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Saito, Tatsuo; Yamazawa, Hiromi*; Mochizuki, Akihito
Journal of Environmental Radioactivity, 255, p.107035_1 - 107035_14, 2022/12
Times Cited Count：0 Percentile：0.00(Environmental Sciences)The seasonal variation of dissolved U (DU) in Lake Biwa was reproduced by the following model and parameter research. The introduced models are the water-DU mass balance, and the ion exchange between UO
and H
on the lakeshore soil. The optimized parameters were the CEC of the lakeshore, TU as the sum of DU and AU (soil adsorbed U), kads and kdes as the first order reaction rate coefficients during rapid soil adsorption and desorption of U, respectively. Tabulated by the chemical equilibria constituting DU and analyzed the contribution of each chemical species, it is shown that the seasonal variation of DU is caused by the seasonal variation of pH. A correction to the ion-exchange equilibrium to shift to first order rate reaction only when the daily AU ratio increased above kads or decreased below kdes, improved the reproducibility of DU measurements and reproduced the delay of the DU peak from the pH peak.
Moriguchi, Yuichi*; Sato, Yosuke*; Morino, Yu*; Goto, Daisuke*; Sekiyama, Tsuyoshi*; Terada, Hiroaki; Takigawa, Masayuki*; Tsuruta, Haruo*; Yamazawa, Hiromi*
KEK Proceedings 2021-2, p.21 - 27, 2021/12
no abstracts in English
-treated column study of Hanford 300 area sediment using a simple ion exchange and immobile domain modelSaito, Tatsuo; Sato, Kazuhiko; Yamazawa, Hiromi*
Journal of Environmental Radioactivity, 237, p.106708_1 - 106708_9, 2021/10
Times Cited Count：2 Percentile：9.66(Environmental Sciences)We succeeded at numerical reproduction of dissolved U concentrations from column experiments with PO-treated Hanford 300 Area sediment. The time-series curves of dissolved U concentrations under various Darcy flow rate conditions were reproduced by the numerical model in the present study through optimization of the following parameters:(i) the mass of U in mobile domain (on surface soil connected to the stream) and the rest of the total U left as precipitation in immobile domain (isolated in deep soil);(ii) the mixing ratio between immobile and mobile domains, to fit the final recovering curve of concentration; and (iii) the cation exchange capacity (CEC
) and equilibrium constant (k) of the exchange reaction of UO and H on simulated soil surface (
), to fit the transient equilibrium concentration, forming the bed of the bathtub curve.
Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident, phase III; Simulation with an identical source term and meteorological field at 1-km resolutionSato, Yosuke*; Sekiyama, Tsuyoshi*; Fang, S.*; Kajino, Mizuo*; Qu
rel, A.*; Qulo, 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 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 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.
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：6 Percentile：22.99(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.
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.
Cs from the Fukushima Daiichi Nuclear Power Plant accident; Simulations based on identical input dataSato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qulo, D.*; et al.
Journal of Geophysical Research; Atmospheres, 123(20), p.11748 - 11765, 2018/10
Times Cited Count：45 Percentile：85.33(Meteorology & Atmospheric Sciences)A model intercomparison of the atmospheric dispersion of Cs emitted following the Fukushima Daiichi Nuclear Power Plant accident was conducted by 12 models to understand the behavior of 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 Cs events, and the figure-of-merit in space for the total deposition of Cs exceeded 80. Our analyses indicated that the meteorological data were most critical for reproducing the 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 Cs concentrations.
Aoyama, Michio*; Yamazawa, Hiromi*; Nagai, Haruyasu
Nihon Genshiryoku Gakkai-Shi ATOMO
, 60(1), p.46 - 50, 2018/01
no abstracts in English
Nagai, Haruyasu; Yamazawa, Hiromi*
Gempatsu Jiko Osen; Fukushima Daiichi Gempatsu No Chikyu Kagakuteki Sokumen, p.175 - 187, 2014/09
no abstracts in English
Kr concentration in JapanTerada, Hiroaki; Nagai, Haruyasu; Yamazawa, Hiromi*
Journal of Nuclear Science and Technology, 50(12), p.1198 - 1212, 2013/12
Times Cited Count：11 Percentile：62.77(Nuclear Science & Technology)The Lagrangian atmospheric dispersion model of the nuclear emergency response system WSPEEDI-II was validated with the measured 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 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.
I and Cs resulting from the Fukushima Daiichi Nuclear Power Plant accidentChino, 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 I and 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 I and Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10
Bq/h of I, occurred on March 15, following to relatively small releases, 10
10
Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10 Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10
10
Bq/h of 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 Cs by using different atmospheric dispersion models with above source term and compared them with observed 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.
I and Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphereChino, 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：752 Percentile：99.97(Nuclear Science & Technology)The release amounts of I and 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
Bq/h of 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 to 10 Bq/h. The total amounts of I and Cs discharged into the atmosphere are estimated about 1.5
10
Bq and 1.210 Bq.
Rn flux and its effect on the atmospheric Rn concentration at Hachijo-jima island, JapanOkura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Iida, Takao*
Hoken Butsuri, 45(3), p.270 - 277, 2010/09
Measurements of Rn flux from the ground and 
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 Rn to the surface air concentration of Rn measured on this island. Averages of Rn flux and Ra content in dry soil were 0.88 mBq m
s
and 6.8 Bq kg at Hachijo-jima and 9.7 mBq m s and 23.2 Bq kg at Nagoya, respectively. The low level Ra content in soil is one of main causes for the small Rn flux at the island. With this Rn flux, the contribution of locally exhaled Rn from the island was estimated by a simple model to occur at concentration of 0.035 to 0.072 Bq m
(relative contribution is 4 to 12%) under typical nocturnal condition. Under diurnal condition effect is lower than that of nocturnal condition. This local Rn component is negligible as compared with concentration of long-range transported Rn of 0.5 to 3 Bq m.
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 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 Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, Rn concentrations level was very low. Seasonal variations of the Rn concentration show that 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 Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric Rn at Hachijo-jima has much to do with transport pathway of air.
derived from soil organic matter decomposition over the incubation timeMoriya, 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 derived from SOM decomposition (SOMD-CO) by using C and C. With the soil incubation, we measured CO production rates of soil and carbon isotopic ratios in SOMD-CO. The CO production rates decreased rapidly at the beginning of incubation, and then decreased slowly. On the other hand, 
C
before incubation was larger than C
. After 40-70 days of incubation, C became smaller than C, and then C after 120-170 days approached C. We consider these results as follows. SOM is composed of three components, rapidly decomposable SOM that has large C, slowly decomposable SOM that has small C and passive SOM that has the same value as C. With the progress of soil decomposition, the dominant component in SOMD-CO changed. Therefore, C changed too.
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 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 Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, Rn concentrations level was very low. Seasonal variations of the Rn concentration show that 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 Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric Rn at Hachijo-jima has much to do with transport pathway of air.
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
Rn and its decay products coupled with a mesoscale meteorological model, 1; Model description and validationNishizawa, 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：5 Percentile：36.73(Nuclear Science & Technology)A three-dimensional Eulerian numerical model for 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 Rn concentration, the monthly variation of 
Pb deposition in Japan and the temporal variation of 
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 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 Pb depositions as long as precipitations are predicted precisely. (3) The model reproduced the rise of dose rate in precipitation accompanied with the cold front passage. In particular, Rn decay products in melted snow and graupel contributed the rise of dose rate.
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：18 Percentile：73.09(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.
Rn concentration profile in soilIskandar, D.*; Yamazawa, Hiromi*; Yamasoto, Kotaro; Ota, Masakazu*; Koarashi, Jun; Moriizumi, Jun*; Bunawas*; Iida, Takao*
Hoken Butsuri, 42(1), p.98 - 104, 2007/03
The Rn concentrations in soil and Rn flux were measured at 6 depths in soil to analyze the seasonal- day-to-day and diurnal variations. The variations of Rn concentrations in soil were larger in shallow depths. It seems that the 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 Rn concentration in soil was also observed.
