MAG38-01

Room:301B

Time:May 26 09:00-09:15

Hourly atmospheric radionuclides after the Fukushima accident by analyzing filter-tapesof SPM monitoring sites
TSURUTA, Haruo1∗ ; OURA, Yasuji2 ; EBIHARA, Mitsuru2 ; OHARA, Toshimasa3 ; NAKAJIMA, Teruyuki1
1

Atomsphere and Ocean Research Institute, the University of Tokyo, Japan, 2 Tokyo Metropolitan University, JAPAN, 3 National
Institute for Environmental Studies, JAPANThe current estimates for the internal radiation doses from inhalation by the Fukushima Daiichi Nuclear Power Station(FD1NPS) accident on March 11, 2011 have large uncertainty, because no observed data has been found of continuous monitoring of radioactive materials in the atmosphere in the Fukushima prefecture (FP) just after the accident. And most of theatmospheric transport models have simulated the surface deposition of radionuclides released by FD1NPS accident, to comparewith many observed deposition datasets in eastern Japan. To retrieve the atmospheric transport of radioactive materials released
from the FD1NPS, we collected the used filter tapes installed in Suspended Particulate Matter (SPM) monitors with beta-ray
attenuation method operated by local governments in the air pollution monitoring network of eastern Japan. Then, we measured
hourly Cs-134 and Cs-137 concentrations in SPM at 40 monitoring sites in the FP and Tokyo Metropolitan Area (TMA) locatedmore than 170 km southwest of the FD1NPS, after more than one year. The period for measurements was during March 12-23,
2011, when atmospheric, aquatic, and terrestrial environments were seriously suffered in most of eastern Japan by a large amountof radioactive materials released from the FD1NPS. In this paper, a comprehensive study will be reported for the first time on a
spatio-temporal variation of atmospheric Cs-137 concentrations in the FP and the TMA. Major results are as follows; (1) Nine
major plumes with Cs-137 concentrations higher than 10 Bq m−3 were found, of which 5 and 4 plumes were transported to the
FP and TMA, respectively. (2) High radioactive materials from the FD1NPS were transported five times (March 12-13, 15, 18,
19, and 20-21) to the northern part of Hamadori located in the east coast of the FP, and which was little known until this study.
Hence, the time-integrated atmospheric Cs-137 concentrations were highest among the FP and TMA during the period. (3) Twoplumes were transported to Nakadori, located in the central part of the FP, on March 15, and March 20-21. The polluted air
masses with high Cs-137 were observed in Nakadori for more than half a day from the evening of March 20 to the morning ofMarch 21, and which was not recognized until now. (4) The radiation dose rate measured at some monitoring posts in Nakadori
did not increase even when the plume (March 20) passed by. It was already too high to detect a new plume, due to the groundshine caused by the deposition of a large amount of radionuclides on the grounds by precipitation. (5) Two plumes transported
to the TMA on March 16 and March 20 were newly found, in addition to the well-known two major plumes on March 15 andMarch 21, 2011. (6) A local area of relatively high Cs-137 deposition density in the TMA by precipitation on the morning ofMarch 21, 2011, was consistent with an area where the time-integrated atmospheric Cs-137 concentrations were also high dueto the transport of a plume on the morning of March 21, 2011. In the Fukushima prefecture, however, the correlation was not
so clear. We thank to all the local governments in eastern Japan who kindly allowed us to measure radionuclides in the SPM
collected on the used filter-tapes in the SPM monitors. We also thank Prof. S. Wakamatsu (Ehime University), and many otherpersons who cooperated to store the filter tapes. We sincerely acknowledge Y. Katsumura and M. Ishimoto in The Universityof Tokyo for supporting the measurements. Part of this study was financially supported by the Ministry of Education, Culture,
Sports, Science and Technology, and the Ministry of Environment, Japan.
Keywords: Atmospheric Cs-137, FD1NPS, Spatio-temporal variation, SPM

1/1

MAG38-02

Room:301B

Time:May 26 09:15-09:30

A new insight into the deposition mechanism of airborne radionuclides from the Fukushima
accident
KANEYASU, Naoki1∗ ; HOSOSHIMA, Mutsuo2
1

National Institute of Advance Industrial Science and Technology, 2 Mibu High School

Introduction
On the radiocesium emitted from Fukushima Daiichi Power Plant (FDNPP) and transported to Eastern Japan, airborne (MEXT,
2012) and car-borne (Tanigaki, 2014) surveys have been conducted to map the horizontal distribution of contaminated area.
In the mapped 134,137 Cs distribution by the airborne surveys, the contamination in the Nikko Mountain area, located 120 km
north of Tokyo, is prominent. From the previously reported results of transport/dispersion/deposition modeling studies, this radioactive contamination appeared to have occurred in the transport event in March 15, 2011.
We thus analyzed the formation mechanism in this area by the on-hoot measurements of ambient gamma dose rate (GDR) in
air at multiple mountains conducted from 2012 to 2014.
Instrumentation and Measurements
Altitudinal distributions of GDR in air were measured in the Nikko Mountainous area at the northern rim of the Kanto Plain,
Japan, using a portable CsI (TI) scintillation gamma-ray detector (Gamma RAE II R, RAE Systems) carried along the mountain
trails. The horizontal position of the observer was pinpointed by a global positioning system.
Results and Discussion
In the Nikko Mountain area, the altitudinal distribution of ambient GDR exhibited maxima at about 900-2,000 m above sea
level (ASL).
Meteorological sounding data indicated that the corresponding altitudes were within the cloud layer. A visual-range monitor
deployed in an unmanned weather station at 1,292 m ASL also recorded low visibility on the afternoon of March 15. In thegridded data products of Japan Meteorological Agency Meso-scale Model, cloud over (%) of low struts started to cover over
the Nikko area at about 1500 JST, as seen in Figure 1. Radar-AMeDAS (Automated Meteorological Data Acquisition System)
analysis shows this area was not affected by precipitation until 2300 Japan Standard Time on March 15, 2011. The mechanism
anticipated to have caused the concentrated deposition in a particular altitudinal range was cloud deposition (or fog/occult deposition). Atmospheric aerosol particles often act as cloud condensation nuclei (CCN) so that cloud (fog) droplets form on them.
With cloud/fog deposition, these droplets, and with them the original aerosol particles are intercepted by vegetation and depositedon the ground.
Airborne radiocesium, one of the major gamma-ray emitting radionuclides deposited onto the land and marine environments
after the FDNPP accident, exists in the aerosol phase. Kaneyasu et al.(2012) reported that sulfate aerosols are a potential carrierof airborne radiocesium. Sulfate aerosol is one of the representative species acting as CCN. Therefore, cloud or fog droplets
activated from CCN, including radiocesium and other gamma-ray emitting radionuclides, have greater deposition velocities thanthat of sulfate aerosol itself. This leads to the transfer of radionuclides from the atmosphere to the forest and ground surface being far more effective. Recently, Katata et al.(2014) incorporated a simple fog deposition scheme into their transport/disposition
model and reproduced the deposition pattern in the mountain area qualitatively.
Conclusion
The proposed mechanism of the altitude-dependent radioactive contamination in Nikko Mountain area was the cloud (fog/occult)deposition process of the radionuclides contained in aerosols acting as cloud condensation nuclei.
Acknowledgement
The figure of cloud cover was produced by Dr. Y. Takane of AIST, Japan.
References
Kaneyasu, N. et al. (2012) Environ. Sci. Technol. , 46 (11), 5720-5726
Katata, G., et al. (2014) Atmos. Chem. Phys. Discuss. , 14 (10), 14725-14832
MEXT (2012) http://radioactivity.nsr.go.jp/ja/contents/7000/6289/24/203 0928.pdf
Tanigaki, M. (2014), In Radiation Monitoring and Dose Estimation of the Fukushima Nuclear Accident; Takahashi, S., Eds.;
Springer: XV; pp.67-77
1/2

MAG38-02

Room:301B

Time:May 26 09:15-09:30

Keywords: radionuclides, ambient gamma dose rate in air, deposition mechanism, altitudinal distribution, cloud deposition

2/2

MAG38-03

Room:301B

Time:May 26 09:30-09:45

Seasonal variation of the atmospheric 137Cs & 134Cs - Concentration and aerosol sizetransporting radioactive Cs ?
KINASE, Takeshi1∗ ; KITA, Kazuyuki2 ; TANAKA, Misako1 ; DEMIZU, Hiroyuki3 ; IGARASHI, Yasuhito4 ;ADACHI, Kouji4 ; MIKAMI, Masao4 ; YAMADA, Keita5 ; TOYODA, Sakae5 ; YOSHIDA, Naohiro5 ;SHINOHARA, Atushi6 ; NINOMIYA, Kazuhiko6 ; OKOUCHI, Hiroshi7 ; ISHIZUKA, Masahide8 ;KAWASHIMA, Hiroto9 ; NAKAI, Izumi10 ; ABE, Yoshinari10 ; ONDA, Yuichi11
1

Graduate school of science and engineering of Ibaraki Univ., 2 Collage of science, Ibaraki Univ., 3 Collage of engineering, Ibaraki
Univ., 4 MeteorologicalResearchInstitute, 5 Tokyo Institute of Tech., 6 Osaka Univ., 7 Waseda Univ., 8 Kagawa Univ., 9 Akita Pref.
Univ., 10 Tokyo Science Univ., 11 TsukubaUniv.
By the FDNPP accident on March 2011, large amounts of radioactive cesium (radiocesium) were released to the atmosphere.
Total release amount of 137 Cs is estimated to 1.3×1016 (Bq) by Chino et al.(2012) and were deposited on the ground, vegetationand ocean. A half-life of 137 Cs and 134 Cs is 30.2 and 20.6 year respectively , and for the radioactive cesium which was diffusedand deposites to repeat resuspention. The influence on a polluted area is expected for an extended period and also feared of risk
to healthBut the physical and chemical form of radiocesium have a lot of undefined , the resuspention system for now and the seasonalvariation of the concentration and aerosol size transporting radioactive Cs is not understood enough. The purpose of our researchis to understand the seasonal variation of the concentration and aerosol size transporting radioactive Cs with a long term monitoring atmospheric radiocesium.
We observed at 4 sites , Site-A(Kawatmata ceder forest) , Site-B(Tsushima school play ground) , Site-C(Tsushima broad leaf
forest) , Site-D(Tsushima decontaminated playground). Site-A and Site-D was decontaminated in August to December 2012 andDecember 2011 to February 2012 respectively , therse sites are lower spatial dose. But Site-B and Site-C is not decontaminated,
spatial dose is higher. This report used the date from December 2012 for research resuspention of radiocesium.
Sampling of techniques in Site-A and Site-C was mainly size distribution by impactor , sometimes only total concentration by
High volume air sampler(HV). In Site-B observed size distribution and total concentration(short time cycle) at the same time.In
site-D observed only total concentration.
Seasonal variation of total radiocesium have the same trend in all sites, lower concentration in winter and high concentrationin summer. Thus in summer, there is 2 peaks , high concentration in May to July and August to September.
There is the seasonal variation of size distribution of transpoating radiocesium. Particles of 10.3˜0.69µm is mainly in summer
and august , particles on backup filter(0.39µm and bounced larger particles) was high in winter and spring. This result suggests
the change of process for resuspention in each seasons.
The spatial dose between site-A and site-B have a big difference , but the distance is very close, only about 0.75km departed.
From this difference , we can expect the scale of broadness. Fraction(site-B divided site-D) is 1.33 in summer and august and2.16 in winter and spring respectively. This result indicates the transpoting scale is larger at the season of high concentration andlarge particles are dominant (in summer and august). Oppositely at the seasons of low concentration and large particles are notdominat (in winter and spring) , transporting scale is very local .

Keywords: radioactivity, cesium, atomosphere, resuspention, FDNPP, ISET-R

1/1

MAG38-04

Room:301B

Time:May 26 09:45-10:00

Identification of aerosol contributing atmosperic re-suspension of radiocesium
KITA, Kazuyuki1∗ ; TAMURA, Sho1 ; TANAKA, Misako1 ; KINO, Himiko1 ; KINASE, Takeshi1 ;DEMIZU, Hiroyuki2 ; ADACHI, Kouji3 ; ZAIZEN, Yuji3 ; IGARASHI, Yasuhito3 ; TOYODA, Sakae4 ;YAMADA, Keita4 ; YOSHIDA, Naohiro4 ; NINOMIYA, Kazuhiko5 ; ABE, Yoshinari6 ; NAKAI, Izumi6 ;OKOCHI, Hiroshi7 ; ISHIZUKA, Masahide9 ; ONDA, Yuichi8
1

Ibaraki Univ., 2 Ibaraki Univ., 3 Meteorological Research Institute, 4 Tokyo Institute of Technology, 5 Osaka Univ., 6 Tokyo Univ.
of Science, 7 Waseda Univ., 8 Kagawa Univ., 9 Tsukuba Univ.
Coming soon
Keywords: radiocesium, atmospheric resuspension, aerosol

1/1

MAG38-05

Room:301B

Time:May 26 10:00-10:15

Impact of the regional climate on the transport of radioactive materials
YOSHIKANE, Takao1∗ ; YOSHIMURA, Kei1 ; SAYA, Akane1
1

Atmosphere and Ocean Research Institute, University of Tokyo

Radioactive materials, which are released from Fukushima-Daiichi unclear power plants (FDUPP) in March 2011, is transported to Kanto and Tohoku areas. From many previous studies, the transport process of the radioactive materials has beenclear. However the relation between the regional climate and transport process still is not sufficient to reveal. We investigated themechanism of the transport to Kanto area using a regional model considering the regional climate in March. From the results, it
is found that the radioactive materials, which are observed on 21th March 2011, is transported by the northeasterly in the lower
layer from FDUPP to Kanto area. Generally, the northeasterly often forms corresponding to the low pressure system and thestationary front, which often form along the southern coastal area of Kanto area and causes the warm front with southerly warm
wind. It is found that the cold air of the northeasterly is formed by cold air surges accompany with winter monsoon and moves tosouth corresponding to the temperature gradient in meridional direction near the surface. Therefore the northeasterly also has theproperty of gravity current. The wind field could be greatly influenced by the local temperature distribution because the cold air
surges are often found in the off-shore of the Fukushima Prefecture. We will report the detailed transport process by numericalexperiences applying the past events.
Keywords: Radioactive materials, Regional climate, Regional model

1/1

MAG38-06

Room:301B

Time:May 26 10:15-10:30

Distribution of radiocesium fallout on forest area throughout Japan after decades fromformer atmospheric nuclear tests
MIURA, Satoru1∗ ; AOYAMA, Michio2 ; ITO, Eriko3 ; SHICHI, Koji3 ; TAKATA, Daisuke1 ;MASUMORI, Masaya1 ; SEKIYA, Nobuhito1 ; KOBAYASHI, Natsuko I.1 ; TAKANO, Naoto4 ; KANEKO, Shinji3 ;TANOI, Keitaro1 ; NAKANISHI, Tomoko M.1
1

The University of Tokyo, 2 Fukushima University, 3 Forestry and Forest Products Res. Inst., 4 Scarabs Corporation

To predict the movement of radioactive contamination caused by Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident is
a strong concern, especially for the forest and forestry sector. To learn from the precedent, we investigated soil samples collected
systematically from 316 forest sites in Japan just before the accident, which retain the global fallout 137 Cs (137 Cs-GFO) from thenuclear test bomb during the 1950s and 60s. We measured the radioactivity of 137 Cs-GFO in three layers of soil samples (0-5,5-15 and 15-30 cm in depth) at each site. We divided 316 sampling sites into 10 groups separated by one longitudinal line andfour transversal lines on the islands of Japan, then analyzed rainfall and geomorphological effects on 137 Cs-GFO inventories. In
addition to the analysis of 137 Cs-GFO above, we examined the behavior of 137 Cs discharged from FDNPP (137 Cs-Fk) within thewhole trees to study a possibility of biological effect on 137 Cs transport to soils from trees. We measured the radioactivity of137
Cs-Fk of above- and belowground tree parts of three 26 year-old Quercus serrata and associated soils at a contaminated areain Fukushima in April, 2014.
We estimated an average of 137 Cs-GFO inventories of forest soils in Japan to be 1.7 ± 1.4 kBq/m2 as of 2008. 137 Cs-GFO
inventories varied largely from 0-7.9 kBq/m2 around the country. We found high accumulation of 137 Cs-GFO in the northwestern part facing to the Sea of Japan. We detected significant rainfall effects on the high accumulation due to winter rainfall.
The vertical distribution of 137 Cs-GFO showed that 44% of 137 Cs-GFO remained within the 5 cm of soil from the surface
whereas the rest of 56% was found in the layer of 5-30 cm in depth, indicating that considerable downward migration of 137 CsGFO occurred during these fifty years in forest soils in Japan. However, multiple linear regression analysis by geomorphologicalfactors related to soil erosion, such as inclination angle or catchment area calculated from Digital Elevation Model, showedalmost no significant effects on the distribution of 137 Cs-GFO.
The radioactivity of 137 Cs-Fk concentrations of fine roots collected from the 0-10 cm layer were 1600-2400 Bq/kg, whichwere comparable to those of one-year old branches (1400-2200 Bq/kg). The radioactivity of the fine roots was 7 times higher
than that found in the soil of 50-100 cm layer (220-350 Bq/kg). This difference the radioactivity of the fine roots among the soil
layers was remarkably small when compared with the 1000 times or more difference of radioactivity of soils in the same layers(one outlier sample in the 40-60 cm layer was excluded). The findings indicated that 137 Cs-Fk circulated through the whole tree
within three years after the accident. Considering root litter fall inside the soils we estimated that contaminated 137 Cs on trees at
the above ground part could be transported to soils through roots.
We clarified that 137 Cs-GFO has been held at deposited site and migrated downward gradually in soil. There are two possible
major driving forces to be considered to explain the downward migration of 137 Cs-GFO. One is the migration of 137 Cs associatedwith vertical water movement and the other one is the transport of 137 Cs by root litter fall or root exudate. Further research isneeded to analyze these processes to obtain reliable prediction of future distribution of 137 Cs-Fk.
Keywords: radioactive contamination, Fukushima Dai-ichi Nuclear Power Plant, 137Cs, forest soil, trees, secondary migration

1/1

MAG38-07

Room:301B

Time:May 26 10:30-10:45

Three-year monitoring study of radiocesium transfer and dose rate in forest environments
after the FDNPP accident
KATO, Hiroaki1∗ ; ONDA, Yuichi1 ; LOFFREDO, Nicolas1 ; KAWAMORI, Ayumi1 ; HISADOME, Keigo2
1

Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 2 Asia Air Survey Co., LTD.

We investigated the transfer of canopy-intercepted radiocesium to the forest floor during 3 years following the Fukushima
Daiichi nuclear power plant (NPP) accident. The cesium-137 (Cs-137) contents of throughfall, stemflow, and litterfall weremonitored in two coniferous stands (plantation of Japanese cedar) and a deciduous broad-leaved forest stand (Japanese oak with
red pine). We also measured an ambient dose rate at different height in the forest by using a survey meter (TCS-172B, HitachiAloka Medical, LTD.) and a portable Ge gamma-ray detector (Detective-DX-100T, Ortec, Ametek, Inc.).
Total Cs-137 deposition flux from the canopy to forest floor for the mature cedar, young cedar, and the mixed broad-leaved
stands were 157 kBq/m2 , 167 kBq/m2 , and 54 kBq/m2 , respectively. These values correspond to 36%, 39% and 12% of total
atmospheric input after the accident. The ambient dose rate in forest exhibited height dependency and its vertical distribution
varied by forest type and stand age. The ambient dose rate showed an exponential decrease with time for all the forest sites,
however the decreasing trend slightly differed among three forest sites. In order to clarify the difference of decreasing trendof ambient dose rate, we investigated the relationship between radiocesium transfer flux from the canopy to forest floor andreduction of ambient dose rate at 1-m height above forest floor. We also evaluated effects of forest decontamination on ambient
dose rate in coniferous stands.

Keywords: Fukushima Dai-ichi Nuclear Power Plant, Radiocesium, Forest environments, Transfer, Ambient dose rate

1/1

MAG38-08

Room:301B

Time:May 26 11:00-11:15

Analysis of each radionuclides discharged by the Fukushima Daiichi Nuclear Power Plant
measured by airborne surveys
NISHIZAWA, Yukiyasu1∗ ; YOSHIDA, Mami1 ; SANADA, Yukihisa1 ; TORII, Tatsuo1
1

Japan Atomic Energy Agency

Many radioactive substances were released by the Fukushima Daiichi nuclear power plant accident occurred on March 11,2011 in the atmosphere. A lot of short half-life nuclides which are 131 I, 132 Te (132 I) and 133 I, etc., in addition to longer halflived nuclides such as 134 Cs and 137 Cs. The estimated release amount of these nuclides from the reactor 1st to 3rd unit isreported, but it’s found to be quite different in the short half-lived nuclides by the reactor units. Because the radioactivity ratioof 134 Cs and 137 Cs was slight different between the reactor units, it can be considered that the valuable source is obtained by themeasurement of 134 Cs/137 Cs ratio in the environment around the Fukushima Daiichi nuclear power station at the present stage
when the nuclides with short half-lives had already decayed. We have measured high-resolution gamma-ray spectrum using an
unmanned helicopter equipped with LaBr3 (Ce) detector in a 3-km range from the power station which was near to the releasesource of the radioactive cesium. Because the LaBr3 (Ce) detector has high resolution of gamma rays, the discrimination of many
nuclides is possible. In addition, there is extremely much number of the data provided by the distribution measurement with theunmanned helicopter. Because a new map was illustrated by the analysis of the 134 Cs/137 Cs ratio, we report the outline.
Keywords: unmanned helicopter monitoring, radionuclide distribution

1/1

MAG38-09

Room:301B

Time:May 26 11:15-11:30

Radiocesium transfer by water and sediment discharge through river networks after the
Fukushima NPP accident
ONDA, Yuichi1∗ ; TANIGUCHI, Keisuke1 ; KATO, Hiroaki1 ; IWAGAMI, Sho1 ; WAKIYAMA, Yoshifumi1 ;YOSHIMURA, Kazuya1 ; TSUJIMURA, Maki2 ; SAKAGUCHI, Aya1 ; YAMAMOTO, Masayoshi3
1

Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 2 Faculty of Life and Environmental Sciences, University of Tsukuba, 3 Institute of Nature and Environmental Technology, Kanazawa University
Our research team has been monitoring the environmental consequences of radioactive contamination just after the Fukushima
Daiichi NPP accident in Yamakiya-district, Kawamata town, Fukushima prefecture. Research items are listed below.
1. Radiocesium wash-off from the runoff-erosion plot under different land use.
2. Measurement of radiocesium transfer in forest environment by hydrological pathways such as throughfall and overlandflow
on hillslope.
3. Monitoring of dissolved and particulate radiocesium concentration in river water, and stream water from the forested catchment.
4. Measurement of radiocesium content in drain water and suspended sediment from paddy field.
5. Continuous monitoring of suspended sediment and river water for 30 locations in abukuma catchments and coastal catchments.
Our monitoring result demonstrated that the Cs-137 concentration in eroded sediment from the runoff-erosion plot has been
almost constant for the past 3 years, however the Cs-137 concentration of suspended sediment from the forested catchment
showed slight decrease through time. On the other hand, the suspended sediment from paddy field and those in river water fromlarge catchments exhibited rapid decrease in Cs-137 concentration with time. The decreasing trend of Cs-137 concentration
were fitted by the two-component exponential model, differences in decreasing rate of the model were compared and discussed
among various land uses and catchment scales . The declining trend such analysis can provide important insights into the future
prediction of the radiocesium wash-off from catchments with different land uses.

Keywords: Fukushima Dai-ichi Nuclear Power Plant accident, Radiocesium, River system, water and sediment discharge, transfer

1/1

MAG38-10

Room:301B

Time:May 26 11:30-11:45

Radioactive Cs-137 discharge by Dissolved water, Suspended Sediment and Coarse Organic Matter from Headwater Catchment
IWAGAMI, Sho1∗ ; ONDA, Yuichi1 ; TSUJIMURA, Maki2 ; KONUMA, Ryouhei3 ; SAKAKIBARA, Koichi3
1

Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 2 Faculty of Life and Environmental Sciences, University of Tsukuba, 3 Graduate School of Life and Environmental Science, Tsukuba University
The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, following the earthquake and tsunami disaster on March 11,
2011, resulted in a substantial release of radionuclides to the environment. Most of the area in which the radionuclides were
deposited was forested area. Therefore it is very important to quantify the discharge of radionuclide from the forested catchment
in headwater region which will be the input of the radionuclide to downstream various land use.
The concentration of dissolved 137 Cs in groundwater and stream water in the headwater catchments in Yamakiya district,located ˜35 km north west of Fukushima Dai-ichi Nuclear Power Plant (FDNPP), was monitored from June 2011 to December
2014. Also 137 Cs concentration in suspended sediments and coarse organic matter such as leafs and blanches were monitored.
Groundwater and stream water were sampled at intervals of approximately 2 months at each site. Intensive sampling was also
conducted during rainstorm events. Compared with previous data from the Chernobyl NPP accident, the concentration of dissolved 137 Cs in stream water was low. In the Iboishi-yama catchment, a trend was observed for the concentration of dissolved
137
Cs in stream water to decline, which could be divided into two phases by October 2011 (after 200 days after the accident).
The highest 137 Cs concentration recorded at Iboishi-yama was 1.2 Bq/L at the peak on August 6, 2011, which then declined
to 0.021-0.049 Bq/L during 2013 (in stream water under normal water-flow conditions). During the rainfall events, the concentration of dissolved 137 Cs in stream water increased temporarily. The concentration of dissolved 137 Cs in groundwater at a
depth of 30 m at Iboishi-yama displayed a decreasing trend from 2011 to 2013, with a range from 0.039 Bq/L to 0.0025 Bq/L.
The effective half-lives of stream water in the initial fast flush and secondary phases were 0.1-0.2 y and 1.0-2.2 y, respectively,in the three catchments. The trend for the concentration of dissolved 137 Cs to decline in groundwater and stream water was
similar throughout 2012-2013, and the concentrations recorded in deeper groundwater were closer to those in stream water. The
declining trend of dissolved 137 Cs concentrations in stream water was similar to that of the loss of canopy 137 Cs by throughfall,as shown in other reports of forest sites in the Yamakiya district.
The 137 Cs concentration in suspended sediments showed 10000-45000 Bq/kg and 137 Cs concentration in organic matter
showed 1000-12000 Bq/kg. The 137 Cs concentration in organic matter showed declining trend through the observation period
and the trend was similar to that of dissolved 137 Cs concentration in stream water. In contrast 137 Cs concentration in suspended
sediment did not showed a clear declining trend in every catchment (before the decontamination works). After the decontamination works in Iboishi-yama catchment, the 137 Cs concentration in suspended sediment declined largely to 200-300 Bq/kg. The
137
Cs concentration in organic matter and dissolved 137 Cs concentration in stream water did not declined largely.
In conjunction with discharge data and turbidity data, 137 Cs discharge flux were calculated for three components (dissolved
water, organic matter, suspended sediments). As a result, it is shown that more than 98% of the 137 Cs discharge was due to thedischarge by suspended sediments. It is also suggested that dissolved 137 Cs concentration have relationship with 137 Cs concentration of organic matter and so it is still important to clarify the process of 137 Cs migration through dissolved water and organic
matter.

Keywords: Cs-137, Dissolved water, Suspended sediment, Coarse organic matter, Headwater catchment, Discharge

1/1MAG38-11

Room:301B

Time:May 26 11:45-12:00

Transport of radiocesium in the Niida River, Fukuhsima Prefecture in 2011-2014
NAGAO, Seiya1∗ ; TADO, Shu1 ; UEMURA, Teruaki1 ; KANAMORI, Masaki1 ; KIRISHIMA, Akira2 ;MIYATA, Yoshiki1 ; OCHIAI, Shinya1 ; YAMAMOTO, Masayoshi1
1Kanazawa University, 2 Tohoku University

Surface deposition of 134 Cs and 137 Cs reveals considerable external radioactivity above 3000k Bq/m2 in a zone extending
northwest from the NPP after the Fukushima Daiichi Nuclear Power Plant (NPP) accident. Therefore, it is important to elucidate
the short-term to long-term impacts of the accident on ecosystems of river watershed environments. This study investigated thetransport of 134 Cs and 137 Cs in a small river, Niida River running through IIdate Viledge, in Fukushima Prefecture, Japan atnormal and high flow conditions during 2011-2014.
Field experiments were conducted at a fixed station (Kinouchi bridge) in the lower Niida River during the period of May
2011-December 2014. The 20 L of surface river water samples were collected at the station using buckets. The radioactivity of134
Cs and 137 Cs in the river waters before and after the filtration was measured with gamma-ray spectrometry using ammonium
molybdophosphate (AMP)/Cs compound method.
Total radioactivity of 137 Cs (dissolved and particulate phases) in the river waters ranged from 0.11 to 4.18 Bq/L during May
2011-December 2014. Highest value was found in May 2011. Total 137 Cs radioactivity indicates the decreasing trend withincreasing time at normal flow condition. However the higher radioactivity was observed after rain events. The 137 Cs radioactivity increased by 1.83 Bq/L after the heavy rain event by Typhoon Guchol in June 2012, and 1.68 Bq/L by Typhoon Jelawat in
October 2012.
Percentage of 137 Cs associated with riverine suspended solids was 47-48% at normal flow condition in July and September
2011, but after December 2011 ranged from 75 to 93% at normal flow condition and 86-91% at high flow condition due to rain
events. The radioactivity of particulate phase of 137 Cs ranged from 20 to 42 Bq/g-riverine suspended solids. Rain events aremainly contributed to the transport of radiocesium in the Niida River.

Keywords: Cs-134, Cs-137, rain event, riverine suspended solids

1/1

MAG38-12

Room:301B

Time:May 26 12:00-12:15

Radiocesium discharge from Niidagawa river basin after the accident of Fukushima Daiichi Nuclear Power Plant
WAKIYAMA, Yoshifumi1∗ ; ONDA, Yuichi1 ; GOLOSOV, Valentin2 ; KONOPLEV, Alexei3 ; TAKASE, Tsugiko2 ;NANBA, Kenji3
1

Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 2 Department of Geography, Moscow
State University, 3 Institute of Environmental Radioactivity Fukushima University

Redistribution of radiocesium through a river system poses potential risks on residents within the river basin. Niidagawa river
basin on north eastern part of Fukushima prefecture is indeed a case in point. The river basin includes highly contaminated area
on its upstream part and the river goes through residential area of its downstream. Quantitative evaluation of radiocesium redistribution associated with discharged sediment is required for mitigating radiological risk on residents and ocean environment.
Previous studies on the environmental monitoring of various contaminants, as well as radiocesium, suggested that large portion ofdischarge of such contaminants should occur during intensive rainfall events. This study aims to quantify radiocesium discharge
within the Niidagawa River Basin and to reveal its discharge processes. For quantifying radiocesium discharge, we installed setsof time-integrative suspended sediment sampler, turbidity sensor and water level sensor on three points in summer 2014. The
points are named as Sakegawa-bashi (N37o 38’33”, E141o 00’20”), Notegami-kita (N37o 39’16”, E140o 47’47”) and Warabi-daira(N37o 36’49”, E140o 48’04”) and specific initial Cs-137 deposition are 752, 810, 1462 kBq/m2 , respectively. We have collectedsuspended sediments trapped in the samplers approximately every 2 months and served them for radiocesium measurements with
HPGe gamma detectors in laboratory. Radiocesium discharge (Bq/hour) were calculated by multiplying radiocesium concentrations of suspended sediment (Bq/kg) with time-series data of turbidity (kg/m3 ) and water discharge (m3 /hour). Mean Cs-137
concentration of suspended sediment (n = 3) at Sakegawa-bashi, Notegami-kita and Warabi-daira were 13, 14 and 31 kBq/kg, respectively. Those concentrations appeared to agree with initial Cs-137 deposition for each point basically. No common temporal
trend of Cs-137 concentration was found among Cs-137 concentrations of these three points. Estimated total Cs-137 discharges
at these points were in magnitude of 1011 Bq. Estimated Cs-137 wash-off rates (%), calculated by dividing specific Cs-137
discharge (Bq/m2 ) with initial Cs-137 inventory, were in magnitude of 0.1 %. For evaluating Cs-137 discharge during intensive
rainfall events, we focused on three large rainfall events during 8-11th August (59 mm), 5-8th October (109 mm) and 13-16th
October (69.5 mm). Ratios of Cs-137 discharges during these events to total Cs-137 discharge through all observation period
approximately were approximately 0.3 at Sakegawa-bashi and approximately 0.7 at both of Notegami-kita and Warabi-daira.
Discharge of Cs-137 from smaller catchment area appeared to be more vulnerable to intensive rainfall events.
Keywords: Radiocesiumu, River, Fukushima Dai-ichi Nuclear Power Plant, Suspended sediment

1/1

MAG38-13

Room:301B

Time:May 26 12:15-12:30

Investigation of the River Particulate Matters in Fukushima and Chernobyl Related to Cesium Behavior
SUGA, Hiroki1∗ ; FAN, Qiaohui2 ; TAKEICHI, Yasuo3 ; TANAKA, Kazuya4 ; SAKAGUCHI, Aya5 ;INAMI, Nobuhito3 ; MASE, Kazuhiko3 ; ONO, Kanta3 ; TAKAHASHI, Yoshio2
1

Department of Earth and Planetary Systems Science, Hiroshima University, 2 Department of Earth and Planetary Science, The
University of Tokyo, 3 Institute of Materials Structure Science, KEK, 4 Institute for Sustainable Sciences and Development, Hiroshima University, 5 Graduate School of Pure and Applied Science, University of Tsukuba
The behavior of the radioactive cesium (radio-Cs), which was emitted by nuclear power plant accident, was different between
in the Abukuma River (Fukushima) and in the Pripyat River (Chernobyl). Previous studies showed that dissolved Cs was dominant in the Pripyat River (approximately 70%). Conversely, Cs in the particulate matters (PMs) was dominant in the Abukuma
River (dissolved Cs is approximately 30%). this difference of radio-Cs behavior was related to the blocking effect by the coatingof natural organic matter (NOM) on clay minerals in the aquatic environments. However, the mechanism of the blocking effectby NOM has not been investigated for environmental samples yet in terms of morphological image and characterization.
Scanning transmission X-ray microscopy (STXM), X-ray microscopy using soft X-ray region, is very confortable to confirm
the blocking effect by NOM. However, STXM had not been installed into synchrotron radiation facilities in Japan until 2012.
Therefore, compact STXM (cSTXM) was newly designed and developed at BL-13A in KEK-Photon Factory (PF) until 2014. Its
size, similar to laptop (A4 paper size), is much smaller than conventional STXM (Bruker’s STXM). Piezo electronic driven stages
were installed to all axis stages in the cSTXM. This system can be fast and precise sufficient to control the nano-scale imaging.
As to spatial resolution using 30 nm outer most zone width FZP, we can attain resolution about 37 nm at sample measurement
position. All detection was conducted by counting system using avalanche photo diode (APD) or photo multiplier (PMT). Soft
X-ray region allow us to measure the light elements such as carbon, nitrogen, and oxygen.
As to samples, suspended water was collected from in the Abukuma River and the Pripyat River, which was filtered initiallyby 3.0 µm membrane filter and subsequently by 0.45 µm membrane filter using a pressurized pumping system. Finally, fine PMs(>0.45 µm) were obtained by this filtration. Before STXM measurement, these PMs were dispersed into water by supersonicwave for 5 min. The water droplet including the PMs was dropped on a 50-nm-thick Si3N4 membrane and air-dried. In addition
to the sampling, the concentration of dissolved organic carbon (DOC) was measured in these rivers. In this study, we analyzed
these PMs obtained from the two rivers using scanning transmission X-ray microscope (STXM) to investigate (i) the chemical
distribution images of NOM (mainly composed by carbon) and clay minerals (mainly composed by aluminum) and (ii) the functional group images of carbon. In addition, (iii) the characteristic of NOM was measured by STXM-near edge X-ray absorption
fine structure (NEXAFS) extracted from target area of NOM adsorbed on clay minerals.
Two distribution images (carbon and aluminum) showed that clay minerals were covered with NOM in the Fukushima andChernobyl samples. By functional group mapping of carbon, it was found that distribution of each functional group was similar
among different functional groups (e.g. aromatic, phenolic, carboxylic) in the PMs obtained from the two rivers. NEXAFS
spectra of carbon were also similar to all samples, suggesting that humic substances (mainly composed of humic and fulvic acid)are the main cause of the blocking effect in these rivers. Based on these results, it is suggested that the blocking effect could
occur in the Abukuma and Pripyat Rivers, which is caused by humic substances covering with clay minerals. Therefore, it isconcluded that the degree of the blocking effect by NOM related to radio-Cs behavior was dependent on the concentration of
DOC in the river (in the River Abukuma: 0.9-1.3 mg/L, in the River Pripyat: 18 mg/L). In addition to the studies on the rivers,
investigation results for PMs obtained from Fukushima pond (DOC value is between the Abukuma and Pripyat Rivers) will be
explained in this presentation.

Keywords: Natural organic matters, river particulate matters, Cs behavior, Scanning transmission X-ray microscopy (STXM),
Fukushima, Chernobyl

1/1

MAG38-14

Room:301B

Time:May 26 12:30-12:45

Identification of radioactive microparticles in the vicinity of the Fukushima Dai-ichi Nuclear Power Plant
SATOU, Yukihiko1∗ ; SUEKI, Keisuke1 ; SASA, Kimikazu1 ; ADACHI, Kouji2 ; IGARASHI, Yasuhito2
1

Graduate School of Pure and Applied Sciences, University of Tsukuba, Japan, 2 Meteorological Research Institute, JapanThe Fukushima Dai-ichi Nuclear Power Plant (FDNPP) disaster in 2011 discharged a large amount of radionuclides to theenvironment. Previous studies already disclosed the source term and inventory of radionuclides. However, physical and chemical
states of radionuclides in the environment have yet to be revealed. Numerous environmental samples have been analyzed to investigate distribution of radionuclides by digital autoradiography using an imaging plate (IP). These studies pointed out that the
spot-type contaminations were appeared and very common not only for the samples collected during the early stage (collecting
until April 2011) of the FDNPP disaster but also for those collected later. In the FDNPP disaster, major forms of radioactive
materials have been assumed to be gaseous. This is because the disaster underwent no reactor explosion nor fire of the reactor
core, which is quite different from the situation in the Chernobyl NPP (ChNPP) disaster in 1986. In addition, it has been revealed
that the emitted nuclear fuel (uranium) and 90Sr was very low. Therefore, elucidation of the cause of the spot-type contaminationis crucial, which could contribute to know about physical and chemical state of radionuclides in the environment, as well as disclose their release processes from the FDNPP. Present study thus aiming at elucidation what makes the spot-type contaminationin the IP analysis.
Surface soil samples were collected in the area about 20 km northwest from the FDNPP in June 2013. Spot-type contaminations were detected by IP analysis. Then, the radioactive particles were isolated by repeated sorting process and measured
by the γ-spectroscopy with the high purity germanium semiconductor detector. The particles isolated were finally observed by
SEM-EDS to determine the elemental composition and the morphology.
So far identified are four particles, and determined radionuclides by γ-spectroscopy were 134 Cs and 137 Cs. The morphologyof the particles exhibited two types; spherical and fragmental. Thus, the spot-type contamination was characterized as due tosuch specific radioactive particles. The particles consist of Si, O, Zn, Fe, etc. and Cs (of which activity matched with the resultsby γ-spectroscopy) were also easily detected by SEM-EDS, suggesting glassy molten material. However, other fission products
were not found in the particles. Tremendous amount of radioactive particles were collected around the ChNPP, and they weretermed hot particle. Dominant components of the hot particle are nuclear fuel and typical fission products such as 90 Sr, 153 Eu
as well as 134 Cs and 137 Cs. In contrast elemental composition of the present particles were dominated by Si. Uranium wasfound for only one of the present particles, but its concentration was very low and localized within the particle. In conclusion,
characteristics of the present particles are quite different from the Chernobyl hot particles, but very similar to those reported forthe particles isolated from HV filter samples in Tsukuba (Adachi et al., 2013, Abe et al., 2014).
Keywords: FDNPP disaster, Radioactive particle, Consist elements, Isotope ratio

1/1

MAG38-15

Room:301B

Time:May 26 14:15-14:30

Desorption behavior of cesium (133 and 137Cs) from the clay minerals distributed aroundthe Power Plant
ASAHI, Kazunari1∗ ; AOI, Yusuke1 ; TOMIHARA, Seiichi2 ; FUKUSHI, Keisuke1
1

Kanazawa Unversity, 2 Environmental Aquarium Aquamarine Fukushima

In 11 March 2011, Tohoku region Pacific Ocean earthquake occurred and Fukushima Daiichi nuclear power plant caused a
steam explosion. AAnd a large amounts of radioactive material was were released around nuclear power plant. Among thereleased radioactive material, from the total emissions and half-life, a major cause of soil pollution around nuclear power plant
has been said to beis radioactive cesium (Cs).
Extensive radioactive Cs around nuclear power plants have been identified retained in the fine materials of the soil surface
and. the The layered clay minerals such as smectite, vermiculate and illite contained in the universal soil is are pointed out thatconsidered to be the main uptake medium Csa for radioactive Cs. Soil of Fukushima Prefecture has Abukuma granite and hostrock, smectite, vermiculite, the presence of illite has been confirmed is the layered clay mineral is its weathering products.Hostrock of soil of Fukushima Prefecture is in Abukuma granite.having a layered clay mineral which is a weathering product, smectite, vermiculite, illite presence has been confirmed. Layered These clay minerals has possess a the layered crystal structureand hydrated cations held in the interlayer, which can be exchanged with the foreign cations in solution. For a particularly highaffinity for the Cs+ to these clay minerals,Therefore, Cs emitted by the nuclear accident is expected that it isto be firmly held
between the layers of the layered clay minerals.
However, if the concentrations of the foreign main cations in the solution is are high concentration, the retained Cs+ by exchange with firmly held Cs+ is a also other cations may be leachedin the clay minerals is possibly released to the solutions.
Natural water the clay particles are contacted in naturegenerally contains a wide variety of the major cations at different concentrations. Thus radioactive Cs which is adsorbed on the natural soil it is feared eluting natural environment. To the understandingof the dynamics of radioactive Cs in the environment, the understanding of Cs leaching desorption behavior by major cationfrom natural soil is essential. This study, by using a soil clay distributed around the Fukushima Daiichi nuclear power plant,
was intended to systematically verify the desorption behavior of Cs from the soil clay minerals distributed around the Fukushima
Daiichi Power Nuclear Plant by adding the majorin cation.

1/1

MAG38-16

Room:301B

Time:May 26 14:30-14:45

A study of Cs-adsorption behavior of clay minerals using autoradiography and considering the actual environments
KOGURE, Toshihiro1∗ ; MUKAI, Hiroki1 ; HIROSE, Atsushi2 ; MOTAI, Satoko1 ; TANOI, Keitaro2 ;NAKANISHI, M.tomoko2
1

Graduate School of Science, The University of Tokyo, 2 Graduate School of Agricultural and Life Sciences, The University ofTokyo
Though there are a number of studies to analyze the soil contamination with radioactive cesium released from Fukushima
nuclear accident, microscopic analyses to investigate, for example, the adsorption sites of radioactive cesium in the actual soil arefew. Recently we found, using autoradiography with special imaging plates (IPs) and various electron microscopic techniques,that weathered biotite originated from Abukuma granite in Fukushima is a major adsorbent in the soil collected from Iitate village(Mukai et al., 2014). On the other hand, the adsorption experiments performed in the laboratory to determine the Cs-adsorption
ability of various clay minerals indicated that weathered biotite or vermiculite did not distinctively adsorbed Cs, compared to theother clay minerals, even at similar contamination level to that in Fukushima (e.g., http://reads.nims.go.jp/). This discrepancy
suggested that actual adsorption of Cs in the soil was controlled by kinetics among multi-minerals and solution, rather than bysimple equilibrium between mono-mineral and solution. Moreover, Cs adsorption experiments to minerals should be performed
at a sub-ppm level in the minerals, employing the actual soil in Fukushima. Considering these ideas, we conducted a new Csadsorption experiment, in which various clay minerals were immersed together in dilute Cs-137 radioisotope solutions and theamount of Cs-137 adsorbed in each mineral was measured by autoradiography using an IP. It was found that a large quantity of
Cs-137 predominantly fixed by the weathered biotite collected in Fukushima, compared to those by the neighboring clay minerals(unweathered biotite, illite, montmorillonite, kaolinite, halloysite, allophan, imogolite, etc.). Moreover, it was also observed that,with the increase of the immersion time, Cs-137 initially adsorbed in the other clay minerals moved to weather biotite, indicatingthat mineral species fixing the Cs-137 were changing with time. This phenomenon might be related to the fixation of radioactive
cesium in the soil of Fukushima, which was reported recently.
Keywords: Fukushima nuclear accident, radioactive cesium, clay minerals, weathered biotite, adsorption, autoradiography

1/1MAG38-17

Room:301B

Time:May 26 14:45-15:00

Characterization of mineral phases in radioactive particles collected from Fukushima contaminated soil using SR-u-XR
MOTAI, Satoko1∗ ; MUKAI, Hiroki1 ; WATANUKI, Tetsu2 ; OHWADA, Kenji2 ; FUKUDA, Tatsuo2 ;MACHIDA, Akihiko2 ; KURAMATA, Chisaki1 ; KIKUCHI, Ryosuke1 ; KIRAZAWA, Hideaki3 ; KOGURE, Toshihiro1
1

Graduate School of Science, The University of Tokyo, 2 Japan Atomic Energy Agency, 3 National Institute for Material Science

The behavior of radioactive cesium is one of important concern about Fukushima nuclear accident. Clay minerals are considered as major radioactive cesium adsorbent in soil from lab experiments reported by previous studies. However, it has been
unclear what adsorbs radioactive cesium, because the amount of radiation in actual soil is too low to detect. Recently, Mukai et al.
(2014) has detected the radioactive particles in actual soil using autoradiography with imaging plates (IPs). They characterized
and classified these radioactive particles into three types using SEM-EDS: 1) weathered biotite, 2) aggregate of fine clay minerals, and 3) organic matter containing clay minerals particulates. On the other hand, it is not enough to identify mineralogicalcharacteristic of particles adsorbed radioactive cesium using only SEM-EDS. Then, we identify and characterize mineral phasesof radioactive soil particles using Synchrotron micro X-ray Diffraction (SR-µ-XRD) at BL22XU of SPring-8. After radioactive
soil particles were separated by autoradiography and divided into above three types from SEM-EDS observation, each particle
mounted on a kapton pin using micro manipulator for the XRD measurement. The incident X-ray with wavelength λ= 0.8273 Å
at 15 keV were collimated to a diameter of 40 or 60 µm. Angle dispersive diffraction patterns were recorded on an imaging plate.
Two-dimensional X-ray diffraction images on the IP were integrated as a function of 2θ to obtain conventional one-dimensional
diffraction profiles. Spotty diffraction patterns of particles, characterized as 1) weathered biotite by SEM-EDS observation, showfeature of single crystal. Broad peaks at ˜10 Å, ˜14 Å and ˜7 Å appear at the low angle diffraction patterns of these weatheredbiotite particles. It indicates that these particles are weathered biotite with varied weathering degree from biotite, via vermiculite,
to kaolinite. There is no clear relationship between the diffraction patterns of weathering biotite and amount of radiations estimated from luminescence on IP autoradiography. 2) The diffraction pattern of an aggregates minerals shows ring pattern ˜14.0
Å indexed smectite, 3) on diffraction patterns of a few organic matter containing particles, there are no clear diffraction patternof clay minerals.
Keywords: Fukushima nuclear accident, radioactive cesium, autoradiography, clay mimerals, weathered biotite, SR-u-XRD

1/1

MAG38-18

Room:301B

Time:May 26 15:00-15:15

Distribution of radioactive cesium in contaminated Fukushima soil particles using FIB
and IP autoradiography
MUKAI, Hiroki1∗ ; MOTAI, Satoko1 ; KOGURE, Toshihiro1
1

Graduate School of Science, the University of Tokyo

Recently radioactive particles in the contaminated soil collected from Fukushima have been specified by imaging plate (IP)
autoradiography and characterized using electron and X-ray microanalyses (Mukai et al., 2014). These particles are several tensof micrometers in size and, in the next step, it is of importance that how radioactive cesium is distributed in the particles to discuss the states and dynamics of Cs in the soil. For this purpose, IP autoradiography itself is no longer useless because its spatial
resolution is around a few hundred of micrometers at best. To overcome this limitation, we successfully applied micro-processing
using the focused ion beam (FIB) technique along with IP autoradiography.
According to the results by Mukai et al. (2014), three types of the radioactive soil particles: (1) weathered biotite, (2) organic
particle containing fine mineral particulate, and (3) aggregate of fine clay minerals, were investigated. The weathered biotite
with plate-like morphology was divided into small pieces of a few micrometers using FIB and they were separated to be distinguished by IP autoradiography, using a micromanipulator. The autoradiography detected radiation from all pieces, indicatingthat radioactive cesium is distributed rather homogeneously in the biotite. Probably a solution containing radioactive cesium
penetrated inside the crystal, through dense cleavage spaces which are well developed in the weathered biotite. On the other
hand, one or two of several pieces from the organic particle were radioactive, meaning that the cesium is localized in the particle,
probably at the mineral particulates and/or organic matter in the particles. Finally, the aggregate of clay minerals were crushed
and spread on IP using the micromanipulator. Most fragments were radioactive, suggesting that the cesium is widely distributedin the aggregate.
Keywords: Weathered biotite, Fukushima nuclear accident, Radioactive cesium, Autoradiography, FIB

1/1

MAG38-19

Room:301B

Time:May 26 15:15-15:30

Measurement of radiocesium in spare seawater samples collected in marine monitoring
for the Fukushima accident in 2011
KUMAMOTO, Yuichiro1∗ ; YAMADA, Masatoshi2 ; AOYAMA, Michio3 ; HAMAJIMA, Yasunori4 ; MURATA, Akihiko1 ;KAWANO, Takeshi1
1

JAMSTEC, 2 Hirosaki University, 3 Fukushima University, 4 Kanazawa University

In March 2011 radionuclides, including radiocesium, were released from damaged Fukushima Dai-ichi Nuclear Power Plants(FNPP1) to the environment. It has been suggested that a large portion of radiocesium was transported into the North Pacific Ocean. However, its transportation process and total amount in the open are still unclear. Just after the accident, from23th March 2011, Ministry of Education, Culture, Sports, Science and Technology (MEXT) started marine monitoring in acoastal area between 30 and 50 km approximately away from the FNPP1. Results of radionuclides (radiocesium, radiostrontium,and radioiodine) measurements had been published by MEXT (after April 2013 those are available on a web page of Nuclear
Regulation Authority). Number of these observational data, however, is not enough to discuss transportation process of the
Fukushima-derived radionuclides in the ocean mainly because of urgent and quick measurements during the marine monitoring.
For example, radiocesium in the seawaters had been measured using a simple method by July 2011. As a result, about threemonths from May to July 2011 was a data-blank period in the open ocean within approximately 200 km from the FNPP1 because
most of the measurement results were under detection limit. During the marine monitoring in 2011, spare seawater samples werealso collected in some cruises conducted by research ships of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We obtained these spare samples from JAMSTEC and measured radiocesium in them using a high-sensitivity method
and present here spreading process of the Fukushima-derived radiocesium from May to July 2011 in the open ocean. The spareseawater samples (10 or 20 liters each) were collected during seven cruises using Niskin samplers. Radiocesium in the spare
samples from four cruises (YK11-E02, NT11-E01, MR11-E02, and KR11-E04) was concentrated by evaporation or additionof ammonium phosphomolybdate and measured with low-background Ge-detectors at the Low Level Radioactivity Laboratory,
Kanazawa University or Mutsu Institute for Oceanography, JAMSTEC. Uncertainty of the measurements, which was derived
from sample preparation and analysis, was about 8%. In the early May 2011, high activity concentration (more than 500 Bq/m3 )of 134 Cs, which was released from the FNPP1 to the North Pacific though direct discharge of contaminated water in April 2011,
was observed within about 50 km from the shore in off of Fukushima and Miyagi Pref. This north/southward spreading could be
explained by prevailing north/southward coastal current in off of Fukushima Pref. On the other hand, a high activity concentration
observed at a station located in 37.5N/142E about 100 km away from the FNPP1 implies eastward spreading of the Fukushimaderived 134 Cs due to a mesoscale eddy. In the early June 2011, the activity concentration decreased in off of Fukushima Pref.
within about 50 km from the FNPP1 while the high activity concentration water had been spread to the Sendai Bay (Miyagi
Pref.) and Kashima-Nada (Ibaraki Pref.). In addition, the high activity concentration water was transported eastward to about
200 km offshore (around 142.5E) along the Kuroshio Extension Current between 36.5 and 37N approximately. The southwardand eastward wide-spreading in June could be derived from erosion of a warm mesoscale eddy off Ibaraki Pref. by the end of
May 2011. In the early July, the high activity concentration of 134 Cs was observed only in the Sendai Bay and Kashima-Nada,
except at stations nearby the FNPP1, suggesting that a main body of the 134 Cs contaminated water due to the direct discharge
had been transported to outside of about 200 km from the FNPP1. Water-column inventory of the Fukushima-derived 134 Cs willbe also presented in our presentation. This work was partially supported by Japan Society for the Promotion of Science (JSPS)
KAKENHI Grant Number 24110005.
Keywords: accident of Fukushima Dai-ichi Nuclear Power Plants, radiocesium, marine monitoring

1/1

MAG38-20

Room:301B

Time:May 26 15:30-15:45

Estimation of total released 134Cs and 137Cs derived from TEPCO-FNPP1 accident into
the North Pacific Ocean by
INOMATA, Yayoi1∗ ; AOYAMA, Michio2 ; TSUBONO, Takaki3 ; TSUMUNE, Daisuke3 ; HIROSE, Katsumi4
1

Asia Center for Air Pollution Research, 2 Fukushima University, 3 Central Research Institute of Electric Power Industry, 4 Sophia
University
The oceanic distribution of 134 Cs and 137 Cs released from the Tokyo Electric Power Company-Fukushima Daiichi Nuclear
Power Plant (TEPCO-FNPP1) accident were investigated by using the optimal interpolation (OI) analysis. In this study, we
conducted the OI analysis during the period from the end of March to the end of May 2011. A data set reported in research
papers and documents was used for the analysis.
During the end of March to early April, extremely high 134 Cs and 137 Cs activities in seawater occurred along the coast near the
TEPCO-FNPP1. The high activities spread to the region of 165o E with a latitudinal center of 40o N in the western North Pacific
Ocean. Atmospheric deposition is also cause to high activities in the region between 180o and 130o W in the North Pacific Ocean.
The total inventory of FNPP1-released 134 Cs in the North Pacific Ocean is estimated to be 15.2±1.8 PBq. In these, about half
(8.3±1.8 PBq) of the total released amount is concentrated in the coastal region near the TEPCO-FNPP1. Considering that thedirect released 137 Cs in the seawater was 3.5±0.7 PBq (Tsumune et al., 2012), atmospheric deposition contribute to the 134 Cs
inventory in the near the TEPCO-FNPP1. The FNPP1-released 134 Cs inventory in the coastal region decreased exponentiallywith half-time of 4.2±0.5 days after cease of the direct discharge (6 April 2011) and become to about 2±0.4 PBq at the middleof May 2011. Considering that the 134 Cs/137 Cs activity ratios for the FNPP1 accident were very close to one and extremely
uniform during the first month, the total amount of 137 Cs released by the TEPCO-FNPP1 accident reached to 20% of a current
North Pacific inventory of bomb-derived 137 Cs injected in the 1950s and early 1960s.

Keywords: TEPCO-FNPP1, 134 Cs, 137 Cs, North Pacific Ocean, Optimal Interpolation analysis, Inventory

1/1

MAG38-21

Room:301B

Time:May 26 15:45-16:00

Modeling dispersal of land-derived suspended radionuclides in the Fukushima coast
YAMANISHI, Takafumi1∗ ; UCHIYAMA, Yusuke1 ; ONDA, Yuichi2 ; TSUMUNE, Daisuke3 ; MISUMI, Kazuhiro3
1

Kobe University, 2 University of Tsukuba, 3 Central Research Institute of Electric Power Industry

Several oceanic dispersal modeling have been conducted on dissolved radionuclides leaked at the Fukushima Dai-ichi Nuclear
Power Plant (FNPP). These models normally consider scenarios where the direct release of radionuclides from the FNPP andatmospheric deposition as the secondary source. In the present study, we view freshwater discharge from the rivers as a missing
piece for the inventory of the radionuclides in the ocean. The land-derived input introduces a time lag behind the direct releasethrough hydrological process because these radionuclides mostly attach to suspended particles (sediments) that are transported
quite differently to the dissolved matter in the ocean. Therefore, we develop a sediment transport model consisting of a multiclass non-cohesive sediment transport model, a wave-enhanced bed boundary layer model and a stratigraphy model proposed by
Blaas et al. (2007) incorporated into ROMS. A 128 x 256 km domain with the grid resolution of dx = 250 m centered at the FNPP
is configured as a test bed within the existing dx = 1 km domain (Uchiyama et al., 2012, 2013). Three classes of sediments, viz.,
fine sand, silt and clay fractions, are considered here. The bed skin stress is evaluated by a combined wave-current stress model ofSoulsby (1995) with the wave field computed with a SWAN spectral wave model at dx = 1 km embedded in the JMA GVP-CWM
wave reanalysis. A total of 20 rivers inclusive of the 6 major rivers located in the domain are considered as point sources of thesediments. The daily-averaged freshwater discharges from the 20 rivers are evaluated with a surface runoff model HYDREEMS(Toyoda et al., 2009). Sediment volume fluxes from the rivers are then calculated with an empirical L’-Q’ (discharge to sedimentflux) relation proposed by Takekawa et al. (2013). Fraction of three sediment classes in the riverine discharge is determined
empirically based on the outcome of a USLE-based river sediment modeling conducted by JAEA.
The developed model successfully reproduces the dispersal of the land-derived sediments and their recirculation processes
associated with resuspension and deposition in the Fukushima coast for 4 months after the accident. The discharged sediments
can be transported about 50 km from the shore with prominent patchiness of deposition and erosion near the mouth of each river.
For instance, the offshore region of the mouth of the Niida River is evaluated to be erosion dominated, consistently with themeasurement. Misumi et al. (2014) estimate suspended 137Cs concentration in the bed with considering static adsorption anddesorption of 137Cs between the seawater and the bed sediments based on the dissolved 137Cs model result of Tsumune et al.
(2012). The inferred bed 137Cs agrees well with the observation in the shallow area, whereas substantially underestimated in theoffshore area at depth deeper than 200 m. They attribute the reason of the underestimate to the 137Cs due to sediment transportthat is omitted in their model. We carefully diagnose our model results and find that although the clay-class sediments reach the
deeper area, the time-integrated deposition is merely about 0.002 kg/m2 that is considered to be a minor fraction. Therefore, it issuggested that detritus and debris of organic matters rather than land-derived minerals likely cause the offshore 137Cs deposition.
We further examine nearshore dispersal patterns and quantify the inventory of 137Cs attached to the sediments originated fromthe land by applying the empirical power law for 137Cs concentration as a function of specific surface area of the suspended
particles proposed by Onda et al. (2014).

Keywords: multic-class sediment transport model, radioactive cesium 137, multiple nesting approach, ROMS (Regional Oceanic
Modeling System)

1/1

MAG38-22

Room:301B

Time:May 26 16:15-16:30

134Cs and 137Cs in the North Pacific Ocean derived from the TEPCO Fukushima Daiichi Nuclear Power Plant accident
AOYAMA, Michio1∗ ; HAMAJIMA, Yasunori2 ; HULT, Mikael3 ; UEMATSU, Mitsuo4 ; OKA, Eitarou4 ;TSUMUNE, Daisuke5 ; KUMAMOTO, Yuichiro6
1

Institute of Environmental Radioactivity, Fukushima University, 2 Low Level Radioactivity Laboratory, Institute of Nature andEnvironmental Technology, Kanazawa Unive, 3 European Commission, Joint Research Centre, Institute for Reference Materials
and Measurements (IRMM, 4 Center for International Collaboration ,Atmosphere and Ocean Research Institute, The Universityof T, 5 Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 6 Research Institute for
Global Change, Japan Agency for Marine-Earth Science and Technology
We collected 2 - 10 litre surface seawater samples at more than 300 stations and water column samples were also collected at
24 stations.
The measured 137Cs concentration in a seawater sample at north 5 and 6 canal of the FNPP1 site reached 68 MBq m-3 on 6
April. It decreased to 1000 ? 10000 Bq m-3 during the period from August 2011 to July 2012 which means that direct discharge
rate became very small, about ca. 100 GBq day-1. After July 2012, the activities of 137Cs in surface water at near FNPP1 sitewere still kept around 1000 Bq m-3 which corresponds about 10 GBq day-1.
After the FNPP1 accident, both 134Cs and 137Cs are observed in a wide area in the North Pacific Ocean and 134Cs activity
and 137Cs activity ranged from 1000 +- 71 to less than 0.4 Bq m-3 and from 1080 +- 60 to 1.2 +- 0.2 Bq m-3, respectively.
A zonal speed of FNPP1 derived radiocaesium in surface water at mid latitude in the North Pacific Ocean was 7 km day-1, 8
cm s-1, until March 2012 just after one year the accident (Aoyama et al., 2014). It after March 2012 till August 2014 was also
estimated to be ca. 3 km day-1, 3.5 cm s-1 which showed apparent decrease of zonal speed. In 2013 and 2014, a maximum of
Fukushima origin 137Cs activity in surface water was already close to pre-Fukushima level and observed at the eastern part of
the North Pacific Ocean.
Until the end of 2011, a main body of Fukushima derived radiocaesium were existed at surface mixing layer, however, after
winter cooling occurred subsurface maximum of Fukushima derived 134Cs and 137Cs due to subduction were observed at about
300 to 400 meters at 35 deg. N to 40 deg. N along 165 deg. E due to subduction. Southward transport due to subduction was
also observed at 24 deg. N, 165 deg. E, too.

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MAG38-23

Room:301B

Time:May 26 16:30-16:45

Temporal change of Fukushima-derived Cs-137 in the sediments in the waters off Fukushima
and nearby Prefectures
KUSAKABE, Masashi1∗ ; TAKATA, Hyoe1 ; INATOMI, Naohiko1 ; HASEGAWA, Kazuyuki1 ; ISONO, Ryosuke1
1

Marine Ecology Research InstituteThe 137 Cs derived from the Fukushima Daiichi nuclear power plant accident in seawater has been transported to the open
ocean with currents and its concentration has decreased exponentially from about 200 Bq/L to several mBq/L, a little higher thanthe pre-accident level, in the outside of 30 km radius of the nuclear power plant. The nuclide in the sediments, however, has notshown such a steep temporal change. Thus, its distribution pattern and temporal change should be systematically studied for along time in order to access quantitatively the impact of the accident to the coastal environment. In addition, it is necessary to
explore the mechanism for temporal change of the distribution in the sediments to predict the environmental recovery in the area.
Soon after the accident, Marine Ecology Research Institute has been monitoring the water off Fukushima and nearby Prefectures
for the radioactivities under the contract with Ministry of Education, Culture, Sports, Science and Technology (currently with
the Nuclear Regulation Authority). We will introduce the distributions of Fukushima-derived 137 Cs in the bottom sediments andtheir temporal change, and factors controlling the changes.
Methods
In the coastal waters off Miyagi, Fukushima, Ibaraki and Chiba Prefectures, bottom sediments were retrieved using a multiple
corer. From May to June 2011, sediments were collected at 12 sites six times. After that, the sites were increased. Now thesampling is done 4 times a year at 32 sites. Surface 3 cm of cores were used to study the surface distributions of 137 Cs. Verticalprofiles of 137 Cs in the sediments were also studied at selected sites. Additional parameters such as sediment grain size, contentsof organic material and elemental composition were also measured.
Results
The concentrations of 137 Cs in the surface sediments shows wide variation ranging from 0.8 to 540 Bq/kg-dry; Almost all of
the data exceeded the level of pre-accident 5yr-average (0.87 +/- 0.41 Bq/kg) in the waters off Fukushima Pref. Proximity of thesampling site did not necessarily correspond to the higher values.
The temporal change of surface concentrations do not indicate steep decrease as that of seawater as a whole and the concentration at each sampling site varies so that it is not evident to see the temporal trend. However, geometric means calculated from
Sept., 2011 to Nov. 2014 reveal the exponential decline trend from 47 Bq/kg to 17 Bq/kg.
Spatial variation of surface 137 Cs concentration and its temporal change would be ascribed to several factors. The former may
be related to grain size distribution of the sediment, chemical composition, riverine input from the land, and pathway of polluted
water after the accident, and the latter desorption of Cs from the sediments, resuspension and subsequent lateral transportation,and bioturbation. The temporal change of vertical distributions of 137 Cs do not show significant increase of the nuclide in the
deeper layer, suggesting that bioturbation may not be the main factor for the surface decrease.
The detail of the spatiotemporal changes of 137 Cs in the sediments and the relevant factors will be presented in the talk.
Acknowledgements
The data presented here have been obtained in the program contracted with MEXT (Mar. 2011-Mar. 2013) and NRA (Apr.
2013-Feb. 2015).
Keywords: Fukushima nuclear power plant accident, Cs-137, bottom sediment

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MAG38-24

Room:301B

Time:May 26 16:45-17:00

Temporal variation of 137 Cs in zooplankton and its primary factor in the waters off Fukushima
and nearby prefectures
IKENOUE, Takahito1∗ ; TAKATA, Hyoe1 ; HASEGAWA, Kazuyuki1 ; KUDO, Natsumi1 ; ISONO, Ryosuke1 ;KUSAKABE, Masashi1
1Marine Ecology Research Institute

The East Japan earthquake on 11 March 2011 and the ensuing tsunami resulted in the release of large amounts of radionuclides
from the accident of Fukushima Dai-ichi Nuclear Power Plant (FDNPP) into the surrounding environment. Cesium has similar
chemical properties with potassium, which is the essential element for living organisms, and is easy to be incorporated into livingorganisms. The half-life of radioactive cesium (134 Cs and 137 Cs) is 2 and 30 years, respectively. For the relatively long half-lifeof 137 Cs compared with 134 Cs, continuous monitoring of the levels of 137 Cs contamination is indispensable.
Zooplankton play a key role in marine biogeochemical cycle as secondary producers in the marine food web because they
are major food for fishes and organisms of higher trophic levels. Therefore it is important to have information on their 137 Cs
concentration and behavior of 137 Cs between zooplankton and surrounding environment such as seawater, surface sediment, andsuspended marine particle.
Methods
In this study, zooplankton samples were collected at seven to eight sampling locations in the waters off Fukushima and nearby
prefectures during May 2012 to January 2014. The 137 Cs concentrations in the samples were measured with Ge detectors andthe compositions of zooplankton species were analyzed by microscopic observation. The zooplankton samples were obtained byhorizontal towing at a depth range of 0-80 m using a large ring net. Seawater and sediment samples were also collected at thecorresponding locations with zooplankton samples.
Results
Concentrations of 137 Cs in zooplankton ranged from 0.26 to 184 (Bq/kg-dry) during the sampling period (May 2012-January2014). The concentration peaks did not appear concurrently at each station. In January 2014, concentrations of 137 Cs in zooplankton ranged from 6.59-40.3 (Bq/kg-dry) and they were still one or two orders of magnitude larger than those detected before
the accident of FDNPP (0.09-0.4 Bq/kg-dry, Kaeriyama et al., 2008). The taxonomic composition varied seasonally and geographically but Maxillopoda were generally dominant throughout the study.
137
Cs in zooplankton are thought to be derived from surrounding environment such as seawater, surface sediments, suspended
particle, and food. Since the 137 Cs concentration in surface sediments has not decreased so fast as that in seawater with time,137
Cs in surface sediments might be incorporated into zooplankton by resuspension of surface sediments. Assuming that aluminum in zooplankton is only derived from surface sediments, the contributions of surface sediments to 137 Cs in zooplankton
were estimated as 10%. 137 Cs in zooplankton in unit volume of seawater (µBq/m3 ) were not correlated with both of 137 Cs inambient seawater (Bq/L) and zooplankton biomass (mg-dry/m3 ). On the other hand, the timings of high relative abundance ofAppendiculata, Osteichthyes and phytoplankton corresponded to the timings of relatively high concentrations of 137 Cs in zooplankton. Therefore it is implied that variability in 137 Cs concentrations in zooplankton attributed to the composition of plankton
species rather than concentration of 137 Cs in surrounding environment and plankton biomass.
Acknowledgements
This work was carried out as part of a research project contact with the secretariat of the nuclear regulation authority.
Reference
Kaeriyama, H., Watabe, T., and Kusakabe, M. (2008). 137 Cs concentration in zooplankton and its relation to taxonomic composition in the western North Pacific Ocean. Journal of environmental radioactivity, 99(12), 1838-1845.
Keywords: Fukushima Dai-ichi Nuclear Power Plant accident, 137 Cs, Zooplankton, community composition

1/1

MAG38-P01

Room:Convention Hall

Time:May 26 18:15-19:30

Revisiting research on the vertical transport of radioactive nuclide from Fukushima Nuclear Accident
KAMOGAWA, Masashi1∗ ; SAITO, Shogen1 ; SUZUKI, Yuko1
1

Dpt. of Phys., Tokyo Gakugei Univ.

We observed spectrum of gamma rays at the summit of Mt. Fuji by means of germanium (Ge) detector (Micro-Trans-SPEC,
ORTEC Ltd. Co.) from July to August of 2014. The detector was installed on the second floor of the first building of Mt. Fuji
Weather Station. The second floor is made of the plywood covered with a vinyl and carpet over the H-steel. The roof and wall
are made of the H-steel covered with the plywood. The weight of the detector equipped with data logging and battery is 6.8
kg. The Ge crystal which is cylindrical with a length of 40 mm and a diameter of 50 mm is electrically cooled. The detection
efficiency is 13 %. Measurable energy of gamma rays ranges from 0 to 3 MeV for 8192 channels. Fig. 10 shows energy spectrum from 0 to 3 MeV versus the number of accumulated counts for one month. All of line spectrum in Figure 1 originated fromnatural radionuclide, while a continuous spectrum, namely a background, originated from cosmic rays and Compton scatteringof measured gamma rays. Fig. 11 shows total counts from July to August of 2014, just one month, and total counts for one day
on August 1, 2014. The counts of Cs134 with 605 keV are below the background for one day data, while the counts of the Cs134
are extremely slightly beyond the background for one month data. Magnified spectrum from 600 to 800 keV is shown in Fig.
12. A half-life and main photon energies of Cs137 and Cs134 are 30.2 and 2.06 years and 662 and 605 keV (Emission rate: 85.1
and 97.6 %), respectively. In this study, we investigate these line spectra to identify Cs137 and Cs134. The counts of Cs134 with
605 keV is almost equal to those of the background, whereas line spectra of Cs137 with 662 keV are clearly found. From thespectrum analysis by means of MAESTRO-32, the net counts of Cs137 and Cs134 are 20425 ± 443 and 434 ± 457, respectively.
Therefore, extremely small amount of Cs134 originating from Fukushima Nuclear Accident was transported into the summit of
Mt. Fuji. On the other hand, the most of Cs137 originates from nuclear tests in the 1950s to 1960s, because the ratio of Cs134 to
Cs137 60 years later is 3.0×10−9 : 1, assuming all counts of Cs137 spectra originates from nuclear tests.
Keywords: Fukushima Daiichi nuclear disaster, Radioactive material, Germanium detector

1/1

MAG38-P02

Room:Convention Hall

Time:May 26 18:15-19:30

Modeling of downward percolation and prediction of concentration of the radionuclide insoil by ADE
OKA, Hiroki1∗ ; HATANO, Yuko1 ; YAMAMOTO, Masahiro2
1

Faculty of Systems and Information Engineering, University of Tsukuba, 2 Graduate School of Mathematical Sciences, theUniversity of Tokyo
By the accident at the Fukushima First Nuclear Power Plant on March 11, 2011, the damage that surrounding environment
was polluted by radioactive materials occurred. Cs-137 stuck in a ground surface soaks into soil and percolates downward. The
underground migration of the radionuclide keeps being studied. The advection diffusion equation (ADE) is proposed as one of
the models of downward percolation of the radionuclide in soil by Walling and He. This model has been used most, because it
is simpler than other ones. However, There is also the report that we cannot express migration in porous medium such as soil by
ADE. This is caused by the fact that differences in soil properties of each land have an influence on the downward percolationof the radionuclide. However, it takes considerable amounts of labor to propose the model included all complicated processes ofsuch various environmental factors. In this study, by having a viewpoint different from such a model, we propose a more versatilemodel by improving the ADE model that used most.
For this ADE model, Robin boundary condition is used. Robin boundary condition is that the inflow and outflow of theradionuclide on a boundary surface does not happen. So, it is the downward percolation model while keeping the total volume of
the concentration fixedly. However, it is difficult to think that the inflow and outflow in a ground surface do not happen at all. So
in this study, by aiming at Robin boundary condition, we improve the ADE model. We derive the analysis solution when we use
ADE as governing equation and Robin boundary condition that was generalized as condition at a boundary surface. From this,
we propose the new ADE model including the case that the inflow and outflow happen in a ground surface. Here, we compare
our model with the data of concentration of Cs-137 in Fukushima soil to inspect the validity of this new model. Then, we get theresult that our model follow the date well.
Keywords: Advection Diffusion Equation, Downward percolation in soil, The accident at the Fukushima First Nuclear Power
Plant, Radioactive Cesium

1/1MAG38-P03

Room:Convention Hall

Time:May 26 18:15-19:30

Correlation-research about fluctuations of the air dose rate and weather conditions
FURUYA, Masato1∗ ; HATANO, Yuko1 ; AOYAMA, Tomoo2 ; KITA, Kazuyuki3 ; IGARASHI, Yasuhito4
1

Faculty of Systems and Information Engineering, University of Tsukuba, 2 Center for Research in Isotopes and Environmental
Dynamics, 3 Ibaraki University, 4 Meteorological Research InstitutePacific Ocean off the coast earthquake of magnitude 9.0 occurred on March 11, 2011. Fukushima Daiichi Nuclear Power
Station has meltdown By the earthquake and tsunami, and Surrounding environment is contaminated with radioactive materials.
International Nuclear Event Scale of the Fukushima Daiichi Nuclear Power Station accident is the level 7 (serious accident).
Accident of the same level is the second case since the Chernobyl nuclear power plant accident that occurred in Ukraine on April
26, 1986. The Cs-134 and Cs-137 are radioactive material released by accident increased significantly the spatial dose rate thatindicates the radiation dose per unit time space, a lot of the people who lived around the Fukushima Daiichi nuclear power station
were no longer able to live in the place. There is a lot of land where decontamination work has not started yet in an area aroundthe Fukushima Daiichi nuclear power station.
Released radioactive materials take atmospheric condition turbulent flow, do advection and stick to a ground level in the atmosphere. After depositing in a ground level, radioactive materials are floating by atmospheric condition turbulent flow and deposit
again to other places. Radioactive materials repeat such process. The weather condition influences such process deeply. The
model of the prediction which indicates attenuation of the new spatial dose rate which considered its weather condition is needed.
In this study, we refer to the correlation that the weather conditions and fluctuation of the air dose rate which is considered theradioactive decay.
To determine the correlation coefficients between the fluctuations of the air dose rate and various weather conditions in considering the periodicity obtained by the spectral analysis. As a result, it became clear that there is a strong negative correlation
between the fluctuation of the air dose rate and the soil water. This result may be the trigger which makes new methods that canestimate exposure risk.

1/1

MAG38-P04

Room:Convention Hall

Time:May 26 18:15-19:30

Development of the radio-aerosol generation system using spray drying method
ZHANG, Zi jian1∗ ; NINOMIYA, Kazuhiko1 ; SHINOHARA, Atsushi1
1

Graduate School of Science, Osaka University, 2 Graduate School of Science, Osaka University, 3 Graduate School of Science,
Osaka University
A large amount of radioactivity was discharged in the FDNPP accident. The radionuclide was transported through the atmosphere in a gas and aerosol forms and deposited to the grand and vegetation. The aerosol consisting radionuclides deposited to
the vegetation mainly in dry deposition mechanism. After the deposition, the foliar uptake could happen and the radionuclide
likes cesium would be absorbed into the vegetation. The foliar uptake process has higher absorption speed than the root uptake
process. The radiocesium deposition through the foliar uptake has great influence when we evaluate the amount of radioactivity
deposition to the environment.
There are some preceding studies for radionuclide foliar uptake with attaching stable element solution on the leave. Changing
the vegetation species, time of cleansing after the deposition and chemical constitution of solution, the foliar uptake process has
understood gradually. However, these experiments using solution wouldn, t reprise the dry deposition process. Madoz-Escande etal. generated cesium oxidation aerosols and studied the foliar deposition process [1]. In the FDNPP, radiocesium was transported
in sulfate aerosl form [2], so the data of oxidation aerosols is not suit for evaluation the deposition in this accident. For evaluationof deposition amount of radiocesium to vegetation, an experiment system simulated the accident condition is demand
The aim of our research is observing the behavior of dry deposition and foliar uptake of radiocesium in sulfate aerosols. We
need to generate radio-aerosol artificially in a controllable environment and attach aerosols on the leaf directly. A radio-aerosol
generation system was developed using spray drying method. Solution contained radiocesium was send to a nozzle by a syringe
pump and spraying by a high speed air flow. The spray was generated in a relatively high temperature chamber and micro-droplet
was drying quickly. The micro size solid aerosols consisting radiocesium were generated. In our poster, we explain the chambercondition, the shape of spray, aerosol physical property and yield.
[1]C.Madoz-Escande, et al., Journal of Environmental Radioactivity, 73 pp49-71, (2004)[2] N. Kaneyasu, et al.,Environmental Science & Technology, 2012, 46 (11), pp 5720?5726

Keywords: radio-aerosol, cesium, foliar uptake, spray drying method

1/1

MAG38-P05

Room:Convention Hall

Time:May 26 18:15-19:30

Atmospheric Radio-Sr and -Cs Depositions at Mt. Haruna
IGARASHI, Yasuhito1∗ ; ZAIZEN, Yuji1 ; ADACHI, Kouji1 ; KAJINO, Mizuo1
1

Atmospheric Environment and Applied Meteorology Res. Dpt., Meteorological Research Institute

The authors have collected atmospheric deposition samples at an isolated mountain located at the northwestern corner of the
Kanto plain and measured 90 Sr and the radio-Cs. This observation was started as a comparison with the similar deposition observation in Tsukuba situated on the ground surface. The chosen site is therefore located as high altitude as in the free troposphere,
in which the aeoliain dust is transported and it would be one of the main constituents of the deposition sample. Nevertheless, thedata obtained there could be served unintentionally for the investigation of the pollution of the atmospheric environment by the
Fukushima Daiichi Nuclear Power Plant (FDNPP) accident.
At Mt. Haruna (Takasaki, Gunma, 36?28’N, 138?52’E, 1,370m above sea level), monthly 90 Sr and 137 Cs deposition observations have been performed. The observation started at the end of 2006. Precipitation samples were filtered by a sieve of 2mm mesh and 100 µm mesh to remove fallen leaves, wooden piece, large particles in size, etc. and processed to concentrate
the whole sample. The desiccated sample was subjected to γ-spectrometry with a Ge detector to measure radio-Cs. Sr-90 wasthen measured by 2 π gas-flow β-counter after that strontium carbonate was radiochemically separated and radio-equilibrium
was attained. Each analytical process was quality-controlled by using the reference fallout sample that was prepared by theMeteorological Research Institute.
Monthly 137 Cs deposition in March, 2011 was 14±0.5 kBq/m2 which is 5 to 6 orders of magnitude higher than the level before
the FDNPP disaster. However, this amount was approximately 60% of that observed at the MRI, Tsukuba. The cumulative 137 Cs
deposition at Mt. Haruna was 18.8 kBq/m2 for the year 2011, which was also approximately 70% of that in Tsukuba. Almost
the same amount of 134 Cs was simultaneously deposited with 137 Cs. Thus, the total cesium deposition at Mt. Haruna reachedabout 40 kBq/m2 . It was revealed that the current observation site had a relatively lighter pollution than those found in Tsukuba.
Although Mt. Haruna was found within the so-called hotspot region distributed over northern Gunma, and heavier radio-Cs pollution (60-100 kBq/m2 -level) was observed around Lake Haruna by the airborne observation mapping conducted by the MEXT.
The current observation site might avoid pollution of wet deposition because of higher altitude than cloud layer height. On theother hand, monthly 90 Sr deposition in March, 2011 was as small as 3.11±0.03 Bq/m2 , which was about 1/4500 of the deposited137
Cs amount. This 90 Sr deposition was also approximately 60% of the value in Tsukuba. Deposition observations at Mt. Harunaconfirmed that the pollution impacts of 90 Sr are relatively minor compared with radio-Cs over the Kanto district.

Keywords: the Fukushima Daiichi Nuclear Power Plant accident, Radioactive deposition, Strontium, Cesium, Resuspension

1/1

MAG38-P06

Room:Convention Hall

Time:May 26 18:15-19:30

Sedimentation processes of radioactive Cs contaminated soil in storage reservoirs in Iwaki,
Fukushima prefecture
AOI, Yusuke1 ; FUKUSHI, Keisuke1∗ ; TOMIHARA, Seiichi2 ; YOSHIDA, Kosuke2 ; ITONO, Taeko1 ;KASHIWAYA, Kenji1 ; NAGAO, Seiya1
1Kanazawa University, 2 Environmental Aquarium Aquamarine Fukushima

The Great East Japan Earthquake (M 9.0) and subsequent tsunami, which occurred along the eastern coast of Japan on March
11, 2011, caused the accident in Fukushima Daiichi nuclear power plant. As a result, large amount of radionuclides were released
from the nuclear power plant and caused radioactive contamination in forest, soil and reservoir. It is recognized that the cause of
the contamination is mainly due to the radioactive cesium (Cs), because of the relatively long half-lives and the released amounts
The attenuation of the actual radiation dose in the evacuation-directed zones in Fukushima prefecture has been greater than thatpredicted form physical half-lives of 134 Cs and 137 Cs (Nuclear Regulation Authority, Japan (NRA), 2013). The radiation dosein Fukushima is related to the abundance of radioactive Cs accumulation per unit area (radioactive Cs inventory). Therefore, theattenuation of the radioactive dose were most likely attributable to (1) desorption of radioactive Cs from soils to natural water andthe subsequent diffusion and/or (2) erosion and transport of the contaminated soils to downstream. The distribution coefficients(Kd) determined from 137Cs concentrations of suspended particles and the solutions in some rivers in the affected area has beenreported to be 105-106 (mL/g), which indicates that radioactive Cs was hardly desorbed to the solution (Sakaguchi et al. 2015;
Nagao et al. 2013). Consequently, the former scenario is more plausible to explain the monitoring results.
It has been documented that the transports of the soil particles with radioactive Cs were accompanied with the natural water
current. Then, it is expected that radioactive Cs tend to accumulate in the places where the retentions of water current occur. In
terrestrial environment, one of such places is strange reservoir. Aoi et al. (2014) suggested that radioactive Cs in the catchment
area had been eroded and continuously deposited in the storage reservoir. Their study suggested that the reservoirs possibly playrole of a sink for radioactive Cs.
Fukushima Prefecture Government (2013) investigated the 134+137Cs concentrations of the bottom sediment of 1640 reservoir in Fukushima Prefecture. The results 134+137Cs concentrations was weakly correlated with the air dose rate. On the other
hand, even the space dose rate is the same in each district, the cesium concentrations of sediment varied 3-4 orders, which indicates that the functions of the storage reservoir as sinks for are depending on not only ambient air doses but also the sedimentation
processes in each catchment of the reservoir.
The continuous observations of the deposition of radioactive Cs into the reservoir is essential to understand the storage functionof radioactive Cs in reservoirs for the future use of the storage reservoir and for the prediction of the migration of radioactive
Cs in the local terrestrial environment. The aim of the study is characterize the sedimentation processes of contaminated soils
contaminated by radioactive Cs by means the sediment traps in two reservoirs in Iwaki City, Fukushima prefecture.

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MAG38-P07

Room:Convention Hall

Time:May 26 18:15-19:30

Behavior and migration of radiocesium in brackish water: A case study of the Matsukawaura lagoon, Fukushima, JapanKAMBAYASHI, Shota1∗ ; ZHANG, Jing1 ; HIROKAMI, Kiyokazu2 ; NARITA, Hisashi2 ; SHIBANUMA, Seiichiro4 ;SOMA FUTABA FISHERIES COOPERATION, Matsukawa-ura branch members5
1

Graduate school of Sci. and Eng. Univ. of Toyama, 2 Lab. of Radioisotope, Univ. of Toyama, 3 School of Marine Sci. and Tech.
Tokai Univ., 4 C-bec, 5 Soma Futaba Fisheries Cooperation Matsukawa-ura branch members
Radionuclides were released into the environment associated with the Fukushima Daiichi Nuclear Power Plant (FDNPP)
disaster. Radiocesium (Cs), released from FDNPP and deposited on the land, will migrate to the ocean through the surface
runoff. In this study, we intended to determine the geochemical transport of Cs in the system of river - estuary - ocean in
Matsukawa-ura Lagoon, northern Fukushima, Japan as a model area. Samples were collected in the study area from September
2013 till now. Sinking particle sampling was involved in the installation of sediment traps from November 26 to December 19,
2013. Surface sediment Cs-137 in the Matsukawa-ura showed apparent spatial and temporal variations, therefore, time seriesof the weighted average sediment Cs-137 was used in the following discussion. It was speculated that some natural purifying
processes affected the sediment Cs in the Matsukawa-ura because the observed effective half-life of Cs-137 in the sediment was
shorter than the theoretically physical half-life. Sinking particles were re-suspended in the Mastukawa-ura and transported tothe ocean by tidal pumping because total sinking particle flux and particulate Cs-137 export flux in the mouth were larger thanthose in the inner lagoon. It is suggested that re-suspension in the lagoon and transport to the ocean of particles were importantnatural purifying processes for Cs in Matsukawa-ura. In water samples, particulate Cs-137 was significant relative to dissolved
Cs-137 in the river; in contrast, dissolved Cs-137 was dominate in brackish water. So, it is found that the outflow of the dissolved
phase is important in the material cycle of Cs because the dissolved abundance ratio increases in brackish water. The enrichment
behavior of dissolved Cs-137 in the brackish water could be attributable to particle desorption. It is suggested seawater exchangewith lagoon water desorbed Cs and outside seawater contribute a natural purifying effect in the Matsukawa-ura.
Keywords: Radiocesium, Blackish water

1/1

MAG38-P08

Room:Convention Hall

Time:May 26 18:15-19:30

Multiple synchrotron radiation X-ray analyses of radioactive microparticles emitted fromthe Fukushima Nuclear Accident
ONO, Takahiro1∗ ; IIZAWA, Yushin1 ; ABE, Yoshinari1 ; NAKAI, Izumi1 ; TERADA, Yasuko2 ;SATO, Yukihiko3 ; NINOMIYA, Kazuhiko4 ; ADACHI, Kouji5 ; IGARASHI, Yasuhito5
1Faculty of science,Tokyo university of science, 2 JASRI/SPring-8, 3 Tsukuba university, 4 Osaka university, 5 Meteorological Research Institute
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred in 2011 is the largest nuclear incident since the 1986
Chernobyl disaster and has been rated at the maximum level of 7 on the International Nuclear Event Scale. Large amounts ofradioactive materials were released into the environment during the accident. Although more than 4 years have passed since theaccident, the radioactive materials emitted from the FDNPP have been detectable in the environment. However, little is known
about the physical and chemical natures of radioactive materials released during the early stages of the accident. We previously
found spherical aerosol microparticles (∼2 µm, diameter) containing radioactive Cs in aerosol samples collected on March 14thand 15th, 2011, in Tsukuba1) . These radioactive microparticles have been commonly called “Cs-balls” . Synchrotron radiation(SR) X-ray microbeam analysis revealed the detailed chemical nature of the Cs-balls in a nondestructive manner, resulting in
better understanding of what occurred in the plant during the early stages of the accident2) . SR-µ-X-ray fluorescence (XRF)
analysis of the Cs-balls detected U as a nuclear fuel and various heavy elements derived from fission products (FPs) of the fuel.
In addition, SR-µ-X-ray absorption near-edge structure (XANES) and SR-µ-X-ray diffraction (XRD) analysis revealed that theCs-balls are glassy materials.
This study aims to demonstrate a hypothesis that water-insoluble radioactive materials similar to the Cs-ball had been extensively emitted to the environment from the FDNPP. We then focused on sediments in a swimming pool near FDNPP to find out
radioactive microparticles. Total six spherical radioactive microparticles were separated from a sediment collected at an outdoor
swimming pool located in Namie Town, Fukushima Prefecture, Japan. The SR experiments were carried out at BL37XU, a hard
X-ray undulator beamline of SPring-8, Japan Synchrotron Radiation Research Institute (JASRI).
Gamma-ray spectra of the six particles detected both 134 Cs and 137 Cs in each particle with activity ratios of ∼1 (decay corrected as of March 2011). It is thus confirmed that these particles are radioactive ones derived from the FDNPP accident.
SR-µ-XRF analysis of the particles detected the following 13 heavy elements: Mn, Fe, Zn, Rb, Zr, Mo, Ag, Sn, Sb, Te, Cs, Ba
and Pb. In addition, U was detected in one of the particles, which was further confirmed by U L3 -edge XANES analysis. We
conclude that the U fuel, FPs, and components of the reactors are very likely the sources of the elements identified within thesix radioactive microparticles, although further investigation will be needed to confirm their sources. We assume that, because
these elements could have originated from multiple sources, they were melted together during the accident and eventually formed
spherical microparticles. SR-µ-XANES spectra of Fe, Zn, Mo, and Sn K-edges for the individual particles revealed that they
were present at high oxidation states, i.e., Fe3+ , Zn2+ , Mo6+ , and Sn4+ in the glass matrix, confirmed by SR-µ-X-ray diffraction analysis. These chemical natures of the six radioactive microparticles separated from the sediment collected in Fukushima
Prefecture are in good agreement with those of the Cs-ball, the radioactive aerosol particle collected in Tsukuba after the FDNPP accident, revealed in our previous investigation2) . This study thus suggested a high possibility that water-insoluble glassy
radioactive microparticles containing U fuel and FPs were emitted from the FDNPP and fell to a widespread area over the East
Japan. In addition, we concluded that these radioactive microparticles in the glassy state may remain in the environment longer
than those emitted as water-soluble aerosol particles containing the radioactive Cs.
1) K. Adachi et al.: Scientific Reports 3, 2554 (2013)
2) Y. Abe et al.: Analytical Chemistry 87, 8521-8525 (2014).

Keywords: Fukushima Daiichi Nuclear Power Plant accident, Radioactive material, Synchrotron radiation X-ray analysis,
aerosol

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MAG38-P09

Room:Convention Hall

Time:May 26 18:15-19:30

Altitude dependent radioactive contamination in the mountain area of Tochigi and Fukushima
prefectures
HOSOSHIMA, Mutsuo1∗ ; KANEYASU, Naoki2
1

Mibu highschool, 2 National Institute of Advance Industrial Science and Technology

Introduction
During the accident of Fukushima Dai-ichi Power Plant (FDNPP), the discharged radionuclides into the air were transported
to the wide area of Eastern Japan and contaminated land and marine environments. For the plain areas where most population
resides, the horizontal distribution contamination has been surveyed intensely. On the other hand, in the mountain areas where
less populated, the studies were limited. Airborne surveys conducted by the Ministry of Education, Culture, Sports, Science, andTechnology, have mapped the contaminated are in Eastern Japan widely, but the obtained horizontal resolution is relatively low,i.e., the horizontally averaged value from a diameter ranging between 300 and 1,500 m underneath the aircraft.
We measured the altitude and horizontal distribution of ambient gamma dose-rate (GDR) in mountain areas of Tochigi and
Fukushima prefectures on foot by use of a portable gamma ray detector carried along. With the results, the contamination patterns are categorized and the possible mechanisms that formed them are proposed.
Results and Discussion
Instrumentation used in the survey is described in Kaneyasu and Hososhima (2015). According to the altitudinal distributionof ambient GDR and the location where the contamination is intense, we classified the contamination pattern into four categories.
[Type A] In Nikko-Kirifuri mountainous area, ambient GDR distributions have same altitudinal pattern showing the maxima
around 900-1400 m (ASL). In particular, sharp peaks were observed at approx. 1,040-1,080 m ASL at Mt. Nakimushi-yama,
Kirifuri Highland, Mt. Gassan, and Mt. Bizen-tateyama. This area is about 20km in width and located approx. 120 km north ofthe central part of Tokyo and 160 km southwest of FDNPP. The variance of GDR is large at the GDR peaks. A hypothesis on theformation mechanism is presented in the separate presentation in the oral session (Kaneyasu and Hososhima, 2015).
[Type B] In Aso-Maenikko mountain area, the altitudinal distribution pattern of GDR is vague and showed constant value withsmall variance.
[Type C] In Mt. Takahata-yama and Mt. Gonta-kurayama (located in the southern end of Oh-u mountain range), the contamination intensity was intermediate, and any particular altitudinal distribution pattern was not observed.
[Multiple types integrated and other formation mechanism] In Abukuma mountain range, which is located closer to the FDNPP, several patterns are identified. Sharp peaks in the altitudinal distribution of GDR exist in Mt. Kamakura-dake and Mt.
Yomogida-dake (Type A). The mountain ridge between Mt. Kittoya-san Mt Futatsuya-san, significantly high GDR values wereobserved (similar to Type A). However, the south-southwest face of Mt. Futatsuya-san (the opposite side from the FDNPP),
the GDR was smaller one order of magnitude than the ridge and had constant values with small variance (Type B). In the othermountains in Abukuma mountain range, the ridge of the mountains were often contaminated intensely. In some mountains, TypeA contamination were observed with an additional contamination localized in the upper part of valleys.
Simple dichotomy paradigm of dry and wet deposition is not enough to explain the formation of these various types of distribution. We presume that Type A is caused by cloud/fog deposition (Kaneyasu and Hososhima), Type B is the result of dry
deposition, and Type C is formed by wet deposition. In Abukuma mountain range, where is close to the FDNPP, the integrationof Type A, B, and C may have occurred in many mountains due to the arrivals of several waves of radionuclides in the form ofclouds, aerosol state (dry deposition), and precipitations, followed by the modification due to experiencing ’weathering effect’.
References
Kaneyasu, N. and Hososhima M. (2015), A new insight into the deposition mechanism of airborne radionuclides from the
Fukushima accident, Proceedings of JpGU 2015.

Keywords: cloud/fog deposition, occult deposition, altitude dependent radioactive contamination, ambient gamma dose-rate

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MAG38-P09

Room:Convention Hall

Time:May 26 18:15-19:30

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MAG38-P10

Room:Convention Hall

Time:May 26 18:15-19:30

The distributions and behavior of radiocaesium according to grain sizes in sediments after
the FDNPS accident
FUKUDA, Miho1∗ ; YAMAZAKI, Shinnosuke1 ; AONO, Tatsuo1 ; YOSHIDA, Satoshi1 ; NAGANUMA, Sho2 ;KUBO, Atsushi2 ; SHIMADA, Keishi2 ; TAKASAWA, Nobue2 ; HOSAKA, Takuji2 ; SATO, Kenichiro3 ;YAMAGUCHI, Seiya2 ; ITO, Yukari2 ; ISHIMARU, Takashi2 ; KANDA, Jota2
1

National institute of Radiological Science (NIRS), 2 Tokyo University of Marine Science and Technology, 3 Marine Works JapanThe Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident in March 2011 led to releases of large amounts of artificial
radionuclides including 134 Cs and 137 Cs (radiocaesium) into the environment (ocean, atmosphere and land). As of February
2015, based on TEPCO’s monitoring data, 137 Cs activities in seawater had exponentially decreased more than 10 times compared to the activities before the FDNPS accident. However, the activities in sediments have decreased more slowly than thosein seawater and they have had large fluctuations. Some controversy remains about the radiocaesium transition process fromseawater to sediments and its behavior after accumulation. In soil and sediments, the radiocaesium activities for finer grain sizes
tend to be higher because specific surface areas of smaller grains are larger (e.g. He and Walling, 1996). Therefore, it is necessary to consider the differences of grain size composition in sediments in order to compare distributions of lateral and verticalradiocaesium activities and inventories in coastal sediments, which are commonly of several grain sizes. This study was aimed
at elucidating spatial variation and the behavior of radiocaesium activities and inventories for different grain sizes in sediments
collected in the Fukushima coastal area in May 2014.
The sediments were divided into four classes based on grain sizes using several mesh sizes: granules (grain size larger than2 mm); very coarse to coarse sand particles (1 to 2 mm); coarse to very fine sand particles (0.063 to 1 mm); and silt particles(smaller than 0.063 mm). Radionuclides were measured for each grain size class using high-purity gamma ray spectrometry andthen corrected to the sampling date.
In collected sediments, the only artificial radionuclides detected were radiocaesium. In the surface layer of sediments (0-5cm), the percentage ranges were: granules, 0 to 23 %; very coarse to coarse sand particles, 0 to 39 %; coarse to very fine sandparticles, 38 to 98 %; and silt particles, 0 to 46 %. The137 Cs activities for coarse to very fine sand particles and silt particles
ranged from 8.5 to 609 Bq kg−1 -dry and 18 to 1487 Bq kg−1 -dry, respectively and the latter particle activities were higher thanthose for the former particles in most layers. The 137 Cs inventories for coarse to very fine sand particles ranged from 972 to 3285
Bq m−2 and those in the water depth range of 100 to 150 m were highest. The 137 Cs inventories for silt particles ranged from1387 to 31321 Bq m−2 and they decreased with increasing water depth.The fractions of 137 Cs inventories in the uppermost layerof sediments (0-3 cm) to those in the surface layer of sediment (F’0−3 ) for coarse to very fine sand particles and silt particles
were 0.33 to 0.88 and 0.24 to 0.77, respectively. The F’0−3 values for silt particles were lower than those for coarse to very finesand particles. It appeared that silt particles more easily adsorbed radiocaesium that had been transported to a deep sedimentlayer compared to coarse to very fine sand particles.
He, Q., and Walling, D., E. (1996) Journal of Environ. Radioact, 20 (2), 117-137.
Keywords: radiocaesium, Fukushima coastal area, marine sediment, grain size, FDNPS

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MAG38-P11

Room:Convention Hall

Time:May 26 18:15-19:30

Evaluation of wide area inventory and migration rate of radioactive caesium based on
USLE model
NAKAMURA, Noriko1∗ ; ONDA, Yuichi1 ; KONDOH, Akihiko2 ; WAKIYAMA, Yoshifumi1
1

Center for research in isotopes and environmental dynamics, University of Tsukuba, 2 Center for Environmental Remote Sensing, Chiba University
The radioactive contaminations which flowed out from the Fukushima nuclear power plant first due to the Great East Japan
Earthquake are still contained great amounts in the soil around the nuclear power plant, and it causes serious concern over thehealth of inhabitants. In this study, for the prediction of the migration dynamics of radioactive caesium deposited on the soil
around the nuclear power plant, the time-spatial variation of deposition and washoff ratio of 137 Cs up to the present was calculated based on the soil erosion rate obtained from the USLE and the initial 137 Cs inventory obtained by the airborne monitoring.
The parameters needed for calculation of USLE were determined from the observation results obtained from the study sites
established in the Fukushima prefecture. The estimation results from the calculation were compared with the measurements of137
Cs washoff ratio obtained from the rivers around the nuclear power plant. As the result, calculated 137 Cs washoff rate wasapproximately underestimate than the measured rate however was consistent qualitatively. And in the view of landuse, in thecatchment of Abukuma river, the ratio of washoff from the paddy was large in the early period from the accident, however, as
time goes on, the ratio of washoff from the paddy has decreased and the ratio of other landuses has increased.
Keywords: the Great East Japan Earthquake, Fukushima nuclear power plant accident, caesium 137, USLE, soil erosion, migration of radioactive contamination

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