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Journal Articles

Report on social communication activities of Young Researchers Association and Students Association of JHPS; Chiba-shi Science Festa

Yamada, Ryohei; Kono, Takahiko; Nakajima, Junya; Hirouchi, Jun; Tsuji, Tomoya; Umeda, Masayuki; Igarashi, Yu*; Koike, Hiromi*

Hoken Butsuri (Internet), 56(1), p.32 - 38, 2021/03

no abstracts in English

Journal Articles

Structural and compositional characteristics of Fukushima release particulate material from Units 1 and 3 elucidates release mechanisms, accident chronology and future decommissioning strategy

Martin, P. G.*; Jones, C. P.*; Bartlett, S.*; Ignatyev, K.*; Megson-Smith, D.*; Satou, Yukihiko; Cipiccia, S.*; Batey, D. J.*; Rau, C.*; Sueki, Keisuke*; et al.

Scientific Reports (Internet), 10, p.22056_1 - 22056_17, 2020/12

 Times Cited Count:1 Percentile:7.33(Multidisciplinary Sciences)

Journal Articles

Classification of the insoluble particles including radioactive Cs found in Okuma town and Futaba town, Fukushima prefecture

Igarashi, Junya*; Zhang, Z. J.*; Ninomiya, Kazuhiko*; Shinohara, Atsushi*; Satou, Yukihiko; Minowa, Haruka*; Yoshikawa, Hideki

KEK Proceedings 2019-2, p.54 - 59, 2019/11

no abstracts in English

Journal Articles

First determination of Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from Fukushima Daiichi Nuclear Power Plant accident

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

Scientific Reports (Internet), 9(1), p.11807_1 - 11807_10, 2019/08

 Times Cited Count:19 Percentile:66.01(Multidisciplinary Sciences)

Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of $$^{239+240}$$Pu and $$^{241}$$Pu were (1.70-7.06)$$times$$10$$^{-5}$$ Bq and (4.10-8.10)$$times$$10$$^{-3}$$ Bq, respectively and atom ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu were 0.330-0.415 and 0.162-0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis.

Journal Articles

Activity of $$^{90}$$Sr in fallout particles collected in the difficult-to-return zone around the Fukushima Daiichi Nuclear Power Plant

Zhang, Z.*; Igarashi, Junya*; Satou, Yukihiko; Ninomiya, Kazuhiko*; Sueki, Keisuke*; Shinohara, Atsushi*

Environmental Science & Technology, 53(10), p.5868 - 5876, 2019/05

 Times Cited Count:19 Percentile:64.21(Engineering, Environmental)

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released abundant radioactive particles into the surrounding environment. Herein, we analyzed the activity of $$^{90}$$Sr in these particles to estimate the contribution of this radionuclide to the overall radiation exposure and shed light on the processes that occurred during the accident. Seven radioactive particles were isolated from the dust and soil samples collected from areas surrounding the FDNPP, and the minimum/maximum $$^{137}$$Cs activities were determined as 224/4,100 Bq. Based on the size, specific activity, and $$^{134}$$Cs/$$^{137}$$Cs activity ratios, we concluded that six of the seven radioactive particles were released from the Unit 1 reactor, while one particle was released from the Unit 3 reactor by a hydrogen explosion. Strontium-90 was detected in all radioactive particles, and the minimal/maximal $$^{90}$$Sr activities were determined as 0.046/1.4 Bq. $$^{137}$$Cs/$$^{90}$$Sr activity ratios above 1000 were observed for all seven particles, that is, compared to $$^{137}$$Cs, $$^{90}$$Sr had negligible contribution to the overall radiation exposure. The $$^{137}$$Cs/$$^{90}$$Sr activity ratios of the radioactive particles were similar to those of terrestrial environmental samples and were higher for particles released from the Unit 1 reactor than for samples collected from the Unit 1 reactor building, which indicates possibility of additional $$^{90}$$Sr -rich contamination after release of the particles.

Oral presentation

Uncategorized radioactive particles isolated from southwest region from the Fukushima Dai-ichi Nuclear Power Station

Satou, Yukihiko; Sueki, Keisuke*; Ishii, Tatsuya*; Igarashi, Junya*; Martin, P.*; Jones, C.*; Scott, T.*

no journal, , 

In Fukushima accident, insoluble radioactive Cs particles found at the northwestern region from the Fukushima Dai-ichi Nuclear Power Station (1FNPS). Presence of Cs particle in other surrounding area from 1FNPS is unclear yet. In the present study, the presence of other particle emission events and the presence of new types of radioactive particles were investigated by expanding the search object to soil samples collected outside the 1FNPS northwest region where insoluble Cs particles were reported. Four radioactive particles found from the samples. The particles look like pebbles and diameter is 0.4 to 2 mm, and the size feature is Type B. Isotopic ratio of Cs is very similar to type A of 1.0. EDS results confirmed the presence of iron and aluminum in addition to silicon. Further, in the CT image, there was an absorption point near the surface indicating that the element is heavier than iron. Although these features are clearly different from the insoluble Cs particles that have been reported in the past, in this implementation item it is not possible to find the location where Cs is adsorbed, and further direct emission from uranium or in the reactor.

Oral presentation

Identification of plutonium isotopes in insoluble particles released by the accident of Fukushima Daiichi Nuclear Power Plant

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

no journal, , 

Plutonium is one of the most notable radionuclides in the nuclear accident. The amounts of Pu released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident were investigated so far. However, the existence of Pu isotopes from the global fallout makes it difficult to accurately assessment of Pu contamination by the FDNPP accident. To avoid this problem, identification of Pu contamination source from the Pu isotopic ratios is important. However, various ratios have been reported by the researches due to the contamination from global fallout. In this work, we focused on the insoluble radioactive Cs particles made of mainly SiO$$_{2}$$ (insoluble particles) released from the FDNPP to determine accurate Pu isotopic ratios. Due to its insolubility, the particles retained the original property at the time of emission from the reactor. Therefore, the insoluble particles are considered to be free from the contamination of global fallout. In addition, the amounts of Pu in the insoluble particles provide the information about their formation process in the reactor. In this study, we identified Pu isotopes in insoluble particles by radioactive analysis and ICP-MS measurement. The isotopic ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu were determined as 0.330-0.415 and 0.162-0.178, respectively and activity ratio of $$^{239+240}$$Pu/$$^{137}$$Cs was about 10$$^{-8}$$ in each particle.

Oral presentation

Long-term stationary monitoring data of KURAMA-II under the on-site environment

Igarashi, Yu; Hamaguchi, Takumi; Maeda, Eita; Yamada, Junya; Muto, Yasunobu; Tanigaki, Minoru*; Nohara, Naofumi

no journal, , 

At the JAEA Oarai Research Establishment, a portable KURAMA equipped with a data transmission function through an autonomous network using the ZETA standard was permanently installed near the MP for the purpose of redundancy in the measurement of monitoring points, and a system for observing radiation doses near the site boundary was developed. In this presentation, we report on the fixed point observation data for about one year using this system.

Oral presentation

Introduction of KURAMA-II with wireless communication "ZETA" for monitoring nuclear operators

Igarashi, Yu; Hamaguchi, Takumi; Maeda, Eita; Yamada, Junya; Muto, Yasunobu; Nohara, Naofumi

no journal, , 

At the Oarai Research Institute of the Japan Atomic Energy Agency, a portable KURAMA equipped with a data transmission function using an autonomous network based on the ZETA standard was permanently installed in the vicinity of the MP, and a system for observing radiation doses around the site boundary was developed. In this presentation, the background to the redundancy of post-measurement monitoring, which is the purpose of this system installation, and the fixed-point observation data for about one year will be reported.

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