Third international challenge to model the medium- to long-range transport of radioxenon to four Comprehensive Nuclear-Test-Ban Treaty monitoring stations

Maurer, C.*; Galmarini, S.*; Solazzo, E.*; Kumierczyk-Michulec, J.*; Bar, J.*; Kalinowski, M.*; Schoeppner, M.*; Bourgouin, P.*; Crawford, A.*; Stein, A.*; et al.

Journal of Environmental Radioactivity, 255, p.106968_1 - 106968_27, 2022/12

https://doi.org/10.1016/j.jenvrad.2022.106968

After performing multi-model exercises in 2015 and 2016, a comprehensive Xe-133 atmospheric transport modeling challenge was organized in 2019. For evaluation measured samples for the same time frame were gathered from four International Monitoring System stations located in Europe and North America with overall considerable influence of IRE and/or CNL emissions. As a lesion learnt from the 2nd ATM-Challenge participants were prompted to work with controlled and harmonized model set ups to make runs more comparable, but also to increase diversity. Effects of transport errors, not properly characterized remaining emitters and long IMS sampling times (12 to 24 hours) undoubtedly interfere with the effect of high-quality IRE and CNL stack data. An ensemble based on a few arbitrary submissions is good enough to forecast the Xe-133 background at the stations investigated. The effective ensemble size is below five.

International Noble Gas joint measurement at Mutsu City, Aomori for CTBT verification

Kijima, Yuichi; Yamamoto, Yoichi; Oda, Tetsuzo

JAEA-Technology 2017-028, 33 Pages, 2018/01

JAEA-Technology-2017-028.pdf:38.85MB

The International Noble Gas Experiment related to monitoring network for radioactive noble gas (xenon) has been carried out all over the world, as part of the International Monitoring System (IMS) of CTBT. Thirty IMS radionuclide stations including the Takasaki station in Japan are monitoring radioxenon. The past measurement results show that several stations often detect radioxenon and the major emission source of these radioxenon is medical radioisotope production facilities. And nuclear power plants and medical institutions used radioxenon for nuclear medicine diagnosis, and so on are also considered as the possible sources of radioxenon, and it is therefore important to understand the background behavior of radioxenon originated from above facilities for enhancement of monitoring capability for nuclear tests. The international joint measurement was conducted in 2012 by the Preparatory Commission for the CTBT Organization, US Pacific Northwest National Laboratory, Japan Chemical Analysis Center and JAEA at the Ohminato site of JAEA Aomori Research and Development Center in Mutsu city, Aomori, as part of investigation on radioxenon background in East Asia region. In 2014, the additional measurement was carried out at the same place for further investigation. A high sensitive Transportable Xenon Laboratory developed by PNNL was used for this measurement. This paper describes the outline and the results of the joint measurement conducted in 2012 and 2014.

Monitoring of radionuclide related to CTBT

Kijima, Yuichi; Yamamoto, Yoichi

Nihon Genshiryoku Gakkai-Shi ATOMO, 58(3), p.156 - 160, 2016/03

JAEA has built and operated two radionuclide stations and a certified laboratory for monitoring of radionuclide out of facilities of the International Monitoring System (IMS) under the CTBT National Operation System of Japan. JAEA also has developed and operated the National Data Center for analysis and evaluation of radionuclide observation data obtained from the IMS station. In this paper, we explain the outline of the CTBT and the CTBT activities of JAEA, and introduce two examples of detection of some anthropogenic radionuclides including the monitoring case for the DPRK's 3rd nuclear test in February 2013 from all observational results obtained from the CTBT radionuclide stations in Japan.

Analysis result of NPE 2012 at Japanese NDC; Event selection using ATM and waveform analysis

Otsu, Takayuki*; Arai, Nobuo*; Nogami, Mami*; Kijima, Yuichi; Yamamoto, Yoichi; Oda, Tetsuzo

no journal, , 

Japan has two kinds of NDCs, one is NDC-1 in charge of analysis of SHI data and the other is NDC-2 in charge of RN issue. Both NDCs participated in the NDC preparedness Exercise (NPE) 2012 and tried to get results collaboratively. In this exercise, NDC-2 made backward and forward tracking using ATM. NDC-1 tried to select one event from among several candidate events by the result of ATM and made some seismo-acoustic analysis. NDC-1 tried to sift through candidate events from REB using the results from NDC-2. Finally two possible candidate events were selected. These events are located around Mezhdurechensk, Kemerovo Oblast, Russia. It was very difficult to distinguish which event was the candidate event, because these waveforms have similar characteristics each other and look like small explosion.

JAEA's recent activities related to Comprehensive Nuclear-Test-Ban Treaty (CTBT)

Kijima, Yuichi; Yamamoto, Yoichi; Oda, Tetsuzo

no journal, , 

More than 80% facilities (275 places) of the International Monitoring System prescribed in the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have already been completed and have been substantially functioning as a global nuclear test monitoring. Of facilities installed in Japan, the JAEA has established 2 radionuclide stations which monitor radionuclides and 1 laboratory which performs detail analyses of samples sent from stations all over the world, and is operating them as certified facilities which meet technical requirements for the Treaty monitoring. The National Data Center installed in JAEA's site receives the data from station network and analyzes it routinely. This paper describes current status of the verification regime and JAEA's recent activities related to the CTBT such as DPRK's 3rd nuclear test event.

Summary report of ATM and radionuclide data analyses of the common exercise in the East Asia Regional NDC Workshop 2014

Yonezawa, Chushiro*; Yamamoto, Yoichi; Kijima, Yuichi; Kalinowski, M.*

no journal, , 

The authors present a summary report of the analysis results of ATM (Atmospheric Transport Model) and radionuclide (RN) data of the common exercise in the 2014 East Asia Regional NDC Workshop 2014 (EARNW 2014) held in Ulaanbaatar, Mongolia from 29 July to 1 August, 2014. The exercise scenario was that CTBT-relevant RNs released from a hypothetical target event were detected in particulate and noble gas samples at the Takasaki station (RN38), and the target event was inferred using estimated explosion time from La-140/Ba-140 ratio in the particulate samples. The possible source area was determined through ATM backward tracking of Xe-133. Real observation noble gas data by a certified IMS station and artificially prepared particulate data were used as the fictitious RN data in this exercise. The analysis results of the RN data by the participating NDCs were evaluated by comparing with the prepared values for the particulate and IDC/RRR for the noble gas data. The results of estimated explosion time were evaluated by comparing to the preset value. Released Xe-133 activity from the event and the observable radioactivity concentration of Xe-133 at the IMS station were compared among the reported ATM results.

Investigation on radioxenon background in Mutsu related to CTBT verification

Kijima, Yuichi; Yamamoto, Yoichi; Oda, Tetsuzo

no journal, , 

The International Noble Gas Experiment (INGE) is being carried out for global measurement networks of radioactive noble gas (xenon), as part of building of the international verification regime of the Comprehensive nuclear-Test-Ban Treaty (CTBT). Since there are many nuclear facilities and medical institutions in Japan and its neighboring countries, which may be possible sources of radioxenon, it is important to understand the behavior of normal radioxenon background for high-precision detection of underground nuclear tests. Therefore, for the purpose of the investigation on radioxenon background in Northeast Asia region, the measurement of radioxenon was conducted in Mutsu city, Aomori in 2012, and the results showed that radioxenon background in Mutsu was regionally specific and different from that in Takasaki. In 2014, the additional measurement was carried out at the same place for further investigation. This report describes the results of background measurement in Mutsu city in 2014.

Study on emission source of radioxenon detected at Takasaki station

Kijima, Yuichi; Yamamoto, Yoichi; Oda, Tetsuzo

no journal, , 

It is very important to understand the behavior of background of radioxenon at the view point of monitoring of underground nuclear tests. Although all nuclear power plants (NPPs) in Japan had been shut down from 15th September 2013 to 10th August 2015, Xe-133 had been sometimes detected far beyond normal background level of the activity concentration at the CTBT Takasaki station (JPX38) during the same period. Therefore, radiopharmaceutical production facilities (RPFs) in Japan can be considered as one of the potential emission sources of Xe-133 detected at JPX38 in this period. We make a study on the possibility of RPFs as the emission source of these Xe-133 detections at JPX38 by ATM simulation.

ATM analysis of the DPRK 2016 event and the potentially relevant Level C episode at the Takasaki station

Yamamoto, Yoichi; Kijima, Yuichi; Oda, Tetsuzo

no journal, , 

The Japanese NDC-2 estimated the movement of virtual radioactive plume by the Atmospheric Transport Modelling (ATM) simulations with regard to the DPRK 2016 event. The simulations were done in two hypothetical cases of coincident and delayed emission of radionuclides. The NDC-2 decided which IMS radionuclide stations should be monitored based on the simulation results. As the result, no radionuclides generated from the nuclear explosion were found in any IMS data obtained from the selected radionuclide stations in January. However, xenon-133 with high activity concentration above the normal background levels was detected 5 times at the Takasaki station in the middle of February. The NDC-2 estimated the location of emission source of the Xe-133 by ATM backward tracking simulations. Some ATM simulations and the analysis results by the NDC-2 are shown in the presentation.

Nuclear test analysis in Japanese NDC-2; Analytical procedure and release condition for ATM

Kijima, Yuichi; Yamamoto, Yoichi

no journal, , 

The flow of analysis for nuclear test event in the Japanese NDC-2 will be presented. When the information on a nuclear test event is obtained from the Secretariat of the CTBT National operation system of Japan (NOSJ), the first thing to be done in the NDC-2 is to forecast a possible movement of a virtual radioactive plume emitted from the nuclear test site by the ATM analysis. Based on the analysis results, radionuclide stations to be monitored are selected and the radionuclide data from the stations are analysed in detail. The results of both the ATM analysis and the radionuclide analysis are reported to the Secretariat of NOSJ. A part of studies on the released condition of the ATM analysis will also be presented.