of Japanese cedar or Japanese cypress, due
to lack of foliage at the time of the accident in the case of
deciduous broad-leaved trees. Surprisingly, Cs-137
activity concentrations in deciduous konara oak leaves
did not change over the five years, although the Cs-137
activity concentrations in the wood significantly increased
year by year. Kanasashi et al. (2020) showed that Cs-137
activity concentrations in growing coppiced shoots ofkonara oak have had a significant positive correlation
with exchangeable Cs-137 in soil in Fukushima after the
FDNPP accident. It may be necessary to examine thecontribution of root uptake as one of the main controlling
factors in determining Cs-137 activity concentrations in
the leaves and stemwood of deciduous broad-leaved trees
as well as translocation from the deposited bark andbranches. Generally, many deciduous broad-leaved trees
have shallower root systems than Japanese cedars andJapanese cypresses, suggesting that they may be able totake up exchangeable Cs-137 in soil supplied by leachingfrom litter more easily.
Since radiocesium cycling caused by transfer todeciduous broad-leaved trees via root uptake will be astrong concern regarding long-term radioactive
contamination of forest ecosystems, countermeasures tothis issue should be considered in future research.
3.2 Freshwater Ecosystems
Since radioactive contamination of fish is a big
concern from the viewpoint of inland water fisheries andthe leisure industry in freshwater ecosystems, theMinistry of the Environment; Ministry of Agriculture,
Forestry and Fisheries; and Fukushima Prefecture havebeen conducting respective monitoring projects to88

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elucidate the state of radiocesium concentrations in fish.
By utilizing these monitoring data, Ishii et al. (2020)
showed that the state of Cs-137 transfer to fish clearly
differed by habitat (river or lake) or feeding habit of fishusing the concentration factor (CF: CF = Cs-137 activity
concentration in fish (Bq/kg-fw)/Cs-137 in water (Bq/L)),
which serves as an indicator of the present state ofradiocesium transfer from the aqueous environment toaquatic organisms. It has also been confirmed that larger
fish show higher radiocesium concentrations than smaller
ones even in the same habitat or among the same species(Wada et al., 2019; Ishii et al., 2020). Freshwater fish
usually supplement cations including radiocesium
through feeding and have a lower excretion rate duringosmoregulation compared to marine fish (Wada et al.,2019). Consequently, since their radiocesium activity
concentration varies depending largely on what they eat,clarifying the flow of radiocesium via the food-web isclearly essential to understanding the mechanism oftransfer to fish.
Generally, radiocesium activity concentrations inomnivorous or carnivorous fish are higher than that in
herbivorous or planktotrophic fish (Wada et al., 2016;
Ishii et al., 2020), so how radiocesium is transferred tofish by the detritus food chain via insects feeding onforest litter is being examined. As an example, it has been
confirmed that differences in radiocesium concentrations
in litter, which is the basal food of forest and stream
ecosystems, are reflected in radiocesium concentrations
in communities of aquatic organism (Sakai et al., 2016).
Factors inhibiting lower of radiocesium activity
concentrations in fish need to be investigated andeffective countermeasures to prevent radiocesium fromtransferring to fish need to be examined as much as
possible based on scientific knowledge obtained from anevaluation of transfer properties through the food web inorder to promote the recovery of industries related to
freshwater fish.
3.3 Wild Animals
As for the transfer of radiocesium originating fromthe FDNPP accident to wild animals, the current andtransition states have been examined mainly with regard
to game animals from the viewpoint of food-safety. From
the reported Cs-137 activity concentrations in game meatdata from Asian black bears (Ursus thibetanus), wildboars (Sus scrofa), sika deer (Cervus nippon), green
pheasants (Phasianus versicolor), copper pheasants(Syrmaticus soemmerringii), and wild ducks (Anaspoecilorhynch and Anas platyrhynchos) in more than 10
prefectures after the FDNPP accident between 2011 and2015, Tagami et al. (2016) confirmed that theconcentrations in wild boars were the highest of all, butwere lower than those reported after the CNPP accident.
Also from a comparison between Cs-137 activity
concentrations in the meat of Asian black bears or wildboars between 2011 and 2016 and Cs-137 inventories in
the areas where they had been trapped, estimated byairborne surveys (Nuclear Regulation Authority 2020),
Nemoto et al. (2018) reported that each concentration
was proportional to the inventory and the concentrationin wild boars was higher than in Asian black bears if they
had been trapped in the same area.
As for the aggregated Cs-137 transfer factor (Tag =activity concentration in meat (Bq/kg-fw)/inventory in2soil (Bq/m )), which is an indicator of transfer properties
from radioactive contaminated land to game animals, thegeometric means (GM) for green pheasant and wild duckremained on the order of 10-4 during the monitoring
period, while those for Asian black bear, wild boar, sika
deer and copper pheasant were one order higher (Tagami
et al., 2016; Nemoto et al., 2018). Compared with the
Tag after the CNPP accident, directly comparable dataobtained for wild boars were in the same range of the GM
values (4 × 10−3 to 6.7 × 10−2) collected within five years
after the CNPP accident by International Atomic Energy
Agency (IAEA; Howard et al., 1996).
The annual change in Tag depends on the species.
While it decreases slightly in some species (wild boar,
green pheasant and wild duck), no significant change has
been found in other species (Asian black bear, sika deerand copper pheasant). Although clear seasonal changes in
Cs-137 activity concentration were found in wild animals
after the CNPP accident (Semizhon et al., 2009), a
uniform opinion has yet to be formed in the case of the
FDNPP accident. While Tagami et al. (2016) concluded
that no seasonal trends could be found in any species
from the collected data, Nemoto et al. (2018) stated thatmuscle Cs-137 varied seasonally and that this seasonalvariation also differed between Asian black bears andwild boars. It might be necessary to conduct more
successive sample collections and detailed analyses
considering differences in feeding among species ordifferences in environment between the areas affected by
the FDNPP and CNPP accidents to gain a clearer
understanding of the properties. Concretely, progress will
be needed in studies focused on gastric contents of wild
animals to elucidate increases in concentrations according
to when and what they eat (Saito et al., 2020). This
pertains especially to the most contaminated wild boars
whose numbers are confirmed to have increased due tothe effects of evacuation orders affecting seriously
contaminated areas (Lyons et al. 2020). More detailed
research on ranging behavior, dietary habits and the longterm behavior of radiocesium in forest ecosystems will beneeded in Fukushima Prefecture and surrounding areas(Hinton et al., 2015).

4. Effects of Radiation and Human Evacuation on
Wild Organisms and Ecosystems in Fukushima
As a result of the FDNPP accident, all of the wildOverview of environmental impact assessment studies
animals and plants have been left behind in highradiation-dose areas, so they are still exposed to radiationin Fukushima. It is, therefore, of high concern whether
any adverse effects have been found in wild organisms in
the Fukushima area resulting from long-term, low-dose
exposures to radiation. In the first half of this chapter, we
focus on radiation effects in wild organisms found in
Fukushima, where small but serious adverse effects ofradiation have been detected. However, the risks fromradiation on wild organisms will diminish becauseradiation doses in Fukushima have been decreasing
through natural decay, weathering and efforts fordecontamination. The area covered by the evacuation2
zones has been steadily decreasing, from 1,150 km in
2
August 2013 to 340 km in April 2019, as air dose rates
have decreased. With the lifting of evacuation orders,
about 58,000 former residents of the evacuation zones,
have been permitted to return to their hometowns, but thearea’s population is only 28% of its total before theaccident. Thus, changes in land use with the cessation ofdaily life activities, such as agricultural and horticulturalwork, continue, and these significantly affect the wildorganisms and ecosystems in the evacuation zones. In the
Fukushima evacuation zones, because the air dose rates
are gradually decreasing with time, it will be necessary to
pay more attention to the effects of the evacuation on
wild organisms and ecosystem rather than direct effects
from radiation hereafter. Therefore, the impacts of rapidchanges in human activities on wild organisms andecosystems are also described in the second half of thischapter.
4.1 Estimated Levels of Exposure of Wild Organisms
to Radiation
Levels of contamination with radioactive materials
and estimated radiation exposure doses in marine andterrestrial organisms living in Fukushima were initiallypredicted to exceed the derived consideration reference
levels (DCRLs) determined by ICRP and reported during
first month after the accident (ICRP, 2008; GarnierLaplace et al., 2011; Strand et al., 2014). According to theprediction, marine organisms including seaweed, benthic
invertebrates and benthic flatfish were expected to havesuffered severe effects from radiation categorized as“reduction in life span” in ICRP’s DCRLs (Tamaoki,2016). However, very few adverse effects were found inmarine organisms living in Fukushima.
The only exception was reported by Horiguchi et al.
(2015), in which the abundance and diversity of intertidal
species decreased significantly with decreasing distancefrom the FDNPP in 2012, and no rock shells (Thais
clavigera) were observed within a radius of 20 km of the
FDNPP. Unfortunately, whether the decrease ordisappearance of these species was caused directly by theincrease of radiation doses or not remains unclear at thismoment.

89

4.2 R adiation Effects in Wild Organisms in Fukushima
In contrast to marine organisms, only rodents were
expected to suffer from radiation at the level categorized
as “reduced production” in ICRP’s DCRLs for terrestrialorganisms (Tamaoki, 2016). Onuma et al. (2020)
calculated exposure dose rates for large Japanese fieldmice (Apodemus speciosus) captured in the “difficult-toreturn zones” in Fukushima Prefecture from 2012 to2016, and they found that the total dose rate (sum ofinternal and external dose rates) was estimated at lessthan 1.0 mGy/day. Exposure exceeding 1.0 mGy/day
could reduce fertility in male and female field miceaccording to ICRP’s DCRLs, indicating that the present
dose rates of the field mice living in the capture sites
were lower than the dose rates that would reduce fertility.
Accordingly, no significant differences in apoptotic cell
frequencies or frequencies of morphologically abnormal
sperm were observed in field mice captured in Fukushima
as compared to the results from two control sites, in
Aomori and Toyama prefectures, in 2013 and 2014
(Okano et al., 2016).
Among organisms living in Fukushima,morphological abnormalities were detected in somespecies such as the pale grass butterfly (Pseudozizeeriamaha) (reviewed by Hiyama et al., 2015), gall-forming
aphids (Tetraneura sorini and T. nigriabdominalis)(Akimoto 2014) and conifer tree species (Japanese firtree; Watanabe et al., 2015, Japanese red pine; Yoschenko
et al., 2016). It is noteworthy that no abnormal
morphologies in the butterfly and aphid have been
observed since 2013 (Akimoto, 2014; Hiyama et al.,2015). This indicates that the abnormal phenotypes inthese small insects only occurred within two years after
the FDNPP accident, and severely malformed individuals
were eliminated by natural selection.
In addition, there is no evidence of genetic mutations
causing abnormal morphologies. Further studies areneeded to obtain positive proof that these abnormal
phenotypes occurred due to radiation, and reproductive
experiments such as irradiation of butterflies, aphids andconifer tree species for long periods at low doses would
also be effective for advancing our knowledge onradiation effects in wild organisms.
4.3 
Effects of Radiation on Abundance of Wild
Populations in Fukushima
Radiation effects on population sizes in insect andbirds were also investigated in the Fukushima evacuation
zones. Møller et al. (2013) took a census of spiders,grasshoppers, dragonflies, butterflies, bumblebees andcicadas at 300 sites in forested areas of the evacuation
zones. They found that the abundance of butterflies andcicadas declined significantly with increasing levels ofradiation doses. Interestingly, the abundance of spiders
showed a positive correlation to the radiation doses at thesites where they were collected. Such positive

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K. IIJIMA et al.

correlations observed in spiders were not observed inparticular in the case of Chernobyl, where all of thearthropods showed negative correlations between theirabundance and radiation dose rates.
The effects of radiation on the abundance ofcommon birds were also studied in Fukushima and theresults obtained were compared to those in Chernobyl(Møller et al., 2012). Fourteen bird species common toboth Fukushima and Chernobyl showed abundance
negatively correlated to radiation doses at the two sites,
but the tendency toward negative effects differed between
Fukushima and Chernobyl. Interestingly, the negative
correlation between the abundance of these 14 common
bird species and radiation doses was more pronounced in
Fukushima than in Chernobyl. The reasons for thesedifferences in radiation-dose-dependent change inabundance of spiders and bird species between
Fukushima and Chernobyl are unclear. Some research
evidence indicates that wild organisms living in
Chernobyl have already finished undergoing adaptation
to and/or selection for high radiation environments
because the investigations in the area started 20 years
after the Chernobyl accident. Thus, it will be very
important to study whether adaptation and/or selection is
occurring in the Fukushima evacuation zones.
4.4 Effects of Human Non-residence by Evacuation on
Population Size in Wild Organisms
To clarify the effect of evacuation on wildorganisms, biota monitoring targeting mammals, birds,
frogs and flying insects inside and outside the evacuation
zones in Fukushima has been undertaken since 2014
(Yoshioka et al., 2016). As reviewed previously, theabundance of carpenter bees (Xylocopa appendiculata)
was lower in the evacuation zone than outside it(Yoshioka et al., 2015; Tamaoki 2016). Moreover, somesmall bees, wasps and beetles were more common inside
the evacuation zone. The causes of these population
changes in some insect species are unclear, but changes
in human activities such as abandonment of cultivation
and/or gardening may affect them. Among frogs, eightspecies have been observed during the monitoring, but
the frequency of observation of each frog species has not
yet been compared inside and outside of the evacuation
zones. The two-year data sets (2014–2015) obtained were
published as a data paper for enabling its use by otherresearchers (Yoshioka et al., 2020).
Mammals have been monitored at 46 sites in ninemunicipalities inside and outside the evacuation zones(locations can be seen at http://www.nies.go.jp/biowm/
map/en_mafu.html). Infrared camera traps were
employed, which automatically respond to infrared
radiation from homothermic animals. Sixteen different
mammal species have been observed through camera
trapping (Fukasawa et al., 2016). Among these, wildboars (Sus scrofa) were caught on camera most often andat the largest number of sites (78% of the monitoredsites). A statistical analysis showed that wild boars weremore abundant in the evacuation zone than outside it,indicating that decreased human activity may help thewild boar population increase. The same tendency was
also found to a lesser extent in other species such as
badgers (Meles meles), Japanese macaques (Macaca
fuscata) and Japanese hares (Lepus brachyurus). The
same result was also reported by Lyons et al. (2020) in
which they found no evidence of impact on population
size in mammals or gallinaceous birds, and showed thatseveral species were most abundant in the evacuation
zones, despite the presence of high radiation doses.
Among them, increased wild boar populations inFukushima have resulted in damage to agriculturaloperations and require control by state-funded hunting
programs. Radiocesium levels in wild boar meat often
exceed government guidelines for food consumption, notonly in and around the evacuation zones but also in the
Aizu area in western Fukushima Prefecture, more than
100 km from the FDNPP. Moreover, wild boars are
considered a pest animal in farmland, and are a major
mediator of classical swine fever which can seriously
damage the pork industry. Indeed, about half of theanimal damage to crop yields in Fukushima is due to wildboars, and wild boars infected by swine fever virus havebeen found in Aizu-Wakamatsu City as of September
2020. Thus, it is important to clarify the population
dynamics and migratory movements of wild boars inFukushima to develop an efficient plan for helping
residents return to the evacuation zones.

5. Summary
In this paper, we have provided an overview ofrecent progress in investigations of the environmental
impact induced by the FDNPP accident, focusing
especially on radiocesium transfer to natural ecosystems
and the effects of deposited radioactive materials onorganisms.
Litter from forests and desorption from the litter/organic soil layer are likely contributors to dissolved
radiocesium concentrations in river systems. The originsof the dissolved radiocesium will evolve with time inaccordance with the source of radiocesium migrating
downward from the litter layer to the mineral layer. In
forest ecosystems, radiocesium is thought to migrate intowood by root uptake and/or uptake from deposits onabove-ground parts followed by translocation. The
contribution of root uptake, however, has not been
evaluated as of this time. As a source of dissolved
radiocesium affecting river systems and forest
ecosystems, the behavior of litter decomposing andleading to the dissolution of radiocesium in forests is a
key issue to be investigated in the future.
The transfer of Cs-137 to freshwater fish is affectedOverview of environmental impact assessment studies
by habitat (river or lake), feeding habit, body size and soon. It has also been pointed out that the concentration ofradiocesium in litter is related to that in communities ofaquatic organism. Among wild animals, wild boars
showed relatively higher radiocesium concentrations, but
the tendencies of concentrations to evolve, such as
through seasonal variation, are still under discussion. To
predict future concentrations in these ecosystems, itwould be desirable to clarify dominant pathways oftransfer of radiocesium via the food-web throughcontinuous systematic sample collection and detailed
analysis.
Direct effects of increased radiation doses have notbeen clearly observed among marine organisms, whilemorphological abnormalities have been detected in somespecies of terrestrial organisms, such as small insects andconiferous trees. However, further investigation will beneeded to obtain evidence as to whether or not genetic
mutations caused these abnormalities. Negative effects ofradiation on population size in insects and birds have also
been observed in areas affected by the FDNPP and CNPP
accidents, respectively, though the tendencies differed insome cases. Conversely, the decrease in human activities
caused by conditions of high radiation are thought to leadto increased wild boar populations. In future work, it will
be important to investigate whether adaptation and/or
selection occur in the Fukushima evacuation zones and to
elucidate the population dynamics and migratory
movements of wild boars.
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93

Kazuki IIJIMA
Kazuki Iijima heads the Fukushima Environmental
Evaluation Research Division at the Collaborative
Laboratories for Advanced Decommissioning
Science, Japan Atomic Energy Agency (JAEA).
He is interested in how radionuclides behave inthe environment, especially the interactions oftrace amounts of radionuclides with minerals andorganic matter of natural origins. Previously, he investigated the behaviorof radionuclides under conditions deep underground (stable and static forlong periods). After the Fukushima Daiichi nuclear power plant accident,
he started studying their behavior at the earth’s surface. (He says it is so
unstable and too dynamic!)

Seiji HAYASHI
Seiji Hayashi is a research group manager at the
Fukushima Branch of the National Institute forEnvironmental Studies. He serves as project
leader for research on radioactive substancebehavior in multimedia environments. His
energetic research activities are contributing to
the environmental recovery of Fukushima
Prefecture and its surrounding region.

Masanori TAMAOKI
Masanori Tamaoki is principal researcher at the
Fukushima Branch of the National Institute forEnvironmental Studies (NIES). He has also been
appointed associate professor at the University ofTsukuba. He has studied plant responses tooxidative stress, especially to air-pollutant ozone.
Ozone is known to generate reactive oxygen
species (ROS) in leaves, harming vegetation. ROS is also produced inorganisms exposed to radiation; hence he launched an investigation into theeffects of radiation on plants in 2011. He transferred to the Fukushima
Branch of NIES from June 2016 and is investigating the impacts ofradiation on wild organisms in Fukushima with his colleagues as project
leader.
(Received 17 December 2020, Accepted 28 December 2020)

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Overview of Open Biodiversity Data around the Fukushima
Disaster Area and the Nuclear Power Plants in Japan
Akira YOSHIOKA1*, Nao KUMADA2, Yui OGAWA2 and Keita FUKASAWA2
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi Ibaraki, 305-8506, Japan*E-mail: yoshioka.akira@nies.go.jp*1

Abstract
Examining the comprehensive impacts of the nuclear accidents in Fukushima on biodiversity continues
to be a challenge. Data availability may be one problem. Previous studies have used hardly any ecological
data from before the accidents. Furthermore, raw data from the previous studies have been not adequately
released for re-analysis and integration into new analyses. To examine the current status and problems with
open biodiversity data and monitoring systems related with nuclear plants, we surveyed (1) datasets registeredin GBIF (the Global Biodiversity Information Facility) around the Fukushima evacuation zone (including the“difficult to return zone,” Fig. 1) and (2) monitoring sites of the Monitoring Sites 1000 Project and JaLTER(Japan Long-Term Ecological Research Network) around Japan’s nuclear power plants. The GBIF databaseshows that few datasets on wild organisms exist covering periods both before and after the Fukushima
accident around the evacuation zone, except on birds. The present monitoring sites near the nuclear power
plants are shown mainly to target wild birds and sites targeting other taxa are limited. In addition, themonitoring surveys have been highly dependent on citizen scientists. To enhance biodiversity data availability
in preparation for evaluating impacts of nuclear emergencies, it would be desirable to improve monitoring
systems and technologies for integrating monitoring by citizen scientists in normal times with monitoring by
scientists belonging to institutes in times of emergency.
Key words :	citizen science, ecology, monitoring, nuclear power plant, open science

1. Introduction
The Fukushima Daiichi nuclear power plant(FDNPP) accident in 2011 following the Great East Japan
Earthquake and Tsunami resulted in increased radiationlevels over a large area owing to radioactive materials
released from the FDNPP. Many studies have examinedthe ecological and biological impacts of that radiation on
biodiversity from the genetic to the population level(Tamaoki, 2016; UNSCEAR, 2017). Some studies havesuggested remarkable negative effects on wild plants andanimals (e.g., Hiyama et al., 2012; Møller et al., 2012,2013; Akimoto, 2014; Ochiai et al., 2014; Watanabe et al.,2015; Horiguchi et al., 2016), while others have not (e.g.,
Matsushima et al., 2015; Yoshioka et al., 2015; Okano etal., 2016; Lyons et al., 2020). It is difficult to explainsome of the remarkable negative results only fromdirect radiation dose effects considering the spatial
distribution of the air dose in the disaster area
(Garnier-Laplace et al., 2011; UNSCEAR, 2017). Wildorganisms and environments not only interact with each
Global Environmental Research
24/2020: 095-104
printed in Japanother in complicated ways, but can also be affected byinterruption of anthropogenic activities as a result ofevacuation orders (Yoshioka et al., 2015; Lyons et al.,2020). Although United Nations Scientific Committee on
the Effects of Atomic Radiation (UNSCEAR) (2017)concluded that any radiation effects would have been
constrained to a limited area and that the potential for
effects on biota beyond that area was insignificant, thelong-term impacts of the nuclear disaster on biodiversity
and ecosystems remain to be seen.
One difficulty in evaluating the impacts on
biodiversity may be limited availability of data. First,
studies based on data covering periods both before andafter the accident are limited. Murase et al. (2015)
compared the data on reproductive performance of thegoshawk Accipiter gentilis before and after the
Fukushima accident and suggested that the reproductive
rate was negatively affected by the radiation doses. The
study site, however, was more than 100 km from the
FDNPP and the air dose rate was quite low (0.27– 0.85
µSv/h) compared to the derived consideration reference©2020 AIRES

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A. YOSHIOKA et al.

level (DCRL) for birds: 0.1–1 mGy/day by International
Commission on Radiological Protection (ICRP, 2008).
Please note that the air dose rate measured using adosimeter (TERRA-P, Sparing-Vist Center, Lviv,
Ukraine) in Murase et al. (2015) was considered tocorrespond to a gamma-ray dose equivalent rate and weassumed that 1µSv≒1µGy (Morishita, 2007). Comparing
data around the FDNPP and the evacuation zone before
and after the accidents would provide morecomprehensive inferences on the direct and indirect
effects of the radiation. Although no one desires a nuclear
accident, preparation in advance for evaluating the impact
is desirable.
The second problem with data availability is
openness and transparency of the data. The biologicalimpacts of the nuclear accidents are of interest not only toscientists in multiple fields, but also to citizens. Amongscientists, lack of underlying data makes appropriate
interpretation difficult (Beresford et al., 2012). Citizens
have become skeptical of science and technology as aresult of the nuclear accident (Ministry of Education,
Culture, Sports, Science and Technology, Japan, 2012).
To meet their expectations with limited information,
accumulating and sharing raw data in the most open andtransparent manner as possible would be helpful. In
addition, considering serious nuclear accidents have been
relatively infrequent (e.g., the Fukushima accident
happened about 25 years after that in Chernobyl.) and theimpacts can continue for a long time, contacting
corresponding authors of papers on past accidents is notalways easy. Sharing data in an open manner (e.g., using
data repositories) would be desirable for integrating pastdata and novel data. Therefore, the concept of open
science and citizen science (Silvertown, 2009) would besuitable as a research theme (Fukasawa et al., 2017a).
Out of 20 papers on the biological and ecologicalimpacts of the Fukushima accident that Tamaoki (2016)
reviewed, however, only two papers (Murase et al., 2015
and Yoshioka et al., 2015) published the raw data they
had used for statistical analysis, which is a basic
component of ecological research (Økland, 2007). After
2016, some research groups that had reported remarkable
results immediately after the accident published related
studies presenting raw analyzed data (Morelli et al., 2017;
Hiyama et al., 2017; Akimoto et al., 2018), but that’s notalways the case (e.g., Hayama et al., 2017; Møller &Mousseau, 2019). Thus, open data has not been astandard assumption under this research theme.
Interdisciplinarity may be one reason open data havebeen uncommon in this area. Differences in the culture ofdata sharing and access between different disciplines, andthe lack of obvious, public, community repositories canpose a significant barrier to public data deposition(Nature Research, 2016). Nevertheless, leading scientificjournals are working to improve the situation. Nature
Research (2019) stated that sharing of data in earth, spaceand environmental sciences will be required through datarepositories at Nature and the related Nature Research
journal; and Scientific Data, a nature research group
journal for data papers, will be updating its list ofrecommended data repositories to help authors from thesefields comply with these new policies. This movement
may encourage researchers studying environmental
impacts of radiation to publish their raw data as well.
As matters stand, there is room for improvement indata availability and openness in research on the
biological and ecological impacts of the nuclear accident.
To improve the situation from the viewpoint of ecologists,
we have published ecological datasets collected inside
and around the Fukushima evacuation zone in the form ofdata papers (Fukasawa et al., 2016; Fukasawa et al.,2017b; Ishiniwa et al., 2019; Yoshioka et al., 2020).
Likewise, compiling open data collected in the past
regardless of the FDNPP may be useful for evaluating theimpact of the accident. Furthermore, current ecologicalmonitoring systems not related to the nuclear disaster
could potentially play an important role in evaluating theecological risks of nuclear accidents in the future. In thispaper, we examine open data and related projects
regarding the distribution and population dynamics ofwild organisms that can potentially play a role inbiodiversity monitoring in the event of nuclear accidents
via two approaches: (i) datasets collected around the
FDNPP and registered in GBIF (the Global Biodiversity
Information Facility), which is one of the largest worldwide platforms for open data on biodiversity, areexamined, and (ii) monitoring sites around nuclear power
plants in Japan and the monitoring targets of the“Monitoring Sites 1000 Project,” a national project formonitoring biodiversity, are examined as indicators of
preparation for future emergencies. Based on theseresults, the characteristics and limitations of data
availability on biodiversity data in Japan from theviewpoint of nuclear accidents are discussed.

2. GBIF Data around the FDNPP
GBIF is an international network and research
infrastructure funded by governments around the world
and aimed at providing anyone, anywhere, open access todata about all types of life on Earth (GBIF, 2020).
Through the GBIF website, datasets on biological
specimens and species distribution data registered byresearch institutes and scientists worldwide are available
for free. Using the filter function of the website, we
extracted datasets within a rectangular area enclosing theevacuation zone of Fukushima registered through June30, 2020 (Fig. 1, GBIF.org, 2020). The latitudes andlongitudes of the corners of the area are (N37.2402º,
E140.61826 º), (N37.2402 º, E141.04526 º), (N37.76172 º,
E141.04526 º), (N37.76172 º, E140.61826 º). Please notethat the filer function on the GBIF web site is able toOpen biodiversity data around nuclear plants

N

FDNPP

Fig. 1 S
 patial distribution of ecological data registered in GBIF
(Global Biodiversity Information Facility) near the FDNPP(Fukushima Daiichi nuclear power plant) through 30th June
2020. The sky blue circles and deeper blue circles show
locations where the data were obtained before and after 2011,
respectively. The latitudes and longitudes of the corners of thedata-extracted area are (N37.2402º, E140.61826º), (N37.2402º,
E141.04526º), (N37.76172º, E141.04526º) and (N37.76172º,
E140.61826º). Please note that GBIF data outside the region
were not extracted. The background map was obtained from
National Land Numerical Information (Ministry of Land,
Infrastructure, Transport and Tourism, 2014). The green, yellow
and red zones correspond to the “areas preparing for the liftingof the evacuation order,” “restricted residential areas” and“areas to which it is difficult to return” sub-zones, respectively.
The evacuation zone classification was based on conditions in
October 2013 (Cabinet Office, Government of Japan, 2013).

10000

extract only simple polygonal regions.
Based on “occurrences” (records of when and wherea species existed, used as a unit in GBIF data), 75,556
occurrence records were extracted. Among them,
however, 137 records lacked information on the year ofsampling. Most of data had been obtained after 2011
(only 2,891 occurrence records had been obtained before
2011, see Fig. 2 also) and consisted of birds (Fig. 3).
Actually, a large part of the data set on birds was obtainedby NIES (National Institute for Environmental Studies,Japan) for monitoring the evacuation zone starting from2014 (Fukasawa et al., 2016; Fukasawa et al., 2017b;
Fig. 4). Excluding avian and mammalian data setsobtained by NIES for its biodiversity monitoring project
after the accident (66,226 and 5,267 records, respectively),
the volume of the remaining data decreased to about 5%.
The remaining data consisted mainly of data on waterfowl
populations and plant specimens (Fig. 3(c)). The waterfowl
population data were based on a continuous census
conducted by the Ministry of the Environment, Japan,
and the abundance data were also published through thenational government’s website (Biodiversity Center ofJapan, 2020a). Thus, the dataset may give someinferences through ecological analysis. On the other hand,the dataset on plant specimens was obtained in thecontext of natural history and most of the data had beenobtained before the accident. Several assumptions areneeded and additional data may be required to analyze
the dataset from an ecological viewpoint. The specimen
data do not always show that the species were absent orrare in locations where specimens were not recorded.
There are some ecological analysis methods for presenceonly data such as Maxent (Phillips et al., 2006), so
inferences of the results should be carefully conducted.
Results of such an analysis will be biased due to spatial
heterogeneity of the monitoring effort. Anyway, the taxa
in the species distribution data available from GBIF arehighly biased toward birds as matters stand. In particular,
data before the nuclear accident are limited conspicuously.
NIES
Others

1000
100
10
1
0.1

1895
1909
1921
1929
1934
1939
1954
1958
1962
1966
1971
1975
1979
1983
1987
1991
1995
1999
2003
2007
2011
2015
2019

Number of occurrence records
registered in GBIF

10000097

year

Fig. 2 Number of GBIF occurrence records registered by NIES (National Institute for Environmental Studies, Japan)
and other institutes near the FDNPP per year as of 30 June 2020.

98

A. YOSHIOKA et al.
(a) ~2010

Names of datasets registered in GBIF.

2,891 records
3%

2%

1% 1%3%

1

Number of occurrence records

10

100

1000

10000 100000

Acoustic monitoring data of avian species inside andoutside the evacuation zone of the Fukushima
Daiichi power plant accident
Mammal assemblages recorded by camera traps
inside and outside the evacuation zone of the
Fukushima Daiichi nuclear power plant accident
Annual Census on Waterfowl (Anatidae) Population

31%

14%

FKSE-Herbarium of Faculty of Symbiotic Systems
Science, Fukushima University, Japan
Vascular plant specimens of National Museum of
Nature and Science (TNS)

17%

Vascular plant specimens of Nagano Environmental
Conservation Research Institute, Nagano Prefecture

28%

Fungal Specimens of National Museum of Natureand Science (TNS)
Ibaraki Nature Museum, Vascular Plants collection(b) 2011~ 72,528 records

Paleobiology Database1%

7%

Geographically tagged INSDC sequences
Vascular Plant Specimen database of Kanagawa
Prefectural Museum of Natural History
Ibaraki Nature Museum, Lichen collection
Royal Botanic Garden Edinburgh Living Plant
Collections (E)Database of Native Plants in Taiwan

92%

Ibaraki Nature Museum, Arthropoda collection
Plant specimens in the Museum of Nature andHuman Activities, Hyogo Prefecture, JapanThe others(c) 2011~ 1,032 records
3%

2%
2%

1%

Fig. 4 Names of datasets containing GBIF data near the FDNPP
and numbers of occurrence records included. The first andsecond largest dataset correspond to data published by
Fukasawa et al. (2017b) and Fukasawa et al. (2016),
respectively.

4%

13%

37%

3. Ecological Monitoring Sites around the
Nuclear Plants in Japan

15%
23%

Animalia
Mammalia
Aves
Insecta

Plantae
Magnoliopsida
Polypodiopsida
Liliopsida

Fungi
Agaricomycetes
Sordariomycetes
Lecanoromycetes
Pezizomycetes

Bacteria
Bacilli
Gammaproteobacteria
OthersFig. 3 
Proportions of GBIF occurrence records of each taxon(class) near the FDNPP (a) through 2010, and (b) from2011. Occurrence records from 2011 other than datasetsfrom NIES (Aves: 66,226 records, Mammalia: 5,267
records, Insecta: three records, respectively) are also shown(c). In each graph, taxa accounting for less than 1% aresummed under “Others.”

Including decommissioned plants such as the
FDNPP, there are 17 nuclear plant location points inJapan as of 2020 (Table 1). Although no nuclear accident
should ever happen again, the existing biodiversity
monitoring systems around the nuclear power plants are
expected to be useful in evaluating the status ofbiodiversity and ecosystems at normal times and the datafrom them to contribute to analysis of changes in status if
nuclear emergencies should happen.
The Monitoring Sites 1000 Project is a long-term
nationwide project for monitoring biodiversity andecosystems that has been conducted by the Ministry of
the Environment, Japan since 2003 (Watanabe et al., 2012;
Kobori et al., 2015). To cover Japan’s wide variety of
ecosystems, the monitoring data are collected not only by
scientists belonging to research institutes, but also trained
citizen scientists associated with the Wild Bird Society ofJapan and the NACS-J (Biodiversity Center of Japan,
2019, 2020b). In long-term and broad-area biodiversity
monitoring projects, citizens’ cooperation has often

Open biodiversity data around nuclear plants

99

Table 1 The existing nuclear power plants in Japan (including decommissioned plants) and “Monitoring Sites 1000 Project” sites,
important for monitoring the current status of the ecosystems around the nuclear plants. The terrestrial area within 30 km of eachnuclear power plant is based on Ministry of Land, Infrastructure, Transport and Tourism, Japan (2014) and calculated using
ArcGIS 10.2 (ESRI Inc.). The land area of Japan overall is based on Geospatial Information Authority of Japan (2020).
Nuclear power plant Prefecture

Monitoring Sites 1000 within 20km
(focal ecosystem)

Tomari
Higashidori

Hokkaido
Aomorin.a.
n.a.

Onagawa

Miyagi

Ashijima (small islet)

Fukushima Daiichi
Fukushima Daini

Fukushima
Fukushima

Tokai & Tokai Daini Ibaraki

n.a.
n.a.

Shiga

Ishikawa

Tsuruga

Fukui

Namekawahama (rural area)
Ibaraki-kenminnomori(forest and grassland)
Koshijihara hill (rural area)
Kashiwazaki-yumenomori park(rural area)
Besshodake (forest and grassland)
Ochigata (lake and wetland)
Nosaka-ikoinomori (forest and grassland)

MihamaFukui

Nosaka-ikoinomori (forest and grassland)

Ohi

Fukui

n.a.

Takahama
Hamaoka

Fukui
Shizuoka

Kashiwazaki Kariwa Niigata

Shimane

Ikata
GenkaiSendai

Kanmurijima & Kutsujima (small islet)
Ogasayama (forest and grassland)Omaezaki coast (sandy shore)
Sagara coast (sandy shore)
ShimaneLake Nakaumi (lake and wetland)
Lake Shinji (lake and wetland)
Esturay of Hii River (lake and wetland)
Sada River (tidal flat)
Ehime
Suwazaki-shizenkyuyorin(forest and grassland)
Sanctuary-donguri (rural area)
Saga
n.a.
Kagoshima
Shibisan (forest and grassland)

played quite an important role (Silvertown, 2009; Bonney
et al., 2009). The compiled dataset has been available
from the project’s website and partly from the GBIF
website, though some parts of the dataset are closed (e.g.,
data on species at risk from poaching and overexploitation). Because this project aims to detectdegradation of ecosystems at early stages through longterm continuous monitoring, the dataset is expected tocontribute to evaluation of the state of biodiversity aroundnuclear plants now and in the future.
Here, we examine the spatial distribution of themonitoring sites (Fig. 5; Table 1; Table 2) based on the
project’s website (Monitoring Site 1000 Project, 2020).
We extracted the geographic coordinates of theMonitoring Sites 1000 within 20 –30km(focal ecosystem)
Nakoma (rural area)
Mutsuyokohama (forest and grassland)
North coast of Shimokita peninsula (lake and wetland)
Obuchinuma (lake and wetland)
North part of Mutsu bay (lake and wetland)
Takasegawa-Mutsuogawara port (tidal flat)
Bentenjima (small islet)
Monomiishiyama forest road (forest and grassland)
Downstream of Kyu-Kitakami River(forest and grassland)
Haden-ya (rural area)
Shizugawa (seaweed bed)
Hirusone-Ohatake forest road (forest and grassland)
Hirusone-Ohatake forest road (forest and grassland)
Estuary of Natsui River (tidal flat)
Tanodairasandou (forest and grassland)
Hinuma (lake and wetland)

The number of sites perterrestial area within
30 km (sites/km2 )
5.26×10-4
6.82×10-3

6.40×10-3

7.19×10-4
1.44×10-3
2.59×10-3

Tsukioka forest road (forest and grassland)

1.96×10-3

Tokinofurusato-Notomaruyama (rural area)
Chirihama (tidal flat)
Sanriyama (forest and grassland)
Kuroko forest road for Mikuniyama(forest and grassland)
Kuroko forest road for Mikuniyama(forest and grassland)
Ashiu (forest and grassland)
Ashiukamitani (forest and grassland)
Kanmurijima & Kutsujima (small islet)
Ashiu (forest and grassland)
Oigawachofujimori-Yaizushitajiri (tidal flat)

3.28×10-3

Hoshikamiyama (forest and grassland)
Esturay of Iinashi River (tidal flat)

4.55×10-3

Dogadani-tonbonosato (rural area)

3.79×10-3

Ochi (forest and grassland)
Urushinosatoyama (rural area)

9.96×10-4
1.65×10-3

Mean ± SD

2.68×10-3 ± 1.90×10-3

Number of sites in Japan (24 June 2020)
Land area of Japan overall (sites/km2 )Density of monitoring sites in Japan (sites/km2 )

1,014
377,975.21
2.68×10-3

1.83×10-3
1.33×10-3
2.06×10-3
1.31×10-3
4.35×10-3

representative points of each monitoring site from the liston the website and examined whether the monitoringsites were included within a 20-km radius of a nuclear
power plant using ArcGIS 10.2 (ESRI Inc.). The
geographic coordinates of nuclear power plants wereobtained from the National Land Numerical Information(Ministry of Land, Infrastructure, Transport and Tourism,2013). We adopted the distance of 20 km here because
the area within the 20 km of the FDNPP was declared atemporary evacuation zone in Fukushima when
information on the spatial distribution of air radiation
doses was inadequate. Considering that the values ofcoordinates of the monitoring sites on the website wererelatively rough (about 0.01– 0.1 degrees), we also

100

A. YOSHIOKA et al.

(a)

(b)

N
N

Copyright of the background map:
Geospatial Information Authority of Japan

Copyright of the background map:
Geospatial Information Authority of Japan

Fig. 5 Spatial distribution of the monitoring points of the Monitoring Sites 1000 Project and nuclear power plants in the (a) eastern and(b) western part of Japan, respectively. The blue points indicate representative points of each monitoring site. The black points
indicate nuclear power plants. The circles of solid and dotted grey lines indicate the areas within a 20 km and 30 km radius fromthe nuclear plant, respectively.

Table 2 Relationships between focal ecosystems and monitoring targets (surveyed indicators) in the Monitoring Sites 1000 Projects.
Please note that only cases within 30 km of a nuclear plant are shown.
Focal ecosystem
Forest and grassland

Monitoring target
Terrestrial birds, Vegetation

Rural area

Flora
Water environment
Vegetation (Anthropogenic impacts)
Birds
Large-middle size mammals
Harvest mouse Micromys minutus
Frogs
Butterflies
Fireflies

Lake and wetland

Waterfowl
Plankton, Benthos, Vegetation

Sandy shore
Tidal flat
Seaweed bed
Small islet

Turtles
Shorebirds
Seaweed vegetation, Benthos
Seabirds

examined areas within 30 km of each nuclear power plant
as a buffer. In addition, areas 30 km from nuclear power
plants usually correspond to “Urgent Protective Action
Planning Zones” based on Japan’s Nuclear Emergency
Response Guidelines (Nuclear Regulation Authority,2019), in which precautionary sheltering and emergency
monitoring of environmental radiation levels are required
under nuclear emergency situations.
As a result, all nuclear power plants in Japan(including decommissioned plants) are located within

Remarks
In addtion, ground-dwelling beetles, litter and tree growth have also beensurveyed in “Ashiu,” which is one of the core sites for forest monitoring.
Targeting indicators of traditional agricultral landscapes in Japan, the socalled “satoyama.” Usually, more than one from the nine targets issurveyed by citizen scientists (see Table 3). In the core sites, multiple
indicators are surveyed (only the “Urushinosatoyama” site in Kagoshima
Pref. is a core site for rural area monitioring within 30 km of a nuclear
power plant).

At “Shinjiko” and “Nakaumi,” plankton, benthos and vegetation have beensurveyed. At the other sites within 30 km of a nuclear plant, waterfowl has
been surveyed.

30 km of one or another of the monitoring sites, though
six of the 17 nuclear power plants have no corresponding
monitoring sites within 20 km. In particular, the numberof monitoring sites in Hokkaido and Kyushu (Saga andKagoshima prefectures) is likely to be small. The numberof the monitoring sites near the nuclear power plants inFukushima Prefecture is also small (three sites in total
within 30 km). However, the mean density of sites within
the 30 km zone (site number per terrestrial area) was-32
2.68×10 sites/km , almost equivalent to the site number

Open biodiversity data around nuclear plants

101

Table 3 Monitoring targets of rural (satoyama) sites of the Monitoring Sites 1000 Project near nuclear power plants, based on Biodiversity
Center of Japan (2019).
Monitoring sites
NakomaHaden-ya
Namekawahama
Koshijihara hill
Kashiwazaki-yumenomori park
Tokinofurusato-Notomaruyama
Sanctuary-donguri
Dogadani-tonbonosato
Urushinosatoyama

Flora Water environment

Vegetation○

Large-middle size mammals

Harvest mouse Frogs Butterflies Fireflies

○

○
○

Birds

○

○

○

○

○

○

○

○

○

○

○

○
○

○

○

○

○

○

○

○

○
○

per land area of Japan overall (Table 1).
Considering focal ecosystems and monitoringtargets, most sites have targeted birds (Tables 1 and 2). In
addition, these bird monitoring surveys have been
conducted by citizen scientists. Therefore, citizen scienceis essential to monitoring the current status of biodiversity
and ecosystems around nuclear plants. Sites surveying
taxa other than birds are quite scarce. Although the sites
focusing on rural areas (so-called satoyama, a traditional
heterogeneous agricultural landscape of Japan; Takeuchi,
2001; Kadoya & Washitani, 2011) have mainly surveyed
flora as well as birds, the total number of these sites isless than 10 (Table 3). There are even fewer sites
surveying mammals, frogs or insects.
Furthermore, we also examined JaLTER (Japan
Long-Term Ecological Research Network) monitoringsites near the nuclear plants. JaLTER was established in
November 2006 to provide scientific knowledge
contributing to conservation, advancement andsustainability of the environment, ecosystem services,
productivity and biodiversity for society by conducting
long-term and interdisciplinary research in ecologicalscience including human dimensions (JaLTER, 2020a).
This scientific network became an official member of the
ILTER (International Long-Term Ecological Research)
project (Ohte et al., 2012), which along with GBIF plays
an important role in ecological data archiving (Osawa etal., 2013). Monitoring of the sites has been mainly
conducted by scientists belonging to research institutes(JaLTER, 2020b) and the datasets have been available
from a database called JalTER Metacat (JaLTER, 2020c).
The 61 representative points of the JaLTER sites wereextracted from a Google Maps map. The Ashiu Forest
Research Station was located within 30 km of the Oi
nuclear power plant, while the Maizuru Fisheries
Research Station was located within 20 km of the
Takahama nuclear power plant and within 30 km of theOi nuclear power plant. The Lake Shinji and Lake
Nakaumi sites were located within 20 km of the Shimane
nuclear plant. The locations and associated institutes of
the JaLTER site in Ashiu, Lake Shinji and Lake Nakaumi
overlapped to some extent with the sites of theMonitoring Sites 1000 Project. Therefore, JaLTER’s sites

○
○

○

○
○

○

○

○

may not adequately complement the Monitoring Site
1000 Project’s.

4. Discussion
In this study, we have obtained an overview of theecological motoring data/sites around Japan’s nuclear
plants that could play an important role owing to theiravailability. The results suggest that datasets on bird
dynamics are relatively abundant, while datasets on othertaxa are inadequate. In addition, the datasets on birds
have been collected by not only researchers, but also
citizen scientists from NGOs such as the Wild Bird
Society of Japan and NACS-J (Biodiversity Center ofJapan, 2019, 2020b), though research institutes such as
NIES play an important role in publishing data aroundthe Fukushima evacuation zone. The waterfowl census
data conducted by the Ministry of the Environment, Japanand registered in GBIF have also been based on
considerable cooperation from environmentalorganizations such as the Wild Bird Society of Japan(Ministry of the Environment, Japan, 2020a). Therefore,
availability of open biodiversity data is highly dependent
on taxa, and interest among citizens will be important.
The caveat here is that our overview is not acomplete review of open biodiversity datasets near
nuclear power plants. We may have overlooked otherfreely available ecological datasets and long-termmonitoring sites which were not registered in GBIF or the
Monitoring Sites 1000 Projects, respectively. In addition,
the datasets from these projects cannot cover certain
types of biodiversity components. For example, detailed
information on endangered species has usually not beenreleased by these projects to avoid poaching andoverexploitation. In addition, data based on hunting andfishing (i.e., economically important data) which havebeen compiled by national or local governments (orrelated organizations) are often not released. Some
databases have been released, but not adequately
integrated into these world-wide projects (e.g., Ministryof Land, Infrastructure, Transport and Tourism, 2007).
Furthermore, it goes without saying that the biodiversity
datasets and monitoring sites have not usually conducted102

A. YOSHIOKA et al.

surveys assuming nuclear accidents. Data and samples oninternal exposure or mutation have not been monitored,
though part of the data followed by preserved samples or
specimens may make it possible to examine thesebiological effects later. Nevertheless, the biodiversity
status should be rapidly assessed in emergent situations
and easily available datasets representing normal
situations will be required for comparison. GBIF and theMonitoring Sites 1000 Project are convenient and readily
accessible to researchers and citizens. The open data
provided by them will be important for rapid assessmentof the status and dynamics of biodiversity.
From the viewpoint of improving preparation for
future emergencies, what is needed is not only to maintainthe current monitoring system, but also to provide asystem for encouraging surveys of taxa diversity. Of
course, the available manpower is usually limited, so
indicator taxa should be well considered. If monitoringtaxa other than birds is difficult, we should know how
birds, which have often been assumed to be a good
indicator of biodiversity (Greenwood, 2007), indicate or
surrogate the status of other taxa in the event of nuclear
accidents. Promoting registration of long-term datacollected by local governments to GBIF or other available
platforms may relieve the bias in monitored taxa in open
biodiversity data. In principal, construction of nuclear
power plants must accompany environmental surveys
based on the Environmental Impact Assessment Act andthe data associated with surrounding biodiversity shouldhave been collected, though only summarized results
were published for a limited period of time under thecurrent system (Ministry of the Environment, 2020b).
Furthermore, as our review shows, enhancing andmaintaining participation of citizen scientists inecological monitoring will be essential. The problem isthat if a nuclear disaster happens, the citizens will not beable to collect data around the nuclear plants as before theaccident. Therefore, methodology for follow-up of citizen
scientists by scientists belonging to research institutes
will also be important. In the case of the Fukushima
accident, NIES has been conducting acoustic bird surveys
using voice recorders and has set up opportunities toshare their recordings of bird songs with local bird
watchers (Fukasawa et al., 2017a). To prepare for futurenuclear emergencies (or other disasters with movement
restricted long term) appropriately and sustainably, ahybrid of surveys by citizen scientists and automateddigital devices may be key. Ideally, a scheme that
integrates monitoring by citizen scientists in normal times
and that by scientists belonging to institutes in emergency
times should be established from the viewpoint of bothtechnologies and systems.

Acknowledgements
We would like to thank Dr. M. Tamaoki (National
Institute for Environmental Studies, Japan) and tworeviewers for their valuable comments.
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Akira YOSHIOKA
Akira Yoshioka is a senior researcher at the
Fukushima Branch of the National Institute forEnvironmental Studies, Japan. To evaluate theimpacts of evacuation orders on biodiversity,
since 2014, he together with the coauthors has
been conducting biodiversity monitoring of theevacuation zones necessitated by the FDNPP
accident. His main field of study has been flying insects in the evacuation
zone and he is now developing original camera traps to monitor red
dragonflies. He has also studied development of an index for satoyama, thetraditional agricultural landscape of Japan, which plays an important role inbiodiversity conservation but is threatened by increasingly prevalent land
abandonment.

Nao KUMADA
Nao Kumada is a specialist at the Center for
Environmental Biology and Ecosystem Studies,
National Institute for Environmental Studies,Japan. She has supported biodiversity monitoringof the Fukushima evacuation zone and her
contributions range from data compilation todevelopment of a novel method for estimating the
population density of birds. She is also a member of the Japan Bird
Research Association and has studied the ecology of cormorants vigorously.

Yui OGAWA
Yui Ogawa is a junior research associate at theCenter for Environmental Biology and Ecosystem
Studies, National Institute for Environmental
Studies, Japan. She has studied citizen scientists’attitudes contributing to biodiversity datacollection, especially on birds, and is now
developing online training tools for assisting
acoustic bird monitoring in the Fukushima evacuation zones.

Keita FUKASAWA
Keita Fukasawa is a senior researcher at theCenter for Environmental Biology and Ecosystem
Studies, National Institute for Environmental
Studies, Japan. He has studied statistical modelingand population density estimation for various
plants and animals from the viewpoint ofmanaging wildlife and alien species, as well as
biodiversity conservation in underused agricultural ecosystems.
(Received 4 September 2020, Accepted 21 December 2020)

105

Role and Effect of a Dam on Migration of Radioactive
Cesium in a River Catchment after the Fukushima Daiichi
Nuclear Power Plant Accident
Seiji HAYASHI* and Hideki TSUJI
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: shayashi@nies.go.jp

Abstract
Positive and negative roles of dam reservoirs in radiocesium behavior in a river catchment were
examined based on the results of comprehensive, long-term hydrological monitoring from 2013 to 2017 at
Matsugabou Dam on the upstream reaches of the Uda River, which is one of the main rivers in the northerncoastal region of Fukushima Prefecture. An estimation of the annual mass balance of Cs-137 associated withsuspended solids (SS) in the reservoir showed that Matsugabou Dam had the effect of reducing the migrationof radiocesium associated with SS from the dam reservoir catchment to the downstream reaches by more than
85% by storing SS in the reservoir bed. Moreover, proactive discharge control for preventing flood inundationin the downstream region had the ability to make this storage function perform even more effectively. On theother hand, the estimated annual mass balance of dissolved Cs-137 in the reservoir showed that the amount in
the water discharged clearly tended to exceed the amount in the inflow, suggesting that substantial amounts ofdissolved radiocesium were presumably produced by dissolution/elution from the stored bottom sediments inthe dam reservoir. This negative role of a dam producing dissolved radiocesium may contribute to long-term
contamination of freshwater ecosystems in downstream water bodies.
Key words :	bottom sediment, dam reservoir, discharge control, dissolution, runoff

1. Introduction
Most of the seriously radioactively contaminatedareas resulting from the Fukushima Daiichi nuclear
power plant (FDNPP) accident consisted of mountainous
forests (Morino et al., 2011). Few forested areas havebeen decontaminated because decontamination operations
have been limited to inhabited areas such as residential
districts, farmland, roads and marginal forests nearresidential districts (Ministry of the Environment, 2019).
Consequently, the remaining vast forested area is left as apotential source of radiocesium penetration into
downstream regions. Therefore, there are concerns aboutrecontamination of the downstream regions as well as
prolonged contamination of freshwater ecosystems by
runoff from forested areas. Meanwhile there are over 90
water supply dams in Fukushima Prefecture, where
agriculture is well developed as one of the mainindustries. Although radiocesium runoff originating fromthe FDNPP accident has been confirmed to be limited toless than 0.3% annually in forest catchments (Shinomiya
et al., 2014; Iwagami et al., 2017; Tsuji et al., 2016), it is
Global Environmental Research
24/2020: 105-113
printed in Japan

also a fact that a successive inflow of radiocesium indissolved or particulate forms has been occurring fromdam reservoir catchments covered mainly by seriously
contaminated forest. As for behaviors of radiocesium
originating from the FDNPP accident in dam reservoirs,
although it is assumed that radiocesium associated withsuspended solids (SS) flowing into a reservoir tends toaccumulate in the bed through the water storage functionof the dams (Kurikami et al., 2014; Huon et al., 2018), a
quantitative evaluation of that function has yet to be fully
accomplished based on long-term monitoring.
Additionally, research on the effects of the re-suspension
or dissolution of radiocesium from bottom sediment isvery limited (Funaki et al., 2020). There is a need toaccumulate scientific knowledge from the viewpoint of
not only understanding the behavior of radiocesium in adam reservoir but also examining the roles of dam
reservoirs in radiocesium dynamics in river catchments.
An approach of clarifying radiocesium dynamics
comprehensively in a significantly contaminated dam
reservoir catchment would contribute to a detailed
examination of radiation exposure risks via various©2020 AIRES

106

S. HAYASHI and H. TSUJI

pathways in river catchments.
The objective of this paper is thus to presentcharacteristics of radiocesium dynamics in a dam
reservoir catchment mainly covered with forest affectedby the FDNPP accident that have been elucidated on thebasis of the data from our observations since 2012.
Moreover, based on these results, the positive andnegative roles of dam reservoirs in radiocesium behavior
in a river catchment are discussed from the viewpoint ofconsidering various pathways of radiation exposure.

deposition of Cs-137 from the FDNPP accident into
the DRC, SFC and WURC was 260 kBq/m2, 170 kBq/m2
and 210 kBq/m2, respectively, based on the third airborne
survey conducted by the Ministry of Education, Culture,
Sports, Science and Technology (2011).
2.2 Sampling and Monitoring
To elucidate temporal changes in radiocesium
activity concentration in the river and water discharged
from the dam and evaluate the mass balance ofradiocesium in the Matsugabou Dam reservoir, automatichydrological observation (2150 Area Velocity Module,
Teledyne Isco, Lincoln, NE, USA) and turbidity
observation (DTS-12, Forest Technology Systems Ltd.,
Victoria, British Columbia, Canada) were conducted in
the stream to measure the flowrate at the outlet of the
SFC (37°48’10.7”N 140°45’28.1”E, #2 in Fig. 1) from
July 2012 with a time interval of 10 min. Turbidity was
automatically measured at the chapter just downstream ofthe dam discharge point (37°47’44.3”N 140°46’23.2”E,#3 in Fig.1) using TC-500 (OPTEX Co., Ltd., Otsu,
Shiga, Japan) from May 2013 and at the observatory at
the outlet of the WURC (37°47’23.6”N 140°54’42.8”E,#1 in Fig. 1) using an INFINITY-Turbi (JFE Advantech
Co., Ltd., Nishinomiya, Hyogo, Japan) from July 2012
with a time interval of 10 min. Measured data with a timeinterval of 10 min. for the dam discharge volume and theflowrate at the downstream observatory were obtained
from Soma City and Fukushima Prefecture, respectively.
Water samples were collected at the hydrologicalobservation point in the SFC from Oct. 2012, theinflow chapter to the dam reservoir (37°47’44.6”N
140°44’43.7”E, #4 in Fig. 1), mainly during low flow
conditions from June 2014, in the chapter justdownstream of the dam discharge point from Oct. 2013,
and at the WURC observatory from Oct.2012. Sixty liters
or more of river water was regularly sampled using a
20 L plastic bucket at two-to-four-week intervals fromthe center of flow during low-flow conditions. During
rain runoff events, an auto water sampler (ISCO

2. Materials and Methods
2.1 Study Area
Matsugabou Dam constructed on the upstream
reaches of the Uda River and completed in 1997 wasselected as the objective of this study (Fig. 1). The Uda
River is one of the main rivers in the northern coastal
region of Fukushima Prefecture, about 50 km northnorthwest of the FDNPP. Matsugabou Dam reservoir,
which has a surface water area of 0.72 km2 and total
storage capacity of 9,710 × 106 m3, is operated mainly tosupply irrigation water to the developed paddy fields inthe middle and lower reaches of the Uda River catchment.
The dam reservoir catchment (DRC, catchment area:
25.4km2) consists mainly of forest (80%), with 7%
paddy fields, 5% farmland and 3% built-up areas. The soilin the DRC is mainly brown soils or red-brown forest
soil. A small forested catchment (SFC, catchment area:
0.34km2) was selected to study the radiocesium
runoff characteristics from a forested area. Additionally,
to estimate the effect of dam storage functions on
prevention of radiocesium migration to downstream
areas, an observation site was set in the downstream
reaches of the Uda River (#1 in Fig. 1) to get an
overview of the radiocesium runoff characteristics of
the whole Uda River catchment (WURC, catchment area:
95.6 km2) consisting of 79% forest, 7% paddy fields, 5%
farmland and 4% built-up areas. The spatially averaged

Matsukawaura
LagoonMatsugabou Dam
reservoir

DRC

Uda Riv.

Fukushima Prefecture

SFC

WURC

Forestcatchment#2#4

Reservoir#1

Uda River catchment
Matsugabou Dam#3: Hydrologic observation & water sampling points: Rainfall observatory by Matsugabou Dam Maintenance Facility: Bed sediment sampling point

Fig. 1 Outline of study site. Data from the third airborne survey (MEXT, 2011) are used for the Cs-137 deposition map.

Role & effect of a dam on radiocesium migration
6712, Teledyne Isco, Lincoln, NE, USA) was used tocollect 3 L of river water for every sample in addition tothat taken in the same manner during low flow conditions
to sample the stream water at 30 – 60 min intervals.
Bottom sediment samples were collected using an
undisturbed sediment core sampler (HR type, RIGO Co. Ltd,Tokyo, Japan) at a site near the dam every late autumn
after the typhoon season from 2012 to 2016. In particular,
three core samples were collected at almost the same
point to get an understanding of the spatial variation inradiocesium accumulation properties in 2015 and 2016.
2.3 Measurement
Particulate and dissolved radiocesium in water
sampled during low flow conditions were collected
separately using two types of cartridge filters (Tsuji et al.,2014; Yasutaka et al., 2015) immediately after sampling.
As for the samples collected during rain runoff events,
either centrifuge separation (15,760×g, 25min) to extract
suspended matter or the cartridge filters described above
were adapted depending on the SS concentration after
being brought back to the laboratory to measureparticulate radiocesium concentration. After centrifuge
separation, the extracted suspended matter was placed in
100-mL plastic containers, dried at 60°C, weighed andanalyzed for Cs-134 and Cs-137. The SS concentration of
all of the water samples was measured by a filtering
method using glass fiber filter papers (pore size, 0.7 µm,
GF/F; GE Healthcare, Tokyo, Japan) to develop an
equation to estimate the respective SS concentration fromturbidity data measured at each observatory site as wellas to evaluate its association with the particulate
radiocesium concentration.
The collected reservoir bottom sediment coresamples were sliced at 1–2 cm intervals from the surface,
and the sliced samples were placed in 100-mL plastic
containers, dried at 60°C, weighed and analyzed for
Cs-134 and Cs-137.
Cs-134 and Cs-137 activities in samples were
measured using a coaxial or a well-type germanium
detector (GC2518 or GCW7023; Canberra, Meriden,
CT). A Spectrum Explorer (Canberra Japan, Tokyo,
Japan) was used to analyze the γ-ray spectra.
MX033U8PP (The Japan Radioisotope Association,
Tokyo, Japan) was used as the standard source for theefficiency calibration. Estimates of the activities ofsamples trapped in the cartridge filters were geometricallycorrected using the formula of (Tsuji et al., 2014;
Yasutaka et al., 2015). The activities were decaycorrected to the sampling date, and then the activity
concentration was determined on a dry weight basis.
Since it was confirmed that the proportion of activity
concentrations of Cs-134 and Cs-137 for each sample
was almost 1.0 after decay correction to Mar. 11, 2011,
only Cs-137 was used, as described in the Results andDiscussion below, from the viewpoint of evaluating longterm radioactive contamination.

107

3. Results and Discussion
3.1 Particulate Radiocesium Runoff Properties from
Forests and Entire River Catchments
The activity concentrations of dissolved Cs-137 werevery low (less than 0.02 Bq/L) at the outlets of both the
SFC and the WURC at the beginning of our observation
period and have also been decreasing since then.
Therefore, only particulate Cs-137 was considered in
evaluating the amount of radiocesium migration at theriver-catchment scale in this study because dissolved
radiocesium contributes little to radiocesium flux during
the rain runoff events that play an important role intransport and dispersion of radiocesium in riverwatersheds and coastal marine environments, as pointed
out by Nagao et al. (2013). Figure 2 shows the temporalchange in the activity concentration of Cs-137 associatedwith SS in the outlets of the SFC and WURC (#2 and #1
in Fig. 1). The temporal change of each respective decline
in concentration was fitted using a single component
exponential model represented by the following equation:
Cs_SS = A ∙ e – λ ∙ t

137

SS

…… (Eq.1)

where 137Cs_SS (Bq/kg-SS) ) represents the activity
concentration of Cs-137 associated with SS, A (Bq/kgSS) and the effective decay constant, λSS (1/y) areempirically determined constants, and t (y) is time
elapsed since deposition. The statistical analysis used todetermine these parameters was performed using Origin
version 2020 data analysis and graphing software(OriginLab Corporation, Northampton, MA, USA). The
concentrations at both sites fluctuated greatly until a hugerain event, tropical storm Etau, occurred in September
2015 with a large amount of rainfall over two days as issaid only to occur every 50 to 100 years. It is especiallycurious that the concentrations at the SFC were relatively

Tropical storm Etau occurrence

137Cs_SS = 15.2e-0.20t

137Cs_SS = 12.2e-0.26t

Fig. 2 
Change over time in activity concentrations of Cs-137
associated with SS in the small forest catchment (SFC) andthe whole Uda River catchment (WURC) after the FDNPP
accident.

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S. HAYASHI and H. TSUJI

higher than those at the WURC, contrary to differences in
the initial amount of Cs-137 deposited between thecatchments. This may be due to the fact that
decontamination operations in farmland and inhabitedareas in the upper reaches of the WURC began in theautumn of 2012. Additionally, no significant decreasing
trend in the activity concentration of Cs-137 associatedwith SS could be confirmed in the forest stream (Hayashi
et al., 2016). However, the concentrations decreased withrelatively small fluctuation after tropical storm Etau,
which consequently brought about a significant
decreasing trend exceeding natural decay at the both sites.
The effective decay constant (λSS) in the SFC wasestimated to be 0.20 (y-1) which is in the range of thevalues (0.15 – 0.44 (y-1)) estimated by Iwagami et al.
(2019) based on monitoring from Apr. 2012 to Nov. 2016
in several small forest catchments in Yamakiya District,
Kawamata Town, located around 35 km northwest of the
FDNPP. Although no detailed analysis has been
conducted to explain these decreases that are much fasterthan natural decay in the activity concentration ofcesium-137 associated with SS in a forest stream, theextreme rain event of 2015 is assumed to have eroded
fine surface mineral soils with high concentrations ofradiocesium or washed highly contaminated forest
organic matter out from the river banks and riparianzones which play a dominant role in sediment production(Sakuma et al., 2018). This might bring about thedecreases shown in Fig. 2 in the concentration andfluctuation of the activity concentration of Cs-137
associated with SS since then. Also for the effective
decay constant (λSS) in the WURC, the estimated value(0.26 (y-1)) corresponds approximately to the reported
values in other major rivers in the northern coastal region(0.06 – 0.41(y-1); Taniguchi et al., 2019). Although theeffects of land use or decontamination operations areassociated with SS (Bq/g)

137Cs activity concentration

25.0
SFC
WURC

20.0
15.0

Table 1 Ratio of annual Cs-137 runoff associated with SS to theamount of Cs-137 deposited, estimated from the third
airborne survey data (MEXT, 2011) in the small forest
catchment (SFC) and the whole Uda River catchment(WURC).

10.0
y = ‒ 1.2ln(x) + 14
R² = 0.26

5.0
0.0

indicated as a cause of the concentration clearlydecreasing (Taniguchi et al. 2019), a detailed mechanism
remains to be clarified by applying an SS source analysis.
Figure 3 shows the relationship between SS
concentration and Cs-137 activity concentration
associated with SS in the SFC and WURC. The plottedCs-137 concentration values are decay-corrected to Mar.
11, 2011 to remove the effect of physical decay on therelationship. While increases in SS concentration easily
exceeding 1,000 mg/L would obviously contribute to
decreases in the activity concentration of Cs-137
associated with SS from huge rain events, resulting in
sediment runoffs with larger amounts of sandy
components, variations in SS concentration were notconfirmed to have a significant effect on Cs-137
concentrations associated with SS at either site whenrelatively high rain events happened. Ratios of annual Cs137 runoff associated with SS to the amount of Cs-137
deposited in the catchments are presented with annual
rainfall amounts observed at the Matsugabou Dam
maintenance facility (Fig.1; 37°47’46.5”N 140°46’13.7”E)in Table 1. Data from the third airborne survey (Ministryof Education, Culture, Sports, Science and Technology,2011) were used to calculate the amount of Cs-137
deposited in each catchment. The annual amount of Cs137 runoff was calculated using sequential data on
flowrates and SS concentrations and by applying theestimated Cs-137 concentration decay equation at eachsite (Fig. 2). The annual runoff ratio varies considerably
whether huge rain events occur or not. In fact, in 2015
when tropical storm Etau hit in September, 90% of theannual Cs-137 runoff amount was produced during thisrain event. Decay in Cs-137 concentrations associatedwith SS is also an important factor influencing the runoff
ratio, because the ratio in 2016 was less than that in 2013by half despite the annual rainfall amount in 2016 being
larger than in 2013.
3.2 Role of Dam Reservoirs in Radiocesium Storage
Functions
As a result of applying Eq. 1 to the time series dataon Cs-137 radioactivity concentration associated with SS

0

1000

2000

3000

SS (mg/L)

4000

5000

Fig. 3 Relationship between SS and activity concentrations of Cs137 associated with SS in the small forest catchment (SFC)
and the whole Uda River catchment (WURC).

Cs-137 runoff ratio (%)
SFC

WURC

Annual rainfall*
(mm)

2013

0.081

0.25

1152

2014

0.084

0.066

1700

2015

0.15

0.47

1732

Year

2016

0.037

0.092

1432

2017

0.027

0.023

1346

*Observed at the Matsugabou Dam maintenance facility.

Role & effect of a dam on radiocesium migrationin the water discharged from Matsugabou Dam, theradioactivity concentration was found to decreasesignificantly faster than the physical decay rate (Fig. 4;
λSS: 0.22 (1/y)), although it showed large variations
among samples. Just as in the cases of the forest stream
or downstream reaches, no SS concentration effects on
Cs-137 associated with SS could be clearly distinguished.
The Cs-137 concentration fluctuated considerably under
low discharge conditions with less than 5 mg/L of SS
concentration (R2=0.03, p=21, N=63). Additionally, it
was not clear whether Cs-137 concentrations associatedwith SS were influenced by increased SS concentrations
in discharged water from pronounced sediment inflows to
the dam reservoir during rain runoff events because of
insufficient sample numbers.
Figure 5 shows the vertical distribution of Cs-137
radioactivity concentration in undisturbed bottom
sediment core samples collected around the deepest point
near the dam itself each year in late autumn from 2012 to2016. The samples for 2015 were collected in November
after tropical storm Etau passed. Since the bottom
sediment in this area with a water depth of more than
30 m is rarely disturbed by water flow, the vertical
distribution of radiocesium in bottom sediment is formed
only through settling and accumulation of inflow
sediment. The most notable point is that the sedimentlayer with the highest concentration of Cs-137 had
obviously migrated downward to deeper levels from 2014
to 2015. Hayashi (2017) suggested that the sedimentlayer with the highest peak in the Cs-137 concentration
be assumed to have been influenced by direct deposition
to the reservoir surface or the initial inflow to thereservoir after the accident. Those layers were located alittle deeper from the surface of the bottom sediments inanalyses using undisturbed bottom sediment core samples
in the Matsugabou Dam reservoir in 2012 and 2013. They109

also suggested that the layer with the highest
concentration apparently continues migrating downward
due to intermittent sediment inflow from the dam
reservoir catchment. From that observation, the settlingand deposition of huge amounts of sediment inflow into
the dam reservoir when tropical storm Etau hit in
September 2015, are considered to be the main reason thelayer with the highest concentration of Cs-137 moved
downward remarkably in the bottom sediment. Also, oneof the core samples collected in 2016 showed the highest
concentrations to be in a deeper layer of the bottom
sediment. This may have been caused by spatial
heterogeneity in the process of sedimentation anddeposition of the inflowing sediment due to complex
topography of the reservoir bed. The huge amounts of
sediment inflow and their accumulation at the bottom arealso confirmed by annual measurements of dam reservoir
sedimentation conducted by the Soma Land Improvement
District (not published). The measurement data show that3
the amount of sand accretion in Jan. 2016 (114,000 m )increased by twice as much as that in Jan. 2015
(53,000m3). Although the amount of Cs-137 accumulatingin the bottom sediment samples showed an annual
increasing trend, it was not significant (R2=0.37, p=0.27).
In addition to insufficient sample numbers, this variation
among the sampling points might be influenced by spatial
heterogeneity in accumulation of Cs-137 on the reservoir
bed.
Since the annual changes in the observed
sedimentation and vertical distribution of Cs-137 activity
concentrations in the bottom sediment showed that thedam acted to store radiocesium associated with SS
pouring in from the reservoir catchment, an attempt toquantify the function was made by annually comparing
137Cs activity concentration

0.0

0

20

(kBq/kg-dry soil)
40

60

80

100

137Cs_SS = 13.4e-0.22t

Mass depth (g/cm2)

2.0
4.0
6.0
8.0
10.0
12.0
14.0

Fig. 4 
Change over time in activity concentrations of Cs-137
associated with SS in the water discharged from Matsugabou
Dam after the FDNPP accident.

2016-a2016-b
2016-c2015-a2015-b2015-c
2014
2013
2012

Fig. 5 
Annual changes in vertical distribution of Cs-137activity
concentrations in bottom sediment collected in theneighborhood of Matsugabou Dam itself. All of the samples
were collected each late autumn after the typhoon season.

110

S. HAYASHI and H. TSUJI

the amount of Cs-137 associated with SS between the
inflow into the dam reservoir and the discharge from thedam. Each annual amount of Cs-137 inflow associatedwith SS was calculated by multiplying the estimatedamount of Cs-137 deposition by each annual runoff ratioof Cs-137 associated with SS in the dam reservoir
catchment. The annual runoff rate in the DRC wasassumed equal to that of the watershed, which is the
WURC minus the DRC. This is because the spatial
distribution of land use in the catchment is similar to thatof the DRC. Specifically, it was estimated by dividing thedifference calculated by subtracting the annual amount of
Cs-137 associated with SS discharged from the dam fromthe annual amount of runoff from the WURC, by theamount of Cs-137 deposited in the area, subtracting the
DRC area from the WURC area. Table 2 presents theannually calculated runoff ratios, inflows and amounts of
Cs-137 discharged associated with SS, and the effects thedam had on storing Cs-137 associated with SS andpreventing its migration to the coastal area. Although the
inflow and amount of Cs-137 discharged varied fromyear to year corresponding to the annual rainfall amount,i.e., the amount of sediment inflow from the dam
reservoir catchment, the runoff ratio was confirmed toremain at more than 84% every year. The contribution ofinternal production to the concentration of Cs-137
associated with SS and its mass balance in the dam
reservoir is not clear but may not be significant, as shown
by Tsuji et al. (2020) in the Yokokawa Dam reservoir on
the Ohta River in the northern coastal region of
Fukushima Prefecture. It is especially curious that theretention ratio in 2015 (93%) when the huge storm event
happened was higher than that in 2017 (84%), which wasa typical dry year. Since the effective decay rate in theconcentration of Cs-137 associated with SS in the WURC
(λSS: 0.26), which was faster than that in the SFC (λSS:0.20) or the dam discharged water (λSS: 0.22), was appliedin estimating the runoff ratio of Cs-137 associated with
SS from the DRC, the runoff ratio of 2017 may have been
underestimated. Moreover, as pointed out by Hayashi
et al. (2016), active water storage management for
preventing flood inundation downstream may haveresulted in a larger retention ratio by promoting thesettling and deposition of the amount of Cs-137 inflow
associated with SS during the huge rain event, accounted

for about 95% of the annual total inflow. When comparedwith the case without a dam, these high ratios also
indicate that the dam plays a role in reducing the amountof Cs-137 inflow associated with SS into the coastal area
(Matsukawaura Lagoon; Fig. 1) by about 30% every year
through its storage function.
While huge amounts of sediment flowed into thereservoir, Hayashi et al. (2016) suggested that proactive
dam discharge control for flood prevention downstream
had accelerated the accumulation of sediment on thereservoir bed. This is also supported by the sedimentation
survey results described above. Additionally, in terms ofusefulness of water storage management for storing
radiocesium associated with SS in dam reservoirs, in asimulation of the Ogaki Dam reservoir Yamada et al.
(2015) found that the amount of clay discharged,
including large amounts of radiocesium from thereservoir, could be reduced by a factor of three by raising
the height of the dam exit. These results clearly show that
not only does a dam function to prevent migration anddiffusion of radiocesium associated with SS by storing itin the reservoir, but also that proactive discharge control
has the potential to help fulfill this function more
effectively.
3.3 Effect of Dam Reservoirs as Sources of
Dissolved Cs
Figure 6 shows the annual changes in dissolved
Cs-137 activity concentration measured every two weeks
or monthly in the dam reservoir inflow stretch and thedam discharge channel. Unlike Cs-137 associated withSS, the activity concentration of dissolved Cs-137
showed annual periodic variations at both sites.
Moreover, since the amplitude as well as the activity
concentration of the dissolved Cs-137 have been
declining with time, the effective decay constant andefficiency half-life (Teff) of the Cs-137 concentration
could be estimated by fitting the data to the following
exponential function equation consisting of the decay
component and the periodical component using Origin
version 2020 (OriginLab Corporation, Northampton, MA,
USA). The curves fitted by the equation have also beendrawn in their respective graphs.
Dissolved 137Cs = exp ( – λdis∙ t + b + e ∙ sin( 2� (cd+ t) ))Table 2 Annual mass balance of Cs-137 associated with SS in the Matsugabou Dam reservoir and the effects of thedam on storing it in the reservoir, preventing its migration to the coastal area.
Year

Ratio of runoff
from the DRC(%)

Amount of inflow
from the DRC(109 Bq)

Amount discharged
from the dam(109 Bq)

Ratio of storage
in the dam
reservoir (%)

Ratio of prevented
migration to the outletof the entire catchment
(%)

2014

0.097

6.4

0.33

95

31

2015

0.68

44

2.8

94

31

2016

0.13

8.6

0.89

90

29

2017

0.031

2.1

0.32

84

28

Role & effect of a dam on radiocesium migration

111

λ: 0.10
Teff: 6.8
λ: 0.28
Teff: 2.5

6.5

Elapsed time from the FDNPP accident (yr)(b) Discharge from the dam reservoir(a) Inflow into the dam reservoir

Fig. 6 Change over time in activity concentrations of dissolved Cs-137 in the inflow (a) into and the discharge(b) from the Matsugabou Dam reservoir. The dark gray lines indicate fitting curves developed by Eq. 1.
The values of the effective decay constant (λ) and effective environmental half-lives (Teff) were estimatedfrom the fitting analyses.

…… (Eq.2)

Where Dissolved 137Cs represents dissolved Cs-137
activity concentration (Bq/L) at the elapsed time t (y)after the FDNPP accident and λdis represents the effective
decay constant (y-1). The constant b representing theinitial value, e representing the amplitude (Bq/L), c
representing the phase difference and d representing theperiod (y-1) are empirically determined. The analyticalresult shows that the tendency of dissolved cesium-137
activity concentration in water discharged from the dam
to decrease (λdis: 0.10 (y-1) ; Teff: 6.8 (y) ) was slower thanthat in the reservoir inflow river ((λdis: 0.28 (y-1); Teff:
2.5 (y)). Moreover, the fitted curves suggest that thetemporal difference in the peaks of concentration, in
which the peak in the discharged water emerges after adelay of about 100 days compared to that in the inflow
water, was generated between them. By applying theequation respectively to the time-series data for the total
inflow volume into the dam reservoir or the amount ofwater discharged from the dam, the annual balance ofdissolved Cs-137 in the dam reservoir was calculated andthe results are organized in Table 3. The trend of
dissolved Cs-137 activity concentration decreasing (Fig.
6) resulted in a tendency of the annual flux of the
dissolved Cs-137 to increase at both the inflow andoutflow of the dam reservoir. Moreover, by reflecting
differences in the rate of decrease in dissolved Cs-137
concentration, the annual amount discharged has
exceeded the annual amount of inflow since 2015, as
markedly shown in 2017 with little annual precipitation(Table 1). Based on long-term monitoring of dissolved
radiocesium in the Ogaki Dam reservoir, Funaki et al.
(2020) showed that the annual dissolved amount of
Cs-137 in the dam discharge water was about 1.6 times
higher than the annual amount of inflow into the dam

Table 3 Annual mass balance of dissolved Cs-137 in the
Matsugabou Dam reservoir.
Amount of dissolved Cs-137 (106 Bq)
Year

A. Inflow
into the dam

B. Discharge
from the dam

B/A

2014

564

537

0.95

2015

481

545

1.13

2016

324

349

1.08

2017

169

319

1.89

reservoir and that the effective environmental half-life of
dissolved Cs-137 in the output water was longer than in
the main input water. He concluded from the measured
vertical distribution of dissolved Cs-137 concentration in
the dam reservoir that dissolution from the reservoir bed
sediment played an important role as an internal source inincreasing the amount of dissolved radiocesium in thewater discharged from the dam. This result strongly
suggests that a substantial amount of dissolved
radiocesium is generated through the contribution ofdissolution from the bottom sediment even in the
Matsugabou Dam reservoir. How the dissolved
radiocesium is produced in the bottom sediment andsupplied to reservoir water, however, should be clarified
in future work, considering that the radioactivity
concentration of Cs-137 has been decreasing in thesurface layer of the bottom sediment as a result ofintermittent sediment inflow from the DRC.
Since the dissolved Cs-137 activity concentration
has remained at less than 0.03 Bq/L for the last few years
in water discharged from the Matsugabou Dam, a
slowdown in the rate of dissolved Cs-137 decrease
through internal production in the dam reservoir would
have very small effects on water uses like drinking or
irrigation. Additionally, no radiocesium activity

112

S. HAYASHI and H. TSUJI

concentrations exceeding the shipping regulatory value(100 Bq/kg wet weight) have been detected in water
bodies downstream since 2015 (Ministry of theEnvironment, 2020). If it is assumed, however, that
dissolution of radiocesium occurs naturally from dam
reservoir bed sediments, there may be considerable
concern about the effects of dam reservoirs on water use
or contamination of freshwater ecosystems in moreheavily contaminated areas. As for the transfer ofradiocesium into fresh water ecosystems in particular, theconcentration ratio (CR=activity concentration inorganisms (Bq/kg fresh weight/activity concentration inwater (Bq/L)), which is an indicator useful for gaining an
understanding of the state of transference of radiocesium
from water to aquatic organisms, shows values on theorder of several hundreds to several thousands in manykinds of freshwater fish (Ishii et al., 2020). Therefore,
radiocesium activity concentrations in commercial fish
could possibly exceed the specified regulatory value forshipment even if the radiocesium activity concentration isaround 0.1 Bq/L in the water. Storing huge amounts ofradiocesium in a dam reservoir bed for a long period
happens to slow down the decrease in dissolved
radiocesium activity concentrations in the water
discharged through dissolution from the bottom sediment.
This might enhance long-term contamination of aquatic
ecosystem in downstream water bodies.
The function of effectively storing radiocesium
associated with SS in a dam reservoir should be actively
utilized to prevent its migration into downstream water
bodies, particularly, the diffusion to urban areas in thedownstream region by flood inundation during extreme
storm events in the future. On the other hand, it may benecessary to pay close attention to changes in
sedimentation storage capacity resulting fromaccumulation of highly radioactively contaminated inflow
sediment. Frequent occurrences of extreme storm rainfall
events due to climate change (Intergovernmental Panelon Climate Change, 2013) will make long-term stablestorage of contaminated bottom sediment difficult in dam
reservoir beds (Mouri et al., 2014). Also for dissolutionof radiocesium from dam reservoir beds, an appropriate
response needs to be examined based on evaluations fromvarious viewpoints such as evaluating economic losses
while also considering ecosystem services at present or in
the future and performing cost-benefit analyses ofcountermeasures to prevent dissolution.

4. Conclusions
Positive and negative roles of dam reservoirs inradiocesium behavior in a river catchment were examinedbased on the results of comprehensive, long-termhydrological monitoring at Matsugabou Dam, which ismanaged on the upstream reaches of the Uda River, oneof main rivers in the northern coastal region of

Fukushima Prefecture. The main results are as follows.
・The activity concentration of Cs-137 associatedwith SS decreased much faster than natural decay in boththe forest stream and the downstream reaches of the Uda
River. Although the runoff ratio of Cs-137 associatedwith SS depends on rainfall characteristics, it tends todecrease due to decreasing activity concentration.
・Matugabou Dam has the function of reducing
migration of radiocesium associated with SS from thedam reservoir catchment to the downstream reaches bymore than 85% by storing SS in the reservoir. Moreover,proactive discharge control has the potential to help fulfill
this function more effectively, decreasing the risk ofexternal exposure through re-contamination downstreamof the dam.
・An estimation of the annual mass balance ofdissolved Cs-137 in the dam reservoir showed that theamount in the discharged water clearly tended to exceed
the amount in the inflow, with substantial amounts ofdissolved radiocesium presumably produced bydissolution from stores in the bottom sediment. Throughits dissolution, long-term storage of radiocesium in dam
reservoir beds may slow down the decrease in dissolved
radiocesium activity concentration in the discharged
water.
Acknowledgement
Hydrological data on the dam reservoir were
provided by the Soma Land Improvement District andMatsugabou Dam maintenance facility. We thank Drs.
Ito, and Nishikiori, and Messrs. Takita and Tsuchiya for
their help with the field survey, and Dr. Nishina for his
advice on statistical analysis of the dissolved Cs-137 timeseries data. This study was partially supported by a Grantin-Aid for Scientific Research (KAKENHI 16H01791)
from the Japan Society for the Promotion of Science.
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Seiji HAYASHI
Seiji Hayashi is a research group manager at the
Fukushima Branch of the National Institute forEnvironmental Studies. He serves as project
leader for research on radioactive substancebehavior in multimedia environments. His
energetic research activities are contributing to
the environmental recovery of Fukushima
Prefecture and its surrounding region.

Hideki TSUJI
Hideki Tsuji is a senior researcher at the National
Institute for Environmental Studies. He is
conducting field research on the transport andaccumulation of radiocesium in rivers and lakes.
He is also carrying out chemical analysis,
constructing a numerical model and developing
equipment to be used for environmental
measurements of bioavailable radiocesium.

(Received 24 September 2020, Accepted 28 December 2020)

Preface-24-1.indd

22020/07/30

17:54:49

115

Dynamics of 137Cs in Water and Phyto- and Zooplankton ina Reservoir Affected by the Fukushima Daiichi
Nuclear Power Plant Accident
Hideki TSUJI1*, Megumi NAKAGAWA2, Kazuki IIJIMA3, Hironori FUNAKI4,
Kazuya YOSHIMURA4, Kazuyuki SAKUMA3 and Seiji HAYASHI1
Fukushima Branch, National Institute for Environmental Studies,
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies,
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan
3
Japan Atomic Energy Agency,
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
4
Japan Atomic Energy Agency,
45-169 Sukakeba, Kaibama, Haramachi-ku, Minamisoma-city, Fukushima, 975-0036, Japan*E-mail: tsuji.hideki@nies.go.jp*1

Abstract
Lake water, phytoplankton and zooplankton were sampled in a total of 12 quarterly surveys from August
2014 to May 2017 at a reservoir in the Fukushima nuclear disaster area, and variations in dissolved forms of137
Cs and planktonic 137Cs were observed. Seasonal variations in dissolved 137Cs concentration becoming highin summer and low in winter were observed in the upstream, midstream and downstream areas of thereservoir, but no seasonal or site-specific differences in planktonic 137Cs concentrations or dominant species
were found. The concentration factors of 137Cs for phytoplankton and zooplankton were 340 and 1,700, whichwere comparable to previously reported values. The amount of planktonic 137Cs in the water was less than
1.4% of the total 137Cs in the reservoir water; therefore the effect of plankton on the dynamics of 137Cs in thereservoir was minimal.
Key words :	 137Cs, concentration factor, dissolved form, phytoplankton, Yokokawa Reservoir, zooplankton

1. Introduction
Following the accident at the Fukushima Daiichi
Nuclear Power Plant (FDNPP) in 2011, a large amount ofradiocesium was deposited in the surrounding area. In themain river catchment of the area within 50 km north of
the FDNPP, radiocesium was deposited at a higher
density in the upper reaches (Ministry of Education,
Culture, Sports, Science and Technology, 2011), and there
are concerns that the future transport of highconcentrations of radiocesium into rivers may result inradioactive contamination of downstream areas. Indeed,in this area, some freshwater fish are still subject toshipping restrictions even nine years after the nuclear
accident, because their radioactivity levels from134
137
radiocesium (mainly Cs and Cs) are still above the−1national limit of 100 Bq kg . (Fukushima Prefecture,
2020a).
On most of the major rivers in this region, dams
were built in the upstream areas for storing irrigationwater. Dams also have the function of storing most of the
Global Environmental Research
24/2020: 115-127
printed in Japan

inflowing sediment and thus intercepting the discharge ofparticulate radiocesium to downstream. However,radiocesium in the bottom sediment of a reservoir can
gradually leach out, especially when promoted underanaerobic conditions (Evans et al., 1983; Kaminski et al.,1994), suggesting that it may act as a source of nonnegligible amounts of dissolved radiocesium in the longterm (Funaki et al., 2020). Furthermore, because
reservoirs usually have a wide distribution of areas withdeep euphotic zones, plankton as one of the main foodsources for fish breeds easily and the transfer ofradiocesium to plankton is promoted in this environment.
Considering these circumstances, dams may play a majorrole in the radioactive pollution of aquatic ecosystems asa source of bioavailable radiocesium. Therefore, it isimportant to focus on the dynamics of radiocesium inreservoirs to predict future ecological pollution in thiscontaminated area.
The fate of dissolved radiocesium, which is a
representative form of bioavailable radiocesium, infreshwater has been reported to show the following©2020 AIRES116

H TSUJI et al.

characteristics: its concentration is generally proportional
to the averaged 137Cs inventory in the catchment (Tsuji etal., 2014a; Ochiai et al., 2015; Yoshimura et al., 2015),
and shows seasonal variation within the environment
with a peak from summer to autumn (Alberts et al., 1979;
IAEA, 2006; Tsuji et al., 2016; Wang et al., 2017;
Wakiyama et al., 2017; Nakanishi & Sakuma., 2019;
Matsuzaki et al., 2020). In addition, dissolved 137Csconcentrations in natural water decrease faster than thephysical half-life (Smith et al., 2005; Onda et al., 2020),
but the decrease in concentration is reported to be slower
than that of particulate 137Cs in the area near the FDNPP(Nakanishi & Sakuma, 2019).
The concentration of radiocesium in plankton ismainly regulated by that in water, and the concentration
factor of radiocesium (ratio of the radiocesium
concentration in organisms to that in water) decreases
with increasing salinity (Ishii et al., 2020). The
concentration factor of plankton living in seawater isreported to be on the order of 100–101 (Tateda, 1998;
Kaeriyama et al., 2008), whereas the concentration factor
for plankton in freshwater environments is 102–104(Knapinska-Skiba et al., 2003; International Atomic
Energy Agency, 2004). Furthermore, because plankton
bodies have a high proportion of chemically bioavailable
components (Mori et al., 2017), their detritus could be afactor in the reproduction of bioavailable forms ofradiocesium.
As described above, the spatio-temporal variation indissolved radiocesium in the aquatic environment ofradioactive contaminated areas and its factors have been
elucidated, but the variation in planktonic radiocesium infreshwater lakes is not well understood. For example, it is
not known how the concentration and total amount ofradiocesium in plankton change seasonally, while theconcentration of dissolved radiocesium fluctuates
seasonally over a year. Because laboratory
137
experimentation has proven that the Cs concentration
factor of plankton increases with water temperature(Wolfe & Coburn, 1970), the hypothesis can be raisedthat the 137Cs concentration in plankton in reservoirs ishigh in summer and low in winter. In addition, the spatial
characteristics of planktonic radiocesium in reservoirs are
unknown because the environmental conditions of lightand nutrients vary spatially in reservoirs and there arelarge spatial diversities in planktonic species composition
and abundance (Seda & Devetter, 2000; Havel &Pattinson, 2004).
In this study, reservoir water, phytoplankton andzooplankton samples were collected from a reservoir
located in the nuclear disaster area. Through observationof radiocesium in these samples, the dynamics of
dissolved, particulate and planktonic forms ofradiocesium were investigated over a total of 12 surveys
during three years, mainly focusing on the characteristics
of temporal and locational variability of planktonic formsof radiocesium. Among the various isotopes of137
radiocesium, Cs was targeted in this article, because it
accounts for the largest residual amount of radioactivity
in the environment several years after the nuclear
accident in 2011.

2. Materials and Methods
2.1 Study Site
The reservoir behind Yokokawa Dam, located 23 km
northwest of the FDNPP in the mountainous region of the
Ota River, was selected as the site for this study (Fig. 1).
This reservoir has geological characteristics
representative of this area, as 99% of its catchment iscovered by forest (Ministry of Land, Infrastructure,
Transport and Tourism, 2020) and most of theradiocesium deposited at the bottom of the reservoir fromradiocesium fallout in March 2011 remains because thebottom sediment has not been dredged extensively since2011.
One of the topographic features of this dam is theshort average residence time of water, 65 days (estimatedfrom the dam discharge and storage water volume,
Takechi et al., in press), compared to natural lakes where
the dynamics of radiocesium have been reported so far,because this dam was constructed in a steep ravine. The
2137
dam’s catchment area is 44.2 km , and the average Cs

45°
NYokokawa
Reservoir

outflowStn.3(downstream)

40°
N

Stn.2
(midstream)

35°
N

130°
E

E
135°

0

E
140°

5

E
145°

N
30°

Stn.1
(upstream)
inflow

10 km

0

0.5

1 km

Pacific
Ocean

Ota Riverwatershed

137Cs deposition (kBq m-2)

＞3,0001,000 – 3,000
600 – 1,000
300 – 600
100 – 300
< 100

Fukushima Daiichi
Nuclear Power
StationFig. 1 
Study site. In the Yokogawa Dam catchment, the upper
reaches have higher 137Cs deposition.

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 117
inventory in the catchment area of Yokokawa Reservoir
as of July 2, 2011 is 1.8 MBq m−2 (Ministry of Education,
Culture, Sports, Science and Technology, 2011). The
dissolved 137Cs concentrations in the reservoir inflow riverin 2014–2015 ranged from 140 to 530 Bq m−3 (Tsuji etal., 2016). The annual precipitation for 2014–2017
observed at the Yokokawa weather station, which islocated in nearly the central part of the catchment area,
was 1,697–1,880 mm (Fukushima Prefecture, 2020b).
The suspended solids in the reservoir water are
thought to be composed of organic and inorganic mineralparticles derived from forest soils in the catchment area,
and also biological particles (seston) such as plankton andtheir detritus, which are generated in the reservoir. Since
these particles are expected to exhibit characteristic
behaviors for each season and location within thereservoir, the field survey was designed to be repeatedthree times in four seasons at three locations within thereservoir.

137
2.2 Collection of Dissolved/Particulate Cs andPlankton in the Reservoir
A total of 12 quarterly surveys were conducted at thereservoir from August 2014 to May 2017 (Table 1). The
survey dates were set to avoid the immediate aftermath ofheavy rainfall events, aiming for conditions where thereservoir water was not excessively turbid. Observation
stations were established in the upstream part of thereservoir (Stn. 1; 37.58492°N, 140.88993°E), at the centerof the reservoir (Stn. 2; 37.59186°N, 140.89536°E), andnear the embankment (Stn. 3; 37.59963°N, 140.90281°E;
Fig. 1). At each station the dissolved, particulate form of
137
Cs, and 137Cs in phyto- and zooplankton were observed.
Based on continuous data on water levels near theembankment measured by the reservoir management
office, the continuous water depth at Stns. 1– 3 estimatedfrom the measured depths at Stns. 1– 3 was as shown in
Fig. 2. When the reservoir bottom appeared at the surface
on some survey dates in Stn. 1, we moved the survey
station to a nearby location where the water depth wasmore than 1 m.
In the reservoir, a rubber boat was launched, andTable 1 Survey dates and water depth, euphotic layer, temperature, pH and electrical conductivity of the surface water at each station(Stns.1–3).
Year

Date

2014

7-Aug

13-Nov

2015

3-Mar

19-May4-Aug

17-Nov

201610-Mar17-May2-Aug

10-Nov

201712-Jan25-MayEC : electrical conductivity

Station No.
〔Stn.〕
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3

Water
depth(m)
5
16
54
9
17
41
4
16
39
6
16
43
2
13
38
5
16
46
8
17
50
2
12
42
1
8
43
9
22
44
9
21
48
6
16
46

Euphotic
layer(m)
5
5
6
7
11
14
4
15
15
6
11
14
2
10
11
5
15
16
7
15
10
2
10
16
1
6
8
5
12
14
5
10
10
6
9
12

Temperature
(°C)
29
29
29
13
13
13
4
4
4
18
19
19
28
29
30
13
14
14
7
6
6
16
17
17
22
27
27
13
13
13
6
6
7
21
21
20

PH
9.1
7.9
8.8
7.4
7.5
7.3
7.2
7.3
7.3
8.9
9.1
9.1
9.0
8.7
8.4
7.3
7.6
7.3
8.0
7.5
7.5
7.4
7.7
7.7
7.8
8.5
8.9
7.6
7.4
8.4
7.4
6.9
7.1
8.6
9.2
9.0

EC
(mS m−1)
4.8
4.6
4.5
5.7
5.6
5.6
5.5
6.2
6.5
5.5
5.5
5.4
5.8
5.6
5.6
3.3
3.3
3.3
3.2
3.2
3.2
3.8
3.8
4.4
4.3
4.5
3.2
3.1
3.2
3.3
3.2
3.3
3.3
3.7
3.8
3.8

118

H TSUJI et al.
60

Water depth (m)

50

Stn.3

40
30
20

Stn.2

10

Stn.1

0
-10
2014

2015

2016

2017

Fig. 2 Survey dates (arrow symbols) and estimated water depth at Stns.1–3 of Yokokawa Reservoir.
The depths estimated in this graph assume no lake water flow.

40 L of surface water was collected using a polyethylene
bucket. The reservoir water was pumped through a
cartridge filter device (Tsuji et al., 2014b; Yasutaka et al.,2015) on board immediately after collection, and solidliquid separation (collection of suspended 137Cs) using a
1 μm pore size filter and assessment of dissolved 137Csconcentration were conducted simultaneously. The
cartridge filters used to collect and concentrate theparticulate and dissolved 137Cs were brought back to thelaboratory, and the radioactivity from 137Cs was measured
with a high-purity germanium detector. The amount of137
Cs in the suspended filter [Bq] was converted to 137Csconcentration per unit weight [Bq kg−1] by dividing thedetected amount of 137Cs by the weight of the suspended
solids, which was calculated from the difference in dry
weight before and after the 48-hour drying process. The
vertical distribution of chlorophyll-a concentrations in thereservoir water was also measured using a multi water
quality profiler (AAQ-RINKO, JFE Advantech Co., Ltd.,
Hyogo, Japan) to observe the vertical distribution of thephytoplankton population.
At the same station, nylon plankton nets with meshsizes of 41 μm and 200 μm with an inner diameter of
30 cm at the top (NXXX25 and NXX7, Rigo Co., Ltd.,Tokyo, Japan) were submerged in the reservoir andrepeatedly hauled vertically to recover mainly
phytoplankton in the former and zooplankton in the latterdevice. Phytoplankton was recovered within the euphotic
zone (Table 1), which was determined at 2.5 times thevisible depth of a transparent plate (Visibility Secchi’s
disk, Rigo Co., Ltd., Tokyo, Japan). When the euphotic
layer reached the bottom of the reservoir, thephytoplankton recovery area was defined as from thesurface to a depth of 1 m above the bottom of thereservoir to prevent contamination by suspended solids
due to disturbance of bottom sediments. Zooplankton wasrecovered from the reservoir surface to a depth of 1 m
above the reservoir bottom. However, scanty volumes ofphytoplankton and zooplankton were collected at Stn. 1(upstream) in May 2016 and August 2016 due to theshallow water depths, so the samples served only for
137
Cs
identification of species composition, withconcentrations not being measured. During this collection
process, the plankton samples were adulterated by someabiotic suspended solids, and these impurities were later
removed manually as much as possible. When using thismethod, it is expected for zooplankton to be included in
the phytoplankton sample collected by the 41-μm net.
However, because the presence of phytoplankton is muchlarger than that of zooplankton and additionally it isdifficult to subtract the effect of zooplankton adulteration
due to the difference in collecting range, 137Cs detected in
the samples filtred at 41 μm was considered entirely due
to phytoplankton.
Plankton samples collected in polypropylene bottles
were frozen for at least 24 h to kill the plankton and afterthawing them, the supernatant was removed. 1 mL of
the supernatant-removed sample was prepared forobservation of plankton species, to which 5 mL ofneutral buffered formalin solution was added to fix thecells, and then the number of each plankton species wascounted using an inverted microscope (TS100, Nikon,
Tokyo, Japan) at ×400 magnification for phytoplankton
and ×40 –100 for zooplankton. The database of the
National Museum of Nature and Science (2011) was used
as a reference for the identification of phytoplankton,
following the method of Takamura & Nakagawa (2012).
For the identification and counting of zooplankton, we
followed the method of Takamura et al. (2017).
For the remaining plankton-enriched samples,particulate impurities that had sunk to the bottom of thebottle were removed manually with tweezers, and the137
amount of Cs radioactivity in the samples was measured
in a 100 mL polypropylene U8 container in a frozen
condition. However, fine mineral particles with high 137Csconcentrations (~5.0×104 Bq kg−1, Takechi et al., in press)
remained in the U8 container, which may have led tooverestimation of 137Cs in the plankton samples.
Therefore, as described below, the Al concentration in thesamples was measured to evaluate the purity of theplankton in the samples. Thereafter, the samples were
freeze-dried for more than three days (FDU-2200, Tokyo
Rikakikai Co. Ltd., Tokyo, Japan) to determine the 137Csconcentration per dry weight of plankton, and this value

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 119
was finally converted to 137Cs concentration per wet
weight of plankton assuming a plankton water content of
90% (Hoekstra et al., 2002; Hammerschmidt & Fitzgerald,2006).
2.3 A nalysis of 137Cs Radioactivity and the Al
Component137
Cs radioactivity [Bq kg−1] in the cartridge filters
used to trap dissolved and particulate 137Cs, and in theplankton-enriched samples were determined using
GEM30-70, GEM60-83, GMX45P4-76 coaxial highpurity germanium detectors (Canberra Japan, Tokyo,
Japan) and Spectrum Explorer software (Canberra Japan,
Tokyo, Japan). The efficiency of the detector wascalibrated using a standard volume radioactivity source
MX033U8PP (Japan Radioisotope Association, Tokyo,
Japan). Background correction was conducted every two
weeks for 200,000 seconds. The measurement time wasdetermined for each sample with a counting error of less137
than 5%, and the measured Cs activities were corrected
for decay on the day of sample collection based on thephysical half-life of 137Cs (30.1 years).
To evaluate the amount of mineral particles
remaining in the plankton-enriched samples, taking
advantage of the fact that very little Al can transfer toplankton bodies (Pempkowiak et al., 2006; Ho et al.,2007), in all, 28 of the freeze-dried plankton-enrichedsamples collected during May 2016 to May 2017 were
decomposed with hydrogen fluoride, and the Alconcentration in each sample was measured using ICPMS (Agilent 8800, Agilent Technologies, Inc., Santa
Clara , CA, USA). Every two samples of bottom sedimentcollected at Stns.1–3 in the same period were also driedat 105°C and decomposed with hydrogen fluoride in thesame way, and the Al concentration was measured.
2.4  Cs Concentration Factor of Plankton and the
Occupancy of Planktonic 137Cs in Reservoir Water
The 137Cs concentration factors for phytoplankton
and zooplankton were calculated using the following
equation:
137

ρ･Cs

CF = Cs pl 
dis

(1)

where CF is the wet weight-based 137Cs concentration
factor for phyto- and zooplankton, ρ is the density ofreservoir water (1.0×103 kg m−3), Cspl is the 137Csconcentration per wet weight of plankton [Bq kg−1], andCsdis is the dissolved 137Cs concentration [Bq m−3]. In theevaluation of 137Cs concentration factors, the purity(weight percentage of plankton) in the plankton-enrichedsamples was calculated from the detected Al
concentration according to the following equation:
P = 1−
pl

Alsample
Alsed (2)where Ppl is the purity of plankton in the sample,
Alsample is the Al concentration in the plankton-enrichedsample, and Alsed is the Al concentration in the bottom
sediment to which the geometric mean value of the two
samples was applied. In this equation, the Al concentrationin pure plankton was assumed to be 0 mg kg−1. The
occupancy of 137Cs in plankton versus reservoir water was
calculated using the following equation:
rpl =Cspl･mpl

α･n･A･l (Csdis+Cspar )(3)

where rpl is the ratio of planktonic 137Cs to 137Cs in the
total reservoir water, mpl is the wet weight of therecovered plankton [kg], α is the correction factor for the
proportion of plankton recovered from the total plankton
in all layers, n is the number of times the plankton net
was hauled vertically, A is the cross-sectional area at the
top of the plankton net (0.071 m2), l is the depth within
which the plankton net was hauled [m], and Cspar is theparticulate 137Cs concentration [Bq m−3]. The correction
factor α was set at α = 1 for zooplankton, as it wasrecovered in almost all layers. While the value of α for
phytoplankton was determined based on the vertical
distribution of chlorophyll-a concentration, by thefollowing equation:α=∫ 0lCChl.a dz 
∫ 0LCChl.a dz(4)

where l is the depth from the reservoir surface to theend of the euphotic layer [m], L is water depth [m], andCChl.a is the chlorophyll-a concentration.
In Eq. 3, it is assumed that the concentrations of
dissolved and particulate 137Cs in the reservoir water are
vertically homogeneous and the same as those in thesurface layer. As to the validity of this assumption, thedissolved 137Cs concentration between surface and bottom
water in Yokokawa Reservoir showed almost no
differences except at the center of the reservoir in summer(Tsuji et al., 2017), and the turbidity was almost uniform
except just above the reservoir bottom (unpublisheddata). Therefore, the total 137Cs concentration in thesurface reservoir water would be a little lower than the
averaged 137Cs concentration in the reservoir water
overall, but the underestimation would not be very large.

3. Results and Discussions
3.1 Dynamics of Dissolved and Particulate 137Cs in
Reservoir Water
The concentration of dissolved 137Cs in surface waterat Stns.1– 3 in the reservoir was in the range of
110 –330 Bq m−3, with concentrations high in summer andlow in winter (Fig. 3(a)), similar to the seasonal
fluctuation observed in the inflowing river (Tsuji et al.,2016), the downstream part of the reservoir (Nakanishi &Sakuma, 2019), and also a natural lake (Matsuzaki et al.,120

H TSUJI et al.

2020). No decreases in dissolved 137Cs concentrations
with time or differences among the stations wereobserved. A uniquely high dissolved 137Cs concentration
was observed at Stn. 3 in January 2017 compared to theother stations, but the dissolved 137Cs concentrations at
Stn. 3 at similar dates in 2015 and 2016 were not so high,suggesting that unexpected 137Cs contamination may haveoccurred during this survey. The particulate 137Csconcentrations were lower than those of dissolved forms
in all the data and ranged from 13 to 185 Bq m−3, tending
to decrease in the downstream flow direction (Fig. 3(a)).
This trend was due to concentration of suspended solids
decreasing toward downstream (Fig.3(b)), which strongly
indicates precipitation of suspended solids to the bottomof the reservoir during the downstream flow process. In
this catchment, a tremendous rainfall event with a total
rainfall of 572 mm was observed from September 6 to 11,

137Cs concentration (Bq m-3)

(a)

400

SS concentration (mg L-1)

dissolved: St.1
particulate: St.1

St.2
St.2

St.3
St.3

1 Aug 10 Nov
2016
2016

12 Jan2017

25 May
2017

300

200

100

0

(b)

2015, but no remarkable change in either form of 137Csconcentration was observed before or after this period.
During the two months from this rainfall event to thesurvey in November 2015, most of the suspended solids
in the influent water from the runoff event would haveprecipitated to the reservoir bottom.
The 137Cs concentrations per unit weight of suspended
solids collected using a 1 μm pore size filter ranged from
3.2×102 to 4.3×104 Bq kg−1 with a geometric mean of
1.6×104 Bq kg−1 (Fig. 3(c)), and no significant decreasing
trend with time was observed at the three stations. As forthe trend in flow direction, there was a period during
which the 137Cs concentration in the suspended solids
increased in the flow direction, especially in theNovember survey in all three years. The distribution
coefficient of 137Cs (Kd), calculated by dividing the 137Csconcentration per unit weight of suspended solids by the

7 Aug
2014

13 Nov
2014

3 Mar
2015

19 May
2015

4 Aug
2015

17 Nov 10 Mar 17 May
2016
2015
2016

40

St.1

St.2

St.3

1 Aug
2016

10 Nov
2016

12 Jan2017

25 May
2017

St.2
St.2

St.3
St.3

12 Jan2017

25 May
2017

30

20

10

0

7 Aug
2014

13 Nov
2014

3 Mar
2015

19 May
2015

4 Aug
2015

17 Nov 10 Mar 17 May
2015
2016
2016

(c)

137Cs in SS (Bq kg-1)

Kd of 137Cs (L kg-1)

106

137Cs in SS :St.1
Kd of 137Cs : St.1

105

104

103

7 Aug
2014

13 Nov
2014

3 Mar
2015

19 May
2015

4 Aug
2015

17 Nov 10 Mar 17 May
2015
2016
2016

1 Aug
2016

10 Nov
2016

Fig. 3 (a) Dissolved and particulate 137Cs concentrations, (b) suspended solid (SS) concentrations, and (c) 137Cs concentrations per unit
weight of suspended solids and distribution coefficient of 137Cs (Kd) in the surface water at Stn.1 (upstream), Stn.2 (midstream),
and Stn.3 (downstream) of Yokokawa Reservoir.

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 121
dissolved 137Cs concentration, ranged from 1.0×104 to
8.0×105 L kg−1 with a geometric mean of 8.7×104 Bq kg−1
(Fig. 3(c)), which differed little from the reported values
in the upstream or downstream parts of the river (Tsuji
et al., 2016; Nakanishi & Sakuma, 2019). The trend of
the 137Cs distribution coefficient in the flow direction was
similar to that of the 137Cs concentration in the suspended
solids.
During a period when 137Cs concentrations in thesuspended solids increased in the flow direction, a clear
decrease in suspended solid concentrations in the flow
direction was also observed (Fig. 3(b)). In this period, it
is inferred that mineral particles derived from forest soil
runoff were abundant in the reservoir water due to somelarge rainfall events. Therefore, the increase in 137Csconcentration in the suspended solids in the flow
direction could be explained by the sedimentation
mechanism of coarse particles being deposited relatively
fast in the upstream area during the flow process(Walling & Moorehead, 1989), and finer particles withhigher 137Cs concentration per unit weight (He & Walling,

3.2 Dynamics of Planktonic 137Cs and its Concentration
Factor
As a species component of phytoplankton in thereservoir, dinoflagellates (Peridinium cinctum) were mostdominant, with their occupancy decreasing as thereservoir water flowed from upstream (Fig.4(a)) to
midstream (Fig.4(b)), to downstream (Fig.4(c)). Amongother species, diatoms (Fragilaria crotonensis,
Asterionella formosa) were representative phytoplankton.

Phytoplankton
100%

100%

80%

80%

Occupancy

Occupancy(a)1996) being transported further downstream. On the other
hand, in periods when the inflow of suspended particles
from upstream is relatively sparse, especially during
winter, the seston particles produced inside the reservoir,
specifically plankton, would dominate as suspended
solids in the reservoir water, and 137Cs concentration insuch particles may obscure the trend of 137Csconcentration in suspended solids in the flow direction.
Accordingly, it has been suggested that 137Cs dynamics inplankton affect the formation of the spatial distribution ofparticulate 137Cs in lakes in seasons with little rain.

60%
40%

0%

0%

2015

2016

2014

2017

Phytoplankton

100%

2015

2016

2017

Zooplankton

100%

80%

80%

Occupancy

Occupancy

40%
20%

2014

60%
40%

60%
40%

20%

20%

0%

0%

2014
(c)

2015

2016

2014

2017

2015

Phytoplankton
100%

100%

80%

80%

Occupancy

Occupancy

60%

20%

(b)

Zooplankton

60%
40%

40%
20%

0%

0%

Peridinium

2015

2016

Fragilaria

Asterionella

2017
Others

2017

60%

20%

2014

2016

Zooplankton

2014

2015

Calanoida
Bosmina2016
Daphnia
Cyclopoida

2017
OthersFig. 4 Components of plankton at (a) Stn. 1 (upstream), (b) Stn. 2 (midstream), and (c) Stn.3 (downstream) in Yokokawa Reservoir.

122

H TSUJI et al.
Chlorophyll-a (mg m-3)
0

0

50

100

0

10

20

30

0

0

5

10

10

2

Depth (m)

0

5

20

4
10

30

6

15

8

Stn.1 (upstream)

1040

Stn.2 (midstream)20

Stn.3 (downstream)50

7 Aug 2014

4 Aug 2015

1 Aug 2016

3 Mar 2015

10 Mar 201612 Jan 2017

Fig. 5 Vertical distribution of chlorophyll-a concentrations in summer and winter at Yokokawa Reservoir (Stns.1–3).
Chlorophyll-a was not measured at Stn.1 in August 2016 because there was very little water depth.

137Cs per wet weight of plankton(Bq kg-1)

104

PP : St.1
ZP : St.1

St.2
St.2

St.3
St.3

103

102

101

100

7 Aug
2014

13 Nov
2014

3 Mar
2015

19 May
2015

4 Aug
2015

17 Nov 10 Mar 17 May
2015
2016
2016

1 Aug
2016

10 Nov
2016

12 Jan2016

25 May2016

Fig. 6 Concentration of 137Cs in the phytoplankton (PP) and zooplankton (ZP) per unit weight of wet sample.

Among zooplankton, copepods (Calanoida copepodid,
Cyclopoida copepodid) and water fleas (Daphnia galeata,
Bosmina spp.) were particularly abundant but nodistinctive seasonal or horizontal trends were observed.
The seasonal trends, however, were unclear for both
phytoplankton and zooplankton.
The peak chlorophyll-a concentration in the reservoir
water was observed at depths of 2 to 3 m at Stns. 1–3,
with higher chlorophyll-a concentrations in summer andin the upper reaches (Fig. 5). Some degree of correlation
appeared between the dry weight of the collected
phytoplankton and the average concentration of2chlorophyll-a in the euphotic layer, (Stn. 1 : R = 0.68,
22Stn. 2 : R = 0.55, Stn. 3 : R = 0.43), suggesting that thechlorophyll-a concentration was an effective indicator ofphytoplankton population density. The vertical distributionof chlorophyll-a concentrations confirmed that most
phytoplankton in the reservoir water lived in the range ofthe euphotic layer.
The 137Cs concentration per wet weight of plankton(converted to 90% moisture content) was 0.86–560
Bq kg−1 (geometric mean: 30 Bq kg−1) (Fig. 6), and the137
Cs concentration factor of phytoplankton calculated
from Eq. 1 was 5.3×101–3.3×104 (geometric mean:
1.3×103). The 137Cs concentrations of zooplankton ranged
from 3.2 to 430 Bq kg−1 (geometric mean: 45 Bq kg−1),
and its 137Cs concentration factor was 1.1×102 to 1.6×104(geometric mean: 2.2×103). These values, however, havea possibility of overestimation due to adulteration bymineral particles with high 137Cs concentrations. The Al

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 123
Table 2 Al concentrations per dry weight in plankton and sediment samples. The percentage of plankton in the samples estimated from the
Al concentrations, the concentration factors (CF) of 137Cs of plankton, and the ratio of planktonic 137Cs to total lake water forplankton-enriched samples collected from May 2016 to May 2017. Samples with planktonic content greater than 95% are shownin bold, and these are considered representative data on the dynamics of planktonic 137Cs.
Sample typeplanktonsediment

phyto
phyto
zoo
phyto
zoo
phyto
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo
phyto
zoo

Collected date
17 May 2016

Station No.
〔Stn.〕
1
2
3

1 Aug 2016

1
2
3

10 Nov 2016

1
2
3

12 Jan 2017

1
2
3

25 May 2017

1
2
3

13 Nov 2014
26 Sep 2018
10 Mar 2016
10 Nov 2016
10 Mar 2016
25 Jul 2016

1
2
3

Al content(mg kg−1)
8,000
2,600
9,700
3,700
6,900
2,300
1,800
4,400
1,300
11,000
710
540
3,000
4,300
3,900
3,500
300
2,500
690
3,500
1,200
1,800
43
2,900
1,100
2,600
1,100
1,400
15,00024,00034,00039,00046,00035,000concentration, which indicates impurities, in 28 plankton
samples collected after May 2016 was 43–11,000
mg kg−1, and the Al concentration in the bottom sediment
samples collected during the same period ranged from15,000 to 46,000 mg kg−1 (Table 2). Accordingly, theplankton content in the 28 samples estimated by Eq. 2
was 58%–100% and nine samples of phytoplankton andthree samples of zooplankton contained plankton with apurity of >95%. In many of the samples, the influence ofinclusion of mineral particles on the 137Cs concentration
was considered not to be negligible. Therefore, the 137Csconcentration factor in this reservoir was evaluated only
for samples with planktonic content of >95%. By thisrefinement, the geometric mean values of the 137Csconcentration factor for phytoplankton and zooplankton
were 340 and 1,700, respectively, which were of thesame order of magnitude as previously reported values(Table 3). Even for these samples, no dependenceof the concentration factor on season or on station
was observed.

Estimation weightpercentage of plankton
58%
93%
73%
91%
81%
88%
95%
88%
97%
70%
96%
97%
92%
88%
90%
90%
98%
87%
98%
90%
97%
95%
100%
85%
97%
93%
97%
96%

CF
18,000
980
5,000
770
2,600
260
650
1,200
280
1,900
360
400
950
1,500
1,100
1,800
250
480
330
7,100
470
5,700
53
1,400
580
1,800
700
2,200

Ratio of planktonic 137Cs
to total lake water (%)
0.06
0.04
0.018
0.016
0.073
0.00540.039
0.0038
0.38
0.011
0.052
0.00130.00440.00140.31
0.0010
0.108
0.036
0.105
0.011
0.83
0.0087
0.028
0.096
0.026
0.0080The percentage of planktonic 137Cs to the whole 137Cs
in the water estimated by equations 3 and 4 ranged from0.0044% (Nov 2016) to 1.4% (Aug 2015) for
phytoplankton and 0.0010% to 0.17% for zooplankton for
all samples. While limited to samples with planktonic
content of >95%, the percentage ranged from 0.012% to0.83% for phytoplankton and 0.00054% (Mar 2016) to
0.096% (May 2017) for zooplankton. This result indicatesthat the effect of 137Cs in plankton larger than 41 μm on
the overall 137Cs dynamics in the reservoir is very limited.
In past laboratory experiments (Twiss & Campbell, 1998;
Thomas et al., 2018), the upper limit of the 137Cs uptake
ratio to zooplankton living in freshwater was reported tobe less than 1%. Therefore, the amount of 137Cs that canbe taken up by zooplankton may be limited to about 1%of the total amount of 137Cs in the water. On the other
hand, Thomas et al. (2018) reported that the amount of137
Cs transferred to freshwater diatomic phytoplankton,
including with cell diameter of 6.5 μm, could exceed 10%of the total 137Cs in the water according to their laboratory

124

H TSUJI et al.

Table 3 137
 Cs concentration factor (CF) of phyto- and zooplankton (wet condition) in the freshwater environment. CFs with a dagger mark(†) were calculated against the total 137Cs concentration, and those without the mark were calculated against the dissolved 137Csconcentration.
Reference

Station/Country

Collected
year

Mesh size ofplankton net

Range ofcollection

PlanktonThis study

Yokokawa dam
Japan2014 – 2017

41 μm

euphotic zone

phyto

〃

〃

2014 – 2017

200 μmwhole depthzooMatsuda et al.
(2015)

2012 – 2013

335 μm1 m depth

phyto and zoo

-

2400

2012 – 2013

335 μm〃phyto and zoo-

3802012 – 2013

335 μm〃phyto and zoo-

1302011 – 2016

100 μm1 m depth

phyto

Aulacoseira sp.

720†

〃

Lake Hayama
Japan
Lake AkimotoJapan
Lake Tagokura
Japan
Lake Onuma
Japan
Lake Onuma
Japan

2011 – 2016

200 μm〃zoo

Bosmina longirostri,
Holopedium gibberum

40†

Knapinska-Skiba et al.
(2003)

Świna River
Poland470†〃〃
Suzuki et al.
(2018)

Ravera and Giannoni(1995)

1997

Lake Monate
1986
Italy
Lake Comabbio
1986
〃
Italy
Saxén et al.
Lake Iso Valkjärvi
1992(2009)
Finland
Lake Valkea Mustajärvi
1987–1990〃
Finland
Lake Halsjärvi
1987–1988〃
Finland
Lake Rahtijärvi
1987–1990〃
Finland
Lake Savijärvi
1987–1990〃
Finland
Lake Vähä Valkjärvi
1988–1989〃
Finland
Lake Mekkojärvi
1988〃
Finland*concentration factor of 137Cs (geometric mean value)

Dominant species
Peridinium cinctum,
Fragilaria crotonensis,
Asterionella formosa
Calanoida copepodid,
Daphnia galeata,
Bosmina spp.,
Cyclopoida copepodid

CF*
340

1700

60 μm

surfacephyto and zoo

phyto:Melosira granulata,
Microcystis aeruginosa
zoo:Daphnia cucullata,
Bosmina coregoni,
Cyclops sternuus

88 μm

whole depth

phyto and zoo

-

220

88 μm

whole depth

phyto and zoo

-

100

-

-

zoo

-

170†

-

-

zoo

-

43†

-

-

zoo

-

110†

-

-

zoo

-

130†

-

-

zoo

-

37†

-

-

zoo

-

38†

-

-

zoo

-

86†

experiment. The difference between the report and thisstudy suggested the possibility that the fraction ofphytoplankton not recovered by the 41-μm mesh size ofthe plankton net held non-negligible amounts of 137Cs.
Accordingly, it would be difficult to discuss the whole
dynamics of planktonic 137Cs in the reservoir by focusing
only on plankton larger than 41 μm in cell length.
Even if the amount of planktonic 137Cs is limited
compared to the total 137Cs in lake water, the dynamics ofplanktonic 137Cs are expected to have a significant impact
on the uptake of 137Cs by aquatic biota as a pathway of137
Cs bioaccumulation through predation. Therefore, it isnecessary to position and consider planktonic 137Cs
dynamics in relation to 137Cs transfer to freshwater fish in
the future.
To summarize the remaining issues in this study, no
seasonal or site-dependent characteristics of planktonic
137
Cs in the reservoir could be observed because it wasdifficult to exclude the effect of adulteration from mineralparticles in the plankton samples. It was also suggested

that uncollected plankton less than 41 μm in length may
make a non-negligible contribution to 137Cs dynamics inlakes. Both of these issues are pertinent to theunderstanding of the dynamics of 137Cs in freshwater
ecosystems, so advances in recovery methods of highpurity plankton in the future are expected to clarify thesedetailed dynamics.

4. Conclusions
The present study of 137Cs dynamics in a reservoir
revealed the following.
1. 	Dissolved 137Cs concentrations in the reservoir’s
surface water at stations in the upstream part, central
part and near the embankment fluctuated seasonally:
they were high in summer and low in winter. No
differences in dissolved 137Cs concentrations between
the stations were observed.
2. 	The particulate 137Cs concentration in the reservoir’s
surface water was lower than that of dissolved 137Cs.

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 125
The 137Cs concentration per unit weight of suspended
solids and the distribution coefficient of 137Cs tended
to be higher toward the downstream direction mainlyin autumn, probably because coarse mineral particles
with low 137Cs concentration predominated assuspended solids in this season.
3. 	No seasonal regularity in composition of plankton
species was observed. No seasonal variations of 137Cs
in phyto- and zooplankton could be observed,
because the effect of mineral particle contamination
was not negligible in many of the samples based on
Al concentrations in the plankton-enriched samples.
4. 	The concentration factors of 137Cs in phytoplankton
and zooplankton were 340 L kg−1 and 1,700 L kg−1,
respectively, which were on the same order as inprevious reports.
5. 	The occupancy of planktonic 137Cs in plankton larger
than 41 μm to total 137Cs in the reservoir water wasmuch less than 1.4%.
Acknowledgements
Hydrological data on the reservoir were provided by
the Yokokawa Dam Management Office. We thank Dr.
Ito and Messrs. Iri, Harada and Narita for their help withthe field survey, and Prof. Kenji Nanba of Fukushima
University for his advice on measuring Al in plankton
samples. We would also like to thank the two reviewers
for their many helpful suggestions. This study was
supported by a Grant-in-Aid for Scientific Research(KAKENHI 15K16129) from the Japan Society for the
Promotion of Science.
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Cs in freshwater lakes: A mass balance and diffusion study ofLake St. Clair, Southeast Michigan, USA. Geochimica et
Cosmochimica Acta, 218, 323–342. Retrieved from http://dx.doi.
org/ 10.1016/j.gca.2017.09.017
Wolfe, D. A. and Coburn, C. B. (1970) Influence of salinity andtemperature on the accumulation of cesium137 by an estuarine
clam under laboratory conditions. Health Physics, 18(5),499–505, Retrieved from http://dx.doi.org/10.1097/00004032197005000-00005
Yasutaka, T., Tsuji, H., Kondo, Y., Suzuki, Y., Takahashi, A. and
Kawamoto, T. (2015) Rapid quantification of radiocesium

Dynamics of 137Cs in water and phyto- and zooplankton in a reservoir affected by the Fukushima Daiichi nuclear power plant accident 127
dissolved in water by using nonwoven fabric cartridge filters
impregnated with potassium zinc ferrocyanide. Journal of
Nuclear Science and Technology, 52(6), 792–800. Retrieved
from http://dx.doi.org/10.1080/00223131.2015.1013071
Yoshimura, K., Onda, Y., Sakaguchi, A., Yamamoto, M. andMatsuura, Y. (2015) An extensive study of the concentrations ofparticulate/dissolved radiocaesium derived from the Fukushima
Dai-ichi nuclear power plant accident in various river systems
and their relationship with catchment inventory. Journal ofEnvironmental Radioactivity, 139, 370–378. Retrieved fromhttp://dx.doi.org/10.1016/j.jenvrad.2014.08.021.

Hideki TSUJI
Hideki Tsuji is a senior researcher at the National
Institute for Environmental Studies. He is
conducting field research on the transport andaccumulation of radiocesium in rivers and lakes.
He is also carrying out chemical analysis,
constructing a numerical model and developing
equipment to be used for environmental
measurements of bioavailable radiocesium.

Megumi NAKAGAWA
Megumi Nakagawa is a specialist working at theCenter for Environmental Biology and Ecosystem
Studies, National Institute for Environmental
Studies. She has identified and counted
phytoplankton and zooplankton in Lake
Kasumigaura, the second largest lake in Japan,
for 25 years. She is also one of the staff at theJapan Focal Point of UNEP's GEMS/Water program.

Kazuya YOSHIMURA
Dr. Kazuya Yoshimura is a researcher at the
Sector of Fukushima Research and Development,
Japan Atomic Energy Agency (JAEA). His
research interests lie in environmental radiation,
especially in the hydrological migration ofradiocesium and its relationship with dose rates interrestrial environments. Recently he hasaddressed evaluation of exposure and radiation protection.

Kazuki IIJIMA
Kazuki Iijima heads the Fukushima Environmental
Evaluation Research Division at the Collaborative
Laboratories for Advanced Decommissioning
Science, Japan Atomic Energy Agency (JAEA).
He is interested in how radionuclides behave inthe environment, especially the interactions oftrace amounts of radionuclides with minerals andorganic matter of natural origins. Previously, he investigated the behaviorof radionuclides under conditions deep underground (stable and static forlong periods). After the Fukushima Daiichi nuclear power plant accident,
he started studying their behavior at the earth’s surface. (He says it is so
unstable and too dynamic!)Kazuyuki SAKUMA

rivers, and reservoirs.

Kazuyuki Sakuma, Ph.D., is a researcher at the
Sector of Fukushima Research and Development,
Japan Atomic Energy Agency (JAEA). He isinterested in the environmental modeling ofradionuclide behavior, watershed modeling,radiation transport simulation in the field, andinvestigation of radionuclide behavior in forests,

Seiji HAYASHI
Hironori FUNAKI
Hironori Funaki is an assistant principal scientist
at the Fukushima Environmental Monitoring
Division, Japan Atomic Energy Agency (JAEA).
He performs research in hydrogeology,
geochemistry and environmental radioactivity.
His current research interests include the transportof radioactive materials in lakes and reservoirs.

Seiji Hayashi is a research group manager at the
Fukushima Branch of the National Institute forEnvironmental Studies. He serves as project
leader for research on radioactive substancebehavior in multimedia environments. His
energetic research activities are contributing to
the environmental recovery of Fukushima
Prefecture and its surrounding region.
(Received 16 October 2020, Accepted 21 December 2020)

Preface-24-1.indd

22020/07/30

17:54:49

129

Cs outflow from Forest Floor Adjacent to a Residential Area:
Comparison of Decontaminated and Non-decontaminated Forest Floor
137

Tadafumi NIIZATO* and Takayoshi WATANABE
Fukushima Environmental Evaluation Research Division,
Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: niizato.tadafumi@jaea.go.jp

Abstract
A three-year monitoring of Cs outflow associated with soil erosion from decontaminated and nondecontaminated sites using an experimental plot was conducted in a mountainous forest of Fukushima
Prefecture during the rainy season. The annual 137Cs outflow from the decontaminated site was 9–13 times
larger than that of the non-decontaminated site. However, the outflow from the decontaminated site decreased
from 2.55% to 0.65% corresponding with recovery of the forest floor cover. When the forest floor coverreached 60% or more, the 137Cs outflow from the decontaminated site began to show relatively minor
fluctuations at a similar level to the non-decontaminated site. The decrease in the 137Cs outflow corresponding
to the restoration of the forest floor cover was due to the recovery of the protective effect of the forest floor
against raindrop splashes and a decrease in the ratio of soil components with relatively high 137Cs activity inthe particulate matter.
137

Key words :	decontamination, forest, forest floor cover, radiocesium, residents returning

1. Introduction
Assessing radiocesium outflow from forests
contaminated by radioactive substances from the
Fukushima Daiichi nuclear power plant (FDNPP) accident
is a key issue in promoting the return of evacuatedresidents. An outflow assessment in a decontaminatedforest adjacent to a living area would be particularly
important scientific knowledge to have for estimating thepossibility of recontamination of the decontaminatedliving area, exposing returned residents to radiation
doses.
The transport processes of radiocesium from theforest floor are mainly divided into a soil erosion process
in a particulate-bound state attached to fine soil particles
and a surface runoff process in a dissolved state in surface
running water during rainfall events (Evrard et al., 2015).
The majority of the radiocesium is transported in theparticulate-bound state. Yamashiki et al. (2014)
established a series of nested monitoring stations within
the Abukuma River basin, which was affected byradioactive fallout from the FDNPP accident. They
estimated that 84% to 92% of the total radiocesium wastransported in the particulate form during the period from
August 10, 2011 to May 11, 2012. Iwagami et al. (2017)
137
monitored Cs discharge via suspended sediment, coarse
organic matter, such as leaves and branches, andGlobal Environmental Research
24/2020: 129-136
printed in Japandissolved 137Cs fraction from a forest headwater catchment
in the Yamakiya district, located approximately 35 km
northwest of the FDNPP from August 2012 to September
2013. They reported that the annual proportion of thecontribution to 137Cs discharge from suspended sedimentaccounted for 96% to 99% of the total 137Cs flux.
The amount of particulate and dissolved 137Cs washoff from the forest floor via surface runoff processes was
examined using experimental plots installed on the floorof a mountainous forest in the Abukuma Mountains(Nishikiori, et al., 2015; Yoshimura et al., 2015; Niizato
et al., 2016). Niizato et al. (2016) installed experimental
plots for 137Cs discharge monitoring on a side slope of avalley-head area with a 27°–31° slope angle forested withJapanese konara oak and cedar in the Abukuma
Mountains during the summer monsoons of 2013 and2014. The 137Cs wash-off associated with the outflow ofparticulate matter was calculated at 85% –94% of the total
137
Cs discharge from the forest floor, based on the data in
Niizato et al. (2016). Nishikiori et al. (2015) monitored
the 137Cs wash-off from a forest floor with slopes of 37°–
39° forested with Japanese cypress, red pine and cedar,and a deciduous broadleaved forest with different floor
coverings for 145 days from May to October, 2013. They
revealed the most of the 137Cs wash-off was associatedwith soil particles and the amount of soil loss was
relatively large in forests with little understory and/or©2020 AIRES

130

T. NIIZATO and T. WATANABE

organic layers (forest floor cover; 5% –15%), suggestingthat forest cover strongly affected 137Cs wash-off.
The protective effects of the forest floor cover, thatis the presence of a litter layer, against soil erosion havebeen reported based on field soil erosion monitoring in
artificially disturbed and undisturbed forest floors of
evergreen needle-leaved and deciduous broad-leaved
forests (e.g., Murai & Iwasaki, 1975; Miura et al., 2003;
Hu et al., 2012). Miura (2000) proposed a new term,“floor cover percentage (FCP),” to quantify the forest
floor cover from the viewpoint of the protective effects
against raindrop erosion. FCP indicates the percentage offorest floor that is covered with either litter or understory
within 50 cm height above the forest floor (Miura, 2000).
This FCP index enables us to evaluate the total protectivefunction of the forest floor. Miura et al. (2003) measured
sediment transport rates using sediment traps in Japanesecypress, cedar and red pine forests located on steep slopes
under a humid climate, before and after removing theforest floor cover. The rates increased immediately after
removing the floor cover, and decreased corresponding toincreased FCP without delay. This result shows thesediment transport rate is sensitive to changes in FCP(Miura et al., 2003). Moreover, the above results indicate
diminishment of the forest floor cover results in increased
amounts of radiocesium outflow via soil erosion on forest
slopes.
From the perspective of reducing radiation doses in
the living environment of residents near a forest, removalof organic layers such as fallen leaves, etc. up to about
20 m from the edge of the forest is effective and efficient(Ministry of Agriculture, Forestry and Fisheries, 2011;
Kaneko & Tsuboyama, 2012; Ministry of theEnvironment, 2016). On the other hand, lining up
sandbags at the edge of the forest or other measures toprevent soil movement and runoff must be taken after theremoval of fallen leaves and other organic sedimentmatter on steep forest slopes (Ministry of theEnvironment, 2016).
Yamamoto et al (2014) conducted experiments
removing organic layers (L, F, and H layers) and137
monitoring the amount of Cs wash-off from a forest
floor with a 31° slope angle in a deciduous broadleaved
forest in the Yamakiya district about 40 km northwest of
the FDNPP. The monitoring was performed in a plot withorganic layers removed and a non-treated plot for fivemonths from July to December 2013. After the removal
treatment, 9.65% and 0.64% – 0.69% of the 137Cs in theforest floor had been washed off from the plot with the
L-F-H layers removed and the plot with the L-F layers
removed, respectively. The wash-off was 0.08% in theplot with no removal treatment (Yamamoto et al., 2014).
This revealed a protective function of organic layers
against radiocesium outflow from a forest floor, although
their discussion of the effect of the forest floor coverage
recovery process in natural environments was inadequate.

Although decontamination work in forests nearliving areas reduces radiation doses in the residents’living environment, radiocesium outflow via soil erosion
from the forest floor is relatively higher compared to a
non-decontaminated forest floor. It is expected, however,that the radiocesium outflow associated with soil erosion
will gradually decrease with time corresponding torecovery of the forest floor cover due to the deposition oflitter and growth of understory on the floor after
decontamination.
This study presents the results of three years ofmonitoring radiocesium outflow via soil erosion and therecovery process of forest floor cover in a forest floor
decontaminated according to the Decontamination
Guidelines of the Ministry of the Environment, Japan.
The natural resilience of the forest floor shown in thisstudy is expected to be applied to measures for preventing
radiocesium outflow in combination with engineering
measures and chemical treatment.

2. Materials and Methods
2.1 Study Area
Radiocesium outflow monitoring was conducted in a
deciduous broadleaved tree forest in the Yamakiya district
within the Abukuma Mountains, 35 km northwest of the
FDNPP (Fig. 1). The level of radioactive contaminationin the district was measured at 497 kBq m−2 (as of April 1,
2013) in 137Cs deposition via the Sixth Airborne
Monitoring results (Ministry of Education, Culture,
Sports, Science & Technology in Japan, 2020). At thismonitoring site, Niizato et al. (2016) carried out
monitoring of the radiocesium outflow associated withsurface wash-off from experimental plots installed in a
non-decontaminated forest floor. The annual 137Cs outflow
was estimated at 0.07% – 0.15% of the total 137Cs deposition
to the site from 2013 to 2014 (Niizato et al., 2016).
The mean annual precipitation in this district overthe past 30 years (1981–2010) has been 1223.8 mm yr−1
at the Yamakiya Meteorological Station, located 2.7 km
northwest of the site (Ministry of Land, Infrastructure,
Transport and Tourism, 2020). This district is mainly
covered by deciduous broad-leaved trees of konara oak(Quercus serrata), mizunara oak (Quercus crispula), andJapanese chestnut (Castanea crenata), except at thesouthern edge of the forest, where Japanese red pine
(Pinus densiflora) trees dominate. The average tree height
and tree density in the canopy layer are 10.9 m and740 ha−1, respectively. Most of the forest floor is covered
with litter composed mainly of fallen branches and leavesof deciduous broadleaved trees. The thickness of the litter
layer is usually 1–3 cm. The undergrowth cover,including mountain azalea (Rhododendron kaempferi)and bamboo grass (Sasa nipponica), ranges from 35% to60%. Brown forest soil is most common in the forest
slopes of the district. The soil down to a 5 cm depth isCs outflow in decontaminated and non-decontaminated forest

137

sandy-loam to loam in conventional textural classes(Niizato et al., 2016).
Removal of understory and organic layers (L, F, andH layers) in decontamination work on the forest floor at
the monitoring site was performed in July–September
2014 and August–September 2015 within 20 m from aliving area by the local government. A mineral soil layer
was exposed on the forest floor after the decontamination
work.
2.2 Monitoring and Sampling
Two experimental plots for monitoring were installed
on a decontaminated forest slope (decontaminated plot)
and a non-decontaminated forest slope (control plot)
facing west with a 27°–30° slope angle (Fig. 1). The
decontaminated plot was located 40 m south of the2
control plot and the plot area was 8 m (2.0 m × 4.0 m).
The control plot had a plot area of 53.4 m2 (6.0 m × 8.9 m)
in 2016 and 26.7 m2 (3.0 m × 8.9 m) in 2017–2018. Bothexperimental plots were located on rectilinear, straightslopes, and had common features of physical geography
except for the forest floor cover. The forest floor in thecontrol plot had an 86% – 94% cover ratio from its litter
layer and understory during the monitoring period, while
the forest floor cover ratio in the decontaminated plot
started from 30% in March 2016 and increased to 83% in
November 2018 through deposition of litter andunderstory growth.
Each experimental plot had a rectangular shape, thelong side of which was oriented along the dip direction of
the slope, and was surrounded with stainless-steel boards

131

for the control plot and with hard vinyl chloride
corrugated sheets for the decontaminated plot to prevent
transportation of particulate matter and surface runoff
water into the plot from the outside (Fig. 1). Particulatematter, composed of soil particles and fine litter
fragments, accumulated in a sediment trap installed at thebottom end of each plot with same width as the plot. The
particulate matter that drained from the plot with its
associated surface runoff water flowed into a 50 L tankfor the decontaminated plot and a 200 L tank for thecontrol plot connected to their respective sediment traps
via a pipe.
The particulate matter samples collected from thesediment traps were passed through a 2-mm sieve, andweighed after drying at 105°C for 24 h. The samples
stored in the tank were mixed well within the tank, thencollected as turbid water using a scoop. The turbid water
samples were passed through a 2-mm sieve, and weighed
after evaporation to dryness at 105°C for more than 24 husing a dry oven. Those samples were homogenized byhand stirring with a dispensing spoon, and then packed
and sealed in a polystyrene container (U-8) for radioassay
per sampling date.
Samples of the particulate matter were collected
within 2- to 8-week intervals in correlation withprecursory rainfall events. Associated field surveys andmonitoring efforts were performed mainly during
Fukushima’s summer monsoon from April to November,in the years 2016–2018. This monthly span was chosen
as most appropriate for research due to rainfall acting as
the principal cause of transportation of particulate matter

Fig. 1 Location of the monitoring site (left) and view of the entire decontaminated plot in May 2017 (right). The topographic data werecreated based on the results of an airborne laser survey conducted by the Geospatial Information Authority of Japan.

132

T. NIIZATO and T. WATANABE

within the forested area.
The forest floor cover percentage of thedecontaminated plot was calculated from the ratio ofintersection points with litter and/or understory on theforest floor with 25 cm square grids in the plot. Theintersection points with litter and understory werecounted using a digital photograph of the floor takenfrom above 50 cm height from the floor (Watanabe et al.,2019). The percentages of forest floor cover in the control
plot were estimated by direct measurement of the area
without the litter layer or understory in the field
investigation.
Soil samples were collected using a scraper plate(Tsukahara-SS Corporation, Japan) with a metal frame of2
450 cm (15 cm × 30 cm), the sampling area for vertical
distribution of 137Cs near both plots. The samples were
homogenized by hand stirring with a dispensing spoon
after drying at 105°C for 24 h, and then packed andsealed in a polystyrene container (U-8) for radioassay per
sampling date.

2.4 Calculation of 137Cs Outflow
Transportation of particulate matter from theexperimental plots was accompanied by the outflow ofparticulate-bond 137Cs. The volume-weighted mean 137Cs
activities of the particulate matter, litter and soil samples
were computed by summing the amounts of 137Cs inindividual samples during the monitoring period and thendividing this value by the total amount of the sample
weight. The 137Cs outflow via soil erosion (Bq m−2) was
calculated by multiplying the weight of the particulatematter (kg) by its 137Cs activity (Bq kg−1) and thendividing this value by the plot area (m2). The annual 137Cs
outflows were calculated by summing up daily flux forthe number of days in the monsoon season (April to
November). The daily fluxes were calculated by dividing
137
Cs outflow during the monitoring period by the numberof monitoring days. The outflow percentage of theparticulate-bound 137Cs was calculated using 137Cs
inventories obtained from decontaminated and nondecontaminated forest slopes near the experimental plots.

2.3 Radiocesium Measurements
137
Cs activity was determined using an n-type highpurity Ge-detector (GSW275L germanium detector,
CANBERRA Industries Inc., Meriden, CT, USA). A
multichannel analyzer (MCA7600, Seiko EG＆G ORTEC,
Tokyo, Japan) with spectrum analysis software (Gamma
Explorer + (Plus), CANBERRA Industries Inc) wasused for pulse-height analysis employing counts at the661.64 keV peak. An efficiency calibration was
performed with a multiple gamma-ray emitting standard
source (including nine nuclides) packed in 100 mL plastic
U-8 containers (Japan Radioisotope Association, Tokyo,
Japan). The radioactivities reported herein were corrected
for radioactive decay with respect to April 1, 2013. The
137
Cs activities of the particulate matter, litter and soil are
shown in dry weight.

3. Results and Discussions
3.1 Annual 137Cs Outflow
The forest floor cover in the control plot showedslight seasonal variation (86% in early June and 94% inlate November) due to leaf fall from October toNovember during the monitoring period from 2016 to2018. The forest floor cover in the decontaminated plot
showed significant change with time (Table 1). A sparse
distribution of bamboo grass and litter (mostly fallen
twigs) was found in March of the year following
decontamination of the monitoring site and the coverratio had increased to 30%. The floor cover percentage
had been restored to about 50% by understory growth andlitter deposition by early December of that year. After thecover percentage reached 70% in September 2017, two

Table 1 Forest floor cover and 137Cs activity of particulate matter in the decontaminated plot during different sampling periods.
abPeriodGross precipitation (mm) Forest floor cover (%) Particulate matter (g m-2 ) 137Cs activity (kBq kg-1 )
15
30.0
9.1
27.7
Mar. 16-Apr. 4, 2016
173
47.5
39.3
23.6
Apr. 4-May 29, 2016
152
50.0
134.5
26.4
May 29-July 11, 2016
436
52.5
416.0
24.4
July 12-Sept. 1, 2016306
no data
52.0
20.9
Sept. 2-Nov. 22, 2016
12
47.5
4.5
28.5
Nov. 22-Dec. 8, 2016
66
42.5
22.3
25.4
Apr. 16-May 14, 2017
60
50.0
58.8
22.2
May 14-June 14, 201781
no data
37.2
38.8
June 14-July 13, 2017
264
52.5
88.3
25.4
July 13-Aug. 10, 2017
132
70.0
51.1
23.1
Aug. 10-Sept. 15, 201783
no data
12.2
18.8
Sept. 15-Oct. 13, 2017
291
80.0
17.2
26.9
Oct. 13-Nov. 30, 2017
91
70.0
34.6
20.0
Apr. 28-May 21, 2018
150
62.5
19.0
16.6
May 21-July 29, 2018142
no data
50.5
23.4
July 29-Aug. 27, 2018
126
77.5
22.1
26.1
Aug. 27-Sept.24, 2018
105
82.5
12.8
17.2
Sept. 24-Oct. 28, 2018
4
82.5
3.0
18.4
Oct. 28-Dec. 5, 2018
c: Decay corrected to April 1, 2013.
a: Data from MLIT (2020).
b: Counting error ranges from 112 to 599 Bq kg-1.

c

Cs outflow (kBq m-2)
0.25
0.93
3.56
10.15
1.09
0.13
0.57
1.31
1.44
2.25
1.18
0.23
0.46
0.69
0.32
1.19
0.58
0.22
0.06

137

Cs outflow in decontaminated and non-decontaminated forest

133

137

Table 2 137Cs activity of particulate matter in the control plot during different sampling periods.
a

b

c

137
137
PeriodGross precipitation (mm)Particulate matter (g m-2)
Cs activity (kBq kg-1)
Cs outflow (Bq m-2)
118
3.8
34.5
132
Apr. 12-May 19, 2016
4
2.8
15.9
44
May 19-May 30, 2016
54
5.0
26.2
132
May 30-June 15, 2016
75
0.7
29.2
22
June 15-June 29, 2016
25
0.2
26.6
6
June 29-July 13, 2016
10
0.4
28.2
10
July 13-July 29, 2016
426
13.0
37.4
488
July 29-Sept. 1, 2016
56
2.3
45.0
104
Sept. 1-Sept. 16, 2016
154
1.2
29.4
34
Sept. 16-Sept. 30, 2016
35
1.7
29.4
49
Sept. 30-Oct. 14, 2016
2
0.4
31.9
14
Oct. 14-Oct. 28, 2016
49
0.1
33.2
4
Oct. 28-Nov. 11, 2016
15
0.2
29.3
6
Nov. 11-Nov. 29, 2016
7
0.5
44.8
24
Nov. 29-Dec. 9, 2016
49
1.2
39.5
48
Mar. 24-Apr. 14, 2017
26
2.2
36.0
78
Apr. 14-Apr. 28, 2017
4
0.7
28.3
21
Apr. 28-May 12, 2017
43
2.0
32.2
64
May 12-May 22, 2017
12
1.4
13.6
19
May 22-May 26, 2017
May 26-June 9, 2017
38
2.1
21.5
44
June 9-June 30, 2017
19
1.0
21.5
22
June 30-July 13, 2017
50
1.2
18.2
22
July 13-July 28, 2017
168
7.5
20.8
157
July 28-Sept. 1, 2017
190
6.0
39.4
236
Sept. 1-Sept. 15, 2017
38
1.3
40.8
51
Sept. 15-Sept. 29, 2017
58
1.8
32.2
57
Sept. 29-Oct. 13, 2017
24
1.3
30.3
39
Oct. 13-Oct. 26, 2017
199
4.4
23.9
104
Oct. 26-Nov. 17, 2017
68
1.6
22.2
36
Nov. 17-Nov. 30, 2017
24
0.7
23.2
16
Nov. 30-Dec. 15, 2017
12
0.4
21.1
9
Apr. 13-Apr. 26, 2018
44
1.0
22.0
21
Apr. 26-May 11, 2018
73
1.5
20.1
31
May 11-June 1, 2018
39
1.3
21.5
29
June 1-June 28, 2018
30
1.0
18.8
19
June 28-July 30, 2018
99
2.9
25.5
74
July 30-Aug. 28, 2018
142
3.6
31.7
115
Aug. 28-Sept. 25, 2018
126
1.3
16.9
22
Sept. 25-Oct. 29, 2018
105
1.8
19.5
35
Oct. 29-Dec. 6, 2018
4
0.2
9.6
2
-1
-1
-1
a: Data from MLIT (2020). b: Counting errors are 210-2124 Bq kg , 150-553 Bq kg , and 122-306 Bq kg in 2016, 2017 and 2018, respectively.
Decay corrected to April 1, 2013. c: Decay corrected to April 1, 2013.

137Cs activity (kBq kg–1)

Depth (cm)Litter layer
0-1
1-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10

50

100

150

0

Litter layer
0-1
1-2
2-3
3-4
137Cs inventory4-5
5-6
110.8 kBq m–2 6-7
Decontaminated plot 7-8
8-9(Dec. 8, 2015)
9-10

14.5
26.3
12.4
3.2
1.1

Depth (cm)

0

50

100

150

9.6
14.3
6.3
5.0
2.1

162.8

38.1

137Cs inventory575.2 kBq m–2

Control plot
(Oct. 21, 2016)

Fig. 2 Vertical distribution of 137Cs to the depth of 10 cm near the decontaminated and control plots. The numbers on the right side of thebar chart indicate the 137Cs activities of litter and soil layers. The counting error was less than 10%.

years after decontamination, the percentage stayed over
70%, except for May−July, 2018 (Watanabe et al., 2019;
Table 1).
The weight of the particulate matter from thedecontaminated plot was 10 –20 times larger than that of
the control plot (Tables 1 and 2). On the other hand, the137
Cs activities of the particulate matter from thedecontaminated plot each year were comparatively lower
than those from the control plot due to decontaminationof the monitoring site (Tables 1 and 2). The 137Cs activityof the soil layer at a depth of 0 –1 cm near thedecontaminated plot was one sixth that of a similar
measurement near the control plot (Fig. 2). The vertical
distribution of 137Cs near the decontaminated plot about

134

T. NIIZATO and T. WATANABE

Table 3 Annual 137Cs outflow accompanied by the transportation of particulate matter.

Grossa Forest floor
Plot
Periodprecipitation
cover (%)(mm)
Decontaminated plot Mar. 16-Dec. 8, 2016
1094
30.0-52.5
Apr. 16-Nov. 30, 2017977
42.5-80.0
Apr. 28-Dec. 5, 2018
618
62.5-82.5
Control plot
Apr. 12-Dec. 9, 2016
1030
86.0-94.0
Mar. 24-Dec. 15, 20171022
86.0-94.0
Apr. 13-Dec. 6, 2018
662
86.0-94.0

Particulatematter(g m-2)
655
287
142
32
37
15

Cs activity(kBq kg-1)

137

b

24.5
25.9
21.4
33.0
27.8
23.7

Annual 137Cs outflow(kBq m-2)
14.7
7.9
3.7
1.1
0.9
0.4

(%)

c

2.55 (13.23)
1.38 ( 7.16)
0.65 ( 3.38)
0.19
0.16
0.06

a: Data from MLIT (2020). b: Volume-weighted mean as of April 1 2013. The counting error ranges from 79 to 128 Bq kg-1.
c: Percentage of annual 137Cs outflow was calculated using the inventory of the decontaminated and non-decontaminated forest
slopes shown in Fig. 2. See text for details of that calculation.

Table 4 Estimation of the weight percentage of litter and soil in the particulate matter.

Plot

Year

Decontaminated plot

2016
2017
2018
2016
2017
2018

Control plota

Cs activity (kBq kg-1)

137

Particulate matter
24.5
25.9
21.4
33.0
27.8
23.7

Weight percentage (%)
LitterSoil (0-1cm depth)

14.5

26.3

9.6

162.8

litter
15
3
42
85
88
91

Soil
85
97
58
15
12
9

a: 137Cs activity shown in Table 3 and Fig. 2.

three months after decontamination indicates that thesurface soil layer was also slightly removed from up to 1
cm depth at maximum in the course of removing the litter
layer and understory during the decontamination work.
The annual 137Cs outflow from the decontaminatedplot was 9–13 times larger than that from the control plot,reflecting of the weight of the particulate matter and its
137
Cs activity in both plots (Table 3). Moreover, theoutflow from the decontaminated plot decreased
corresponding with recovery of the forest floor cover
during the monitoring period from 2016 to 2018. The
outflow in 2018 from the decontaminated plot was one
fourth that in 2016, an outflow percentage of less than
1%. This is a similar level of 137Cs outflow percentage aswith the control plot. When we calculated the 137Cs
outflows of the decontaminated plot based on the 137Cs
inventory in the decontaminated forest floor, they were
estimated to be 13.2%, 7.2%, and 3.4% in 2016, 2017,and 2018, respectively (Table 3).
The particulate matter containing 137Cs wascomposed of litter and soil components on the forest
floor. The weight percentages of the litter and soil were
estimated from an end-member mixing analysis using the137
Cs activities of the particulate matter, litter and soil
layers in the forest floor (Table 4). The soil component of
the particulate matter in the decontaminated plot ranged
from 60% to 90%, though it was less than 20% in thecontrol plot. The weight percentage of the soil component
in the decontaminated plot had decreased to 58% by
2018.
A significant amount of splashed soil was attached tothe 30-cm-high hard vinyl chloride corrugated sheets
bordering the decontaminated plot (Fig. 3, left). There
were many 5–25-mm-height pedestals and soil pillars in
the decontaminated forest floor (Fig. 3, right).
Destruction of these pedestals or soil pillars was observed
but no rills developed on the floor. These forest floor
conditions indicate that the main factor in thetransportation of the particulate matter on thedecontaminated forest floor was raindrop splashing ofparticulate matter on the forest floor.
137
The above results indicate the decrease in Cs
outflow corresponding to restoration of the forest floor
cover is the result of recovery of the protective effect of
the forest floor against raindrop splashes and a decreasein the amount of soil components with relatively high137
Cs activity in the particulate matter.
3.2 137Cs Outflow and Forest Floor Cover
The monitoring and sampling periods varied byexperimental plot (Tables 3 and 4). For comparing thesame unit interval, the 137Cs outflows from the forest floor
described above were converted to daily flux (Bq m−2
day−1). In addition, high rainfall intensity events tended to
produce a greater geomorphological impact since rainfall
intensity determines the size frequency distribution ofraindrops that fall (e.g., Anderson & Anderson, 2010). To
normalize by rainfall intensity per hour, daily fluxes of137
Cs outflow were divided by the sum of squares ofrainfall intensity per 1 h during the monitoring periods(Bq m−2 day−1 mm−2).
The daily flux of 137Cs outflow normalized by rainfall

Cs outflow in decontaminated and non-decontaminated forest

137

135

Fig. 3 Soil splashed by raindrops attached to the 30-cm-heigh hard vinyl chloride corrugated sheets (left) and pedestals (right) on theforest floor in the decontaminated plot (July 14, 2017).

Fig. 4 Daily flux of 137Cs outflow normalized by rainfall intensity
per 1 h in the decontaminated and control plots (upper).
Normalization by rainfall intensity was calculated using thedata from MLIT (2020). The forest floor cover percentages
in the decontaminated plot are shown in the lower graph.

intensity in the decontaminated and control plots areshown in Fig. 4. The daily flux of 137Cs outflow from thedecontaminated plot decreased from 2016 to 2018, while
no obvious change occurred in the control plot except for
May 11, 2017. In detail, there were major fluctuations in
the daily flux of the outflow (about 0.5−9.0 × 10−4 Bq m−2
day−1 mm−2) from the decontaminated plot in the period
from March 2016 to August 2017. After September 2017,
they turned into relatively minor fluctuations (about
0.5−3.7 × 10−4 Bq m−2 day−1 mm−2) corresponding withrecovery of the forest floor cover to 60% or more (Fig. 4,
lower).
Our three-year monitoring results from the year
following decontamination work in 2016 showed 137Cs
outflow decreasing to one fourth at the monitoring site inthis study. The annual 137Cs outflow percentage decreased
to less than 1% of the 137Cs inventory compared to before
decontamination. Though the forest floor cover in thedecontaminated plot reached 60% or more, the amount of137
Cs outflow and its fluctuation range in thedecontaminated plot remained larger than those of thecontrol plot installed in a non-decontaminated location(Tables 1 and 2). There were seasonal variations in forest
floor cover percentages in the decontaminated site from
60% in May−June to 80% or more in October−November
after August 2017 (Fig. 4, Table 1). This suggests thefallen leaves and twigs did not remain on the forest floor
after deposition but were transported from the floor, thenprobably deposited at the bottom of the forest slope. In
the non-decontaminated forest floor, protective effects of137
the forest floor against Cs outflow via soil erosion
appeared to be maintained by the pre-existing litter layer
when fallen leaves were transported immediately after
their deposition on the forest floor due to the effects ofwind or raindrop impacts. Thus, for restoration of theprotective effects of the forest floor to a predecontamination condition, it is important to promote
growth of understory, to prevent the transport of fallen
leaves and twigs away and to prepare conditions for litter
layer formation on the decontaminated forest floor.

4. Conclusion
We conducted monitoring of 137Cs outflow associatedwith soil erosion at decontaminated and nondecontaminated sites using experimental plots from April
2016 to November 2018 during the rainy season in
Fukushima. Our three-year monitoring results showedthat the 137Cs outflow from the decontaminated site was
9–13 times larger than that of non-decontaminated site.
The outflow from the decontaminated site, however,decreased from 2.55% to 0.65% corresponding to therecovery of the forest floor cover during the monitoring
period from 2016 to 2018. The outflow percentage in2018 was at a similar level to that of the nondecontaminated site. An end-member mixing analysis of137
Cs activities between litter and soil on the forest floor
and particulate matter flowing out from the experimental
plot showed that the decrease in the 137Cs outflow
corresponding to the restoration of the forest floor cover
was the result of recovery of the protective effect of theforest floor against raindrop splashes and a decrease in
the soil component with relatively high 137Cs activity inthe particulate matter. When the forest floor cover

136

T. NIIZATO and T. WATANABE

reached 60% or more, the 137Cs outflow from thedecontaminated site began showing relatively minor
fluctuations at a level of outflow percentage similar tothat of the non-decontaminated site. To restore theprotective effects of the forest floor against radiocesium
outflow to a pre-decontamination condition, it will be
important to promote understory growth resulting in litter
layer formation.
Acknowledgement
The authors thank the local landowner who provided
us his hill for our monitoring site. We are grateful tomembers of the Fukushima Environmental Evaluation
Research Division and Fukushima Environmental
Monitoring Division of Japan Atomic Energy Agency for
their helpful suggestions and technical support during thecourse of this work. Our thanks also go to Messrs. Okino
Ryo, Ikeda Makoto and Kawamura Makoto of Mitsubishi
Materials Techno Co. for their technical support in137
Cs outflow in the noncompiling data on
decontaminated area.
References
Anderson, R.S. and Anderson, S.P. (2010) Geomorphology−The
mechanics and chemistry of landscapes. Cambridge University
Press, UK.
Evrard, O., Laceby, J.P., Lepage, H., Onda, Y., Cerdan, O. and
Ayrault, S. (2015) Radiocesium transfer from hillslopes to the
Pacific Ocean after the Fukushima nuclear power plant accident:
A review. Journal of Environmental Radioactivity, 148, 92–110.
Hu, H., Ishikawa, Y., Siraki, K., Wakahara, T. and Biligetu,
Uchiyama, Y. (2012) Influence of change of forest floor coverpercentage on overland flow rate on beech forest slopes. Journalof Japanese Forest Society, 94, 167–174. (in Japanese withEnglish abstract)
Iwagami, S., Onda, Y., Tsujimura, M. and Abe, Y. (2017)
Contribution of radioactive 137Cs discharge by suspended
sediment, coarse organic matter, and dissolved fraction from aheadwater catchment in Fukushima after the Fukushima Dai-ichi
Nuclear Power Plant accident. Journal of Environmental
Radioactivity, 166, 466–474.
Kaneko, S. and Tsuboyama, Y. (2012) Radioactive contaminationand decontamination in forest area. Trends in the Sciences(Gakujyutu-no-Doukou) , 17(10), 10–16. (in Japanese)
Ministry of Agriculture, Forestry and Fisheries (2011) Result of
distribution condition and analysis of radioactive substances inforest (Interim report), 30th September, 2011. (in Japanese)
Retrieved from https://www.rinya.maff.go.jp/j/kouhou/jisin/
attach/pdf/H27izen -18.pdf (Accessed 1 June 2020)
Ministry of Education, Culture, Sports, Science & Technology ofJapan (MEXT) (2020) Extension site of distribution map ofradiation dose, etc., Digital Japan. Retrieved from http://ramap.
jmc.or.jp/map/eng/ (Accessed 16 June 2020)
Ministry of Land, Infrastructure, Transport and Tourism (MLIT)(2020) Water information system. (in Japanese) Retrieved fromhttp://www1.river.go.jp/ (Accessed 30 June 2020).
Ministry of the Environment (2016) Decontamination guidelines
2nd ed. with supplements (September, 2016). (in Japanese)
Miura, S. (2000) Proposal for a new definition to evaluate thestatus of forest floor cover and floor cover percentage (FCP)

from the viewpoint of the protection against raindrop splash.
Journal of Japanese Forest Society, 82, 132–140. (in Japanesewith English abstract)
Miura, S., Yoshinaga, S. and Yamada, T. (2003) Protective effect offloor cover against soil erosion on steep slopes forested with
Chamaecyparis obtuse (hinoki) and other species. Journal ofForest Research, 8, 27–35.
Murai, H. and Iwasaki, Y. (1975) Studies on function of water andsoil conservation based on forest land (I) Influence of differencein forest condition upon water run-off, infiltration and soil
erosion. Bulletin of the Government Forestry Experiment
Station, No. 274, 23–84. (in Japanese with English abstract)
Niizato, T., Abe, H., Mitachi, K., Sasaki, Y., Ishii, Y. and Watanabe,
T. (2016) Input and output budgets of radiocesium concerning
the forest floor in the mountain forest of Fukushima released
from the TEPCO’s Fukushima Dai-ichi nuclear power plant
accident. Journal of Environmental Radioactivity. 161, 11–21.
Nishikioiri, T., Ito, S., Tsuji, H., Yasutaka, T. and Hayashi, S.
(2015) Influence of forest floor covering on radiocesium washoff associated with forest soil erosion. Journal of Japanese
Forest Society, 97, 63–69. (in Japanese with English abstract)
Watanabe, T., Sasaki, T., Niizato, T., Mitachi, K. and Ito, S. (2019)
Temporal change of radiocesium loss in a decontaminateddeciduous broad-leaved forest. Proceedings of the 20th Workshop
on Environmental Radioactivity, KEK, Tsukuba, Japan, March
12–14, 2019, 114–119.
Yamamoto, R., Kobayashi, T., Ebata, C., Shinozaki, K., Kojima,D., Ota, S., Miyamoto, U., Takahashi, T., Suzuki, H., Sekizaki,
M., Hoshizawa, Y., Kotakemori, T., Yasutaka, T. and Tsuji, H.
(2014) Radioactivity reduction experiment and the subsequenterosion in broadleaf hill forest after Fukushima Ⅰ NPP accident.
Journal of the Japanese Society of Revegetation Technology,
40(1), 130–135. (in Japanese with English abstract)
Yamashiki, Y., Onda, Y., Smith, H.G., Blake, W.H., Wakahara, T.,
Igarashi, Y., Matsuura, Y. and Yoshimura, K. (2014) Initial fluxof sediment-associated radiocesium to the ocean from the largest
river impacted by Fukushima Daiichi nuclear power plant.
Scientific Reports, 4, 3714. Retrieved from https://org/10.1038/
srep03714.
Yoshimura, K., Onda, Y. and Kato, H. (2015) Evaluation ofradiocaesium washoff by soil erosion from various land uses
using USLE plots. Journal of Environmental Radioactivity, 139,
362–369.

Tadafumi NIIZATO
Dr. Tadafumi Niizato heads the Environmental
Research Group of the Sector of Fukushima
Research and Development, which conducts
environmental dynamics research on the effectsof radiocesium from the Fukushima Dai-ichi
nuclear power plant accident. He enjoys potted
plant cultivation with his wife on weekends in
Miharu Town, which is famous for a very old weeping cherry tree, Takizakura.

Takayoshi WATANABE
Mr. Takayoshi Watanabe is an engineer at theEnvironmental Research Group studying theenvironmental dynamics of radiocesium inforested environments in Fukushima. He enjoys
motor scooter touring, feeling the turn of theseasons through his touring.
(Received 4 September, Accepted 21 December, 2020)

137

Summary of Radioactive Cs Dynamics Studies in Coastal Areas andAssessment of River Impacts
Toshiharu MISONOU*, Tadahiko TSURUTA, Takahiro NAKANISHI and Yukihisa SANADA
Remote Monitoring Research Group, Fukushima Environmental Monitoring Division, Japan Atomic Energy Agency
45-169 Sukakeba, Kaibama, Haramachi-ku, Minamisouma-shi, Fukushima, 975-0036, Japan*E-mail: misono.toshiharu@jaea.go.jp

Abstract
A large amount of radioactive Cs was released into the environment from the Fukushima Daiichi nuclear
power plant (FDNPP) following the 2011 Great East Japan Earthquake. Nine years have passed since this
accident, and the radioactive Cs concentration in seabed sediments has decreased. The behavior of radioactive
Cs in coastal areas, however, is complicated due to the influence of rivers, waves and so on. The Japan Atomic
Energy Agency has conducted several studies at the mouth of the Ukedo River. Here, we review previous
studies and evaluate the impact of the radioactive Cs supplied by rivers using a sediment trap. In this study, amooring system consisting of a sediment trap was installed in the Ukedo River estuary near the FDNPP in
2017. The results showed 137Cs flux in winter accounting for 60% of the annual flux. This suggests thatmobilization of radioactive Cs in the coastal area is primarily due to resuspension and not river discharge.
estuary, Fukushima Daiichi nuclear power plant accident, resuspension, sinking particle,
Key words :	
Ukedo River

1. Introduction
The Tokyo Electric Power Company Holdings(TEPCO) Fukushima Daiichi Nuclear Power Station(FDNPP) released a large amount of radioactive Cs into
the environment following the 2011 Great East Japan
Earthquake and Tsunami. The released radioactive Cs was
deposited over wide land and sea areas (Hirose, 2016;
Mishra et al., 2019). The amount of 137Cs released fromthe FDNPP has been reported to be 18 PBq (Katata et al.,2015). In particular, the 137Cs inventory of seabedsediments shallower than 100 m is 0.16 PBq (Otosaka &Kato, 2014) and tends to be higher in coastal areas(Kusakabe et al., 2013). The 137Cs inventory of surface
sediments shallower than 100 m decreased by 27%
annually from 2011 to 2015 (Otosaka, 2017). While theradioactive Cs concentration in coastal seabed sediments
has been decreasing yearly, seabed sediments withrelatively high radioactive Cs content have been observed
locally (NRC, 2018). Radioactive Cs in seabed sediments
is strongly adsorbed on fine sediment particles and has alow elution rate to seawater (Otosaka & Kobayashi,2013). Therefore, it is suggested that seabed sedimentfunctions as a sink for radioactive Cs in marine
environments. Previous sampling of seabed sediments
has been as shallow as the layer to approximately 20 cm
from the surface (Arita et al., 2014; Ambe et al., 2014). It
137
is difficult, however, to evaluate the Cs inventory of
Global Environmental Research
24/2020: 137-144
printed in Japan

seabed sediments, because information concerning
radioactive Cs in the depth direction has been insufficient.
Therefore, it is important to collect deep cores andanalyze the amount of radioactive Cs with depth.
As mentioned above, the coastal area is expected to
be a dynamic area with respect to radioactive Cs evenseveral years after the accident because of the impact ofriverine 137Cs discharge. For evaluating the future
distribution of radioactive Cs throughout the entire sea
area, it is important to predict radioactive Cs distribution
in the estuary. Therefore, in this paper, we first review
several studies conducted by the Japan Atomic Energy
Agency (JAEA) in the Ukedo River estuary. In addition,
to determine the relationship between seafloor sediments
and radioactive Cs supplied from rivers, we focused on
evaluating the amount of radioactive Cs from rivers andsinking particles collected using sediment traps (Fig.1).

2. Distribution of Radioactive Cs in
the Ukedo River Estuary
JAEA has conducted several studies focusing on the
behavior of radioactive Cs in the Ukedo River area since2012. From calculation of the amount deposited using
data from the 4th Airborne Monitoring Survey (MEXT,
2011), the amount of radioactive Cs deposited in the
Abukuma River basin (578 TBq) and the Ukedo Riverbasin (536 TBq) is almost the same. However, the©2020 AIRES

138

T. MISONOU et al.

River inflow(Particulate 137Cs)

Sinking

Sediment trap isinstalled to understandthe behavior of sinking
particles.
(This study)

Variation of 137Cs concentrationin seabed sediments(Sanada et al., 2018)

Resuspension
Distribution of seabed sediments and 137Cs inventory(Tsuruta et al.,2017)

Vertical disturbanceFig. 1 Positioning of this study.

Fig. 2 Predicted seabed sediment map (Tsuruta et al, 2017). Location of FDNPP and Ukedo River estuary.

catchment area of the Ukedo River is 1/10 that of the
Abukuma River, meaning that the concentration ofradioactive Cs supplied to the ocean by the Ukedo Riveris much higher than that supplied by the Abukuma River(Sakuma et al., 2019a). Therefore, the Ukedo River likely
has a large impact on the surrounding coastal area.
The distribution of seabed sediments (silt, fine tomedium sand, coarse sand to granules, bedrock, andartifacts) in the Ukedo River estuary has been
investigated using two methods, depth measurements andacoustic soundings (Tsuruta et al., 2017). The surface
area ratios of bedrock and seabed sediments are 65% to2
35% (the total area investigated was about 30 km ),

respectively (Fig. 2). Sediment accumulation is restricted
to the area south of the Ukedo fishing port in two
elongated zones. Fine to medium sand (with a surface
ratio of 24%) is the main constituent of the seabedsediment. Fine sediment containing a large amount ofclay minerals (such as silt) is thought to have highradioactive Cs concentrations (Bostick et al., 2002), but
the proportion of fine sediments (≦0.064 mm) was foundto be only 0.4%. From results of core sampling of seabedsediments using vibrocoring techniques (to a maximum
depth of 100 cm), an inventory of radioactive Cs in the
Ukedo River estuary sediment was made (Tsuruta et al.,1372017). Figure 3 shows the relationship between Cs

Summary of radioactive Cs dynamics studies in coastal areas and assessment of river impacts

139

Fig. 3 Relationship between 137Cs inventory and water depth (Tsuruta et al., 2017).

Fig. 4 Contour maps of 137Cs concentrations in sea sediment (surface) near the Ukedo River estuary (Sanada et al., 2018).

inventory and water depth. The results obtained fromJanuary to March 2014 at the mouth of the Ukedo River(Tsuruta et al., 2017) are compared with the results of
Otosaka and Kato (2014) (sampling period from 2011 to2012) and Black and Buesseler (2015) (sampling period
from 2012 to 2013). The 137Cs inventory in the shallow
area (water depth: < 30 m) is remarkably larger than that
offshore. This suggests that the 137Cs distribution near theestuary, where the basin has a high level of radioactive
contamination, is significantly affected by discharged
137
Cs from the Ukedo River.
A secular change in the 137Cs concentration in seabedsediments has been reported (Sanada et al., 2018). An in
situ measurement of the radioactive Cs concentration inseabed sediments has been attempted by focusing on
unmanned surface vehicle technology (Rathour et al.,2015) to enable continuous and wide-area monitoring.
The distribution of radioactive Cs concentrations in theseabed sediments was measured using an unmanned
observation ship, Windy3S, at the mouth of the Ukedo
River seven times from October 2015 to October 2017
(Sanada et al., 2018; Fig. 4). In the measurement area set
137
in the estuary, the Cs concentration in the surface layer
tended to differ for each observation period. Also, the137
Cs inventory tended to decrease over time. This was ingood agreement with the physical decay of 137Cs. There
are also reports that radioactive Cs has been detected
relatively deep in sediments (Tsuruta et al., 2017). These

140

T. MISONOU et al.

Table 1 137Cs discharge ratio from different catchments (Sakuma et al., 2019a).

River
AbukumaOdaka
Ukedo
Takase (Ukedo River tributary)
Maeda
Kuma
Tomioka
Total of 13 rivers in Fukushima coastal regionaa

Cs discharge (TBq) and discharge ratio (%)

137

11 March 2011 – 27 September 2011
18 TBq (3.1%)
0.12 TBq (0.34%)
3.2 TBq (0.89%)
1.6 TBq (0.88%)
1.0 TBq (1.1%)
0.91 TBq (1.0%)
0.25 TBq (0.64%)
11 TBq (0.79%)

11 March 2011 – 31 December 2017
25 TBq (4.3%)
0.27 TBq (0.75%)
6.3 TBq (1.8%)
3.7 TBq (2.0%)
1.9 TBq (2.0%)
2.0 TBq (2.3%)
0.55 TBq (1.4%)
23 TBq (1.7%)

 stimated using catchment137 Cs inventory at each other catchment in the Fukushima coastal region and the average137 Cs discharge ratio from six riverEbasins such as the Odaka, Ukedo, Takase, Maeda, Kuma, and Tomioka Rivers.

Fig. 5 ( a) Bathymetric map and vibrocoring sampling points (Tsuruta et al., 2017). The black circle shows where the sediment trap was installed(St.B). (b) Water depth along Line 2. The solid line shows the surface of the seafloor, and the green range represents the distribution ofseabed sediments (Tsuruta et al., 2017). (c) The sediment trap was installed 1.5 m above the sea floor using the mooring system.

results suggest that radioactive Cs remains in themeasurement area. Therefore, it is suggested that there isa high possibility of local sediment movement near theestuary.
The discharge of 137Cs from the Ukedo River was
estimated using a tank model and L-Q equation (Sakuma
et al., 2019a). The release of 137Cs in the six months
following the FDNPP accident to the Ukedo Riveraccounted for approximately half of the total in thesubsequent period (approximately six years). After theaccident, 10 TBq (from the Ukedo and Takase rivers) of137
Cs was supplied to the Ukedo River estuary (Table 1).
The 137Cs inventory of seabed sediments in the Fukushimacoastal area (≦100 m) in 2011 was 160 TBq (Otosaka &Kato, 2014), so the influence of the Ukedo River cannot
be ignored.

3. Evaluation of Radioactive Cs Flux in the
Ukedo River Estuary
3.1 Materials and Methods
We installed a sediment trap to investigate themigratory behavior of sinking particles, which affect the
distribution of radioactive Cs in seabed sediments. Study
points were set up at the mouth of the Ukedo River,which is located approximately six kilometers from the
FDNPP (Fig. 5(a)). Our targets were points where studiesof the topographical shape and core sampling of theseabed sediments had been performed for a previous
report (Tsuruta et al., 2017). Because southward flow is
predominant along the Fukushima Prefecture coast (Yagiet al., 2013), we selected the area around Line 2 (Fig.
5(a)) on the south side of the Ukedo River. Line 2
includes flat and depressed terrain. Depressions tend tocontain high levels of radioactive Cs (Thornton et al.,Summary of radioactive Cs dynamics studies in coastal areas and assessment of river impacts2013), but they also suggest that sediment migration
might be restricted. Since depressions are a characteristic
place, we chose the area around No. 13 on the flat partand moored the earth and sand trap (Fig. 5 (b)).
We installed the mooring system shown in Fig. 5(c)at the study points (N 37.46866°, E141.0614°, water
depth: 16 m). The mooring system was equipped with asediment trap (SMC-7S500, NiGK Corporation, Japan).
During high water periods such as typhoons, sinking
particles were collected each day (measurement intervalof one day). Table 2 summarizes the sampling period forthe sediment trap. The 500-ml collection bottles in thesediment trap were pre-filled with 3.5% NaCl solution to
Table 2 Sampling period and measurement intervals of thesediment trap system

500

800

400

600

300

400

200

200

0

02/04
02/05
02/06
02/07
02/08
02/09
02/10

100

1600

1000

Mass flux (g m-2 day-1)

1400

800

1200

700

1000

600

800

500
400

600

300

400

200

200

08/31
09/01
09/02
09/03
09/04
09/05
09/06

100

0

1000

600
500

800

400

600

300

400

200

200

100
0

1600

1000
900

1400

800

1200

700

1000

600

800

500
400

600

300

400

200

200

100
0

0

0

1400

800

1200

700

1000

600
500

800

400

600

300

400

200

200

100
0

1600

1000
900

1400

800

1200

700

1000

600

800

500
400

600

300

400

200

200

100
0

0

0

1600

1000
900

1400

800

1200

700

1000

600

800

500
400

600

300

400

200

200

100
0

0

1000

9000

900

8000

800

7000

700

6000

600

5000

500

4000

400

3000

300

2000

200

1000

100
0

137Cs concentration (Bq kg-1)

900

0

0

1200

700

1600

900

08/22
08/23
08/24
08/25
08/26
08/27
08/28

1000

600

1400

800

1000

10/27
10/28
10/29
10/30
10/31
11/01
11/02

Mass flux (g m-2 day-1)

1200

700

900

137Cs concentration (Bq kg-1)

1400

800

1600

1000

06/06
06/07
06/08
06/09
06/10
06/11
06/12

900

3.2 Results
The eight sediment trap observations from February
2017 to November 2017 collected 55 sinking particle
samples. The mass fluxes and 137Cs concentrations of thesinking particles are shown in Fig. 6. Mass flux showed a

1day

03/08
03/09
03/10
03/11
03/12
03/13
03/14

1600

1000

measurement pitch

prevent backflow of the sinking particles.
The sinking particles were separated from theseawater using a centrifuge (CR22N, Hitachi, Japan).
Centrifugation was performed for 20 min at 3,000 rpm,
and the supernatant was discarded. To remove the salt
from the sample, deionized water was added to theremaining sample, which was then stirred andcentrifuged. This process was repeated three times. The
centrifuged sinking particles were dried at 105°C for
24 h, homogenized and then placed in a U-8 container.
137
The radioactive concentration of Cs in the sinking
particles was determined via gamma-ray spectrometry
using a high purity germanium detector (GMX40P4-76,
ORTEC, USA). The measurement times were from3,600 s to 302,400 s. The activity concentrations of 137Cs
in the samples were decay-corrected to the sampling date.
The 137Cs flux was obtained by multiplying the mass fluxof the sinking particles by the 137Cs concentration.

10/13
10/14
10/15
10/16
10/17
10/18

Number of samples
7
7
7
7
7
7
6
7

09/22
09/23
09/24
09/25
09/26
09/27
09/28

Sampling period
2017/2/4 – 2/10
2017/3/8 – 3/14
2017/6/6 – 6/12
2017/8/22 – 8/28
2017/8/31 – 9/6
2017/9/22 – 9/28
2017/10/13 – 10/18
2017/10/27 – 11/2

141

0

Fig. 6 Mass flux and 137Cs concentration data gathered in this study. Sediment trap observations were conducted
eight times in 2017. The black points show the 137Cs concentration (dry). The bars show the mass flux.

T. MISONOU et al.

large fluctuation range of 0.68–850 g m−2 day−1 and tended
to be high from winter to spring (February to June). Highmass fluxes were seen in September, which were thought
to be due to typhoons (Sanvu) and low pressure. The 137Csconcentrations varied from 91 to 7,900 Bq kg−1 andtended to increase from summer to autumn (August to
November).
3.2.1 Differences in 137Cs Flux between Coastal andOffshore Regions
137
Cs flux was calculated by multiplying the massflux by the 137Cs concentration. Figure 7 shows the sum of
the 137Cs fluxes for each observation period. The 137Cs
fluxes varied from 18 to 550 Bq m−2 day−1 and had large
fluctuations during each observation period. The 137Cs
flux of the sinking particles was compared to theminimum–maximum values reported in offshore regions(depth: 873 m) 100 km away from the FDNPP. The
offshore results indicated that the 137Cs flux ranged from
9.4 × 10−4 to 9.8 × 10−2 Bq m−2 day−1 (Otosaka et al., 2014).
There was a difference of several orders of magnitude
between the coastal and offshore 137Cs fluxes. Even
though these results cannot be unequivocally comparedbecause of the different collection periods and mooring
positions of the sediment trap, it is thought that the 137Cs
flux near the coast is higher than that offshore.
3.2.2 Estimation of the Origin of the Sinking 137Cs Flux
We examined variations in mass flux and 137Csconcentrations to estimate the origin of 137Cs fluxes. The
relationship between mass flux and 137Cs concentration
was found by linear regression analysis. The correlation
coefficient and P-value were found to be 0.01 and 0.43,
respectively (Fig. 8). The quantitative correlation between
the mass flux and the concentration of 137Cs is considered
to be low. On the other hand, Spearman’s rank ordercorrelation coefficient (Hogg & Craig, 1978) was − 0.71.
Therefore, it is thought that mass flux and radioactive Csconcentration tend to have a negative relationship. As
described in Section 3.2, the 137Cs concentration ofsinking particles tended to increase from summer toautumn. In particular, the maximum 137Cs concentration

137Cs flux (Bq m-2 day-1)

600
500
400
300
200
100
0

was observed in November. According to a reportpresenting measured particulate 137Cs concentrations in
the Ukedo River on October 27, 2017, the 137Csconcentration was 24.7 Bq g−1-dry. This was under highflow conditions (Nakanishi & Sakuma, 2019). Therefore,
it is suggested that the river flow increases from summer
to autumn (August to November), and the amount ofradioactive Cs inflow from the land area also increases.
In contrast to river discharge, the mass flux in thesediment trap experiment tended to be high from winterto spring (February to June) when the 137Cs concentration
was low. In winter, sediment discharge from the Ukedo
River tended to decrease (Sakuma et al., 2019b). It has
been reported that seabed sediments containing
radioactive cesium are resuspended in winter andtransported offshore (Otosaka et al., 2014). Moreover,resuspension due to waves has been reported in a coastal
area (Yagi et al., 2015). Therefore, it is thought that
seabed sediments with low 137Cs concentrations werecollected in the sediment trap due to resuspension caused
by waves in winter. The 137Cs flux obtained from theobservations was divided into winter to spring (February
to June) and summer to autumn (August to November).
As a result, the 137Cs flux in winter was found to be about
1.5 times that in summer. The contribution of winter 137Cs
flux to the annual 137Cs flux was 60%, suggesting that
resuspension had a significant impact in coastal areas.
3.2.3 Estimation of Annual Cs Deposition
The annual total deposition of 137Cs estimated fromthe observation results of 137Cs flux was 11.4 kBq m−2.
The 137Cs inventory of the seabed sediments sampled in2014 was 72 kBq m−2 (Tsuruta et al., 2017). The
contribution of 137Cs flux of sinking particles to the seabedsediments was about 16% (including river inflow andseabed sediment resuspension). It has been reported that
rates of desorption and resuspension of seabed sediments
range from 0 –29 % (Otosaka, 2017), and the results ofthis study are also within that range.
It will be necessary to consider diffusion into
R2: 0.01
P-value: 0.43
y=0.015x

1000

Mass flux (g m-2 day-1)

142

100
10
1
0.1

10

100

1000

10000

137Cs concentration (Bq kg-1)

Fig. 7 Total value of 137Cs flux for each sampling period.

Fig. 8 
Relationship between mass flux and 137Cs concentration(dry). The R2, P-values and regression equations were
determined by linear regression analysis.

Summary of radioactive Cs dynamics studies in coastal areas and assessment of river impacts
seawater and the possibility of leaching of radioactive Cs
by seawater in future studies. It will also be necessary toconsider the balance of radioactive Cs supplied via rivers,and determining the contribution of sediment deposition
and resuspension by acquiring sinking particles and dataon seabed sediments and sea conditions will be important.

4. Summary
We obtained the following conclusions from a
review of previous studies in the Ukedo River area andthe results of measuring radioactive Cs concentrations ofsinking particles caught in a sediment trap.
• The radioactive Cs concentration in seabed sedimentsshows a decreasing trend. However, the location of
the peak value of the radioactive Cs concentration
tends to change. In addition, the results of the 137Cs
inventory during each observation period wereconsistent with the physical decay of 137Cs, suggestingthat the radioactive Cs flowing in from the river ismoving locally near the estuary (Sanada et al., 2018).
137• The Cs flux in winter to spring (February to June)is 60% of the annual flux, suggesting that
resuspension plays a significant role in coastal areas.
137• The total annual deposition of Cs in 2017 isestimated to have been 11.4 kBq m−2. The 137Cs
inventory of seafloor sediments sampled in 2014 was
72 kBq m−2 (Tsuruta et al., 2017), and thecontribution of subsiding particles to the seafloor
sediments was about 16%.
Acknowledgments
The authors wish to express sincere thanks to Sanyo
Techno Marine Co., Ltd. for providing measurement data.
The Soma Futaba Fisheries Cooperative is thanked forproviding a fishing boat. Sincere thanks are extended toanonymous reviewers for their valuable and constructive
comments, which helped improve the clarity of themanuscript.
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Toshiharu MISONOU

since 2014.

Toshiharu Misonou is a researcher at the
Fukushima Environmental Monitoring Division,
Japan Atomic Energy Agency (JAEA). His
research field is environmental radioactivity incoastal area. After earning his PhD in Civil
Engineering, he has been engaged in the studyof environmental radioactivity in coastal areas

Tadahiko TSURUTA
After majoring in geology at his university,
Tadahiko Tsuruta worked in uranium resource
exploration, focusing on R&D related togeological disposal of high-level radioactive
waste. He participated in R&D for environmental
resilience in Fukushima after the Fukushima
nuclear power plant accident. In his R&D in
Fukushima, He was in charge of research on the mobilization behavior ofradioactive cesium in coastal areas, especially for promoting seabedsediments and suspended particle sampling to estimate the future
distribution of radioactive cesium in seabed sediments.

Takahiro NAKANISHI
Takahiro Nakanishi is an assistant principal
scientist at the Fukushima Environmental
Monitoring Division, JAEA. He has been engaged
in the study of environmental radioactivity,
mainly in oceans and forests. His current researchinterests include the assessment of radiocesiumtransport behavior on the catchment scale. He is
also interested in the global carbon cycle.

Yukihisa SANADA
After obtaining his PhD in Radiation
Measurement, Dr. Sanada’s research has been
primarily related to radiation management, theuse of gamma spectrometry systems to measureradionuclide activity concentrations andworkplace dose rates at nuclear facilities. Since
the Fukushima Daiichi NPP accident in 2011, hehas been performing remote radiation surveys such as aerial radiation
monitoring using manned or unmanned helicopters. He is now developing a
new type of radiation detector to study decontamination effects, andresearching migration of radioactive substances. He is a group leader at the
Sector of Fukushima Research and Development, Japan Atomic Energy
Agency (JAEA).
(Received 24 August 2020, Accepted 23 December 2020)

145

Case History: Decontamination Challenge of Iitate Village
Yuuzou MAMPUKUInstitute for Agro-Environmental Sciences, National Agriculture and Food Research Organization
3-1-1 Kannondai, Tsukuba-shi, Ibaraki, 305-8666, Japan*E-mail: manpuku@affrc.go.jp

Abstract
The nuclear power plant accident that occurred at the Fukushima Daiichi Nuclear Power Station operatedby Tokyo Electric Power Co. in the aftermath of the Great East Japan Earthquake of 2011 resulted inradioactive contamination of a substantial portion of the surrounding area, mostly in Fukushima Prefecture.
Immediately after the accident, direct contamination of crops occurred in areas where radioactive cesium
falling from the atmosphere was deposited on plant leaves or branches. As the effects of direct contamination
subsided over time, indirect contamination of crops, caused by absorption of radioactive cesium from the soil,
became a problem. The local authorities overseeing accident control in Fukushima Prefecture decided tosuspend all farming in the area, prohibiting planting of paddy fields within a 30 km radius of the Fukushima
Daiichi Nuclear Power Station with soil radiocesium concentrations of more than 5,000 Bq Kg−1. Although thedamage caused by the earthquake was relatively minor in Iitate Village in the Date district of Fukushima
Prefecture, the influence of radioactive fallout forced all of the villagers to evacuate their homes. Whiledecontamination of the entire region and environmental restoration by the government is in progress, thevillage is still confronted with various problems, including promoting public awareness of nuclear materials
and disposing of radioactively contaminated waste. The author was dispatched to Iitate Village as a specialist
for the Industry Promotion Section from April 2012 to the present (FY2020) to collaborate with staff of themunicipal government. He partook in various activities, including negotiating with relevant government
ministries, attending resident information sessions, and addressing issues of decontamination, waste disposal
and agricultural business. In this paper, the process from decontamination to resuming agricultural businessand progress toward environmental restoration with disposal of decontamination wastes is discussed in detail.
Key words :	decontamination, environmental restoration, radioactive contamination, removed soil,
resuming agricultural business

1. Details on the Nuclear Power Plant Accident
and Iitate Village
On March 11, 2011, the accident at the Fukushima
Daiichi Nuclear Power Station operated by Tokyo
Electric Power Co. (TEPCO; hereafter referred to as the
TEPCO Fukushima Daiichi nuclear accident) caused a
substantial part of the Tohoku Region to be contaminatedwith radioactive cesium, among which Fukushima
Prefecture sustained the most severe contamination. Units
1 to 3 were operating, and 4 to 6 were not, due toscheduled safety inspections when the earthquake hit thearea; although all of the active reactors scrambled
automatically, they lost all external power. The
emergency diesel generators (EDGs) went online
immediately, but all of the EDGs, except for one at Unit
6, ceased functioning due to flooding from the tsunami.
The reactor cores at Units 1 to 3 were exposed because
coolant circulation provided by the emergency core
Global Environmental Research
24/2020: 145-158
printed in Japancooling system (ECCS) failed for a certain duration,
leading to core meltdowns (Annual Report on Energy for
FY2011). Moreover, chemical reactions between steam
and zirconium on the fuel cladding tubes and otherequipment produced massive amounts of hydrogen. At
Units 1 and 3, hydrogen explosions probably caused byhydrogen leaking from the reactor containers occurred in
the upper structure of the reactor buildings. Anotherexplosion presumably caused by hydrogen occurred at
Unit 4, whose core fuel had been transferred before theaccident to the spent fuel pool for a safety inspection. As
a result of these explosions, a considerable amount ofradioactive cesium was released into the surrounding
environment (Ministry of Economy, Trade and Industry,2012).
The Japanese Government, thereafter ordered
residents within a 20 km radius to evacuate and residents
within a 20 to 30 km radius of the Fukushima Daiichi
nuclear power plant to take shelter. Leakage of©2020 AIRES

146

Y. MAMPUKU

radioactive cesium continued, and depending on winddirection and velocity, rainfall and other weather
conditions, deposition of radioactive cesium of varying
severities could be observed throughout Japan.
As a result of the TEPCO Fukushima Daiichi nuclear
accident, direct contamination occurred, in whichradioactive cesium falling from the atmosphere wasdeposited directly onto crop leaves or branches,increasing plants’ radioactive cesium concentrationlevels. On March 19, radioactive contamination beyond
the provisional regulation value (below 500 Bq Kg−1 ofradiocesium concentration) was detected in milk inFukushima Prefecture and spinach in Ibaraki Prefecture.
On March 20, vegetables and raw milk produced in six
prefectures in the Kanto and Tohoku regions also showedradioactive contamination beyond the regulation value.
While the influence of direct contamination subsided
over time, indirect contamination caused by absorption ofradioactive cesium from the soil became a problem, andthe Local Headquarters for Accident Control in
Fukushima Prefecture suspended all farming. On April 8,
the government announced the prohibition of planting
paddy fields in the area within a 30 km radius of the
Fukushima Daiichi Nuclear Power Station where readings−1of more than 5,000 Bq Kg radiocesium concentration
were found in the soil. A considerable range of crops andproducts in the area, including brown rice, herbage andgreen tea, were affected, exceeding the provisional
regulation value. A new regulatory value for radiocesium
concentration was set (100 Bq Kg−1) in April 2012, andsince 2012, all brown rice produced in Fukushima
Prefecture has undergone inspection before shipment(Ministry of Agriculture, Forestry and Fisheries, 2011;
Ministry of Health, Labour and Welfare, 2011; Fukushima
Prefecture, 2012a). In 2020, some municipalities shiftedto extraction inspection.
Iitate Village is a beautiful place located in thenorthern Abukuma Mountain range, richly blessed withnature. Forest cover accounts for approximately 75% of
its total area of 230.12 km2, and the terrain is relatively
gentle. The Manogawa River in the north, Niidagawa
River and Itoigawa River in the center, and HosokawaRiver in the south run through the village, providing
water to farm fields of approximately 2,200 ha around thesettlements. The average temperature is approximately
10°C, and the annual precipitation is approximately
1,300 mm, exhibiting a typical cool highland climate(Iitate Village, 2020).
Iitate Village did not sustain tsunami damage, but theearthquake measured just under six on the Japanese scale,causing roofing tiles to fall and roads to collapse (Fig. 1).
On the night of March 12, the Haramachi-Kawamata
town road (Prefectural Road 12) was jammed withvehicles trying to evacuate as far as possible away fromthe nuclear power plant, and a considerable number ofrefugees came to the village to take shelter. Many

Fig. 1 A road blocked by a rockslide in Iitate Village.

villagers, including members of the village office, firefighting team, local women’s association and social
welfare council, worked nonstop at the emergency shelterto accept refugees evacuating from the Hamadori region(coastal Fukushima). The weather on March 15 was rainy,
which turned to snow during the night. The radiationlevel indicated by the radioscope located in front of the
Ichibankan Building suddenly rose drastically the same
−1
day, with the highest level reaching 44.7 μS vh at 6:20
pm. Fear spread among the people, the village authority
took various initiatives, including discussing emergency
evacuation with Kanuma City in Tochigi Prefecture,
implementing screening tests and thyroid exposure tests
for children, and holding information sessions to enhancepeople’s knowledge about radiation. However, the villageauthorities were forced to handle demands or inquiries
resulting from the daily news being discussed among the
refugees, including news about high radiation readings in
the village, an announcement from the International
Atomic Energy Agency (IAEA) regarding extremely highconcentration levels of radioactive cesium detected in thevillage’s soil on March 20, and a report on March 21 by
the national government regarding highly concentrated
radioactive cesium detected in tap water in the village.
In the course of accident response, Japan’s
government issued guidelines for a directed evacuationand the areas targeted for it on April 11. Iitate Village wasincluded in an area-update issued on April 22 and theentire village was evacuated. By June 22, the village
office functions had been relocated to shelters in Iinomachi, Fukushima City to continue attending to theaftermath of the accident (Iitate Village, 2011).

2. Contamination Level Evaluation
Various studies have been conducted in Iitate Village
involving environmental restoration to resume
agricultural business and revive agriculture in the area.
These have included assessments of soil contaminationlevels in the polluted lands, environmental air dose rateevaluations and development of decontamination
techniques for removing radioactive cesium.

Case history: decontamination challenge of Iitate Village
The Institute for Agro-Environmental Sciences(NIAES) of the National Agriculture and Food Research
Organization (NARO) has conducted radioactive cesium
monitoring studies continuously since 1959, and theinformation they had gathered was the only long-termmonitoring data regarding radioactive contamination in
farmland soil and crops produced in the soil. These
particular data were used as the control data in an
investigation of soil and contaminated crops in the area
(National Agriculture and Food Research Organization,2010). The level of radiocesium concentration in the soil
was measured in each farming field as well, and theresults were published on each prefecture’s respective
website. Later, radiocesium concentration readings infarmland soil at a depth of 15 cm were organized andpublished in a distribution map based on an air dose rate
map compiled through aircraft radiation monitoring by
the Ministry of Education, Culture, Sports, Science andTechnology, a digital farmland soil map, and actual
radiocesium concentration level measurement values. As
of November 2011, areas with high radiocesium
concentrations in the soil were distributed northwest of
the Fukushima Daiichi nuclear power plant, and in thesouth and north of the Nakadori region (inland) of

147

Fukushima Prefecture (Fig. 2). Several areas with highradiocesium concentrations (hotspots) were confirmed
locally outside of Fukushima Prefecture, and otherhotspots were confirmed within Fukushima Prefecture incities such as Fukushima or Date. From investigative
results in 2011, farmlands that exceeded the regulatory−1
standard for cultivation, set at below 5,000 Bq Kg ofradiocesium concentration in the soil, were estimated tototal approximately 8,900 ha in Fukushima Prefecture(Kohyama et al., 2013). Information was publishedindicating that radiocesium concentrations in the
farmland would steadily decrease due to the subsequentphysical decay of radioactive cesium or a phenomenon
called weathering, in which radiocesium percolates ordrains off.
Municipal governments subjected to full evacuation
suffered a severe decrease in government office functions
at that time because of the overwhelming amount ofissues requiring immediate attention, including securing
places of refuge for the people, addressing insufficient
information about radioactive cesium, and assisting
officials of Japan’s government and relevant ministries.
Resident information sessions regarding radioactive
contamination, with which no one had ever had any

Fig. 2 Soil Concentration Map of the zones directed to evacuate (total amount of cesium 134, 137 deposited on the ground surface)(as of March 11, 2013) (Nuclear Regulation Authority, 2013).

148

Y. MAMPUKU

previous experience, were also challenging. There were
instances in which the meanings of the words “radiation,”“radioactive cesium,” and “radioactivity” were confused.
In addition, explaining various technical terms in plain
language for the people was highly challenging, such asalpha ray, beta ray, gamma-ray, X-ray, neutron ray andthe “becquerel” unit that indicates the radiation emission
capacity of radioactive cesium, as well as “Sievert,” ameasure of radiation’s impact on human health. Many
residents directly linked the influence of the nuclear
power plant accident with that of the atomic bomb, andsessions were nearly in a state of total chaos. The author
also attended these resident information sessions held in
Iitate Village and other places, fielding a wide variety ofquestions regarding the relationship between theregulatory standard for radioactive concentration levels
for paddy rice cultivation and the radiation exposure of
farmers, or the credibility or certainty of information
scattered on SNS or broadcast in the news. He realized
the difficulty of explaining technical terms plainly orpresenting the current situation with the utmost care andconsideration to avoid offending the feelings of theresidents. As mentioned earlier, these sessions for the
residents involved had to be held repeatedly so that theresidents could live without anxiety.

3. Forms of Radiocesium Existing in the Soil
Radiocesium enters the soil and dissolves in water tobecome a monovalent cation (Cs+); thus, it is captured bynegative charges in the soil. The negative charges derived
from soil organic matter or clay minerals have different
levels of affinity for Cs+, and the composition or content
of organic matter/clay minerals differs among soils. In
this chapter, the forms of cesium in the soil, themechanism of Cs+ adsorption by negatively charged soil,
and characteristics of soil constituents, which areessential for characterizing Cs+ adsorption sites, as wellas their distribution in the soil in Japan are discussed indetail. In addition to the above, the soil distribution in
Fukushima Prefecture is thoroughly reviewed according
to the properties and types of each soil — the radiocesium
concentration levels in the farmland soil of Fukushima
Prefecture have been reported to the public accordingly.
In this report, the impact of radioactive cesium on crops
was estimated according to the soil characteristics ofFukushima Prefecture, the distribution of radiocesium
concentrations in the soil, and predictions of the behaviorof radioactive cesium in the soil of Fukushima Prefecture(Yamaguchi et al., 2012). It has been vital to provide suchinformation to the farmers and their families, but the
information available at that time was mostly academic
documents requiring scientific expertise. It was
regrettable that the relevant authorities could not provide
the local residents with such vital information in simple
and easily understandable terms.

4. Development of Decontamination Techniques
It was the first time in Japanese history for thecountry’s farmland to be contaminated with highly
concentrated radioactive cesium. According to an
investigation of the Chernobyl accident in 1986, the
IAEA reported that the soil contamination fromradioactive cesium fallout was concentrated at the surfaceof the soil (Sugiura, 2011). The same condition was
suspected in the case of Fukushima so it was expectedthat by removing the surface soil the contaminatedfarmland could be restored to a status suitable forcultivation. The National Agricultural Research Centerestablished an operating system to reduce the amount of
in-soil radioactive cesium mainly by using agricultural
machinery available on the market (e.g., power harrows
and front loaders) with consent from the farmers of Iitate
Village. It was assumed that farmers would work in theaccessible areas with simple protection, such as masks.
The Institute for Rural Engineering developed a selfpropelled top-soil stripping method for construction
machinery (Fig. 3). The decontamination techniques
mentioned above were based on land categoryclassification (e.g., paddy fields or plowed fields) andcontamination level considerations and application
policies. Details of various farmland soil decontamination
techniques were reviewed and organized into an operation
manual for radioactive cesium removal techniques(decontamination techniques) for farmland (National
Agriculture and Food Research Organization, 2011).

Preliminary survey

Crush the topsoil

Crush the topsoil

Strip the topsoil

Carry out stripped soil

Strip the topsoil

Pack in a flexible
container pack

Carry out stripped soil
Fig. 3 
Decontamination operation flowchart and images ofoperations (NARO, 2011).

Case history: decontamination challenge of Iitate Village
These systemized techniques are highly valued because
farmers themselves can implement decontamination withequipment available nearby. At the same time, heavymachinery, such as backhoes or bulldozers, was used in
actual decontamination practice. Introducing heavymachinery enhanced the efficiency of decontamination
work, yet the heavy weight and large vibrations wereconfirmed to damage the vegetation foundation layer or
rupture under drainage. In addition, the Japan Atomic
Energy Agency and other relevant authorities conducteddecontamination model verification. Subsequently,
decontamination of houses, cleansing of school buildings,
stripping of schoolyard top-soil, cleansing of roadpavement and other measures were investigated (Ministryof the Environment, 2012).
During this period, Iitate Village was designated as
one of the special areas under the direct control of thegovernment (according to the “Special Measures” of Act
No. 110 of 2012), and resident information sessions
provided by the Ministry of the Environment regarding
decontamination of houses, farmlands and wood edges
were held almost every day. Decontamination practices in
Iitate Village were implemented over an area ofapproximately 5,600 ha that included approximately
2,100 houses, 2,400 ha of farmland, 2,100 ha of forest(wood edges), and 330 ha of roads, producing
3
approximately 2,000,000 m of stripped soil, which has
been stored at 96 temporary storage sites (TSSs) in thevillage (Fig. 4). Transportation of removed soil to aninterim storage facility (ISF) began in 2016, andapproximately 730,000 m3 had been transferred outside
the village by September 2020 (Ministry of theEnvironment, 2012; Ministry of the Environment,
2016a).
The top-soil stripping method was implemented forthe entire farmland area of Iitate Village according to theresidents’ intentions. The method conducted by the
Ministry of Environment effectively decontaminated theradiocesium deposited on the top-soil of the farmland.
Uncontaminated decomposed granite available in theFig. 4 
Temporary storage site for decontaminated soil (picture
taken in August 2016; a total of 96 sites were set up in Iitate
Village).

149

village was used for soil dressing, however, and as aresult, farmers accused the Ministry of the Environmentof turning their farms into sand boxes. In addition, the cut
slopes and ridges in the farmlands were left mostly
unattended except for deep pruning of weeds, leaving
radioactive cesium in the soil. Decontamination ofhouses, farmlands, and wood edges has now been
completed in all areas except for those in the “difficultto-return zones,” and projects for resuming agriculturalbusiness and farmland maintenance and management
have gradually begun to be initiated. Approximately
3
14 million m of removed soil including thedecontamination waste (hereinafter referred to as
removed soils) was generated across the whole of
Fukushima Prefecture. The transportation of the removed
soils to the ISF has commenced across the prefecture(Ministry of the Environment, 2016a).
The removed soils will be stored for a specificduration at the ISF, and then their final disposal will be
conducted outside the prefecture, as decided by the
Cabinet Council. The Ministry of the Environment andIitate Village are currently verifying the possibility ofrecycling the removed soils-after implementing antiscattering measures or placing protective covers-for
public construction projects under the ‘Verification
Project for Recycling of Removed Soil,” as a part of the“Reconstruction and Revitalization Project for theSpecific Area of Restoration,” subject to the consent of
the village’s residents (Ministry of the Environment,2013).

5. 
Purpose and Significance of Removed Soil
Recycling
According to the Basic Guidelines for the
Reconstruction and Revitalization of Fukushima (issued
on July 13, 2012, by Cabinet decision) and other relevant
guidelines, the removed soils are to be transported to the
ISF, and the national government is to take responsibility
for their final disposal, as described in the guidelines,
which say that the government “will implement necessary
measures to complete the final disposal of theradioactively contaminated waste outside of Fukushima
Prefecture, within 30 years after the commencement ofwaste storage at the ISF.”
According to calculations by the Ministry of theEnvironment, the total amount of removed soils is3
estimated at 14,000,000 m (Ministry of the Environment,
2012; Ministry of the Environment, 2013). Some say that
it is impossible to dispose of such an immense amountbecause of the difficulty in securing final disposal sites
with adequate handling capacities. Moreover, theestimated amount does not include waste from the places
subjected to the Reconstruction and Revitalization Project
for the Specific Area of Restoration. Implementing
environmental restoration is being discussed for those150

Y. MAMPUKU

places, including the “difficult-to-return zones,” where
quantitative estimation is impossible. The estimatedamount does not include wastes with over 100,000 Bq/Kg.
As mentioned above, it is possible that the burden at the
ISF may increase. Therefore, it is necessary to formulatea method to use the removed soils partially for publicconstruction projects because the soil itself is a valuable
natural resource. However, it should not be used as it isbecause it contains radioactive cesium.
The Ministry of the Environment has been holding“Meetings for the Development of Reduction andRecycling Technology of Removed Soil Stored at ISF”
since July 2015. Referring to the investigation results of
the Working Group for the Safety Assessment ofRadiation Effects in Recycling of Removed Soil andRelevant Waste and Working Group for the Developmentof Reduction and Recycling Methods of Removed Soiland Relevant Waste Stored at ISF, the ministry hasorganized guidelines titled Basic Concept Regarding the
Safe Use of Removed Soil Recycled as the Resource(Ministry of the Environment, 2016b), which were issuedin June 2018.
“Recycled resource” has been defined at theStrategic Meetings as removed soils that have undergone
proper pre-processing and several contamination-levelreduction stages of physical processing, as well as aquality management control process to satisfy therequired criteria to be used as material at target sites.
Likewise, the term “recycle-use” is defined as using
recycled resources for strictly limited purposes, such as
public construction projects, in which the management
body or responsible party is public. These would takeforms such as embankment materials in structural
foundations, in which the material properties would not
likely be subject to alteration by humans, so that therecycled resources would be used under proper
management control, including setting radiation

concentration thresholds to reduce and minimize
secondary exposures, sealing them with protective covers,
taking anti-scattering measures, and organizing/storing
record documents. “Recycle-use” differs from less strict
counterparts like the Clearance Program, which excludes
materials from the regulatory framework of radiation
protection and grants the free distribution of recycledmaterials without restriction. “Recycle-use” as defined
here follows the regulation standard set in the Special Act
on Countermeasures Against Radiation Contamination byRadioactive Cesium Released in the nuclear power plant
Incident Due to the Great East Japan Earthquake on
March 11, 2011 (Act No. 110 of 2011), which is supposed
to be practiced under proper management. As for the
byproducts of chemical/heat processing of the removed
soils or relevant subsequential waste, such as heatprocessing ash, they are not currently included as the
subject of the Basic Concept because not all of the preand post-processing properties or the quality/possible useof those byproducts have thus far been confirmed.
To evaluate recycled resources technically, it isnecessary not only to promote technical development of
reduction/recycling technology to maximize the reductionof removed soils but also to establish a system forrecycling soil obtained from reduction processing withlow radioactive concentrations, after securing a properlevel of safety and receiving the consent of the local
residents. The Ministry of the Environment has
implemented a verification project for recycled resources(used as foundation materials for road embankments; it iscurrently continuing as an environmental monitoring
project) in Minamisoma City since 2017, and anotherverification project (of foundation material in land fordevelopment) commenced in Iitate Village in 2018 withthe understanding and cooperation of the residents ofNagadoro administrative district (Fig. 5) (Ministry of theEnvironment, 2012).

Fig. 5 Concepts on safe use of the soil from off-site decontamination work after recycling (Ministry of theEnvironment, 2016c).

Case history: decontamination challenge of Iitate Village

6. Concept and Awareness of the Recycle Use of
Removed Soils
The removed soils processed in the decontaminationof Iitate Village are planned to be provided for limited
use under proper management control. After undergoingappropriate pre- and post-processing or physicalprocessing such as classification, the quality of therecycled material will be modified to suit the conditionsof the target site and used strictly as structural foundationmaterial such as embankment material in publicconstruction projects, in which the management body or
responsible party is public, and in which the material
properties would not likely be subject to alteration byhumans (Ministry of the Environment, 2018a).
In final disposal outside the prefecture or otherrecycle-use of the removed soils, it will be criticallyimportant to foster a nationwide consensus and trust
regarding the concept and implementation oftechnological developments, recycle-use of removed soils
and safety measures against radiation. Conducting averification project requires detailed information
disclosure to the municipal government and local
residents. The findings and experiences obtained in theseverification projects should be reflected in future
recycling projects.
The Ministry of the Environment conducted anationwide internet survey in November 2018, targetingmen and women in their 20s to 60s (3,600 responses; 400
each in nine regions of Hokkaido, Tohoku (except for
Fukushima), Fukushima Prefecture, Kanto, Chubu, Kinki,
Chugoku, Shikoku, and Kyushu/Okinawa). The response
rate of each region corresponded to its respective
population composition ratio. The result was that morethan half of the respondents answered “Never heard of it
before” regarding the recycle-use of removed soils,
revealing that nationwide awareness of this is extremely
low (Ministry of the Environment, 2015).

7. Evaluating Amounts of Secondary Exposure
To minimize amounts of secondary exposure toresidents, facility users and construction workers in therecycle-use of removed soils, the material is to be used
for limited purposes, and all necessary measures are to betaken accordingly, including setting standard radioactive
concentration levels for recycled materials and securing
proper thicknesses of covering soil. Concentration levelsof radiocesium (134Cs+137Cs) in recycled material were
calculated under the condition of secondary exposures
not exceeding 1 mSv/y throughout the period during
which secondary exposure amounts were evaluated. In
practice, additional measures such as radiation shielding
are implemented to reduce exposure amounts further, so
as not to exceed 1/100 of the threshold (Reconstruction
Agency, 2017).

151

8. Initiatives in Nagadoro, Iitate Village
The Nuclear Emergency Response Headquarters of
the Japanese Government reviewed the area that had
undergone planned evacuation in Iitate Village in June2012 and designated within it a “zone in preparation of
the lifting of the evacuation order,” “restricted residencearea,” and “difficult-to-return zone,” according to theyearly integrated radiation amount. In this particularreview, Nagadoro, a settlement in Iitate Village, wasdesignated as a “difficult-to-return zone” due to readingsof over 50 mSv/y. The Revised Act on Special Measures
for the Reconstruction and Revitalization of Fukushima
was enacted in May 2017 to establish a base forreconstruction and revitalization of the “difficult-to-returnzone.” The establishment of a special reconstruction andrevitalization base is now in progress in Nagadoro aswell.
In addition to establishment of the base, a series of
discussions among the national government, municipal
government and local residents have been conducted
repeatedly regarding the recycle-use of materials in theEnvironmental Restoration Project.
November 11, 2017: The Environmental Restoration
Project was approved in an extraordinary general
meeting of Nagadoro administrative district in Iitate
Village.
November 13, 2017: Nagadoro administrative district
informed the Mayor of Iitate Village in writing
regarding the affirmative vote at the general meeting.
November 14, 2017: The Environmental Restoration
Project was approved by the Iitate Village Council
and a conference with all village members.
November 20, 2017: The Iitate Village Council
submitted the request for implementation of theEnvironmental Restoration Project to the Ministry of
the Environment.
The request demanded that the nation and relevant
ministries provide Nagadoro with proper support,
including recycling of soil removed from the village,
environmental reformation through land development/
concentration of Nagadoro, and other necessary support
to ensure long-term land use, such as cultivation ofgardens/resource crops in the settlement after
environmental restoration through implementing findings
regarding the recycle-use of removed soils currently
being investigated by the national government.
November 22, 2017: Confirmation of the Environmental
Restoration Project Initiation among Iitate Village,
Nagadoro administrative district, and the Ministry of
the Environment
The Ministry of the Environment and Iitate Village

152

Y. MAMPUKU

agreed that both parties would work closely on theEnvironmental Restoration Project, including recyclingof the removed soils in Nagadoro, to contribute to therevitalization of not only Nagadoro but also of Iitate
Village and Fukushima Prefecture. The Ministry of theEnvironment, Iitate Village and the Naganuma settlementin the adjacent Iwase District were to collaborate andinitiate verification projects, reflecting experts’recommendations and paying utmost consideration tosafety and security in the environment.
January 28, 2018: An information session presenting
the restoration project was held during an
extraordinary general meeting of Nagadoro
administrative district in Iitate Village.
March 25, 2018: Another information session
presenting the restoration project was held during an
extraordinary general meeting of Nagadoro
administrative district in Iitate Village.
April 20, 2018: The Restoration and Revitalization
Program for Areas Requiring Special Attention wasapproved for implementation in Iitate Village.
June 3, 2018: An information session for residents on
the restoration project was held targeting theresidents of Nagadoro.
In considering residents’ feelings, verification
projects regarding the recycle-use of removed soils mustbe evaluated from every possible aspect, employing theexpertise of the “Environment Restoration Project
Organizing Committee for Restoration and Revitalizationof Nagadoro in Iitate Village” so that the project cancommence with proper care and consideration for safety
and security through efforts to review and confirm factors
causing anxiety among residents. The accomplishments averification project previously conducted in Minamisoma
City will be introduced in these projects. A series of crop
cultivation tests will be conducted as well, targeting
gardening/resource crops in response to a request from
Nagadoro (Ministry of the Environment, 2012; 2017).

30,000 bags of removed soils being held in the village’s
TSS to a stockyard designated in Nagadoro administrative
district and establish a recycling plant in the vicinity ofthe designated recycling facility (Fig. 6) (Ministry of theEnvironment, 2012; 2017).
The recycling procedure consists of two processing
phases: a pre-processing phase to break the container
bags and remove unnecessary components for farmland
development (e.g., garbage, irrelevant organic materials
and metals), and a quality control phase to manage thesoil quality according to the target use of the recycle-soil.
To maximize the amount of recycled material andreduce unnecessary organic materials or metals, the soil
will be sifted using a vibrating screen in the preprocessing phase to remove alien substances larger than aspecific size. The recycle-soils will be evaluated in thequality control phase to determine if it satisfies therequired quality standard (e.g., density, ignition loss,
moisture weight percentage and particle size distribution)
for use as embankment material in farmland development.
Those that fail to satisfy the standard will be evaluated todetermine if the quality could be improved by mixing andstirring with the soil to be used as the shielding.
The recycle-soils will then be measured by aradioactive concentration measurement/sorting device
and categorized according to their concentration levels;
those that do not meet the designated threshold will not
be used as recycled material. The soil processed in
Nagadoro will be categorized as either over 5,000 Bq Kg
or below 5,000 Bq Kg. Specifically, the soil is put into
the hopper of the radioactive concentration measurement/sorting device and lands on a conveyor (transfer speed:
35 cm/sec) equipped with a belt scale and a cesium iodide(CsI) scintillator detector (with a 1.2-second detection
interval) to measure its weight and radiation dose. Thenthe radioactive concentration measurements are sent tothe sorting device, in which the sorting chute divides thesoil into groups with over 5,000 Bq Kg and under
5,000 Bq Kg. The soil to be recycled as embankment

9. Outline of Verification ProjectThis project aims to verify various aspects ofremoving soil stored in the TSSs in the village to berecycled as embankment materials for farmland
development. The aim is to establish a technicalframework for promoting the recycle-use of materials
from the viewpoint of their management, including
examination of practical management methods forprotection from radiation during the recycling process
and assurance of quality as embankment materials forfarmland development, and securing safety from radiation
during the experimental recycle-use of soil (Ministry of
the Environment, 2012; 2017).
The first step is to transfer and store approximately

Fig. 6 Inside the recycling plant.

Case history: decontamination challenge of Iitate Village

153

Area for producing recycled soil (Nagadoro)Fig. 7 Image of the demonstration project (in Iitate Village) (Ministry of the Environment, 2018b).

Agricultural cultivation demonstration

Regeneration plant↑Warabitaira

Presentation room

Agricultural greenhouse (cultivation demonstration)↓Hiso

Fig. 8 Location of candidate area for recycling (Ministry of the Environment, 2018b).

material for farmland development will then be verified
accordingly.
The recycled material will undergo a rollingcompaction process to secure more than 50 cm ofshielding soil pressure (shielding thickness) in theconstruction of the embankment, in which the relevant
data, including hydraulic conductivity, cone index,
compaction degree, settlement of the embankment,
surface dose rate, air dose rate, soil radioactive
concentration level and other data after the compaction ofeach layer are recorded. The productivity of the actual
construction project is also estimated accordingly by
investigating key elements, such as cycle time at eachconstruction stage.
The ground at the site of the recycled material
verification project has been cured with an impervious
sheet or other materials wherever necessary to prevent
contamination of the local panel, and its rainwaterdrainage system is being properly attended by placing
required facilities such as gutters so that the level ofradioactive concentration can be measured appropriately.

Tents (100 m×30 m) have been set up at the recycledmaterial verification project site, and all work has been
conducted inside the tents to prevent infiltration of
rainwater or outflow of the removed soils. Upon resolving
technical issues, the full-scale Environmental Restoration
Project, which will encompass the farmland stretchingfrom east to west between the Hisokawa River and theprefectural road, will use the quality-controlled recycling
materials obtained by the above method (Figs. 7 and 8)(Ministry of the Environment, 2012; 2017).

10. O utline of the Cultivation Verification Project
A cultivation verification project assuming therecycle-use of materials for the planting base material has
been implemented. In this verification project, the area of
farmland development is approximately 0.1 ha, on which
various garden crops and other crops premised on the useof biomass have been tested in greenhouses. The safetyof using recycled materials is being evaluated in thesecultivation tests using shielding materials and recycled

154

Y. MAMPUKU

Fig. 9 Cultivation of ornamental plants in the greenhouse.

materials in pot culture, greenhouse cultivation (on-site),and open‐field culture (Fig. 9) (Ministry of theEnvironment 2012; 2017).The residents of Nagadoro
have also participated in the project. Their participation
seems to have had a positive effect, including a renewed
understanding of radioactive cesium and increased desire
among them to return to their homes in Nagadoro. At thesame time, however, those who have decided to return are
relatively advanced in age, posing a severe problem insustaining the community’s future.

11. Reducing Amounts of Radiocesium
Transferred to Crops
Research institutes in the prefectures of Fukushima,
Ibaraki, Tochigi and Gunma collaborated with NARO ina paddy rice cultivation experiment in 2011 to investigate
the influence of potassium fertilizer on the transfer ofradiocesium in the soil to cultivated brown rice (Ministryof Agriculture, Forestry and Fisheries, 2015) The results
showed that the transfer coefficient of radiocesium tobrown rice could be reduced, except for in soil with a lowtransfer coefficient, by applying an amount of potassium
fertilizer three times greater than the usual application.
This fertilizer was rich in clay minerals and had a highradiocesium fixation capacity. The concentration levels of
exchangeable potassium were relatively high in soil
applied to cow dung compost for a long period in addition
to a chemical fertilizer, showing a low concentration level
and transfer coefficient of radiocesium to brown rice.
Soils containing zeolite or vermiculite as clay minerals
were evaluated, and a recommendation was made to
reduce radiocesium concentration by adjusting the usual
amount of applied fertilizer in each area with a low
potassium content in the paddy field to the level at which
the amount of exchangeable potassium was around−1
25 mg-K2O (100 g) (Fig. 10). According to the above
results, a countermeasure to radioactive absorption was
implemented to increase the amount of potassium inapproximately 84,000 ha of paddy fields in Fukushima

Fig. 10 C orrelation between the transfer coefficient of exchangeable
potassium and radioactive cesium in the soil for brown rice
(National Agriculture and Food Research Organization,
2017b).

and other prefectures during implementation of theAgricultural Business Restoration Project in 2013
(Ministry of Agriculture, Forestry and Fisheries, 2011).
In soybean cultivation, it was also revealed that thepotassium concentration in the soil contributed tosuppression of radiocesium absorption in the same way
as observed in paddy rice cultivation, and the same target
level of exchangeable potassium was set at approximately−1
25 mg K2O100g in practice. It was reported, however,that application of potassium chloride in soybean
cultivation would prohibit root nodule adhesion;
therefore, the influence of the potassium concentration insoybean cultivation was evaluated and the reduction ofroot nodule adhesion was confirmed to be minimal at thetarget level of around 25 mg K2O100g−1, posing no ill
effect on the growth or harvest of the crop. For buckwheat
cultivation, this countermeasure was recommended witha target level of approximately 30 mg K2O100g−1(Ministry of Agriculture, Forestry and Fisheries, 2011;
Kato et al., 2015).
Pasture renovation can reduce the radiation air dose
rate at the pasture surface and the radiocesium
concentration level in newly seeded pasture. A total
renovation method combining plowing with burial ofradiocesium deep in the soil has been found highly
effective as a countermeasure in pasture cultivation.
When thorough soil turnover is accomplished, the surface
turnover by disc harrows should be enough to reduceradioactive absorption in the crop.
Potassium fertilizer has also been applied in Iitate
Village after soil decontamination. However, work
involving commuting between where the evacuatedfarmers have relocated and the village imposes a
significant burden on the farmers. Since someradiocesium remains after decontamination, continuous
practice of radioactive countermeasures, such as surface

Case history: decontamination challenge of Iitate Village
soil scraping, should be mandatory. It is vital to build asolid awareness among farmers regarding the significanceof these countermeasures. Moreover, anxieties about
radiation remain among the public, and despite thetremendous efforts of the local citizens, the damage
caused by harmful rumors falsely accusing the crops
grown in Fukushima of being contaminated withradiocesium is still problematic.

12. Dynamic Analysis of Radiocesium in
Cooking and Processing of Crops
It has been nearly ten years since the accident, andthe natural decay of radioactive cesium released to theenvironment should be progressing, yet consumers’
anxiety about the influence of radiocesium (137Cs) remains
dominant; thus the validity of the measurement standard
for radioactive concentrations in food has been evaluated.
The Food Sanitation Law defines the standard value ofradiocesium concentrations in typical food as below
100 Bq Kg−1, and it is necessary to examine the dynamismof radiocesium in the cooking and processing of the target
foods for accurate risk assessment and management(National Agriculture and Food Research Organization,
2017b). In brown rice cooking, it has been confirmed thatradiocesium is removed with the rice bran and washingwater during the polishing and boiling of brown rice(Fig. 11) (Ministry of Agriculture, Forestry and Fisheries,2015). In milled rice, the radiocesium concentration in155

polished and boiled rice has been found to be one-eighththat of brown rice, revealing the dynamics of radiocesium
during cooking and processing. Along with foodprocessing technology, a systematic procedure to easily
measure radiocesium concentrations in food has alreadybeen established in each municipality, contributing toconsumers’ safety. The radiocesium concentrations inmountain vegetables and mushrooms, however, remains
high, and residents often demand appropriate actions toresolve the situation. Relevant initiatives have been taken
since 2012 in Iitate Village so that farmers can measureradioactive concentration levels in crops they cultivatethemselves to ensure safety (Ministry of Agriculture,
Forestry and Fisheries, 2015; Ministry of Health, Labourand Welfare, 2011).

13. Environmental Restoration of Fukushima
The decontamination of the entire region of
Fukushima Prefecture, except for the “difficult-to-returnzones,” was completed by the end of 2018. A considerable
amount of contaminated soil was produced in the process,reaching a total of approximately 16,500,000 m3 inFukushima Prefecture alone. These contaminated wastes
have been stored at either TSSs set up at approximately
1,300 sites during the peak period or on residential
quarters/open ground in areas where it is difficult to set
up storage deposits (e.g., densely populated areas such as
Fukushima City or Koriyama City). All of the wastes will

Fig. 11 P ercentage of radioactive cesium removed during processing from brownrice to cooked rice(%) (National Agriculture and Food Research
Organization, 2017b).

156

Y. MAMPUKU

Fig. 12 Trends in numbers of temporary storage sites in Fukushima Prefecture (quarterly for each fiscal year, published on the Ministry of
the Environment’s Environmental Remediation website) (Ministry of the Environment, 2018b).

Volume of transportationachived in FY2020:
approx.1648 (as of Aug. 6, 2020)

Cumulative volume of transported
approx. 8,331 (as of Aug. 6, 2020)
Volume transported on
single-year basis(103 m on bar graph)

Cumulative volume of transported
approx, 6,683 (as of the end of 2019)

Completion oftransportation ofalmost the entire amountof soil and waste planned
for the end of FY2021

Cumulative volume of transported
approx. 2,624 (as of the end of FY2018)
Cumulative volume of transported
approx. 785 (as of the end of FY2017)

Cumulative
Volume transported
3(10 m on line graph)Fig. 13 Ad-hoc policy on transportation to the ISF (Ministry of the Environment, 2018b).

be transferred to SSFs set up in Okuma Town and Futaba
Town. Transportation (Figs. 12 and 13) began in 2015
with an initial transportation test run with 46,000 m3 fromeach municipality in the prefecture. A total of 4,059,000 m3of temporarily stored soil/waste was transported to the
ISF in 2019, and as of 2019, a total of 8,509,000 m3(August 2019 under the direct control and June 2019
under the indirect control of the Ministry of theEnvironment, with information updated daily on its
website) has been transported. By the end of FY2021, thetransportation should be almost complete. Once this iscompleted, the lands used as TSSs, which were leased to
the national government, will be restored to their previous
state before use for storage deposits and returned to thelandowners) (Ministry of the Environment, 2012; 2016b).
As for the ISFs, a total of approximately 1,600 ha ofland has been allocated for their creation, and the remainsof the TSSs, including deposit/sorting facilities forcontaminated soil/waste transported from temporary
dumping sites and soil storage facilities, and other wastes,such as sorted logs or materials from dismantled
buildings, will be compacted by combustion and theresulting incineration ashes with high concentrations ofradiocesium will be sent to radioactively contaminatedwaste storage facilities. The storage time at the ISF is set
at within 30 years, after which the contents will bedisposed of at waste disposal sites set up outside
Fukushima Prefecture (the location of which is to be
decided). At the ISF, the waste is being stored in two
groups, that below and that above a threshold of
8,000 Bq Kg, to prevent rainwater infiltration withnecessary curing to limit infiltration of the groundwaterby contaminated soil particles or radiocesium. Regarding
the final disposal of radioactively contaminated waste at

Case history: decontamination challenge of Iitate Village
the ISF, relevant laws and guidelines, including the “Basic
Guidelines for the Reconstruction and Revitalization of
Fukushima” issued on July 13, 2012 (Cabinet decision),determine that “necessary measures must be taken tocomplete the final disposal of soil outside Fukushima
Prefecture within 30 years from the start of interim
storage.” Further actions will be required in the future(Ministry of the Environment, 2012).
In Iitate Village, where the author was dispatched, it
seems that the level of awareness among farmers
regarding radioactive cesium has been enhanced greatlycompared to during the farmland decontamination
measures verification project, which encompassed
approximately 40 ha of farmland in Iitate Village (in thesettlements of Nagadoro, Komiya, and Kusanomukaioshi)
and Kawamata Town (in the settlements of
Yamakiyahosoda and Yamakiyahinada), and after theevacuation order was lifted in the “zones in preparationof the lifting of the evacuation order” and “restricted
residence areas.” The residents can prepare to protect
themselves against lingering undiscovered radioactive
cesium and recover from their evacuation to the present.
Although environmental restoration by decontamination
is in progress, there remain various issues in resuming
life in the village after environmental restoration,
including some residents’ lack of desire to return to thevillage after their prolonged evacuation and discontent
with the slow reconstruction of village infrastructure. As
for resuming agricultural business in the area, a reductionin the number of residents and the increasing age of those
who wish to return and resume farming will have a great
impact, requiring close attention in the future.

14. Conclusion
A multi-perspective approach to countermeasuresagainst contamination by radioactive cesium is extremely
vital to the environmental restoration of Fukushima
Prefecture, the area most severely affected by radioactive
cesium in our country. A substantial augmentation ofcontrol technologies and data contributing to resumptionof agricultural business should be mandatory, and crosssectional initiatives to defend against radioactive cesium
must be implemented continuously in close collaboration
among the national and municipal governments, research
institutes, private corporations and other relevantorganizations.
Acknowledgments
Extremely careful yet swift actions are required in
response to radioactive cesium contamination. The author
was dispatched to Iitate Village in the Date district ofFukushima Prefecture where he served as a specialist in
the Industry Promotion Section. The author wishes toexpress profound gratitude to the following individuals

157

for their guidance and understanding:Doctor Makoto Nakatani, Vice President of NARO;
Doctor Masami Yasunaka, NARO; Dr. Takeshi Kimura,
National Federation of Agriculture Co‐operative
Associations; Professor Takuro Shinano, Hokkaido
University; Drs. Takeshi Ota, Hisaya Matsunami,
Yoshisada Nagasaka, Namiko Yoshino, Sachie Horii,
Kazunori Kohyama, Noriko Yamaguchi, Hideshi Fujiwara,
Yasuko Togamura, Mayumi Hachinohe, Tomijiro Kubota,
and Takeo Tsuchihara, NARO; Associate Professor,
Moono Shin, Fukushima University; Drs. Mutsuto Satoand Takashi Saito, Fukushima Prefecture; Drs. Masaya
Suzuki and Hirohisa Yamada, National Institute ofAdvanced Industrial Science and Technology; Prof.
Tsutomu Saito, Hokkaido University; and all the staff
members of the Iitate Village Restoration andReconstruction Division. Lastly, the author wishes toexpress gratitude from the bottom of his heart to all those
who have supported us in relevant organizations.
References
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Marketing Division, Fukushima Prefecture (2018) Fukushima
prefecture agriculture, forestry and fisheries products processedfood monitoring information. Retrieved from https://www.newfukushima.jp/top (Accessed 30 September 2020)
Fukushima Prefecture (2012a) Radioactive material inspection
information. Retrieved from https://fukumegu.org/ok/contentsV2/
kome_summary.html?targetyear=12 (Accessed 25 September
2020)
Fukushima Prefecture (2012b) Transfer coefficient to brown rice.
Retrieved from https://www.pref.fukushima.lg.jp/download/1/
ganba24H240410.pdf (Accessed 25 September 2020)
Institute for Agro-Environmental Sciences, National Agriculture
and Food Research Organization (2010) Monitoring ofradioactive isotope in crops and farmland soils. Retrieved fromhttp://www.naro.affrc.go.jp/archive/niaes/topics/radioactivity.
html (Accessed 30 September 2020)
Iitate Village (2011) Public relations. Retrieved from https://www.
vill.iitate.fukushima.jp/site/kouhou/ (Accessed 30 September
2020)
Iitate Village (2020) Village overview. Retrieved from https://www.vill.iitate.fukushima.jp/soshiki/1/63.html (Accessed 30
September 2020)
Kato, N., Kihou, N., Fujimura, S., Ikeba, M., Miyazaki, N., Saito,
Y., Eguchi, T. and Itoh, S. (2015) Potassium fertilizer and othermaterials as countermeasures to reduce radiocesium levels inrice: Results of urgent experiments in 2011 responding to the
Fukushima Daiichi nuclear power plant accident. Soil Scienceand Plant Nutrition, 61, 179–190.
Kohyama, K., Takada, Y., Obara, H., Taniyama, I. and Saito, T.
(2013) A Distribution of Radio Cesium Concentration in
Farmland Soil in Eastern Japan, Inventory, 11, 51–54.
Ministry of Agriculture, Forestry and Fisheries (2011) Annual
Report on Food, Agriculture and Rural Areas in Japan FY2011.
Retrieved from https://www.maff.go.jp/e/data/publish/attach/
pdf/index-10.pdf (Accessed 30 September 2020)
Ministry of Agriculture, Forestry and Fisheries (2015) Factors thatcause soybeans with high radioactive cesium concentration andcountermeasures. Retrieved from https://www.maff.go.jp/j/kanbo/joho/saigai/pdf/youin_daizu_3.pdf (Accessed 25 September

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2020)
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outline.pdf (Accessed 30 September 2020)
Ministry of the Environment (2012) Interim storage facility.
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Ministry of the Environment (2013) Environmental remediation.
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Ministry of the Environment (2016a) Transportation to ISF from
Iitate village, interim storage facility. Retrieved from http://
josen.env.go.jp/chukanchozou/situation/status_by_municipality/
iitate.html (Accessed 25 September 2020)
Ministry of the Environment (2016b) Basic principle in safety useof recycled materials obtained from removed soil. Retrieved fromhttp://josen.env.go.jp/chukanchozou/facility/effort/investigative_
commission/pdf/investigative_commission_160630.pdf (Accessed
25 September 2020)
Ministry of the Environment (2016c) Concepts on safe use of thesoil from off-site decontamination work after recycling.
Retrieved from http://josen.env.go.jp/en/storage/ (Accessed 25
September 2020)
Ministry of the Environment (2017) Demonstration project forrecycling in Iitate village 2017. Retrieved from http://josen.env.
go.jp/chukanchozou/facility/recycling/project_iitate/ (Accessed
25 September 2020)
Ministry of the Environment (2018a) Verification program of therecycling use of removed soil in Iitate village, Ministry of theEnvironment, presentation material of the Iitate village Nagadoro
district environmental restoration project organizing committee
meeting held on August 27 2018. Retrieved from http://josen.
env.go.jp/chukanchozou/facility/effort/recycling/pdf/recycling_iitate_1808.pdf (Accessed 30 September 2020)
Ministry of the Environment (2018b) Image of the demonstration
project. Retrieved from http://josen.env.go.jp/en/storage/(Accessed 25 September 2020)
Ministry of Health, Labour and Welfare (2011) Information
associated with the Great East Japan Earthquake. Retrieved fromhttps://www.mhlw.go.jp/english/topics/2011eq/index_food.html(Accessed 30 September 2020)
National Agriculture and Food Research Organization (2011) Topsoil scraping technique using agricultural machinery in removing
soil contaminated with radioactive materials. Retrieved fromhttp://www.naro.affrc.go.jp/project/results/laboratory/narc/2011/a00a0_01_68.html (Accessed 25 September 2020)
National Agriculture and Food Research Organization (2017a)
Radioactive cesium in food. Retrieved from http://www.naro.
affrc.go.jp/laboratory/nfri/contens/riwg_cecium_en.pdf(Accessed 25 September 2020)
National Agriculture and Food Research Organization (2017b)
Percentage of radioactive cesium removed during processing
from brown rice to cooked rice (%). Retrieved from http://www.
naro.affrc.go.jp/laboratory/nfri/contens/riwg_cecium_en.pdf(Accessed 25 September 2020)
Nuclear Regulation Authority (2013) Results of the airborne
monitoring in the evacuation-directed zones. Retrieved fromhttps://radioactivity.nsr.go.jp/en/contents/7000/6936/24/270_0513.
pdf (Accessed 25 September 2020)
Reconstruction Agency (2017) Specified reconstruction andregeneration base area reconstruction and regeneration plan.

Retrieved from https://www.reconstruction.go.jp/topics/maincat1/sub-cat1-4/saiseikyoten/20170913162153.html (Accessed
30 September 2020)
Sugiura, N. (2011) Environmental impact after the Chernobyl
accident. Atomic Energy Society of Japan, 53(6), 419–425.
Yamaguchi, N., Takada, Y., Hayashi, K., Ishikawa, S., Kuramata,M., Eguchi, S., Yoshikawa, S., Sakaguchi, A., Asada, K., Wagai,R., Makino, T., Akahane, I. and Hiradate, S. (2012) Behavior ofradiocesium in soil-plant systems and its controlling factor,
NIAES Bulletin, (31), 75–129.

Yuuzou MAMPUKU
Yuuzou Mampuku is a researcher at the Institutefor Agro-Environmental Sciences, National
Agriculture and Food Research Organization.
His research interests and specialties areenvironmental circulation system engineering andagricultural civil engineering. He has been
making efforts to restore the environment inFukushima Prefecture after the Great East Japan Earthquake.
(Received 19 October 2020, Accepted 28 December 2020)

159

Experimental Study on the Mechanism of Cs Removal fromContaminated Soil and Incineration Ash by Pyroprocessing
Kazuo YAMADA1*, Kazuhiko TOKOYODA1, 2and Masahiro OSAKO3
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Taiheiyo Cement Corporation
1-1-1 Koishikawa, Bunkyo-ku, Tokyo, 112-8503, Japan
3
Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-city, Ibaraki, 305-8506, Japan*E-mail: yamada.kazuo@nies.go.jp
1

Abstract
After the Fukushima Daiichi nuclear power plant accident, a large region of northeastern Japan was
contaminated by radio-Cs (r-Cs). Contaminated soil and incineration ashes are generated throughdecontamination processes and daily human activities, respectively. To reduce the volume of such substances,
several kinds of pyroprocessing techniques have been developed. R-Cs is thought to be trapped within
aluminosilicates. With the addition of Ca to these compounds, alkali metals may be readily removed. Next, Cl
is added and the alkali metals are volatilized in the order of Cs > K > Na. On the basis of this estimation, thehighest Ca content is expected to produce the best conditions for the removal of Cs. Calcium silicate andaluminate with the highest Ca concentration are found in Portland cement. To understand the mechanism of
Cs volatilization, the effect of the Ca/(Si+Al) ratio on the ratio of Cs remaining is introduced on the basis ofdata from the literature. A high-efficiency Cs removal process in cement is also investigated using a small
scale rotary furnace for real contaminated soil and ashes, and by pilot-scale experiments with model soil.
Additionally, through detailed experiments using pollucite — a cesium aluminosilicate — Cs removal behaviors
were found to correspond to phase change, depending on the Ca/Si and Cl/Cs ratios. At high Ca/Si ratios,even without adding Cl, a significant amount of Cs could be removed. Potassium existing in or added to theinitially contaminated samples facilitated Cs removal such that Cs was reduced to an undetectable level even
without the addition of Cl.
Key words :	aluminosilicate, cesium removal, chloride volatilization, incineration ash, pollucite, Portland
cement, pyroprocessing, radio-cesium

1. Introduction
After the Fukushima Daiichi nuclear power plant(FDNPP) accident, a wide region of northeastern Japanwas contaminated with radio-Cs (r-Cs) (IAEA, 2015) .
Because of the nature of this accident, the majorcontaminant was limited to volatile r-Cs.
To reduce the additional radiation dose to 1 mSv/y,the target level determined by the Japanese government,
the surface soils in many regions surrounding the FDNPP
have been removed and are currently being transported to
an interim storage facility (ISF) (MOE, 2018a). From thissoil, combustibles are removed and sent to temporal
incinerators to reduce their volume; here, contaminatedincineration ash (IA) is generated. In addition, daily
human activities generate various kinds of wastes, suchas municipal solid waste (MSW) and sewage sludge,
Global Environmental Research
24/2020: 159-172
printed in Japan

which are then contaminated by r-Cs. In Japan, themajority of these wastes are sent to incinerators forvolume reduction; here, contaminated IA is also generated
in concentrated form. Because of the limited space in
ISFs, the volumes of this IA and relatively highly
contaminated soils must be reduced. For this purpose,
various technologies have been proposed in Japan for theremoval of Cs from these contaminated substances(JESCO, 2016 –2020). One of the most efficient methods
is based on chloride volatilization (Spalding, 1994).
Two major pyroprocessing systems using chloride
volatilization have been proposed; one involves the useof a melting furnace to reduce the volume of MSW-IA(Kamata et al., 2015), and the other involves a rotary kilnthat is used for Portland cement production (Tokoyoda
et al., 2018a). In both systems, a high temperature,
approximately 1,300ºC to 1,500ºC, is required. From both©2020 AIRES

160

K. YAMADA et al.

pyroprocessing systems, concentrated Cs is obtained as
CsCl salt. The decontaminated product obtained by themelting system is a slag, while that from the rotary kiln
system is a hydration-inactive sintered mineral
agglomerate or cement clinker (which is the raw material
used for Portland cement). These systems require quite
high temperatures, but the decontaminated products may
be used as commercial materials such as slag, sinteredagglomerates that may be used as aggregates, or Portland
cement. The management of decontaminated wastes is ofgreat importance. If it is difficult to find a use fordecontaminated materials, then a landfill site must be
used. In 2018, the Japanese Ministry of the Environment
ordered the construction of two kinds of pyroprocessing
systems, and in March 2020, the systems began operation(Yamada et al., 2020) although the rotary kiln system was
not adopted.
Considering the mechanism of Cs removal using
these pyroprocessing techniques, we note an interesting
report. After the FDNPP accident, intensive surveys ofvarious incinerators were conducted, and it was foundthat r-Cs tended to concentrate in fly ash rather than inbottom ash. The ratio of these concentrations depended
on the nature of the original combustible wastes (Yui etal., 2018; Fujiwara et al., 2017). When a significant
amount of Cl was included in the combustible wastes, theCs tended to become fly ash in a water-soluble form, suchas CsCl. Without Cl, Cs remained in aluminosilicate
form. This suggests that even at relatively low
temperatures such as 800ºC to 900ºC within incinerator
furnaces, chloride volatilization of Cs may occur. The
melting and boiling temperatures of CsCl are 645ºC and1,295 ºC, respectively. Exceeding the boiling temperatureof CsCl is not needed to achieve volatilization, and some
vapor pressure of CsCl may be estimated enough at such
low incineration temperatures.
According to previous reports on pyroprocessing
systems for volume reduction of IA and contaminatedsoils (Kamata et al., 2015; Tokoyoda et al., 2018a;
Honma et al., 2014; Manpuku et al., 2017), r-Cs is
assumed to exist within clay, pollucite and glass minerals,
and others. The phases containing Cs are assumed to bealuminosilicates. As was determined experimentally(Kamata et al., 2015; Tokoyoda et al., 2018b; Honma etal., 2014; JAEA, 2011; MOE, 2018b) by adding CaO and
CaCl2, the majority of Cs in an aluminosilicate may bevolatilized at an appropriately high temperature. The
mechanism of Cs volatilization can be assumed asfollows:- In an aluminosilicate, cations exist within thismaterial depending on its mineralogical structure,and its cation content varies significantly.
- By adding a large amount of CaO to such analuminosilicate, alkali metal oxides including Cs2O
may be easily released from the aluminosilicate
structure by replacement of Cs with Ca.

- Upon addition of Cl, excess alkali metals oxides
form alkali chlorides and these phases exhibit
significant vapor pressures at high temperatures that
may be lower than the boiling temperature of Cs2O.
- Alkali metals transition from solid to vapor phases atthese temperatures. The tendency of volatilization ofalkali metals follows the order of Cs > K > Na; Cs,
including r-Cs, is therefore preferentially volatilized.
- The vapor may then be cooled in a cooling system
and recrystallized as solid alkali chlorides, which arecollected in a bag filter system. From the flue gas
following this bag filtration, the r-Cs content in theflue gas is reduced to undetectable levels even whenusing a high-volume sampler.
Considering the above-mentioned concepts, higher
ratios of Ca/(Al+Si) and Cl/Cs should be suitable forpromoting the removal of r-Cs from IA and soil. From theviewpoint of a high Ca/(Al+Si) ratio, the use of Portland
cement provides the most favorable system. In this study,a series of experimental investigations on the effects of
the Ca/(Al+Si) and Cl/Cs ratios for Cs removal from
pollucite (CsAlSi2O6) were conducted to elucidate theremoval mechanism of Cs via pyroprocessing treatments.
These were done after reviewing the characteristic
mineral combination of Portland cement.

2. Chemical Reactions in Portland Cement
Production
To understand the mechanisms underlying theformation of the minerals considered in this paper, a basic
understanding of Portland cement must be introduced.
Portland cement is one of the largest industrially
produced materials. It is a mixture of burned minerals,
known as cement clinker, and calcium sulfate. The basic
components of cement clinker are 3CaO∙SiO2 (known asalite), 2CaO∙SiO2 (known as belite), 3CaO∙Al2O3, and
4CaO∙Al2O3∙Fe2O3, which have mass fractions of roughly65, 20, 7.5, and 7.5 w/w% (mass percent), respectively.
These mass fractions are determined on the basis of thetotal balance of performance of the Portland cement usedin concrete.
3CaO∙SiO2 and 3CaO∙Al2O3 are the most Ca-richsilicate and aluminate minerals in the CaO–SiO2–Al2O3
ternary system. Upon burning of the raw powders ofthese materials and after the decarbonation of CaCO3 toform free lime, 2CaO∙SiO2 crystals and the Ca–Al–Fe–O
liquid phases are generated within the temperature rangeof 900ºC to 1,300ºC. At temperatures of 1,300ºC to
1,450ºC, 2CaO∙SiO2 reacts with free lime to form
3CaO∙SiO2. The amounts of the Ca–Al–Fe–O liquid
phases affect the formation speed of 3CaO∙SiO2, whichmust be controlled within an appropriate range. This
reaction does not proceed well when these quantities are
too small. When these quantities are too large, the burnedmaterial adheres to the inner surface of the kiln, and theExperimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 161
products are not discharged from the kiln. After burning,
the burned materials, known as clinker, which arecomposed of particles a few centimeters in diameter, aresent to a cooler. Rapid cooling is important for thestabilization of the high-temperature phases of 3CaO∙SiO2
and 2CaO∙SiO2. 2CaO∙SiO2 may be stabilized as
β-2CaO∙SiO 2 via rapid cooling, but thethermodynamically stable phase is γ-2CaO∙SiO2, which
does not express hydration reactivity. The Ca–Al–Fe–O
liquid phase constitutes a matrix (known as an interstitial
phase) of these calcium silicates, and with a decrease intemperature, this liquid phase crystallizes into two
different phases, 3CaO∙Al2O3 and 4CaO∙Al2O3∙Fe2O3.
The chemical compositions are shown in the CaO–
SiO2–Al2O3 ternary phase diagram with the chemicalcomposition of ordinary Portland cement (Fig. 1). In
actual cement, alkali metals and sulfur at quantities on theorder of 0.1 w/w% exist as contaminants that derive fromthe raw materials. Na exists mainly in 2CaO∙SiO2 andorthorhombic 3CaO∙Al2O3, while K exists mainly in alkali
sulfate. In 2CaO∙SiO2, more cations may be contained ascompared with 3CaO∙SiO2. 3CaO∙Al2O3 is known to haveboth orthorhombic and cubic crystalline structures. Whenthe alkali/sulfur molar ratio exceeds 1.0, the excess
amount of alkali materials is included in orthorhombic
3CaO∙Al2O3.
In modern production processes for cement, with the
exception of typical raw materials including limestone,
silica sand, clays and the iron and heat sources provided
by coal, a large variety of wastes are used as raw
materials and alternative fuels. Only the chemicalcompositions of the raw materials for the production ofPortland cement must be controlled. There is no need tocontrol either the mineral or chemical forms of thesematerials. During thermal processing at approximately
1,450ºC, all components are decomposed to form clinker

Mole fraction SiO2

CaO‒Al2O3 ‒SiO2 T=1400℃, P=1.01325bar

Mole fraction Al2O3

Fig. 1 CaO–SiO2 –Al2O3 ternary phase diagram at 1,400ºC withclinker mineral compositions (modified according to aprevious study from Research Institute of Computational
Thermodynamics Inc.).

minerals. A typical alternative heat source is processed
MSW, in which vinyl chlorides are included. When Cl isincluded in a raw material, potassium is preferentiallyvolatilized as KCl in rotary kilns. In general, thevolatilizing tendencies of alkali chlorides follow the orderof Cs > K > Na, and the boiling temperatures of thesematerials follow the order of 1,295 < 1,420 < 1,465ºC.
However, the Cs content of cement is assumed to be 1 to
10 ppm, which is much less than that of K, which is on
the order of 0.1 w/w%. Because of the volatilization
tendencies and the molar ratios of the existing elements,
the ratio of Cs remaining in Portland cement is not easily
estimated and should be examined in real systems.
The behaviors of alkali elements and Cl in Portland
cement production are similar to those in the incinerators
for MSW, which both involve chloride volatilization fromalkali materials. However, differences exist in theprocessing temperatures and Ca content.
In Japan, a unique type of Portland cement plant has
been introduced, known as “eco-cement,” because morethan half of the raw materials that are used are wastes
such as IA rich in Cl. The Cl content of cement must be
controlled because Cl may cause steel corrosion when
Portland cement is used in reinforced concrete. In an ecocement system, Cl is removed via the volatilization ofalkali chlorides by adding alkali carbonates. Without theaddition of alkali elements, Cl forms a calcium
chloroaluminate liquid phase at burning temperatures ofover 1,350ºC, and in this phase, alkali metals may
dissolve. Therefore, the volatilization behaviors of alkali
chlorides have been of great interest in the cement
industry.

3. Cs Removal in Pyroprocessing
3.1 
Literature Review of Several Systems for the
Removal of Cs
In nature, r-Cs is thought to be fixed within clay
minerals (Manpuku et al, 2017) and is difficult to remove
via simple heating processes (Honma et al., 2019). As
explained in Chapter 1, the addition of a sufficientamount of Ca to aluminosilicate may aid this removal
process. On the basis of three previous studies (Kamata etal., 2015; Tokoyoda et al., 2018a; Honma et al, 2014)
discussing the effects of adding CaO and CaCl2 at varying
Ca/(Si+Al) ratios and temperatures, the removal of Cs
through various pyroprocessing techniques was therefore
studied.
Honma et al. (2014) investigated several types ofcontaminated soil with a maximum r-Cs concentration of
25 kBq/kg. By adding CaO and CaCl2 and heating the
mixture to 1,350ºC, they were able to reduce the r-Cs
content of the pyroprocessed materials to 50 Bq/kg. The
performance of this system was also demonstrated usinga large-scale rotary kiln with a 10 t/day capacity (Honma
et al., 2019; Tokoyoda et al, 2018b). By adjusting theK. YAMADA et al.

Ca/Si and Cl/K ratios and temperature, the r-Cs
concentrations in soils contaminated with 21 kBq/kg of
r-Cs and incineration ashes with contamination levels of
1 to 111 kBq/kg were successfully reduced to less than
100 Bq/kg (the clearance level) in the majority of thetested batches. These operations were carried out in 26
runs from May 2018 to January 2019, for 470 t ofcontaminated soil and ashes. The amounts ofcontaminated wastes were reduced by approximately one
tenth. In this system, the Cl content was controlled interms of the K concentration ratio of the contaminatedsamples because Cs is considered to be more easily
volatilized than K. If the Cl content is sufficient tovolatilize K, then all of the Cs may volatilize. Moreover,
the applicability of the decontaminated samples as
aggregates for civil engineering works or concrete was
examined in their study.
Kamata et al., 2015 demonstrated the highperformance of a different system involving a surface
melting furnace. The optimized parameters of that weresimilar to those of the rotary kiln system described above.
The differences between the two systems pertain to thematerials obtained after decontamination. The former
process mainly results in 2CaO∙SiO2 and gehlenite, while
the latter produces slag. By adjusting the processparameters and by considering model soil and ashes
containing 0.2 w/w% of stable Cs, a 99.9% removal of Cs
was achieved. In this system, the chemical compositions
were adjusted to result in a sufficient amount of alkali
elements with Cl/K molar ratios ranging from 4.6 to 22 inorder to obtain a molten phase at 1,400ºC.
Tokoyoda et al. (2018b) examined the performanceof a Portland cement system at laboratory scale using realcontaminated materials. They used a larger rotary kiln
with an inner diameter of 450 mm, length of 8,340 mm,
and capacity of 30 kg/h using a model soil containing
0.1 w/w% of stable Cs. To obtain the cement clinker,
the Ca/Si molar ratio was controlled to around 3.0. The
Cl/K molar ratio was controlled at 1.0, as performed by
Honma et al., 2014.
The chemical compositions of the materials
examined by the three studies are shown in Fig. 2 for the
CaO–SiO2–Al2O3 ternary system at 1,400ºC. As shown, awide range of chemical compositions were examinedwhile considering the melting system. In the rotary kiln
system, two chemical compositions were examined. One
was a typical hydration reactive Portland cement, while
the other involved non- or less-hydration reactive
minerals.
In Fig. 3, the ratios of Cs remaining to the respective
original concentrations of the treated materials are plottedagainst the Ca/(Si+Al) molar ratio. Kamata et al. (2015)
proposed an optical basicity considering various elements
as an additional index because other minor elements may
behave as cations or anions. For example, under oxidizing
conditions, Fe may behave similarly to Al. P2O5 can

CaO‒Al2O3 ‒SiO2 T=1400℃, P=1.01325bar

Mole fraction SiO2

162

Mole fraction Al2O3

Fig. 2 Chemical compositions examined in previous studies(data points are plotted on the CaO–SiO2 –Al2O3 diagramat 1,400 ºC). Blue: Kamata et al., 2015, Red: Honma
et al., 2014), Green: Tokoyoda et al., 2018a.

Fig. 3 Relationship of the ratio of Cs remaining from contaminatedsources to the Ca/(Si+Al) molar ratio. The legend refers toreference sources and pyroprocessing temperatures from
Kamata et al. (2015), Honma et al. (2014) and Tokoyoda etal. (2018a).

participate in calcium silicates as part of the silicate. As
shown in the above figure, a higher Ca/(Si+Al) ratio
results in a lower ratio of Cs remaining. For the Portland
cement composition utilized by Tokoyoda et al. (2018a),
Cs was reduced to an undetectable level. However, as thedetection limit was 0.01%, the actual efficiency may behigher than was indicated in this study. As indicatedabove, the Ca ratio in terms of cation capacity inaluminosilicates appears to be a key factor that is
independent of the pyroprocessing system. Judging fromthe aforementioned results, we expect Portland cement toprovide the best chemical composition for removal of Csfrom various sources.
As a decontamination material, cement composed of

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 163
model soil at 1,450ºC demonstrated normal performanceas Portland cement, satisfying Japanese Industrial
Standard JIS R 5210: 2019 (Tokoyoda et al., 2018a).
3.2 Detailed Effects of Temperature and Cl/K Ratios
in a Portland Cement System
3.2.1 Experiments
From the discussion in the former chapter
considering the system with the highest Ca concentration,
Portland cement is expected to provide a highly efficientsystem for removing Cs. The effects of temperature and
Cl/K ratio from the viewpoint of the ratio of Cs remaining
may next be examined on the basis of data provided by
Tokoyoda et al. (2018b) with additional IA data.
The samples used in this study were obtained fromresidential land soils, pond deposits and incineration fly
and bottom ashes generated in Fukushima Prefecture. The
chemical compositions and radiation concentrations of
r-Cs in the examined samples are shown in Table 1. The
examined samples are examples of real contaminatedmaterials that require treatment, but because of limited
capacity to treat radioactive materials in our laboratory,
only samples with relatively low contamination levels
were used. Therefore, the detection ability for
determining the removal efficiency of the overall system
was also limited. The chemical compositions for theexperiments were adjusted to those of Portland cement byusing reagent-grade free lime (CaO) and CaCl2, as well as
commercial silica sand. The target mineral compositions
were 60, 20, and 20 w/w% for 3CaO∙SiO2, 2CaO∙SiO2,
and 3CaO∙Al2O3-4CaO∙Al2O3∙Fe2O3, respectively.
The major factors examined were the types ofsamples, heating temperature and Ca/Si and Cl/K ratios.
The pyroprocessing conditions are shown in Table 2. The

samples were ground, mixed and then heated in a rotary
furnace. The homogeneous heating zone was φ = 50 ×
120 mm. The samples were heated at a rate of 5ºC/min
and maintained at their respective target temperatures for
60 min.
Radioactivity was measured by using a Ge detector,
and other major elements were measured by X-ray
fluorescence (XRF) analysis. The detection limit ofradioactivity depends on measurement time; hence, thedetection limits in this study varied from 3 to 15 Bq/kg
depending on the available machine time.
From X-ray diffraction/Rietveld analysis, the mineralcompositions determined for the samples 3CaO∙SiO2,
2CaO∙SiO2, 3CaO∙Al2O3, and 4CaO∙Al2O3∙Fe2O3 treated at
1450ºC were 62, 21, 6, and 10 w/w%, respectively. At
this temperature, we confirmed that the target clinker
minerals formed.
3.2.2 Results
1) Effects of temperature
Figure 4 shows the effects of the pyroprocessing
temperature on the ratio of Cs remaining. In this series,
the Cl/K molar ratio was controlled at 1.0, and theamount of Cl was controlled at an excess in terms of theCs content. The ratio of Cs remaining was calculated
from the original irradiation concentration and thatexisting after pyroprocessing. The detectable ratio of Cs
remaining depended on the original value and detection
limit. This is the reason for the wide variation in thedetection limits shown in Fig. 4.
Under these conditions, the amounts of all alkali
metals were also reduced at higher temperatures. The
order of the ease of removal was Cs > K > Na, as
expected even under conditions of their significantly
different concentrations. Cs was reduced to undetectable

Table 1 Chemical compositions of the examined materials.
Chemical composition (w/w%)

Bq/kg

Sample

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

P2O5

Cl

Ig.Loss

Total

r-Cs

Residential land soil

21.26

5.83

2.03

64.20

0.92

0.07

0.82

0.78

0.10

0.59

7.43

104.02

793

Pond deposits

18.29

3.56

2.31

53.08

0.34

0.00

0.21

0.34

0.10

0.55

35.94

114.692250

Incineration fly ash

20.37

3.36

4.47

58.54

0.62

1.59

0.30

1.19

0.15

0.89

9.12

100.606819

Incineration bottom ash

21.83

4.93

2.00

63.93

0.90

0.12

0.72

1.14

0.23

0.86

2.72

99.38

8198

Table 2 Experimental conditions.
FactorSample type andtemperature

Ca/Si, Cl/K, andtemperature

Sample

Ca/Si

Cl/K

Temp. (ºC)

Residential land soil

3.0

1.0

1200, 1250, 1300,
1350, 1400, 1450

Pond deposits

3.0

1.0

1200, 1250, 1300,
1350, 1400, 1450

Incineration fly ash

3.0

1.0

1400

Incineration bottom ash

3.0

1.0

1400

Residential land soil

3.0

0.0, 0.2, 0.5, 1.0

1400

Residential land soil

2.20.0, 1.1

1400

Pond deposits

3.0

0.0, 1.0

1450

164

K. YAMADA et al.

levels at temperatures higher than 1,300ºC. The
volatilizations of the alkali metals did not occur in theorder of Cs > K > Na, but rather simultaneously. Only theratios of each element differed. Although the ratios of K
and Na remaining depended on the sample type, those of
r-Cs were similar for all subjects. Simply all data were
below the detection limit and the differences were
thought to be unobservable. Residential land soil andbottom ash samples demonstrated similar behaviors. The
pond deposits showed much lower ratios of Na and K
remaining, and the fly ash exhibited the smallest values.
The mechanisms underlying these removal processes areunclear.
2) Effects of the Cl/K ratio
Figure 5 shows the effects of the Cl/K molar ratio on
the ratio of Cs remaining. In this series, the temperature
was modified to 1,400ºC or 1,450ºC, and the Ca/Si molar
ratio was modified to 3.0 or 2.2. A ratio of 3.0 is requiredfor Portland cement, while 2.2 is required for an
aggregate. The order of ease of alkali metal volatilizationis the same as that shown in Fig. 4. Cs is the most easily
volatilized, followed by K and Na, which are much lesseasily volatilized. All alkali metal concentrations werereduced by increasing the Cl/K ratio.
At 1,450ºC, without the addition of Cl, the ratio of
Cs remaining decreased to the detection limit. The
mechanism of volatilization is unclear, but Cs may bevolatilized as Cs2O. At 1,400ºC without Cl, 2.8% and5.6% of Cs remained at Ca/Si ratios of 3.0 and 2.2,
respectively. In both cases, Cs was reduced to thedetection limit by increasing the Cl/K ratio.

4. E
 ffects of Ca/Si and Cl/Cs Ratios on Behaviorof Cs from Pollucite at High Temperatures
4.1 Use of Pollucite
As seen in the discussion above, the optimal
conditions for the removal of Cs from various sourceswere determined. The Cs content was very limited and it
was difficult to clarify the behavior of Cs in the solidphase materials. Therefore, pollucite, which is a Cs
aluminosilicate (CsAlSi2O6), was used in this study to
examine the detailed behaviors of Cs during
pyroprocessing.

Fig. 4 The effects of temperature on the ratios of remaining alkali
metals. (Circles indicate residential land soil and triangles indicate
pond deposits.)

4.2 Experiments
4.2.1 Materials
Pollucite was synthesized according to processdescribed in a previous study (Kobayashi et al., 1991).
The chemical composition of the synthesized pollucite
analyzed by XRF analysis is shown in Table 3. The X-ray
diffraction (XRD) pattern of the obtained pollucite isshown in Fig. 6. All peaks of the obtained material
matched the standard data for cubic pollucite well.
4.2.2 Experimental conditions
As explained in the previous chapters, the additionof CaCl2 and CaO is important for removing Cs. The
combined effects of these additions at a temperature
range of 900ºC to 1,100ºC were reported by Jiao et al.

Fig. 5 The effects of the Cl/K ratio on the ratios of alkali metals
remaining. (Circles indicate residential land soil and triangles
indicate pond deposits.)

Table 3 Chemical composition of the synthesized pollucite (w/w%).
Ig. loss

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

Cs2O

P2O5

Cl

Total

0.29

37.9

16.3

0.02

<0.01

0.0

<0.01

0.12

0.04

39.7

0.00

0.00

99.81

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 165(2018). In this series of experiments, the generation ofcommercially valuable slag, aggregate, or Portland
cement as decontaminated products was examined using
an applied temperature reaching 1,450ºC.
The chemical composition parameters examined
were the Ca/Si and Cl/Cs ratios. The Ca/Si molar ratios
were set at 3.3, 2.2 and 1.0, and the Ca/(Si+Al) molar
ratios were set at 2.4, 1.6 and 0.72, respectively, with theassumption of the formation of a cement clinker, nonhydration reactive aggregate and slag, respectively. To
retain the appropriate amount of liquid phase at theburning temperatures, the Si/(Al+Fe) ratio was also
controlled at 2.2, 2.1 and 2.0, respectively, for each of theaforementioned products.
To adjust the chemical compositions for eachpurpose, reagent-grade CaO and CaCl2, as well as silica
sand, were added to the synthesized pollucite. Minor
elements such as Fe, Na and K were brought from thesilica sand. Under each condition, the Cl/Cs molar ratio
was modified to range from 0.0 to 5.0.
Pyroprocessing was carried out using the same rotary
furnace described in Sub-section 3.2.1. The heating
temperature was 1,450ºC, which was maintained for
60 min. The temperature was increased at a rate of
5ºC/min. The volatilized materials were recollected ina HEPA filter from the exhaust gas after cooling.
Sampling from the HEPA filter was carried out following
all experiments, but was not performed for each batch.
4.2.3 Measurements
The chemical compositions of the pyroprocessedmaterials were measured by XRF. The mineral phasecompositions of these materials and the phase changes
that occurred during heating were evaluated qualitatively
by XRD. To conduct the high-temperature XRD analysis,
the temperature was increased at a rate of 10ºC/min from
25ºC (room temperature) to 1,400ºC, and measurements
were performed at every 100ºC increment. The scanning
range of 2θ was from 5º to 65º, and the scanning speed
was 50º/min. For observing the formed textures of thepyroprocessed materials, back-scattered electron imaging

Fig. 6 X-ray diffraction (XRD) pattern of the synthesized cubic pollucite.

(BEI) was used. The chemical composition of each phaseincluding element distributions was analyzed by electronprobe micro analyzer (EPMA).
4.3 Results
4.3.1 Cs Volatilization Behaviors
The effects of the Cl/Cs ratio on the ratio of Cs
remaining at different Ca/Si ratios after pyroprocessing at
1,450ºC are shown in Fig. 7. The Cl/Cs ratio affects theratio of Cs remaining differently at different Ca/Si ratios.
Without the addition of Cl (i.e., at a 0.0 Cl/Cs molar
ratio), a higher Ca/Si ratio results in a lower ratio of Cs
remaining.
At a Ca/Si ratio of 1.0, without added Cl, almost of
all the Cs remained in the solid phase. By increasing the
Cl/Cs ratio from 0 to 1.0, the ratio of Cs remaining was
decreased to 3%.
At a Ca/Si ratio of 2.2, the effects of Cl/Cs werelimited to the range of less than 0.4. With an increase in
the Cl/Cs ratio to 0.6, the ratio of Cs remaining decreased
from 16 to 8%. When the Cl/Cs ratio was increased to
1.1, the ratio of Cs remaining became less than 0.06%.
When the Ca/Si ratio was 3.4, even without theaddition of Cl, the ratio of Cs remaining was 4.8%, and it
decreased to less than 0.06% at a Cl/Cs ratio of 1.0.
Therefore, a higher Ca/Si ratio resulted in a lower
ratio of Cs remaining, as was expected.
4.3.2 Phases Generated after Pyroprocessing
To investigate the reactions occurring during
pyroprocessing, the phase composition was evaluated via
XRD. The material obtained in the filter system of theexhaust gas after all experiments was pure CsCl, as
shown in Fig. 8. This finding, however, does not deny thepossibility of Cs2O formation because Cs2O reacts
strongly with water to form CsOH. Because CsOH ishighly deliquescent, it is difficult to detect via XRD.

Fig. 7 Cs volatilization in terms of the Cl/Cs ratio at different
Ca/Si ratios (1,450 ºC).

166

K. YAMADA et al.
○：Ca3SiO5 (Alite, 00-055-0739)
×：β-Ca2SiO4 (Carnite, 01-076-3608)△：Ca3Al2O6 (00-038-1429)
×◇：CaO (Lime, 01-077-9574)
××□：Ca12Al14O32Cl2 (00-029-0407)

(a)

×

×

Intensity[a.u.]

×

×
××
×

× ×

×

×

Cl/Cs=1

×Fig. 8 XRD pattern of material collected from the exhaustgas filter.

Cl/Cs=5

×

10

20

30

40

50

60

2θ[°](CuKα)(b)

×：β-Ca2SiO4 (01-076-3608)＋：γ-Ca2SiO4 (01-070-2450)★：Cs2Ca2Al8O15 (00-041-0536)▲：Ca12Al14O32Cl2 (00-029-0407)

××

Intensity[a.u.]

★

×

×

×

★

★ ★★× ×× ×★
×★ × ＋ × ×★ ×
★ × ×
★ ××★ ★★
★
★
★ ×
★
×★
＋

▲

＋

＋
＋

×

×

▲

＋×

＋ ▲

×

×＋＋
×

＋

×

10

×

×

▲

20

×

＋× ＋▲
＋

＋

＋
＋ ＋

▲

＋
＋×

▲

▲
▲

▲

＋

×

×

＋

×
＋
＋
＋
＋×＋ ▲ ＋
×
×

×
×

▲

×★
××
★
××

Cl/Cs=1

▲

×

＋

▲

＋

▲

＋

＋
＋ ＋

Cl/Cs=0

× ×
×
×
× ×
× ×
×× ★ ★× ★× ××

＋

×

▲

＋

▲×

× ×

30

Cl/Cs=5

×

×

×
▲
▲
××××××▲＋× ××＋××
× ×× × ×

40

50

60

2θ[°](CuKα)

(c)
◎
◎

×：Ca2SiO4 (Calcio-olivine, 01-087-1257)◎：CsAlSiO4 (Orthorhomic, 00-031-0346)◎

Intensity[a.u.]

Figure 9 shows the XRD patterns of thepyroprocessed materials at 1,450ºC. At a Ca/Si ratio of
3.4 (Fig. 9(a)), the original pollucite content was reduced
to zero for all Cl/Cs ratios, and typical clinker mineralssuch as Ca3SiO5 and β-Ca2SiO4 were identified. Hereafter,
chemical compositions are described in total, such as
Ca3SiO5, and not as separate components such as
3CaO∙SiO2. The phase composition of the interstitial
phase, however, varied with the Cl/Cs ratio. At Cl/Cs
ratios of 0 and 1, Ca3Al2O6 was identified, while at a ratio
of 5, Ca12Al14O32Cl2 was identified.
Figure 9(b) shows the XRD patterns for a Ca/Si ratioof 2.2. At all Cl/Cs ratio values, the original pollucitecontent disappeared while the identified mineralcompositions differed depending on the Cl/Cs ratio.
Without the addition of Cl, the major phases identified
were β-Ca2SiO4 and Cs2Ca2Al8O15. As the Cl/Cs ratio
increased to 1.0, the crystalline form of Ca2SiO4 changed
from β to γ. This is suitable for use as a pyroprocessed
product such as a non-hydration-reactive aggregate.
Moreover, the phase containing Cs disappeared as expectedfrom Fig. 7 and Ca12Al14O32Cl2 was detectable. At a higher
Cl/S ratio (5.0), the crystalline form of Ca2SiO4 changed
from γ to β again, but the amount of this form decreased
compared to Fig 9(a). The interstitial phase, Ca12Al14O32Cl2,
was identified as possessing an amorphous phase, which
was suggested by a hollow region at 2θ ≈ 32º.
Figure 9(c) shows the XRD patterns at a Ca/Si ratioof 1.0. Without the addition of Cl, a limited amountof Ca2SiO4 (in different crystalline forms from Figs. 9(a)and 9(b)) formed, while the majority of the material
was unreacted pollucite as expected from Fig. 7. The
crystalline form of pollucite changed from a cubic stablestate at room temperature to an orthorhombic stable state
at higher temperatures. With the addition of increasing
amounts of Cl, only the amorphous phase without any
crystalline phases was detected.

Cl/Cs=0

×
× ×
×
× ××
×
× ××

×

◎

◎

×
×

◎

×××
×

×

◎
◎ ◎

×
◎

×

×
×
×
×
×

◎

◎
× ◎
◎ ◎◎
◎

× ×
×

◎

Cl/Cs=0

◎×

◎

◎◎
◎

Cl/Cs=1
Cl/Cs=5
10

20

30

40

50

60

2θ[°](CuKα)Fig. 9X
 RD patterns of the pyroprocessed material at 1,450ºC.
PDF-2 numbers are shown in parentheses.
		(a) Ca/Si ratio = 3.4,
		(b) Ca/Si ratio = 2.2,
		(c) Ca/Si ratio = 1.0.

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 167
Decomposition of Pollucite with Increasing
4.3.3 Temperature
The decomposition of pollucite and phase changes
were dependent on both the Ca/Si and Cl/Cs ratios. To
understand the decomposition behaviors of pollucite,high-temperature XRD analysis was utilized for several
combinations of Ca/Si and Cl/Cs ratios and the obtained
results are shown in Fig. 10, showing only the major peakof pollucite.
At a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 1.0, thepollucite peak disappeared at 1,000ºC with a slight shift
at 900ºC. When the Ca/Si ratio was decreased to 2.2 at asimilar Cl/Cs ratio, the peak remained until 1,100ºC.
Therefore, a greater Ca content facilitates thedecomposition of pollucite at lower temperatures. When
the Cl/Cs ratio was decreased to 0.6, the peak remained
Ca/Si
=3.4
(Cl/Cs
=1.0)

Ca/Si
=2.2
(Cl/Cs=1.1)

until 1,300ºC, even at a Ca/Si ratio of 3.4. In the case of a
Ca/Si ratio of 2.2, we observed a peak shift at 900ºC, but
the peak remained until 1,300ºC. Cl may therefore also
play an important role in the decomposition of pollucite.
 extures of Mineral Phases after Pyroprocessing
4.3.4 T
Considering the observed Cs removal behaviors andphase changes analyzed by XRD, we carried out direct
observations and compositional analysis of the textures ofthe mineral phases formed after pyroprocessing.
Figure 11 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 0. Three major
phases are indicated: many rectangular and small,rounded gray particles; small, round white spots within
the gray particles, and a darker matrix. Figure 12 shows
the EPMA mapping of the same area. As indicated, thewhite spots correspond to high concentrations of Cs.
Ca/Si
=3.4
(Cl/Cs
=0.6)

Ca/Si
=2.2
(Cl/Cs
=0.6)

Fig. 10 Changes in the XRD peaks of pollucite with increased temperature.

Fig. 11 Back-sacttered electron imaging (BEI) of the pyroprocessed material (Ca/Si ratio = 3.4, Cl/Cs ratio = 0).

Fig. 12 Electron probe micro analyzer (EPMA) mapping of elements (same area as Fig. 11; warm colors such as white or
red indicate higher concentrations).

168

K. YAMADA et al.

The chemical compositions of these three phases
analyzed by EPMA are shown in Table 4. From theanalysis data and with utilization of the major elements,
the molar ratios are also indicated. Point A of therectangular phase is considered to be Ca3SiO5, the major
clinker phase. Point B of the matrix is essentiallyconsidered to be Ca3Al2O6, as estimated from the resultsof XRD, but 5 mol % of aluminate is replaced withsilicate. The white spots (C) indicate cesium calcium
aluminosilicate. From the texture of the region
surrounded by Ca3SiOs, the white spots may be remnantsof the original pollucite particles that decomposed during
pyroprocessing. Because of the limited area of thesespots, no clear diffraction pattern could be obtained by
XRD. From Fig. 7, 4.8 w/w% of Cs remained after

pyroprocessing. Judging from the texture shown in
Fig. 11, the reason Cs remained can be surmised as Cs
bearing phases remained in the crystalline 3CaO.SiO2
phases and Cs was prevented from volatilizing but not as
an issue of phase equilibrium. Therefore, if the raw
materials are ground finer, the ratio of Cs remaining may
decrease more.
Figure 13 shows a BEI analysis of the pyroprocessedmaterial at a Ca/Si ratio of 2.2 and a Cl/Cs ratio of 0.
Figure 14 shows an EPMA mapping of the same area.
From these figures, three phases can be distinguished:large gray rounded particles, white rectangular grains at
the grain boundary of the gray particles, and a small
amount of a dark matrix. In Table 5, the chemicalcompositions of these phases are shown. Points A, B and

Table 4 Chemical compositions of the three phases (A, B, and C) shown in Fig.11 (upper: w/w%; lower: mol %).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

25.26

72.12

0.81

0.02

0.34

0.02

0.02

0.00

0.02

0.00

98.61

B

4.61

58.37

29.03

0.43

1.02

0.14

0.03

0.00

0.02

0.01

93.64

C

13.96

44.48

22.19

0.14

0.29

0.06

0.01

18.56

0.00

0.00

99.68

Position

SiO2

CaO

Al2O3

Cs2O

Total

A

24.5

75.0

0.5

0.0

100.0

B

5.5

74.2

20.3

0.0

100.0

C

17.8

60.6

16.6

5.0

100.0

Fig. 13 BEI of the pyroprocessed material (Ca/Si ratio = 2.2, Cl/Cs ratio = 0).

Fig. 14 EPMA mapping of elements (same area as indicated in Fig. 11; warm colors such as white or pink indicate
higher concentrations).

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 169
C, indicating the white grains, have similar chemicalcompositions and are considered to be cesium calcium
aluminate. We identified Cs2Ca2Al8O15 from XRD fitting,while the results obtained by EPMA differed. This phase
may be some solid solution of different Cs/Ca ratios. The
compound cesium calcium aluminate is therefore thought
to have formed from the pollucite, CsAlSi2O6. The Cs
containing phase was transformed from aluminosilicate
to calcium aluminate. There are two types of grayparticles in different crystalline phases indicated from theresults obtained by XRD and represented as the samechemical composition of Ca2SiO4 by points D and E.
Point F in the dark matrix indicates Ca12Al14O33 gehlenite,
but the quantity was limited and undetectable by XRD.
Figure 15 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 5. Figure 16
shows an EPMA mapping of the same area. From thesefigures, three phases can be distinguished: gray

Table 5 Chemical compositions of the six points indicating the two phases (A, B, C, D, E, and F) shown in Fig. 13 (upper:
w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

0.59

18.53

38.82

0.20

0.08

0.15

0.12

26.45

0.03

0.01

84.97

B

1.59

17.88

39.37

0.18

0.00

0.25

0.08

26.13

0.00

0.00

85.48

C

0.83

17.83

39.82

0.19

0.09

0.22

0.14

26.98

0.01

0.00

85.21

D

33.02

63.94

1.01

0.07

0.18

0.04

0.03

0.00

0.03

0.00

98.33

E

32.55

64.57

1.14

0.04

0.16

0.04

0.02

0.00

0.07

0.00

98.60

F

5.37

45.11

38.63

0.62

1.75

0.22

0.08

0.00

0.01

0.00

91.79

Position

SiO2

CaO

Al2O3

Cs2O

Total

A

1.2

40.5

46.7

11.5

100.0

B

3.2

38.7

46.9

11.2

100.0

C

1.7

38.9

47.8

11.7

100.0

D

32.3

67.1

0.6

0.0

100.0

E

31.8

67.6

0.7

0.0

100.0

F

7.0

63.2

29.8

0.0

100.0

Fig. 15 BEI of the pyroprocessed material (Cs/Si ratio = 3.4, Cl/Cs ratio = 5).

Fig. 16 EPMA mapping of elements (same area as shown in Fig. 15; warm colors such as pink or red indicate
higher concentrations).

170

K. YAMADA et al.

rectangular particles, darker gray dendritic particles and abright matrix. Table 6 shows the chemical compositionsof these phases. Point A, indicating gray rectangularparticles, represents Ca3SiO5. Point B, indicating darker
gray particles, represents Ca2SiO4. Point C, indicating thebright matrix, represents calcium chloroaluminosilicate.
From the results obtained by XRD analysis, this phase
was identified as Ca12Al14O32Cl2, although the actual
chemical composition was found to contain a greater
amount of Cl, and some Al2O3 was replaced by SiO2.
Figure 17 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 2.2 and a Cl/Cs ratio of 5. Figure 18
shows an EPMA mapping of the same area. From thesefigures, four phases can be distinguished: small amounts ofa dark phase between the interparticle spaces; gray, roundparticles; and darker-gray, irregularly shaped particles

showing exolution and a bright matrix. In Table 7, thechemical compositions of these phases are shown. Point
A, indicating the dark phase, represents calcium
chloroaluminosilicate (Ca12Al14O32Cl2) as detected by the
XRD analysis, but with a greater Cl content. Point B,
indicating a gray round particle, represents Ca2SiO4. Point
C, indicating a darker-gray, irregularly shaped particle,
represents calcium chloroaluminosilicate with a low Cl
content. According to the texture of these particles, they
may be composed of multiple phases such as Ca2SiO4 and
Ca12Al14O32Cl2. Point D, indicating the bright matrix, also
represents calcium chloroaluminosilicate, but with alower aluminate content and greater silicate content ascompared with point A. This phase is surmised to be an
amorphous phase, as detected by XRD.

Table 6 Chemical compositions of the three phases (A, B, and C) shown in Fig. 15 (upper: w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

A

25.30

73.14

0.51

0.01

0.23

0.00

0.01

0.00

0.06

0.04

Total
99.30

B

32.08

64.04

0.99

0.01

0.10

0.00

0.02

0.00

0.09

0.23

97.56

C

8.03

61.35

9.11

0.28

0.00

0.00

0.05

0.00

0.03

26.31

105.17

Position

SiO2

CaO

Al2O3

Cl

Total

A

24.3

75.3

0.3

0.1

100.0

B

31.6

67.5

0.6

0.4

100.0

C

6.5

53.1

4.3

36.0

100.0

Fig. 17 BEI of the pyroprocessed material (Cs/Si ratio = 2.2, Cl/Cs ratio = 5).

Fig. 18 EPMA mapping of elements (same area as shown in Fig. 17; warm colors such as white, pink and red
indicate higher concentrations).

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 171
Table 7 Chemical compositions of the four phases (A, B, C, and D) shown in Fig. 17 (upper: w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

8.54

44.07

33.43

0.05

0.00

0.01

0.01

0.00

0.04

10.01

96.14

B

33.67

64.79

0.08

0.00

0.11

0.00

0.04

0.00

0.11

0.04

98.84

C

30.07

60.34

5.54

0.00

0.10

0.00

0.00

0.00

0.06

2.74

98.84

D

26.76

50.78

3.45

0.17

0.00

0.00

0.03

0.00

0.07

21.14

102.40

Position

SiO2

CaO

Al2O3

Cl

Total

A

9.2

51.1

21.3

18.3

100.0

B

32.6

67.3

0.0

0.1

100.0

C

29.3

63.0

3.2

4.5

100.0

D

22.5

45.7

1.7

30.1

100.0

4.4 Discussion
To achieve removal of Cs from pollucite, thismaterial must first be decomposed. The Ca/Si,
Ca/(Si+Al), and Cl/Cs ratios affect the decomposition
process; higher values of these quantities result in moreadvanced decomposition. At low Ca/Si ratios and without
Cl, pollucite is stable and no Cs is removed. When the
Ca/Si ratio is adequately high, a Cl/Cs ratio of 1.0 iseffective for the complete removal of Cs. However, as the
Cl/Cs ratio is increased at a low Ca/Si ratio, a Clcontaining glass phase forms and alkali metals including
Cs may dissolve into this phase, thereby preventing thecomplete removal of Cs. These complicated phenomena
are related to the formation of different mineral phases
depending on the Ca/Si and Cl/Cs ratios. Therefore, theaddition of too much Cl may produce undesired results;
an appropriate amount of Cl is recommended for use athigh Ca/Si ratios.
In Section 3.2, we showed that Cs was removed toundetectable levels from pond deposits without theaddition of Cl. A significant amount of Cs resulting from
pollucite remained, however. This difference may be
accounted for by the existence of potassium. Considering
the samples examined in Section 3.2, we included around
1 w/w% of potassium and determined the amount of Cl
using the Cl/K ratio. This means that Cl/Cs is in excess,and the excess Cl volatilizes as KCl and no glass phaseforms. Potassium acts as an accelerant in Cs removal.
Cs removal under high Ca/Si ratio conditions may beachieved by simple volatilization of Cs2O, but Cl
volatilization is not always required. Considering theexperimental results, we consider a higher Ca/Si ratio tobe preferential for the efficient removal of Cs.

Ca/(Si+Al) ratio was used to produce slag and Portland
cement.
The dependence of the Cs removal efficiency on the
Ca/(Si+Al) ratio was shown on the basis of data obtained
from the literature.
The highest Ca/(Si+Al) ratio could be realized in thesystem producing Portland cement. The optimal
conditions of pyroprocessing were then examined. We
showed that higher temperatures and a higher Cl/K ratio
are preferential for Cs removal from various
contaminated wastes. All kinds of alkali metals were
removed with different efficiency, and Cs levels werereduced preferentially, with the ease of volatilization
following the order of Cs > K > Na at 1450ºC, even
without the addition of Cl. Potassium in the target
subjects is considered to act as an accelerant for theremoval of Cs.
The effects of the Ca/Si and Cl/Cs ratios on mineralphase changes were analyzed through experiments using
pollucite. A higher Ca/Si ratio was observed to facilitate
the decomposition of pollucite and the efficient removalof Cs.

5. Conclusions

Fujiwara, H., Kuramochi, H., Nomura, K., Maesato, T. and Osako,
M. (2017) Behavior of radio cesium during incineration ofradioactively contaminated wastes from decontamination
activities in Fukushima. Journal of Environmental Radioactivity.
178–179, 290–296. https://doi.org/10.1016/j.jenvrad.2017.08.014
Honma, K., Takano, H., Miura, K., Sasaki, T., Kimura, T. andManpuku, Y. (2014) Removal of Cs from the soil
contaminated with radioactive materials by heat treatment.

We discussed efficient conditions for Cs removalfrom radioactive solids contaminated by r-Cs, such as soil
and incineration ashes, via pyroprocessing. Afterdecontamination, the resulting materials may be
preferentially used for other purposes. Therefore, a target

Acknowledgment
This study was conducted in collaboration with the
National Institute for Environmental Studies, Taiheiyo
Cement Corp., and the National Agriculture and Food
Research Organization.
The discussion with Mr. Kenichi Honma of Taiheiyo
Cement Corp. was very helpful to summarize this study.
References:

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K. YAMADA et al.

The Clay Science Society of Japan, 52: 71–73. (in Japanese)
https://doi.org/10.11362/jcssjnendokagaku. 52.2_71
Honma, K., Yohiskawa, T., Kataoka, M., Tamashige, T., Takahashi,
Y. and Hisaoka N. (2019) Reports of entrusted research anddemonstration work for Cs removal and recycling technology toturn radioactive soil and incineration ash into construction
materials at a pilot plant in Warabidaira area, Iitate village,
Fukushima prefecture. Journal of the Society Remediation ofRadioactive Contamination in the Environment, 7, 227–239.
International Atomic Energy Agency (IAEA) (2015) The
Fukushima Daiichi Accident. Description and Context of theAccident. IAEA: Vienna, Technical Vol. 1, 1–225.
Japan Atomic Energy Agency (JAEA), Department of Partnership
Operations for Environmental Remediation (2011) Investigationof radiocesium volatilization from soil by in-situ ground heating.
JAEA-Research, 2011, 026. (in Japanese) Retrieved from https://jopss.jaea.go.jp/pdfdata/JAEA-Research-2011-026.pdf (Accessed
4 August 2020)
Japan Environmental Strage & Safety Corporation (JESCO)(2020) Demonstration projects on the volume reduction ofremoved soil and others, 2016–2020. (in Japanese) Retrieved
from https://www.jesconet.co.jp/interim/information/josenjissho.
html (Accessed 4 August 2020)
Jiao, F., Kinoshita, N., Kawaguchi, M., Asada, M., Honda, M.,
Sueki, K., Ninomiya, Y., Sergeev, D., Blasing, M. and Muller,
M. (2018) Synergitic mechanisms of CaCl2 and CaO on thevaporization of Cs from Cs-doped ash during thermal treatment.
Energy & Fuels, 32, 5433–5442. https://doi.org/10.1021/acs.
energyfuels.8b00620
Kamata, Y., Abe, S., Kawamoto, K., Yui, K., Kuramochi, H. andOsako, M. (2015) Plant demonstration test on the thermal
separation of cesium by melting technique for soil. Journal of
the Society Remediation of Radioactive Contamination in theEnvironment, 3, 49–64. (in Japanese)
Kobayashi, H., Terasaki, T., Moi, T., Ishihara, C., Saito, S.,
Yamamura, H. and Mitamura, T. (1991) Preparation and thermal
expansion behavior of pollucite poders by sol-gel processing.
Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi, 99, 686–691.
(in Japanese) https://doi.org/10.2109/jcersj.99.686
Manpuku, Y., Hatta, T., Yaita, T. and Sato, T. (2017) Mineralogicaland chemical properties of the melting products of soils. The
Clay Science Society of Japan, 56, 28–40. (in Japanese)
Ministry of the Environment (2018a) Progress status of the strategy
on technology development of volume reduction/reuse, 9thInvesting Meeting on the Strategy of Technology Development
for Volume Reduction/reuse of removed soil and others in
the interim storage site, document #4, 2018.12. (in Japanese)
Retrieved from http://josen.env.go.jp/chukanchozou/facility/
effort/investigative_commission/pdf/proceedings_181217_04.pdf(Accessed 4 August 2020)
Ministry of the Environment (2018b) Temporal facility formaterialization at Warabidaira district, Information site on
treatment of radioactively contaminated wastes. (in Japanese)
Retrieved from http://shiteihaiki.env.go.jp/initiatives_fukushima/
waste_disposal/iitate/pdf/materials_warabidaira_result_1801.pdf(Accessed 4 August 2020)
Research Institute of Computational Thermodynamics Inc. Phase
Diagram, CaO-Al2O3-SiO2 1400ºC. Retrieved from https://sites.
google.com/site/catcalcphase/home/ceramics/al2o3/cao-al2o3sio2_1400 (Accessed 4 August 2020)
Spalding, B.P. (1994) Volatilization of Cesium-137 from soil withchloride amendments during heating and vitrification.
Environment Science & Technology. 28, 1116−1123. Retrieved
from https://doi.org 10.1021/es00055a022
Tokoyoda, K., Yamada, K., Honma., K, Ishida, Y., Takano, H. andOsako, M. (2018a) Decontamination of radio-cs in soil andincineration fly ash to the clearance level by pyrolysis. WM2018
Symposia, Abstracts, 18247.
Tokoyoda, K., Yamada, K., Honma, K., Ichimura, T., Ishida, Y.,
Takano, H., Manpuku, Y. and Osako M. (2018b) Study on reuseof soil contaminated with radio-cesium using calcination
technology. Journal of the Society Remediation of Radioactive
Contamination in the Environment, 6, 63–72. (in Japanese)
Yamada, K., Osako, M. and Yasutaka, T. (2020) Study on thestrategy for final disposal and reuse of decontamination wastes
after the Fukushima Daiichi NPP accident. WM2020 Conference,
20426.
Yui, K., Kuramochi, H. and Osako, M. (2018) Understanding the
behavior of radioactive cesium during the incineration ofcontaminated municipal solid waste and sewage sludge bythermodynamic equilibrium calculation. ACS Omega, 3, 15086–
15099. https://doi.org 10.1021/acsomega.8b01113

Kazuo YAMADAAs a materials scientist with a specialty incement-related materials, Kazuo Yamada, whoholds a doctorate of engineering, works at the
Wastes and Material Cycles Research Section of
the Fukushima Regional Collaborative ResearchCenter, National Institute for Environmental
Studies (NIES). He joined NIES in 2012 and has
worked on technologies for reducing the volume of contaminated soil andwastes, and on safe disposal of concentrated wastes in concrete facilities.
He is also active in the Society of Remediation of Radioactive
Contamination in the Environment as secretary of a research committee ontechnological strategies for final disposal of nuclear wastes out of
Fukushima.

Kazuhiko TOKOYODA
Kazuhiko Tokoyoda holds a master ofengineering. He was formerly a special researcher
at NIES’ Fukushima Branch (currently renamed
the Fukushima Regional Collaborative ResearchCenter). He is a mechanical/chemical engineer
with experience in the construction and operationof various production facilities at Taiheiyo
Cement Corp. spanning more than 20 years. He joined NIES in 2017 andhas worked there for three years, focusing especially on optimization andmechanism analysis of Cs volatilization by pyroprocessing in Portland
cement production systems.

Masahiro OSAKO
Masahiro Osako, who holds a doctorate ofengineering, serves as director of the Material
Cycles Division, National Institute forEnvironmental Studies (NIES). His specialty isenvironmental engineering, focusing on waste
management. Since the Fukushima nuclear
accident that resulted from the Great East Japan
Earthquake in 2011, he has been dedicated not only to conducting various
researches to properly manage radioactively contaminated wastes but also
to playing an important role in the relevant policy-making by the national
government. He also chairs the research committee on technologicalstrategies for the final disposal out of Fukushima in the Society of
Remediation of Radioactive Contamination in the Environment.
(Received 4 August 2020, Accepted 27 December 2020)

173

Insolubilization of Cesium Contained in Fly Ash by Co-heatingwith Potassium Feldspar
Yasumasa TOJO
Graduate School of Engineering, Hokkaido University
N13 W8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan*E-mail: tojo@eng.hokudai.ac.jp

Abstract
At present, reducing the volume of decontamination wastes/soils is an indispensable task in Japanbecause to secure final disposal sites with vast capacity is considered difficult. One promising option isthermal treatment to separate radioactive cesium (Cs) from wastes/soils. This, however, generates Csconcentrates in which Cs is thought to have high solubility. From a long-term viewpoint on ensuring safety,
the solubility of Cs itself in the concentrates should be reduced even though it will be stored in containers. In
this study, insolubilization of Cs by co-heating with potassium feldspar (hereafter, K-feldspar) wasinvestigated. This process can insolubilize almost 100% of Cs when only Cs carbonate and K-feldspar are coheated. However, concentrates in actuality consist mainly of fly ash and contain various elements. Thus theobjective of this study was to elucidate the influence of the presence of fly ash. In particular, elements that
inhibit Cs capture were focused on. Various co-heating experiments on mixtures of CsCl, K-feldspar, fly ash
and alkali metal compounds were conducted. As a result, the following findings were obtained: 1) the
efficiency of Cs insolubilization decreased in the presence of fly ash, 2) Ca in fly ash inhibited Cs
insolubilization. Notably, when Ca was in chloride form, this inhibition was at a maximum, 3) converting
CaCl2 in fly ash to CaCO3 by use of Na2CO3, improved the efficiency of Cs insolubilization. When the ratio of
fly ash to K-feldspar was increased, however, the efficiency showed a gradual decrease.
Key words :	cesium, decontamination waste, fly ash, insolubilization, K-feldspar

1. Introduction
After the nuclear accident in 2011, various
decontamination activities were carried out in the region
affected by radioactive fallout. As a consequence, hugeamounts of contaminated wastes and other substanceswere generated, the majority of which were incineration
ash from combustible wastes and soil removed duringdecontamination of environments. It is estimated thatthe amount of wastes and soils generated throughdecontamination activities was about 14 million m3(Ministry of the Environment, Japan, 2019). There areplans to store these wastes at interim storage sites for
30 years hereafter and then they are to be disposed of
at a final disposal site. It is thought, however, that to findand secure a suitable site with vast capacity will be
extremely difficult because of opposition from residents.
Therefore, the government is planning to reduce thevolume/mass of these wastes/soils. First, soils of low
radioactivity will be utilized as construction material. The
remainder, 380 thousand tons that cannot be thus utilized,
will be subjected to thermal treatment to separate out
radioactive cesium (Cs). After treatment, soils/wastes
Global Environmental Research
24/2020: 173-180
printed in Japan

from which Cs has been removed are to be used as
construction materials at interim storage sites. On theother hand, however, residues with highly concentrated
Cs will be generated simultaneously as a byproduct. The
residues (mainly composed of fly ash) are planned to be
stored in rigid containers with sufficient durability forlong-term storage. From various previous studies, it has
been reported that Cs in fly ash generated from manymunicipal solid waste (MSW) incinerators after theaccident is soluble because most of it is in chloride form
(National Institute of Environmental Studies, 2012). Cs
concentrates produced through thermal treatment of
decontamination wastes are thought to have the samecharacteristics, since some volatilization acceleration
agents (such as CaCl2) are added during the heatingprocess for Cs separation (Kamata, 2015; Abe, 2015).
Thus, from a long-term viewpoint on securing safety
related to leakage of Cs from stabilized fly ash bodies afterthermal treatment, it would be better to insolubilize Cs.
Past studies (Saffarzadeh, 2014; Dote, 2014; Tojo,2016) have clarified that Cs in bottom ash is hardly
soluble at all unlike Cs in fly ash. The authors
investigated why Cs in bottom ash is insoluble and©2020 AIRES

174

Y. TOJOrevealed that Cs in bottom ash is captured in an
amorphous phase formed around a specific oxide mineralcomposed of K, Al and Si. That mineral was identified as
potassium feldspar (KAlSi3O8) (hereafter, K-feldspar)(Tamura, 2016). The surface of K-feldspar particles,
when heated at 700˚C to 900˚C in the presence of Cs,
melts and captures Cs in the amorphous melt phase,making the Cs insoluble. In order to reproduce thiscapturing mechanism, the authors mixed K-feldspar with
Cs2CO3 and heated the mixture at 900˚C. As a result,nearly 100% of the Cs remained in the sample after
heating in an insoluble state, and particles with Cs
concentrated in the peripheral region (white region aroundthe particle in back-scattered electron images (BEI) or
bright part in Cs mapping images in energy dispersive
spectrographs) were found as shown in Fig. 1 (Sakamoto,2017). When the Cs compound was changed to CsCl,
however, the efficiency of insolubilization drasticallydecreased. (Hereafter, the term “insolubilization
efficiency” is used to express the ratio of insolubilized Cs,
which cannot be extracted by water after co-heating, tothe initial amount of Cs.) Thus, the effects of pretreatmentof K-feldspar and optimum heating temperature wasfurther examined. Grinding K-feldspar as a pretreatment,
resulting in amorphization of K-feldspar by grinding itover long periods, significantly increased insolubilization
efficiency even if the Cs was in CsCl form. Additionally,a 700˚C heating temperature produced the highest
insolubilization efficiency.
As mentioned above, the previous studies had been
conducted mainly under pure conditions (only feldspar
and Cs compounds present). However, the actual Cs
concentrates generated from thermal processing of soils/
wastes from decontamination activities, are deemed tocontain many other elements. Therefore, it is crucial toconfirm whether Cs insolubilization by K-feldspar works
when fly ash containing various other elements is present.
If any element interferes with Cs insolubilization, thereason should be elucidated. In addition, measures toprevent such interference must be developed. Therefore,
in this study, the following objectives were set: 1) toconfirm the influence of fly ash on the insolubilization

efficiency of Cs, 2) to identify substances contained in fly
ash that interfere with Cs insolubilization and 3) todevelop a method to prevent such interference.
Concretely, the following experiments were performed.
First, co-heating experiments using mixtures of fly
ash, CsCl and K-feldspar were conducted to confirm theinfluence of fly ash on Cs capture. From the co-heating
experiments above, increasing the ratio of fly ash to
K-feldspar resulted in decreased Cs insolubilization
efficiency. To elucidate the reason, a pure system free of
fly ash was set up and the effects of alkali elements on Cs
insolubilization were examined. The reason alkali
elements were focused on was that this Cs capturing (andinsolubilization) is thought to be related to the chargebalancing ability of cations in K-feldspar’s matrix. In+
K-feldspar (KAlSi3O8), part of the Si4 in the silicate (SiO4
tetrahedral matrix) is substituted with Al3+. Potassium ispresent to compensate for the positive charge deficiency.
In albite (NaAlSi3O8), Na plays this role and in anorthite(CaAl2Si2O8), Ca plays it. Cs is also a monovalent alkali
element. In this study, the capture was considered tooccur mainly through replacement of the “K” in
K-feldspar by Cs. Thus, what may interfere with thisreplacement was thought to be alkali elements which canbehave similarly. Thus, Na, K, and Ca were selected. An
additional reason was that they are contained in large
amounts in fly ash.
From co-heating experiments using certain alkalisalts, it was found that the proportion of insoluble Cs wasparticularly low when using CaCl2. Therefore, subsequent
experiments were conducted to confirm whether
specifically only CaCl2 interferes with Cs insolubilizationor the presence of Ca itself interferes, by trying Ca(OH)2and CaCO3. The reason these two compounds wereselected as the Ca compounds was that fly ash generally
contains slaked lime (Ca(OH)2) blown in for hydrogenchloride removal, and CaCl2 is produced as aneutralization product. Furthermore, Ca(OH)2 reacts with
CO2 in the air relatively easily in the presence of water,converting to CaCO3.
From the above experiments, it was found that only
CaCl2 causes a decrease in Cs insolubilization efficiency.
Therefore, it was thought that by replacing the CaCl2 in
fly ash with other Ca compounds interference in Cs
insolubilization could be avoided. Therefore, a few
pretreatment methods to change the form of Ca were
examined.

2. Materials and Methods

Back-scattered electron images (BEI)

Cs mapping images

Fig. 1 SEM-EDS images of a K-feldspar particle after co-heatingwith Cs2CO3 (Sakamoto, 2017).

2.1 Materials
2.1.1 Fly Ash
MSW fly ash was obtained from an MSW incinerator(stoker type). If it had been possible, it would have been
better to use fly ash generated from an actual thermal
treatment process for decontamination soils/wastes, but

Insolubilization of Cs in fly ash by co-heating with K-feldspar

175

Table 1 Elemental composition of the MSW (Municipal Solid Waste) fly ash used in this study.
Element

Ca

Cl

Na

K

Zn

Si

S

OthersContent (wt%)

40.1

32.3

10.3

8.1

2.3

2.3

2.0

2.6

Measurement conditions: device: Horiba MESA-500, method: fundamental parameter method, qualitative: automatic, voltage: automatic (15kV, 50kV onceeach), current: automatic adjustment, display of results: element)

no full-scale plants were in operation yet, so its
characteristics were not known. Thus, MSW fly ash wasused as an alternative. Table 1 gives the elemental
composition of the fly ash as determined by X-ray
fluorescence (XRF) analysis (Horiba MESA-500). Since
the Cs concentration in the MSW fly ash was too low toanalyze after co-heating experimentation, the Cs content
of the fly ash was artificially increased by adding CsCl
(hereafter, this fly ash is termed as “Cs-fly ash”). For Cs,
stable Cs was used.
2.1.2 K-feldspar
For K-feldspar, Indian feldspar (Quantum®, ceramic
grade potassium feldspar CAS# 68476-25-5) purchasedfrom a ceramics raw material supplier (Nittorengenryo
Co., Ltd) was used. According to an XRD (X-ray
Diffraction) analysis and phase identification by Match!
Version 2 (Crystal Impact GbR.), the major components
were 68.6% microcline (KAlSi3O8) and 31.4% albite(NaAlSi3O8). As a pretreatment, the feldspar was groundfor 1,000 hours in a ball-mill to break down its crystalline
structure and make it amorphous. Grinding was
performed by placing 50 g of the K-feldspar and 1,000 gof alumina balls with a diameter of 1.8 cm in a ceramic
pot. Confirmation of amorphization of this K-feldspar
was made by XRD, though it isn’t shown here.
2.1.3 Chemical ReagentsThe following chemical reagents were used:
Cesium chloride (99%, FUJIFILM Wako Pure
Chemical Corporation), sodium chloride (99.5+%,
FUJIFILM Wako Pure Chemical Corporation), potassium
chloride (99.5+%, FUJIFILM Wako Pure Chemical
Corporation), calcium chloride (95.0+%, FUJIFILM
Wako Pure Chemical Corporation), calcium hydroxide(96.0+%, FUJIFILM Wako Pure Chemical Corporation)and calcium carbonate (99.5+%, FUJIFILM Wako Pure
Chemical Corporation).
2.2 Methods
2.2.1 Confirmation of the Influence of Fly Ash on Cs
Insolubilization by K-feldspar
Three grams of pretreated K-feldspar were added to
Cs-fly ash. The amount of CsCl in the Cs-fly ash was
fixed at 0.6 g and the amount of fly ash was varied from0 to 2.0g. In other words, the influence of fly ash underratios of fly ash to K-feldspar of from 0 to 0.67 was
examined. A sample without K-feldspar was also
prepared. Then, the mixture was put into a ceramic
combustion boat and heated in a tubular electric furnacefor 2 h. The temperature was set at 700ºC.

The sample after heating was treated in the order ofwater washing, aqua regia digestion, and hydrofluoric
acid digestion to fractionate soluble Cs and insoluble Cs.
The fraction obtained by water washing was regarded assoluble and fractions obtained by the two acid digestions
were regarded as insoluble. The liquid solutions obtained
from these three processes were analyzed by atomic
absorption spectrometry (Shimadzu AA-6800).
2.2.2 Identification of Substances in Fly Ash that
Interfere with Cs Insolubilization
Five grams of pretreated K-feldspar were added to
1g of CsCl reagent and 1g of powdered reagent ofeither NaCl, KCl or CaCl2. Then they were mixed wellusing a mortar and pestle. The mixed sample was placedin a crucible and heated in a muffle furnace for 2 h.
The heating temperature was set at 700°C.
After heating, the sample was removed after thetemperature in the furnace became sufficiently low, andtransferred to a desiccator to cool further. The cooled
sample was treated in the order of water washing andhydrofluoric acid digestion to quantify soluble Cs andinsoluble Cs in the sample. Among the added Cs, theportion which could not be detected in the solutions
obtained by either water washing or acid digestion was
regarded as volatilized Cs.
2.2.3 Interference by Ca in Cs Insolubilization fromDifferent Ca Compound Forms
Five grams of pretreated K-feldspar were added to
1 g of CsCl reagent and 1 g of powdered reagent of Ca
compound (i.e., Ca(OH)2 or CaCO3). Then they weremixed well using a mortar and pestle. The procedures ofheating and subsequent chemical analysis were the sameas described above in Sub-section 2.2.2. In thisexperiment, analysis of Ca was also performed on thesolution obtained by washing and acid digestion toconfirm the form of Ca after heating. Thermogravimetricanalysis was also carried out to elucidate the behavior ofeach Ca compound in the heating temperature range ofthis experiment. For TG-DTA analysis, a Thermo plus
EVO-II (Rigaku) was used.
2.2.4 Pretreatment of Fly Ash to Change the Form of
Ca to Prevent Interference
To make Cs-fly ash, the amount of fly ash was set at0.75 g, 1.12 g and 2.24 g. To each of these three fly ashes,
1g of CsCl reagent was added. Thus three types of Cs-fly
ash were prepared. For the co-heating experiment,
pretreated K-feldspar was used.
Three pretreatment methods were examined:• Adding water to the Cs-fly ash to dissolve the CaCl2,

Y. TOJO• Moistening the Cs-Fly ash and exposing it to a CO2
gas environment for 48 hours to form CaCO3• Adding Na2CO3 to the Cs-fly ash with water,
dissociating Ca from CaCl2 to form CaCO3. This
carbonation reaction can be expressed as [CaCl2 +Na2CO3 = CaCO3 + 2NaCl].
The water-added sample was subjected directly toheating with 5 g of pretreated K-feldspar. For Cs-fly ash
subjected to carbonation with CO2 gas or carbonation
with Na2CO3, the sample was dried after treatment andthen mixed with 5 g of pretreated K-feldspar. Then thesemixtures were heated in a furnace at 700°C for 2 h. After
heating, the sample was subjected to water washing andacid digestion to determine the ratio of soluble andinsoluble Cs by the same methodology as describedabove in Sub-section 2.2.2. In addition, the residue after
washing was examined by SEM-EDS (JSM-6360LA(JEOL)) to confirm the presence of insoluble Cs.

3. Results and Discussion
3.1 
Influence of Fly Ash on Cs Insolubilization by
K-feldspar
Figure 2 shows the ratios of insoluble Cs andsoluble Cs after co-heating of K-feldspar with Cs-fly
ash. The horizontal axis shows the amount of fly ash
added to the 3 g of K-feldspar. Although more than 90%of the Cs became insoluble when no fly ash was present,
the ratio of insoluble Cs decreased drastically as theamount of fly ash was increased. When the amount of
fly ash was almost half that of the feldspar (i.e., amountof fly ash of 2.0 on the horizontal axis), the ratio of
insoluble Cs decreased to less than 40%.To secure morethan 80% insoluble Cs, the mass of the fly ash must be
only 10% that of the feldspar. From this result, it can besaid that the presence of fly ash reduces the ratio of
insolubilized Cs.

3.2 
Substances in Fly Ash that Interfere with Cs
Capture and Insolubilization
Figure 3 shows the results of the experiment inwhich three types of alkali salts were used to confirm
their influence on Cs insolubilization by co-heating withfeldspar. The vertical axis indicates the ratio of soluble,
insoluble and volatilized Cs to the total amount of Cs
added. When NaCl, KCl and CaCl2 were mixed and coheated, the ratio of insoluble Cs decreased compared tothe case in which no alkali salt was added. In particular,
the ratio of insoluble Cs decreased significantly when
CaCl2 was added. Therefore, it was thought that thedecrease in the ratio of insoluble Cs confirmed in the coheating experiment conducted in Section 3.1 above wasmainly attributable to Ca in the fly ash.
3.3 Identification of Ca Compounds that Inhibit Cs
Insolubilization
Figure 4 shows the ratio of Cs in the sample after
heating when CaCO3 or Ca(OH)2 was added as a Cacompound. For comparison, the results with CaCl2 andwithout any Ca compound are also shown. Compared to100
Ratio of Cs form (%)

176

Insoluble Cs

Soluble Cs

Volatilized Cs

80
60
40
20
0

None

KCl

NaCl

CaCl2

Alkali salts added in co-heating
Fig. 3 Ratios of Cs forms after co-heating with CsCl, K-feldspar
and each alkali salt.

100%

40%
20%
0%

Without
0.0 0.33 0.53 0.75 1.29 2.0 K-feldspar
Amount of fly ash (g) added to 3 g of feldspar and 0.6 g of CsCl

Fig. 2 
Changes in the ratio of insolubilized Cs resulting fromaddition of fly ash in co-heating with K-feldspar.

100
Ratio of Cs form (%)

Soluble60%

Insoluble

Ratio of Cs form

80%

Insoluble Cs

Soluble Cs

Volatilized Cs

80
60
40
20
0

None

CaCl2

Ca(OH)2

CaCO3

Ca compound added in co-heating
Fig. 4 Ratios of Cs forms after co-heating with CsCl, K-feldspar
and each Ca compound.

Insolubilization of Cs in fly ash by co-heating with K-feldspar

Insoluble Ca

80
60
40
20
0

CaCl2
Ca(OH)2 CaCO3
Calcium compounds added in co-heating
Fig. 5 Forms of calcium present in the same experiment as shownin Fig. 4.

(a) Ca(OH) 2
1220

TG (mg)

10

-20
8
6

-40

0

200

400
600
Temp. (ºC)800(b) CaCO3
15

TG

-60
1000

30
20

DTA (μ V)

10

TG (mg)0

DTA (μV)

DTA

TG

10

DTA

5
0

0

200

400
600
Temp. (ºC)0800(c) CaCl2
18

TG

16

-10
1000

20

DTA

0

DTA (μ V)

Ratio of Ca form (%)

100

Soluble Ca

captured in the glassy amorphous phase created at thesurface of the feldspar particle as indicated in Fig. 1.
If this phenomenon is inhibited by Ca, there is apossibility that the Ca in CaCl2 is also likely to movewhen heated at 700°C, similar to Cs and K. Figure 6
shows the results of a thermogravimetric analysis of the
Ca(OH)2, CaCO3, and CaCl2 used in this study.
In the case of Ca(OH)2 in Fig. 6(a), a significant
decrease in TG and an endothermic peak in the DTA canbe confirmed above 400°C. This is because Ca(OH)2 isthermally decomposed as it approaches 580°C andbecomes CaO. The reaction of CaO with KAlSi3O8 to

TG (mg)the ratio obtained in the case of adding CaCl2, no
significant decrease in the ratio of insoluble Cs was
confirmed with the addition of CaCO3 or Ca(OH)2. Thatis, it is thought that the decrease in insoluble Cs was
mainly due to CaCl2 in the fly ash. It is inferred that thisis related to the state of the Ca compound at the heating
temperature used in this study (i.e., 700°C).
The ratio of Ca forms after the co-heating
experiments is shown in Fig 5. The ratio was calculated
based on recovered amounts, i.e., the sum of the soluble
fraction and insoluble fraction was regarded as 100%.
When CaCl2 was used as the Ca source, the ratio of
insoluble Ca was low, and the majority of the added Ca
was soluble. On the other hand, when CaCO3 or Ca(OH)2
was used as the Ca source, most was in an insoluble form
and there was almost no soluble Ca. That is, when CaCl2
was added and co-heated with K-feldspar and CsCl, mostof both the Cs and Ca existed in a soluble form in thesample after heating. Thus, it is thought that the fact thatboth Ca and Cs remained in the soluble state even whenheated at 700°C was related to inhibition of Cs
insolubilization.
The phenomenon of Cs capture and insolubilization
by K-feldspar applied in this study is most efficientaround 700°C. The reason for this is thought to be as
follows: the melting point of CsCl is 645°C. Based on
Bowen’s Reaction Series, which describes formation
steps of minerals from magma, K-feldspar is formed ataround 750° to 800°C (Earle, 2019). This means that at
around this temperature range, K-feldspar has both asolid phase and melt phase. In a state in which both CsCland K-feldspar melt and both K and Cs can become
readily mobile, substitution of Cs and K is thought tooccur. Since Cs has a higher charge balancing ability than
K (Hess, 1991), the K in K-feldspar is replaced by Cs,
and Cs is as consequence captured in the melt phase andinsolubilized. There is a big difference in their ion
radiuses, however. Cs cannot enter into the crystal matrixof K-feldspar. The author thinks this is why Cs is

177

14

-20

12

-40

10

0

200

400
600
Temp. (ºC)

800

-60
1000

Fig. 6 Results of thermogravimetric analysis of the Ca compounds
used in this study.

178

Y. TOJO

form compounds such as CaAl2Si2O8 is said to be a
general reaction in the cement manufacturing process(Arai, 1990). That is, the mobility of Ca is low because
Ca(OH)2 has already been converted to other compounds
in the heating temperature range used in this study. Thus,
it is thought not to be involved in the Cs capture reaction.
The thermal decomposition temperature(decarbonation temperature) of CaCO3 is said to be about
890°C. In Fig. 6(b), the decrease in TG is confirmed fromaround 700°C, and the DTA shows a large endotherm ataround 800°C. It is reported that CaCO3 reacts with Al2O3,
SiO2, etc. to form compounds even below the thermal
decomposition temperature in the cement clinker
formation process (Arai, 1990). Thus, since CaCO3 also
participates in such reactions, CaCO3 is thought not to
inhibit the Cs capture reaction.
In the case of CaCl2 as shown in Fig. 6(c), there is adecrease in TG and an endotherm before 200°C, which isconsidered to be due to dehydration of absorbed moisture.
The melting point of CaCl2 is 772°C. In the figure, agradual decrease from around 700°C in TG and an
endotherm at around 770°C are observed. This indicatesthat CaCl2 starts melting and the mobility of Ca becomeshigh in the heating temperature range adopted in thisstudy. That is, in the case of CaCl2, it only melts around
700°C, and the mobility of Ca becomes high. However,
because conversion to other compounds does not occur, itis thought to be involved in the Cs capture reaction.
3.4 Effect of Pre-treatment of Fly Ash on Interferenceof CaCl2
Figure 7 shows the ratio of Cs that became insoluble
after co-heating of Cs-fly ash with K-feldspar. The ratio
of insoluble Cs was 74% when the amount of fly ash was
0.75 g and no pretreatment of the Cs-fly ash was done.
This, however, improved to 100% when a carbonation

Ratio of insoluble Cs (%)

100

Carbonation(by Na2 CO3 )80
No pretreatment

60
40
20
0
0.5

Water addition
Carbonation (by CO2 gas)

1.0

1.5

2.0

2.5

Amount of fly ash added to 5 g offeldspar and 1 g of CsCl.
Fig. 7 
Ratio of insoluble Cs after co-heating of Cs-fly ash
pretreated by each method and K-feldspar.

pretreatment for the Cs-fly ash using Na2CO3 wasconducted. On the other hand, in the case of ionization
and CO2 gas exposure, the efficacy was slightly reduced.
Though the results are not shown, from XRD analysis of
the samples after pretreatment, a clear increase in the
CaCO3 peak was observed for carbonation with Na2CO3,
but not for the sample after CO2 gas exposure. In addition,
when a theoretical calculation using PHREEQC(Parkhurst & Appelo, 2013) was performed, no CaCO3
precipitate was formed through contact of the CaCl2
solution with CO2 gas. These results corroborate theobservation that only in the case of Na2CO3 could an
increase in the ratio of insoluble Cs after co-heating be
confirmed. When the amount of fly ash was small relativeto K-feldspar (K-feldspar 5 g: fly ash 0.75 g), carbonation
with Na2CO3 was sufficiently effective.
In any pretreatment, however, the ratio of insoluble
Cs decreases as the added amount of fly ash is increased.
In the carbonation pretreatment with Na2CO3, although
the amount of Na2CO3 was increased according to any
increase in the amount of fly ash, there is a possibility
that sufficient carbonation of the Ca did not proceed.
Alternatively, since inhibition of Na and K on Cs
insolubilization was not zero according to theexperiments done in 3.2 (as indicated in Fig. 3), theincreased amount of Na may also have had an effect.
Especially in carbonation by Na2CO3, although Ca isconverted to carbonate, NaCl is generated in the same
reaction. That is, it is thought that increased Na in thesystem may have contributed to the inhibition of Cs
insolubilization.
SEM-EDS images of the particles after water
washing of the sample obtained by co-heating of the Csfly ash pretreated by carbonation using Na2CO3 andpretreated K-feldspar are shown in Fig. 8.
Particles having a high concentration of Cs have thefollowing characteristics; in BEI (Backscattered electron
images), the particles have a gray core at the center, awhite area surrounding it, and a shell-like gray surface
existing outside it. The center is considered to be
K-feldspar (KAlSi3O8) because it is rich in Al, Si and K,
and also no Cl, Ca, and Na are confirmed in the elemental
mapping image. The structure in which Cs concentrates
around K-feldspar is the same as the concentrating
mechanism of Cs identified so far (Fig. 1) (Tojo, 2014;
Tamura, 2016; Sakamoto, 2017). That is, Cs is trappedwhere the feldspar surface melts and becomes glassy andamorphous. A further characteristic newly observed isthat the outer surface is rich in Ca or Na. The positions
where Cs and Ca or Na concentrate are reciprocal andthey are located so as to avoid each other.

4. Conclusions
In this study, aiming to facilitate long-term safe
management of Cs concentrate generated from thermalInsolubilization of Cs in fly ash by co-heating with K-feldspar

179

Fig. 8 SEM-EDS image of particles obtained from co-heating of Cs-fly ash pretreated with Na2CO3 together with pretreated K-feldspar.
The sample contained only insoluble Cs because the particles were obtained after water washing.

treatment of decontamination waste, a method of
capturing and insolubilizing Cs using K-feldspar wasinvestigated. The insolubilization efficiency of Cs by
K-feldspar decreased as the amount of fly ash present
was increased. To boost the ratio of insoluble Cs to 80%
or more, it was necessary to reduce the amount of fly ash
to 10% of the amount of K-feldspar. The salt in fly ashthat inhibited Cs insolubilization by K-feldspar was
CaCl2. Inhibition by NaCl and KCl was found to be slightcompared to that by CaCl2. Besides, no inhibition was
identified when CaCO3 or Ca(OH)2 were present. The
reason was thought to be the state of CaCl2. The heating
temperature applied in this study was 700°C. At thistemperature, both K-feldspar and CsCl melt, so
replacement of Cs and K, which are both monovalentcations, was likely to occur. Since CaCl2 is also in a
molten state at that temperature, the high mobility of Ca
is thought to interfere with the substitution reaction of Cs
and K. By converting the CaCl2 in fly ash to CaCO3 by
pretreatment with Na2CO3, it was possible to avoid
inhibition from Ca. When the amount of fly ash wasincreased, however, the total amount of alkali elements
increased and as a result, the Cs insolubilization

efficiency gradually decreased. The most significant issue
in the management of decontamination waste is to reduce
its mass/volume because to secure a final disposal site isextremely difficult. Thus, it will still be necessary todevelop a method that realizes a higher insolubilization
efficiency of Cs using minimal amounts of K-feldspar
even if the total amount of fly ash is increased.
Acknowledgements
This research was supported by the Environment
Research and Technology Development Fund (3K153015
and 3-1803 [JPMEERF20183003]) of the Environmental
Restoration and Conservation Agency of Japan.
References
Abe, S., Kamata, Y., Kawamoto, K., Kuramochi, H. and Osako, M(2015) Experiment and feasibility study on the thermal
separation of cesium by melting technique from soil. Journal of
the Clay Science Society of Japan, 54(1), 43–53. (in Japanese)
Retrieved from https://doi.org/10.11362/jcssjnendokagaku.54.1_43
Arai, Y. (1990) Material chemistry of cement. Dainippon Tosho
Co., Ltd., ISBN 978-4-477-03039-5. (in Japanese)

180

Y. TOJO

Dote, Y., Sekito, T., Morooka, R., Shimaoka, T., Tojo, Y., Yoshida,
H. and Kawano, T. (2014) Effect of pH and temperature onleaching of cesium from municipal solid waste bottom ash.
Journal of Japan Society of Civil Engineers, Ser. G, 70, 217–
223. (in Japanese)
Earle, S. (2019) Chapter 3.3 crystallization of magma. PhysicalGeology – 2nd Edition, BCcampus, ISBN: 978-1-989623-71-8.
Retrieved from https://opentextbc.ca/geology/ (Accessed 13
August 2020)
Hess, P.C. (1991) The role of high field strength cations in silicate
melts. In: Perchuk, L.L. and Kushiro, I. (eds.), Physical
Chemistry of Magmas, 152–191, Springer-Verlag. New York.
Retrieved from https://doi.org/10.1007/978-1-4612-3128-8
Kamata, Y., Abe, S., Kawamoto, K., Yui, K., Kuramochi, H. andOsako, M. (2015) Plant demonstration test on the thermal
separation of cesium by melting technique from soil. Journal of
the Society for Remediation of Radioactive Contamination in theEnvironment, 3(2), 49–64. (in Japanese)
Ministry of the Environment, Japan (2019) Environmental
remediation in affected areas in Japan. Retrieved from http://
josen.env.go.jp/en/pdf/environmental_remediation_1905.pdf(Accessed 13 August 2020)
National Institute of Environmental Studies (2012) Proper
treatment of wastes contaminated by radioactive substances.
Retrieved from http://www.nies.go.jp/fukushima/pdf/techrepo_
publicver_e_121128.pdf (Accessed 13 August 2020)
Parkhurst, D.L. and Appelo, C.A.J. (2013) Description of input andexamples for PHREEQC version 3: A computer program forspeciation, batch reaction, one-dimensional transport, andinverse geochemical calculations, U.S. Geological Survey
Techniques and Methods. Retrieved from http://pubs.usgs.gov/
tm/06/a43 (Accessed 13 August 2020)
Saffarzadeh, A., Shimaoka, T., Kakuta, Y. and Kawano, T. (2014)
Cesium distribution and phases in proxy experiments on theincineration of radioactively contaminated waste from the
Fukushima area. Journal of Environmental Radioactivity, 136,
76–84. Retrieved from https://doi.org/10.1016/j.jenvrad.2014.
05.009
Sakamoto, S., Tojo, Y., Matsuo, T. and Matsuto, T. (2017)
Immobilization and insolubilization of cesium contained inwaste by co-incineration with aluminosilicate. Proceedings ofthe 28th Annual Conference of Japan Society of Material Cycle
and Waste Management, 331–332. (in Japanese)
Tamura, K., Tojo, Y., Matsuo, T. and Matsuto, T. (2016)
Identification of mineral species in incineration bottom ash
particularly accumulating cesium on its peripheral region.
Proceedings of the 27th Annual Conference of Japan Society ofMaterial Cycle and Waste Management, 461–462. (in Japanese)
Tojo, Y., Ishii, M., Matsuo, T., Matsuto, T. and Shimaoka, T. (2014)
Study on the existence form of hardly-soluble cesium contained
in incineration bottom ash and its long-term stability.
Proceedings of the 26th Annual Conference of Japan Society ofMaterial Cycle and Waste Management, 477–478. (in Japanese)
Tojo, Y., Iwamoto, S., Ishii, M., Matsuto, T. and Matsuo, T. (2016)
Influence of weathering of bottom ash on the leaching behaviorof cesium. International Journal of GEOMATE, 12(32), 43–49,
Retrieved from http://dx.doi.org/10.21660/2017.32.6600

Yasumasa TOJO
Yasumasa Tojo is an associate professor at the
Solid Waste Disposal Laboratory, Hokkaido
University. His main fields of interest are thelong-term behavior of substances in landfills,
landfill stabilization, insolubilization of hazardous
elements, heavy metal leaching from wastes andrecycled materials, long-term management of
cesium, and landfill management under extreme conditions.

(Received 26 August 2020, Accepted 22 December 2020)

181

A Study on the Durability of Covering Sheets Used at
Temporary Storage Sites in Fukushima Prefecture
Yusuke TAKAHASHI1* and Masahiro KOISO2
Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan
2
Fukushima Prefectural Centre for Environmental Creation
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: takahashi.yusuke@nies.go.jp

1

Abstract
The durability of the covering sheets used for storage of decontamination soil and waste at temporarystorage sites (TSSs) in Fukushima Prefecture was investigated. In this study, we investigated durability fromthree viewpoints, accelerated UV exposure tests, comparisons among several municipal TSSs, and material
aging. The results indicated that the water resistance of gas-permeable/waterproof sheets (GWSs) used formore than two years at TSSs was much lower than its standard value in many cases, which means thepossibility of rainwater intrusion to storage containers holding decontamination soil. On the other hand, thetensile strength and water resistance of the geomembrane used at TSSs remained above the standard values.
The results of accelerated UV exposure tests showed no significant damage observable in the microstructureof the microporous membranes of GWSs, even after accelerated UV exposure equivalent to 10 years of
outdoor use. On the other hand, sunlight exposure for more than two years at TSSs caused significant damage
among GWSs to the microporous membrane and its water resistance. The aging of GWSs at TSSs might bestimulated not only by UV radiation and moisture but also by other factors not considered in the accelerated
UV exposure tests.
Key words :	gas-permeable/waterproof sheet, geomembrane, tensile strength, water resistance,
temporary storage site

1. Introduction
Soil removed and waste generated duringdecontamination work in Fukushima Prefecture following
the Fukushima Daiichi nuclear power plant accident on
March 11, 2011 are being kept in storage containers fordecontamination soil at temporary storage sites (TSSs)
and on-site storage locations. The two main types ofstorage containers for decontamination soil and waste are
flexible containers and large weather-resistant sandbags(MOE, 2018; FPG, 2019). The former generally consistof polyethylene or polyester woven fabric and the latterof polypropylene woven fabric which is weatherproofed
by use of light stabilizers and antioxidants. Generally, thestorage containers are covered with a sheet to avoid
deterioration from exposure to sunlight, wind and rain
(MOE, 2013). The two main types of covering sheet are gaspermeable/waterproof sheets (GWSs) and geomembrane.
GWSs are a type of geocomposite that combines nonwoven fabric and waterproof microporous membranes,
while geomembrane is a flexible waterproof sheet material
made of ethylene propylene diene monomer rubber,
Global Environmental Research
24/2020: 181-190
printed in Japan

polyvinyl chloride, polyethylene and other compounds(JIGS, 2016). In addition, a degassing pipe is required in
the case of using a geomembrane, while it is not necessary
with a GWS.
The transportation of decontamination soil and wastefrom TSSs to interim storage facilities began in 2015, andthe amount of decontamination soil and waste is estimatedto be about 14 million m3 in total while its transportation
to the interim storage facilities was about 60% complete
as of October 2020, with 551 TSSs continuing to store
decontamination soil and waste according to the Ministryof the Environment’s website with information on interim
storage facilities (MOE, 2020). As a result, there are still
many sites where decontamination soil and waste havebeen stored for longer than the originally anticipatedperiod of three years, and there are concerns aboutdamage to the above-mentioned materials used at TSSs
(MOE, 2015; MOE, 2016). There have been some cases
where the sheets covering them were damaged by sunlight
exposure at TSSs in Fukushima Prefecture (Fig. 1),
which can cause deterioration of storage containers due
to ultraviolet exposure, enabling rainwater to intrude.
©2020 AIRES

182

Y. TAKAHASHI1 and M. KOISO

Fig. 1 Fractures in waterproof sheets covering the flexible containers of decontaminationsoil and waste at a temporary strage site (TSS).

To collect knowledge for the proper management of
decontamination soil and waste and TSSs, the authors
have reported their survey results on long-term durabilityof the flexible containers and large weather-resistantsandbags used as storage containers for decontaminationsoil and waste. They found that some exposed materials
had experienced significant strength loss (Takahashi,
2018; Takahashi et al., 2019).
In this study, the authors investigated the long-term
durability of the covering sheets (i.e., GWSs andgeomembrane) which have actually been used at TSSs for
two to six years to protect the storage containers fordecontamination soil and waste.

2. Experimental Study
2.1 Collection of Sheet Materials Used at TSSs
In this study, two types of GWS and one type ofgeomembrane were collected from TSSs managed bymunicipalities in Fukushima Prefecture (Fig. 2). All thesesheet materials were used in sun-exposed conditions. The
three municipalities managing the TSSs where the sheet
materials were collected in this study are referred to here
as “Municipality a/b/c,” with the TSS in Municipality abeing called “TSS (a),” the TSSs in Municipality b being
called “TSS (b-1),” “TSS (b-2),” “TSS (b-3),” and the
TSS in Municipality c being called “TSS (c).” Thegeomembranes used in this study were made of PVC(polyvinyl chloride) with a thickness of 1.5 mm.
Photographs and low-magnification SEM images of
two types of GWS are shown in Fig. 3. The microporous
GWS membranes consists of polyethylene and a non-

woven fabric consisting of polyethylene or polyethylene
terephthalate (Nishimura et al., 2012). Type 1 uses a thin
non-woven fabric for the exposed side, and the overall
thickness of the sheet is about 5 mm (Fig. 3 (A)), while
Type 2 uses same non-woven fabric on both sides, withthe overall thickness of the sheet being about 4.5 mm(Fig. 3 (B)). Type 1’ has a different microporous membrane
structure from Type 1 (Fig. 3 (C)), but their basic structureis almost the same. Therefore, in this study, Type 1 andType 1’ are treated as similar materials with the same
weatherability and mechanical properties. The materials
collected from the TSSs in this study were GWS types 1
and 2 and the test procedures used for them are described
below in Sub-sections 2.3.2 and 2.3.3, while the test
targets of the accelerated UV exposure test described in
Sub-section 2.3.1 were GWS types 1’ and 2.
In addition, unused GWSs and geomembrane wereprepared as undamaged materials for comparison with thematerials collected from TSS.
2. 2 Method
2.2.1 Tensile Test
Tensile tests were performed using a universal tester(AGS-10kNG, Shimadzu) on the GWS and geomembranematerials prepared in Section 2.1, and the tensile strengthof the sheet body in the cross-machine direction was
calculated from the following formula:p = P / B		(1)

where p is maximum tensile strength [N/cm], P is the
maximum tensile load [N], and B is the width of the test
specimen [cm].

A Study on the durability of covering sheets used at temporary storage sites in Fukushima Prefecture

Sandbags forshielding eﬀect

183

Sandbags forshielding eﬀect

Fig. 2 Surveyed municipal TSSs (temporary strage sites) and collected sheet materials.

(A)

(B)

(C)

Fig. 3 SEM (scanning electron microscope) images of GWSs.
( A) Gas-permeable/water-proof sheet (GWS) (types 1 and 1’), (B) Gas-permeable/water-proof sheet (GWS) (Type 2),(C) Microporous membrane of GWS

The tensile strength for sheet joints was also
determined in the cross-machine direction. The
fabrication and testing conditions of the test specimens
conform to the voluntary standards of Japan Lining
Systems and Technology Association (JIS L 1908 for
GWS and JIS K 6251 for geomembrane) (JLSTA, 2014).
The number of replications was set at three.
2.2.2 Puncture Resistance Test
The conditions for preparation and testing of the test
specimens were in accordance with the method (ASTM

D 4833) specified in the voluntary standards of JLSTA.
The number of replications was set at three.
2.2.3 Water Resistance Test
The conditions for fabricating and testing thespecimens were in accordance with the method (JIS L
1092 B method (high water pressure method)) specified
by JLSTA. The number of replications was set at three.
2.2.4 Morphological Observation
The surface and cross-sectional microstructures ofthe specimens were observed using a scanning electron

184

Y. TAKAHASHI1 and M. KOISO

Table1 Covering sheet material types and test methods.
Material
condition
Material type

Accelerated UV-exposedmaterial

Unused material

Material used at municipal TSSs
a

b-1

b-2

b-3

c

GWS
GWS
GWS Geomem- GWS
GWS Geomem- GWS
GWS
GWS Geomem- GWS
GWS Geomem(Type 1) (Type 1’) (Type 2)
brane (Type 1’) (Type 2)
brane(Type 1) (Type 1) (Type 1)
brane(Type 1) (Type 2)
brane

Elapsed year0

(UV 900/1500/3000 hour)43

2.5~4.4

2

2.5~5.5

3

4

Tensile test

-

○

○

○

○

○

○

○

○

○

○

○

○

○

Water
resistance

○

○

○

○

○

○

○

○

○

○

○

○

○

○

Puncture
resistance index

-

○

○

○

○

○

○

-

-

-

-

-

-

-

microscope (SEM) (JEOL, JSM-7800F) on the GWS andthe geomembrane prepared in 2.1. The specimens werepretreated with platinum deposition.
2.2.5 Light-shielding Test
The light shielding ratios of the test specimens were
calculated from the following equation in accordancewith JIS L 1055:2009 “Testing methods for light blocking
effect of curtain materials”:
S = (1 - It / I0) × 100 (2)where S is the light shielding ratio [%], It is theilluminance with the specimen attached [lx] and I0 is theilluminance without the specimen attached [lx]. In thisstudy, I0 = 100,000 [lx]. The number of replications was
set at three.
2. 3 Test Procedure
In this study, the durability of sheet materials wasevaluated from three points of view: an accelerated UV
exposure test with UV exposure, a comparison among
several municipal TSSs, and aging of the material.
The types of prepared sheet materials andexperimental methods used are summarized in Table 1.
2.3.1 Accelerated UV Exposure Test
Unused sheet materials were exposed to UV lightusing a sunshine carbon arc lamp weathering apparatus(JISC, 2007). The tested specimens were GWS types 1’
and 2 and PVC geomembrane, shown as “accelerated UV
exposure material” in Table 1. The exposure conditions
were in accordance with the JIS L 1096 weathering test,
where the black panel temperature was 63 ± 3°C and thewater spray time was 18 minutes per cycle of 120
minutes. Under these conditions, 300 hours of accelerated
exposure is considered to be equivalent to one year of
outdoor use (JLSTA, 2014; PWRC, 2012). Three different
exposure times (900, 1500, and 3000 hours) were
examined in this study.
Tensile tests and puncture resistance tests wereconducted on the materials that were subjected to theabove accelerated UV exposure. For some of thematerials, water resistance tests were also conducted.
2.3.2 Comparisons among Municipal TSSs
The tested specimens were GWS (Type 1) andgeomembrane (PVC) shown as “material used at TSS” in

Table 1 and they were collected from the TSSs managed
by municipalities a, b and c. The same type of GWS(Type 1) was used in municipalities a and b, and the same
type of geomembrane was used in municipalities b and c.
Tensile tests and water resistance tests were conducted on
the above sheet materials. Here, the number of
replications was set at five or 10.
2.3.3 Aging of Material
The tested specimens were GWS types 1 and 2
shown as “material used at TSS” in Table 1 and they werecollected from TSS (b-2) and TSS (b-3). Tensile tests andwater resistance tests were conducted on the above sheet
materials. The tensile strength of the sheet body wasevaluated in the machine-direction and cross-machine
direction. For some of the materials, light shielding tests
were also conducted. There were fewer test specimens ofType 2 compared to Type 1. Aging of the sheet materials
was evaluated as a function of elapsed years by
calculating elapsed time from the TSS construction date.
It is important to note that the test procedures in Subsections 2.3.2 and 2.3.3 evaluated different specimens.
This is because the timing of collection and detailed
testing conditions were different, even though bothmaterials were collected from the same TSS. The test
results for Sub-sections 2.3.2 and 2.3.3 are described in
Sections 3.2 and 3.3 below, respectively.

3. Results and Discussion
3.1 Accelerated UV Exposure Test
Figure 4 summarizes the tensile curves of the sheet
materials after accelerated UV exposure.
In the GWS sheet body (Type 1’), the tensile strength
first decreased significantly due to fracturing of thesurface textile at a strain of 20 –30 mm, and then thetensile strength based on the non-woven fabric on theunexposed surface reached a maximum at a strain of
90 –100 mm. The tensile strength based on the nonwoven fabric of the unexposed surface did not change
significantly when comparing the unexposed product andthe UV exposure time of 900/1,500/3,000 hours, while
the tensile strength based on the surface textile showed aclear decrease in tensile strength depending on the UV
exposure time. This means that in the whole GWS sheet

A Study on the durability of covering sheets used at temporary storage sites in Fukushima Prefecture

185

Fractures in surface textile

Fig. 4 Tensile curve of GWS and geomembrane after accelerated UV exposure.

(Type 1’) the surface textile was susceptible to UV light
exposure. In addition, the sheet joints also showed a clear
decrease in tensile strength as a function of exposure timeto UV light, which may have been because the structureof the sheet joints peeled off when the surface textile wasfractured.
In GWS Type 2, unlike Type 1’, preferential
deterioration of the surface textile was not observed.
Comparing the unused sheet with the one exposed to UV
light for 900 hours, there was a clear decrease in strength
in both the sheet body and the joint, but the decreases instrength at 1,500 hours and 3,000 hours were less thanthat of sheet joints and surface textile of the Type 1’ sheet

body. There was no significant difference in tensile
strength between the sheet body and the joint.
Unlike in the two types of GWS, there was no clear
reduction in tensile strength of the geomembrane underunused and UV exposure conditions of 900, 1,500 or
3,000 hours. However, a decrease in maximum strain wasshown at 3,000 hours of UV exposure.
The maximum tensile strength of the sheet materials
that underwent accelerated UV-exposure is summarized
in Fig. 5. For GWS Type 1’, the tensile strength of thesurface textile was added to the tensile strength of the
sheet body. After 3,000 hours of accelerated UV
exposure, the maximum tensile strength of the surface

186

Y. TAKAHASHI1 and M. KOISO

Fig. 5 Tensile strength of GWS and geomembrane
after accelerated UV exposure.

Fig. 6 Puncture resistance of GWSs and geomembrane
after accelerated UV exposure.

textile of Type 1’ was about 53% (96.7 [N/cm]) that of theunused material, and the maximum tensile strength of theType 1’ joints was about 20% (32.8 [N/cm]) that of theunused material. On the other hand, the strength of theType 2 joints after 3,000 hours of UV exposure was about
59% (133.6 [N/cm]) that of the unused material. Thisvalue is higher than the standard value (57 [N/cm] after
1,000 hours of accelerated UV exposure) specified in thevoluntary standard of JLSTA.
The results of the puncture resistance tests of the
sheet materials that underwent accelerated UV-exposure
are shown in Fig. 6. Unlike the results of the tensile test
(Fig. 5), both GWSs Type 1’ and Type 2 were found tomeet the standard value even after 3,000 hours ofaccelerated UV exposure (the standard value for GWSs
was 500 [N], while no standard value for geomembrane
had been set) (JLSTA, 2014). This is presumably due tothe non-woven fabric on the unexposed surface retaining
its puncture resistance.
SEM images of GWSs that underwent accelerated
UV-exposure are shown in Fig. 7. The observation targets
were limited to the GWSs, with geomembrane notincluded in this study because no significant strength
reduction had been observed. Regarding both Type 1’ andType 2, the fiber structure of the surface textile wasdamaged after 3,000 hours of accelerated UV exposure.
On the other hand, the microporous membranes of the
GWSs maintained their microstructure after 3,000 hours
of accelerated UV exposure, suggesting that the water
resistance of the GWSs was maintained. We have alreadyconfirmed that after 3,000 hours of accelerated UV
exposure, GWSs types 1’ and 2 met the standard value(1,000 [mmH2O] ≈ 9.81 [kPa]) of the water resistance test
(data not shown), supporting the SEM observation result.
Therefore, GWS Type 2 and the geomembraneretained practical durability (tensile strength, puncture
resistance and water resistance) even after 3,000 hours of

Fig. 7 SEM images of GWSs (types 1’ and 2), unused material and after accelerated UV-exposure (3,000hr).

A Study on the durability of covering sheets used at temporary storage sites in Fukushima Prefecture
accelerated UV exposure equivalent to 10 years of
outdoor use. On the other hand, GWS Type 1’ showed asignificant loss of strength at the surface textile andjoints. This result confirms the fractures in GWS seen in
actual TSS environments (Fig. 1).
3.2 Comparisons among Municipal TSSs
Figure 8 shows the results of the tensile test of GWS
Type 1 and the geomembrane collected from the TSSs
managed by municipalities a, b and c. It was confirmedthat the tensile strength of GWS Type 1 collected from
TSSs (a), (b-1) and (b-2) exceeded the standard value
specified by JLSTA (57 [N/cm]). Considering that unused
Type 1’ material showed a tensile strength of 182.8[N/cm], the deterioration of the tensile strength isconsidered to be limited regarding GWS Type 1 used at
TSSs. In addition, tensile strength of the joints of thegeomembrane in the TSSs of municipalities b and c wasroughly equivalent to tensile strength of the unused sheet(184.2 [N/cm]) shown in Fig. 5, and it was confirmed thatthey maintained sufficient durability. Considering thatthe sheet body of GWS Type 1’ and geomembrane
maintained tensile strength after 3,000 hours ofaccelerated UV exposure (equivalent to 10 years of
outdoor use) as shown in Fig. 5, the results with thematerials used at TSSs are basically consistent with thetendencies of the accelerated UV exposure tests in termsof tensile strength.
Next, the results of the water resistance tests of GWS
Type 1 and geomembrane are shown in Fig. 9. Unlike thetensile tests, water resistance of GWS Type 1 was reduced
to below its standard value (9.81 [kPa]) for most samples.
Many cracks were observed on the microporous
membranes of the GWS by visual observation, which
confirmed the loss of waterproofing performance ofthe microporous membranes (no image). There were nodifferences in water resistance among the GWSs in
TSSs (a), (b-1) and (b-2). However, a few specimens

Fig. 8 Comparison among TSSs (tensile strength of the covering
sheets).

187

collected from the ponding part of the sheet maintained
their water resistance. This is presumably because theponding part of the sheet had less damage from sunlight
exposure (JAG, 2016).
The water resistance of GWS Type 1 was clearly
reduced, while the water resistance of the geomembrane
was maintained. These results indicate that GWS Type 1
used at TSSs for more than two years lost its water
resistance regardless of the location of the installation.
The possibility of fracture of the surface textile and thejoint under UV exposure was indicated in Section 3.1, butthese results show that GWS Type 1 may lose its water
resistance through sunlight exposure even if no fractures
are observed on the surface textile. Although themicroporous membranes did not show any damage under
3,000 hours of accelerated UV exposure (equivalent to 10
years of outdoor use), the water resistance deteriorated
after about two years of sunlight exposure, indicating that
degradation of the GWS in the actual TSS environment
was stimulated by factors not considered in theaccelerated UV exposure tests, such as temperaturechanges between day and night, freezing, creep stress due
to strong wind and others.
3.3 Material Aging
The results of the tensile tests of GWS types 1 and 2
collected from TSSs (b-2) and (b-3) are shown in Fig. 10.
The elapsed time of the tested sheets ranged from 2.6 to
5.5 years. As the results in Section 3.2 (Fig. 8) indicate, it
was confirmed that all specimens met the standard value(57 [N/cm]). While the tensile strength of the sheet bodywas roughly constant over time, the tensile strength of the
sheet joints had a tendency to decrease with time.
Figure 11 shows the results of the water resistancetest of the same GWS. Similar to the results in Section
3.2 (Fig. 9), these results show that GWS Type 1 lost its
water resistance after 2.5 years of use at the TSS. On theother hand, the water resistance of GWS Type 2 wasFig. 9 Comparison among TSSs (water resistance of covering
sheets).
(Results for samples below the lower measurement limit aremarked as zero.)188

Y. TAKAHASHI1 and M. KOISO

Fig. 10 
Relationship between elapsed years and tensile
strength of GWSs used at TSSs (arrow indicatesType 2; the rest are Type 1).

Fig. 11 
Relationship between elapsed years and water
resistance of GWSs used at TSSs (arrow indicatesType 2; the rest are Type 1).

found to be maintained after about three years of use.
SEM images of GWS types 1 and 2 collected from
TSSs (b-2) and (b-3) are shown in Fig. 12. Comparedwith the SEM images of the materials after accelerated
UV exposure shown in Fig. 7, the materials used at the
TSSs showed damage not only to the surface textile but
also to the internal microporous membrane. Many cracks
with width exceeding 50 μm were found on the
microporous membrane of Type 1, which clearly
indicated its structural failure. This observation confirms
the test results in Figs. 9 and 11. On the other hand, GWS
Type 2 had voids of less than 10 –50 μm in diametercompared to the unused sheet, indicating damage to themicroporous membrane structure. The damage in Type 2
was limited compared to that in Type 1, which confirms
the result of the water resistance test of GWS Type 2
shown in Fig. 11. These results show that the water
resistance of GWS Type 1 decreased after about 2.5 yearsof use, while Type 2 maintained its water resistance undersimilar conditions.
To investigate differences in weatherability between
Type 1 and Type 2, light shielding tests of the GWSs
were conducted and the results are shown in Table 2.
The results show that the light shielding ratio of the
GWSs (entire sheet) was 100%, and the ratio of thesurface textile removed from the GWSs was more than
99.9%. There was almost no difference between Type 1
and Type 2. These results suggest that the difference inweatherability between Type 1 and Type 2 does
not depend on the shading performance of the
non-woven fabric, but is influenced by other factors, suchas adiabatic performance and mechanical properties of
the non-woven fabric.

Fig. 12 SEM images of GWSs (types 1 and 2), unused or used at TSSs for three years.

A Study on the durability of covering sheets used at temporary storage sites in Fukushima Prefecture
Table 2 Light shielding ratio of GWSs (types 1 and 2) used at TSSs.

Surface textile

Entire sheet

SampleElapsed time[years]1

2

3

Average[%]

GWS (Type 1)

5.5

99.97 99.93 99.82

99.91

GWS (Type 2)

2.899.94 99.95 99.94

99.95

GWS (Type 1)

4.4

100 99.99 99.99

100

GWS (Type 2)

2.8

100

100

100

100

4. Summary and Conclusion
The durability of covering sheet materials after
accelerated UV exposure or sunlight exposure for two to
six years at TSSs for decontamination soil and waste in
Fukushima Prefecture was investigated. The GWSs
showed clear decreases in tensile strength and water
resistance, while the geomembrane did not change
significantly over time at the TSSs. In particular, thedecrease in water resistance was difficult to judge fromthe appearance of the sheet materials, and the possibilityof rainwater intrusion into the storage containers under
the sheet needs to be taken into consideration for proper
management of TSSs. Our experimental results show thatthe water resistance of GWS Type 1 was more severely
reduced by use at a TSS for 2.5 years than by accelerated
UV exposure equivalent to 10 years of outdoor use,suggesting that the deterioration rate at TSSs is
accelerated by factors not considered in the accelerated
UV exposure tests (e.g., temperature differences between
day and night, creep stress from strong winds, etc.).
Meanwhile, GWS Type 2 had a limited loss of strengthcompared to Type 1 and maintained its water resistanceeven after three years of use at TSSs.
The number of TSSs in Fukushima Prefecture has
already peaked, and the phase of TSS restoration to theoriginal state rather than managing them has begun. On
the other hand, there are still some TSSs outside of
Fukushima Prefecture where plans for transporting thewaste have not been developed. Technical issues regarding
decontamination soil and waste from decontamination
work still require a long time and continuous research toresolve before completing their final disposal.

Acknowledgement
In this study, collection of the samples tested andmeasurement of data were conducted with support fromthe municipalities maintaining TSSs (especially Nishigo
Village and Iwaki City). Also, some of the experiments inthis study were conducted with support from the
Fukushima Technology Centre. We would like to express
our gratitude to them.

189

References:
Fukushima Prefectural Government, Japan (FPG) (2019) Technicalguidelines for temporary storage sites, 6th Edition. Retrieved
from https://www.pref.fukushima.lg.jp/site/portal/kariokibagijutsushishin.html (Accessed 25 September 2020)
Japan Chapter of International Geosynthetics Society (JIGS)(2016) Manual of geomembrane for temporary storage sites ofwaste from decontamination work, 2nd Edition.
Japan Lining Systems and Technology Association (JLSTA) (2014)
Voluntary standards for covering and bottom sheet in on-sitestorage sites and temporary storage sites, 3rd Edition. Retrieved
from http://www.nisshakyo.gr.jp/kijyun_rev3.pdf (Accessed 25
September 2020)
Japanese Association of Geosynthetics (JAG) (2016) Efforts forproper storage of decontaminated waste: Gas permeable
waterproof sheet, 78–89. Retrieved from http://geo-ken.jp/pdf/
tekiseihokan_all.pdf (Accessed 25 September 2020)
Japanese Industrial Standards Committee (JISC) (2007) JIS B
7753:2007 Light-exposure and light-and-water-exposure apparatus(Open-flame carbon-arc type).
Ministry of the Environment, Government of Japan (MOE)(2013) Guidelines for waste from decontamination work, 2nd
Edition. Retrieved from https://www.env.go.jp/jishin/rmp/attach/haikibutsu-gl04_ver2.pdf (Accessed 25 September 2020).
Ministry of the Environment, Government of Japan (2015) Aboutmaintenance of temporary storage site. The 15th Review meetingfor environmental restoration. (in Japanese) Retrieved fromhttp://www.env.go.jp/jishin/rmp/conf/15/mat02-1.pdf (Accessed
25 September 2020)
Ministry of the Environment, Government of Japan (2016)
Conference note of the 17th review meeting for environmental
restoration, p.30. Retrieved from http://www.env.go.jp/jishin/
rmp/conf/17-gijiroku.pdf (Accessed 25 September 2020)
Ministry of the Environment, Government of Japan (MOE) (2018)
Decontamination Guidelines, 2nd Edition. Retrieved from http://
josen.env.go.jp/material/pdf/josen-gl-full_ver2_supplement_
1803.pdf (Accessed 25 September 2020)
Ministry of the Environment, Government of Japan (MOE) (2020)
Information centre for interim storage site, About transportationof removed soil, etc. Retrieved from http://josen.env.go.jp/
chukanchozou/transportation/ (Accessed 6 October 2020)
Nishimura, M., Akai, T. and Kamon, M. (2012) Durability andcharacteristics on seam of gas-permeable/waterproof sheet for
landfill cap cover. Geosynthetics Engineering Journal of Japan.
Retrieved from https://www.jstage.jst.go.jp/article/jcigsjournal/
27/0/27_47/_article/-char/ja (Accessed 25 September 2020)
Public Works Research Center (PWRC) (2012) Design andinstallation manual for the stacking method of large weatherresistant sandbags. Retrieved from http://www.pwrc.or.jp/books/
book_030.html (Accessed 17 April 2021)
Takahashi, Y. (2018) Study on long-term durability of flexible
containers at temporary storage site of removed soil, etc. in
Fukushima prefecture. Geosynthetics Technical Information, 34(2), 4.
Takahashi, Y., Sawai, H. and Nishimura, M. (2019) Study on longterm durability of the polymeric materials used at temporarystorage site in Fukushima Prefecture. 18th Global Joint Seminaron Geo-Environmental Engineering, 82.

190

Y. TAKAHASHI1 and M. KOISO

Yusuke TAKAHASHI
Yusuke Takahashi is a postdoctoral fellow at the
National Institute for Environmental Studies,Japan. He specializes in analyzing the degradation
behavior of plastic materials. He is elucidating thedegradation process of civil engineering materials
such as water-proof sheets and flexible containers
used in temporary storage sites. His research has
contributed to the proper management of decontamination waste generated
in Fukushima Prefecture. He is currently working on developing methods
to predict fragmentation behavior of degraded plastics.

Masahiro KOISO
Masahiro Koiso is a researcher in the Research
Department of the Fukushima Prefectural Centre
for Environmental Creation. He specializes inmeasures for handling technical issues at
temporary storage sites for wastes generated fromdecontamination activities in Fukushima
Prefecture. The research results he has obtained
are contributing to the proper management of decontamination waste
generated in Fukushima Prefecture. Currently, he is conducting research on
how to address technical issues involved in restoring former temporarystorage sites to their original state.

(Received 9 October 2020, Accepted 27 December 2020)

191

Promoting Local Revitalization to Solve Issues on Degraded Forests
in Japan: A Case Study in Oku-Aizu, Fukushima
Makoto OOBA*, Shogo NAKAMURA and Takuya TOGAWA
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: ooba.makoto@nies.go.jp

Abstract
The degradation of forest ecosystems due to depopulation, aging and economic depression of industries
in rural areas, has been extensively discussed, while at the same time, increased demand for renewable energy
from woody biomass has resulted in much attention to forestry and rural areas. This study provides an
overview of regional circulation in a small woody biomass energy system in a typical Japanese rural area,
Mishima Town, Fukushima Prefecture. To resolve the problem of forest degradation, two issues (energy andforests) in the study area are focused on and discussed in light of the national-level background. We havederived two constraints (circulation radius and feasible size) and conducted four research activities (focused
respectively on forest resources, production, energy infrastructure and the social system and scenarios) for
local revitalization. To address implementation of an energy system, Mishima Town established a council thathas working groups strongly related to our research activities. Finally, it can be stressed that the goal of our
project is identical to the concept of "regional circular and ecological spheres" (regional CESs).
Key words :	cogeneration system, forest management, regional circulation, renewable energy,
woody biomass

1. Introduction
The degradation of forest ecosystems has been
extensively discussed in Japan. This degradation can be
attributed to decreasing population in rural areas and a
decline in local industrial activity, as well as to synergistic
effects arising from these factors. Meanwhile, power
generation from woody biomass has gained attention
because of the renewable energy feed-in tariff (FIT)
system implemented in 2011 after Japan’s nuclear disaster(METI, 2017). Increased demand for woody biomass canresult in higher biomass production and promote forest
harvesting. The latter includes forest carbon sinks andsites where carbon dioxide is absorbed, leading to climatechange mitigation and implementation of policies tosubstitute biomass fuel for fossil fuels.
However, the FIT system is based on large biomass
power plants, which may require an annual supply in thetens of thousands of tons of woody-biomass (Sakai et al.,2017). This implies that biomass procurement from local
forests to produce fuel should require sustainablemeasures assessed through planned deforestation.
Although FIT is a policy aiming to promote thedevelopment and installation of renewable energy at theinitial stage, the permanence of high purchase prices
compared to the price of electricity from conventional
Global Environmental Research
24/2020: 191-198
printed in Japan

electric power companies is not guaranteed. After 2017,
new solar power-generation facilities of 2,000 kW
production or higher were no longer eligible for FITs (andthat number was lowered to 500 kW in 2019). Although
future power plants will need to operate on wholesale andretail schemes, it is difficult to implement them in largescale domestic woody-biomass power plants. Thus,
almost all of them will need to expect conditions ofreliance on use of the FIT system.
This study addresses general issues related toJapanese forests and describes the efforts that have been
conducted to achieve local revitalization and provide
solutions for environmental problems. Subsequently, it
discusses the adoption of renewable energy in Japan
within the context of woody biomass and explores
socioeconomic constraints on the use of forest resources
as a modern energy source. Then it provides an overview
of the regional circulation in a small combined heat andpower (CHP) woody biomass energy system, which is thegoal of this study. It describes the initiatives proposed in
Mishima Town, Fukushima Prefecture, and their current
results. Finally, it addresses the convergence of these
initiatives with similar ones, such as the Regional
Circular and Ecological Spheres (CESs) and Sustainable
Development Goals (SDGs).

©2020 AIRES

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M. OOBA et al.

2. Issues Affecting Forests in JapanDue to a lack of timber for construction in the 1960s,
Japan made a major transition from firewood and naturalforests to plantation forests. However, timber importation
regulations were relaxed and price competition arose
between domestic and imported timber. As a result,timber prices decreased, resulting in difficulties fordomestic forestry industries. Labor forces have declined
due to aging, and there has been a population decrease inrural and mountainous areas; thus a shortage of workers
able to manage forests has arisen. Moreover, someplantation forests were not well managed before the FIT
system was introduced for timber production. The
management rate of these forests was approximately 45%(Amano, 2007).
Forests have various ecological functions, and theirbenefits to human society have ecosystemic importance(ecosystem services). The functions of forest ecosystems
include prevention of sediment discharge, headwater
conservation, water purification, carbon absorption,
timber and forest product supply, and biodiversity
conservation. These functional issues are affected(quantitatively and qualitatively) by forest management
and the degree of forest conservation. Well-managed
forest ecosystems exhibit higher carbon absorption rates(Hiroshima & Nakajima, 2006) and improved
photosynthesis rates after thinning (Han & Chiba, 2009).
In contrast, soils in unmanaged forests have lower waterholding capabilities and exhibit erosion (Miyata et al.,2009).
Those conditions currently prevail because of theincreased demand for biomass power plants. Because
clear-cutting is simpler to implement than thinning, andreforestation is difficult due to economic and laborfactors, resource depletion could potentially occur due tothe lack of adequate systems for achieving a managed
degree of logging and reforestation in the affected forests.
In addition to the amount of resources available, theeffects of ecosystem functions have major impacts onenvironmental issues such as disaster prevention.
In 2019, the Forestry Agency launched the New
Forest Management System, which establisheddistinctions between forest ownership and forest
management, thereby encouraging harvesting by
operators interested in promoting municipal forest
management (Forestry Agency of Japan, 2020; Uchiyama& Kohsaka, 2020). Currently, an economic andsustainable framework for forestry at the municipality
level needs to be developed as soon as possible,
considering the advantages of that system.

3. Renewable Energy and Regional Circulation
3.1 Renewable Energy in Japan
After the first oil crisis (1973), Japan’s dependence

on foreign energy sources became evident along withenvironmental issues due to the use of fossil fuels (airpollution and greenhouse gas emissions). Thus
development of novel energy sources was initiated,aiming to solve those problems. “New energy” is a term
used in Japan in a unique context because it refers to nonfossil fuels under the Act on the Promotion of New
Energy Usage (New Energy Act). Currently, the definition
by law is similar to that of the renewable energy concept,
including biomass, solar thermal energy, snow and ice
thermal energy, along with geothermal, wind and solar
power generation.
The Great East Japan Earthquake and consequent
nuclear disaster in 2011 became an opportunity for Japanto reconsider its energy sources. In addition to theexisting trend in “fossil-free” sources for international
security reasons, Japan considered renewable energy atthat time as a means of decentralizing energy andmanaging local resources well autonomously. In addition,international treaties related to climate change haveprogressed, and promoting renewable energy is consistent
with global agreements to phase out carbon energy andreduce future climate risks, according to the Paris
Agreement. Although solar power was initiallyconsidered as a potential source of renewable energy,
power generation from un-utilized woody resources has
attracted attention, as it also maintains a relatively highpurchasing price under the current system.
3.2 Regional Use of Woody Biomass and its
Constraints
Historically, woody biomass has been used not only
as construction material but also as an energy source. In
Japan, firewood and charcoal were widely used as energy
sources before households turned to fossil fuels in thefirst half of the 20th century (Totman, 1995). Additionally,
firewood forests were located around populated areas.
Currently, however, profits from woody biomass as anenergy source have not returned to their earlier values.
Households need energy for a variety of purposes
and high amounts of energy are consumed. In the past,
the energy demand in Japan arose primarily for warmth,
hot water, and cooking. Nowadays, there is also demandfor cooling, equipment operation and transportation,
which are powered by electricity and fossil fuels (diesel
fuel and gasoline). Consequently, energy demand in thepast was low compared to current requirements. For
instance, the annual electricity consumption in Fukushima
6
Prefecture is 17,207 × 10 kWh (as per the 2010 record
before the earthquake), which represents 6.757 × 106 tonsof woody biomass in terms of heat demand. That amountis approximately four times the joint timber volume fromplantation forests in the five towns and villages aroundMishima. Togawa et al. (2019) also indicate such large
demands (14,000 tons/y in the case of maximum use ofwoody biomass) that is supplied only to Mishima

Promoting local revitalization to solve issues on degraded forests in Japan: a case study in Oku-Aizu, Fukushima 193
compared to the potential supply of woody biomass(4,000 tons/y). Converting that volume of resources into
energy would lead to forest depletion in less than threemonths. In contrast, approximately 40 years would be
required before harvesting a standard cedar forest.
One difficulty with woody biomass energy
applications is the geographical limitation caused by theneed for transporting materials from the supply area tothe production area. To benefit from regional resources,
including forest reserves, we should consider a“circulation radius” (Fig. 1) that is socioeconomically
viable. The radius has been studied in the context ofwaste collection areas (e.g., Fig. 5 in Ohnishi et al.,2016). Although the present study area has an abundanceof forest resources, there is a maximum limit regardingtransportation distances of raw biomass corresponding to
50–125 km based on previous studies (e.g., for largescale power plants in Hokkaido, Sakai et al., 2017).
Furthermore, when a resource is considered an energy
source, the range that electricity generated from it canreach using self-operated power lines is limited to a few
kilometers due to economic constraints (Agency for
Natural Resources and Energy, 2019; e.g., for casestudies, Shima & Nose, 2014; Haruta & Muraki, 2017).
Electricity(Local distribution)

SecondHeat
Woody
Biomass
Raw woodYear

Time scale

Day

Forest resources
100m

1km

10km

100km

Distance

Fig. 1 Circular radius (geographical) and life span (temporal) of
local resources (see text).

Similarly, the supply range when using self-operated
pipes for thermal energy is a few hundred meters.
Regarding electricity, it is possible to transport power
generated by a small local power plant through a power
grid owned by a regional power company that operates
across a larger area. Grid-use fees, however, would be
included in the retail electricity price, which would not be
economical for consumers. Obtaining profits fromregional resources requires socioeconomic principles thatmaintain this “circulation radius.” On a temporal scale,the life spans of local resources should be also
considered. For example, electricity must be consumed
immediately after power generation, while woody
biomass in forest stands can be saved (or grown) for thelong term.
Therefore, utilizing forest resources is not enough toresolve forest and energy issues entirely in a modern
society. That conclusion, however, is based on anassumption of unrestricted forest usage and energy
consumption in an environment where only market
competition exists. We have derived that it may bepossible to construct a system that can provide solutions
to biomass usage and forest issues according to two
constraints described as follows:[1] The geographic and temporal range that allows forresource circulation is limited.
[2] Facilities of feasible size within that range arelimited.
These constraints were not explicit at the beginning of
our research in local areas but rather were establishedmore clearly as our research progressed.

4. Case Study: Mishima Town
4.1 Location and Forests
Oku-Aizu and Mishima in Fukushima Prefecture aresnowy areas located in the southwest region of Aizu,
close to the border with Niigata Prefecture (Fig. 2).

Fig. 2 Location of the Oku-Aizu region and Mishima Town.

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M. OOBA et al.

According to the Automated Meteorological Data
Acquisition System (AMeDAS) in Kaneyama (a town
located next to Mishima), the average annual temperaturein the area is 10.4°C, the annual rainfall is 2,020 mm, andthe maximum snow depth is 177 cm. Because Mishima
has a robust water supply due to snowmelt, the TadamiRiver has been used as a power source since the end ofWorld War II. At that time, Mishima’s population wasover 7,000. Its current population, though, is less than
1,600, and Mishima exhibits one of the highest aging
rates (53.0%) in Fukushima Prefecture.
The general environmental issues of Japan also
affect Mishima, as forests cover 88% of its total area.
While the town has a wealth of forest resources, cedar
forests, which account for almost all of the privatelyowned forest land, are often owned by small-scaleowners. There is also a lack of clarity regarding theownership of these lands. Timber prices have remained
low for approximately 50 years, and not enough thinningor materials production have been conducted.
Furthermore, the timber produced in the Aizu region
presents issues, such as bending or excessive knots,
rendering it a low-quality product in Japan.
The results of a questionnaire survey on forestrelated awareness in Mishima (Nakamura & Togawa,2020) showed that local people perceive that a
combination of issues, such as the delineation ofboundaries to subdivide forests and unclear ownership,leads to forest degradation. The details of this survey are
discussed below.
Some areas of Mishima have adopted the Fukushima
Forest Restoration Project (Fukushima Prefecture, 2018),
which was implemented by the prefecture after theearthquake and nuclear accident. Future benefits fromassessment of knowledge on forest boundaries throughthe project are expected.
4.2 Toward Renewable Energy from Forests
Aiming to promote forest management and profits
from woody biomass, Mishima formulated the Mishima
New Energy Vision Program in February 2006 and theDetailed Mishima New Energy Vision Program thefollowing year. In particular, these programs proposed
replacing petroleum-based boilers and stoves with units
that can handle easy-to-use pellets as combustible sources
to make use of the town's abundant forest resources. In
cooperation with nearby towns and villages (Yanaizu,
Kaneyama, Showa and Tadami), the Oku-Aizu FiveTowns Revitalization Council was established in April
2010 to achieve biomass utilization. However, the Tohoku
Earthquake in 2011 and major damage from torrential
rains in Niigata and Fukushima have contributed todecreased biomass processing.
The chambers of commerce of 13 cities, towns andvillages in the Aizu area worked together to establish the
Aizu 13 Project Council in 2016, with the participation ofMishima Town and its Chamber of Commerce. The goalof the project was to expand production of materials fromthe Aizu area, obtaining high-performance plywood
materials, and additionally biomass as energy fuelsources. The project is currently being managed andactively implemented by both the Aizu Forest Resource
Utilization Promotion Council and the Aizu Forest
Utilization Organization, based on collaboration with thenational governmental. Our project was affectedindirectly by the Aizu 13 project, but it was not directly
connected to the project.
4.3 Research Activities and Their Outputs
The Fukushima branch of the National Institute forEnvironmental Studies (NIES) holds surveys andperforms studies which are assessed primarily by regional
development researchers. It also conducts collaborative
research with specialists from other universities andinstitutes. To ensure and promote regional research, NIES
signed a collaborative agreement (memorandum of
understanding) with Mishima Town in 2017.
With constraints [1] and [2] in mind, the researchteam listed problems in Mishima and the surroundingarea, initiatives to solve those problems, the effects of theinitiatives, and details regarding the research required toaddress those effects (Table 1).
Further details on the research activities in Table 1
are provided below.
4.3.1 D etailed Survey of Forest Resources, Questionnaire
Survey on Forest-related Awareness
The first problem that arises in forest resource usageis that forest boundaries are frequently not well-definedor geographically accurate, as required for forestry
practices. Furthermore, most forests are unmanaged, andthe actual timber volume of the forest is unknown.
To reconfirm forest boundaries and estimate amountsof resources, we used a drone to take aerial images andlaser measurements. We studied a forest area ofapproximately two hectares in a commonly owned forest
in the Mishima area, contributing to understanding by theresidents. The aerial images and laser measurements weretaken in August 2019, whereas the field studies wereconducted in February and May of 2020 (Fig. 3). With
the cooperation of the Graduate School of Engineering at
Osaka University, we used 3D-point cloud data toestimate tree top positions and crown sizes for each tree
through machine learning. After its use in an initial
analysis and validation, this technique continued to be
improved for accuracy. These data show the amount ofeach type of tree located in each owner's forest and theavailable timber volume. In addition, the detailed aerial
images and point cloud data may also be useful indefining boundaries of forest ownerships and planning
forest practices. Data are currently being compiled forpresentation to the residents of the town and the region.

Promoting local revitalization to solve issues on degraded forests in Japan: a case study in Oku-Aizu, Fukushima 195
Table 1 Problems and related initiatives in Mishima and its surrounding area.
ProblemInitiative

EffectSecondary effectResearch contribution(1) Forest
degradation

Forest management

Forest consolidation, stabilized
production, and reforestation

Disaster prevention,
environmental conservation, andcarbon sink development(2) Decline of
the forestry
industry(3) Reliance on
external energy
sources(4) Economic
decline of local
communities

Promotion of the forestry
industry

Development of raw wood
production with hi techmachineries
Introduction of small CHP,
attracting demand for thermalenergyPromotion of local cooperation

Revitalization of local demandand development of humanresources
Provision of low-cost energy,
energy security, and attraction ofprojects that use thermal energy
Revitalization of local
communities/economies

A detailed survey of forest
resources and questionnaire
survey on forest-related
awareness
Estimation of potential
production and analysis of
the resource circulation area
Energy conversion
technology and a detailed
survey of energy demand
Community system theory
and research on futurecommunity scenarios

Utilization of woody
biomass
Industry, government, andprivate sector initiatives(establishment of councils
and study groups)

about subsidies they would need to keep managing theirown forests, we obtained several answers related tofinancial issues (timber prices/supply chain: 56 responses,
logging/transportation subsidies: 30 responses), as well as
80 responses related to boundary definition/forest roaddevelopment.
This survey received significant attention fromresidents regarding disaster prevention and reduced forest
functionality. Although the Great Tohoku Earthquake andnuclear disaster in 2011 had little impact on the region,
torrential rain and flooding occurred in the same year.
The relationship between forests, landslides and floods isunderstood well in this region, and biomass utilizationplans should be considered.

Fig. 3 (a) LiDAR image (cross section and overview) (b) Data
processing images images (detection of tree crowns and treetops).

This will also lead to higher consolidation and better
forest land management.
Additionally, a questionnaire survey on forest-related
awareness was conducted in 2018 (Nakamura & Togawa,2020). We randomly selected 599 Mishima residents(aged 18 or older) and obtained responses from 264
people (44.1% response rate). The results showed that
76% of the respondents knew the location of the forest
they owned, and only 58% were aware of its boundaries,
indicating a need to reconfirm boundaries. However,
because most owners did not manage their forests, when
asked about owners’ management difficulties, theymentioned “low timber prices” as the most frequent
response, followed by “lack of manpower,” “undeveloped
work roads,” and “unclear boundaries.” Another common
response was “aging of the population.” When asked

4.3.2 Estimation of the Production Potential andResource Circulation Area
A study on the biomass potential of privately owned
forests in the Oku-Aizu area (Ooba et al., 2018) produceda cost analysis of chip production to obtain energy(including logging and transportation). It demonstrated
that, for forestland with extremely low management rates(percent of area managed annually: 0.36% per year), chipproduction to obtain energy was not possible from an
economic viewpoint. However, the study showed that it
might be possible to produce chips at a cost of 7,000
3
JPY/m or less (in a scenario where the amount harvested
was increased by conducting extensive thinning) and that
future production could be ramped up to approximately
10,000 m3.
 nergy Conversion Technology, a Detailed Survey
4.3.3 Eon Energy Demand
The feasibility of implementing a biomass energy
system was also studied at typical hot spring facilities in
the region (Togawa et al., 2018). Based on data from asurvey jointly conducted with Mishima, energy demandby season and time was estimated in facilities along theTadami River. It was demonstrated that a small biomass
co-generation system (operating continuously during all
seasons) would consume approximately 700 tons/year of

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M. OOBA et al.

woody biomass. However, when the economics of this
scenario were analyzed, there were concerns about
profitability.
We installed Home Energy Management Systems(HEMS) in Mishima Town, which are currently studying
the actual energy consumption of houses in the cold
Oku-Aizu region and modeling that consumption. Fromthese data, energy charts for each community in Mishima(Togawa et al., 2019) were prepared and efforts toestimate the distributed energy systems’ potential in termsof demand were conducted (Fig. 4).
Based on this research, Mishima used a subsidy forpromoting smart communities from Fukushima Prefecture
to conduct a foundational study (pre-feasibility study, FS)
in 2017 with a company, Nippon Koei Co., Ltd., onenergy production for local demand using local resources,
such as woody biomass in Mishima. In a study performed
by a different welfare institution, a scenario in whichelectricity was sold to an electric company under the FIT
system resulted in a profitable business and an estimatedbiomass consumption of approximately 800 tons/year.
4.3.4 Social System Theory and Research on Future
Social Scenarios
Constraints [1] and [2], as well as the research
described above, suggested that in Mishima, woody
biomass materials can only be produced as fuel sources at
a relatively small scale. This implies that the town needs
a community system centered on introducing CHP
systems with an electricity output of 50 kW or less. In
addition, we may surmise that it would be realistic to start
the project up relying on the current FIT system to someGeographicaland social
information
on target
settlement

Penetration
rates ofheating andcooling facilities,
boilers,
photovoltaic
panels, etc.

extent to ensure business revenues.
As a starting point for social implementation, in
2018, Mishima Town implemented small initiatives as afirst step towards promoting woody biomass utilization.
One of those initiatives was a Tree Station-style program,which has also been conducted by many municipalities
and non-profit organizations, collecting firewood in
3
December. In Mishima, 1 m of logs can be exchanged
for 4,500 JPY in local gift certificates. The heating andcooling system of the Mishima Local Crafts Museum, acore institution that shares the town’s braided handicrafts
tradition, was switched to a system based on a wood-fired
boiler. This fuel is produced from firewood collected in
Mishima using the method mentioned above.
The research team has not only promoted
collaborative-scientific research in Mishima but has also
held collaborative research meetings with civilengineering, architecture and regional policy officials atleast once a month. Additionally, we have also provided
our research results to the Mishima Town Forestry Policy
Development Committee, through on-demand lectures in
Mishima and public meetings that brought stakeholders
together.
To address the implementation of an energy system,in 2019, the NIES proposed that Mishima establish acouncil. This council would divide tasks related to woody
biomass utilization issues into forest/energy productionrelated (supply-related) and energy-consumption tasks,
and form working groups with stakeholders comprised ofboth local and external parties that could consolidate theopinions of the higher-level coordination council andmake decisions. Therefore, Mishima and four surrounding

Heat and
electricity
demands(monthly andseasonally)

Analyticalresults(Proposals forfacilities andmitigationof climatechange)Fig. 4 Visualization of the current and recommended energy systems in each settlement in Mishima Town (a) Heat and electricity
demands (b) Analytical results: proposals for facilities and decreased CO2 emissions.

Promoting local revitalization to solve issues on degraded forests in Japan: a case study in Oku-Aizu, Fukushima 197
towns established the Oku Aizu Five Towns and Villages
Revitalization Council with a subsidy from the Ministryof the Environment. The council is currently making
efforts to develop an energy system that relies on the useof municipal facilities.

5. Concluding Remarks
The Fifth Basic Environmental Plan approved by the
Cabinet in 2018 focuses on the concept of “regional
circular and ecological spheres” (regional CESs, MOE,
2020). Contributing to that plan, the Ministry of theEnvironment has elaborated several projects based onmodel cases of regional CESs. This concept can beconsidered an integrative version of conventional socialconsciousness environmental goals, such as low-carbon
or decarbonizing societies, recycling-oriented societies,
and harmonious relationships with nature. The
achievement of regional CESs infers the embodiment of
the SDGs. Woody biomass usage, as presented by thisproject in Mishima and the Oku-Aizu region, has thepotential to create a society that can achieve such goals(Fig. 5).
In addition to academic and technological support,
this project will require public-private partnerships.
Several businesses and non-profit organizations in
Mishima are enthusiastic about renewable energy andwoody biomass usage. Creating more effective andsustainable biomass, as well as regional economic
circulation, will require higher logging than predictedfrom the energy center studies and FSs conducted so far.
The amount of wood available for logging is limited,

ForestPromotingDecreased
Management costs
Forestry

however, (and the energy demand is predicted to besignificant). Local operators using local resources willconduct this biomass supply project; therefore, we would
assume that the energy system the town might install
could be a relatively small one and that the service area
could be a district of Mishima (a community). Although
it is small-scale, implementing this community
revitalization energy project will not only ensure
economic profits for the community, but also havedefinite secondary effects in terms of the development ofindustrial and human resources and stable local
employment. This project would have a significant
impact as a local service and could also be an initial step
towards promoting future projects addressing a wider
range of social services, similar to Germany’s Stadtwerke
project (Ando, 2019) and responding to the problems ofdepopulation and aging. This demonstrates the potentialof the project to scale into a major sector in the rural
regions.
We plan to continue our research on sustainableregions like regional CESs, ensuring that the local needs
are considered through their potential environmental
effects, which allows for an integrated approach.
Furthermore, a thorough estimation of future full-scalebiomass utilization is required, considering its impacts on
the Oku-Aizu forests, where the vegetation has remained
unchanged for several decades. We are also planning tobegin research on adaptation to climate change in the
Oku-Aizu region, including a survey aimed at creatinghazard maps for landslides and other disasters, while
actively providing information to local governments.

Promoting
Sustainable Woody Biomass Use
supplies

Supply of heatand electricity
More return toforest ownerConservation of
ecosystems

Wood material

Sustainable
demands

Renewable
Mitigation ofenergyclimate change
Prevention ofdisasters
HEMS, CEMS, IoT

Housing
construction

Circular- andBio-economy

Public facilities

Distributed
energysystemPromotingRegional
Business

Regional
Collaboration

Smart control
Fig. 5 Sustainable revitalization inside Oku-Aizu through the regional circulation of local resources from production
to distribution and consumption as the goal of “regional circular and ecological spheres” (CESs).

198

M. OOBA et al.

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M. (2019) Design of distributed energy system considering village
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Makoto OOBA
Dr. Ooba heads the Environmental Renovation
Laboratory at the Fukushima Branch of the
National Institute for Environmental Studies,Japan. From 2007 to 2012 and from 2014 to thepresent, he has participated in a study on spatialassessment of Japan’s regional forests using
process-based models and remote sensing by
NIES. Based on these studies, he has analyzed sustainability of forestry andharvested wood products. He has also worked at Osaka University, Nagoya
University and the Tokyo University of Agriculture. He holds a Ph.D. inenvironmental science from Hokkaido University, 2002.

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch. He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Takuya TOGAWA
Takuya Togawa is a senior researcher at the
National Institute for Environmental Studies,
Fukushima Branch. He received his doctorate inengineering from the Graduate School ofEnvironmental Studies, Nagoya University in2010. He is engaged in research on mechanisms
for realizing disaster recovery and regional
revitalization by effectively utilizing local environmental resources.
(Received 10 October 2020, Accepted 29 December)

199

Smart Community Recovering from the Tsunami-Disaster:Case Study of the Community Energy Supply Projectin Shinchi Town, Fukushima
Yujiro HIRANO1*, Shogo NAKAMURA1, Takuya TOGAWA1, Tsuyoshi FUJITA2
and Kenichi ADACHI 3
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Center for Social and Environmental Systems Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan
3
Japan Environment Systems Co., Ltd.
5-5-5 Koishikawa, Bunkyo-ku, Tokyo, 112-0002, Japan*E-mail: yhirano@nies.go.jp
1

Abstract
The present study was aimed at investigating urban reconstruction development in Shinchi Town, which
is located on the northeastern coastal edge of Fukushima Prefecture. Shinchi Town experienced major damage
from the Great East Japan Earthquake in 2011. Thereafter, an environmentally friendly community energy
supply system was planned and introduced as a core project for reconstruction of the town. The National
Institute for Environmental Studies, Japan, provided academic support for designing and planning of systems,
determining energy conservation and CO2 emission reduction, and feasibility studies. As a part of the project,
a community-based energy organization, named Shinchi Smart Energy, was newly established near the town’s
rebuilt railway station. This organization supplies electric power and heat energy in the area undergoingredevelopment around the station. Shinchi Smart Energy employs a cogeneration system that uses waste heatfrom electricity generation for heating and hot water provision and an absorption chiller (Genelink), whichuses waste heat to chill water for air conditioning, enabling high-efficiency energy management. Evaluationof the project reveals that it is being properly operated at this stage, although the facilities on the demand side
have not been fully completed since the arrival of COVID-19 and the resulting socioeconomic impacts. Futurestudies will focus on furthering the introduction of renewable energy and expanding the area receiving thepower supply in Shinchi Town, as well as spreading the knowledge gained from this town to other areas.
Key words :	CO2 emission reduction, cogeneration, community energy management,
distributed power source, district heating and cooling, reconstruction town development

1. Introduction
The Great East Japan Earthquake (GEJE), which
occurred in 2011, was the first major disaster experienced
by Japan since its population began declining. Afterprevious similar disasters, urban reconstruction plans
were made, aimed at extensive urban expansion with thegoal of providing substitutive town functions to thedamaged districts. The GEJE, however, accelerated the
depopulation trend, especially outmigration, fromdisaster areas that were already scarcely populated even
before the GEJE, resulting in further population decline
in the region. It has already been argued that in Japan,
population decline is causing deterioration of central
Global Environmental Research
24/2020: 199-206
printed in Japan

districts and sprawling decentralization of towns andcities, which increases their CO2 emissions per capita
and makes them less carbon efficient; these observations
have been confirmed in the case of municipalities indisaster-prevalent areas. Hence, municipalities undergoingreconstruction focus on developing compact cities
characterized by higher traffic efficiency and higher
housing density, thereby increasing efficiency in terms of
reducing air conditioning load and optimizing the heat
supply. Furthermore, CO2 reduction is also attained via
efficient local energy systems employed for cooling andheating buildings. A number of disaster-affected municipal
governments have created a basis for residential andcommercial activities in the reconstruction process by©2020 AIRES

200

Y. HIRANO et al.

redeveloping into compact cities with more efficientenergy supply and demand in the local system (Hayashi,
2014; Kitakaze, 2016).
The situation regarding energy use has changed
significantly since the GEJE (Komiyama & Fujii, 2012;
Benjamin, 2014; Zhang and Mclellan, 2014). Before
the GEJE, reducing CO2 emissions was an important
policy issue for medium-to-long-term global warming
countermeasures. After the event, however, not only haveglobal warming countermeasures been considered, butalso policy issues on energy. The government has
implemented several power-saving measures to mitigate
peak loading of the power system; these include:
addressing issues associated with nuclear power
generation, imposing a renewable energy feed-in tariff,
liberalizing power retailers, and separating power
production from power distribution and transmission.
This is because the large-scale energy supply network,
which previously served the entire nation, was obviously
vulnerable. The supply network for power and gas was
disrupted during the GEJE and the energy supply wasinterrupted in several areas, even in the areas that wererelatively less affected. This led to a keen interest in
renewable energy as an emergency power source during
disasters, in addition to its contribution toward adecarbonized future. The Fukushima Daiichi Nuclear
Power Station accident (Hall, 2011; Yamane et al., 2013;
Suzuki, 2014) further complicated the perspective. To
mitigate peak loading of the power system, in a situation
where a nuclear power plant lost function, it was foundthat rolling blackouts and legally binding power usage
restrictions needed to be implemented. Radioactive
contamination led to a large-scale evacuation order forresidents in various localities that had social andeconomic impacts, leading a large number of citizens toreconsider their perceptions regarding energy supply
issues. From the perspective of both disaster prevention
and environmental re-creation, coordinated managementof energy supply and demand has become more efficientat the local scale through the introduction of distributed
power supplies and construction of autonomous energy
networks (Iwamura, 2015).
Against this backdrop, efforts to develop towns inwhich distributed community energy management was
introduced have been promoted in the process of disasterrecovery in Shinchi Town, Fukushima Prefecture. In the
districts around the JR Shinchi Station, reconstruction
from severe damage by the tsunami following the
GEJE has been progressing, and various facilities havebeen constructed thus far (Fig. 1). A high-efficiency
community energy system has started to supply electricity
and heat energy to facilities built in the vicinity of JR
Shinchi Station.
In this study, the planning and evaluation process ofthe community energy supply project were evaluated via
collaboration among the local government of the town of

26 January 2016

9 April 2019

Fig. 1 Reconstruction around JR Shinchi Station.
(photograph taken from Shinchi Town Hall)

Shinchi, private companies and research professionals.
This paper is organized as follows: Chapter 2 gives an
overview of Shinchi Town, and the process ofreconstruction after the GEJE in conjunction withcooperation from the National Institute for Environmental
Studies (NIES). Chapter 3 outlines the community energy
supply project. As this community energy supply project
cannot be evaluated using full-year data, Chapter 4
introduces the results of evaluating environmental
performance at the planning stage. Chapter 5 reports theresults of an evaluation using the actual data currently
available. Lastly, Chapter 6 provides a summary of thefindings and introduces future perspectives.

2. Post-Disaster Reconstruction Process in
Shinchi Town
Shinchi Town is a small municipality with apopulation of about 8,000 and a total area of 46.53 km2,
located near the border between Miyagi and Fukushima
Prefectures, at the northern end of Fukushima Prefectureon the Pacific Ocean side (Fig. 2). It is approximately
300 km north of Tokyo. The temperature is low ascompared to that in Tokyo, and the winters are especiallycold (Fig. 3). The population of this town peaked in 1995
and has declined since, owing to reduced birthrate andageing of the remaining population; this is the case formost Fukushima localities.
In Shinchi Town, the number of casualties wasapproximately 120 in the GEJE and subsequent tsunami.
The tsunami inundated a large land area below theelevation of 10 m, with the flooded area encompassing

Smart community recovering from the tsunami-disaster
about 20% of the town. As a result of the tsunami,
516 houses were damaged, and JR Joban Line Shinchi
Station was destroyed, while 40% of the agricultural land(420 ha) was inundated.
For the post-disaster reconstruction of Shinchi Town,
the town’s government presented “a smart hybrid town
concept” to increase the values of the environment,
economy and society. The aim of this concept was toreconstruct the area by combining information andcommunication technology (ICT) with the social
mechanisms that support the community. This concept
proposes a new community information infrastructure for
local residents networked with the municipal government,
research facilities and business sectors and involves abidirectional information system of sharing informationon the local environment and lifestyle. Based on thisconcept, Shinchi Town, as a disaster-affected site, wasselected as a “future city” by the Prime Minister’s
Cabinet Office in December 2011. With its selection as a“future city”, discussion on cooperation with NIES
toward the reconstruction of the town started, and in
March 2013, a basic agreement on cooperation was

drawn up between the Shinchi Town government and
NIES. Based on research knowledge resources such associal communication, NIES has supported the planningof future visions of the town, and aided in investigations
and formulation of the local comprehensive plan andlocal reconstruction plan (Fujita & Hirano, 2016; Hirano
et al., 2017a). We developed an information system thatserves as a residential interface for the information
infrastructure, and it is presently in the phase of social
demonstration experiments (Hirano et al., 2018). Various
functions of this information system such as visualizationof energy use on the demand side are already available.
Community energy conservation campaigns have alreadybeen implemented using this information system,
contributing to improved awareness regarding energy
conservation and a more active community (Otsuka et al.,2019). The energy-saving campaign was a demonstration
experiment, involving implementation of energy
conservation activities; meaningful results were obtainedon provision of energy conservation information andadded economic incentives for residents.
As part of this reconstruction and community
development support, we have put forth proposals andplanning support for regional energy management linked
to community development (Togawa et al., 2013; Togawa
et al., 2014). This effort has progressed, and the social
implementation of the regional energy supply in thereconstructed community has been achieved. As a core
project of the urban reconstruction project around JR
Shinchi Station, a community energy center, i.e., Shinchi
Energy Center, was constructed, with local heat conduits,
a community power grid, and CO2 supply pipes being
installed (Fig. 4). Details on the project are provided in
the next chapter.

N
Shinchi-Town

Fukushima
prefecture

Tokyo

Fig. 2 Location of Shinchi Town.
(a) January

30

Air temperature [˚C]

Air temperature [˚C]

10
8
6
4
2

201

(b) July

28
26

Shinchi

24

Tokyo

22
20

0
3

6

9

12

15

Hour

18

21

24

3

6

9

12

Hour

15

18

21

24

Fig 3 Variations in air temperature in Shinchi and Tokyo in January and July.

Shinchi Energy Center: Main building

Heat supply conduits on the north side of the building

Site area: 7,606.36 m2 / Building area: 714.48 m2 / Total floor area: 687.96 m2 / Structure: Steel frame (1 story) / Completion: November 2018

Fig. 4 Shinchi Energy Center.

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Y. HIRANO et al.

3. Outline of the Community Energy Project
In February 2018, a community-based energyorganization, named Shinchi Smart Energy, was newly
established by 12 entities comprising the local
government of Shinchi Town and multiple companies andorganizations. In November 2018, the Shinchi Energy
Center, which provides a highly efficient energy supply,
was completed. The Shinchi Energy Center is acommunity energy supply facility that supplies electricity
and heat to facilities around JR Shinchi Station by
utilizing cogeneration systems, solar panels, storage
batteries and a heat source equipment system. Figure 5
shows an energy flow chart of the system, and Fig. 6
shows photographs of the main equipment. The Shinchi
Energy Center has five gas engine cogeneration systems
with a power output of 35 kW (175 kW in total) thatutilize liquefied natural gas (LNG); the systems are
regulated by the number of units in operation depending
on energy demand. The cogeneration system utilizes
waste heat from power generation to increase the totalenergy efficiency. LNG, an energy source, is supplied tothe center via an LNG pipeline that branches off from theSoma LNG terminal. In addition to utilizing LNG, thecenter also has solar panels with a rated output of 50 kW
installed, providing effective use of renewable energy.
Electricity and heat are supplied from the Shinchi Energy
Center to facilities in the area through private lines andheat supply conduits. In the energy supply area (the area
supplied with electricity and heat), a hotel and hot bathfacility with relatively high heat demand have been
constructed for commercial use, and hot water suppliedby the cogeneration systems is effectively utilized inthese facilities. In addition, cooling during summers by
operating the cogeneration system is also a feature of thisproject. In Japan, power peaks occur during summer

when air conditioners are in use; thus, to reduce peakloads, cooling technology using gas with absorption
chiller heaters has come into widespread use. What iscalled “Genelink,” is a set of waste heat recovery
absorption chiller heaters that produce cold and hot waterusing waste heat from power generation, such as fromgas engines. Some cogeneration systems obtain steam
using gas turbines. Because the scale of this project issmall, however, it uses gas engines, and the waste heatprovides only hot water. Therefore, in the Shinchi Energy
Center, cooling and heating are performed with hotwastewater from power generation using Genelink.
Energy began being supplied to consumers in March
2019 (Fig. 7). All the facilities in the supply area shownin Fig. 7 were newly constructed after the tsunami
disaster. In addition, the Shinchi Energy Center functions
as a regional base for energy distribution. For example, inthe event of a power outage during a large-scale disaster,
it will be possible to provide an uninterrupted power
supply to the energy supply area of the center.
A community energy management system (CEMS)
provides integral management of these facilities as wellas energy utilization. One of the functions of CEMS is toprovide the information necessary for community energy
center management. Management is required for when
the cogeneration equipment is combined with multiple
auxiliary heat sources and power purchased from existing
power companies (grid power), thus reducing excess heat
while not exceeding the contract power from the grid. In
this case, the prediction of demands and power generation
via solar power, which depends on climate conditions,becomes essential. Under such complex conditions,information necessary for energy management personnel
to make appropriate decisions is provided, contributing tomore efficient operations.

Grid power(backup/aggregated power
supply for region)

Shinchi Energy Center
Storagebattery

Solar power
generation
50 kW

50 kWh, 50 kW

Electricity Demand

Cogeneration system
GE 35 kW × 5

Natural gas

Exhaust heat
918 MJ/h(255 kW)[Within region: 378 kW]Power generation
175 kW

Electric chiller

17RT × 1

GENELINK(exhaust heat input
water chiller)[Within region: 3894 MJ/h]

120RT × 1

Gas absorption
water chiller
Boiler

Cooling Demand

Heating Demand[Within region: 5412 MJ/h]

120RT × 2

Hot Water Demand[Within region: 1729 MJ/h]

581kW × 3

Energy demand assumed in themaster plan

Fig. 5 Electricity/heat supply system and energy flows in the Shinchi Energy Center.

Smart community recovering from the tsunami-disaster

203

Start
Calculation of the monthly-hourly
demand on the building side
(electricity, cooling, heating)Electricity and heat demanddata for building use(electricity, cooling, heating,
hot water)

Hourly calculation

Waste heat recovery
absorption typechiller/heater (Genelink)

Gas engine cogeneration system

Monthly calculation

Calculation of the monthly-hourly
demand for the plant(electricity, cooling, heating)Calculation of thecogeneration system (CGS)
allotment

CGS equipment data

Calculation of exhaust heatuse equipment allotment

Exhaust heat use
equipment data

Calculation of the quantity ofheat load allotment for theheat source equipment

Heat source equipment
data

Calculation of monthly andannual total

End

Fig. 8 Flow chart of stimulation evaluation calculations.
Solar panels

Control room

CO2 emission [t-CO2/year]

Fig. 6 Main equipment at the Shinchi Energy Center.
Shinchi Energy Center

Hotel / Bath Facility(4,584 m2)

Agricultural
production plant(under consideration)

Community Center(1,827 m2)

Commercial
ComplexSports Facility

Energy Supply Area

Heating duct (heating)
Heating duct (cooling)
Electricity(2,084 m2)(807 m2)

Solar
power
generation

1000

LNG

100

Oil

Electricity
500

Electricity
ShinchiEnergyCenterConventional
systemFig. 9 Calculation results of the CO2 emissions.

N
0

LPG

1500

0

JR Shinchi
StationElectricity and heat supply area
covered by the Shinchi Energy Center

Cogeneration
system200m

Fig. 7 E nergy supply area covered by the Shinchi Energy Center in
the JR Shinchi Station Development Area. Floor areas areshown in parentheses.

4. Evaluation of Environmental Performance
We are conducting research on evaluating andimproving the efficiency of community energy supply
and demand management around JR Shinchi Station. We
aim to improve energy efficiency and reduce CO2
emissions in this region and generalize knowledge about
efficient operation methods for applications in otherregions. However, due to delays in the construction ofcommunity centers and agricultural facilities, as well as
the socioeconomic impact of COVID-19, the energy
supply record at Shinchi Energy Center is currently
inadequate, and investigations using available data areincomplete. For this reason, we first present the results ofa study based on the master plan (Shinchi Town et al.,2016). In this case study, although the data andcalculation conditions are primarily based on the master
plan, the capacity of the solar panels has been modified tocorrespond to practical conditions and recalculated
accordingly.
Energy simulations were used to calculate electricity
and gas consumption. In the simulations, input data were
provided, and calculations were conducted for the load
allotment of various heat sources based on input data andoperational priority settings. Subsequently, city gas andelectricity consumption were calculated based on thecoefficient of performance (COP) of the heat source
equipment, efficiency data and other factors. Based onthese results, the energy savings, CO2 reduction, and costsof this system were calculated. The various facilities
shown in Fig. 7 were considered in the energy demand,and the demand pattern was set based on the existingenergy consumption intensity data. (The supply system
for the energy center and the assumed energy demand areshown in Fig. 5.) Then, the operating conditions of each
item of equipment for supply were evaluated, as shown in
Fig. 8.
Based on the above conditions, we calculated thetotal yearly CO2 emissions when all facilities were in
operation (Fig. 9). We also calculated the CO2 emissions

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Y. HIRANO et al.

in the case of a conventional system being installed ineach building for comparison. The results show that a
CO2 reduction of approximately 20% can be expected bymodifying the community energy system based on thehighly efficient community energy supply provided by
the Shinchi Energy Center. In addition, the seasonal andtime-dependent operation patterns of each device werealso comprehensively examined. For example, various
improvements have been made: approximately 10% of
power consumption can be supplied by solar power
generation during daytime peak hours and approximately
30% of cold heat consumption can be supplied by a
Genelink using cogeneration exhaust heat (figuresomitted).

5. Energy Evaluation Based on Available Data
We are conducting energy conservation diagnosis at
the Shinchi Energy Center as part of developing
technology for planning and evaluating community
energy utilization. This is a tentative evaluation result,however, because the expected number of consumers
assumed during the planning stage has not yet beenachieved.
As an example of the midsummer season, Fig. 10shows the recorded electricity, cold heat and warm heat
supplies for August. In August, cold water was supplied
to consumers at 381 GJ and hot water at 222 GJ; althoughmainly cold water was supplied, one-third of the total

demand was for hot water. The number of operationalcogeneration units was reduced during the night, but theoverall cogeneration system operated 24 hours a day. For
the power supply, along with solar power generation,
distributed power sources provided approximately half ofthe local power demand. Energy for cooling was suppliedby Genelink, which used exhaust heat from cogeneration,
for more than 60% of the total demand. Owing to thedemand for hot water in the public bath facilities andhotels, there was some heat demand in summer.
Cogeneration exhaust heat and a boiler were used to meetthis heat demand.
Fig. 11 shows the energy supply in December as an
example of winter conditions. Because there was almost
no demand for cold water in December, this aspect was
not included in Fig. 11. On the other hand, the demandfor hot water increased to 877 GJ owing to its use in bothwater and space heating. Based on the results of ourenergy conservation diagnosis, the operation of thecogeneration system was modified in November, and thecogeneration system was stopped during the midnight
power time zone of the grid power system. This operation
contributed to cost reduction and grid power loadsmoothing. Correspondingly, heat was supplied from thecogeneration exhaust heat and boiler during day and fromthe boiler during night.
Fig. 12 shows the cogeneration operation results
based on the practical supply and demand data for theseven months from June to December 2019. Since the
機器別製造熱量（時刻別）(b) Cold heat
supply

冷水製造熱量発電・ 買電電力量[kW][MJ/h](a) Power発電・買電電力量（時刻別）
supply

機器別製造熱量（時刻別）(c) Heat supply

Abbreviation

温 水製 造 熱量[MJ/h]

GE: Gas engine cogeneration
PV: Solar power
WH-R1: Power reception from the main line
GEN: Genelink
GAR: Gas absorption type chiller/heater
ESC: Electric screw chiller
HB: Heat boiler
HEX: Heat exchanger (utilization of CGS heat)Fig. 10 Hourly energy supply in August.

機器別製造熱量（時刻別）(b) Heat supply[MJ/h]

温水製造 熱量

発電・ 買電電力量[kW ](a) Power 発電・買電電力量（時刻別）
supplyFig. 11 Hourly energy supply in December. The abbreviations in the legends are the same as in Fig. 10.

Smart community recovering from the tsunami-disaster205

6. Summary and Future Perspective

Fig. 12 Operational status of the cogeneration system from June
to December 2019.

impact of COVID-19 is currently unclear, this paper only
presents data for the period before the impact of
COVID-19. However, the community center was still
under construction during this period. In addition, theplanning of agricultural facilities was delayed owing to
the effects of a massive typhoon in 2019. Therefore,
Fig. 12 shows the results under the condition of insufficientenergy consumers as compared to the number assumed at
the planning stage.
For these seven months, Fig. 12(a) shows that thefive cogeneration units generated approximately 80–100
MWh/month during summer. After November, thecogeneration operation method was modified and theamount of power generation shifted to approximately
40 MWh/month, which is approximately half of that insummer. Five cogeneration units were operating at almost
equal operating time. The output was adjusted bycontrolling the number of operating units; hence, they
were not always under simultaneous operation. However,
to match maintenance timings, five units were controlled
to have the same cumulative operating time. Fig. 12(b)shows that the utilization rate of cogeneration exhaust
heat was approximately 80% – 90% each month; thepower generation exhaust heat was confirmed to beeffectively used for heat supply. As shown in Fig. 12(c),the overall efficiency of cogeneration was stable atapproximately 70%. In December, the overall efficiency
was 75%, confirming good operating conditions.

This paper describes a case study on the planningand evaluation of an environmentally friendly energy
supply project that is being developed in the central areaof Shinchi Town. This project is being carried out as partof reconstruction of the town after considerable damage
caused by the tsunami following the GEJE. In thisproject, the Shinchi Energy Center was constructed tosupply energy to the facilities around JR Shinchi Station.
Although the current evaluation is tentative, the overall
efficiency of cogeneration is approximately 70%, and theutilization efficiency of exhaust heat is approximately
80–90%, confirming that it is in good operating condition.
In the future, we plan to evaluate its environmental
performance using practical data as the surrounding
facilities on the demand side are completed and the
supply records are collected.
Our subsequent goal is to apply the knowledge
obtained in Shinchi Town to other regions. Therefore, weare currently working on developing a general-purpose
evaluation system for evaluating the feasibility of acommunity energy supply system in accordance withvarious regional conditions. In this system, in addition to
the data on energy supply and demand management
realized at the current Shinchi Energy Center, various
models for energy demand forecasting and optimal
operation forecasting will be incorporated to evaluate
efficient energy management. For the residential sector,
we have constructed an energy demand forecast modelusing energy monitoring data in Shinchi Town
(Lubashevskiy & Hirano, 2018) and estimated theelectricity demand distribution to calculate the potential
for introducing a community energy supply. For thecommercial sector, because the data available on facilities
in Shinchi Town are insufficient for obtaining generalized
knowledge, we are investigating forecasting methods
based on regional climate conditions using existing
databases (Hirano et al, 2017b). Based on these results,
we aim to conduct data analysis and evaluation forhorizontal expansion in other regions, and study methods
for evaluating renewable energy as well as the potential
for introducing cogeneration by incorporating demand
forecasting.
Acknowledgements
The project introduced in this paper is being carriedout under the smart community adoption promotion
project with NIES acting as the academic advisor, basedon the Basic Cooperation Agreement, for supervising
Shinchi Town with the cooperation of related companies.

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Shinchi Town, UR Linkage, NTT Facilities, Keiyo Plant
Engineering and NEC Corporation (2016) Master plan
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centered around the use of energy produced and consumed in
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Yujiro HIRANO
Yujiro Hirano is a senior researcher at theRegional Environmental Renovation Section of
the National Institute for Environmental Studies,
Fukushima Branch. He holds a doctorate ofengineering and has long been engaged in researchon low-carbon lifestyles remote sensing of urban
surfaces, urban heat island countermeasures andurban energy system. His recent research interests are in modeling andanalysis of regional energy use for environmental renovation plans.

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch. He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Takuya TOGAWA
Takuya Togawa is a senior researcher at the
National Institute for Environmental Studies,
Fukushima Branch. He received his doctorate inengineering from the Graduate School ofEnvironmental Studies, Nagoya University in2010. He is engaged in research on mechanisms
for realizing disaster recovery and regional
revitalization by effectively utilizing local environmental resources.

Tsuyoshi FUJITA
Tsuyoshi Fujita is a principal researcher at theCenter for Social and Environmental Systems
Research, National Institute for Environmental
Studies. He is concurrently a professor in the
Department of Urban Engineering, University ofTokyo. His main fields of interest are the regional
SDGs, regional circular and ecological systems,
and urban industrial symbiosis. He is also a registered professional engineer
in the field of civil engineering and architecture.

Kenichi ADACHI
Kenichi Adachi is director of Japan Environment
Systems Co., Ltd. He graduated from the Facultyof Engineering, Yokohama National University.
He is currently engaged in research and planning
related to architecture, energy and theenvironment in cities and regions, particularly on
the themes of district heating, low-carbon
community development, smart communities, microgrids and hydrogenutilization supply chains.
(Received 7 September 2020, Accepted 21 December 2020)

207

Longitudinal Evaluation of Energy-saving Effects and Their Implication
Using Electricity Monitoring Data in Shinchi Town, Fukushima
Ayami OTSUKA1* Yujiro HIRANO2 Shogo NAKAMURA2 Tsuyoshi FUJITA3
and Daisuke NARUMI4
Faculty of Social Sciences, Waseda University
1-6-1 Nishi Waseda, Shinjuku-ku, Tokyo 169-8050, Japan2
Regional Environmental Renovation Section, Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
3
Center for Social and Environmental Systems Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506 Japan
4
Faculty of Environmental and Information Sciences, Yokohama National University
79-7 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa, 240-8501 Japan*E-mail: aotsuka@aoni.waseda.jp
1

Abstract
This study evaluated the energy-saving effects of electricity consumption monitoring and energy-saving
campaigns in Shinchi Town, Fukushima, Japan, where a community energy management system wasintroduced as part of recovery efforts after the Great East Japan Earthquake of 2011. First, a longitudinalevaluation through all six energy-saving campaigns conducted since 2014 illustrates that the first campaign
showed the highest energy-saving effect, indicating the energy-saving potential brought by visualization of
one’s own energy consumption by home energy management systems (HEMS). Declining trends in energysaving were observed over time. In addition, the correlations between the effects of energy-saving campaigns
and trends in longer-term electricity use were noted to be minimal, indicating that the effects of energy-saving
campaigns did not continue beyond the campaign period. It appears, however, that electricity consumption
rates were restrained during each campaign implementation period. The fact that repeated appeals for energy
savings were met with responses by the study target each time provides good prospects for demand-response
processes that incorporate consideration of renewable energy usage.
Key words :	electricity monitoring, energy-saving campaigns, residential sector, supply-demand balance

1. Introduction
The 2015 Paris Agreement was signed in response to
an increased need to tackle global warming. To
accomplish the aims of the Agreement, saving energy andpromoting a low-carbon society are issues of utmost
urgency. Under the Paris Agreement, Japan pledged toreduce CO2 emissions in the residential and commercial
sectors by 26% compared to 2013 levels. Of this,approximately 22% is to be reduction of CO2 originatingfrom energy use, wherein the residential sector is to
reduce CO2 emissions by approximately 40% (Global
Warming Prevention Headquarters, 2020).
Providing information to energy consumers is
considered essential for promoting energy-saving
activities. One means of doing so is to develop homeenergy management systems (HEMS) that enable“visualization” of energy usage. A variety of efforts,
including energy-use diagnostics, offering advice
Global Environmental Research
24/2020: 207-216
printed in Japan

regarding energy conservation, and various ways ofmaking energy “visible” within the home, often conducted
as part of smart-city empirical social experiments, havebeen performed using HEMS data for promoting energysaving.
The Great East Japan Earthquake (GEJE) of 2011
made Japan’s citizens more inclined to save energy in
general. It also changed the situation surrounding energy
issues in Japan. A fixed-price feed-in-tariff (FIT) system
for renewable energies, for instance, was put in place.
Progress was also made toward liberalizing electrical
power retailing.
Amid these changes, energy demand-and-supply
management on a regional scale is becoming increasingly
important. Indeed, 13% of the targeted 40% reduction forthe household sector under the Paris Agreement concerns
low-carbonizing of electrical power, increasing
anticipations of more aggressive introduction ofrenewable energy (Global Warming Prevention©2020 AIRES

208

A. OTSUKA et al.

Headquarters, 2020). Community energy-management
systems centered on renewable energies are essential toenable active transformation of energy demand to meetthe fluctuating output levels of renewable energy, which
is highly dependent on weather conditions, and this is a
key means of ensuring stability in the power supply-anddemand balance.
This demand-response (DR) method can be defined
as inducing leveling of electricity demand by shifting
electricity consumption patterns via such measures aselectricity price setting or payment of incentives, assummarized under the terms used by the Agency for
Natural Resources and Energy (2020). In other words,
DR is a mechanism by which energy consumers cancontribute to balancing of supply versus demand forelectricity. During “smart city” social demonstration
experiments conducted shortly after the Earthquake, anumber of studies were conducted regarding peak-cut
effects in times of “tight” supply and demand for seasonalreasons, namely air-conditioning and heating. In
Yokohama City, a maximum 15% peak-cut (compared tothe past performance baseline) was reportedly observed
for seasonal demand in the household sector (City of
Yokohama, 2017). A study in Kitakyushu City also
showed 10% –20% peak-cut effects via price setting(New Energy Promotion Council, 2014). On the other
hand, concurrent with the more widespread use ofrenewable energy in the future, increased needs for DR
are likely, particularly for balanced-adjustment effects
with regard to weather-induced fluctuations of supply.
However, there is a lack of knowledge on this issue since
there have been few case studies on regional energy
systems, especially with regard to the establishment ofsmall smart communities in rural areas.
A broadly common issue in promoting energy
conservation to counter global warming and energy
supply/demand (S/D) management is that changes inenergy demand depend on the behavior of energy
consumers, that is, individuals in society. In this regard,
knowledge about ways of inducing energy-saving
behavior can provide cues for evaluating future energydemand flexibility. In fact, Shimoda et al. (2020) statethat there is a need to accumulate more research andknowledge in energy demand science, a newinterdisciplinary science that integrates natural,behavioral and data science, whereby two conflicting
requirements for promoting energy saving while at thesame time seeking to increase energy demand flexibility
should be effectively addressed.
In this regard, the aims of this paper are three-fold.
The first is to present a longitudinal evaluation of theresults of six energy-saving campaigns conducted using
electricity usage data from HEMS in Shinchi Town,
Fukushima Prefecture. This system was established as asmart-community development project, part of the townrevitalization plan aimed at recovery from the damage

caused by the Earthquake. The second is to attempt toevaluate electricity-consumption trends over a longer
term, also using HEMS data. The final aim is, by
combining the results of the above-mentioned two sets oflongitudinal evaluation, to draw implications forcontrolling electricity demand towards introduction of
low-carbon community energy systems.

2. Overview of the Study
2.1 Study Target
In this paper, a case study from Shinchi Town,
Fukushima Prefecture is presented. Shinchi is a small
municipality with a population around 8,000, located at
the northernmost tip of the Fukushima coastline,
bordering with Miyagi Prefecture to the north and west,
Soma City to the south, and the Pacific Ocean to the east
(Fig. 1). It is approximately 300 km north of Tokyo.
In Shinchi, around 20% of the town area wasdamaged or destroyed during the Earthquake of March
2011. In December 2011, Shinchi was selected as an“environmental future city” under the Japanese
government’s “FutureCity” Initiative. Since then, the“Smart Hybrid Town” concept has been applied as part of
the town’s redevelopment efforts to enhance its
environmental, economic and societal values. A local
information network system (regional ICT system) wasestablished to disseminate information about energyconservation activities in the area, provide regional
information and bulletin boards and support the daily
lives of senior persons among other functions. Energy
usage has been made visible from 2014 through smart
meters and electronic display terminals under the“Shinchi Daily Life Assistance System (SDLAS)”
utilizing this ICT system. In addition, with the long-term
vision of meeting a portion of the region’s energy needs
by local energy companies using thermal power andnatural energy, Shinchi Smart Energy, a special purpose
company, was established in February 2018 to supply
energy locally. It began supplying energy to a certain partof the redeveloped areas by the end of the 2018 fiscal
year (FY). Subsequently, it has aimed to perform S/Dadjustment via DR during actual operations (Shinchi

Fig. 1 Location of Shinchi Town.

Longitudinal evaluation of energy-saving effects and its implication using electricity monitoring data

209

Fig. 2 Main demographic attributes of the study targets.

Town, 2018).
The target of this study is the households that havevolunteered to be monitored under the above-stated
SDLAS. Energy monitoring started from June 2014 in theorder of the participants’ selection. While the number ofhouseholds peaked at 75 during FY2015, data from 68
households were used in this study, due to withdrawal
from the program and system connection status. Figure 2
presents the main demographic attributes of thehouseholds, summarized from responses to aquestionnaire survey conducted at the time of volunteer
recruitment. As shown in the figure, characteristics ofhouseholds in Shinchi differed from those of urban area
households, in that many were three-generation
households with a large number of family members, andthat they frequently used kerosene for heating and waterheating purposes. Although not described in the figure
due to sample-number differences, Shinchi residencescharacteristically had large houses with 5 –15 rooms each
(38 of 39 households covered in a lifestyle survey
conducted in December 2014). While it is not clear how
the target households of this study had been affected by
the Earthquake, it is reasonably presumed that physicaldamage to their houses was not so severe, judging fromthe fact that a majority continued to live in houses
constructed before the Earthquake.
2.2 Electricity Monitoring
The HEMS units used in Shinchi were installed in
the monitors’ existing detached homes. Each household
participating as a monitor under SDLAS chose six lines
for monitoring whereby visualization of electricity wasenabled. The six measuring points, therefore, differedaccording to household: some chose individual lines suchas air-conditioning in each room, whereas others chose
six rooms such as kitchen, bedroom, child room, etc. In
this respect, the electricity monitoring system in Shinchi
differed from the standardized HEMS collectively
installed in newly built apartments where what wasmonitored was consistent for all households. Total values
for each monitoring line, as well as the total electricity
consumption for the entire household, all measured
hourly, were stored on a cloud server. A tablet computer

Table 1 Average electricity consumption per household.
SpringSummerFall

Winter

1-2 persons

12.98

14.97

11.47

18.69

3-4 persons

12.30

13.43

11.08

20.05

5-6 persons

16.57

19.19

15.67

24.20

> 7 persons

24.02

27.38

24.30

38.66
(unit: kWh/day)

was distributed to each household to provide information
on energy consumption and other life-related details
described above.
Table 1 summarizes the daily average electricity
consumption per household by number of persons and byseason, according to the HEMS monitoring data.
The seasonal data comprised the following from2015 to 2017: spring and fall, i.e., two-week periods withlow variability in average temperatures; summer, i.e., a
two-week period with higher average temperatures withthe least fluctuation; and winter, i.e., a two-week periodwith lower average temperatures and the least variability.
While demand increased during summer and winter due
to air-conditioning and heating, considering that Shinchi
is located in a coastal district, a comparatively cooler
climate meant that summer peaks were lower comparedto those for the Tokyo Metropolitan Area. Conversely,
while there was comparatively little snowfall in the area
despite its location in the Tohoku region, the winters werecold, leading to high peaks in demand for heating andkerosene. Households having a larger number of
inhabitants (especially for households of seven or more
persons) typically had higher electricity consumption.
The exception was that households with one to two
persons had higher electricity consumption in all seasons
other than winter compared to households with three tofour persons. This was possibly because one-to-two
person households in urban areas often have one or both
adults working and not home during the daytime.
Meanwhile, one-to-two person households in Shinchi
would have higher consumption given the characteristics
of rural towns in Japan with their higher elderly
population ratios, where either one or both adults are
already retired and staying home during daytime, leading

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A. OTSUKA et al.
Table 2 Energy-saving campaigns conducted in Shinchi.
PeriodNo. of households

Incentives

Information provision

Energy-saving effects*

1

Sept. 201422 / 46

Yes (top 3)

Via tablet PC

0.96%

2

Nov. 201412 / 46

Yes (top 3)

Via tablet PC-5.09%

3

Mar. 201524 / 55

Yes (top 3)

Advisory report (customized)

2.86%

4

Dec. 2015

75

None

Advisory report (customized)

1.58%

5

Mar. 2017

75

None

Advisory report (non-customized)-

6

Nov. 2017

68

None

Advisory report (customized)

2.80%* Energy-saving effects are averaged for all households. Due caution is needed for comparison as the evaluation method for each campaign
differed. Negative figures indicate an increase in electricity use. Details on each evaluation method are available in Shiraki et al. (2016) for
campaigns 1–3, Nakamura et al. (2018) for campaign 4, and Masuda et al. for campaign 6.

Fig. 3 Examples of “Shinchi Energy Savings Newsletter.”to higher electricity consumption. In addition, in terms ofhourly electricity usage, data from the monitoring systemwere characterized by a morning peak at around 6 a.m.
and a nighttime peak from around 6 p.m. and thereafter.
2.3 Energy-saving Campaigns
Since the establishment of the monitoring systemand start of measurement, six different electricity-saving
campaigns have been promoted (Table 2). In campaigns
1–3, the top-ranking households were awarded coupons
for local shopping. However, no such incentives were
offered during subsequent campaigns.
In the first two campaigns (campaigns 1–2), realtime assessment of power consumption was enabled inindividual households as details of power consumption(including rankings that allowed comparisons between
households) were made “visible” to householders(Masuda et al., 2018). In the four subsequent campaigns(campaigns 3–6), in addition to the above information,
households were provided paper-based reports titled“Shinchi Energy Savings Newsletter (kawara-ban)”containing advice and suggestions (Fig. 3). Information
was provided in Japanese and customized for eachhousehold, including consumption percentages by thehour of day and system type. Moreover, other general
information on energy saving tips was provided, such as
the amount of energy-conservation expected from
replacing existing electrical devices with more energyefficient equivalents.
With the exception of Campaign 5, where noverification was made of per-household energy-savings
effects, in each campaign, the average energy-savings
effects of participating households ranged from –5.0% to+2.9% (Shiraki et al., 2016; Nakamura et al., 2017;
Masuda et al., 2018). The negative figure of –5.0%
indicating an increase in electricity use for Campaign 2
was reportedly due to “wear-out” effects, according to
Shiraki et al. (2016), as the first and the second campaign
took place only one month apart from each other. It
should be noted, however, that as evaluation methods
differed by campaign, no overall comparisons across the
six campaigns were possible.
2.4 Methods of Longitudinal Evaluation for Electricity
Consumption and Energy-savings Effects
A suitable method was needed to evaluate energy-Longitudinal evaluation of energy-saving effects and its implication using electricity monitoring data

211

Fig. 4 An example of scatterplots and prediction formulas.

savings effects longitudinally across the past campaigns
as well as changes in energy consumption over time after
introduction of the electricity monitoring system. For
this, following the method used in the most recent
campaign (Campaign 6), a prediction formula wasemployed that was derived from temperatures and actual
electricity consumption of each household.
The daily electricity consumption of each household
against the daily average outside temperature for Shinchi
Town as published by the Japan Meteorological Agency(2017) was plotted for the period from June 2014 throughAugust 2017. Quadratic polynomial approximation lines
were then drawn on the scatterplot for each fiscal year,
and the derived equation was used as the prediction
formula for per-household electricity consumption foreach fiscal year (Fig. 4). Hence, scatterplots andprediction formulas were created for all the selected 68
households.
To assess electricity consumption over time, year-toyear changes were first computed for three values oftemperature representative of each season, viz. 5°C(winter), 15°C (spring and fall) and 25°C (summer). For
assessing change rates over time, the change rates foreach fiscal year, and change rate between FY2015 andFY2017 were calculated to assess the changes over alonger period of time. Then, to assess the effectiveness ofpast energy-saving campaigns, actual daily averagetemperatures were included in the prediction formulas forthe fiscal years wherein the campaign was conducted.
Subsequently, the differences between the predictedvalues (from which temperature effects were excluded)
and actual measured values within the campaign period
were considered “energy-saving effects” (or, vice versa,
energy-increase effects).
It is noteworthy that for evaluating energy-saving
campaigns, the use of randomized controlled trials(RCTs, which involve the random allocation of test
subjects to the control group) is recommended for greater

accuracy. However, it is also often considered difficult toperform strict RCTs (Bhushan et al., 2018) for any
experiment involving the household sector, largely
because of costs, and secondarily because it often requires
voluntary participation in questionnaire surveys to enable
researchers to understand background factors forbehavioral changes. This conflicts with the nature of
RCTs. There is a commonly recognized need for more
appropriate evaluation methods in cases where RCTs
cannot be performed (Bhushan et al., 2018; Vine, 2014).
The same issue was shared in this study: the participatinghouseholds were originally voluntary, and it was difficult
to include non-monitored households to serve as acontrol. Hence, in the present study the method used wasbased on actual data from each household and predictedvalues estimated using the formula.
2
However, the prediction accuracy (i.e. R value of theprediction equation) varied by fiscal year. In the case ofhouseholds in Fig. 4, the R2 value for the same householdvaried from 0.47 to 0.79. This variation was considered
due to limited data availability: for FY 2014 and FY
2017, the data used for analysis included only specificperiods, possibly lowering R2. Moreover, factors that
could potentially explain increases in electricity
consumption in particular fiscal years (e.g., FY 2014) are
unknown. Although questionnaire surveys aimed at
identifying factors that could potentially influenceelectricity consumption (e.g., purchase of energy-saving
household electrical appliances, or changes in family
composition) were conducted, but it proved difficult toascertain all factors. These limitations were taken into
consideration during the analysis and attempts were madeto estimate energy-saving and increase effects fromelectricity monitoring data and the results of the energysavings campaigns.

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3. Results and Discussions
3.1 
Longitudinal Evaluation of the Energy-saving
Campaigns
Results of longitudinal evaluations of the past six
energy-saving campaigns are indicated in Fig. 5. The
horizontal axis depicts the campaign period and thepreceding and succeeding two-week periods. However, as
noted in the discussion regarding Table 2, the horizontal
axis is not continuous, as there was more than one year’s
gap between campaigns 4 and 5.
It is evident that the effect of the energy-saving
campaign was up to 7.7% for subject household averages
during one campaign period (Campaign 1). The
corresponding values for campaigns 2, 3, and 4 were,respectively, 6.8%, 0.8%, and –3.9%, i.e., a continuous
decline in its energy-saving effects. (Notably, in
Campaign 3, since there were no data available to identify
the participating households and their energy data, thefigure indicates the average measurement values for all
households). With respect to the above declining trend,and considering that only volunteer households
participated in campaigns 1 and 2 during the early periodof the electricity monitoring system, the results suggestthat the effects of making energy usage “visible” to users
were large, as these were new and of novel interest. As
for Campaign 4, the large consumption increase was
likely due to the fact that the campaign period covered
the year end and New Year’s period. This season isassociated with substantial changes in normal daily-life
patterns (e.g., household members spending a longer time
at home, and relatives and guests coming to visit fromoutside). For campaigns 5 and 6 these figures were 0.1%
and –1.3%, respectively. While these indicate improved
energy-savings rates compared to those for Campaign 4,these figures showed a slight increase vis-à-vis predictedvalues used for longitudinal evaluation, i.e., prediction
values from which atmospheric temperature effects were
excluded. Energy-savings effects were particularly
evident during the period following the end of Campaign
6. This campaign was designed such that upon its
conclusion the participants were provided individualized
information concerning results from the campaign period(Masuda et al., 2018). It is possible that the effects ofpresenting this information were thus delayed until after
the campaign.
As mentioned earlier, repeated requests to the same
study subjects to save energy showed a trend of
progressively weaker responses to such appeals. Yet, wefound that electricity consumption was lower during
campaigns compared to the periods before and after eachcampaign.
3.2 Trends in Electricity Consumption over Time
During the energy-saving campaigns, households
were provided with various information to promote
behavioral changes. One example of such information isadvice on replacing electricity-consuming household
appliances with energy-efficient ones. With the purposeof measuring the rate of application of information in thedaily life of householders, changes in electricity
consumption after the introduction of the monitoring
system were analyzed.
The frequency distributions of change rates of eachhousehold at each of the three air temperature values: 5°C(winter), 15°C (spring and fall), and 25°C (summer) arepresented in Fig. 6. Here, negative figures in change rates
indicate increases in electricity use. According to thefigure, the most frequent change rates were in the range
of 0% –5% decreases for winter, at 5°C, for all FY

Fig. 5 Results of longitudinal evaluation.

Longitudinal evaluation of energy-saving effects and its implication using electricity monitoring data

213

Fig. 8 Correlation between the two energy-saving effects.

Fig. 6 Frequency distributions of change rates.

Fig. 7 Average change rates in electricity consumption.

periods. The mode value for spring and fall, at 15°C,
changed from a 0% –5% increase for FY 2014–2015 to0% –5% decrease for FY2015-2016, which again shiftedto a 5% –10% increase in FY2016-2017. As for summer,
mode values showed divergent results in the early period
after system introduction (FYs 2014–2015), i.e., a0% –5% decline followed by a 5% –10% increase. Morerecent trends in FY2015-2016, and FY2016-2017 showeven more divergence among the households, where themode is within the 0% –5% increase range while thenumber of households with decreasing trends have also
increased.
The average electricity consumption change overtime for all households at the same air temperature of
5°C, 15°C, or 25°C, presented in Fig. 7, indicates thesetrends more clearly. Considering the comparably longer
period from FY2015 through FY2017, average change
rates showed a slight increase in electricity use by
1.2% –2.3% for all three temperatures. The trends inchange overtime varied by season, however. In winter,they started with a decline in the FY2014 and FY2015
periods, which turned into an increase subsequently. That
increase was especially large in the more recent period
from FY2016 to FY2017. The trends in spring and fall
were opposite: starting with a large increase in the
beginning which then turned into a gradual decrease. The
trend in summer indicated mixed results: an initial large
increase turning into a decrease, as in spring and fall, but
it shifted to an increase again more recently in the
FY2016-FY2017 period, yet the increase is somewhat
restrained. An overall increasing trend on average, withparticularly large increases during winters, suggests thatthe average values were impacted by households thatshowed large increases, despite there being a number ofhouseholds showing a decreasing trend, as discussed
regarding Fig. 6 above.
3.3 Correlation between the Two Energy-saving
Effects
From these results, the relationships between
previous energy-saving campaigns and changes in overtime electricity consumption rates were explored by aseries of correlation analyses. For instance, in Fig. 8, thevertical axis represents change over time rates (at 5°C)
from FY 2015 to FY 2017, while the horizontal axis
shows average energy-saving effects for each household
during campaigns 1 through 6. This figure suggests thatthe energy-saving effects (reduction rates) of campaigns
and electricity consumption change rates over time were
mostly uncorrelated. The same was observed for othertemperatures (at 15 °C and 25 °C), or for individual
analyses by each campaign. In other words, the effects ofeach energy-saving campaign did not translate to steady,long-term energy-saving effects.
The probable reasons for this are as follows.
Reduction effects from energy-saving campaigns
appeared to be due, in a relatively pure fashion, tochanges (reductions) arising from engagements during
the campaign period. Meanwhile, rates of changes overtime are likely to have been more strongly impacted byfactors other than purely energy-saving effects, such as,changes in household member configurations. This is214

A. OTSUKA et al.

Table 3 Factors influencing rate of change over time.
Name of variables

Standardized β
5℃

Family size
Family size (increased)
Family size (decreased)
No. of persons at home (weekday)
No. of persons at home (weekend)
Residence area
Age (at application)Age of family (infants)
Age of family (juniors)
Age of family (>65)
Occupation
Family income
Year built
Solar panel installed
All electric
Air-conditioning typeNo. of air conditioners
Heating typeNo. of heating units
No. of elec. appliances
No. of lights
Active in energy-saving behavior
Life satisfaction
Prospect for Shinchi Town
Adjusted R2

15℃

25℃

0.328

-0.205-0.260
0.356
0.320
0.281

0.383

-0.729

0.366
0.507

-0.212-0.342-0.4520.396-0.299
0.432

0.171

0.515

p < 1%, 5%, 10%; Step-wise regression analysis was used: empty cells in
the Table therefore mean that these were not identified as influencing
factors although these were also included in the analysis. There are no VIF
figures, suggesting multicollinearity among the variables.

indeed indicated in the results of a series of step-wise
regression analyses (Table 3). Here, the rates of changeover FY2015 to FY2017 at each temperature were usedas dependent variables, whereas households’ demographic
and housing attributes, partly presented in Fig. 2, wereused as independent variables. People’s subjective
cognition on energy issues as well as general well-being
obtained from a survey conducted during one of theenergy-saving campaigns, namely Campaign 4, were also
included in the analysis (though limiting the sample size,i.e., 35). Cognition of energy-issues, such as societal
responsibility and efficacy, is known to have certain
influences on energy-saving behaviors and thus energy
consumption (e.g., Otsuka et al., 2017), so it wasconsidered important to include similar cognitive
variables as this study directly addresses the effect ofenergy-saving campaigns the purpose of which is tochange people’s cognition and/or awareness andbehaviors. The variable “actively taking energy-saving
behavior” was used here to represent such conventional
cognition, whereas variables “life satisfaction” and“prospects for Shinchi Town” were something unique but
important for this study, which looks at redevelopmentfrom the aftermath of the Earthquake.
The results show that changes (increase/decrease) infamily size as well as age of the house, normally known

to be factors affecting energy consumption, are found tobe have an influence with statistical significance. The
number of electric appliances was associated with anegative influence (i.e., decrease in change rate) – theopposite of what is normally expected. One of the reasonsfor this could be that it gave opportunity for people toreplace these appliances with more efficient ones
according to the energy advice given during the energysaving campaigns. Although there were no data available
which could be used as a variable indicating practices in
replacing appliances to back-up this reasoning, the factthat this variable was included as an influencing factor
for spring and fall (at 15°C), when the increased sample
number (n=68) was used without the inclusion of
cognitive variables, may reasonably imply such a
possibility, especially given the overall trend in thedecreasing change rate at 15°C as discussed earlier.
It is also noteworthy that cognitive variables such as“actively conducting energy-saving behavior” and“having good prospects for town redevelopment in the
future” contribute to energy-saving. This is especiallytrue for winter, when the cognitive variable “actively
taking energy-saving behavior” shows the strongest
influence on the change (decrease, in this case) rate. The
fact that the age of the house is the second mostinfluential factor (in the increasing direction) in winterhighlights the need for promoting better insulation. This
is in line with the current energy-saving promotion policy
in Japan, and will be an important agenda to raise, given
the location of Shinchi in the Tohoku region with a cold
winter climate. Implementation of such measures forexisting houses poses a challenge, however, as it issomething not simply achievable through behavioral
changes in everyday life.
On the other hand, “installation of solar panels” hasbeen one of the factors pointing toward increased
electricity consumption over time in summer. The same
trend for having solar panels was observed in otherseasons, at both 5°C and 15°C, when the analysis was
conducted with a larger sample number (n=68) without
cognitive variables. The link between the increase inelectricity consumption and having solar panels per se is
not necessarily a problem as it represents a low-carbon
energy source, especially if the solar-powered electricity
is used towards enabling net-zero electricity in a house. If
the increase in electricity consumption is indeed related
to the in-situ (i.e., self-produced) use of solar power, it
then makes the challenge of effective S/D management a
reality. There is a need to investigate this relationshipfurther with increased samples, though it was not possible
in this study due to limited availability of data. It is also
noted that a new awareness arising for DR in terms ofclimatic fluctuation is necessary. Again, that “actively
taking energy-saving behavior” was also associated withan increase, rather than decrease, in electricity
consumption in summer poses a challenge, but the fact

Longitudinal evaluation of energy-saving effects and its implication using electricity monitoring datathat people’s attachment to locality as shown in theprospects for the future of the town contribute to anenergy-saving effect gives hope in terms of community
energy-management systems.

4. Conclusion
This study used electricity monitoring data for
independent households within Shinchi Town, Fukushima
Prefecture to investigate: 1) energy-(electricity)-saving
effects during energy-saving campaigns and, 2) long-termchanges in electrical power consumption, in an aim tolearn from them and assess the implications of S/Dbalancing effects in the future. The conclusions drawn
from the results are summarized as follows.
The energy-saving effects due to the implementationof each energy-saving campaign showed declining trends
over time. It appears, however, that electricity
consumption rates were restrained during each campaign
implementation period.
With regard to changes related to over-timeelectricity consumption tendencies beyond the period of
the energy-saving campaigns, while there was anincreasing tendency overall, there were also numerous
households that showed a declining tendency. This wasapparent when considering changes during each fiscalyear period and changes within individual households.
There were also households that showed restraint in theirincrease of electricity consumption. Notably, however,
the effects of energy-saving campaigns were limited andmostly did not continue beyond the campaign period.
Hence, it follows that measures are required, especiallyregarding seasonally increased electricity consumption
trends, to promote and stabilize further energy savings.
To summarize the study’s findings, considering thatthe effects produced during the energy-saving campaigns
did not translate into long-term effects, it can be said thateven stronger engagement and educational/awarenessraising efforts are needed. In doing so, new issues such asbuilding insulation, noted to be quite influential during
wintertime, may need to be addressed. Moreover, given
the fact that households responded to repeated appeals forenergy savings, it sheds light on future prospects thatrequests made to consumers via processes such as
demand-response (DR), that are likely to be long-term,
continuous and more frequent within community energy
management systems than in the energy-saving
campaigns used as the case study in this paper will also
be responded to by the targeted consumers, implying that
consumers are ready to make changes when so requested.
This gives further positive prospects that the results of theenergy-saving campaigns would have been more positive
if evaluation by randomized control tests had been
available.
With regard to further work in the target area of thepresent study, this study was limited to covering only the215

electricity usage in the households. Given the climaticconditions, where heating is often conducted using energy
sources other than electricity as well as warmer summer
temperatures in the most recent years, it would be
worthwhile to study people’s behavioral responses tosimilar requests regarding heating as well as in hotter
summers.
Further, similarly to energy-saving campaigns
conducted in the past, it is also important to investigate
and verify the people’s responses and behavioral changes
in settings whereby actual demand-and-supply balanceadjustment requests, although virtual, are given thatincorporate considerations for renewable energy usage.
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Ayami OTSUKA
Ayami Otsuka is an assistant professor at theFaculty of Social Sciences, Waseda University.
Holding a Ph.D. in environmental studies, she
served as a visiting research fellow at the National
Institute for Environmental Studies from October
2017 to March 2019. Her main research interest
lies in integrating energy research and social
sciences, with a particular focus on citizens’ roles in realizing a sustainable
society.

Yujiro HIRANO
Yujiro Hirano is a senior researcher at theRegional Environmental Renovation Section of
the National Institute for Environmental Studies,
Fukushima Branch. He holds a doctorate ofengineering and has long been engaged in researchon low-carbon lifestyles remote sensing of urban
surfaces, urban heat island countermeasures andurban energy system. His recent research interests are in modeling andanalysis of regional energy use for environmental renovation plans.

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch.
He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Tsuyoshi FUJITA
Tsuyoshi Fujita is a principal researcher at theCenter for Social and Environmental Systems
Research, National Institute for Environmental
Studies. He is concurrently a professor in the
Department of Urban Engineering, University ofTokyo. His main fields of interest are in regional
SDGs, regional circular and ecological systems,
and urban industrial symbiosis. He is also a registered professional engineer
in the field of Civil Engineering and Architecture.

Daisuke NARUMI
Daisuke Narumi is a professor at Yokohama
National University. He received his PhD inengineering from Osaka University in 2003. His
doctoral thesis was titled, "Study on the Planning
Methods of Urban and Architectural Environment
in Harmony with Surrounding Climate
Characteristics." His specialty is urban andarchitectural environmental engineering, and he has been working inresearch on a wide range of subjects, from energy consumption in cities andbuildings to analysis of the environmental impacts associated with energy
consumption. His major awards include the Encouragement Prize from AIJ
and Paper Award from the Society of Heating, Air-Conditioning andSanitary Engineers of Japan.
(Received 23 September 2020, Accepted 25 December 2020)

217

Impact of TEPCO Nuclear Accident and Associated Evacuation to
the Demography in Fukushima
Kei GOMI
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: gomi.kei@nies.go.jp

Abstract
The nuclear accident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station
resulted in evacuation orders being issued for the surrounding municipalities. These have been lifted one byone, and people have begun to return to their hometowns. When considering the reconstruction and long-term
development of these areas, population recovery is the most fundamental factor. In this study, I analyze thedemographics of these areas, including how the inhabitants’ return is proceeding, from multiple statisticalsources. The results show that out-migration according to official registration has returned to its previous
trend again since 2013, that progress in evacuees’ return after the lifting of the evacuation order varies fromregion to region, and that the proportion of women of reproduction age is low among residents in the areas
where the evacuation orders have been lifted.
Key words : demographic transition, disaster recovery, evacuation, nuclear accident

1. Introduction
The accident at Tokyo Electric Power Company’s(TEPCO’s) Fukushima Daiichi nuclear power plantfollowing the Great East Japan Earthquake in 2011,
resulted in evacuation orders being issued for thesurrounding areas. Since then, as the accident was
brought under control and radiation levels dropped, theevacuation orders have been lifted one by one. In areas
where the orders have been lifted, residents who had been
evacuated are now returning to their hometowns. For
areas forcibly evacuated due to the disaster, population
recovery is the most basic element of reconstruction.
Therefore, it is important to understand the demographicsof these areas so as to plan for future recovery. It remains
unclear, however, how many people will eventually returnto the areas affected by radioactive contamination, as wehave no experience in recovery from such large-scaleevacuations and the longer the evacuation period, themore settled the residents will become in their evacuationsites. For example, according to a survey conducted by
the Reconstruction Agency and local governments, morethan half of the people in some areas have decided not toreturn (Reconstruction Agency, 2020). In this study, we
will investigate the demographics of the evacuation areasfrom the time of the disaster to the present situation,
analyze trends by factor, clarify the actual circumstances
and identify issues from the perspective of recovery.
Global Environmental Research
24/2020: 217-226
printed in Japan

Morita et al. (2018) analyzed the evacuation
behavior of people in Minamisoma, Japan, when theevacuation orders were issued in the month after thedisaster, and found that (1) males were more likely tohave stayed there against the evacuation orders thanfemales, and (2) residents aged 40 – 64 years old weremore likely to have stayed there than were those aged 75
years or older. Heuer et al. (2020) analyzed population
migration patterns from the affected areas before andafter the disaster on a prefecture-by-prefecture basis bycomparing evacuees (those who remained registered attheir original address) and out-migrants (those who had
registered in other prefectures). Their results showed thatthe composition of the areas to which the out-migrants
had moved had not changed from before the disaster,while the evacuees, unlike the out-migrants, chose to livein more neighboring areas. Higuchi et al. (2012) analyzed
a variety of statistics for the first ten months after thedisaster and found the number of excess out-migrants
from the three affected prefectures to be four times
greater than in 2010, with the largest number in April
2011, nearly 80% of the total number of the excess, waspeople moving out from Fukushima Prefecture, with thelargest number of people moving to Tokyo. Hashimotoand Kawakami (2015) conducted an analysis of population
movement by municipality based on the Basic Resident
Registration System (BRRS) and found that the higher
the average income and the greater the degree of damage,©2020 AIRES

218

K. Gomithe higher the out-migration rate tended to be, and thateven after adjusting for economic factors and the degreeof earthquake and tsunami damage, the out-migration rate
was higher from municipalities in Fukushima Prefecture
than from the other two (Iwate and Miyagi). In relation todeaths, it has been noted that Fukushima Prefecture had ahigher incidence of disaster-related deaths than otherareas affected by the Great East Japan Earthquake due tothe nuclear disaster (Kubo et al., 2017). It has also beenshown that among the elderly in the same affected areasin Fukushima, the mortality rate was higher among theevacuees than among those who did not evacuate(Nomura, 2016).
Based on the fact that several more years havepassed since the previous studies above, and that
evacuation orders have been lifted and people have beenreturning to their hometowns in the meantime, this study
targets the areas affected by the nuclear disaster, with a
special focus on the areas where evacuation orders had
been issued, and clarifies the overall demographic
picture, including progress in evacuees’ return, frommultiple statistical sources. We present the results in
Chapter 3 and discuss their implications from theperspective of recovery in Chapter 4.

and some of which are still in place today, were
established in August 2013: Zones in preparation for thelifting of the evacuation order (herein, Zone 1), restricted
residence areas (herein, Zone 2), and difficult-to-returnzones (herein, Zone 3). In Kawauchi Village, all villagers
were evacuated in 2011 after the accident and then began
to return to their homes on January 1, 2012, except forsome areas (later becoming zones 1 and 2), and then in
2016, evacuation orders for Zones 1 and 2, which
together accounted for about 10% of the village’s
population, were lifted. Because of this history and thelack of detailed population information from the town,
we treat the entire town as one area without
distinguishing between the evacuation zones. Table 1 lists
these municipalities and the populations of the evacuation
zones, the timing of the lifting of the evacuation orders,
and the scope of analysis of evacuees’ return in this study.
In principle, the period covered is until the end of June(or July 1, 2019). This is because, in Japan, the new fiscal
year begins in April and many people relocate between
March and April, and this kind of movement is thought tohave settled down by the end of June. However, different
time periods may be used in the individual analyses. In
such cases, the periods are indicated in each item. In
addition, most of the evacuation orders for Zones 1 and 2
had been lifted by that time.
2.2 Information Sources and Analytical Methods
Currently, there are four main sources of information
for determining the population of the evacuated areas.
The BRRS, national census, resident population according
to municipalities’ tallies, and mobile phone location
information. Each of these has its own strengths andweaknesses, but by combining them, we can see the2. Method
2.1 Target Areas and Periods
The target area was the 11 municipalities where
evacuation orders had been issued. The scope and type ofevacuation orders changed several times since
immediately after the disaster. The following three zones,
some of which were in place for a relatively long time
Table 1 Basic profile of target municipalities in this study.

This study examines the 11 municipalities that appear in this table. They have different proportions of the three categories of evacuation zone (Zones 1, 2 and 3).
Population (July 31, 2013)

Evacuation order lifted before July 1, 2019

Total

Zone infor Restricted
Total area preparation
residence Difficult-tothe
liftingofreturn zone
evacuated the evacuation
area(Zone 3)(Zone
2)
order (Zone 1)

Other
areas

Minamisoma City

65,175

12,238

12,238510

252,425

Iitate Village

6,250

784

784

5,192

274

0

Kawamata Town

15,086

1,077

1,077

127

0

13,882

Katsurao Village

1,511

1,329

1,329

64

118

0

Tamura City

39,996

351

351

0

0

39,645

Namie Town

19,505

7,902

7,902

8,260

3,343

Futaba Town

6,492

255

255

0

6,237

Okuma Town

10,958

23

23

362

Tomioka Town

14,413

1,319

1,319

8,821

Naraha Town

7,575

7,525

7,525

Kawauchi Village

2,809

276

189,770

33,079Total

This stydy’s
target area
for return
analysis

Lifted in July 12, 2016 except for Zone 3

Lifted area

Lifted in March 31, 2017 except for Zone 3

Lifted area

Lifted in March 31, 2017

Whole town

Lifted in July 12, 2016 except for Zone 3

Lifted area

Lifted in April 1, 2014

Lifted area0

Lifted in March 31, 2017 except for Zone 3

Lifted area0

Not lifted yet

10,5710

Lifted in April 10, 2019 except for Zone 3

None

4,273

0

Lifted in April 1, 2017 except for Zone 3

Lifted area

0

0

50

Lifted in September 5, 2015

Whole town

276

58

0

2,475

33,07923,394

24,818108,477

None

All residents evacuated in 2011. Return started
on January 1 2012 except for Zone 1 and Zone 2. Whole village
The rest was lifted in June 4 2016.

Demographic impact of TEPCO nuclear accident
whole picture. Table 2 summarizes the advantages anddisadvantages of each statistical source and how they areused in this study. The details of each statistical source
and method of survey and analysis in this study are
discussed below.
The BRRS is municipality-based, middle-frequency
and detailed. It contains basic demographic statistics thatprovide a complete picture of births and deaths by sex
and age, and are usually compiled by local governments
on a monthly basis, while annual reports are madeavailable to the public by the central government ofJapan. However, because the data are based onregistration by residents, people are sometimes registeredin a different place from where they currently live. For
this reason, it is not possible to obtain the actual
population of areas from which residents have evacuatedand begun returning to in this study. In addition, BRRS
does not have information on the daytime population
because it does not include information on where people
work and go to school. Therefore, for example, if abusiness has reopened in the area due to reconstruction,
but the employees do not live in the area but commute towork there from outside the area, it is not possible todetermine the daytime demographics of the area from the
BRRS. In this study, from the BRRS, we obtained thetotal population, net social change, net natural change andcomposition by sex and age on an annual basis. We
compared pre-disaster trends between municipalities
designated as evacuation areas and the rest of Fukushima
Prefecture, focusing on 2011 and covering seven years
before and after the disaster (2004 – 2018). However, due
to municipal mergers within the region, social changes
are calculated from 2007 to 2018, the year after themerger (as it is not possible to determine retrospective
movements between merged municipalities). Regarding
the composition of the population by sex and age, we
compare the residential data for each municipality on

219

January 1, 2018 with the composition of the number ofresidents in the area based on mobile spatial statistics (seethe following chapter).
The number of residents in the municipality tally
was compiled by the local governments in whose areas
the evacuation orders had been lifted, and they asked
returning residents to report on the status of their return.
Many of the municipalities publish the population andnumber of households present as well as those stillevacuated monthly on their websites. This information isvery important for identifying the actual situation ofpeople living in the evacuated areas. Each municipality,
however, differs in whether it publishes the information,
how long it is available on the websites, the details onage, sex and location of the population, and whether itclassifies people who have moved into the area fromoutside after the disaster. In addition, because the system
is not as enforceable as BRRS, there may be residents
who do not report their immigration status or return totheir hometowns, or residents who report theirimmigration status but actually live outside the area. In
this study, we collected the number of residents andevacuees published by each municipality from the monthwhen the evacuation order was lifted until June 30 (orJuly 1) 2019 to calculate the rate of return. The rate isdefined as the sum of the number of residents in the area
where the evacuation order was lifted plus the number ofregistered evacuees in the area, divided by the number ofregistered residents in the same area, and is calculated forthe area and time period for which the information isavailable. To confirm progress toward population
recovery and differences in rates, we show changes in therate over time. We also briefly examine the factors behindthe differences.
The census is the most fundamental source ofstatistics in the nation on a municipal basis. In the case of
the evacuation in question, an individual is counted

Table 2 Comparison of information sources on population in the target areas.

 our different statistical information sources were adopted in this study to get an overall picture of the demography in the target area. Each of themF
has strengths and weaknesses as shown in the table, so it is necessary to combine them.
CensusBasic Resident Registration
System (BRRS)

Municipality tally

Mobile phone information

Temporal resolution

Low (every 5 years)

Middle (monthly, yearly)

Middle (monthly)High (hourly)

Spatial resolution

Low (municipality)

Low to Middle(sub-municipality)

Middle (municipality,
evaculation area)

High (500m mesh)

Demogprahic profile
resolution

High (sex, age, working
status, marriage status)

Middle (sex, age)

Low (total only in manycases)

Middle (sex, age)

Availability

High (provided on Web)High (provided on Web)

Middle (varies bymunicipality)

Low (fee for use)

Use in this study- Indicators of basic- Comparison of nighttime
demographic dynamics of- Analysis of gender and age
and daytime population and- Progress of return to theeach municipality (social andstructure in the areas where
gender ratio in theareas where evacuation orders
natural increse, birth andevaculation orders were lifted
municipalities before and after
were lifted - Analysis ofdeath rate) on an annual basis- Comparision of age anddisaster (2010 and 2015) differences in progress- Comparision of age andgender composition against
Analysis of commuting
between areas
gender composition against
BRRS
structure in 2015
mobile phone information

220

K. Gomiamong the population of current residents if the person isstill evacuated, and among the population of theevacuated area if the person has returned. Thus, thepopulation living in the area can be determined in detail
and with considerable accuracy. In addition, since thecensus also surveys work and school commuting areas,
the daytime population and commuter OD (origin anddestination) can be determined. On the other hand, thetemporal resolution is low because it is conducted every
five years. At the time of this study, the latest census had
been conducted in 2015, the first survey conducted after
the disaster, and evacuation orders had not yet been liftedin many areas. In addition, many of the tabulations are at
the municipal level, making it impossible to distinguishbetween evacuated and non-evacuated areas within amunicipality. In this study, we examine the 2010 and2015 census data on the nighttime population, daytime
population and sex ratios in municipalities with
evacuation areas to identify changes in the basic
population structure before and after the disaster. To
determine the commuting structure, the residence of
employees in municipalities with evacuation areas isdetermined from the census. The census is the only
source of information on mobility in the evacuated areas
available free-of-charge.
As a population estimate based on mobile phone
location data, we used mobile spatial statistics in thisstudy. Mobile spatial statistics are population estimatesfrom NTT DoCoMo, Inc. based on the location of theirown mobile phone users. They have a high spatiotemporal resolution and are provided in hourly,
administrative boundary or 500-meter mesh units. Since
they are based on the number of mobile phone users who
were present at a given location at a given time, it ispossible to estimate the daytime population and also tocapture temporary increases in the number of people due
to stays or events. On the other hand, the estimates are
uncertain because they are based on the percentage ofmobile phone subscribers of that company. This isespecially true in areas with small populations. The sameis true for younger and older people, who are less likely
to have mobile phones. In addition, it should be notedthat the number of residents who are staying in the area
without being registered is also estimated (e.g.,
employees of businesses involved with work such as
decontamination, decommissioning of the nuclear plantand interim storage of decontamination waste). With thisinformation, in this study, the total number of people in
December 2017 (average at night between 18:00 and 8:00
a.m.) is compared with the BRRS data (January 1, 2018).
The profile of residents in the area (composition ratios bysex and age) is compared between BRRS and mobile
spatial statistics to identify relatively greater or fewer
people by sex and age using the Jaccard distance. The
Jaccard distance is an application of the Jaccard
coefficient, which was proposed by Jaccard (1912) as amethod of comparing the size of the common parts of
two sets, and it has been applied in various ways sincethen. To determine the similarity of two vectors, we
compute the Jaccard distance Jd using the formula below.
This indicator is for two non-negative vectors of the same
dimension. It ranges from 0 to 1, taking the minimum
value 0 when the two vectors coincide perfectly. The
larger the value, the greater the difference between thetwo vectors. Here, i is the population profile (by sex andage), xi is the population composition ratio based on
mobile spatial statistics, and yi is the population
composition ratio based on the BRRS.

J d（x, y）= 1 -∑ i min（x i ,y i ）
∑ i max（x i ,y i ）...... (1)3. Results
3.1 BRRS Data
Figure 1 shows the total population (ratio to that ofJanuary 1, 2011). The population of most areas had been
decreasing even before the disaster (the exception being
Okuma Town), and after a significant decrease from 2011
to 2012, the pre-disaster trend of population decline
resumed again. However, the post-disaster population ofmost of the 11 municipalities has declined at a greaterrate than in the rest of Fukushima. The social growth rate
(Fig. 2) has been negative in most areas, including therest of Fukushima, for most of the period since before thedisaster. An exception is Okuma town. Before 2011,
relatively young workers were constantly migrating to thetown because of steady growth in industries related to the
nuclear power plants (Okuma Town, 2016). In 2011, inseven out of 11 municipalities, the rate was lower thanthat of the rest of Fukushima. After a significant drop in
2012, the rate of natural increase remained stable in therest of Fukushima. Nine of the 11 municipalities, except
for Okuma and Tomioka, had a lower rate of natural
increase in 2012 than did the rest of Fukushima. Moremunicipalities had lower natural growth rates than rest of
Fukushima in other periods as well. Although the crude
birth rate has been declining over the long term, there arelarge year-to-year fluctuations in each of themunicipalities involved, so a clear trend cannot be readily
discerned from the figure. In the rest of Fukushima,
because of the smoothing effect of aggregation of manymunicipalities, there is a clear trend toward lower birthrates in 2012 and 2013 than in the other years. This may
be because people were discouraged from having children
due to the 2011 disaster. Crude mortality rates had been
increasing overall since before the disaster, with an
overall increase in 2011 and an even higher rate in 2012.
The increase in mortality rates in 2012 compared to 2011was higher in all 11 municipalities in the study area thanin the rest of Fukushima Prefecture.

Demographic impact of TEPCO nuclear accident

221

1.20

1.15

Total population (2011.Jan.1st = 1)

1.10

Envelope of 11 municipalities
Other Fukushima

1.05

TamuraMinamisoma
Kawamata
Naraha1.00

Tomioka
Kawauchi
Okuma

0.95

FutabaNamie
Katsurao

0.90

Iitate

0.85

0.80

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

Fig.1 Time-series of registered population in target municipalities and rest of Fukushima Prefecture.

1.0

2.0

0.5

Minamisoma-1.0

Kawamata

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

b) Natural increase rate

1.2

Okuma
Futaba2.0

Crude death rate (%)

1.0
0.8
0.6
0.4

Namie
1.5

Katsurao
Iitate

1.0

0.5
0.2

2018

2017

2016

2015

d) Crude death rate

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

c) Crude birth rate

Fig. 2 Factors in population changes before and after 2011 in BRRS.

2004

0.0

0.0

Tomioka
Kawauchi

2.5

1.4

Crude birth rate (%)

Naraha

2004

2018

2017

2016

a) Social increase rate

2015

2014

2013

2012

2011

-2.0

2010

-8.0

2009

-1.5

2008

-6.0

2008

-4.0

Tamura

-0.5

2007

-2.0

a)All of
Fukushima
Otherb)c)d)Other
Fukushima
Fukushima

0.0

2006

0.0

2005

Natural increase rate (%)

4.0

2007

Social increase rate (%)

 he registered population of the target area in the Basic Resident Registration System shows thatT
the 11 municipalities experienced a faster population decline than rest of Fukushima Prefecture.

 ut-migration from Fukushima was larger in 2012 than in other years. The main contributor to the natural decrease in year 2012 wasOa high death rate, rather than a low birth rate. Death rates in 2012 in the target municipalities were higher than in the rest of
Fukushima, indicating that evacuation from the nuclear accident caused excess deaths among the evacuees.

222

K. GomiTable 3 Population living in the evacuated areas.

 ocal governments in the target area have reported the numbers of residents living in the areas where evacuation orders have been lifted. ProgressLin population recovery varies significantly region by region. Large differences are found in the populations reported by local governments andestimates from mobile phone information.
June 30 or July 1, 2019*

End of 2017 or January 1, 2018

Registerd
population in
the evacuatedarea

Population
living in theevacuated
area

Ratio

9,542
4,240
1,022
1,570
277
16,074
12,905
6,881
2,677
55,188

4,161
1,324
480
421
225
729
1,064
3,761
2,165
14,330

43.6%
31.2%
47.0%
26.8%
81.2%
4.5%
8.2%
54.7%
80.9%
26.0%

Minamisoma
IitateKawamata
Katsurao
Tamura
Namie
TomiokaNarahaKawauhci
Total

Average increase
Nighttime population
Months since
Populationin ratio ofby mobile phoneevacuation
living in the
population in theinformation (averageorder lifted**
evacuated area
area per monthof December 2017)
34
26
26
34
36
26
26
44
63
-

1.28%
1.20%
1.81%
0.79%
2.26%
0.17%
0.32%
1.24%
1.28%
-

2,798
602
279
267
230
291
358
2,203
2,197
9,225

4,841
2,487
1,413
640
3,131
6,689
5,924
1,852
26,976

Difference indemographic
composition(Jaccard
distance)***
0.156
0.376
0.218
0.439
0.326
0.316
0.282
0.288
0.252

* August 31, 2019 in Kawauchi.
** Months by the ratio of population living in the region exceeds 80%.
*** Comparison of sex and age composition between registered population in BRRS and mobile phone information.

0.9

0.9

Tamura0.8

Minamisoma
Kawamata

0.7

0.7

NarahaTomioka

0.6

0.6

Kawauchi
Namie

0.5

0.5

Katsurao
0.4

0.4

Iitate

2019/4/1

2018/12/1

2018/4/1

2018/8/1

2017/12/1

2017/4/1

2017/8/1

2016/12/1

2016/4/1

2016/8/1

2015/12/1

2015/4/1

2015/8/1

2014/12/1

2014/4/1

0
2014/8/1

0
2013/12/1

0.1

2013/4/1

0.1

2013/8/1

0.2

2012/12/1

0.2

2012/4/1

0.3

2012/8/1

0.3

2011/12/1

Share of residents living in the evacuation zone

0.8

0 3

6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87

MonthsFig. 3 Progress in population recovery in areas where evacuation orders were lifted.

 he figure shows the share of population living in the area of the population registered there after the evacuation order was lifted. A “jumping”
Tincrease occurs in March or April, when the new fiscal and school year starts in Japan. The rate of recovery (slope of the lines) varies regionby-region, and is especially low in Namie and Tomioka, which are near to the nuclear power plant and experienced severe contamination.

3.2 Municipality Tally Data
Table 3 shows the status of the percentage of people
living in the area at the end of June or beginning of July
2019. The changes in the percentage of people living in
the area are shown in Fig. 3. The left side of the figure
shows the rate by each year and month, and in Tamura
and Kawauchi, where the evacuation orders were lifted
early, it has recently leveled off at about 80%. A large
increase in March or April is common, probably because
in Japan, the new fiscal year and school year start on

April 1, so the evacuees are expected to return in Marchor April. The right-hand side of the figure shows thepercentage of people living in the region according to thenumber of months after the evacuation order was lifted.
The larger the slope, the greater the increase in the rate ofsettlement per given period, and the faster the return andrecovery of the population. There is considerable
variation in the progress in population recovery by region(see also the “Average increase of …” column inTable 3). The variation might be explained partly by theDemographic impact of TEPCO nuclear accident

223

Table 4 Basic statistics from censuses of 2010 and 2015.

 he census is the most basic form of population statistics in the nation. The region is the area of the municipalities, i.e., in the case that aTmunicipality has evacuation zones and non-evacuation zones, this table will not differentiate between them but shows the total in the municipality.
Even in municipalities with zero nighttime population, a significant daytime population existed in 2015. The sex ratio (number of males divided bynumber of females) is quite large in some regions, i.e., there are many more males than females.
Nighttime population

Minamisoma
IitateKawamata
Katsurao
TamuraNamie
FutabaOkuma
TomiokaNarahaKawauhci
Total

2010
70,8786,209
15,5691,531
40,422
20,905
6,932
11,51516,0017,700
2,820
200,482

2015
57,79741
14,45218
38,503
0
0
0
0
975
2,021
113,807

Daytime population
2015
/2010
0.82
0.01
0.93
0.01
0.95
0.00
0.00
0.00
0.00
0.13
0.72
0.57

2010
69,455
5,628
14,4961,240
36,27019,041
6,462
15,817
15,837
8,046
2,572
194,864

2015
60,143
3,246
14,928979
34,412
1,597
322
3,701
2,961
3,002
1,899
127,1907 speciﬁc municipalities
100%
90%
80%
70%
60%
50%

Other pref.
Other Fukushima Pref.
Fukushima City
Iwaki
Soma

40%

MIharu30%

Hirono20%
10%0%KawauchiNarahaTamuraKawamata
Minamisoma

Fig. 4 Composition of residential locations of employees inthe target municipalities in 2015.

ensus data show where the employee in each municipality
Ccommutes from. In several specific municipalities that had
relatively large evacuation zones compared to their whole area,
many of the employees commute from outside even after
evacuation order was lifted. Iwaki City has been a residential place
for many of them in particular.

timing of lifting of the evacuation orders. In short, therate is higher in Tamura (where the order was lifted in2014) and Naraha (2015) than Namie and Tomioka (bothin 2017). However, variation is also observed between
the areas where the order was lifted at the same time(e.g., the rate was much higher in Iitate than Namie, eventhough the orders were lifted at the same time in bothareas). A detailed quantitative analysis of the variation inprogress is beyond the scope of this study, but morediscussion is provided later in this paper.
3.3 Census Data
Table 4 provides the main information fromcensuses: areas with zero nighttime population in 2015,
and areas with significantly fewer employees than in
2010, also have a decent sized daytime population. In

Daytime/Nighttime Sex ratio (nighttime) Sex ratio (daytime)
2015
/2010
0.87
0.58
1.03
0.79
0.95
0.08
0.05
0.23
0.19
0.37
0.74
0.65

2010
0.98
0.91
0.93
0.81
0.90
0.91
0.93
1.37
0.99
1.04
0.91
0.97

2015
1.04
79.17
1.03
54.39
0.89
3.08
0.94
1.12

2010
0.95
1.00
0.95
1.12
0.94
0.95
0.95
0.99
1.06
0.94
1.01
0.96

2015
1.17
0.21
1.02
2.00
0.99
6.56
1.53
1.11

2010
0.93
0.93
0.89
1.04
0.89
0.87
0.85
1.41
1.06
1.09
1.01
0.96

2015
1.24
9.64
1.10
14.30
0.92
14.50
17.94
29.84
16.73
5.60
1.34
1.36

2015, the sex ratio in daytime was greater than 1 in allmunicipalities but Tamura, i.e., more males than females
were there during the day. Especially in municipalities
near the nuclear plant, the ratio was quite large (nearly 30
in Okuma and 18 in Futaba). Figure 4 shows the resident
locations of employees by municipality to facilitate
analysis of commuting OD. In Minamisoma, Kawamata,Tamura and Kawauchi, where the evacuation orders werelifted early, many employees commuted to work in theirown municipality. On the other hand, in the areas where
the evacuation orders had not been lifted or where they
had been issued later, many people commuted from otherareas. The total of seven specific municipalities with aparticularly low or no daytime population are shown inthe same figure. Many of the employees in these areas
were commuting from nearby towns where no evacuation
orders had been issued. This is especially true in Iwaki
City, the southernmost coastal city and the most populated
city in the prefecture.
3.4 Mobile Phone Location Information
There are differences in the numbers of people livingin each area between the municipality tally and thenighttime population based on mobile spatial statistics(Table 3). In some areas, the latter is significantly higher
than the former. This suggests the presence ofreconstruction-related workers, temporary outsiders,
residents who return without reporting to the municipality
and residents who live primarily outside the area but
frequently visit their homes or other places of residence.
The Jaccard distance, an aggregated indicator ofvariations in demographic composition between two
information sources, was the highest in Katsurao (0.439),
followed by Iitate (0.376). It was lowest in Minamisoma(0.156) followed by Kawamata (0.218). These results
indicate that the difference tends to be larger in areas
where the ratio of people living in the evacuation area islower (Table 3). Figure 5 shows the population pyramids
for a total of the eight regions based on BRRS data (for224

K. GomiRegistered population in the municipalities(Basic Resident Registration System, June 1, 2018)

75~

75~

70~74

70~74

65~69

65~69

60~64

60~64

55~59

55~59

50~54

50~54

45~49

45~49

Age

Age

Population staying in the evacuation zone
(mobile phone information, Dec. 2017)

40~44

40~44

35~39

35~39

30~34

30~34
25~29

25~29

Female

20~24

Male

15~19

00~14

00~14
0

500

1000

1500

2000

Female

20~24

15~19

0

2500

2000

4000

6000

8000

10000

Male

12000

Population

Population

Fig. 5 Population pyramids in evacuation zones where the orders were lifted and whole municipalities, from different sources(a total of eight municipalities).
T he figure indicates the population in a total of eight municipalities that have areas where evacuation orders had been lifted by the end of
2017. The age and sex composition in the former evacuation area (left) versus the whole municipality (right) are significantly different. In
sex compositions, more males are found than females in most of the age groups in the left figure, while there are more females in the right.

mobile phone information against registered population

Ratio of age and gender composition of population in the zone estimated with

2.5

2.0

Katsurao

1.5

KawauchiKawamata
NarahaMinamisoma
Iitate1.0

Tomioka
Namie
Average
8地域平均

0.5

70~74M
70~74F65~69M
65~69F60~64M
60~64F55~59M
55~59F

50~54M
50~54F45~49M45~49F40~44M
40~44F35~39M35~39F30~34M
30~34F25~29M
25~29F

20~24M
20~24F15~19M
15~19F00~14M00~14F

0.0

Fig. 6 Differences in population composition between evacuation zones where the orders havebeen lifted and whole municipalities.
 ifferences in population composition (age and sex) vary region-by-region, but in general, males ofDworking age have a higher share in areas where evacuation orders have been lifted, while younger
people and females of reproductive age have lower shares.

the entire municipality) and mobile spatial statistics (forareas where the evacuation orders had been lifted).
According to a comparison of mobile spatial statistics
with BRRS data, males are more likely to be there thanfemales, and the working-age population is more likely tobe there than the other age groups. The ratio of thecomposition of the two information sources is shown in
Fig. 6. A higher value indicates a higher proportion of theresident population in each age and sex group in themobile phone information compared to the registeredpopulation. There is considerable variation among
regions. Among the working-age population, there are
more males and females between the ages of 45 and 59.
Among the younger age groups, there are more males
than females in the same respective age group.

Demographic impact of TEPCO nuclear accident

4. Discussion
From the results presented above, in general, we cansay that the demographic phenomena are not uniform
among the different municipalities. In this chapter we
discuss implications of the above results to the recovery
and sustainable development of this region.
4.1 Changes in Registered Population
It has been pointed out that the Earthquake, tsunami
and accident have had an impact on the population
decline in Fukushima Prefecture as a whole. The 11
municipalities that had been designated as evacuation
zones have been affected more heavily than others. As forsocial changes, the tendency to move out of the areas
evacuated has been higher in many areas than in the restof Fukushima Prefecture. However, this trend was clear
only until 2012. The number of registered residents
declined significantly immediately after the disaster but
has not changed much since 2013. This suggests thatmany people decided to move out in the first two years
after the disaster, but from the third year onwards, thetrend has been the same as it was before the disaster. In
terms of natural increase or decrease, the 2012 mortality
rate increase was higher in municipalities with evacuatedareas than in the rest of Fukushima. This is consistent
with the facts reported by Nomura (2016).
4.2 Population Composition
Fewer young people living in the area are in theirteens or younger; there are more men in their late 40s to
50s, and fewer women in their 20s to 30s. This suggeststhat households with children to care for and women ofchildbearing age have tended not to return. If thisstructure does not change in the future as the number ofresidents increases, the long-term demographic structureof the area will be one of extreme aging, followed by a
sharp decline in population. This may have a significant
impact on communities’ sustainability in the future.
4.3 Progress in Evacuees’ Return
In Tamura and Kawauchi, the percentage of people
living in the region has remained almost unchanged ataround 80%. This value is nearly identical to the
combined total of “want to return” and “have not decided”
in an opinion survey by the Reconstruction Agency(2015). Whether this applies to other regions as well is
not clear at this time, but it may serve as a reference or abenchmark for the long-term population outlook. Fromthe comparison of progress in evacuees’ return and timingof the lifting, as we mentioned above, it has beensuggested that the timing of lifting of the evacuation
orders may be a factor affecting differences in the
progress in evacuees’ return (i.e., increase in the annual
rate of residence in the area). Among the areas where theevacuation orders were lifted at the same time, the townsof Namie and Tomioka have town centers close to the
nuclear power plant, and in Namie, where progress has
been slower than in Tomioka, the proportion of Zone 3

225

areas is higher than in Tomioka in terms of both area andpopulation (actually it is the highest of the all 11
municipalities). The same discussion may apply to
Tamura, where contamination was relatively low andevacuation was ordered for only a small part of the city.
These conditions suggest that factors that slow progress
may include proximity to the nuclear power plant andlarge proportions of residents in areas that have not yet
had their orders lifted . We think this is an important
finding for predicting the progress in evacuees’ return to
the towns of Okuma and Futaba, which were not includedin the analysis of evacuees’ return, as well as to otherspecific centers for reconstruction and rehabilitation in
Zone 3.
4.4 Commuting Structure
Where evacuation orders have been lifted, in general,many people commute from the outside, instead of livingin those areas. Results of a survey by the Reconstruction
Agency (2020) may explain the reason for that. Many
respondents reported that a lack of medical and shopping
facilities and support for housing were the main barriers
hindering their return. From our results and the survey,
even though economic activity has recovered thanks topolicy initiatives, without such facilities and support, thenighttime population may not recover. Based oncomparison of the areas where the evacuation orders havebeen lifted so far, though, the percentage of commutersfrom outside the areas is expected to decrease as the
population recovers. However, especially in the areas
where the evacuation orders have been lifted or will belater, many commuters will continue to commute fromthe outside until the population recovers. To mitigate this,
it is important that those who wish to return should be
able to do so as soon as possible. In addition, among
those who work in the region, some were not residents
before the accident, but arrived because new industrial
development led by the government necessitated different
expertise among employees compared to before thedisaster. It will be necessary to remove obstacles forpeople moving into the area and joining the community.

5. Concluding Remarks
In this study, migration and return to the areas
affected by the nuclear power plant accident were
investigated using multiple sources of data to clarify the
demographic situation. Each source had its own inherent
limitations, and care needed to be taken in interpreting
the results. Analysis using mobile spatial statistics isparticularly subject to uncertainty: since the estimates are
scaled up according to the percentage of subscribers to
NTT DoCoMo’s mobile phone service, deviations fromthe true values may be large, especially in small areas. In
addition, in many areas, there is no differentiation amongpeople living in the evacuation zone, evacuees andnewcomers. Therefore, this study has not been able to226

K. Gomidiscern how many of the residents in the area are
returnees.
The information we have been able to obtain so far
in this study is limited, and many issues remain to beaddressed in analyzing the population of the evacuatedareas. First, it will be necessary to continue to survey thesituation among newer returnees, including those to areas
where the evacuation orders have been lifted very
recently. Next, quantitative analysis of factors affecting
regional differences in the progress in evacuees’ return
could help project future progress of their return andidentify what is needed to enable residents who wish to
return to their homes to do so more quickly. Once theseissues are addressed, many of the insights needed for
estimating the future of the population over the long term
will be available, allowing for a long-term socioeconomic outlook that explicitly takes uncertainty into
account.
References
Hashimoto, N. and Kawakami, Y. (2015) An empirical analysis of
migration in the area affected by the Great East Japan
Earthquake. Japan NPO Research Association Discussion Paper.
(in Japanese) Retrieved from https://www.janpora.org/dparchive/
pdf/2015001J.pdf (Accessed 26 November 2020)
Hauer, M.E., Holloway, S.R. and Oda T. (2020) Evacuees andmigrants exhibit different migration systems after the Great East
Japan Earthquake and Tsunami. Demography, 57, 1437–1457.
Higuchi, Y., Inui, T., Hosoi, T., Takabe, I. and Kawakami, A. (2012)
The impact of the Great East Japan Earthquake on the labormarket: Need to resolve the employment mismatch in thedisaster-stricken areas. Japan Labor Review, 9(4), 4–21.
Kubo, M., Tsuchida, S. and Shizuma, K. (2017) A study of deaths
related to the Great East Japan Earthquake in Fukushima
Prefecture. Journal of Atomic Energy Society of Japan, 59(129),
49–53. (in Japanese)
Morita, T., Nomura, S., Furutani, T., Leppold, C., Tsubokura, M.,
Ozaki, A., Ochi, S., Kami, M., Kato, S. and Oikawa, T. (2018)
Demographic transition and factors associated with remaining inplace after the 2011 Fukushima nuclear disaster and related
evacuation orders. Plos One, 13(3), e0194134. Retrieved fromhttps://doi.org/10.1371/journal.pone.0194134
Nomura, S., Blangiardo, M., Tsubokura, M., Nishikawa, Y.,
Gilmour, S., Kami, M. and Hodgson, S. (2016) Post-nuclear
disaster evacuation and survival amongst elderly people in
Fukushima: A comparative analysis between evacuees and nonevacuees. Preventive Medicine, 82, 77–82. Retrieved from http://dx.doi.org/10.1016/j.ypmed.2015.11.014
Okuma Town (2016) Creation of Towns, People and Jobs:
Population Vision. (in Japanese) Retrieved from http://cms.town.
okuma.fukushima.jp/uploaded/attachment/4513.pdf (Accessed
26 November 2020)
Reconstruction Agency (2015) Heisei 27 Resident Intention Survey
in Evacuation Area due to the Nuclear Disaster. (in Japanese)
Retrieved from https://www.reconstruction.go.jp/topics/maincat1/sub-cat1-4/ikoucyousa/ (Accessed 30 August 2020)
Reconstruction Agency (2020) Reiwa 1 Resident Intention Survey
in Evacuation Area due to the Nuclear Disaster in Fukushima
Prefecture. (in Japanese) Retrieved from https://www.reconstruction.
go.jp/topics/main-cat1/sub-cat1-4/ikoucyousa/ (Accessed 30
August 2020)

Kei GOMI
Dr. Kei Gomi is a senior researcher in the
Regional Environmental Renovation Section of
the National Institute for Environmental Studies,
Fukushima Branch. His research activities havefocused on integrated modeling for climate action
and sustainable society scenario development inmunicipalities across Japan and in other Asian
countries. Since 2014, he has been involved in research toward recovery
and renovation from the Great East Japan Earthquake and Tsunami of 2011.
His recent research interests are integration of the SDGs into planning
processes and comprehensive recovery from nuclear disasters. He received
his Ph.D in global environmental studies from Kyoto University in 2010.

(Received 16 October 2020, Accepted 21 December 2020)

227

A Study on Sustainable Energy Systems
for Small Villages in Fukushima
Takuya TOGAWA1*, Yi DOU 2, Shogo NAKAMURA1 and Makoto OOBA1Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan*E-mail: togawa.takuya@nies.go.jp*1

Abstract
We investigated the design and operation of distributed energy systems for the central area of Mishima
Town in the Oku-Aizu area of Fukushima Prefecture. These systems were tailored to the characteristics of theregion. Although we found that the deployment of an energy system utilizing forest biomass resources wasdesirable from the perspectives of CO2 emissions and economic circulation based on local natural resources,
the cost of energy was relatively high. Based on these results and related information, we considered theprocesses required for implementing energy systems utilizing forest biomass resources. Our results show thatto create sustainable communities based on renewable energy in rural areas with low population density, it isimportant to integrate energy system development with community development from a medium- to longterm perspective.
Key words :	autonomous distributed system, mathematical optimization, mixed integer linear programming,
regional revitalization, renewable energy

1. Introduction
Interest in renewable energies has grown against the
backdrop of global environmental issues, with the Great
East Japan Earthquake revealing the vulnerabilities oflarge-scale centralized electric power supply systems.
These two considerations have led to increased
nationwide momentum to promote the introduction of
distributed energy systems utilizing renewable energies(Nakata, 2015). In addition, frequent abnormal weather
events such as heavy rains and snowfalls in recent years
further have spurred this trend. This is particularly ofgreat concern in Fukushima Prefecture, Japan, which is
now suffering from all of these problems, necessitating acomprehensive solution for revitalization.
Up to now, however, technology and policies related
to resources and energy have been regarded as nationaland global issues and, therefore, “given conditions” that
could not be altered at the level of local living andeconomies. Adverse impacts have arisen due to the large
gap between the given conditions and local situations.
For example, in mountainous and other remote areas,
energy supply infrastructure such as gas pipelines has notbeen sufficiently developed. Thus energy prices havetended to be higher there than in urban areas. Rural
Global Environmental Research
24/2020: 227-236
printed in Japan

communities have been unable to implement effective
measures to address such situations. Especially in cold
regions where there is great demand for space heatingand hot water supply, utility costs are a burden forhouseholds. Furthermore, inadequate space heating andhot water supply systems along with poor building
insulation lower residents’ quality of life.
Meanwhile, Japan’s 5th Basic Environmental Plan
has advocated maximizing the vitality of regions by using
regional resources to build self-reliant, decentralizedsocieties based on the characteristics of regions and, tothis end, proposes the concept of regional circular andecological spheres that complement and support regional
resources. The introduction of renewable energy isregarded as a substantive measure that will contribute to
the creation of such regional circular and ecologicalspheres (Shirai, 2018a; Shigeto et al., 2018). Effective
use of forest resources has been recognized as a key issue
for revitalizing local economies and sustainable regional
development in rural communities especially inmountainous areas (Uragami & Itogami, 2007). In
addition, development of technologies such as small
biomass cogeneration systems for converting forest
resources into energy are being actively promoted (Japan
Woody Bioenergy Association, 2017a, b).
©2020 AIRES

228

T. TOGAWA et al.

Previous studies related to sustainable community
development in mountainous areas have been carried out
at the village or regional scale comprising single ormultiple local governments. Research at the village scale
has focused on specific energy projects and their impacts(Asano & Takaguchi, 2015). A number of studies at theregional scale have focused on regional circulation effectsof biomass and other resources (Sumitomo et al., 2015;
Miura et al., 2018; Nakamura & Shibata, 2013).
However, since these previous studies have been carriedout in parallel at each scale, inter-scale effects—for
example, the impact of village-scale energy systems on
resource circulation at a regional scale—have not beenadequately investigated.
Therefore, this study examined the feasibility oftransition to next-generation energy systems utilizing
local resources in mountainous villages of Japan, andquantified the impacts of introducing such systems on thebalance of resource supply and demand, as well as on theregional environment and socio-economy.

2. Study Area and Data
2.1 Study Area
This study targeted the central area of Mishima
Town in the Oku-Aizu area of Fukushima Prefecture.
According to the 2015 census, the population of Mishima
was 1,792, and the proportion of the population 65 orolder had already reached 49% (compared to the averagefor Japan of 26.6%). The main industries included
construction and electric power connected with a local
Tohoku Electric Power hydroelectric power plant(maximum output 94,000 kW), followed by agriculture,
forestry and tourism. The area of the town is 1,518 km2
with approximately 80% of that area being forested.
Therefore, regional development based on effective
utilization of woody biomass resources as energy has
become a goal of public policy. The use of woody
biomass resources, however, has been limited to theintroduction of wood pellet stoves and firewood stoves inForestWelfare facility

Prefectural
hospital

some public facilities and houses.
Figure 1 and Table 1 provide an outline of the study
area. The area inside the dotted line in Fig. 1 is the central
area of Mishima Town, which is the subject of this study.
Facilities such as the town hall, prefectural hospital, Aizu
Miyashita Station and welfare facilities are locatedcentrally and play a central role in the town. Solar panels
have been installed on the welfare facilities. Althoughhousing accounts for only a small proportion of buildingsin the central area of the town, that area has the town’slargest population concentration .
We estimated spatial information for the area thatwas required for energy system assessment. This included
the length of the heat distribution pipes that would be
required for deploying district heating and the area ofland where solar panels could be installed. The pipe
length was assumed to be the length of the shortest road
network required to connect the buildings in the area. It
was assumed that solar panels would be installed on theroofs of buildings in the central area of the town.
However, since roof area data were not available, thebuilt-up area was assumed to be the roof area. Building
data were estimated based on information from Zenrin
Tatemono Pointo (2014 version) and road network data
based on Zenrin Data Zmap-Town II (2015 version) using
GIS.
2.2 Establishing the Renewable Energy Supply
Potential
Since the renewable energy supply potential depends
on the characteristics of the region, we set assumptions
regarding the biomass resources and photovoltaic power
generation potential required for subsequent analysis. The
NEDO estimate (2011) for available biomass resources(forest residuals from harvesting and trimming) is 4,085
tons/year for Mishima Town and 43,746 tons/year if theresources of the four nearby towns and villages (Tadami
Town, Yanaizu Town, Kaneyama Town, and Showa
Village) in the Oku-Aizu area are included. This value isreferenced in the evaluation of the regional circularsphere. The photovoltaic power generation potential was
set based on monitoring data collected by the authors in
Mishima Town. Figure 2 shows the power generated by a
1 kW solar panel. The figure shows hourly data for one
week from January 1 to 7 as well as monthly data. The
Oku-Aizu region is a heavy-snowfall area that receives
approximately 60 cm of snow annually in the winter. The
Table 1 Overview of study area.

Town office

Aizu Miyashita
Station

ForestFig. 1 Study area (central district in Mishima Town).

No. of Households

Households

211

Population

Individuals390

Building Floor Area

2

[m ]

64,339Conduit Length

[m]

4,663

Roof Area[m ]32,2622

A study on sustainable energy systems for small villages in Fukushimaeffect of this snowfall is confirmed as reduction of power
generation during the winter months in Fig. 2. It is
assumed that the solar panels were covered with snow
from Jan 3 to 6. These data are referenced in subsequent
analyses as the potential amount of photovoltaic power
generation.

[kWh]

2.3 Energy Demand
Hourly energy demand data were set for the study
area for the following use categories: electric power,
cooling, heating and hot water supply. First, annual
energy demand was calculated by multiplying the floorarea for each use in each neighborhood by the energy
load intensity. Then, hourly energy demand was
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0

0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 1823

[kWh]

160
140
120
100
80
60
40
20
0

Oct

Noｖ

Dec

Jan

Feb

Mar

Apr

2017

May

Jan 6(Sat) Jan 7(Sun)

Jun

Jul

Aug

Sep

2018

Electricity

CoolingHea�ngHot water supply

Superstructure
Demand

3.5
3
2.5
2
1.5
1
0.5
0

3.1 Overview of the Planning Process Model
To examine the effect of introducing alternative
energy systems, it is necessary to evaluate detailed systemdesigns and optimal operation of each general system
type comparatively. In this study, the planning processmodel reported in previous studies (Togawa et al. 2017;
Togawa et al., 2020a) was used to determine theconditions resulting in minimal cost for design andoperation. The basic structure of the planning processmodel is shown in Fig. 4.
An energy system converts power supplied by thegrid or fuel from outside the system (gas, kerosene,
biomass resources, etc.) into electric power, heating andcooling, and hot water supply for use on the demand side.
First, we set up an energy system study framework.
Figure 4 shows a general structure including all candidate
energy systems that is referred to here as the

Supply[MWh]Fig. 2 Monitoring data of photovoltaic power
generation in the study area.
The upper graph for each case shows the hourly data (for one
week in January). The lower figure shows the monthly data.

0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18 0 6 12 18
Jan 1(Mon) Jan 2(Tue) Jan 3(Wed) Jan 4(Thu) Jan 5(Fri)

CoolingHea�ngHot water supply

DemandElectricity

DesignJan 6(Sat) Jan 7(Sun)Supply[MWh]calculated by multiplying the annual energy demand by
the monthly and hourly proportions. The values reported
by Kashiwagi (2008) were used for the ratio of energy
load intensity and for monthly and hourly proportions; toreflect circumstances in the Tohoku region for energy
load intensity, we used the correction coefficient fromJapan District Heating & Cooling Association (2002).
Regarding the housing sector, the authors monitored
energy consumption at 12 all-electric homes in Mishima
for one year from October 2017 to September 2018.
Hourly and monthly electric power consumption wasmeasured by meters for each use category, and power
consumption for each use category was corrected using
the measurement results. Figure 3 shows the calculated
energy demand results (hourly values for the week ofJanuary 1 to 7 and monthly values for the year) for the
study area.

3. ModelJan 1(Mon) Jan 2(Tue) Jan 3(Wed) Jan 4(Thu) Jan 5(Fri)

Selected
Not selected

Operation
Noｖ
2017

Dec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

2018

Fig. 3 Energy demand in study area.

The upper graph for each case shows the hourly data (for one
week in January). The lower figure shows the monthly data.

Sep

DemandOct

Supply

900
800
700
600
500
400
300
200
100
0

229

On status
Oﬀ status

t=1

t=2

Fig. 4 Basic structure of planning process model.

t=2016

230

T. TOGAWA et al.

“superstructure,” following the nomenclature used inprevious research (Yokoyama, 2014). The superstructure
is represented by the subsystems that represent thecandidate devices that make up the system and thepotential flows of energy between them (input/output
relationships).
Next, we simultaneously specified the system
configurations that minimize the cost function, which
combines flow values such as fuel consumption withstock values, such as installed capacity, and the operatingplans for each season and time period. Fuel consumption
was calculated by multiplying the energy demand of thebuildings shown in Fig. 3 by the energy conversion
efficiency of the equipment. Depending on the purpose, asubsystem can be selected from the superstructure, andthe equipment to be operated and the input/output levelfor operation can be specified for each season and time
for the selected equipment. For this reason, equipmentthat needs to be operated even once must be selected at
the design stage and the capacity of the equipment must
be greater than or equal to the annual maximum output
value.
However, for this study, because the calculation load
would be prohibitively high if the analysis were
performed for 8,760 hours a year, the calculations were
performed for 2,016 hours based on the data for one week
extracted from each month. It was also assumed that thesame type of energy system was installed in all thebuildings in the study neighborhood.

3.2 Establishing the Superstructures
Taking into consideration the availability ofresources and technological progress (Nakamura et al.,2018) in mountainous areas, we assessed the impact of
three different cases involving introduction of alternative
energy systems that combine biomass-related
technologies and photovoltaic power generation withthe currently deployed system. Figure 5 shows thesuperstructure of the system. Here, the energy systems
were treated as an aggregated unit for a givenneighborhood; the capacity of each component of theenergy systems could be set from continuous variables
except in the case of biomass cogeneration (BCHP:
Biomass Combined Heat and Power), which has arelatively large capacity per unit.
Case 1: Conventional System
Room air conditioners, kerosene heaters and gas
water heaters are used for cooling, heating, and hot watersupply, respectively. The energy supply sources are grid
power, kerosene, and LPG (liquefied propane gas).
According to survey results, this is the most common
system configuration in the study area (Nakamura et al.,2018).
Case 2: Photovoltaic Power Generation+ All-Electric System
All energy is supplied by the grid and solar panels.
Room air conditioners and heat pump water heaters areused for cooling, heating, and hot water supply. The
installation of storage batteries and heat storage tanks ispossible. As mentioned above, the maximum installation
Solar
batteries
Grid interconnection

Grid
Grid

Electricity
Air
conditioner
Kerosenestove
Gas waterheater

Kerosene
LPG
SourceElectricity

Storagebatteries

CoolingHeating

Sourcea) Case 1: Conventional System

HeatingHeat pump

Hot water

Consumer

Cooling

Air conditioner

Consumer

Hot water

Storagetankb) Case 2: Photovoltaic Power Generation+ All-Electric System

Solarbatteries
Grid

Grid interconnection

Storagebatteries
PelletSourceElectricity
Air conditioner
Pellet
Stove
Pelletboiler

CoolingHeating

Woody
Chips

BCHP
Storagetank

Hot water
SourceConsumerc) Case 3: Photovoltaic Power Generation

Absorption
chiller

District system

Air conditioner

Electricity
CoolingHeat
exchange

Heating
Hot water

Heat pipe

Consumerd) Case 4: Biomass Combined Heat and+ Biomass Heat Supply System
Fig. 5 Energy system alternatives.

Power System (BCHP)A study on sustainable energy systems for small villages in Fukushima

231

Table 2 BCHP unit parameter values.

Generation
System Type

Cost (1,000 JPY/Year)

Electric Power
OutputGeneration
Efficiency

ThermalEfficiency

Gasifier

45 kW

0.25

0.56

2,000

460

2,700

Gasifier

180 kW

0.30

0.45

22,000

5,900

2,700

ORC

600 kW

0.19

0.69

74,000

9,100

5,400

Capital Costs

Maintenance

Labor

Sources: Japan Woody Biomass Association (2017a, b), Nakagawa (2015), Bartenstein (2015).

area for solar panels equals the building roof area. In
recent years, all-electric houses, which are considered to
be one of the directions for future energy system
conversion, have been constructed in the study area
(Mishima Town, 2018).
Case 3: Photovoltaic Power Generation+ Biomass Heat Supply System
Although grid power and solar photovoltaic panels
are used as in Case 2, stoves and boilers that use biomasspellets as fuel are used for heating and hot water supply.
Given that the stoves and boilers are installed by eachcustomer, installation of heat distribution pipes is notnecessary. This scenario assumes the deployment to eachcustomer of photovoltaic power generation and biomass
heat supply systems that have already been installed insome buildings in the study area.
Case 4: Biomass Combined Heat and Power System(BCHP)The BCHP system generates the necessary electric
power and uses the waste heat for heating, cooling andhot water supply. Therefore, a heating pipe network is
required for the district. BCHP assumes the deploymentof a 10 to several hundred kW-class system similar to
those being developed mainly in Europe. The available
BCHP devices are shown in Table 2, with up to two units
being selectable for each system. This scenario proposes
the introduction of leading-edge technology of which
only a few examples exist in Japan.
The set values of other components required for eachenergy system were specified based on vendor catalogs,
and the unit prices for electricity, kerosene and LPG wereset based on the prices in the study area (Togawa et al.,2017).

4. Results
4.1 System Design and Operating Plans
Table 3 gives a summary of the system designs foreach case and lists the installed capacity of major
components of the energy systems shown in Fig. 5. First,
we confirmed the capacity of the solar photovoltaic
systems for Cases 2 and 3. In Case 2, a photovoltaic
system with a capacity equivalent to about 60% of theinstallable area (building roof area) was selected. The
capacity of the photovoltaic system in Case 3 was slightly
smaller than in Case 2 due to the lower electricity demand

Table 3 Summary of system components.

Case 1Case 2

Case 3

Case 4

Room Air Conditioner

(kW)

3,630

Kerosene Stove

(kW)

3,853

Gas Water Heater

(kW)

524

Photovoltaic Panels

(kW)

1,922

Room Air Conditioner

(kW)

3,630

Heat Pump Water Heater

(kW)

598

Photovoltaic Panels

(kW)

1,817

Pellet Heater

(kW)

3,853

Pellet Boiler

(kW)

475

BCHP

(kW)

870

Storage Batteries

(kWh)

5,359

Heat Exchange Unit

(kW)

6,380

for heating and hot water, which were covered by woodpellets instead. Next, we examined factors fordetermining the capacity of the pellet stoves and thepellet boilers in Case 3 by comparison with the demand
shown in Fig. 3. The installed capacity of the pellet stoves
was set at 3,853 kW, which corresponds to the peakheating demand in winter (January). For the week shownin Fig. 3, the peak heating demand was about 3,000 kW.
However, as the peak times for residential and businesssystems differ, the combined total of the peak heating
demands is about 3,853 kW. On the other hand, theinstalled capacity of the pellet boiler was set at 475 kW,
which is about half the peak demand for hot water supply
in winter (January) (about 800 kW for the week shown in
Fig. 3). Given the high cost of biomass boilers, it was
assumed that heat storage tanks would be installed to
optimize the systems and minimize boiler size.
4.2 Operating Plans
Next, to confirm how the systems operated, we
examined the energy supply and demand by hour andmonth (Fig. 6). The supply and demand data forelectricity and hot water for each case are presented. The
upper graph for each case shows the hourly data (for one
week in January) while the lower figure shows themonthly data. The equipment used to supply energy inresponse to demand is shown. Negative values for the
supply from storage batteries and hot water tanks in thehourly diagrams indicate energy is being stored. First,

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T. TOGAWA et al.

Photovoltaic

Grid power

Electric power demand

Electricity supply and demand (Case 2)
Photovoltaic

Grid power

Electric power demand

Electricity supply and demand (Case 3)
BCHP

Storage battery

Electric power demand

Electricity supply and demand (Case 4)

Heat pump

Heat storage tank

Hot water demand

Hot water supply and demand (Case 2)
Pellet boiler

Heat storage tank

Hot water demand

Hot water supply and demand (Case 3)
BCHP

Heat storage tank

Hot water demand

Hot water supply and demand (Case 4)

Fig. 6 Supply and demand data for electricity and hot water in each case.

The upper graph for each case shows the hourly data (for one week in January). The lower figure shows the monthly data. Negative values forthe supply from storage batteries and hot water tanks in the hourly diagrams indicate energy is being stored.

A study on sustainable energy systems for small villages in Fukushima

-450

6,000
30

4,000
2,000

-2,000-4,000

Case1

Case2

Case3

Case4

0

-30

-6,000-8,000-60[million[million Yen]
Yen/year]0Fig. 8 
Results of evaluating CO2 emissions and the economic
value of these CO2 reductions.

Contribution to regional
economic circulation-400[million Yen/year]

60

8,000
2

4.3 Impacts of System Deployment
Figure 7 shows the results of estimating energy costs
for the entire study area for each case. The energy cost
including equipment associated with Case 1 wasapproximately 300 million JPY. The energy cost
reductions associated with Cases 2 and 3 were on theorder of 20%. However, Case 4 resulted in a 34%
increase in cost.
Next, we examined the effect of system deployment
on economic circulation. In Cases 1 and 2, most of theeconomic benefits are thought to flow out of the region.
The items that are likely to contribute to regional
economic circulation (personnel costs, maintenance costs,
pellet charges, chip charges) amounted to 52 million JPY
for Case 3 and 175 million JPY for Case 4. These costs
only accounted for approximately 1% in Case 3 and 3%
in Case 4 of Mishima Town’s total production, which is
6.1 billion JPY (Ministry of the Environment & ValueManagement Institute, 2013). These results indicate theimportance of expanding measures beyond the central
area to the surrounding areas if they are to have an impact
on revitalizing the regional economy.
Figure 8 shows the impact of each case on CO2emissions and emissions reduction. Cases 2 and 3
reduced CO2 emissions by 28% and 43%, respectively,
compared to Case 1. In Case 4, CO2 emissions were zero
because energy from fossil fuels was not used. Using a
CO2 transaction price of 4,355 to 8,710 JPY/ton-CO2(40 to 80 USD/ton-CO2) from the World Bank (2019), theeconomic value of these CO2 reductions is estimated tobe 6 to 47 million JPY. In all cases, the value is about
10% to 40% compared to the increase/decrease in directenergy costs, indicating the importance of taking thevalue of environmental benefits into account whenselecting energy systems.
Next, we examined the consumption of biomass
resources. Here, the amount of woody biomass resources
used as raw materials was evaluated in a unified manner.
We assumed that both pellets and chips were produced
from woody biomass resources with a moisture content
of 50%, which is equivalent to that of raw wood, andconverted biomass mass into energy units assuming 1 kg
= 2.33 kWh. The results are shown in Fig. 9 together withthe available woody biomass resources in Mishima Town.
In Case 3, the consumption of biomass resources wasapproximately 40% of the amount available to Mishima[ton-CO2/year]][ton-CO

from the electric power supply and demand for Cases 2
and 3, it can be seen that photovoltaic power generation
exhibits substantial seasonal and daily fluctuations, withthe amount of power generation in winter being
particularly limited. Furthermore, from the hourly supply
and demand for hot water supply in Case 2, it can be seenthat the heat pump water heater is operated using lowcost nighttime electricity. In addition, from the hourly
supply and demand for hot water supply in Case 3, it isevident that hot water is stored during the low-demand
period with the 475 kW biomass boiler operating at full
capacity, which is lower than the peak demand; the stored
hot water is consumed during the peak demand period in
the evening. Similarly, from the results for Case 4, it canbe seen that the BCHP system operates steadily at
870 kW throughout the year, storing surplus electricity atnight when demand is low and distributing the stored
electricity during peak daytime demand periods when the
BCHP system output is lower than demand. As above,
appropriate system designs and operating plans were
derived for each case.

233

-350
-300
-250
-200
-150
-100
-50
0

Case1

Case2

Case3

Case4

Deprecia�onDepreciation
Deprecia�on(plumbing)(Distribution pipes)

Maintenance fee

Labor costs

Electricity charges

Gas charges

Kerosene charge

Pellet fee

Chip fee

Fig. 7 Cost evaluation results.

Fig. 9 Results of evaluating biomass resource consumption.

234

T. TOGAWA et al.

Town, while the consumption in Case 4 greatly exceededavailable resources. However, in all cases, the amountconsumed was small compared to the total annual
biomass resources available in the Oku-Aizu area
(48,736 tons/year according to NEDO, 2011). Thus, we
believe that the use of biomass energy can contribute torevitalization of forestry in Mishima Town and the OkuAizu area.

5. Discussion
As shown in Fig.7, we found that it would be
difficult to introduce neighborhood energy systems basedon BCHP due to the substantial initial investment
associated with neighborhood BCHP systems. However,the system is expected to have a positive regional effect(Figs. 8 and 9). Also, these results are based on thecurrent socio-economic situation. It is important to take
into consideration that technological development ofsmall-scale energy supply systems suitable forneighborhood energy systems is actively progressing(Murugan & Horák, 2016). In particular, small 10 kWclass biomass cogeneration system units have beendeveloped and are being deployed mainly in Europe. In
Japan, studies have been carried out addressing
component technologies related to biomass power
generation. Yanagida et al. (2015) analyzed therelationship between the break-even point and raw
material procurement cost for biomass power generation
businesses at various output scales. They found that, even
if a relatively high feed-in-tariff purchase price isassumed, the amount of power generated must be 5 MW
or greater to be profitable. Sasauchi (2015) examined thetechnical characteristics of steam turbine power
generation, gasification with gas engine power
generation, and ORC (Organic Rankine Cycle) power
generation, which are typical power generation methods
for woody biomass, and reviewed the profitability ofsmall-scale projects for each method. They found that thesteam turbine method is not profitable for small-scale
power generation businesses of about 2 MW. However,profitability is greatly improved for gasification with gas
engine power generation and ORC power generation,
which can supply heat along with power, indicating thebusiness potential of such systems. Similarly, Kuboyama
et al. (2016) and Komata et al. (2016) point out the needfor cogeneration when using small-scale biomass
generators. As described above, technologies for practical
distributed energy systems that can contribute to local
economies by utilizing forest resources in mountainous
areas are being developed. The output of the 870 kW
BCHP examined in this study was less than half that of
the 2 MW-class systems evaluated in the above studies.
Moreover, as can be seen from Fig. 6, the efficiency ofheat utilization is not always high. These points alongwith those mentioned above indicate that increasing

demand and improving heat utilization efficiency arechallenges that must be overcome.
Based on the above, the key to implementing local
energy systems is improving energy utilization efficiency
through cogeneration. However, as the ability to transport
thermal energy is limited, efforts must be integrated with
regional development plans that include, for example,
concentrating energy consumers. In a previous study(Shirai, 2018b) field studies were conducted in eightpioneering examples of integrated energy business andcommunity development, clarifying the roles played bystakeholders such as local companies, citizen networks,
regional organizations and universities. It has also been
pointed out that these examples are not based on topdown deployment but, rather, the result of co-creative
processes by diverse stakeholders in a community. A casestudy conducted by the authors in Shiwa Town, Iwate
Prefecture, which is an environmentally leading
municipality, found that budding efforts in resource
circulation that started around 2000 have spawned otheractivities including the development of various spaces by
diverse stakeholders through co-creative processes(Togawa et al., 2020b). These results show that to create
sustainable communities based on renewable energy inrural areas with low population density, it is important tointegrate energy system development with community
development from a medium- to long-term perspective.
However, no general design schemes that can be applied
to different complex problems have been sufficiently
developed, and past approaches have tended to rely on
local experience. In our research as well, we examined a
top-down method for designing a distributed energy
system. Frameworks for bottom-up design of sustainablecommunities that complement this top-down approachneed to be developed.
In addition, various social benefits associated with
deployment of distributed systems have also been
identified. These include the stabilization of employment
by building energy supply systems in local communities,
enhanced continuity of the energy supply in the event of
a disaster, and improved safety and security of the region(Nakata 2015). Therefore, it is important to develop
systems that are competitive in function with large scale
systems while also being tailored to the unique
circumstances of each community through co-creative
processes and multidimensional perspectives that cover
the environment, economy and society.

6. Conclusions
In this study, we developed designs and operatingplans for and evaluated the deployment potential of
alternative energy systems taking into account thestructure of the neighborhoods that made up the area andthe supply characteristics of renewable energy. Ourfindings were as follows:A study on sustainable energy systems for small villages in Fukushima● Based on hourly energy supply and demand, wedeveloped a planning process model that cansimultaneously derive optimal energy system design andoperating plans and conducted analyses using dataobtained through monitoring in the actual community.
● We conducted analyses using models based on
information that we had obtained for the central area ofMishima Town, Fukushima Prefecture, which has
characteristics typical of the mountainous areas of Japan.
Our results showed that it is possible to reduce energy
costs by introducing a fully electrified system that uses
photovoltaic power generation. We also showed that the
introduction of biomass boilers and biomass cogeneration
systems that utilize forest biomass resources is desirablefrom the perspective of CO2 emissions reduction andlocal resource circulation.
● We considered issues for implementation ofregional energy systems in rural areas with low
population densities. We found that a framework wasnecessary for comprehensively designing sustainablelocal communities that incorporates regional developmentin the surrounding area with selection of appropriate
distributed energy systems that are tailored to regional
characteristics.
References
Asano, H. and Takaguchi, H. (2015) Research on the planning ofvillage that self-sufficient in energy on the time of aggregationin Kumano, Mie: Proposal for the planning of village that selfsufficient in energy in semimountainous area. Technical Papersof Annual Meeting the Society of Heating, Air-conditioning andSanitary Engineers of Japan, 10, 233–236. (in Japanese)
Bartenstein, O. (2015) Spanner wood cogeneration plant. Journalof the Japan Institute of Energy, 94(11), 1198–1203. (inJapanese)Japan District Heating & Cooling Association (2002) District
Heating and Cooling Technical Guidebook, Revised Edition,
Tokyo. (in Japanese)
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Bioenergy for Combined Heat and Power. (in Japanese)
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Kashiwagi, T. (2008) The Japan Institute of Energy: Natural Gas
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Takuya TOGAWA
Takuya Togawa is a senior researcher at the
National Institute for Environmental Studies,
Fukushima Branch. He received his doctorate inengineering from the Graduate School ofEnvironmental Studies, Nagoya University in2010. He is engaged in research on mechanisms
for realizing disaster recovery and regional
revitalization by effectively utilizing local environmental resources.

Yi DOUYi Dou is a project researcher for the Presidential
Endowed Chair for “Platinum Society,”
University of Tokyo. He received his doctorate
in engineering from Nagoya University in 2019,and his research interests are closely related tourban sustainable development, especially
focusing on promoting circular economies andproliferation of emerging technologies through regional energy planning.

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch. He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Makoto OOBA
Dr. Ooba heads the Environmental Renovation
Laboratory at the Fukushima Branch of the
National Institute for Environmental Studies,Japan. From 2007 to 2012 and from 2014 to thepresent, he has participated in a study on spatialassessment of Japan’s regional forests using
process-based models and remote sensing by
NIES. Based on these studies, he has analyzed sustainability of forestry andharvested wood products. He has also worked at Osaka University, Nagoya
University and the Tokyo University of Agriculture. He holds a Ph.D. inenvironmental science from Hokkaido University, 2002.
(Received 2 December 2020, Accepted 27 December 2020)

237

Survey on Household Wood Biomass Use and Energy Consumption
in the Oku-Aizu Region
Shogo NAKAMURA* and Takuya TOGAWA
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: nakamura.shogo@nies.go.jp

Abstract
We surveyed and analyzed the current status of household energy consumption and use of firewood andother wood biomass in the town of Mishima, Fukushima Prefecture for the purpose of building a supply chain
model for forest resource use in mountainous regions. The number of questionnaires returned was 341, with a
response rate of 48.6%. The survey results revealed that approximately 9% of households were using woodbiomass combustion devices. Annual firewood consumption per household was 3 m3, and over 90% of the
raw logs used were procured inside the town. The difference in the ages of the houses of firewood users andnon-users suggests that building structure may have influenced this result.
Key words :	firewood, household energy consumption, mountainous area, questionnaire survey, wood stoves

1. Introduction
Ascertaining the status of wood biomass utilization
for household wood stoves and other wood-burning isimportant from the perspective of utilizing regional forest
resources and tackling climate change. Although cold
mountainous regions tend to be sparsely populated, percapita energy consumption for heating is likely to be highand, therefore, deserves detailed investigation.
Several studies have already been conducted on theuse of wood biomass from the viewpoint of solving
environmental problems simultaneously. Nemoto et al.
(2017a, b) investigated household use of wood biomass
combustion devices from a nationwide view. Regionally,
Hatanaka et al. (2011, 2012) surveyed household use ofwood-burning devices in 10 municipalities in Nagano
Prefecture from the viewpoint of effects of carbon
emissions reductions. From the viewpoint of promoting
usage of unused biomass, Ogasawara et al. (2017)
investigated the use of firewood in fruit-producing areas
and found higher use of wood stoves and other woodburning devices than in other areas owing to the readyavailability of tree prunings. Many case studies at a local
scale have also been conducted, for example, Izumi et al.
(2018) conducted a random electoral-register-based
sampling survey to ascertain the level of firewood use in
Shiwa Town, Iwate Prefecture. Harashima et al. (2014)
researched the utilization of wood stoves and other woodburning devices and firewood consumption in the
Minowa district of Ina, Nagano Prefecture, through avisual survey and questionnaire. Uezono (2018) also
Global Environmental Research
24/2020: 237-242
printed in Japan

conducted a questionnaire survey on household energy
consumption in both mountainous and urban areas of theSan’in region in western Honshu. These studies indicatedthat currently the consumption of firewood is stable inboth mountainous and urban areas, but the amount offirewood consumption is very limited compared to therich potential of this resource from domestic forests. The
role of woody biomass energy should be reconsidered
compared to other energy (electricity, gas, and so on)
based on reliable field surveys with promotion to asuitable environmental policies such as transformation toa decarbonized society.
With regard to energy consumption in theresidential sector, the Ministry of Internal Affairs andCommunications’ Family Income and Expenditure
Survey (2018) includes data on household expenditures
for electricity, kerosene, gas and other energy sources
broken down by city classification, drawn from a subsetof the survey sample. Data on household energy
consumption by city classification nationwide are alsoavailable in the form of estimates for the residential
sector in the Agency for Natural Resources and Energy’s
Energy Consumption Statistics by Prefecture (2018) andthe Ministry of the Environment’s Statistical Survey ofResidential Sector CO2 Emissions (2018).
Few studies, however, have looked specifically at
the level of wood biomass use in relation to household
consumption of various energy resources in mountainous
regions. The town in Fukushima Prefecture that was
selected as our studied area decided to promote usage ofwoody biomass and started to survey the current situation©2020 AIRES

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S. NAKAMURA et al.

of forest and biomass consumption inside and near the
town. In this study, in collaboration with the town, we
conducted a questionnaire survey of all households in a
mountainous district to shed light on the trends andcharacteristics of household energy consumption and useof wood biomass, which is a forest resource. This study
provided the town the basic information on instituting
environmental policy regarding woody biomass asenergy.

2. Survey and Analysis Methods
2.1. Study Area
The mountainous location chosen for this study was
the town of Mishima in the Oku-Aizu region of
Fukushima Prefecture (Fig. 2 in Ooba et al., 2020). The
Oku-Aizu region is colder than Aizuwakamatsu Cityand other locations at the same latitude, with mean
temperatures approaching those of northern Tohoku, thenorthernmost region of Japan’s main island of Honshu.
Depending on the year or month, Oku-Aizu can receive
more than double the snowfall of Aizuwakamatsu.
Mishima is a small municipality with a populationof about 1,600 people living in approximately
750 households scattered among 18 villages. Its elderly
ratio (percentage of the population aged 65 or older) is
54.1% (Fukushima Prefecture, 2020). At its peak during
the development of the Tadami River hydroelectric dam,Mishima’s population topped 7,700; since then, however,the population has steadily declined, prompting the town
to launch various initiatives to attract young residents
from other parts of Japan and otherwise curb
depopulation. Given that it has a forest coverage of 88%(Forestry Agency, 2018), the town is also considering
measures for exploiting its forest resources, including theTable 1 Items surveyed in the questionnaire.
Category

Item

House

Type of house, building structure, age, total floor area,
number of buildings, number of rooms, owned/rented,
renovation/rebuild history, building structure at rebuilding

Number ofheatingdevices

Kerosene stove/kerosene fan heater,electric stove/oil heater, gas stove, heated floor, kotatsu,
air conditioner

Households
that usefirewood

Number of devices, annual firewood consumption,
procurement method, purchase price, source,
raw wood production location, intention to continue
using equipment, problems, reasons for quitting,desired support measures

Households
Type of equipment, reason for quitting, conditions forthat stopped
using firewood again
using firewood
Energyconsumption
statusMonthly electricity, kerosene, and LPG costs, electricity
billing plan, installed energy-saving equipment, numberof people at home during the day (weekdays, holidays)

Attributes

Family age/gender composition, occupation, residential
district name, confirmation of respondent’s family
relationshipuse of wood biomass energy in public facilities andsubsidies for using firewood.
2.2 Survey Method
We conducted a questionnaire survey of 702
households, representing all of the households in
Mishima except occupants of homes for elderly people
requiring special care. The survey was conducted from
October 20 to November 6, 2017, with questionnaires
being distributed to each household by the town throughward chiefs and returned by postal service. The numberof questionnaires returned was 341, with a response rateof 48.6%.
The questionnaire, which was to be filled in by thehead of each household, asked about type of house, useof heating equipment, use of wood biomass combustion
devices, consumption of electricity, kerosene, and othersources of energy, and household attributes. Table 1
shows the items surveyed in the questionnaire. We went
through these by hand, and based on the questionnaire
responses, identified the characteristics of households
using wood biomass combustion devices and comparedthem with households not using such devices.
For converting the amount of firewood used into3
wood biomass consumption, we assumed that 1 m offirewood = 800 kg and that one bundle = 13 kg.

3. Results and Discussion
3.1 Use of Wood Biomass Combustion Devices
Figure 1 shows a breakdown of devices owned byhouseholds using wood biomass. Approximately 9% of
the households were using wood biomass combustion
devices (wood stoves, fireplaces, cookers, boilers) at thetime of the survey. Although this was lower than values
found by previous studies (13.5%: Izumi et al., 2018;27.4%: Yasumura et al., 2011). Wood stoves and boilers(firewood-heated baths etc.) accounted for most of thewood biomass combustion devices being used, with 11%
11%
3%
30%

46%

5%
5%

Wood stove
Fireplace
Other
CompoundCookerBoilerFig. 1 Breakdown of household wood biomass combustion devices.

Survey on Household Wood Biomass Use and Energy Consumption in the Oku-Aizu Regionof firewood-using households using more than one typeof device.
The number of years since households started using
firewood combustion devices varied from several decades
to several years prior; of these households, 28% started
using these devices in 2010 or later. Looking at therelationship with house renovation/rebuilding and woodbiomass utilization, although 17% of firewood-using
households installed devices when renovating or
rebuilding, no such relationship was observed in mosthouseholds. Among households not currently using woodbiomass, approximately 19% of all respondents indicatedthat they intended to use firewood combustion devices in
the future subject to availability of cheap firewood andsubsidies for installing devices. This indicates that,combined with existing users, a potential 27% ofhouseholds may use firewood combustion devices given
the right conditions.
Most existing users obtained their firewood either byproducing it themselves or procuring it for free fromacquaintances rather than purchasing it from vendors.
Over 90% of the raw logs used were procured in Mishima
Town, either from the users’ own forest plots or from theplots of acquaintances.
3.2 Number of Heating Devices
Table 2 shows heating device ownership ofhouseholds in Mishima Town. The percentage ofhouseholds equipped with air conditioners was relatively
low in Mishima, with most households using kerosene
stoves and fan heaters for heating purposes. A comparisonof the number of other heating devices owned by users

239

and non-users of wood stoves and fireplaces shows thatusers of firewood for heating purposes owned fewer
kerosene stoves and fan heaters than non-users. However,ownership of other heating devices such as kotatsu orheated floors was higher among firewood users than nonusers, albeit only slightly. Among households using woodstoves, all but one household owned only one stove. Thissuggests that almost all of the households using woodbiomass also used fossil fuels or grid electricity forheating purposes. The percentage of household energy
consumption used for heating is a matter for future
investigation. The sample size of firewood users for thisquestion was small, and statistical tests found no
significant differences in mean values.
3.3 Household Energy Expenditure
Table 3 shows the mean household energy
expenditure in Mishima and other locations in Japan’s
Tohoku region in 2017. Energy expenditure in Mishima
was high compared with mean values in the Tohoku
region, indicating high energy consumption for heating
purposes. Kerosene and electricity consumption tended to
be lower among firewood-using households (Table 4),
while consumption of LPG (Liquid Petroleum Gas) was
almost double compared to the amount consumed by nonusers. These differences, however, were not found to bestatistically significant (t-test, p<0.05), and a moredetailed statistical analysis would be needed such as
factor analysis (covariance structure analysis or statisticalcausal analysis) according to the building age of thehouse related to the performance of thermal insulation.

Table 2 Heating device ownership and mean number of devices owned.
Device type

Ownership as a percentage of
all households (%)

Mean number of devices owned
by firewood users

Mean number of devices owned
by firewood non-users

Kerosene stove/fan heater

93.8

2.23

3.10

Kotatsu

80.4

1.31

1.08

Air conditioner

42.2

0.62

0.75

Electric stove/oil heater

26.4

0.15

0.39

Heated floor

6.2

0.08

0.07

Wood stove

3.5

1.08

-*

Gas stove

1.8

0.00

0.03

*This question was not asked of firewood non-users

Table 3 Mean annual household energy expenditure (unit: JPY/year)
Electricity

Mains gas

LPG

Kerosene

Mishima Town

130,656-

65,41858,585

Fukushima City*

127,437

19,08833,38925,386Morioka City*

100,629

18,24837,17731,723

Tohoku region*

114,770

15,51636,026

40,113* Source: Family Income and Expenditure Survey 2016 (Ministry ofInternal Affairs and Communications, 2018)

Table 4 Firewood use and energy costs (JPY).
Energy (per month) Firewood use Number
Kerosene
LPG
Electricity

MeanStandard deviation

User

13

9,700 (94.8%)

16,000Non-user278

10,000 (100%)

9,900

User

11

8,900 (172%)

15,000Non-user254

5,200 (100%)

5,400

User

13

9,800 (89.7%)

5,300

Non-user306

11,000 (100%)

9,300

240

S. NAKAMURA et al.

3.4 Wood Biomass Consumption and Substitution
EffectAnnual firewood consumption per household was
3
3 m . Assuming this firewood was used in wood stoves,
the amount of heat generated by burning this amount is
6.55 GJ, which is equivalent to 208 L of kerosene or
31.5% of mean annual household kerosene consumption(660 L) in Mishima. In terms of costs, almost all firewoodin Mishima was either self-procured by felling trees or
obtaining logs for free from acquaintances. Only one
household surveyed purchased firewood, but at theextremely low price of JPY 200/m3. Assuming that the
firewood used in Mishima households lowered kerosene
use by 208 L at the prevailing price of JPY 89/L and thatno costs were incurred in firewood procurement, use of
firewood reduced annual household heating costs byapproximately JPY 18,500.
3.5 Wood Biomass Use and Energy Expenditure
We conducted independent sample t-tests to compareenergy expenditure for kerosene, LPG, and electricity
between firewood-using households and non-using
households (Table 4). Although mean energy expenditure
between the two groups differed, this difference was notstatistically significant. The lack of differences may be
due to other factors such as the small sample size,
differences in usage of heating and hot water supply, ordifferences in household attributes.
3.6 Wood Biomass Use and Household Characteristics
To investigate the reasons for no statisticallysignificant difference being found between the energy
costs of firewood-using households and non-using
households, we conducted independent sample t-tests on
the difference in means with building age, floor area,
number of buildings, number of rooms, renovation/
rebuilding history of the households surveyed as separate
dependent variables and use/non-use of firewood as theindependent variable. The homes of firewood-using
households tended to be older (Table 5).
As shown in Fig. 2, we also compared the number ofpeople per household. Only mean building age wasfound to differ between firewood-using and non-using
households at the p <0.05 level (Table 5), with the homesof firewood-using households tending to be older.
Owing to poor insulation and other factors related tohouse structure in firewood-using households, energy
expenditure would likely be even higher than inTable 5 Use/non-use of firewood and household attributes
Firewood use

NumberMeanStandard deviation

Building age(years)

User

12

110

69

Non-user

303

71

55

Floor area
(m2 )

User

13

190

210

Non-user

328

160

179

Number of rooms
Persons per household

Number of hea�ng devices owned

Persons at home during the day(weekdays)

User

12

7.8

3.7

Non-user

314

7.5

2.8

User

12

2.8

1.9

Non-user

293

2.4

1.5

User

12

1.8

0.75

Non-user

299

1.6

0.97

120
100

User

Non-user

80
60
40
20
0

1
No
response

2

3

4

5

6

7

8

9

10

Persons per household

Fig. 2 Persons per household in relation to number of heating devices owned for use/non-use of firewood.

Survey on Household Wood Biomass Use and Energy Consumption in the Oku-Aizu Region
Kerosene cost
(JPY/month)
Firewood use
User
Non-user

LPG cost (JPY/month)Fig. 3 Use/non-use of firewood and energy expenditure
per month.
Kerosene cost per month(during usage period)

241households procuring their own firewood for free. Annual
firewood consumption per household was 3 m3, assuming
this firewood was used in wood stoves, the amount ofheat generated was equivalent to 31.5% of the meanannual household kerosene consumption in the town.
Usage of firewood is economical, bringing a reduction in
annual household heating costs of approximately JPY
18,500. These findings showed firewood still to be major
heat resource in this town, and this trend is the same as
was seen in previous studies (e.g., Izumi et al., 2018).
Total demand for firewood inside the town can be selfsupplied from the forest resources (Ooba et al., 2020).
In 2019, Mishima Town installed a new air
conditioner system using fire-wood boilers in one of thetown’s public facilities, Seikatsu Kogei-Kan (Mishima
Local Crafts Museum), referring to our policy suggestion
based on this study and other studies conducted byour project team (e.g., Ooba et al., 2020). This boiler
system was coupled with the startup of a new small-scale
firewood supply chain inside the town. Local companies
in the town with the potential to provide more firewood
intend to expand the biomass supply (personalcommunications). In the future, suppliers need to bematched with consumers of firewood at the local scale.
Additionally, to transform this heat resource froma depletable to a renewable energy to achieve a
decarbonized town, more detailed field surveys andanalyses of related policies for not only biomass but also
house building and renovation should be conducted.
References

Fig. 4. Energy expenditure in relation to building structure.

households where firewood was not used, but further
research and analysis would be required to identify
exactly which factors are important.
Figure 3 shows the relationship between firewood
use and energy expenditure. Although we found nodecrease in energy consumption as a result of firewood
use, the relationship between building structure andfirewood use shown in Fig. 4 indicates that firewood use
may be effective in reducing energy consumption inwooden houses, which require higher energy
consumption.

4. Conclusions
We conducted a questionnaire survey of allhouseholds, the town of Mishima, Fukushima Prefecture
to shed light on wood biomass use and household energy
consumption in a mountainous region. The survey results
revealed that approximately 9% of households were usingwood biomass combustion devices, with most suchAgency for Natural Resources and Energy (2018) Energy
Consumption Statistics by Prefecture 2016. (in Japanese)
Retrieved from https://www.enecho.meti.go.jp/statistics/energy_
consumption/ec002/ (Accessed 16 December 2020)
Forestry Agency (2018) Fukushima Prefecture Forest and Forestry
Statistics 2018. (in Japanese) Retrieved from https://www.pref.
fukushima.lg.jp/uploaded/attachment/320010.pdf
Fukushima Prefecture (2020) Number of Aged Persons inFukushima Prefecture. Retrieved from https://www.pref.
fukushima.lg.jp/sec/11045b/16903.html (Accessed 16 December2020) (in Japanese)
Harashima, Y., Terada, T., Yamamoto, H. and Kihira, E. (2014)
Current status of the small-scale firewood utilization in Ina City,
Nagano, Japan. Landscape Research Japan, 77 (5), 575 –578. (inJapanese)
Hatanaka, K., Kuga, H. and Ide, M. (2011) Katei no eneregi
shohiryo to CO2 haishutsuryo: Nagano-kennai 10 shicho de no
ankeito kara (Household energy consumption and CO2
emissions: results of a questionnaire survey of 10 cities andtowns in Nagano Prefecture). Nagano-ken Kankyo Hozen
Kenkyusho Kenkyu Houkoku (Journal of the Nagano Prefecture
Institute for Environmental Conservation), 7, 13–18. (inJapanese)
Hatanaka, K., Kuga, H. and Ide, M. (2012) Nagano-ken ni okeru
maki stove no riyo jittai to CO2 haishutsu sakugenryo no suikei(Use of wood stoves in Nagano Prefecture and estimated CO2
emissions reduction). Nagano-ken Kankyo Hozen Kenkyusho
Kenkyu Hokoku (Journal of the Nagano Prefecture Institute for242

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Environmental Conservation), 8, 25–30. (in Japanese)
Izumi, K., Odanaka, F. and Otsuka, I. (2018) Current status andfuture availability of fuelwood use in Shiwa Town, Iwate
Prefecture. Journal of Forest Economics, 64 (3), 26–35. (inJapanese)
Ministry of Internal Affairs and Communications (2018) Family
income and expenditure survey 2016. Retrieved from http://www.
stat.go.jp/data/kakei/2016np/gaikyo/index.html (in Japanese)
Ministry of the Environment (2018) Statistical Survey of Residential
Sector CO2 Emissions 2017. (in Japanese) Retrieved from http://
www.env.go.jp/earth/ondanka/ghg/kateiCO2tokei.html
Nemoto, K., Inuzuka, H., Nakamura, S. and Mori, Y. (2017a)
Supply chain analysis for determining the requirements forcontinuous woody biomass energy utilization systems:
comparison of the actual management conditions in Japan.
International Journal of Environmental and Rural Development,
8(1), 203–209.
Nemoto, K., Nakamura, S. and Mori, Y. (2017b) Diffusion ofwooden biomass heating devices for domestic use and their fuelconsumption. Journal of Forest Economics, 63 (3), 82 – 91. (inJapanese)
Ogasawara, M. and Yamamoto, S. (2017) Reality and futureavailability of fuelwood use in fruit tree production area for an
example of nanawa district, goshogawara city, Aomori
Prefecture. Tohoku Journal of Forest Science, 22 (2), 49–53. (inJapanese)
Ooba, M., Nakamura, S. and Togawa, T. (2020) Promoting local
revitalization to solve issues on degraded forests in Japan: A casestudy in Oku-Aizu, Fukushima. Global Environmental Research,
24, 191– 198.
Uezono, M. (2018) Trends of energy consumption in the householdin the San’in area. San-in Kenkyu (San’in Research), 11, 25 – 35.
(in Japanese)
Yasumura, N. (2011) Economy of woody biomass in households.
Abstract of the 122th Annual Meeting of the Japanese Forestry
Society, p.270.

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch. He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Takuya TOGAWA
Takuya Togawa is a senior researcher at the
National Institute for Environmental Studies,
Fukushima Branch. He received his doctorate inengineering from the Graduate School ofEnvironmental Studies, Nagoya University in2010. He is engaged in research on mechanisms
for realizing disaster recovery and regional
revitalization by effectively utilizing local environmental resources.
(Received 21 December 2020, Accepted 28 December 2020)

243

Community Governance in Decontamination Policy
after the Fukushima Nuclear Accident: Two Case Studies fromthe Naka-dori Region, Fukushima, Japan
Takashi TSUJI*, Shogo NAKAMURA and Makoto OOBA
Regional Environmental Renovation Section, Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan*E-mail: tsuji.takashi@nies.go.jp

Abstract
The aim of this study is to explore the influence of community governance on the determination andimplementation of decontamination policies in local communities, focusing on Miharu Town and Koriyama
City in the Naka-dori region of Fukushima Prefecture. This study is based on fieldwork undertaken in Miharu
Town and Koriyama City. Data were gathered from local documents and interviews. Interviews wereconducted with the municipal administrations and neighbourhood associations in charge of post-accident
decontamination policies. The results showed that the procedures and contents of the resulting
decontamination policies were formulated on the basis of organizational cooperation among municipal
administrations and neighbourhood associations in both municipalities. Immediately after the accident,neighbourhood associations participated in the process of determining the decontamination policies of these
two municipalities. Networks comprising several neighbourhood associations tackled decontamination in
educational facilities and along school routes. In some districts, neighbourhood associations participated indecisions on location and management of temporary storage yards for waste generated by decontamination
work. In addition to these institutional factors, land-use-related factors in the spaces used in daily life
influenced the procedures and contents of the decontamination policies. These defined the differences
between methods of establishing temporary storage yards in Miharu Town and Koriyama City. Our findings
suggest that the relationship between community governance and land use deserves more attention in thiscase, as in the case of other environment problems.
Key words :	community governance, decontamination policy, Fukushima nuclear accident, Naka-dori region

1. Introduction
Decontamination is one of the main methods foreliminating radioactive contaminants and reducing
radiation exposure in areas used in daily life. Afterradioactive materials escaped and spread as a result of the
Fukushima Daiichi Nuclear Power Station accident inMarch 2011, the Japanese government legislated a legal
framework for decontamination, and the Act on Special
Measures concerning the Handling of Radioactive
Pollution came into operation from January 2012. Basedon ICRP standards, the act set guidelines fordecontamination aiming to reduce exposure doses. In theact, two types of decontamination areas were designated:
Special Decontamination Areas and Intensive
Contamination Survey Areas.
Table 1 presents an overview of the decontamination
areas. Special decontamination areas were established in
the evacuation zones, which had high level radiation
Global Environmental Research
24/2020: 243-251
printed in Japandoses. The Japanese government has overseen
decontamination policies in these areas directly.
Meanwhile, Intensive Contamination Survey Areas(ICSA) were established outside the evacuation zones,
where the radiation doses were relatively low level.
As shown in Fig.1, 102 municipalities in eight
prefectures were designated as ICSA on December 28,
2011. In ICSA, decontamination was left up to thestakeholders in the local communities. The Japanese
government argued that decontamination by the these
local communities themselves would most effective
because the administrative functions were present, theresidents were living there, and it was easy for them tounderstand the circumstances and the residents’ needs(Basic Policy for Emergency Response on
Decontamination Work, published by Japanese Nuclear
Emergency Response Headquarters on August 26, 2011).
The municipalities designated as ICSA, however,
had few experts in radiation and radioactive materials and©2020 AIRES

244

T. TSUJI et al.

Table 1 Overview of decontamination areas.
Areas

Degree ofGoal for reducing Decontamination
contamination radiation exposure program operator

SpecialHigh level
decontamination area

20 mSv/year or less

The Japanese
government

Intensive
contamination survey Low level
area

Below 1 mSv/year

Municipalities

Fig. 1 Intensive contamination survey areas.
ource: Results in the Intensive Contamination Survey Area,
S
Ministry of the Environment, Government of Japan (http://josen.
env.go.jp/en/decontamination/)few people with experience in decontamination, which is
the method of removing radioactive materials. Therefore,
decontamination was promoted while learning about
radioactivity and radioactive materials through trial anderror based on collaboration and cooperation among
stakeholders such as municipal administrations,neighbourhood associations, citizens’ groups and experts.
These stakeholders determined the procedures andcontents of the decontamination policies.
Against this background, the content of and progressin decontamination projects differed between
municipalities. Kawasaki (2016) noted that there weredifferences in the formulation and implementation
statuses of decontamination implementation plans among
municipalities designated as ICSA. According to datafrom his questionnaire survey on municipalities
designated as ICSA, of 40 that carried out
decontamination, 12 had completed decontamination(30%) and 28 were in the course of decontamination(70%) as of the end of September 2015 (Kawasaki,2016). Sato and Abe (2013) noted that policies onbuilding temporary storage yards for radioactively

contaminated soil differed from one municipality toanother. In some municipalities such as Fukushima City,no temporary storage yards were set up to begin with.
Decontamination waste was stored at the decontaminationsites. In other municipalities such as Kawauchi Village,
temporary storage yards were set up and radioactively
contaminated soil was amassed in several places (Sato &Abe, 2013).
Decontamination is a sensitive issue not only forresidents, but also municipal officials. Hence, it isdifficult for the stakeholders to build consensuses andwork together when dealing with decontamination
programs (Edgington, 2017; Isono, 2015). In ICSA,
because there may be discrepancies in awareness among
stakeholders inside and outside the local communities
regarding the implementation of decontamination
procedures and the provision of temporary storage sites,
measures may not proceed smoothly. In thedecontamination policy-setting process, miscommunications
and conflicts among stakeholders have been common in
local communities since the Fukushima nuclear accident.
In some local communities, however, decontamination
has been implemented smoothly, and consensuses among
stakeholders have ensured they are conflict-free. Basedon the above, it is conceivable that collaboration among
various stakeholders involved in decontamination
programs may determine their content and quality in thelocal community.
In other words, it is important to focus oncommunity governance to get a clear view of theinstitutionalization of decontamination policies in local
communities. The aim of this study is thus to explore theinfluence of community governance on decontamination
policy determination in local communities, focusing on
Miharu Town and Koriyama City in the Naka-dori regionof Fukushima Prefecture.

2. B rief Review of Community Governance
Literature and Decontamination Case Studies
In this study, we focused on the local community asa place of political decision making where governance isbuilt during disaster recovery. Peters and Pierre (2016)
defined governance as a process, where each group ofdifferent types of stakeholders congregates towards somecollective goal. Above all, local governments play animportant role in setting collective goals. Banner (2002)
claimed that in recent years, local governments had beenshifting their role from administrative to politicalleadership in civil society. In this study, community
governance was regarded as a political process by which
various stakeholders—including local governments as apolitical leader—converged toward the collective goal of
decontaminating the local community.
When decontamination is regarded as a politicalprocess, it is necessary to pay attention to how risk

Community governance in decontamination policy after the Fukushima nuclear accident
assessment and management are performed. This is basedon risk communication with dialogue and deliberation byvarious stakeholders, which is necessitated by insufficientand uncertain information on radioactivity and radiation(Renn & Klinke, 2015: 24–26). Decontamination is
intimately connected with risk communication in thelocal community.
Some research and theories suggest that there are
pitfalls to risk communication in a ‘top down’ mode. A‘top down’ mode of risk communication may miss what
the public and stakeholders feel they need to know about
environmental radioactivity (Mabon & Kawabe, 2018).
In the decontamination policy process, a ‘bottom up’mode of risk communication is required. Regarding how
to formulate a ‘bottom up’ mode of risk communicationin the decontamination policy process, Kinoshita notesthat risk communication is not limited to issues of
information transmission from administrative authorities
to the public and stakeholders. He suggests that it isessential to focus on collaboration and coordination
among the various organizations involved in the risk
(Kinoshita, 2008).
Previous studies have focus on organizational
communication by various stakeholders in local
decontamination policy processes. Some studies havefocused on communication with municipal
administrations and community organizations. Thesestudies have affirmed that municipal administrations andcommunity organizations should communicate startingfrom the occurrence of the accident until formulation of
the decontamination implementation plan is complete,ensuring that the decontamination policy proceedssmoothly. For example, Isono notes that municipal
administrations that lacked communication withneighbourhood associations at the decontamination
implementation planning stage met opposition from theneighbourhood associations and residents when setting
up temporary storage yards and were unable to proceedwith decontamination as planned (Isono, 2015).
Some studies emphasize the role of experts inmediating communication between municipal
administrations and various community organizations in
the local decontamination policy process. In Kashiwa
City, Chiba Prefecture, an ICSA, a round table meeting
was organized in collaboration with the municipal
administration, agricultural groups and consumers
associations with the support of sociologists prior to
implementing decontamination. They examined radiationdose measurement methods for agricultural land and set
voluntary standard values for the radioactivity ofagricultural products (Igarashi & Anshin Anzen no
Kashiwa San Kashiwa Shou Round Table, 2012). In thedecontamination implementation phase, Kashiwa City
administrative officials called on neighbourhood
associations, to cooperate in decontamination and set up
a “decontamination advisor” to assist these associations

245

in implementing decontamination from an expert’s
standpoint (Fukuda & Akita, 2014; Nakano & Deguchi,
2014; Iimoto et al., 2018). Kashiwa City is known as a
successful case in which decontamination was able toproceed smoothly through collaboration among themunicipal administration, community organizations andexperts.
These studies suggest that the ability of municipal
administrations to coordinate and the support of experts
are required to facilitate decontamination policy.
However, little attention has been given to structural
conditions surrounding the community organizations andthe ability of community organizations to coordinate inprevious studies. To get a clear view of theinstitutionalization of decontamination policy, it isimportant to consider the role of community
organizations for building consensus among stakeholders
from the occurrence of the accident until theimplementation of the decontamination policy.

3. Methodology and Case Study Areas
Miharu Town and Koriyama City are located in thecentral Naka-dori region of Fukushima Prefecture, about
45–60 km from the Fukushima Daiichi Nuclear Power
Station (Fig. 2).
Miharu Town has a population of around 18,200,
with a satoyama landscape and historic townscape of anold castle town. Koriyama City has the second largest
population of any municipality in Fukushima Prefecture,with around 335,000 persons (Table 2). This city is thefinancial capital of Fukushima Prefecture. Urban
functions and industries are concentrated and citizen
groups and research institutes are gathered here.
Radioactive fallout contaminated the area as a result

Fig. 2 The locations of Miharu Town and Koriyama City.

246

T. TSUJI et al.

Table 2 Overview of Miharu Town and Koriyama City.
Miharu Town

Koriyama City

Population(National Census in 2010)

18,191

335,444

Employment in each sector(National Census in 2010)

Primary sector: 8.3% Primary sector: 3.6%
Secondary sector: 33.0% Secondary sector: 23.8%
Tertiary sector: 58.1% Tertiary sector: 68.9%

Spatial radiation dose rate
0.51 μSv/h(Published by Fukushima(Miharu Town Hall)
Pref. in 2011.4.1)

2.14 μSv/h(Koriyama City Hall)

Decontamination of houses(Published by Fukushima 5,159
Pref. in March 2018)

98,485

Temporary storage yard
construction policy

Construct in each district Based on on-site storage(in 7 districts)(in each household)of the accident. Miharu Town and Koriyama City are
specified municipalities among the ICSA, anddecontamination has been carried out according to adecontamination implementation plan formulated at theend of 2011. There was a slight difference in the extent ofradioactive contamination between Miharu Town andKoriyama City. In Miharu Town, the environmental
radiation dose rate varied by district. In some districts, it
exceeded 0.23 μSv/h, which was set by the national
government as the post-decontamination numerical target
for FY2016. In Koriyama City, the environmental
radiation dose rate was relatively higher than that in
Miharu Town. Especially in the central area of the city,radiation contamination of over 2.0 μSv/h was recorded.
In accordance with the scale of these municipalities, thenumber of cases of decontamination also differed
between the two. Koriyama City had the largest numberof housing decontamination cases listed in thedecontamination implementation plan in Fukushima
Prefecture.
There was also a difference between the procedures
and contents of the decontamination policies. In Miharu
Town, a temporary storage yard was set up in each ofseven districts in the town. In Koriyama City, on the other
hand, basically no temporary storage yards were set up,
but decontamination waste was stored at thedecontamination sites, meaning at each household.
By using qualitative research methods, weinvestigated the policy processes involved in
implementing decontamination policy in Miharu Town
and Koriyama City, focusing on policy networks formed
after the accident. Based on fieldwork conducted in 2017and 2018, the following survey methods were used in thecurrent study.
The first was a document analysis. In this study, we
analysed regional data before and after the nuclear
accident. The local documents analysed included
newspaper articles (from Fukushima Minpo andFukushima Minyu), administrative council minutes, local
governmental public relations magazines and various

materials concerning local organizations. Materials
available about community organizations from before thenuclear accident were collected without setting a target
period. Meanwhile, materials issued in the six-year period
from March 11, 2011 to March 31, 2017 were collected
as materials from after the nuclear accident.
The second survey method was by interview survey.
In this study, interviews were held with administrative
department officials in charge of decontamination policies
in Miharu Town and Koriyama City, and leaders ofcommunity organizations such as town planningassociations, neighbourhood associations and agriculturalgroups.

4. Decontamination Policy Process in Miharu
Town
From this chapter, the time between the accident andthe ICSA designation of Miharu Town and Koriyama
City is classified as the “emergency phase” and the time
thereafter as the “reconstruction phase” and an overview
is provided on how community governance functioned in
the stream of decontamination policy processes in the twomunicipalities.
4.1 Emergency Phase in Miharu Town
In Miharu Town, the “First Representative Ward
Mayors Meeting” was held on March 12, 2011, the day
after the accident. This meeting doubled as anautonomous disaster prevention association meeting, andinformation on the damage status and number of evacuees
in the town’s seven districts was exchanged. It was
decided that a “district disaster response headquarters”
would be set up in each of the seven districts of the town,
and the community development associations(machizukuri kyokai) in each district would manage them.
In addition, the representative mayors of eachneighbourhood association (gyousei-ku) became membersof the town disaster response headquarters, and a systemfor collaboration between the town hall and each district
was established.
Miharu Town’s administration collected informationon the situation, namely the release of radioactive
materials into the atmosphere due to damage to the
nuclear reactor, and on March 15, unilaterally decided to
distribute a stable iodine agent that was effective in
reducing thyroid exposure to residents aged below 39(7,269 people), without instruction from the government
or prefecture (Miyazaki, 2013). Although the decision on
the stable iodine agent was made by the upper level of thetown administration, two district disaster response
headquarters meetings were held before its distribution,and the district disaster response headquarters played aleading role in sharing information prior to the
distribution and its related administrative procedures.
This suggests that the community development

Community governance in decontamination policy after the Fukushima nuclear accident
associations, which were responsible for operating the
district disaster response headquarters, were at the core ofcommunity governance in Miharu Town immediately
after the nuclear accident before the decontamination
policy was launched.
Thereafter, the protection of children from radiation
became an urgent issue in Miharu Town, as in other areasof the prefecture. The town administration conducted aradiation dose investigation of the schoolyards andplaygrounds of the elementary and junior high schools
and kindergartens of the town on May 14, 2011, and it
was decided that the topsoil would be removed at 16
facilities in the June 23, 2010 fiscal supplementarybudget.
In addition, to reduce the radiation dose fromradioactive materials in spaces used in daily life such as
school roads and parks, where children spend a lot oftime, Fukushima Prefecture decided to implement a“Dose Reduction Activity Support Project (DRASP).” In
Miharu Town, this project was utilized by residents
voluntarily to decontaminate school roads in each district
from November 6 to December 8, 2011. The mainstakeholders in implementing this voluntarydecontamination were the community development
associations, neighbourhood associations and parentteacher associations (PTAs) in each district.
In the case of voluntary decontamination, thecommunity development associations played the role ofcoordinator for the administration and each regionalorganization. In Sawaishi district, a rural area in thenorthern part of the town, the community development
association conducted the “Sawaishi District
Environmental Protection Measures Meeting” on October18, 2011 to discuss the implementation system andcontents of the DRASP in the district.
However, during the emergency phase in Miharu
Town, emergent collaboration involving experts outside
the region was also seen. After research volunteers
specializing in radiation physics at the Tohoku University
Graduate School of Science lobbied experts in the town,
and it appeared in the mass media, the “Miharu Misho
project” was launched on June 20, 2011. A town subsidy
was used to cover the operating costs of the project, andthe town’s General Affairs Section (Planning Information
Group) served as the secretariat. In the project, a surveyof individual cumulative doses among elementary andjunior high school students (around 1,700 people) using abadge type dosimeter was conducted along with a soil
radiation dose survey at the educational facilities.
4.2 Reconstruction Phase in Miharu Town
On August 26, 2011, the Nuclear Emergency
Response Headquarters formulated Guidelines for
Decontamination by Municipalities. Subsequently, after
the enactment of the Act on Special Measures, theMinistry of the Environment formulated and announced

247

Decontamination Guidelines on December 14, 2011.
These guidelines provided policies on radiation dose
survey measurement methods and decontamination
methods for buildings, roads, soil, plants and trees. Since
then, whole-area decontamination became the focus of
measures against radioactive materials in the ICSA.
Based on these guidelines, Miharu Town’s administration
formulated a decontamination plan on December 1, 2011.
The town administration held discussions with theresident representative (union organization ofneighbourhood associations, Gyousei-kuchokai) and thetown council prior to formulating the decontamination
plan. When formulating the decontamination
implementation plan, however, they had no opportunity
to inform the residents of the plan and hear their requests.
Miharu Town established a policy of proceedingwith decontamination from the areas where the temporarystorage yards for decontamination waste such as soil
generated by decontamination were located. In thisinstance, the community development associations were
responsible for determining the location of the temporarystorage yards and carrying out routine management ineach district. Some community development associationsin the town established departments and committees
within the association for sharing information on surface
decontamination and determining and managing thelocation of temporary storage yards.
In Iwae district in the western part of the town, the“Iwae District Decontamination Promotion Council” wasestablished on June 27, 2012 within the association toshare information on the decontamination implementation
plan from the town’s Decontamination Measures Section
and hold discussions on the location of temporary storage
yards.
The officers included representatives of the town
council and landowners, in addition to the head of theneighbourhood associations. The technical conditions(required area, land lease fees, etc.) of the temporarystorage yards presented by the town administration werealigned with the residents’ interests (inclinations oflandowners and reactions by surrounding residents) (Fig. 3).
To realize consensus building for the construction of
temporary storage yards, it was important to focus on theFig. 3 Temporary storage yard for decontamination waste in Iwae
district, Miharu Town. (Photo by authors on March 21,
2018)

248

T. TSUJI et al.

role of community development association leaders. They
found suitable private land in their district and negotiatedwith the landowners for construction of temporarystorage yards. One of the study interviewees, a
representative of Iwae district’s community development
association, described the actual state of communication
among stakeholders such as neighbourhood associations
and landowners in the temporary storage yard
construction process as follows:
We decided where to put the waste fromdecontamination. In our Iwae district, there was nosuitable public land for temporary storage yards. So weheld a meeting of the community development
association, where presidents of the neighbourhood
associations exchanged information about private landwith each other.
In the end, we argued over details, negotiated withthe landowners and got approval.

policy process. They consistently cooperated with thetown government starting from just after the accident.

5. Decontamination Policy Process
in Koriyama City
5.1 Emergency Phase in Koriyama City
After the accident occurred, Koriyama City’s
administration launched topsoil removal fromschoolyards at 15 public elementary and junior highschool and playgrounds at 13 public nursery schools
before any other municipality from the end of April 2011
(Fukushima Minyu, April. 26, 2011). However, the cityadministration faced resident’s strong opposition in its
briefing session held on April. 27, 2011 for residents who
were candidates for hosting storage yards for removed
soil.
Koriyama City’s administration failed to build aconsensus for decontamination with residents from the
beginning of the decontamination policy process.
According to an evaluation of the city administration
officials, the radioactive substances contained in theremoved soil did not reach a level that would impair theenvironment or health. However, not only the residents
but also the city administration officials lacked sufficientknowledge and technical skills regarding radioactivity atthat time. It is assumed that uncertainty regarding
radioactivity then may have generated this consequence.
On the other hand, there was a swift response fromthe private sector regarding decontamination. From April
2011, community organizations such as neighbourhood
associations (Chounai-kai, Gyousei-ku) and PTAs
launched decontamination work and radiation dose
surveys in areas used in daily life such as school roads( Source: Interview of Iwae Community Development Association
representative, on December. 22, 2017.)

His narrative indicated that there were many chances
for discussion among the leaders of the community
development associations. They persistently negotiatedwith landowners to construct temporary storage yards.
This was possible because leaders of the community
development associations were familiar with theownership of private land in their districts.
Figure 4 illustrates the decontamination policy
process in Miharu Town. The vertical columns list thedecontamination policy items of each fiscal year on thehorizontal axis. It is necessary to focus on the emergenceof an organization in each district. This row shows thateven immediately after the accident, community
organizations were involved in the decontamination

Policies

Fiscal Year2011
(3 ‒ 9)Decontamination
Work

Removal of
topsoil inschoolyards andplaygrounds(2011.6.22–)

Fiscal Year2011
(10 ‒ 3)Fiscal Year
2012
Modeling of
decontaminationwork(2012.4–)

Local Gov.
andresidents
communication

Fiscal Year2014 ‒

Decontamination ofhouses and roads(2012.6 – 2016.12)

Decontamination of public facilities(2011– 2016.9)

Construction of
temporary storage yards(2012.4 – 2015.3)

Temporarystorageyards
Emergenceof anorganizationin eachdistrictFiscal Year
2013

Disaster
controlheadquarters(2011.3.12–)

Voluntarydecontamination
activities

Decontamination Promotion Committee(2011.11.26–
12.18)

Study sessions on
the Great East Japan Earthquake(2011.5.5 – 2012.5.29 / 4 times)

Briefing session forresidents about
topsoil removal atschoolyards (2011.6.2–)

Consultation on
decontamination plan
between town gov. andneighborhood associations(2011.11 –12)

Briefing session for residents about theconstruction of temporary storage yards(2012 – 2015)

1

Fig. 4 Decontamination policy process in Miharu Town.
Source: Authors, referring to Fukushima Action Research on Effective Decontamination Operation (FAIRDO), 2013.

Community governance in decontamination policy after the Fukushima nuclear accident
and school facilities. Table 3 indicates that the main
voluntary decontamination related activities in each
district had multi-organizational cooperation.
In Koriyama City, community organizations had
already launched their decontamination activities before
the city government released its manual on
decontamination to the citizens on October 1st, 2011. In
addition to that, their decontamination activities were notbased on the city administration’s requests.
5.2 Reconstruction Phase in Koriyama City
Koriyama City’s administration formulated adecontamination plan on December 27, 2011. The cityadministration held briefing sessions for all households
and districts to formulate a decontamination plan. In thisplan, the city administration promoted a policy of
carrying out the decontamination program incollaboration with residents, neighbourhood associations,
PTAs, volunteers and local companies (Murayama et al.,2015).
Utilizing the DRASP, Koriyama City’s
administration gave grants to community organizations
for decontamination activities in areas used in daily life.
A total of 919 community organizations applied for the
grants in three years: 622 in 2011, 264 in 2012 and 33 in
2013. It was the neighbourhood associations—who werethe main parties responsible for voluntarydecontamination—that utilized the grants. Before theaccident, Koriyama City had 662 neighbourhood
associations. Of these neighbourhood associations, 385(58.2%) applied for the grants. DRASP was carried out
throughout the city, but there were some districts where it
was not possible to construct temporary storage yards
because no suitable land could be found.
In some districts, decontamination wastes generated
by the community decontamination activities were storedin parks and open spaces of their respective districts after
Table 3 Voluntary decontamination activities in Koriyama City.
District

Organizations

Contents

Participants

26 April 2011

SaikonElementary
schoolDecontamination
work―

11 March 2011

TomitaPTA

Decontamination
work

50

16 June 2011

Akagi

Voluntary
disasterprevention
organization

Radiation dose
survey―9 July 2011

HouzanRadiation dose
Neighborhood survey
Decontamination
associations
work―

Late September,
2011

Small-scale
Citywide enterprises
PTAs

Radiation dose
surveyDecontamination
work

50

Date

Source: Fukushima Minyu, Fukushima Minpou and Public Relations
Koriyama (Kouhou Koriyama).

249

coordinating among the city administration andcommunity organizations. In Kikuta district in thenorthern part of the city, decontamination wastes wereburied underground in public land (city-owned land) at asports park (Fig. 5). The city administration proposed thismethod to the leaders of community organizations(Kikuta-machi Kucho-kai, the chounai-kais and PTAs).
The city administration and community
organizations cooperated with the construction industry
association in implementing storage of decontamination
waste by this method. The fact that the leader of theconstruction industry association lived in the Kikuta
district and was friends with the leader of the community
organization also helped facilitate adoption of thismethod. The background to realization of this method of
decontamination and temporary storage of
decontamination waste is the existence of collaboration
among city administration, neighbourhood organizations
and the construction industry association.
In some districts, decontamination wastes wereburied underground in private land. In Kurume district in
the central part of the city, around 5,000 square meters ofshrine-owned land was designated a temporary storageyard for the soil removed during decontamination of aresidential area after mutual consultation between theresidents.
The district’s federation of neighbourhood
associations (Kurume-machi Choukai Rengokai) had
responsibility for overall land use management for theconstruction of temporary storage yards. The federation
set up a countermeasures headquarters within theassociation to carry out decontamination. The headquarters
conducted voluntary decontamination activities incoordination with 13 neighbourhood associations andPTAs. After the voluntary decontamination was completed
and the decontamination of residential areas was launchedby the city administration, the leader of the federation
negotiated with organization owning the land (the shrine
association), decontamination contractor and city

Fig. 5 Work to bury waste generated by decontamination of schoolroads in city-owned land (sports park) in Kikuta district,Koriyama City. (Photo by Kikuta-machi kucho-kai )250

T. TSUJI et al.

Policies
DecontaminationWork

Fiscal Year2011
(3 ‒ 9)Removal of
topsoil inschoolyards
andplaygrounds

Fiscal Year2011
(10 ‒ 3)Fiscal Year2012

Fiscal Year2013

Decontamination ofhouses and roads

Modeling of
decontaminationwork(2012.10 –)(2012.2 – 8)

Decontamination of public facilities(2011.4 – 5)

(2011 – 2016.11)

Constructionof temporarystorage yards(2014.8 –)Temporarystorageyards
Emergenceof anorganizationin eachdistrict

Local Gov.
andresidents
communication

Fiscal Year2014 ‒

Voluntary decontamination activities(2011.4–2013)

Briefing
session forresidents about
topsoil removalof theschoolyards(2011.4.27)

Briefing session oncommunity
decontamination
programs (2011.10.20)
Briefing session on
decontamination
plan (2011.12.11)

Briefing session on decontaminationin each district (2012.10 –)Briefing session onmodeling of
decontamination
work (2012.5.19)

Fig. 6 Decontamination policy process in Koriyama City.
Source: Authors, referring to Fukushima Action Research on Effective Decontamination Operation (FAIRDO), 2013.

administration. The background to realization of this land
use management for construction of temporary storage
yards was the leadership of the federation uniting the
district’s community organizations. Since the president of
the federation also served as an officer in the community
organizations in the district, it was easy to coordinate
with the leader of each organization.
Figure 6 illustrates the decontamination policy
process in Koriyama City. It is necessary to focus onconsensus building between the city administration andresidents, which was difficult in the emergency phase. It
also bears repeating that, voluntary decontamination
activities by community organizations precededadministrative efforts in Koriyama City.

6. Conclusions and Discussion
In this paper, we explored the influence ofcommunity governance on the determination of
decontamination policies in local communities, focusingon Miharu Town and Koriyama City. The findings of thispaper can be summarized in three points.
First, the procedure and contents of decontamination
policies in Miharu Town and Koriyama City were
formulated based on continuous organizational
cooperation among municipal governments andcommunity organizations starting from immediately after
the accident. As shown in the case of Kashiwa City,
opportunities and venues to coordinate the interests ofmultiple stakeholders before the details and policies ofthe measures for radioactive materials are determined andimplemented are also required (Igarashi & Anshin Anzen
no Kashiwa San Kashiwa Shou Round Table, 2012). By
necessity, the procedure and contents of decontamination
policies in local communities are determined based onlimited information on radioactivity, and it is necessary
for stakeholders to share awareness when making
decisions and implementing measures. The state ofconsensus building on topsoil removal from theschoolyards in Koriyama City during the emergency
phase suggests as much.
Second, the procedure and contents of thedecontamination policies of Miharu Town and Koriyama
City were formulated based on land ownership in local
communities. When public land is used as a temporarystorage yard for removed soil, coordination between themunicipal administration that owns the land and thecommunity organization that represents the residents isrequired. On the other hand, when using private land,
coordination between organizations owning the land andcommunity organizations such as neighbourhood
associations is required.
Third, micro-negotiation tactics, which are carriedout by community organizations leaders, contribute tosmooth progress of decontamination policies such as
establishment of temporary storage yards. Previous
studies have pointed out the importance of residents’
involvement in governance in the decontamination policy
process (Moriguchi, 2015). The findings of this study
suggest a role of community organization leaders as
actors in community governance for decontamination
policies. There should be more attention to power
structures that serve in the relationship among community
leaders in decontamination policies.
As shown in Figs. 4 and 6, there were differences inthe decontamination policy processes between Miharu
Town and Koriyama City. In Miharu Town, smoothcommunication between the town administration andresidents was observed immediately after the accident.
On the other hand, in Koriyama City, there wereCommunity governance in decontamination policy after the Fukushima nuclear accident
miscommunications between the city administration andresidents at the same time. It is presumed that the key
factor determining the difference is experience incommunication between the government and residents
during the emergency phase.
Decontamination constitutes risk communication
over land use in the local community. The findings of thisstudy suggest that the relationship between community
governance and land use deserves more attention, as it
does with regard to other environment problems.
However, it cannot be said that among the ICSA,
Miharu Town and Koriyama City had particularly highair dose rates. In terms of future tasks, it may benecessary to analyse cases by controlling non-social
factors such as air dose rates and categorizing community
governance in the ICSA.
Acknowledgment
This work was supported by National Institute forEnvironmental Studies Fukushima branch grant-in-aid for
exploratory research from fiscal year 2017 to 2018.
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Takashi TSUJI

community development.

Takashi Tsuji completed his Ph.D. in sociology at
Nagoya University in 2019. Now, he is a
researcher at the National Institute forEnvironmental Studies, Fukushima Branch. His
research interests include disaster governance andcommunity resilience, focusing on disaster/
environmental policy processes with long-term

Shogo NAKAMURA
Shogo Nakamura is a researcher in the Regional
Environmental Renovation Section of the
National Institute for Environmental Studies,
Fukushima Branch. He holds a Ph.D. inagricultural science. He has played a central rolein developing the energy monitoring systems in
Shinchi as well as many other areas in
Fukushima. Recently his interests have led him to participate in theEnvironment-Economy-Society Integration Research program.

Makoto OOBA
Dr. Ooba heads the Environmental Renovation
Laboratory at the Fukushima Branch of the
National Institute for Environmental Studies,Japan. From 2007 to 2012 and from 2014 to thepresent, he has participated in a study on spatialassessment of Japan’s regional forests using
process-based models and remote sensing by
NIES. Based on these studies, he has analyzed sustainability of forestry andharvested wood products. He has also worked at Osaka University, Nagoya
University and the Tokyo University of Agriculture. He holds a Ph.D. inenvironmental science from Hokkaido University, 2002.
(Received 1 December 2020, Accepted 28 December 2020)

Preface-24-1.indd

22020/07/30

17:54:49

253

Overview of the Environmental Emergency Management Studies
in National Institute for Environmental Studies (NIES)
Ryo TAJIMA* and Masahiro OSAKO
Centre for Material Cycles and Waste Management Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan*E-mail: tajima.ryo@nies.go.jp

Abstract
Despite its significance in achieving sustainability in an era of frequent disasters, environmental
emergency management (EEM) is a field that has not attracted enough attention from policy makers. This
article provides an overview of and outlook for EEM studies at the National Institute for Environmental
Studies (NIES). For this, a framework is presented for EEM based on recent international literature, andrepresentative works undertaken by NIES are presented in line with this framework to examine research gaps
and outlook. Our analysis shows good coverage of research topics aimed at enhancing understanding of the
impact of environmental emergencies and advancing both pre- and post-disaster actions for disaster waste
management (DWM). Some research gaps are also identified: namely, research on post-disaster assessment ofenvironmental impacts and decision making under emergency circumstances, research on responses andrecovery actions against impacts from hazardous substances released in the course of natural hazard events,
and research collaboration within the EEM discipline and between natural hazard experts (especiallyregarding physical countermeasures).
Key words :	disaster waste, environmental emergency, management, toxic release, Natech

1. Introduction
Environmental emergencies are a serious concern forboth developed and developing countries (Liao et al.,2012; Srinivas & Nakagawa, 2008). They are defined assudden-onset disasters or accidents resulting from natural,technological or human-induced factors, or a combinationof these, that cause or threaten to cause severe
environmental damage as well as harm to human healthand/or livelihoods (UNEP, 2002). They may occur in theform of a discharge of pollutants such as oil,hydrocarbons, hazardous chemicals or radioactive
substances, or the generation of disaster waste that could
result in public sanitation issues and environmental
pollution (Srinivas & Nakagawa, 2008). Compared withgeneral environmental pollution in normal times,
environmental emergencies are characterized by sudden
onset, typically a large volume of pollutant discharge in ashort period of time, and the need for urgent decisions to
be made under stressful circumstances (French &Geldermann, 2005; Liao et al., 2012). The aim ofenvironmental emergency management (EEM) is to
mitigate these environmental impacts by taking
systematic pre-and post- disaster actions.
Despite its significance in achieving sustainability inan era of frequent disasters, EEM is a field that has not
Global Environmental Research
24/2020: 253-260
printed in Japan

attracted enough attention from policy makers. The Joint
UNEP/OCHA Environment Unit points out the policy
gap and highlights the need for a new (or improved)
preparedness framework that integrates environmental
emergencies into disaster preparedness planning andemergency response (JEU, 2013a). In terms of research, aquick search in a scientific database (Web of Science
Core Collection) shows an increasing trend in the numberof studies related to EEM especially in the last ten years.
Some focus on specific types of environmental
emergencies, such as oil spills (e.g., Peterson et al., 2003;
Kujawinski et al., 2011) or “Natechs,” i.e., natural-hazard
triggered technological accidents (e.g., Young et al.,
2004; Krausmann et al., 2011); and others focus on
specific aspects of EEM such as decision making on
initial responses (e.g., Hernandez & Serrano, 2001; Liaoet al., 2012; Wang et al., 2020). There has been noattempt, however, to construct an integrated theory on
EEM.
The aim of this article is to present an overview ofrecent EEM studies as a first step toward constructing acomprehensive EEM theory, with a special focus on theworks undertaken at the National Institute forEnvironmental Studies (NIES), where EEM research has
been conducted extensively and most comprehensively inJapan, mainly since the 2011 Tohoku Earthquake. The©2020 AIRES

254

R. TAJIMA and M. OSAKOEEM framework is presented in Chapter 2 based onrecent international literature, and the representative
works undertaken at NIES are presented in line with theframework in Chapter 3 to discuss research gaps andoutlooks. Details on issues and research related toradioactive substances are dealt with in other articles inthis special issue.

2. Environmental Emergency Management
Framework
2.1 Object of Environmental Emergency Management
The environmental impacts of disasters can be
categorized by being triggered by natural hazard events(e.g., earthquakes, flooding, tsunamis) or technologicalhazards (e.g., chemical factory accidents). Another aspect
is whether the impact is caused directly by the disaster orfrom response and recovery from the disaster. Based onthese two aspects, at least four types of disaster-induced
environmental impacts can be indicated (Table 1). The
first is disturbances in the natural environment. An
example is the damage caused by the 2004 Indian Ocean
Tsunami to coral reefs, sea grass beds and other elementsof coastal ecosystems (Srinivas & Nakagawa, 2008). This
type of impact may have both negative and positive
impacts on local sustainability.
The second is disaster waste generated through thedestruction of the built environment. Disaster wastes aredifferent from wastes disposed of in normal times as they
include both household waste and industrial waste andare often mixed at source. They pose short-term sanitation
risks (e.g., odor, pests) and public health risks (e.g.,
infection), and over the longer term, environmental risks
from inappropriate treatment and disposal (Brown et al.,2011; JEU, 2013b). Serious environmental impacts may
occur when disaster wastes are contaminated withhazardous substances such as asbestos.
The third is release of hazardous substances. The
cause of such releases may be industrial accidents
triggered by human/ system errors, or Natechs triggeredby natural hazard events, such as power plant explosions
triggered by tsunamis (e.g., Young et al., 2004;
Krausmann et al., 2011). Releases of hazardous
substances may result in acute environmental and healthimpacts. In addition, recent studies highlight chronic

environmental and health impacts. For example, the 1989
Exxon Valdez oil spill had delayed, chronic and indirect
effects from petroleum contamination in the marine
environment, including, e.g., decreased sea otter survival
due to chronic exposure to residual petroleumhydrocarbons from sediment contact and ingestion ofbivalve prey (Peterson et al., 2003).
The fourth is impacts caused by disaster recovery
and reconstruction, from both natural and technologicalhazards. As disaster recovery is a resource intense project,environmental concerns from intensified resource
depletion can have detrimental effects on the long-termsustainability of disaster-impacted countries (UNEP &SKAT, 2007; Chang et al., 2010). Reconstruction projects
may also have direct and long-term environmental
impacts, e.g., impacts on water quality caused by landclearing projects to develop new housing sites (Spaling &Vroom, 2007).
Among the environmental impacts listed in Table 1,“(1) Disturbances in the natural environment” and “(4)Environmental impacts of disaster recovery” are different
from “(2) Generation of disaster wastes” and “(3) Releaseof hazardous substances” in that the impact on humansociety does not appear in the immediate aftermath of thedisasters, and thus their management does not share thecommon characteristics of EEM, i.e., urgent need andstressful circumstances of decision making (French &Geldermann, 2005). In this manuscript we focus on (2)and (3) in Table 1 as the target of EEM. However, thisdoes not mean ecosystem disturbances and environmental
impacts of reconstruction are less important. They canhave a significant impact on sustainability of the strickenarea after reconstruction and rehabilitation and should bemanaged under different management theories and tools.
2.2 P rocess of Environmental Emergency Management
Similar to the disaster management cycle (Collins,2009), which embraces both pre-disaster activities(mitigation, preparedness, early warning) and postdisaster activities (relief, recovery, rehabilitation), EEM
also has both pre- and post-disaster dimensions as
illustrated in Fig. 1.
2.2.1 Post-disaster EEM Actions
The first two steps of post-disaster EEM are
identification and assessment of potential environmental

Table 1 Environmental impacts of disasters and target ofenvironmental emergency management (EEM).
Direct result of the hazard
Triggered bynatural hazard

Result of disaster
response(1) Disturbance on natural (4) Environmental
impact of disasterenvironment
recovery(2) Generation of disaster
waste

(3) 
Release of hazardous (4) Environmental
Triggered bysubstance
impact of disastertechnological hazard
Object of EEM
recovery(including Natech)

Fig. 1 Environmental emergency management framework.

Overview of the environmental emergency management studies
impacts. This can be done at two different levels ofconcreteness. At a relatively abstract level, the type ofenvironmental impact (disaster wastes, hazardous
substances, etc.) and its urgency is identified, to guidecommon-sense response actions. Rapid Environmental
Impact Assessment (REA) is a tool for this, in which
potential environmental impacts in disaster situations canbe defined and prioritized shortly after the disasteroccurrence (Hauer & Kelly, 2018). At a more concretelevel, actions to identify potential impacts differ
according to the type of environmental impact. The
impact of disaster wastes is identified by estimating theamount and composition of disaster wastes. Here,
identification of impact (=estimation) is undertaken fordifferent purposes at different phases of the disaster waste
management (DWM) process. In the early response
phase, a very rough estimation is made to decide the scaleof DWM and necessary resources and external assistance.
In later phases, after undertaking the initial response
actions and initiating disaster waste treatment, morecertain numbers can be acquired through measurement
and calculation to facilitate decisions on the selection oftreatment and disposal options (Tajima et al., 2018). To
assess the potential impact of disaster wastes and theurgency and scale of DWM, the amount of disaster
wastes is compared with the waste disposal capacity ofthe stricken area, the existence of putrefactive andhazardous wastes is ascertained, and the degree ofseparation (or mixture) of accumulated disaster wastes isevaluated (JEU, 2013b). In terms of hazardous
substances, it is important to identify the released
substances quickly through emergency monitoring andassess their impact in terms of toxicity, concentration andquantity (Young et al., 2004). Simulation of thetransportation and dispersion of hazardous substances istypically undertaken. Identification and assessment of
impacts may become problematic when the released
substance is unknown, especially in the case of largescale Natechs that involve multiple industrial accidents.
In these cases, there are risks from released chemicals
and their side products (e.g., from fires) that are notanticipated in normal times. The Flash Environmental
Assessment Tool (FEAT) can help responders prioritize
measures to reduce impacts from chemicals throughdecision trees and lookup tables (Posthuma et al., 2014).
The next two steps of post-disaster EEM are initial
response to the impact (impact reduction) and treatment/
disposal of the impact sources. For disaster wastes,
collection and treatment of hazardous and putrefactive
disaster wastes are the highest priority (JEU, 2013b).
Following this is the collection of other non-hazardous
disaster wastes (e.g., concrete from demolition) to reduce
sanitation risks. Recycling and reuse of materials andappropriate treatment and disposal are then undertaken,
considering the balance between the conflicting
environmental (recycling rate, carbon footprint) and255

economic (direct cost) benefits and impacts (Amato et al.,2019). Mathematical models to support decisions on
disaster waste processing systems under high uncertainty
are being widely studied (e.g., Habib et al., 2019; Chenget al., 2018). To implement collection, treatment anddisposal, DWM requires specific management tasks
including procurement, financing, and planning (Tajima,2020). For hazardous substances, measures to reduce
impact, including emission reduction (limiting thesources), dispersion (limiting the pathways) andevacuation (removal of impact receptors) are
implemented (Posthuma et al., 2014). In some occasions,prophylactic drugs and antidote agents are used to reduce
health impacts (Georgiadou et al., 2010). Such decisions
are based on the characteristics of the site (e.g., location,
surrounding environment) and the environmental andhealth standards to follow. Studies on methods andmodels to support decisions on initial response, based for
instance on a case-based reasoning approach, have been
widely studied (e.g., Hernandez & Serrano, 2001; Liao etal., 2012; Wang et al., 2020). After these response actions,the released substances and contaminated water/soils arecollected using adsorbent materials or by physicalremoval to a reasonable extent and disposed of throughthe usual hazardous waste management stream.
Another important element of post-disaster EEM isoverall management of the response and recovery
process. The entire post-disaster EEM process needs tobe monitored and evaluated because situations
surrounding environmental emergencies become clear
and new issues and needs arise over time. Overallmanagement is also important because environmental
impacts at the intersection of disaster wastes andhazardous substances can occur, such as contamination ofdisaster wastes by hazardous substances.
2.2.2 Pre-disaster EEM Actions
The aim of pre-disaster actions is to effectively
reduce and respond to the impact of a foreseeable
disaster. The lessons learnt through post-disaster EEM
should guide pre-disaster EEM. Based on theoreticalgrounds in capacity development for disaster risk reduction(Hagelsteen & Becker, 2013), we considered four key
elements of pre-disaster EEM actions: preparedness
planning, training, institutional arrangements and physicalcountermeasures (Fig. 1). Pre-disaster EEM should be
dynamic and continuous, and to enhance synergistic
effects, these actions should not be undertaken in
isolation (Karunasena & Amaratunga, 2016).
The first element is preparedness planning, the coreof preparedness (USEPA, 2008; JEU, 2013b). Scholars inemergency management state that preparedness planning
is a process of generating emergency response measuresand protocols, and the written plan represents a snapshotof that process (Perry & Lindell, 2003). Anotherimportant implication of preparedness planning in EEM
is that considering the large uncertainties of the256

R. TAJIMA and M. OSAKO

emergency context, the fundamental principles of
response and priorities should be specified whereas theamount of operational details should be minimized (Perry& Lindell, 2003). For DWM this means identification ofdifferent waste management approaches and required
resources including personnel, vehicles, staging anddisposal sites, and recycling technology/facilities (Brown& Milke, 2016). The same principle applies to hazardous
substances, but current research and practice seem more
inclined to use detailed quantitative risk assessments forplanning. One example is the procedure for Natech risk
assessment which consists of (1) characterization of thenatural event, (2) identification of target equipment, (3)identification of damage states and reference scenarios,(4) estimation of damage probability, (5) evaluation ofconsequences in reference scenarios, (6) identification of
credible combinations of events, (7) frequency/
probability calculations for each combination, (8)consequence calculations for each combination, and (10)calculation of risk indices (Antonioni et al., 2009).
Mapping of those risks is also an effective practice(Girgin & Krausmann, 2013). Another importantcomponent of preparedness planning is to establish acoordination framework and personal relationships
between organizations that will be required to coordinate
in post-disaster EEM (Perry & Lindell, 2003). Unlike
waste management and chemical accident management innormal times, EEM requires involvement of natural
hazard experts and other disaster respondents such as
military, civil engineers and social welfare staff.
The second element is training, which increases theeffectiveness of preparedness plans. Preparedness plans
are only effective when knowledge, skills and attitude(KSA) are transferred to emergency responders, and that
KSA is applied effectively to real world performance(Ford & Schmidt, 2000). Typical training methods
include lectures, workshops, drills, tabletop exercises andfunctional exercises, the latter being a more active type oflearning. Training courses are also effective venues fordeveloping inter-organizational coordination (Perry &Lindell, 2003).
The third element is institutional arrangements suchas enactment and revision of laws and regulations.
Legislation on waste management (e.g., mandatory
recycling targets) can either enhance or compromise
recycling of disaster wastes (Brown & Milke, 2016).
Restricting industrial development in disaster-prone areas
through land-use planning, building codes and safety
regulations may reduce the risk of toxic releases after
natural hazard events (Krausmann & Cruz, 2013).
Regarding hazardous substances, standards for
emergency exposure play a critical role because
environmental standards developed for environmental
management in normal times may not be applicable toacute and short-term exposures.
The final element, physical countermeasures,

reduces the impact of natural hazard events and ensures
the availability of resources and functions needed for
response actions. Regarding disaster wastes, flood
prevention facilities and anti-seismic reinforcement of
housing can decrease the amount of disaster wastes,
which in turn facilitates environmentally friendly disposal
in terms of pollutant emissions (Hirayama et. al., 2013;
Wakabayashi et al., 2017). Reinforcement of installations
and equipment in various ways such as by anchoring andusing safe equipment design can also help reduce theimpact of disasters (Krausmann et al., 2011).
Just as with post-disaster EEM, it is important to get
an overview of the capacity development process andactions for preparedness. As environmental emergencies
are dependent on local situations, analysis of the existingrisks and capacity of the responding organizations isnecessary for effective preparedness capacity
development (Hagelsteen & Becker, 2013).

3. Environmental Emergency Management
Studies at NIES
3.1 Understanding Impacts of Environmental
Emergencies
NIES has conducted research aimed at elucidating
the impact of environmental emergencies, focusing
mainly on the 2011 Tohoku earthquake and tsunami, as
little was known about the environmental impact oftsunamis and tsunami-induced industrial accidents.
Regarding disaster wastes, the characteristics of disaster
wastes from the 2011 Tohoku earthquake and theirdisposal process were summarized by Osako and Tajima(2014). A large concern regarding these disaster wastes,
apart from those radioactively contaminated, was impactof tsunami sediments, amounting to ca. 10 million tons.
Oguchi et al. (2013) summarized the state of chemical
pollution and concluded that although some reports
indicated levels in excess of environmental standards forlead, arsenic, fluorine and oil, the overall level ofpollution was low. In terms of hazardous substances,
Kanaya et al. (2016) investigated the ecologicalconsequences of the fuel spills and subsequent
conflagrations that resulted from the tsunamis following
the 2011 Tohoku earthquake. The results indicated that
although sediment in the bay still contained high levels ofpolycyclic aromatic hydrocarbons (PAHs) four years after
the disaster, no negative impacts of the PAHs weredetected in the dominant macrozoobenthos. A series ofenvironmental emergency monitoring actions were also
conducted to clarify the release and impact of someinorganic elements, persistent organic pollutants (POPs),
microorganisms and pests, mainly near the evacuation
centers and temporary storage/treatment sites for disaster
wastes (Nakajima et al., 2019). Hashimoto et al. (2019)
investigated the health and sanitation risks of debris
stored at a temporary storage site on its surroundings andOverview of the environmental emergency management studies
found higher outdoor concentrations of certain
microorganisms known to be respiratory allergens
compared to in a normal environment. The effects ofparticulate matter (PM) derived from tsunami sediments
on human health were studied and it was concluded thatthe overall concentration of PM was low but thatvulnerable people may need special care (Suzuki et al.,2019). The impact of the 2011 Tohoku tsunami on thelocal ecology and population were also evaluated. It was
found that a large-scale tsunami caused mass mortality ofintertidal organisms over a broad spatial scale but did not
significantly affect the genetic diversity of the local
populations (Miura et al., 2017; Miura et al., 2019).
Kanaya et al. (2019) reached a similar conclusion fromstudies in Fukushima and Ibaraki prefectures, but theyalso pointed out the detrimental impact of restoration
work after 2016 on faunal diversity and mortalities ofsome marine taxa.
Comparing among the four types of environmental
impacts of disasters indicated in Table 1, the research at
NIES seemed to cover (1) ~ (4) relatively well, and somework has been done at the intersection of (2) and (3).
Studies on other disasters could enhance generalization of
their findings, as most of the work solely concerns the2011 Tohoku earthquake.
3.2 
Development of Post-disaster EEM Theory andTechnology
Studies on post-disaster EEM at NIES aresummarized in Table 2. Regarding identification of
impacts, methods to estimate the amount of disaster
wastes were developed, implemented and reviewed toenhance their accuracy (e.g., Hirayama et al., 2013;
Tajima et al., 2018). A rapid screening method forasbestos was developed to help enhance disaster waste
treatment while controlling health risks (Yamamoto et al.,2018). For hazardous substances, works related todeveloping and applying a technology that could quickly
identify and quantify substances existing in post disasterenvironments, namely AIQS-GC (Automated
Identification and Quantification System using gas
chromatograph-mass spectrometry), were undertaken(e.g., Nakajima et al., 2019). On the other hand, there has
been no particular research regarding assessment of the
impact that could facilitate decision-making in the initial
response.
Regarding the response and treatment/disposal step,257

research efforts have focused mainly on disaster wastes.
For example, based on practical experience in providing
technical assistance to management of temporary storagesites, management methods to prevent spontaneous fires,a potential risk during the initial response phase of DWM,
were clarified (Endo & Yamada, 2012). Regarding
disposal of disaster wastes, work has been done toconfirm the risk of generating dioxins from incinerationof wooden disaster wastes saturated with sea water, andergonomic studies have been done on factors related toefficient hand separation. To enhance recycling oftsunami deposits, their properties were investigated andmethods and standards for environmentally andphysically safe recycling as geomaterials were clarified(e.g., Katsumi et. al., 2017). These research activities
contributed to production of guidelines for effective
utilization of reconstruction materials recycled fromdisaster wastes (Japanese Geotechnical Society, 2014).
Research on overall management was intensely
undertaken regarding disaster wastes. Tasks and functions
necessary for a DWM project were clarified from in
depth research on various DWM cases in Japan, anddifferences related to the scale of the responding local
government were analyzed (e.g., Tajima, 2020)
The first research gap indicated in Table 2 is researchon assessing impacts, a missing link between results ofimpact identification and response actions. The research
outputs mentioned above could contribute more to EEM
by linking the results of impact identification to existingassessment tools such as REA, or by developing tools or
systems to aid post-disaster EEM decision making.
Another research gap in EEM worth noting is research on
response methods and processes and their overallmanagement, specifically for toxic releases underemergency circumstances. The current response methods
and procedures summarized in the Japanese guidelines do
not anticipate Natechs (Ministry of the Environment,2009), which could hinder effective responses to toxic
releases after large-scale natural hazard events andNatechs under stringent resource restrictions.
3.3 Development of Pre-disaster EEM Theory andTechnology
Research on pre-disaster EEM at NIES issummarized in Table 3. With regard to preparedness
planning, DWM planning principles have beensummarized (e.g., Tajima et al., 2013a), extensively

Table 2 Main research items of post-disaster EEM (environmental emergency management) research at NIES.
Identification of impacts(debris, pollutants, etc.)
Assessment of impacts
Initial response to (reduction of) the impacts
Treatment and disposal of impact sources
Overall management

Disaster wastes
Estimation of disaster waste
Rapid screening for asbestos
No particular research output
Methods of managing temporary storage sites
Methods and strategies for recycling tsunami sediments
Tasks and functions of DWM (disaster waste management)

Hazardous substances
Environmental monitoring system
No particular research output
No particular research output
No particular research output
No particular research output

258

R. TAJIMA and M. OSAKO

Table 3 Main items studied in pre-disaster EEM (environmental emergency management) research at NIES.
Preparedness planning
Training

Disaster wastes
Principles of DWM (disaster waste management) planning
Development of training methods and theories

Institutional arrangements
Physical countermeasures
Overall capacity management

Impact of institutional arrangements on the DWM process
No particular research output
Online tools to evaluate resilience of local waste management systems

guided by principles of preparedness planning for
emergency management (Perry & Lindell, 2003). Other
works related to overall management in post disaster
DWM also help inform the planning process by pointing
out the necessary tasks, functions and resources. No
particular work has been done to develop preparedness
planning for hazardous substances, including research
related to development of quantitative planning models
and tools using linear programming and its applied
methods, which have been rather well studiedinternationally (see 2.2.2 above). Training has gained
special attention and works have been undertaken withregard to both disaster wastes and toxic releases. Notably,
theories and methods for DWM training have beendeveloped, including workshops (Tajima et. al, 2015) andfunctional exercises for local government officers (Tajima
et al., 2019), with workshops applied to enhance civic
action among residents (Mori et al., 2020). Thesemethods were developed based on understanding of thenecessary KSAs for DWM personnel (Tajima et al.,2014). Research has been undertaken in collaboration
with several prefectural governments and citizen groups
in Japan, referring to the theory of action research(Stringer, 2014). Training to gain technical skills needed
to use AIQS-GM has also been undertaken (Nakajima etal., 2019).
Another item that has received attention regarding
both disaster wastes and hazardous substances isinstitutional arrangements. For disaster wastes, the effects
of definitive and provisional institutional arrangements
for DWM on actual management processes in the 2011
Tohoku earthquake have been analyzed, and suggestions
have been made for future development (Tajima et al.,2013b). For hazardous substances, domestic and overseas
efforts in response to accidents and disasters with releaseof chemical substances have been investigated, mainly
from the viewpoint of exposure levels, and a list of
substances deserving high-priority management has beendeveloped (Koyama & Suzuki, 2019). In addition, NIES
researchers have been extensively involved in thedevelopment of various EEM guidelines, including, e.g.,
the DWM guidelines of Japan’s Ministry of theEnvironment (Ministry of the Environment, 2018). No
particular research has been conducted so far regarding
physical countermeasures for disaster wastes andhazardous substances. For overall capacity management,
online tools to evaluate the resilience of local waste

Hazardous substances
No particular research output
Implementation of training to familiarize people with
AIQS-GC
Development of priority lists of chemicals in emergencies
No particular research output
No particular research output

management systems from various viewpoints have beendeveloped (e.g., Tajima & Osako, 2017). They areintended to help local governments plan for capacity
development, by recognizing the risks in their waste
management system and their current capacity to respond,
adapt to and cope with disaster wastes. This is associatedwith an online information platform for disaster waste
management developed by NIES, in which technical andadministrative guidance, reports on DWM experience, a
database of local DWM plans and other materials forindividual and organizational learning are consolidated.
One gap obvious from Table 3 is research on
physical countermeasures. This is usually studied bystructural dynamics experts. Collaboration with external
natural hazard experts on physical countermeasureswould have important implications in preparedness
planning (e.g., the role of treatment facilities, postdisaster functionality of disposal facilities) andinstitutional arrangements (e.g., provision of incentives).
Another issue regarding collaboration is inadequate
interaction between disaster waste and hazardous
substance researchers on preparedness planning, training
and capacity management. For example, methods andtheories on training for EEM could be developed andimplemented more efficiently by integrating the findings
from works undertaken for disaster wastes and toxic
releases. A tool to evaluate the capacity to manage
hazardous substance releases similar to the tool developed
for disaster wastes could benefit from integration toenhance awareness of both issues by local governments.

4. Conclusions
Since 2011, research on EEM has been undertaken
extensively by NIES, mainly driven by the needs andissues recognized in EEM practice. This article has
attempted to clarify the overall framework of EEM, andgive an overview of associated research conducted at
NIES. Our analysis shows good coverage of research
topics aimed at enhancing understanding of the impact ofenvironmental emergencies and at advancing both preand post-disaster actions for DWM. Some research gaps
have also been identified, namely, research on postdisaster assessment of environmental impacts anddecision making under emergency circumstances,
research on response and recovery actions against
impacts from hazardous substances released by natural

Overview of the environmental emergency management studies
hazard events, and research collaboration within the EEM
discipline and among natural hazard experts (especiallyregarding physical countermeasures) . Finally, we shouldnote that to enhance EEM in an age of limited publicresources (budgetary and staff), future research should
focus on synergetic benefits for development in normal
times and response in emergencies. Innovations intechnologies and governance structures of normal-timeenvironmental management are required in a way thatmainstreams EEM.
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Ryo TAJIMA
Ryo Tajima is a senior researcher at the Centre forMaterial Cycles and Waste Management
Research, National Institute for Environmental
Studies, Japan. His main research field is policy
and planning for waste management underdisaster and normal circumstances. He is involved
in local and national efforts to draft guidelines
and plans and to design training programs for disaster waste management.

Masahiro OSAKO
Masahiro Osako, who holds a doctorate ofengineering, serves as director of the Material
Cycles Division, National Institute forEnvironmental Studies (NIES). His specialty isenvironmental engineering, focusing on waste
management. Since the Fukushima nuclear
accident that resulted from the Great East Japan
Earthquake in 2011, he has been dedicated not only to conducting various
researches to properly manage radioactively contaminated wastes but also
to playing an important role in the relevant policy-making by the national
government. He also chairs the research committee on technologicalstrategies for the final disposal out of Fukushima in the Society of
Remediation of Radioactive Contamination in the Environment.
(Received 17 September 2020, Accepted 21 December 2020)

261

Systematic Analysis of Environmental Release Process andEmergency Response in Chemical Accident
Yosuke KOYAMA*, Yoshitaka IMAIZUMI and Noriyuki SUZUKI
Center for Health and Environmental Risk Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan*E-mail: koyama.yosuke@nies.go.jp

Abstract
Various harmful substances have been released into the environment due to increased occurrences ofchemical accidents. However, only a limited number of the cases have been analyzed from the perspective of
health and environmental risks to the general environment. In this study, we conducted questionnaire andinterview surveys with site operators to collect information related to substance release processes andresponses to them in past accidents. In addition, we extracted factors relevant to the emergency responses tothe accidents and systematically analyzed the release processes.
Key words :	accidental release, case analysis, chemical substances, emergency response

1. Introduction

2. Methods

Various harmful substances have been released into
the environment during chemical accidents such as fires,
explosions and spills. The number of accidents at
facilities handling hazardous materials has been
increasing since the 1990s (Fire and Disaster
Management Agency, 2016). Quick and appropriate
responses to accidental releases are essential forminimizing health and environmental risks. It is not easy
to obtain information on risk assessment due to thedifficulty of identifying substances and fluctuations in theamounts released and concentrations in the environment.
Therefore, only a limited number of cases have been
analyzed from the perspective of risks to the generalenvironment despite the many accidents that haveoccurred. Systematizing the behaviors of released
substances and accident patterns is important for ensuring
quick and appropriate responses to accidents.
In this study, we have systematically analyzed theprocesses of chemical releases and responses of facilities
and government bodies to accidents based onquestionnaire and interview surveys. The questionnaires
were designed to collect a variety of information related
to release processes and responses in past accidents. Theinterview surveys were conducted to obtain detailed
information on situations and personal opinions whichwere hard to obtain from the questionnaire. In addition,
we paid attention to practical information that had been
useful in responses soon after accidents based on thesurvey results.

2.1 Questionnaire Survey on Chemical Accidents
For the purpose of collecting information as a basis
for categorizing chemical accidents, we conductedquestionnaire surveys and interview surveys with site
operators about accidents that had occurred in thepast. To list up target accidents for these surveys,
past accidents in Japan that may have involved
releases of chemical substances were extracted fromthe Database of Disasters and Accidents (Accident
and Disaster Information Center (ADIC)). Thesesurveys were carried out twice. The first (Survey 1)
was conducted in April 2019 and the second (Survey 2)
was conducted in April 2020. Survey 1 covered
accidents that had occurred in recent years (2017 to2019) with no limit on the type of industry, andthe Survey 2 covered accidents that had occurred
at industrial sites involved in “manufacture of chemical
and allied products” after 1990 except for casesthat would duplicate those in Survey 1. Survey 2 wasintended to collect more information about thechemicals released. The number of questionnaires
distributed in Survey 1 was 100, and in Survey 2, 51. In
both surveys, the interviews were conducted after
the questionnaire survey (Survey 1: 20 interviews, Survey
2: 18 interviews).
The questions asked in the questionnaire surveys
were mainly concerned with the handling of substances at
the time of the accident, the state of the released
substances in the environment and the emergency

Global Environmental Research
24/2020: 261-266
printed in Japan©2020 AIRES

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Y. KOYAMA et al.

Table 1 Questions asked in the questionnaire (outline).
No.

Questions

Q1

Were there any investigations or guidance given by administrative authorities after the accident?

Q2

Was a report on the accident prepared by the operator or the administrative authorities?

Q3

Can the report in Q2 be provided?

Q4

What was the cause of the accident?

Q5

Please list substances handled that were related to the accident.

Q6

How much of the substances handled was stored?

Q7

What purposes do the substances handled have in the processes at the site? (e.g., raw materials, by-products, waste products)

Q8

Please list any chemicals that were thought to be unintentionally produced by the accident, if any.

Q9What is the reason that you judge the unintentionally produced chemicals to have been produced?

Q10

For how long were the substances released after the accident?

Q11

Were any substances released into the general environment during the accident?

Q12

Regarding Q11, what and how much of the substances were released into the general environment?

Q13

Were any concentration measurements performed in the general environment after the accident?

Q14

Regarding Q13, please give the name and concentration of the substance.

Q15

Please describe the time-series transition of events from the occurrence of the accident to the convergence.

Q16

Is it possible for you to cooperate with an interview survey?

responses to the accident. Table 1 outlines the questions.

3. Results and Discussions

2.2 Considering Practical Information in Emergency
Responses
Based on the results of the surveys in Section 2.1,
information desirable to obtain for emergency responses
was examined. Methods of identifying released chemicals,considered to be a particularly important factor in
conducting environmental surveys, were compared. Here,the advantages and disadvantages of interviews with site
operators and utilization of the Pollutant Release
and Transfer Register (PRTR) notification data werecompared. In addition, examples of other factors andcriteria that could characterize chemical accidents wereidentified.

3.1 Analysis of Questionnaire Replies
Table 2 shows the number of replies to thequestionnaire survey by industry. In Survey 1, as forclassification of industry, “manufacturers of chemical andallied products” (7 respondents) accounted for the highest
number of respondents. Next were “manufacturers of
petroleum and coal products” (4 respondents), “manufacturersof transportation equipment” (4 respondents), and “waste
disposal businesses” (4 respondents). They accounted forabout 70% of the total respondents (19 of 29 respondents).
In Survey 1, accidental fires (including explosions)accounted for the majority of cases (27/29). On the other
hand, in Survey 2, accidental fires comprised less than
30% (9/34 cases). In many of the cases investigated inthis study, especially regarding accidental fires, thereports on the accidents were prepared by the operator or
administrative authorities (obtained from Q2 in Survey
1). There were few cases, however, from which
information on releases to the general environment could
be obtained, because most of the reports were on
investigations into causes and suggestions for
improvement of facilities and operations.
Regarding whether chemical substances had beenreleased into the general environment or not (Q11), in
Survey 1, seven respondents replied “They were released
to the general environment,” and about 30% (10respondents) replied that it could not be ascertained(“Unknown” or no reply). In Survey 2, about 40% (13/34
respondents) replied “They were released to the generalenvironment,” while all other respondents replied “Thereleased substances remained within site boundaries.”
Regarding the handling substances related to theaccident (Q12), relatively detailed information was

2.3 Classification of Release Processes and Responses
To manage the risks to the general environment from
accidental releases of chemical substances from industrialsites, it is important to analyze systematically the
behaviors of substances in the environment from the timeof release of the chemical substances to the time of
exposure. The concept of a migration process of released
substances in environmental media had been brought up
in several studies (International Atomic Energy Agency(IAEA), 2002; Moriguchi, 2013; World HealthOrganization, 2009), but there were differences in thesettings of the environmental media. In this study, for the
purpose of covering various possible situations, attempts
were made to classify the migration processes ofsubstances in the environment and the corresponding
emergency responses. Possible emergency responses
were listed in consideration of both possible general
responses and replies to the questionnaire survey.

Analysis of environmental release and response in chemical accident

263

Table 2 Number of replies to the questionnaires.
Survey1

2Year

2017–20191990–2016

Industrial classification*
Code

Name

Number of
replies

16

Manufacture of chemicals and allied products

7

17

Manufacture of petroleum and coal products

4

18

Manufacture of plastic products, except as otherwise classified

3

21

Manufacture of ceramic, stone and clay products

224

Manufacture of fabricated metal products

1

25

Manufacture of general-purpose machinery

1

27

Manufacture of business-oriented machinery

1

29

Manufacture of electrical machinery, equipment and supplies

1

31

Manufacture of transportation equipment

4

55

Miscellaneous wholesale trade1

88

Waste disposal business

4

16**

Manufacture of chemical and allied products32*
The industrial classification (code and name) shown in this table are based on Japan Standard Industrial Classification(Ministry of Internal Affairs and Communications, 2013).
** In Survey 2, a four-digit industrial classification was used, but here they are indicated as the main group by the first two digits.

obtained for leakage accidents from “manufacturers ofchemical and allied products,” but from the others, there
were few cases in which details on those substances could
be identified. This was because the causal substances in
the accidents were often uncertain in the cases of fires or
explosions.
Regarding release duration (Q10), in Survey 1,
excluding “unknown” cases (9 cases), five cases were“instantaneous releases due to explosions” and 11 cases
were “1 to 6 hours,” indicating the time it took to
extinguish the accidental fires. In Survey 2 where manycases were leakage accidents, many (23 cases) replied“within an hour” (of which one was an instantaneous
release), while in one case, it was estimated that leakage
due to corrosion of buried piping had continued forseveral months.
Regarding unintentional reaction products (Q8), in
both surveys, about half replied “There was no possibilityof producing them.” In Survey 1, “Unknown” accounted
for about 25% (7/29 cases), while in Survey 2,“Unknown” accounted for only two cases and more than
40% (14/34 cases) replied “There was a possibility of
producing them” (due to combustion or unintended
chemical reactions). Since Survey 2 covered accidents inchemical plants, it was thought they had knowledge ofthe substances being handled and reaction products in theaccident. Generally, it is thought that unintentional
reaction products are generated in accidental fires. In
these surveys as well, many of the replies regarding
accidental fires were “There was a possibility of
producing them.” Therefore, understanding ofunintentional reaction products in accidental fires isthought to be important.
Regarding measuring concentrations in the generalenvironment (Q13), in both surveys, approximately 25%(Survey 1: 7/29 respondents, Survey 2: 8/23 respondents)
replied that it had been conducted in some way after theaccident. However, most of these were not conducted by
the emergency response, but referred to data obtained byconstant monitoring at site boundaries or periodic surveysof the surrounding environment. Estimations ofenvironmental concentrations (model calculations, etc.)
had been performed in only two cases in Survey 2.
The results of the questionnaire survey clarified that
there were few cases of emergency response that involved
environmental monitoring for the general environment.
In the interview survey, some site operators said that the
emergency responses at the time of the accident had been
multiple and complicated, and environmental monitoring
was not given very high priority.
3.2 Practical Information for Emergency Responses
The results of questionnaire survey in this study
revealed that information on chemical substances releasedin the course of accidents was unavailable in many cases.
Therefore, it is important to establish methods for
identifying the chemical substances released into thegeneral environment. The methods currently available toidentify released substances are summarized below, alongwith their advantages and disadvantages.
As to methods of identifying released chemical
substances, it is conceivable not only to ask the site
operators, but also to use the related notification data on
annual emissions or amounts handled.
Interviews with the site operators may provide a
possible way to obtain information useful for risk
assessment such as on substances handled during theaccident, amounts released and so on. However, it islikely that they will not be able to reply immediately after
the accident. In addition, even if it is possible, it will takesome time to conduct. Therefore, this is not a realistic
approach, especially in the case of emergencies.
PRTR notification data in Japan (Ministry of
Economy, Trade and Industry, published annually) is

264

Y. KOYAMA et al.

readily available. PRTR data cover 462 substances withrelatively high environmental risks and provide locationsof business sites where they may be released ortransferred at normal times. However, an analysis ofSurvey 1 (Koyama et al., 2019) revealed that only in a
few cases were PRTR substances reported by the site
operator related to the substances released during theaccident. (In Survey 2, many cases had occurred before
the start of the PRTR system, so a sufficient comparison
could not be made.) Therefore, it can be said that PRTR
data cannot always be used effectively regarding
emergency responses.
None of the methods shown here is sufficient, so it is
not easy to quickly identify a target substance using asingle method. To carry out an appropriate environmental
survey, the best way at present to estimate the substancesthat may have been released is by using a combination ofthese methods. Therefore, it is important to collect andanalyze relevant information from before the accident sothat the necessary information can be quickly obtained infuture accidents or disasters.
There are thought to be some key factors defining
the characteristics of chemical accidents, although not all
relevant information could be obtained due to lack of
information from the questionnaire surveys. These factors
may be divided into those related to characteristics ofchemicals (e.g., visibility, specific gravity, solubility,
toxicity) and those related to characteristics of accidents(e.g., release destination, duration, quantity, types ofsurrounding areas).
It is important to set criteria for such factors toenable quick and appropriate responses. As an example ofAccident site

ReleaseAtmosphere

3.3 S
 ystematic Classification of Environmental Release
Processes and Responses
To systematically classify the processes of release ofchemical substances, the migration of chemical
substances between media is expressed as a matrix in
Fig. 1 referring to the migration matrix of radioactive
materials (IAEA, 2002). In addition, the possible
responses to this are summarized in Table 3 and Fig. 2.
Here, responses are classified into two categories,“Identification” and “Management.” In addition, theresponses are separated into what is done for the media
and what is done for transfers between the media.
Regarding responses for the media, examples of“Identification” responses were “visible observation(smoke, crop damage, etc.),” “atmospheric monitoring”
and “atmospheric concentration model calculation,”while an example of a “Management” response was

ReleaseDry and wet
deposition

Volatilization

Rivers, lakes

Re-suspension

Translocation

Re-suspension

Translocation

Re-suspension

Translocation

Volatilization

criteria for toxicity, there are five levels (A to E) of
classification based on the toxicity categories of the GHS
classification system (Osaka Prefectural Government,2014). This classification is useful in that it can beapplied to various chemical substances. For substanceswith high acute toxicity, it may be possible to use criteria
for emergency responses such as Acute Exposure
Guideline Levels (US Environmental Protection Agency).
As a next step, through a detailed study of thesefactors and criteria, it may be possible to classify
chemical accidents with similar features. In the future,reviewing and classifying the responses actually taken or
to be taken in similar cases will make these factors more
useful in responses to future accidents.

ReleaseDry and wet
deposition

Dry and wet
deposition

Translocation

Translocation

Forested land

Translocation

Dry and wet
deposition

Dry and wet
deposition

Inhalation

Translocation

Ingestion(drinking water)
Ingestion(forest products)

Translocation

Ingestion(agricultural
products)

FarmlandResidential areas

Sea

Ingestion(seafood)
The publicFig. 1 An interaction matrix which describes the migration of released substances in the general environment.
The diagonal elements are components of the system and the off-diagonal elements are the interactions between
them. To identify the transfer processes the matrix should be read clockwise from the upper left.

Analysis of environmental release and response in chemical accident“decontamination.” Regarding the responses to transfers
between media, examples of “Identification” responses
included “sensing odors (strange tastes)” and “personal
exposure measurement,” while examples of“Management” responses included “spraying water infirefighting,” “oil fence installation,” “mask wearing,”“indoor evacuation” and “limiting water supplies.”
In “Management” responses, an action may have a
new impact on substance migration between media. For
Table 3 P ossible responses for the components of the environmental
system in Fig.1.
Identification

Management

Accident site

On-site personnel interview
Use of notification information(e.g., PRTR)

Atmosphere

Visible plume,
Air monitoring,
Atmospheric dispersion modelRivers, Lakes

Death of fish,
Water quality monitoring

Diffusion prevention(e.g., oil fence)

Forested land

Damage to forest

Decontamination

FarmlandDamage to agricultural products Decontamination

Residential areas
Sea

Decontamination
Death of fish

Diffusion prevention(e.g., oil fence)

265

example, fire extinguishing activities may reduce theamount transferred to the atmosphere, but they may
increase the amount transferred to rivers or lakes or result
in releases of other substances. Therefore, it is also
important to sort out changes in the transfer process due
to passage of time or response actions.
It should also be noted that the process from release
to exposure varies depending on the accident type and thelocation of the release site. Emergency responses also
vary depending on the accident type, chemical propertiesof the substances involved, available capacity to deal
with accidents and so on. These classifications of media
and migration processes are tentative, and some
improvement may be needed. For example, scattering ofchemical substances by explosions to forested land fromindustrial sites is classified as migration via atmosphere,
but it may be more practical to classify such short-periodmigrations as direct migration. The blank cells in Figs. 1
and 2 do not necessarily indicate that a process does notexist or that a response is unnecessary, and it will benecessary to make corrections and additions in the future.
To lead to appropriate responses to future accidents ordisasters, it will be important to analyze release processes
after chemical accidents as comprehensively as possible
and examine responses that were (and were not) taken inpast cases and the reasons for that.

The public

Accident site

Constant
monitoring
Water spray

Atmospheremodel estimation?

model estimation?

model estimation?

model estimation?

model estimation?

Constant
monitoring
Interception(e.g., oil weir)Interception(e.g., oil weir)Odor, Personal
Deposition model Deposition model Deposition model Deposition model Deposition model
exposure
estimation
estimation
estimation
estimation
estimation
measurement
Evacuation/
Sheltering,
Mask wearing
Strange taste

Rivers, Lakes

Suspension ofwater supply
Strange taste

Forested land

Shipment
restriction
Strange taste

Farmland

Shipment
restriction
Residential areas

Sea

Strange taste
Shipment
restriction
The publicFig. 2 Possible responses to migration of chemicals. The top half of each square shows the identification responses
and the bottom half shows the management responses.

266

Y. KOYAMA et al.

4. Conclusion
We conducted questionnaire and interview surveys
on chemical accidents and analyzed their characteristics.
From these surveys, it became clear that few
environmental surveys on the general environment havebeen conducted when accidents have occurred, and thatthe extent of information on released substances varies byindustry and type of accident. We have revealed that
information from existing notification systems such as
PRTR has been insufficient for identifying target
substances soon after accidents and it is important tocollect information on amounts of chemical substances
stored, including non-PRTR substances, for effective
responses to accidents. We have also systematicallyanalyzed release processes and the emergency responses
to them. Expansion of this information will enable rapid
and effective risk management of chemical substances
released into the general environment in emergencies.
Acknowledgements
This research was performed under the auspices of
the Environment Research and Technology Development
Fund (JPMEERF18S11701) of the Environmental
Restoration and Conservation Agency of Japan.

lg.jp/attach/4460/00157380/manual_saigai.pdf (Accessed 4
September 2020)
US Environmental Protection Agency, Acute Exposure Guideline
Levels for Airborne Chemicals. Retrieved from https://www.epa.
gov/aegl (Accessed 5 September, 2020)
World Health Organization (2009) Manual for the Public HealthManagement of Chemical Incidents. Retrieved from https://www.who.int/environmental_health_emergencies/publications/
Manual_Chemical_Incidents/en/ (Accessed 28 August 2020)

Yosuke KOYAMADr. Yosuke Koyama is a researcher at the Centerfor Health and Environmental Risk Research,
National Institute for Environmental Studies(NIES), Japan. He received his Ph.D. in
Environmental Engineering from Kyoto
University. He is interested in health andenvironmental risk management in emergencies
such as the aftermaths of chemical incidents. His research interests include
strategic approaches to comprehensive chemical risk management andcontrol, and indoor-scale chemical dynamics.

References
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www.adic.waseda.ac.jp/rise/member/ (Accesed 28 August 2020)
Fire and Disaster Management Agency (2016) 2016 White Paper
on Fire Service. (in Japanese) Retrieved from https://www.fdma.
go.jp/publication/hakusho/h28/items/h28_all.pdf (Accessed 26
August 2020)
International Atomic Energy Agency (IAEA) (2002) Modelling the
migration and accumulation of radionuclides in forest
ecosystems. Report of the Forest Working Group of the
Biosphere Modelling and Assessment (Biomass) Programme,
Theme 3.
Koyama, Y., Imaizumi, Y. and Suzuki, N. (2019) Case analysis andscenario development regarding accidental release of chemical
substances, Proceedings of the 2019 Annual Meeting of the SRA
Japan, 76–81. (in Japanese)
Ministry of Economy, Trade and Industry, PRTR seido ni motozuku
todokede data no kōhyō ni tsuite (Publication of notification data
based on the PRTR system). (in Japanese) Retrieved fromhttps://www.meti.go.jp/policy/chemical_management/law/prtr/6a.html (Accessed 28 August 2020)
Ministry of Internal Affairs and Communications (2013) Japan
Standard Industrial Classification (Rev. 13, October 2013).
Retrieved from https://www.soumu.go.jp/english/dgpp_ss/seido/
sangyo/san13-3a.htm#e (Accessed 28 August 2020)
Moriguchi, Y. (2013) Houshasei-bussitsu ni yoru kankyo-osen to
hibaku-keiro. Gakujutsu no Doukou, 18 (5), 66–71. (in Japanese)
Osaka Prefectural Government (2014) Osaka Prefecturechemical substance management system notification manual:
Environmental risk reduction in preparation for a large-scaledisaster. (in Japanese) Retrieved from http://www.pref.osaka.

Yoshitaka IMAIZUMIDr. Yoshitaka Imaizumi is a senior researcher at
the Center for Health and Environmental Risk
Research, National Institute for Environmental
Studies (NIES), Japan. He is interested inenvironmental risk assessment and management,
and relevant environmental fate models forchemical contaminants, including agricultural
pesticides, radioactive substances, and industrial chemicals. He has
investigated emission estimation methods and related fate models. He is
also contributing to the public disclosure of risk-related information about
regulations, amounts distributed, environmental monitoring results, andenvironmental measurement methods for chemicals, as part of his activitiesof the Risk Assessment Science Collaboration Office at NIES.

Noriyuki SUZUKI
Dr. Noriyuki Suzuki directs the Center for Healthand Environmental Risk Research at the National
Institute for Environmental Studies (NIES),
Japan. His research fields are chemical
contaminant risk assessment and relevant
environmental fate analysis based on both fatemodels and monitoring approaches. He chairs theWorking Group on PRTR at OECD and is also one of several working
members engaged in OECD and UNEP projects on chemical risk
management. He now is involved in a research project on integrating global
mercury emissions, fate/transport, material flows and impacts, in addition
to a project on chemical risk management in emergencies.

(Received 7 September 2020, Accepted 22 December 2020)

267

Strategy to Promote Residents’ Behaviors
for Appropriate Disaster Waste Management
Tomoko MORI* and Ryo TAJIMA
Centre for Material Cycles and Waste Management Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan*E-mail: moritomo517@gmail.com

Abstract
This paper aims to clarify appropriate disaster waste management behaviors by citizens based on anunderstanding of frequently experienced problems in past disaster waste management cases. We also discuss
methods and strategies to promote citizens’ behaviors based on examples in disaster risk reduction fields.
From our results, we have identified three problems that have often occurred in past disaster waste treatment:
generation of large amounts of mixed disaster waste, creation of unauthorized temporary storage sites, andinsufficient support for clean-up. In municipalities where large open spaces for temporary storage sites fordisaster waste are difficult to find, residents also have to establish and operate the community’s storage sites
in cooperation with other residents. To promote these behaviors among citizens, there are three key factors:
preparedness by municipalities for disaster waste management, citizens’ understanding and motivation, andthe existence of community networks. Based on examples of public involvement in the disaster risk reduction
field, participatory training and planning involving citizens is effective at promoting their understanding andproper behaviors for disaster waste management. We propose three strategies to implement participatory
methods and promote appropriate disaster waste management behavior by citizens. Firstly, seizing existing
opportunities such as disaster drills would be a promising approach to communicating with residents andimplementing participatory methods. Secondly, it would be important to identify citizen groups active indisaster risk reduction or waste management activities and collaborate with them. Thirdly, leveraging
experience with disasters would be an effective way to promote disaster waste management because citizens’
awareness of disaster waste issues is enhanced after disasters.
Key words :	collaborative behaviors, mutual help, participatory training and planning, public involvement

1. Introduction
Natural disasters have occurred frequently in Japanin recent years, and each time, a large amount of disaster
waste, such as damaged household goods and demolishedhouses, has been generated. If we fail to implement
disaster waste management (DWM), sanitary conditionsin the damaged area become very poor and restoration isdelayed. The national government of Japan has promoted
policies for DWM especially since the Great East Japan
Earthquake in 2011. Municipalities that have
responsibility for DWM have also promoted measures for
effective DWM such as preparedness planning andcapacity building (Tajima et al., 2019).
In the field of Japanese disaster risk reduction, it issaid that three aspects of preparedness are important: selfhelp, mutual-help and public help. “Self-help” refers toactions by individuals and families, “mutual help” tocollaborative actions among citizens, and “public help” tocountermeasures by government (Wada, 2018;
Global Environmental Research
24/2020: 267-274
printed in Japan

Yamashita, 2010). So far Japanese policies for DWM
have focused on public help. It is very difficult, however,
to manage disaster wastes properly and promptly because
devastated municipalities have to allocate their very
limited resources to various disaster response activities in
the confusing situation after a disaster. Therefore, selfhelp and mutual help become important.
What kinds of self-help and mutual help are expected
for appropriate DWM? And how can we promote them?
This paper clarifies citizens’ behaviors as self-help andmutual help for DWM based on experiences with DWM
in past disasters. We also discuss methods and strategies
to promote self-help and mutual help for DWM byreviewing examples of public involvement in activities
for disaster risk reduction.

2. Frequent Problems in DWMWhen a disaster strikes, DWM starts with thedisposal of damaged household goods by the affected©2020 AIRES

268

T. MORI and R. TAJIMA

Impacts

Frequent problems
Genera�on of
mixed disaster
waste

Insuﬃcient
support forclean-up

Crea�on ofunauthorized TSS• Heavily commingled atsource (e.g. tsunamis,
collec�on without
separa�on)• Dropped oﬀ at TSS
without segrega�on• Insuﬃcient number of
TSS• Heavy traﬃc• Lack of vehicles• Available fortransporta�on• Informa�on on TSS
not conveyed• Poor sanitary condi�ons• Delay in city’s recovery• Increased costs• Increased environmental
burden• Insuﬃcient volunteer
staﬀ• Residents who need
generous support(e.g. the elderly,
handicapped persons )Background of problems
Fig. 1 Frequent problems in DWM and their impacts and backgrounds.

people. These disaster wastes are typically transported by
the affected people to temporary storage sites (TSS) or
collected by the local government. Subsequently,
damaged houses and buildings are repaired ordemolished, generating additional disaster wastes. This
paper focuses on the phases of disposal (clearing) fromdamaged houses and transportation to the TSS since thesephases are closely related to citizens’ behaviors.
The problems that have typically occurred in theclearing and transportation phases of past disasters areshown in Fig.1, along with their impacts, and theirbackgrounds. One of the most frequent problems is thegeneration of large amounts of mixed disaster wastes at
the TSS. If the disaster waste is separated properly, moreof it can be recycled or reused.
Perishable wastes should be separated andincinerated first. Once mixed disaster wastes are
generated, the separation process takes more time, andwaste treatment facilities will not accept them without
separation. Increased processing results in higher costs
and time requirements . The burden on the environment
also increases since recycling rates decrease and theamount of waste going to landfills increases. Different
types of disaster wastes get mixed when they are heavily
commingled at source (e.g., in cases of tsunami disasters
or when damaged household goods are collected with noconsideration for separation), or when they are dropped
off at the TSS without segregation.
A second frequent problem is the creation ofunauthorized TSS, i.e., TSS set up by local residents but
unknown to the municipality. In many cases at this kindof storage site, cleared wastes are mixed improperly,
generating foul odors and vermin which may harm
human health. It also costs money to collect and treat
mixed waste. This has become an issue due to various
factors including but not limited to: insufficient numbersof TSS established by the municipality, heavy traffic in
the stricken area that hinders the ability to transportdisaster waste to a TSS located at a distance, lack ofvehicles (e.g., small trucks) available for transportationand failure to inform the people affected by the disaster
about the location of the TSS.
A third frequent problem is insufficient support forcleaning up. Disaster volunteer activities have become
popular in recent years and many volunteers enter disasterareas to help affected people clean up their houses after
disasters. However, it is difficult to get enough support
from volunteers if the disaster causes widespread damage
and there are requests for help from many places, which
was the case after the heavy rain disaster in western Japan
in 2018. In addition, elderly and handicapped residents
and those who have young children need generous
support since it is difficult for them to clean up their
damaged houses and transport large amounts of disaster
wastes.

3. Citizens’ DWM Behaviors
What kind of citizens’ behaviors can mitigate theimpacts of the frequent problems mentioned in Chapter 2.
We discuss citizens’ DWM behaviors both before andafter disasters.
3.1 Following Separation and Clearing Rules
Separation of disaster wastes at source and at TSS
can only be achieved by appropriate waste disposal
behavior by citizens. For this, information on separationand clearing rules should be provided to them.
Collaborative action to share correct information about
rules using bulletin boards or SNS in the community isimportant, too. However, getting to know the rules andfollowing them are not as easy after disasters occur,
because of the confusion in the disaster area with people
who have been harmed physically or mentally by thedisaster. Therefore, it is important to check rules
predetermined by one’s municipality before disasters
occur. It is also important to discuss information sharing
schemes in the community before disaster strikes.

Strategy to Promote Residents’ Behaviors for Appropriate Disaster Waste Management
3.2 Storage at Community TSS
In some municipalities that have high-density
population areas, it is difficult to find large open spaces
for disaster wastes TSS. In such areas, the use of small
open spaces such as local playgrounds as TSS may be asolution, provided that they are properly managed incollaboration with neighbors. Because it is quite difficult
to decide on community TSS locations and management
rules once disasters have happened, ideally discussions
on where to establish community TSS and how tomanage them in the community should be held before
disasters occur.
3.3 Clean-up by Mutual Help
Cleaning up houses damaged by disasters is very
tough work. The amount of waste is large and the weightof some household goods such as soaked carpets andtatami (traditional Japanese straw floor mats) is very
heavy. Thus, the residents of disaster areas can help eachother and collaborate with volunteers to clear andtransport disaster wastes. Community meetings before
disasters to discuss collaboration among residents andsupport systems for vulnerable neighbors could enhancemutual help after disasters. Such community meetings
would be effective not only for DWM but also
comprehensive disaster preparedness of the community
overall because collaboration among residents is neededin various ways after disasters, such as for evacuation andmanagement of the community’s shelters.

4. Key Factors for Promoting Citizens’ DWM
Behaviors
4.1 Preparedness by Municipalities for DWMWhen disaster strikes, some municipalities cannot
decide on and announce rules for separation and clearing
immediately because they lack advance preparation. As
of 2019, about the half of Japan’s municipalities had not
developed a DWM preparedness plan (Ministry of theEnvironment, 2020). The residents living in such areas
will not be able to get information on rules immediately.
Therefore, preparedness for DWM by municipalities is
one of the most important key factors in promoting
citizens’ DWM behaviors. Ideally, separation and clearing
rules should be announced to the residents before
disasters because it is difficult to distribute information toresidents during times of disaster. Some municipalities
have communicated with their residents by brochures or
public relations magazines (Sakai City, 2017; Kawasaki
City, 2019).
4.2 Gaining Citizens’ Understanding and Motivation
for DWM
Obtaining citizens’ understanding and motivation for
DWM is important in promoting citizens’ DWM
behaviors because people do not always take action even269

if they know the rules. Hirose (2015) advocated a twophase model for pro-environmental behaviors based on
the theory of planned behaviors by Ajzen (1991) andproposed that risk perception of the problem,
responsibility for dealing with the problem, and perceived
effectiveness of the desired behavior influence people’s
intention to contribute toward solving the problem. There
are many existing studies using Hirose’s theory. Asato
and Kimiya (2008) found that a sense of responsibility
for dealing with problems has a strong positive influence
on behavioral intentions toward cooperation withseparation and collection of municipal wastes. Matsui etal. (2004) revealed that the perceived effectiveness of abehavior is one of the most important determinants ofrecyclable waste separation behavior. These studies
indicate that having citizens understand the risks
associated with poor DWM, i.e., health risks andhindrance of reconstruction, is an effective way topromote appropriate DWM behavior by the citizens. Thismay be further enhanced by recognizing that these risks
can be reduced by following rules of separation, storage
and transportation.
Educational materials on disaster wastes are apossible tool for promoting citizens’ understanding. Somemunicipalities provide their residents with brochures fordisaster preparedness (Tokyo Metropolitan Government,2015). Information about proper clearing andtransportation of disaster waste is needed because existing
brochures on disaster preparedness do not mention
disaster wastes in many cases. It may be effective toinclude information about disaster wastes in the existingeducational materials on disaster risk reduction because
people tend to have considerable interest in information
regarding disaster response in general. More study isneeded to clarify effective ways to provide information
about disaster wastes.
To promote citizens’ motivation not only for selfhelp such as checking pertinent rules before disasters but
also for mutual help such as discussion at community
meetings, the citizens have to know what mutual help for
DWM is and how to perform it. Mori and Tasaki (2019)
pointed out that a sense of responsibility for collaborative
behaviors and perceived effectiveness of collaborative
behaviors have strong positive influences on behavioral
intentions toward collaborative behaviors. Therefore, it isimportant to provide them examples of mutual help
before and after disasters and foster the cognition thatmutual help is a meaningful action for citizens and an
effective means of appropriate DWM. Ideally citizens’
recognition of their stake in mutual help for DWM should
be fostered through dialogue or disaster drills in thecommunity.
4.3 Community Networks
Community networks are important to haveespecially for promoting mutual help among residents.

270

T. MORI and R. TAJIMA

Mutual trust among community members fosteredthrough regular communication is the basis for helping
each other in difficult times. It may also promote effective
sharing of information on separation and clearing rules
among residents after disasters. Common risk perceptions
toward disasters in communities are also importantbecause the residents will have higher motivation for
DWM if many of them share a sense of crisis about
disasters.
Matsumoto et al. (2012) revealed that making proenvironmental behaviors, such as waste reduction
behaviors at schools, visible to other citizens, strongly
influences social norms, i.e., cognition of other people’s
behaviors and expectations for proper behaviors fromfamily, friends and neighbors. Social norms affectpeople’s behavior strongly in communities in which theresidents know each other. Therefore, social norms will
have a positive influence on promoting residents’appropriate clearing of disaster wastes in communities
that have rich networking.

5. Methods for Developing Capacity in the
Disaster Risk Reduction Field and their
Applications in DWM
To promote citizens’ DWM behaviors, it is importantto foster their understanding of DWM and develop
community networks. How can we put that into practice?
We refer to examples of public involvement in the fieldof disaster risk reduction and discuss their application to
DWM.
5.1 Disaster Drills with Stakeholders
Disaster drills constitute pre-training in which
disaster situations are simulated to promote proper
behaviors in times of disaster. Disaster drills such as
evacuation drills and emergency communication
exercises are very popular in Japan. The residents cansimulate their situation in a disaster and experiencecollaborative actions such as emergency food cooking
and shelter operation through disaster drills. Some studies
have pointed out that experiencing collaborative actions
can enhance a sense of capability in collaborative action
and promote greater collaborative efforts (Chawla &Cushing, 2007; Mori & Tasaki, 2019). Therefore,
experiencing collaborative actions through disaster drills
may be an effective way to promote mutual help after
disasters.
Disaster drills for DWM are not yet common, butthere are a few examples. One is a field exercise thatinvolves setting up and managing a TSS using a real site
and actual waste, conducted by Kakegawa City,
Kikukawa City and the sanitation facility associations ofboth cities (National Institute for Environmental Studies,2017). The residents who participate in this TSS exercise,gain an appreciation of how big an effort separating andtransporting large amounts of disaster wastes can be andthe importance of cooperation among residents. Morestudy is needed to find effective methods of
implementing disaster drills for DWM.
5.2 Imagination Games and Map Exercises
Disaster Imagination Games (DIG) are a popular
type of simulation training in Japan. Participants break up
into small groups and make notes of the high-risk placeson their town’s map, then discuss with each other how to
avoid or reduce the risks (Cabinet Office, Japan). The
Meguro Method is another imagination tool for disaster
simulation developed by Dr. Kimiro Meguro (Meguro.
2001). People imagine and write down their specificsituation and behaviors in a disaster along a time axis.
This method is useful for gaining an understanding ofindividual risk. It also has the effect of increasing thecommunity’s or organization’s readiness for disasters if
participants share their results and discuss them with eachother (Abe & Meguro, 2005). Participatory disaster map
making is another popular method. This method includes
not only discussion at a table but also walking around thetown to find disaster risks and consider measures. Toyoda
and Kanegae (2012) studied the effect of participatory
disaster map making and found it to be effective atenhancing participants’ disaster awareness and promoting
action for disaster preparedness.
Studies and practices on these methods in thedisaster risk reduction field indicate that to imagine
individual concrete disaster situations and behaviors, on
top of general knowledge about disaster situations, is an
important way to enhance citizens’ disaster awareness.
Therefore, imagination drills simulating clearing andtransporting of disaster wastes may be effective. For
example, participants examine the possible disaster
wastes in their house on the assumption that they haveflood damage with inundation above the floor level.
Then, they imagine and discuss how they would clear andtransport their disaster waste to the planned TSS.
However, information and support by disaster experts isessential because it is difficult for residents without
disaster experience to form a concrete image of a disastersituation.
5.3 Risk Communication in Workshops
There are some studies on workshop methods
involving stakeholders. Nomura et al. (2013) conducted aworkshop targeting municipal government staff andresidents who had experienced the Noto Peninsula
earthquake in 2007 and found that by promoting risk
communication they could help residents gain anunderstanding the importance of self-help and mutual
help. Ushiyama et al. (2009) developed a workshop
method focusing on risk searches in the community andrevealed that it was effective at promoting people’s
disaster risk reduction actions. These examples focusedStrategy to Promote Residents’ Behaviors for Appropriate Disaster Waste Management
on risk communication. Workshop methods are effective
not only at promoting communication among
stakeholders but also at enhancing people’s understanding
and actions. Therefore, workshops for residents that
include discussion of local DWM risks and production of
items such as maps and action lists in cooperation withother participants would also be effective in the field of
DWM. If the residents can grasp concrete DWM risks
and share this understanding with other community
members through workshops, residents’ DWM actions
can be promoted.
5.4 Preparedness Planning with Stakeholders
To enhance people’s sense of responsibility fordisaster wastes, participatory planning provides a goodreference. Tamura et al. (2004) developed a planning
method for disaster risk reduction using workshops withstakeholders and revealed that their planning method
could enhance the participants’ proactive attitude towarddisaster management issues and foster a sense ofownership. Not only in the disaster risk reduction field
but also in the city planning field, public involvement inplanning is known as an effective way of enhancing
residents’ sense of ownership in activities (Kinoshita etal., 2018).

Many municipalities face the risk that they will not
be able to provide sufficient public services because ofdepopulation and staff shortages. Therefore, it becomes
more important for the residents to realize that they haveimportant roles in waste management, not leaving
everything to their municipalities. Many DWM plans
have been made without the residents’ involvement. It
would be helpful for residents to get involved indevelopment of DWM plans and discuss effective ways
to clear disaster waste with their municipality.
Additionally, residents can hold discussions in theircommunity about preparing operation manuals forcreating and managing a community TSS or support
scheme for people needing special assistance in clearing
and transporting disaster wastes. Such activities would bean effective way to enhance residents’ sense of ownershipwith DWM. Collaboration with the municipality andsupport by experts would be indispensable for the successof this kind of activities.

6. Strategies to Promote Residents’ DWM
Behaviors
Figure 2 gives an overview of the discussion in theprevious chapters. It depicts targets and residents’
Municipali�es

Residents
Appropriately collected and separated disaster waste

TargetResidents’behaviorA�er
a disaster

Beforea disasterCollect wastes from
community TSSInform the communityof the TSS status
Store wastes atcommunity TSS

Target271

Strongercommunity
network

Follow the disaster waste
separa�on / discharge rules
Clean up withmutual help

Predetermined rules
for community level
DWM

Conﬁrm the disaster waste
separa�on / discharge rules

Set up public TSS

Amend and announce disaster
waste separa�on / dischargerules

Acknowledgement ofdisaster waste separa�on/ discharge rules

Acknowledgement of risks andresponsibili�es associated with DWMResidents’behaviorPar�cipatory training and planningConﬁrma�on of the disaster
waste separa�on / discharge
rules

Predetermined rules
for disaster waste
separa�on / discharge/ collec�on

TSS: Temporary Storage Site, DWM: Disaster Waste Management

Fig. 2 Targets and related behaviors of residents and municipalities.

272

T. MORI and R. TAJIMA

behaviors and related actions by municipalities before
and after disasters. Based on examples of public
involvement in the disaster risk reduction field,
participatory methods involving the residents such asworkshops, DIG and creation of map and plans arehelpful in developing networks among stakeholders andpromoting residents’ understanding and behaviors.
Therefore, implementation of participatory methods forthe residents is desirable from the standpoint ofpromoting residents’ DWM behaviors. Below, we discuss
three aspects of strategies to implement participatory
methods for the residents: seizing existing opportunities,
identifying and collaborating with the groups driving
community’s DWM, and leveraging experience fromdisasters.
6.1 Seizing Existing Opportunities
One promising way to implement participatory
DWM methods is to incorporate some exercises involving
disaster wastes in existing disaster drill opportunities. For
this, it is important to hold discussions with related
stakeholders at an early stage.
It is also possible to use existing events forpromoting public awareness to promote waste
management as well. For example, Yokohama City has
exhibited posters and created games involving disaster
wastes at open days at the city’s incineration plant. These
open days are held once a year, and many residents living
around the incineration plant visit (National Institute forEnvironmental Studies, 2020). This example is not aparticipatory method. It is an effective way, however, tohelp the residents recognize disaster waste problems andserves as a first step toward implementation of aparticipatory method. If a festival or event related toenvironmental problems is held regularly, it is possible touse it as an opportunity for raising awareness about
disaster waste problems.
6.2 Identifying and Collaborating with Citizen Groups
Active in Disaster Risk Reduction or
Environmental Activities
The citizens groups active in disaster risk reduction
or waste management activities play an important role in
implementing participatory methods and promoting
residents’ DWM behaviors. Possible groups that could
energize communities’ DWM include neighborhood
associations and local NPOs working on environmental
problems or disaster risk reduction. If there are suchgroups in the community, collaboration with themunicipality and these groups would be an effective way
to implement participatory DWM methods. Mori et al.
(2020) tried a workshop on DWM for the residents of
Kawasaki City in collaboration with a local NPO (Fig. 3).
The participants of this workshop were residents engaged
in local activities to resolve environmental problems orfor disaster risk reduction. The aims of this workshop

Fig. 3 Residents’ workshop for DWM in Kawasaki City.

were not only to promote understanding of DWM but
also to foster key persons for promoting the community’s
DWM and developing a network. It was effective
especially for developing a network of participantsbecause most of the participants started planning originalactivities together after the workshop.
Municipalities should take the initiative toimplement participatory methods and promote residents’
DWM behaviors if there are no groups active in disasterrisk reduction or waste management activities. It may bedifficult to implement participatory methods from theoutset. Thus it would be helpful to start communicatingwith residents using existing opportunities such as
disaster drills or public events. Such communication
activities would be useful for finding future collaborators
or partners to implement participatory methods.
6.3 Leveraging Experience of Disasters
Once a municipality suffers from a natural disaster,
local politicians, governmental staff and residents havegreat interest after that in DWM. Experiencing a disasteris tough and unfortunate, but it is important not to missthe opportunity when everyone’s awareness of disaster
waste problems is high. Kurashiki City was severely
damaged by heavy rain in 2018 and many problems
related to disaster wastes occurred. After this disaster, theKurashiki City municipality conducted interview surveys
on disaster waste treatment with the afflicted people tolearn about problems they had had with DWM. Based on
this survey, they made a handbook for residents about
disaster waste disposal (Kurashiki City, 2020). Moreover,they plan to make a DWM instruction manual for earlyphases of disasters in collaboration with stakeholders.
Their work is a good example of promoting DWM for
residents by leveraging their experience in the disaster.

7. Conclusions
This paper has attempted to clarify appropriate
DWM behavior by citizens based on an understanding of
frequently experienced problems in past DWM cases. We
have also discussed methods and strategies of promotingStrategy to Promote Residents’ Behaviors for Appropriate Disaster Waste Management
these behaviors based on examples in the disaster risk
reduction field.
From our results, we could identify three factors key
to promoting citizens’ DWM behaviors for before andafter disasters. Firstly, preparedness for DWM bymunicipalities is indispensable. Secondly, encouraging
citizens’ understanding and motivation for DWM is
crucial to promoting their DWM behaviors. Thirdly,
community networks must be developed to promotemutual help before and after disasters.
Based on examples of public involvement in thedisaster risk reduction field, it is thought that participatory
training and planning involving citizens is effective at
promoting their understanding and encouraging DWM
behaviors. We have discussed three strategies for
implementing participatory methods for citizens: seizing
existing opportunities, identifying and collaborating withcitizens groups active in disaster risk reduction or waste
management activities, and leveraging experience indisasters.
DWM implementation using the proposed methods
and strategies in real communities and evaluation of theireffectiveness should be topics of future research.
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T. MORI and R. TAJIMA

Tomoko MORI
Tomoko Mori is a Research Associate at theCentre for Material Cycles and Waste
Management Research, National Institute forEnvironmental Studies, Japan. She received her
Ph.D. in Environmentology from the Universityof Tokyo in 2018. Her research field is education
for sustainable development to promote civic
action for the environment. She also engages in research on capacity
building among government officers and public involvement in disaster
waste management.

Ryo TAJIMA
Ryo Tajima is a senior researcher at the Centre forMaterial Cycles and Waste Management
Research, National Institute for Environmental
Studies, Japan. His main research field is policy
and planning for waste management underdisaster and normal circumstances. He is involved
in local and national efforts on drafting guidelines
and plans and designing training programs for disaster waste management.
(Received 25 September 2020, Accepted 21 December 2020)

275

Expanding the Scope of Environmental Emergency Research
towards Disaster-resilience and Environmental Sustainability
Toshimasa OHARA1*, Ryo TAJIMA2, Yujiro HIRANO1, Shigenori IINO1 and Seiji HAYASHI1
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima 963-7700, Japan
2
Centre for Material Cycles and Waste Management Research, National Institute for Environmental Studies,
16-2 Onogawa, Tsukuba-shi, Ibaraki, 305-8506, Japan*E-mail: tohara@nies.go.jp
1

Abstract
Climate change is already showing its influence in natural disasters and is likely to exacerbate natural
disasters in the future. Given these circumstances, the results of and experience in research on disasters andthe environment should facilitate the creation of a sustainable, disaster-resilient society. In this regard,
systematic consideration of the knowledge gained from environmental emergency research conducted since
the Great East Japan Earthquake would help establish a new research field based on disaster-related
environmental research of the past. Here, we propose a conceptual framework for expanding the scope ofenvironmental emergency research towards disaster-resilience and environmental sustainability.
Key words :	disaster resilience, environmental emergency research, Great East Japan Earthquake,natural disasters, sustainability

1. Introduction
In recent years the sustainability of society has been
impaired by environmental problems resulting fromsudden-onset natural disasters. The Great East Japan
Earthquake (GEJE) and the subsequent tsunami in 2011that caused the Fukushima Daichi nuclear power plant
accident (hereinafter the “nuclear accident”) is one such
example. The accident released radioactive substancesthat caused environmental pollution and necessitated theremoval of large amounts of radioactive waste andcontaminated soil. Since then, major natural disasters
have occurred almost every year with great impacts onsociety and the environment. The existing academic
discipline of environmental science is inadequate foraddressing these circumstances. A new knowledge
system for environmental issues is needed that unites
the accumulated environmental knowledge fromenvironmental emergency response, disaster recovery inthe disaster prevention/mitigation and sustainablecommunity development. A new approach is necessary in
the present age when knowledge from “normal times” isinadequate for dealing with the various large-scaledisasters, accidents and sudden-onset situations, such as
the global COVID-19 pandemic, that are occurring. Suchan approach can be developed further into “discontinuity
science” and “non-steady-state science” for seamlessly
linking normal times and states of emergency.
Global Environmental Research
24/2020: 275-278
printed in Japan

2. Disaster-related Environmental Researchin Japan
2.1 Summary of Disaster-related Environmental
Research in Japan before the GEJE
Up to now in Japan, environmental issues anddisasters have been addressed in research as separate
issues in terms of environmental protection measures anddisaster prevention/mitigation. There were two main
impetuses that led to the launching of a movement in theearly 2000s to address these issues simultaneously(National Institute for Environmental Studies, 2013). The
first was the 2nd Science and Technology Basic Plan
(Government of Japan, 2001), which stressed theimportance of research on river basin management inharmony with nature. Based on this plan, technologicaldevelopment was conducted to link disaster prevention/
mitigation measures with fundamental ecosystem services(such as hydrological cycle control) and regulatory
services (such as natural disaster control) in river basin
management. The second impetus, based on experiencesof the 1995 Great Hanshin-Awaji earthquake, 2004
Niigata Chuetsu earthquake and 2004 Sumatra-Andaman
earthquake, stemmed from the view that environmental
infrastructure and disaster prevention/mitigation projects,
both falling under the category of social infrastructuredevelopment, could be implemented more efficiently if
carried out together and, furthermore, could contribute to©2020 AIRES

276

T. OHARA et al.

local community development. For example, the Japan
Society of Civil Engineers (2006) report titled Technology
and System Coordination for Environmental and Disaster
Prevention lays out the impacts of natural disasterprevention measures on the environment, and conversely,
the impacts of environmental measures on disasterprevention. The report stresses the importance of
coordination between the two.
2.2 Disaster-related Environmental Research after
the GEJE
After the GEJE, a wide range of research on thedisaster was carried out by newly-formed organizations
including the Tohoku University International ResearchCenter of Disaster Science, Fukushima University
Institute of Environmental Radioactivity, Waseda
Resilience Research Institute, and Fukushima Prefectural
Centre for Environmental Creation, as well as existingorganizations such as the Kyoto University Disaster
Prevention Research Institute and Nagoya University
Disaster Mitigation Center, which had been conducting
disaster prevention and mitigation research prior to the
GEJE. However, while much research has been conductedfrom the perspectives of disaster prevention andresilience, few studies have addressed post-disasterreconstruction and community development. Also,
environmental perspectives have not always beenadequately addressed.
As the papers included in this special issue show,
many studies have addressed environmental emergency
aspects including post-disaster environmental impacts ofpollutants, environmental recovery and management ofdisaster wastes (e.g., Iijima et al., 2020). With regards tothe nuclear accident caused by the GEJE, a wide range of
research has been conducted and many results havealready been reported on the environmental impacts of
the large amounts of radioactive substances released into
the environment (Science Council of Japan, 2020). These
environmental emergency studies have made a major
contribution to reconstruction efforts and environmental
recovery in areas affected by the GEJE and nuclear
accident. In addition, research on sustainable community
development, including the establishment of sustainableregional environments, environmentally conscious
reconstruction and the creation of disaster resilient
regions is being carried out to some extent, as evident
from the papers included in this special issue (e.g., Hirano
et al., 2020; Otsuka et al., 2020; Gomi, 2020; Togawa etal., 2020). However, much less research is being
conducted in these areas on the environmental impacts,
environmental recovery and management of disaster
wastes. Given the progress toward reconstruction of thedisaster areas, further research is needed, especially in the
nuclear disaster-affected areas of Fukushima Prefecture.
Furthermore, systematic research is needed toaddress the series of processes for increasing theresilience and sustainability of society during normal
times, achieving the mitigation and appropriate
management of environmental impacts during disasters,
and accelerating the transition to sustainable society
through environmental recovery.

3. Conceptual Framework of the New Research
Field for Disaster-resilience and Environmental
Sustainability
3.1 Necessity and Aim of the New Concept
In recent years, frequent large-scale natural disasters
have occurred with substantial impacts on theenvironment. There is a high risk that the frequency ofdisasters will increase due to the accelerating impacts ofclimate change. The existing disciplines of environmental
science and environmental engineering are inadequate foraddressing these circumstances. A new body ofknowledge on environmental issues is needed for
integrating the knowledge gained on emergency responseand disaster reconstruction through disaster science.
However, as laid out in Chapter 2, while such researchhas been conducted to some extent, this research has notbeen organized within a theoretical framework. In
particular, up to now, the conceptual framework andmethodologies that seamlessly link different phases—from preparation for disaster resilience during normal
times to systematic emergency response immediately
following a disaster, rapid environmental recovery anddevelopment of a sustainable society in the medium tolong-term—have not been explored either in Japan orabroad.
Given the frequent occurrence of various disasters,
to have science contribute to the building of a sustainable,disaster-resilient society, a new research field needs to beestablished that can systematize the knowledge andexperience accumulated through disaster response andcontribute scientifically to the creation of a sustainable,disaster-resilient society. This research field would be
defined as a body of knowledge with the objective ofachieving sustainable societies in the long term by
improving the sustainability and resilience of societies
during normal times, achieving mitigation andappropriate management of environmental impacts during
disasters, and using disaster reconstruction to improvesustainability further.
Tajima and Osako (2020) organized environmental
impacts of disasters into four categories: (1) disturbancesof the natural environment, (2) generation of disaster
wastes, (3) release of toxic chemical substances and (4)environmental impacts associated with disaster recovery
and reconstruction. The purpose of the disaster-resilienceand environmental sustainability research field will be tosystematize the knowledge related to the mitigation andmanagement of the above environmental impacts
associated with disasters.

Towards disaster-resilience and environmental sustainability
3.2 Methodology
In addition to the aspects addressed by conventional
environmental emergency management such as the
mitigation and management of environmental impacts
associated with disasters, it is important for the newresearch field to aim to improve the sustainability anddisaster-resilience of societal systems during normal
times, use disaster reconstruction to increasesustainability, and promote cycling and interrelationships
between these three phases. Although there are various
arguments regarding whether it is possible to achieveboth sustainability and disaster resilience based on
existing general principles proposed for accomplishingthese two goals simultaneously (Redman, 2014; Elmqvist
et al., 2019), the methodology for the disaster-resilienceand environmental sustainability research field can belaid out by phase in a timeline from before to after
disasters as shown in Fig. 1.
(1) Simultaneous improvement of sustainability anddisaster resilience of social systems during normal times
Research to facilitate smooth implementation ofenvironmental impact management during disasters,
research on improving sustainability through disasterreconstruction, and research on environmental impact
mitigation during disasters.
(2) Environmental impact management during
disasters
Research on the overall management of the series ofprocesses from the identification of pollution sources andassessment of impacts to emergency measures to mitigate
impacts and treatment and disposal of pollution sources.
(3) Increasing sustainability by transforming social
structures through reconstruction
Projects and community development utilizing local

Sustainability

Ensuresustainability and resiliencein human activities

Mainstreaming
resilience andsustainability indecision making

environmental resources to ensure sustainability in therecovery and reconstruction process and research toresolve environmental, social and economic issues
existing in communities prior to disasters as part ofregional disaster reconstruction.
It will be important to establish the new research
field in collaboration with various stakeholders in disasterareas and to accumulate and systematize specialized
knowledge and experience through the lateral transfer of
research results to non-disaster areas.

4. Summary
There is a high risk of natural disasters increasing in
the future due to the accelerating impacts of climatechange. Given these circumstances, it is necessary tocontribute scientifically to the building of a sustainable,disaster-resilient society based on the results from andexperience gained through research on disasters and theenvironment. This report proposes a conceptual
framework for expanding the scope of environmental
emergency research towards disaster-resilience andenvironmental sustainability based on a review ofdomestic research trends. We plan to discuss andcontinuously revise our proposal with the input of many
stakeholders. We hope that this paper will stimulate lively
discussions towards the establishment of a new research
field for disaster-resilience and environmental
sustainability.
References
Elmqvist, T., Andersson, E., Frantzeskaki, N., McPhearson, T.,
Olsson, P., Gaffney, O., Takeuchi, K. and Folke, C. (2019)
Sustainability and resilience for transformation in the urban

Controlenvironmental
impacts of disasters

Mitigating impactsof released
Preparedness
hazardous
planning andsubstances
training

Pre-disasterrecoveryplanning

Ecosystembased disasterrisk reduction(Eco-DRR)

277

Transition tosustainable society
through recovery
Ensuring sustainability
in recovery
process

Environmentally
resilient society

Creation of newvalues from local
environment
Adaption to disturbancesof the natural environment

Business
as usualManagement and 3R
for disaster waste
time

Fig. 1 Outline of research areas for achieving a sustainable and resilient society.

278

T. OHARA et al.

century. Nature Sustainability, 2, 267–273.
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Toshimasa OHARA
Toshimasa Ohara is a fellow at the National
Institute for Environmental Studies. Immediately
after the Fukushima accident, his groupcommenced atmospheric simulations ofradionuclides and published the first results on
temporal and spatial variations in deposition rates
on a regional scale. Currently he leads theEnvironmental Emergency Research Program for contributing toenvironmental reconstruction and creation in Fukushima.

Ryo TAJIMA
Ryo Tajima is a senior researcher at the Centre forMaterial Cycles and Waste Management
Research, National Institute for Environmental
Studies, Japan. His main research field is policy
and planning for waste management underdisaster and normal circumstances. He is involved
in local and national efforts to draft guidelines
and plans and design training programs for disaster waste management.

Yujiro HIRANO
Yujiro Hirano is a senior researcher at theRegional Environmental Renovation Section of
the National Institute for Environmental Studies,
Fukushima Branch. He holds a doctorate ofengineering and has long been engaged in researchon low-carbon lifestyles remote sensing of urban
surfaces, urban heat island countermeasures andurban energy system. His recent research interests are in modeling andanalysis of regional energy use for environmental renovation plans.

Shigenori IINO
Shigenori Iino is a researcher at the RadiologicalContaminated Off-site waste Management
Section of the National Institute forEnvironmental Studies, Fukushima branch. He
holds a Doctor of Engineering degree, and his
recent research interests lie in formation of aregional circular and ecological sphere centeredon waste management in Fukushima.

Seiji HAYASHI
Seiji Hayashi is a research group manager at the
Fukushima branch of the National Institute forEnvironmental Studies. He is serving as project
leader for research on the behavior of radioactive
substances in multimedia environments. His
energetic research activities are contributing to
the environmental recovery of Fukushima
Prefecture and its surrounding region.
(Received 20 December 2020, Accepted 28 December 2020)

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Global Environmental Change
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