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Kido H.,Visible Information Inc. | Kido H.,Ibaraki University | Nemoto M.,Visible Information Inc. | Tomita K.,Visible Information Inc. | And 3 more authors.
Fusion Science and Technology | Year: 2011

The Rokkasho Reprocessing Plant, located in northeastern Aomori prefecture, is currently undergoing the final commissioning test using actual spent nuclear fuels (the Active Test). Tritium had been discharged from the reprocessing plant and some effects to the environment were observed since the Active Test had been started at the reprocessing plant on March 31, 2006. The purpose of this study is to predict the environmental impact of the reprocessing plant once it becomes operational. An atmospheric dispersion simulation system, developed by the authors, has been utilized to predict the expected tritium dispersion during the plant future operations. In this study, a simulation of tritium dispersion was carried out using wind velocities and wind directions as prediction factors for future HTO activity. The simulation results were compared with actual HTO activity measurements taken during the autumn of 2006 and the spring and autumn of 2007. The results of the simulation appear to accurately reflect the actual measured results from HTO measurements in the autumn seasons of both 2006 and 2007, however, there were discrepancies between the data set from the spring of 2007 and predicted results formulated by the simulation for that same period. Source


Kitabatake S.,Aomori Prefectural Nuclear Power Safety Division | Kimura H.,Aomori Prefectural Nuclear Power Safety Division | Kimura Y.,Aomori Prefectural Nuclear Power Safety Division | Igarashi A.,Aomori Prefectural Nuclear Power Safety Division | And 5 more authors.
Fusion Science and Technology | Year: 2011

Aomori Prefectura Government (Aomori Pref.) and Japan Nuclear Fuel Limited (JNFL) have been carrying out tritium monitoring of many kinds of environmental samples around the Rokkasho Reprocessing Plant (RRP) as part of environmental radiation monitoring. Similarly, Aomori Pref. and Tohoku Electric Power Co., Inc. have been carrying out monitoring around the Higashidori Nuclear Power Station. Results which exceeded the background levels of environmental tritium were observed in water vapor, some seawater samples and some fish samples (measured as tissue free-water tritiumÇTFWT)) since the final commissioning test using actual spent nuclear fuels (Active Test) was started at the RRP on March 31 2006. Therefore, we examined causes for these results by considering the operational status of the RRP and meteorological and hydrographie conditions. The committed effective dose estimated by using the results for the effect of the RRP was far below the annual dose limit for the public (1 mSv). Source


Kudo S.,Aomori Prefectural Nuclear Power Safety Division | Igarashi K.,Aomori Prefectural Nuclear Power Safety Division | Kimura H.,Aomori Prefectural Nuclear Power Safety Division
Radiation Protection Dosimetry | Year: 2015

Radioactive nuclides with a short half-life, such as 131I and 134Cs, were detected in environmental samples collected in Aomori Prefecture after the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. In addition, the observed 137Cs concentration was increased over the background level. The gaseous 131I concentration in air observed in April was higher than that observed in March immediately after the accident. Using a backward trajectory analysis, the authors found that the air mass had passed the vicinity of the Fukushima Dai-ichi Nuclear Power Plant when the gaseous 131I concentration in air was increasing. Maximum 131I and radioactive Cs concentrations in daily fallout samples collected in Aomori city were observed on 28 April, when 131I was also detected in air. 134Cs and 137Cs concentration ratios in pine needles and pasture grass were nearly equal to 1, which indicates that the source of these radionuclides was the nuclear power plant accident. © The Author 2015. Published by Oxford University Press. All rights reserved. Source


Kumagai K.,Aomori Prefectural Nuclear Power Safety Division | Ookubo H.,Aomori Prefectural Nuclear Power Safety Division | Kimura H.,Aomori Prefectural Nuclear Power Safety Division
Radiation Protection Dosimetry | Year: 2015

In this study, a method to discriminate between natural and other γ-ray sources from environmental γ-ray dose rate monitoring data was developed, and it was successfully applied to actual monitoring data around nuclear facilities. The environmental dose rate is generally monitored by NaI(Tl) detector systems in the low dose rate range. The background dose rate varies mainly as a result of the deposition of 222Rn progeny in precipitation and shielding of the ground by snow cover. Increments in the environmental dose rate due to radionuclides released from nuclear facilities must be separated from these background variations. The method in the present study corrects for the dose rate variations from natural sources by multiple regression analysis based on the γ-ray counting rates of single-channel analysers opened in the energy ranges of γ-rays emitted by 214Bi and 208Tl. Assuming a normal distribution of the results and using the one-sided type I error of 0.01 while ignoring the type II error, the detection limit of the γ-ray dose rate from artificial sources was 0.77 nGy h-1. © The Author 2015. Published by Oxford University Press. All rights reserved. Source

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