3D position and radioactivity estimation of radiation source by a simple directional radiation detector combined with structure from motion

Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*

Radiation Measurements, 142, p.106557_1 - 106557_6, 2021/03

https://doi.org/10.1016/j.radmeas.2021.106557

Construction of virtual reality system for radiation working environment reproduced by gamma-ray imagers combined with SLAM technologies

Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*; Torii, Tatsuo

Nuclear Instruments and Methods in Physics Research A, 976, p.164286_1 - 164286_6, 2020/10

https://doi.org/10.1016/j.nima.2020.164286

Study on magnetic property change on neutron irradiated austenitic stainless steel

Nemoto, Yoshiyuki; Oishi, Makoto; Ito, Masayasu; Kaji, Yoshiyuki; Keyakida, Satoshi*

Hozengaku, 14(4), p.83 - 90, 2016/01

Authors previously reported that magnetic data obtained by using Eddy current method and AC magnetization method showed correlation with the increase of susceptibility of the irradiation assisted stress corrosion cracking (IASCC) on neutron irradiated austenitic stainless alloy specimens. To discuss the mechanism of the correlation, microstructure observation was conducted on the irradiated specimen, and magnetic permalloy phase (FeNi) formation along grain boundary was revealed in this work. From this result, the radiation induced magnetic phase formation along grain boundary seems to be a factor of the magnetic property change of the irradiated materials, and related to the correlation between magnetic data and IASCC susceptibility. In addition, sensor probe development was conducted in this work to obtain higher sensitivity and resolution. It was applied for magnetic measurement on type304 stainless steel irradiated up to different doses. In this case, magnetic ferrite phase was existed in the type304 stainless steel sample before irradiation therefore it was concerned that magnetic measurement on the irradiated ones would be disturbed by the magnetic signal from the pre-existing ferrite phase. In the magnetic measurements, increase of the magnetic data was clearly seen on the irradiated specimens. Thus, it was thought that the developed magnetic measurement technics can be applied for the irradiated austenite stainless steels which contain certain quantity of ferrite phase before irradiation.

Applicability of meteorological statistics over a 5-year period to evaluation of annual average of radionuclide concentration in surface air; Based on meteorological statistics for 20 years at Oarai Research and Development Center, JAEA

Seya, Natsumi; Hashimoto, Makoto; Nemoto, Koji*; Shimizu, Takehiko; Takasaki, Koji

Hoken Butsuri, 49(1), p.29 - 38, 2014/03

http://doi.org/10.5453/jhps.49.29

http://doi.org/10.5453/jhps.49.1

Evaluation of annual average of radionuclide concentration in surface air obtained from atmospheric dispersion factor is intended to determine a public dose as a primary source for the safety analysis of nuclear facilities in normal operation. Oarai Research and Development Center (ORDC) of the JAEA have used fixed 5-year meteorological statistics for derivation of atmospheric dispersion factors as average conditions. To show that the meteorological statistics for any 5-year period could be used as representative data for evaluation of average conditions, annual average (1-year average) and 5-year average of evaluated radionuclide concentrations derived from the meteorological data observed from 1991 to 2010 at ORDC were analyzed. The fluctuations of evaluated radionuclide concentrations of any 5-year averages were smaller than those of 1-year averages during 20 years, and any 5-year averages contained no rejections by the F-test (5% significance level). It means that any 5-year averages of radionuclide concentration evaluations are well representative for the safety analysis under normal condition in ORDC.

Handling of HTTR second driver fuel elements in assembling and storage working

Tomimoto, Hiroshi; Kato, Yasushi; Owada, Hiroyuki; Sato, Nao; Shimazaki, Yosuke; Kozawa, Takayuki; Shinohara, Masanori; Hamamoto, Shimpei; Tochio, Daisuke; Nojiri, Naoki; et al.

JAEA-Technology 2009-025, 29 Pages, 2009/06

JAEA-Technology-2009-025.pdf:21.78MB

The first driver fuel of the HTTR (High Temperature Engineering test Reactor) was loaded in 1998 and the HTTR reached first criticality state in the same year. The HTTR has been operated using the first driver fuel for a decade. In Fuel elements assembling, 4770 of fuel rods which consist of 12 kinds of enrichment uranium are loaded into 150 fuel graphite blocks for HTTR second driver fuel elements. Measures of prevention of fuel rod miss loading, are employed in fuel design. Additionally, precaution of fuel handling on assembling are considered. Reception of fuel rods, assembling of fuel elements and storage of second driver fuels in the fresh fuel storage rack in the HTTR were started since June, 2008. Assembling, storage and pre-service inspection were divided into three parts. The second driver fuel assembling was completed in September, 2008. This report describes concerns of fuel handling on assembling and storage work for the HTTR fuel elements.

Replacement of the criticality accident alarm system in the Tokai reprocessing plant

Sanada, Yukihisa; Nemoto, Makoto*; Suzuki, Kei*; Kawai, Keiichi*; Momose, Takumaro

Proceedings of 12th International Congress of the International Radiation Protection Association (IRPA-12) (CD-ROM), 7 Pages, 2008/10

http://www-pub.iaea.org/MTCD/Publications/PDF/Pub1460_web.pdf

The purpose of this study is to show the design principle and the determination procedures for the adequate relocation of the CADs in TRP. When the alarm trip point was 2.0 mGy/h, it is possible to detect a criticality accident even under conservative conditions (i.e. : 10 m distances from the equipment to the CAD and 140 cm concrete shield between them; neutron: 15 m distances and both 60 cm concrete shield and 60 cm steel shield). Consequently, it was found the seven CADs at these locations could monitor PCDF adequately. This study was reflected in the determination of the new CAD location.

Wave excitation in magnetically confined plasmas with an anisotropic velocity distribution

Ichimura, Makoto*; Higaki, Hiroyuki*; Kakimoto, Shingo*; Yamaguchi, Yusuke*; Nemoto, Kenju*; Katano, Makoto*; Kozawa, Isao*; Muro, Taishi*; Ishikawa, Masao; Moriyama, Shinichi; et al.

Fusion Science and Technology, 51(2T), p.150 - 153, 2007/02

https://doi.org/10.13182/FST07-A1337

In magnetically confined plasmas, fluctuations in the ion cyclotron range of frequency (ICRF) will be driven by the presence of non-thermal ion energy distribution. In strong ICRF heating experiments on the GAMMA 10 tandem mirror, plasmas with a strong temperature anisotropy have been formed. Alfven-ion-cyclotron (AIC) modes are spontaneously excited due to strong temperature anisotropy. High-energy ions are trapped in the local mirror and will form the velocity distribution with the strong anisotropy. To study the relation among the AIC modes, ICEs and beam-driven electrostatic instabilities with non-thermal energy distribution is the main purpose of this work. When the NBs are injected, the magnetic fluctuations due to injected beams and FP ions are detected by ICRF antennas used as pickup loops on JT-60U. The wave excitation near ion cyclotron and its higer harmonic frequencies are studied experimentally and theoretically in plasmas with non-thermal ion energy distribution.

Report of investigation on malfunction of reserved shutdown system in HTTR

Hamamoto, Shimpei; Iigaki, Kazuhiko; Shimizu, Atsushi; Sawahata, Hiroaki; Kondo, Makoto; Oyama, Sunao; Kawano, Shuichi; Kobayashi, Shoichi; Kawamoto, Taiki; Suzuki, Hisashi; et al.

JAEA-Technology 2006-030, 58 Pages, 2006/03

JAEA-Technology-2006-030.pdf:10.69MB

During normal operation of High Temperature engineering Test Reactor (HTTR) in Japan Atomic Energy Agency (JAEA), the reactivity is controlled by the Control Rods (CRs) system which consists of 32 CRs (16 pairs) and 16 Control Rod Drive Mechanisms (CRDMs). The CR system is located in stand-pipes accompanied by the Reserved Shutdown System (RSS). In the unlikely event that the CRs fail to be inserted, the RSS is provided to insert BC/C pellets into the core. The RSS shall be designed so that the reactor should be held subcriticality from any operation condition by dropping in the pellets. The RSS consists of BC/C pellets, hoppers which contain the pellets, electric plug, driving mechanisms, guide tubes and so on. In accidents when the CRs cannot be inserted, an electric plug is pulled out by a motor and the absorber pellets fall into the core by gravity. A trouble, malfunction of one RSS out of sixteen, occurred during a series of the pre-start up checks of HTTR on February 21, 2005. We investigated the cause of the RSS trouble and took countermeasures to prevent the issue. As the result of investigation, the cause of the trouble was attributed to the following reason: In the motor inside, The Oil of grease of the multiplying gear flowed down from a gap of the oil seal which has been deformed and was mixed with abrasion powder of brake disk. Therefore the adhesive mixture prevented a motor from rotating.

Neutron spectra and angular distributions of concrete-moderated neutron calibration fields at JAERI

Yoshizawa, Michio; Tanimura, Yoshihiko; Saegusa, Jun; Nemoto, Hisashi*; Yoshida, Makoto

Radiation Protection Dosimetry, 110(1-4), p.81 - 84, 2004/09

https://doi.org/10.1093/rpd/nch198

The facility of Radiation Standards (FRS) of JAERI has equipped with the concrete-moderated neutron calibration fields as simulated workplace neutron fields. The fields use an Am-Be (37GBq) neutron source placed in the narrow space surrounded by concrete wall and bricks to produce scattered neutrons. The neutron spectra of the fields were measured with Bonner multi-sphere spectrometer system (BMS), spherical recoil-proton proportional counters (RPCs), and a liquid scintillation counter (NE-213). The results were compared with each other, and the neutron spectra and the ambient dose equivalent rate, (10), were agreed well within the uncertainty. The angular distributions of neutron fluence were calculated by the MCNP-4B2 Monte Carlo code to obtain the reference personal dose equivalent rate, (10). The calculated results show that the scattered neutrons have a wide variety of incident angles. The reference (10) values considered the angular distribution were found to be 10-18% smaller than those without consideration.

Characteristics of Alfvn eigenmodes, burst modes and chirping modes in the Alfvn frequency range driven by negative ion based neutral beam injection in JT-60U

Kusama, Yoshinori; Kramer, G. J.; Kimura, Haruyuki; Saigusa, Mikio*; Ozeki, Takahisa; Tobita, Kenji; Oikawa, Toshihiro; Shinohara, Koji; Kondoh, Takashi; Moriyama, Shinichi; et al.

Nuclear Fusion, 39(11Y), p.1837 - 1843, 1999/11

https://doi.org/10.1088/0029-5515/39/11Y/324

no abstracts in English