A Modeling approach to estimate H discharge from rivers; Comparison of discharge from the Fukushima Dai-ichi and inventory in seawater in the Fukushima coastal region

Sakuma, Kazuyuki; Machida, Masahiko; Kurikami, Hiroshi; Iwata, Ayako; Yamada, Susumu; Iijima, Kazuki

Science of the Total Environment, 806(Part 3), p.151344_1 - 151344_8, 2022/02

https://doi.org/10.1016/j.scitotenv.2021.151344

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2019-002, 235 Pages, 2019/08

JAEA-Research-2019-002.pdf:21.04MB

The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

A Streak camera study of superfluorescence at multiple wavelengths from helium atoms excited using free electron laser pulses

Harries, J.; Iwayama, Hiroshi*; Nagasono, Mitsuru*; Togashi, Tadashi*; Yabashi, Makina*; Kuma, Susumu*; Nakajima, Kyo*; Miyamoto, Yuki*; Ohae, Chiaki*; Sasao, Noboru*; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 48(10), p.105002_1 - 105002_9, 2015/05

https://doi.org/10.1088/0953-4075/48/10/105002

Superfluorescence from 1snp excited helium studied using a streak camera

Harries, J.; Iwayama, Hiroshi*; Nagasono, Mitsuru*; Togashi, Tadashi*; Kuma, Susumu*; Nakajima, Kyo*; Shigemasa, Eiji*

no journal, , 

Multiple-transition superradiance from EUV-FEL excited helium atoms, 1; Experiment

Nakajima, Kyo*; Harries, J.; Iwayama, Hiroshi*; Kuma, Susumu*; Miyamoto, Yuki*; Nagasono, Mitsuru*; Ohae, Chiaki*; Togashi, Tadashi*; Shigemasa, Eiji*; Sasao, Noboru*

no journal, , 

no abstracts in English

Mathematical modeling of radio-cesium migrations and air dose rate changes in eastern Fukushima Prefecture

Kitamura, Akihiro; Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Okumura, Masahiko; Itakura, Mitsuhiro; Yamada, Susumu; Machida, Masahiko

no journal, , 

Radioactive cesium that was deposited over Fukushima after the accident at the FDNPP is one of the major concerns regarding health physics. In order to predict the future distribution of radioactive cesium and resulting air dose rate at any location in Fukushima, we have integrated a number of mathematical models covering different time and scales. We present simulation results of sediment movement and radioactive cesium migration using semi empirical and physics based watershed models, and that of sediment and radioactive cesium behavior in a dam reservoir using one and two dimensional river simulation models. We also present a tool for calculating air dose rates from arbitrary radio cesium depth profiles and spatial distributions. The predicted dose rates were compared against dose rates measured in the field with handheld survey meters and good correlation was found between the two.

Integrated watershed modeling for simulation of radio-cesium migration after flood events in the catchment near the Fukushima Dai-ichi Nuclear Power Plant

Sakuma, Kazuyuki; Kurikami, Hiroshi; Malins, A.; Yamada, Susumu; Funaki, Hironori; Niizato, Tadafumi; Machida, Masahiko; Kitamura, Akihiro

no journal, , 

The environments of Fukushima near the Fukushima Dai-ichi Nuclear Power Plant have been contaminated by the explosion accident of the plant caused by the Great East Japan Earthquake on 11 March 2011. The contamination level and air-dose rate behavior at present and in future are significant concern for the people used to live nearby. Most dominant radioactive material is Cs at present and its migration is considered to be driven by soil erosion and subsequent transport. To estimate the amount of soil sedimentation and the Cs migration, a three-dimensional hydrological model of the catchment was developed focused on the Ogi-no-sawa catchment, located 15 km southwest of the Fukushima Dai-ichi Nuclear Power Plant. Base on the developed hydrological model, top soil transport and resulting radio-cesium movement was simulated. For the modeling and simulation, physics based code the General-purpose terrestrial fluid-flow simulator GETFLOWS model, which is one of the tools for watershed modeling, was applied. The simulation results were compared with monitored data of the amount of water discharge and concentration of suspended solids for model testing. As a result of the study, the soil and Cs redistribution patterns at various scales of flood events could be predicted based on the results of modeling and simulation.

Models on radiocesium migration in the surface water system in Fukushima Prefecture

Kurikami, Hiroshi; Yamada, Susumu; Sakuma, Kazuyuki; Kitamura, Akihiro

no journal, , 

A comprehensive scheme that involves several models for migration of radiocesium has been developed to assess various issues such as air dose rate prediction and accumulation of radiocesium onto lake bed sediment. This paper shows some examples of modeling studies including the evolution of radiocesium distribution in regional scale up to hundred years after the fallout.

Estimation of particulate and dissolved Cs discharge from rivers to the ocean near the Fukushima Dai-ichi Nuclear Power Plant using a simple model

Sakuma, Kazuyuki; Aoyama, Michio*; Nakanishi, Takahiro; Kurikami, Hiroshi; Machida, Masahiko; Yamada, Susumu; Iwata, Ayako

no journal, , 

MERCURY is one of the models developed to simply predict Cs discharge from rivers to the ocean for understanding of Cs migration from seawater and sediment to the ecosystem and for estimating Cs discharge under heavy rainfall immediately. It is composed of a tank model, relationships between water discharge and suspended solids load, and two-component exponential models for river water Cs concentration. Using the MERCURY, Cs discharge to the ocean from five rivers near the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in 2018 and 2019 was estimated to be 0.23 and 0.81 TBq. Cs discharge in 2019 was larger than in 2018 due to the two huge typhoons in October 2019, Hagibis and Bualoi. Although the model has some limitations such as underestimating the Cs discharge during a heavy rainfall due to lack of modeling dependence of Cs concentration on sediment size, it can quickly evaluate the effect of Cs discharge from rivers to the coastal area near FDNPP.

Investigation on distribution of radioactive substances in Fukushima, 8; Improvement of the MERCURY model and its application to the Fukushima

Sakuma, Kazuyuki; Machida, Masahiko; Yamada, Susumu; Kurikami, Hiroshi

no journal, , 

In order to estimate the amount of radioactive materials discharged into the ocean via rivers more accurately, a GIS-based parameter setting method and parameter optimization method were incorporated into the radionuclide discharge estimation model MERCURY. The elevation (at 100 m intervals), slope (at 10-degree intervals), land use, soil, and surface geology area ratios in the target river basins were calculated using GIS, and multiple regression equations were developed using the five parameters in MERCURY as objective functions and the area ratios for each basin as explanatory variables. The parameters were determined from the multiple regression equations created for the Maeda, Kuma, Ukedo, and Abukuma Rivers and the area ratio obtained for the Takase River, and calculations were conducted. Four optimization methods, the Newton, the PSO, the SCE-UA, and the Bayesian optimization, were implemented as automatic calibration functions and applied to the above five rivers. The results of the verification for the Takase River showed that the relative squared error RSE was about 0.44. Although the number of rivers used in the multiple regression equation was only four, the results were good. On the other hand, for the automatic calibration function, the RSE ranged from 0.29-1.5 for the Newton method (0.29-0.5), 0.28-0.56 for the PSO method, 0.18-0.39 for the SCE-UA method, and 0.29-0.42 for the Bayesian optimization method.