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Journal Articles

A Model intercomparison of atmospheric $$^{137}$$Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident, phase III; Simulation with an identical source term and meteorological field at 1-km resolution

Sato, Yosuke*; Sekiyama, Tsuyoshi*; Fang, S.*; Kajino, Mizuo*; Qu$'e$rel, A.*; Qu$'e$lo, D.*; Kondo, Hiroaki*; Terada, Hiroaki; Kadowaki, Masanao; Takigawa, Masayuki*; et al.

Atmospheric Environment; X (Internet), 7, p.100086_1 - 100086_12, 2020/10

The third model intercomparison project for investigating the atmospheric behavior of $$^{137}$$Cs emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident (FDNPP-MIP) was conducted. A finer horizontal grid spacing (1 km) was used than in the previous FDNPP-MIP. Nine of the models used in the previous FDNPP-MIP were also used, and all models used identical source terms and meteorological fields. Our analyses indicated that most of the observed high atmospheric $$^{137}$$Cs concentrations were well simulated, and the good performance of some models improved the performance of the multi-model ensemble. The analyses also confirmed that the use of a finer grid resolution resulted in the meteorological field near FDNPP being better reproduced. The good representation of the wind field resulted in the reasonable simulation of the narrow distribution of high deposition amount to the northwest of FDNPP and the reduction of the overestimation over the area to the south of FDNPP. In contrast, the performance of the models in simulating plumes observed over the Nakadori area, the northern part of Gunma, and the Tokyo metropolitan area was slightly worse.

Journal Articles

Intercomparison of numerical atmospheric dispersion prediction models for emergency response to emissions of radionuclides with limited source information in the Fukushima Dai-ichi Nuclear Power Plant accident

Iwasaki, Toshiki*; Sekiyama, Tsuyoshi*; Nakajima, Teruyuki*; Watanabe, Akira*; Suzuki, Yasushi*; Kondo, Hiroaki*; Morino, Yu*; Terada, Hiroaki; Nagai, Haruyasu; Takigawa, Masayuki*; et al.

Atmospheric Environment, 214, p.116830_1 - 116830_11, 2019/10

 Times Cited Count:1 Percentile:73.29(Environmental Sciences)

The utilization of numerical atmospheric dispersion prediction (NDP) models for accidental discharge of radioactive substances was recommended by a working group of the Meteorological Society of Japan. This paper is to validate the recommendation through NDP model intercomparison in the accidental release from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Emission intensity is assumed to be constant during the whole forecast period for the worst-case scenario unless time sequence of emission is available. We expect to utilize forecasts of surface air contaminations for preventions of inhalations of radioactive substances, and column-integrated amounts for mitigation of radiation exposure associated with wet deposition. Although NDP forecasts have ensemble spread, they commonly figure out relative risk in space and time. They are of great benefit to disseminating effective warnings to public without failure. The multi-model ensemble technique may be effective to improve the reliability.

Journal Articles

Dispersion modelling of radioactive materials

Nagai, Haruyasu; Yamazawa, Hiromi*

Environmental Contamination from the Fukushima Nuclear Disaster; Dispersion, Monitoring, Mitigation and Lessons Learned, p.230 - 242, 2019/08

An overview of SPEEDI is provided in the context of it development, functions, and role in the framework of nuclear emergency management. Thereafter, we examine how it was used and how it should be used for the Fukushima Daiichi Nuclear Power Station accident from a system developer perspective. We believe that our review can provide lessons or tasks for improving the prediction system and for considering better utilization of the system; it is also beneficial to consider reconstructing the framework of nuclear emergency management. Furthermore, we hope this review will prove useful in understanding and effectively using the atmospheric dispersion predictions from the system in the case of a similar accident in the future.

Journal Articles

Model intercomparison of atmospheric $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident; Simulations based on identical input data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

Journal of Geophysical Research; Atmospheres, 123(20), p.11748 - 11765, 2018/10

 Times Cited Count:9 Percentile:29.71(Meteorology & Atmospheric Sciences)

A model intercomparison of the atmospheric dispersion of $$^{137}$$Cs emitted following the Fukushima Daiichi Nuclear Power Plant accident was conducted by 12 models to understand the behavior of $$^{137}$$Cs in the atmosphere. The same meteorological data, horizontal grid resolution, and an emission inventory were applied to all the models to focus on the model variability originating from the processes included in each model. The multi-model ensemble captured 40% of the observed $$^{137}$$Cs events, and the figure-of-merit in space for the total deposition of $$^{137}$$Cs exceeded 80. Our analyses indicated that the meteorological data were most critical for reproducing the $$^{137}$$Cs events. The results also revealed that the differences among the models were originated from the deposition and diffusion processes when the meteorological field was simulated well. However, the models with strong diffusion tended to overestimate the $$^{137}$$Cs concentrations.

Journal Articles

Current state of atmospheric and oceanic environmental researches on the Fukushima Daiichi nuclear accident; What is known about/from the accident

Aoyama, Michio*; Yamazawa, Hiromi*; Nagai, Haruyasu

Nippon Genshiryoku Gakkai-Shi, 60(1), p.46 - 50, 2018/01

no abstracts in English

Journal Articles

Dispersion modeling of radioactive materials

Nagai, Haruyasu; Yamazawa, Hiromi*

Gempatsu Jiko Osen; Fukushima Daiichi Gempatsu No Chikyu Kagakuteki Sokumen, p.175 - 187, 2014/09

no abstracts in English

Journal Articles

Validation of a Lagrangian atmospheric dispersion model against middle-range scale measurements of $$^{85}$$Kr concentration in Japan

Terada, Hiroaki; Nagai, Haruyasu; Yamazawa, Hiromi*

Journal of Nuclear Science and Technology, 50(12), p.1198 - 1212, 2013/12

 Times Cited Count:7 Percentile:41.35(Nuclear Science & Technology)

The Lagrangian atmospheric dispersion model of the nuclear emergency response system WSPEEDI-II was validated with the measured $$^{85}$$Kr concentrations in tens-of- to hundreds-of-km (middle-range) scale area by conducting dispersion simulations with the release rate from the Rokkasho reprocessing plant in Japan. The calculated weekly concentrations of $$^{85}$$Kr during April and September in 2008 agreed with the measurements within a factor of two. However, the sensitivity analysis to horizontal grid resolution of the meteorological model ranging from 2 to 54 km showed the calculated results had the dependency on the grid resolution. An empirical modification of the horizontal diffusion parameter was attempted based on the sensitivity analysis to reduce the redundant diffusion effect in dispersion simulations with relatively high grid resolution. The modified parameter contributed to reduce the dependency of calculated concentrations on the grid resolution.

Journal Articles

Reconstruction of the atmospheric releases of $$^{131}$$I and $$^{137}$$Cs resulting from the Fukushima Daiichi Nuclear Power Plant accident

Chino, Masamichi; Terada, Hiroaki; Katata, Genki; Nagai, Haruyasu; Nakayama, Hiromasa; Yamazawa, Hiromi*; Hirao, Shigekazu*; Ohara, Toshimasa*; Takigawa, Masayuki*; Hayami, Hiroshi*; et al.

NIRS-M-252, p.127 - 135, 2013/03

We estimated the release rates and total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere from March 12 to April 5, 2011. The applied method is a reverse estimation by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq/h). It calculates release rates of radionuclides (Bq/h) by dividing measured air concentrations of $$^{131}$$I and $$^{137}$$Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10$$^{15}$$ Bq/h of $$^{131}$$I, occurred on March 15, following to relatively small releases, 10$$^{13}$$ $$sim$$ 10$$^{14}$$ Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10$$^{14}$$ Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10$$^{11}$$ $$sim$$ 10$$^{12}$$ Bq/h of $$^{131}$$I on the beginning of April. The estimated source term was examined on the point of the time trend, total releases and the ground depositions of $$^{137}$$Cs by using different atmospheric dispersion models with above source term and compared them with observed $$^{137}$$Cs deposition distribution. These examinations showed that the estimated source term was reasonably accurate during the period when the plume flowed over land in Japan.

Journal Articles

Preliminary estimation of release amounts of $$^{131}$$I and $$^{137}$$Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere

Chino, Masamichi; Nakayama, Hiromasa; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki; Yamazawa, Hiromi*

Journal of Nuclear Science and Technology, 48(7), p.1129 - 1134, 2011/07

 Times Cited Count:589 Percentile:0.02(Nuclear Science & Technology)

The release amounts of $$^{131}$$I and $$^{137}$$Cs into the atmosphere due to the Fukushima Daiichi Nuclear Power Plant is preliminary estimated by coupling monitoring data on air concentrations and atmospheric dispersion simulation assuming unit release rate (1 Bq/h). The estimated results show that the large amount of release, the peak value of about 10$$^{16}$$ Bq/h of $$^{131}$$I on March 15, continued for a week after the accident, and, after March 23, the release rates have generally been declining to the order of 10$$^{11}$$ to 10$$^{12}$$ Bq/h. The total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere are estimated about 1.5$$times$$10$$^{17}$$ Bq and 1.2$$times$$10$$^{16}$$ Bq.

Journal Articles

Estimation of $$^{222}$$Rn flux and its effect on the atmospheric $$^{222}$$Rn concentration at Hachijo-jima island, Japan

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Iida, Takao*

Hoken Butsuri, 45(3), p.270 - 277, 2010/09

Measurements of $$^{222}$$Rn flux from the ground and $$^{226}$$Ra content in soil were made on Hachijo-jima, which is a solitary island in the Pacific about 200 km to the south of the main island of Japan, to evaluate effect of locally exhaled $$^{222}$$Rn to the surface air concentration of $$^{222}$$Rn measured on this island. Averages of $$^{222}$$Rn flux and $$^{226}$$Ra content in dry soil were 0.88 mBq m$$^{-2}$$ s$$^{-1}$$ and 6.8 Bq kg$$^{-1}$$ at Hachijo-jima and 9.7 mBq m$$^{-2}$$ s$$^{-1}$$ and 23.2 Bq kg$$^{-1}$$ at Nagoya, respectively. The low level $$^{226}$$Ra content in soil is one of main causes for the small $$^{222}$$Rn flux at the island. With this $$^{222}$$Rn flux, the contribution of locally exhaled $$^{222}$$Rn from the island was estimated by a simple model to occur at concentration of 0.035 to 0.072 Bq m$$^{-3}$$ (relative contribution is 4 to 12%) under typical nocturnal condition. Under diurnal condition effect is lower than that of nocturnal condition. This local $$^{222}$$Rn component is negligible as compared with concentration of long-range transported $$^{222}$$Rn of 0.5 to 3 Bq m$$^{-3}$$.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Journal Articles

The Change of the carbon isotopic ratio in the CO$$_{2}$$ derived from soil organic matter decomposition over the incubation time

Moriya, Koichi*; Moriizumi, Jun*; Yamazawa, Hiromi*; Koarashi, Jun; Atarashi-Andoh, Mariko

KURRI-KR-153, p.53 - 59, 2010/03

To understand the decomposition mechanism in the soil, we researched the relationship between compositions of SOM and CO$$_{2}$$ derived from SOM decomposition (SOMD-CO$$_{2}$$) by using $$^{13}$$C and $$^{14}$$C. With the soil incubation, we measured CO$$_{2}$$ production rates of soil and carbon isotopic ratios in SOMD-CO$$_{2}$$. The CO$$_{2}$$ production rates decreased rapidly at the beginning of incubation, and then decreased slowly. On the other hand, $$delta$$$$^{13}$$C$$_{rm SOMD-CO2}$$ before incubation was larger than $$delta$$$$^{13}$$C$$_{rm SOM}$$. After 40-70 days of incubation, $$delta$$$$^{13}$$C$$_{rm SOMD-CO2}$$ became smaller than $$delta$$$$^{13}$$C$$_{rm SOM}$$, and then $$delta$$$$^{13}$$C$$_{rm SOMD-CO2}$$ after 120-170 days approached $$delta$$$$^{13}$$C$$_{rm SOM}$$. We consider these results as follows. SOM is composed of three components, rapidly decomposable SOM that has large $$delta$$$$^{13}$$C, slowly decomposable SOM that has small $$delta$$$$^{13}$$C and passive SOM that has the same value as $$delta$$$$^{13}$$C$$_{rm SOM}$$. With the progress of soil decomposition, the dominant component in SOMD-CO$$_{2}$$ changed. Therefore, $$delta$$$$^{13}$$C$$_{rm SOMD-CO2}$$ changed too.

Journal Articles

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Taiki Kankyo Gakkai-Shi, 44(1), p.42 - 51, 2009/01

Monitoring network of $$^{222}$$Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations $$^{222}$$Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, $$^{222}$$Rn concentrations level was very low. Seasonal variations of the $$^{222}$$Rn concentration show that $$^{222}$$Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric $$^{222}$$Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric $$^{222}$$Rn at Hachijo-jima has much to do with transport pathway of air.

Journal Articles

Reliability evaluation of SPEEDI's prediction by comparison with calculated results based on meteorological observation data

Rintsu, Yuko*; Serizawa, Shigeru*; Yamazaki, Tetsuo*; Umeyama, Nobuaki*; Moriuchi, Shigeru*; Handa, Hiroyuki*; Onishi, Ryoichi*; Takemura, Morio*; Chino, Masamichi; Nagai, Haruyasu; et al.

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

no abstracts in English

Journal Articles

Development of three-dimensional numerical model for $$^{222}$$Rn and its decay products coupled with a mesoscale meteorological model, 1; Model description and validation

Nishizawa, Masato; Nagai, Haruyasu; Chino, Masamichi; Moriizumi, Jun*; Yoshioka, Katsuhiro*; Okura, Takehisa; Yamazawa, Hiromi*; Iida, Takao*; Mukai, Hitoshi*; Tojima, Yasunori*; et al.

Journal of Nuclear Science and Technology, 44(11), p.1458 - 1466, 2007/11

 Times Cited Count:4 Percentile:65.57(Nuclear Science & Technology)

A three-dimensional Eulerian numerical model for $$^{222}$$Rn and its decay products coupled with a mesoscale meteorological model has been developed and applied to the reproduction of the daily and monthly variations of $$^{222}$$Rn concentration, the monthly variation of $$^{210}$$Pb deposition in Japan and the temporal variation of $$gamma$$ dose rate after the cold front passage in the coastal area of the Japan Sea for the verification of model capability. The results are as follows: (1) The model reproduced the monthly variation of surface $$^{222}$$Rn concentration in remote islands, but underestimated inland concentration due to coarse vertical resolution near the surface of the model. (2) The model reproduced the seasonal variation of the observed and the long-term yearly averaged $$^{210}$$Pb depositions as long as precipitations are predicted precisely. (3) The model reproduced the rise of $$gamma$$ dose rate in precipitation accompanied with the cold front passage. In particular, $$^{222}$$Rn decay products in melted snow and graupel contributed the rise of $$gamma$$ dose rate.

Journal Articles

Suppression of radon exhalation from soil by covering with clay-mixed soil

Ota, Masakazu*; Iida, Takao*; Yamazawa, Hiromi*; Nagara, Shuichi; Ishimori, Yuu; Sato, Kazuhiko; Tokizawa, Takayuki

Journal of Nuclear Science and Technology, 44(5), p.791 - 800, 2007/05

 Times Cited Count:12 Percentile:31.82(Nuclear Science & Technology)

A study on the effectiveness of clay-mixed soil as a barrier against radon exhalation from soil surface was carried out at a closed uranium mine in Japan. Continuous observations of radon flux at a clay-covered soil surface and a bare soil surface, radon concentration in soil air and soil moisture content were carried out for 80 days. The mean of radon flux of the clay-covered plot was one fifth of that of the bare plot. This result indicates that clay-mixed soil worked effectively for reduction of radon exhalation from the soil surface. A numerical analysis with a one-dimensional radon transport model for unsaturated soil was carried out to evaluate the effectiveness of the barrier under dry weather conditions. Calculation results suggested that the barrier works effectively even under the dry condition.

Journal Articles

Diurnal and seasonal variations in $$^{222}$$Rn concentration profile in soil

Iskandar, D.*; Yamazawa, Hiromi*; Yamasoto, Kotaro; Ota, Masakazu*; Koarashi, Jun; Moriizumi, Jun*; Bunawas*; Iida, Takao*

Hoken Butsuri, 42(1), p.98 - 104, 2007/03

The $$^{222}$$Rn concentrations in soil and $$^{222}$$Rn flux were measured at 6 depths in soil to analyze the seasonal- day-to-day and diurnal variations. The variations of $$^{222}$$Rn concentrations in soil were larger in shallow depths. It seems that the $$^{222}$$Rn concentration in soil during night-time was slightly lower than day-time especially at depth of 15 cm. The precipitation may have affected the concentration insoil differently depending on its amounts. The large decrease in air pressure during one day increased the concentration in soil at shallow soil layers. The effect of soil water content on $$^{222}$$Rn concentration in soil was also observed.

Journal Articles

Evaluation of aerosol sizing characteristic of an impactor using imaging plate technique

Rahman, N. M.*; Iida, Takao*; Saito, Fumihiro; Koarashi, Jun; Yamasaki, Keizo*; Yamazawa, Hiromi*; Moriizumi, Jun*

Radiation Protection Dosimetry, 123(2), p.171 - 181, 2007/02

 Times Cited Count:11 Percentile:34.67(Environmental Sciences)

no abstracts in English

Journal Articles

Development of a source term estimation method for nuclear emergency by long-range atmospheric dispersion simulations

Furuno, Akiko; Chino, Masamichi; Yamazawa, Hiromi*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 5(3), p.229 - 240, 2006/09

This paper describes a method of estimating source term, i.e., location, period and amount of atmospheric release of radioactive material in real-time during nuclear emergency. This method consists of: (1) trial simulations of atmospheric dispersions on the possible combinations of these parameters and (2) statistical comparison of model predictions with off-site measurements of air concentrations of radionuclides and/or air does rates from monitoring stations, to find a set of release condition providing model predictions that best fit to the measurement. A parallel execution method for efficiently processing many possible initial conditions is also developed. The performance of this method is favorably evaluated by a verification study by using the dataset from European Tracer Experiment.

Journal Articles

Experimental verification for real-time environmental emergency response system; WSPEEDI by European tracer experiment

Furuno, Akiko; Terada, Hiroaki; Chino, Masamichi; Yamazawa, Hiromi*

Atmospheric Environment, 38(40), p.6989 - 6998, 2004/12

 Times Cited Count:20 Percentile:54.05(Environmental Sciences)

We have been developing the computer-based emergency response system WSPEEDI which predicts long-range atmospheric dispersion of radionuclides discharged into the atmosphere due to a nuclear accident. The first version of WSPEEDI has a shortage that the spatial and temporal variation of the atmospheric boundary layer was very simply parameterized. Therefore we have developed the new version accomplished with the atmospheric dynamic model, in which the turbulent diffusivity in the mixing layer is calculated with a turbulence closure model. This paper describes the results of performance evaluation of the new version of WSPEEDI by comparing the simulation results with the European Tracer Experiment data. As a result of the verification, it was shown that the increase in the horizontal resolution largely improved the accuracy of the model prediction. The use of the turbulence closure model instead of the simple parameterization largely contributed to improve reproducibility of horizontal distribution of plumes.

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