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

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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

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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

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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

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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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