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Furuno, Akiko; Terada, Hiroaki; Tsuzuki, Katsunori; Kadowaki, Masanao; Nagai, Haruyasu
no journal, ,
We analyzed hemispherical atmospheric dispersion of Cs-137 released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) due to the accident in March 2011, by comparing simulations with observation data from CTBT International Monitoring Systems. We used WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information version II), which consists of the atmospheric dynamic model WRF and particle dispersion model GEARN, developed by Japan Atomic Energy Agency for atmospheric dispersion simulations. It was shown in our simulations that calculated Cs-137 concentrations generally agreed well with the measurements. By using atmospheric dispersion simulations with limited release period, we investigated release time of Cs-137 observed at CTBT stations. It was found that the Cs-137 released from March 12 to 14 was dispersed almost all over the northern hemisphere and the most of Cs-137 observed in Europe is due to the release during this period. Meanwhile, the Cs-137 released from March 17 to 19 mainly reached around the Pacific Islands area and the West Coast of the USA. These results might be useful for re-estimation of the release amount of Cs-137 from the FDNPP.
Beziat, G.*; Kalinowski, M.*; Inoue, Naoko; Kusmierczyk-Michulec, J.*; Bar
, J.*; Gheddou, A.*; Bourgouin, P.*; Yamamoto, Yoichi; Tomita, Yutaka
no journal, ,
In early 2018, two mobile noble gas measurement systems were deployed and have started measurement at Horonobe and Mutsu in Japan. Together with a third mobile system that will be deployed at Fukuoka, Japan, in spring 2019, and the operating IMS noble gas system at station RN38, Takasaki, Japan, this creates a high density configuration of noble gas measurement systems. The objective of this configuration is to generate a database of detections which will be used to develop and test methods for better understanding the contributions of known sources from across Eurasia. Contributions from these sources are frequently observed at IMS station RN38. The high density configuration will provide a framework to test and optimize source location algorithms and to better understand level C episodes, specifically at JPX38. The three mobile noble gas measurement systems used in this experiment and their operation are externally funded. The planned duration of this experiment is two years.
Purtschert, R.*; Kalinowski, M.*; Riedmann, R.*; Fontaine-Lagrand, J.-E.*; Kusmierczyk-Michulec, J.*; Gheddou, A.*; Bourgouin, P.*; Tomita, Yutaka
no journal, ,
Argon-37 (
Ar) is produced in the high troposphere by spallation of argon through 
Ar(n,4n)Ar and by neutron capture, 
Ar(n,
)Ar. The resulting natural equilibrium concentration of Ar in the mixed troposphere is about 0.5-1 mBq/m
. This value may define the background level for the use of Ar for search area reduction by means of atmospheric Ar measurements in downwind direction of a potential test area in the course of an OSI. In order to investigate long term atmospheric activity levels of Ar, bulk air samples were collected close to the CTBTO IMS Radionuclide station located in Takasaki, Japan. In the years 2016-2018 in total 105 air samples were taken and analyzed for their Ar activity concentrations with no value exceeding 10 mBq/m.