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JAEA Reports

Decontamination simulation and future prediction of air dose rate in difficult to return zone in Fukushima Prefecture

Yamashita, Takuya; Sawada, Noriyoshi*

JAEA-Research 2019-010, 227 Pages, 2020/03

JAEA-Research-2019-010.pdf:21.44MB
JAEA-Research-2019-010(errata).pdf:0.5MB

In order to support the decontamination activities proceeded by the national government and municipalities in terms of technology, we have developed a simulation system "RESET" which predicts the effect of decontamination. We also developed a "two-component model" for the purpose of predicting long-term changes in the air dose rate. We use these tools to perform decontamination simulation and predictive analysis of the air dose rate after decontamination, and provide information to the national government and municipalities aiming for reconstruction. In this report, the verification result of the prediction methods implemented using actual measurement data obtained in the "Decontamination model demonstration project in difficult-to-return zone" and "Survey result on transition of air dose rate after decontamination model demonstration project" conducted by Ministry of the Environment. In addition, the decontamination simulation conducted for the entire difficult-to-return area and the results of future prediction of the air dose rate after decontamination are shown.

Journal Articles

Technical support of decontamination projects and communication activity for residents to understand radiation; Activities for the environmental recovery by JAEA, 3

Yamashita, Takuya; Itabashi, Kiyoshi

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 57(10), p.656 - 661, 2015/10

Effective method for environment restoration has been examined after the accident of Fukushima Daiichi Nuclear Power Station following the Great East Japan Earthquake and Tsunami on 11 March 2011. JAEA conducted many activities for environment restoration in Fukushima just after the accident, JAEA' efforts concerning decontamination and Communication are reported.

Journal Articles

JAEA's technical supports for decontamination project in Fukushima prefecture conducted by Japanese government

Oshimi, Kazuyuki; Yamashita, Takuya

Hozengaku, 12(1), p.17 - 21, 2013/04

In order to support the decontamination activities of the Ministry of the Environment in Fukushima, "decontamination activity promotion member" was organized by 20 persons' all members on February 1, 2012 in the Headquarters of Fukushima Partnership of Japan Atomic Energy Agency (JAEA), and started the support activities, such as technical advice in decontamination sites, meetings to explain to local residents, and consent document acquisition. This paper reports the technical assistance in the decontamination sites among the support activities by the "decontamination activity promotion member".

Journal Articles

R&D on maintenance technologies for FBR plants in JAEA; The Status quo and the future plan

Tsukimori, Kazuyuki; Ueda, Masashi; Miyahara, Shinya; Yamashita, Takuya

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles (FR 2009) (CD-ROM), 10 Pages, 2012/00

Journal Articles

Development of an ISI robot for the fast breeder reactor MONJU primary heat transfer system piping

Tagawa, Akihiro; Ueda, Masashi; Yamashita, Takuya; Narisawa, Masataka*; Haga, Koichi*

Journal of Nuclear Science and Technology, 48(4), p.504 - 509, 2011/04

This paper describes the development of a new inspection robot for the in-service inspection of the heat transfer system of the fast breeder reactor MONJU. The inspection was carried out using a tire-type ultrasonic sensor for volumetric tests at high temperature (atmosphere, 55 $$^{circ}$$C; piping surface, 80 $$^{circ}$$C) and radiation exposure condition (dose rate, 10 mGy/h; piping surface dose rate, 15 mGy/h). An inspection robot using a new tire type for the ultrasonic testing sensor and a new control method was developed. A signal-to-noise ratio S/N over 2 was obtained during the functional test for a calibration defect with a depth of 50%t (from the tube wall thickness). In the automatic inspection test, an EDM slit with a depth of 9% from the pipe thickness was detectable and with an S/N ratio = 4.0 (12.0 dB).

Journal Articles

Development of inspection and repair technology for the micro cracks on heat exchanger tubes

Nishimura, Akihiko; Shobu, Takahisa; Oka, Kiyoshi; Yamaguchi, Toshihiko; Shimada, Yukihiro; Mihalache, O.; Tagawa, Akihiro; Yamashita, Takuya

Reza Kako Gakkai-Shi, 17(4), p.207 - 212, 2010/10

A prototype probe system with a hybrid optical fiber scope was designed for inspecting and re-pairing the micro cracks on heat exchanger tubes in fast breeder reactors (FBRs). It comprised a laser processing head combined with an eddy current testing unit. Ultrashort laser pulse ablation was used to remove work-hardened layers. And spot laser welding was used to repair the micro cracks. This system has both safe and economical options for the maintenance of FBRs because it extends the lifetime of the heat exchangers.

Journal Articles

Development of a laser processing head using a composite-type optical fiberscope to inspect and repair 1-inch heat exchanger pipes

Oka, Kiyoshi; Nishimura, Akihiko; Seki, Takeshi*; Akatsu, Tomohiro*; Yamashita, Takuya

Hozengaku, 8(4), p.37 - 42, 2010/01

A composite-type optical fiberscope was combined with a laser processing head to repair heat exchange pipes of Fast Breeder Reactor (FBR). The head can rotate axially and move back and forth longitudinally in the 1-inch pipes. The property of fiberscope and the motion of the head can successfully observe the pipe's inner surface to find the cracks which should be repaired by laser welding. The project, which aims for developing the integrated system of inspection and repair, proposes an effective cost reduction for maintenance of FBRs by extension of the heat exchanger's lifetime. This report describes the outline of the laser processing head and the basic performance.

Journal Articles

Development of inspection and repairing technology for FBR heat exchanger tubes, 2; Preparation of operation software and performance check

Nishimura, Akihiko; Oka, Kiyoshi; Yamaguchi, Toshihiko; Akatsu, Tomohiro*; Seki, Takeshi*; Mihalache, O.; Shimada, Yukihiro; Tagawa, Akihiro; Yamashita, Takuya

Nihon Hozen Gakkai Dai-6-Kai Gakujutsu Koenkai Yoshishu, p.250 - 253, 2009/08

In order to maintain FBR heat exchanger tubes, a new probe system was designed. A coupling unit and operational software are key components in the second year. The coupling unit to combine a high energy laser beam and optical fiberscope images was developed. The operational software successfully controlled an eddy current testing device and a laser processing head.

Journal Articles

Development of a SH wave single unit electromagnetic acoustic transducer (EMAT) for MONJU reactor vessel in-service inspection

Xu, Y.*; Tagawa, Akihiro; Fujiki, Kazunari*; Ueda, Masashi; Yamashita, Takuya

Proceedings of 17th International Conference on Nuclear Engineering (ICONE-17) (CD-ROM), 9 Pages, 2009/07

In-service inspection is carried out to confirm the integrity of the main components of "MONJU". The ambient temperature during the inspection is 200 $$^{circ}$$C and the irradiation field is 10 Gy/hr. A Periodic Permanent Magnet (PPM) structure has been used for electromagnetic acoustic transducer (EMAT). The PPM structure is the structure of putting in order alternately the S pole and N pole laterally magnetized magnets. A Halbach magnet structure is the structure which sandwiched the longitudinally magnetized magnets between each magnet of PPM structure. Thereby, magnetic flux density is improved 1.4 times. Moreover, it also checked aiming at 4 times as many improvement in detection sensitivity as this by a new signal processing method. The high temperature characteristic and high temperature durability of Halbach type EMAT in 200 hours which corresponds the twice of inspection time under the 200 $$^{circ}$$C inspection environment are reported.

Journal Articles

Investigation of the on-line monitoring sensor for a pipe wall thinning with high accuracy

Tagawa, Akihiro; Fujiki, Kazunari; Yamashita, Takuya

E-Journal of Advanced Maintenance (Internet), 1(1), p.52 - 62, 2009/05

In Japan, the safety of nuclear power plants has been secured by performing a time-based maintenance. However recently, NPPs were taking into consideration a new procedure using a condition-based maintenance, aiming to improve both reactors safety and operation availability. Therefore, it is needed to develop new sensors that can monitor, during reactor operation, the integrity of both piping system and pressure vessel. Also, a proper measurement method has to be chosen in order to carry out an effective on-line monitoring. In the present investigation, it was used the electromagnetic acoustic transducer (EMAT) because it does not need a couplant in a high-temperature environment (up to 200 $$^{circ}$$C). Based on this method, two measurements techniques have been employed using a new developed sensor, depending on the required purpose. The 1st technique is based on the Pulse Echo (PE) method. The paper analyses different methods for carrying out plates thickness measurement using EMAT and supplying a vertical ultrasonic wave. The 2nd technique is based on the electromagnetic acoustic resonance (EMAR) that is usually used for material fatigue assessment. The developed sensor measures, at 200 $$^{circ}$$C, a minimum 5 mm (0.04 mm) plate thickness using PE, and 2 mm (0.01 mm) using EMAR, respectively. Moreover, it was found no attenuation of the sensor signal even when the sensor performed a 200 hours continuously measurement.

Journal Articles

The Pipe health monitoring method by Hybrid measurement using ultrasonic

Tagawa, Akihiro; Ueda, Masashi; Miyahara, Shinya; Yamashita, Takuya

Nihon Hozen Gakkai Dai-5-Kai Gakujutsu Koenkai Yoshishu, p.470 - 472, 2008/07

This paper describes the development of a new sensor for the pipe health monitoring. The Hybrid measuring using EMAT was made as a trial. It examined and checked that it could measure. The result confirmed that the high accuracy of 200 $$^{circ}$$C at high temperature was acquired in pipe surface temperature, pipe wall thinning, and water temperature.

Journal Articles

Investigation of an on-line pipe wall thinning monitoring using a high accuracy sensor

Tagawa, Akihiro; Fujiki, Kazunari*; Yamashita, Takuya

Proceedings of 13th International Symposium on Applied Electromagnetics and Mechanics (ISEM-13), p.243 - 244, 2007/09

Until now, in Japan, the safety of nuclear power plants (NPP) has been secured by performing a time based maintenance. However, recently, NPPs were taking into consideration a new procedure using a condition based maintenance, aiming to improve both reactors safety and reactors operation ratio. Therefore, it is needed to develop new sensors that can monitor in the same time, during reactor operation, the integrity of both piping system and pressure vessel. Two measurements techniques have been employed using a new developed sensor, depending on the required purpose. The 1st technique is based on the Pulse echo method. The 2nd technique is based on EMAR that is usually used for a material fatigue assessment. The developed sensor measures at 200 degrees C a minimum plate thickness 5mm $$pm$$ 0.03mm using pulse echo, and 2mm $$pm$$ 0.003mm using EMAR.

Journal Articles

Development of ISI system for FBR MONJU reactor vessel

Tagawa, Akihiro; Okamoto, Hisahiko; Ueda, Masashi; Yamashita, Takuya

Nihon Hozen Gakkai Dai-3-Kai Gakujutsu Koenkai Yoshishu, p.376 - 379, 2006/07

no abstracts in English

Journal Articles

Development of the ISI device for fast breeder reactor MONJU reactor vessel

Tagawa, Akihiro; Ueda, Masashi; Yamashita, Takuya

Proceedings of 14th International Conference on Nuclear Engineering (ICONE-14) (CD-ROM), 8 Pages, 2006/07

In-service inspection (ISI) is carried out to confirm the integrity of the main components of the Fast Breeder Reactor (FBR) "MONJU". The weld-joints are examined by using an inspection device which has a glass fiber scope for visual examination and a horizontally polarized shear (SH) wave electromagnetic acoustic transducer (EMAT) for volumetric testing. The ambient temperature during the inspection is 200 $$^{circ}$$C and the irradiation field is 10 Sv/hr. A new inspection device has been developed in order to improve the visual test performance, volumetric test performance and controllability of the inspection device reflecting the experience of the original test. In this paper, detail of the new inspection device and the test results of sensors such as the CCD camera, EMAT and bead sensor are reported. The paper also reports on the CCD camera cooling system and other components.

Journal Articles

Research program for ageing of nuclear power plant based characteristics of Fukui area

Sakakibara, Yasuhide; Isomura, Kazutoshi; Yamashita, Takuya; Watashi, Katsumi; Doi, Motoo; Okusa, Kyoichi; Tagawa, Akihiro; Hirahara, Kenji

Nihon Hozen Gakkai Dai-3-Kai Gakujutsu Koenkai Yoshishu, p.283 - 286, 2006/06

This study was performed to enrich the contents of measures for an ageing of the nuclear power plants at Fukui area, where infrastructures of research works, for example, institutes, universities etc. are intensively existed., according to the Road-Map established by the Atomic Energy Society of Japan at 2005.

Journal Articles

Detection of small defects in magnetic SG tubes using multiple vertical and horizontal remote field Eddy currents coils

Mihalache, O.; Yamaguchi, Toshihiko; Ueda, Masashi; Yamashita, Takuya; Date, Koji*

Dai-9-Kai Hyomen Tansho Shimpojiumu Koen Rombunshu, p.57 - 62, 2006/02

no abstracts in English

JAEA Reports

JAERI-JNC joint research report; A Study on degradation of structural materials used under the irradiation environment in nuclear reactors

Ueno, Fumiyoshi*; Nagae, Yuji; Nemoto, Yoshiyuki*; Miwa, Yukio*; Takaya, Shigeru; Hoshiya, Taiji; Tsukada, Takashi*; Aoto, Kazumi; Ishii, Toshimitsu*; Omi, Masao*; et al.

JNC TY9400 2005-013, 150 Pages, 2005/09

JNC-TY9400-2005-013.pdf:37.33MB

None

JAEA Reports

JAERI-JNC joint research report; A Study on degradation of structural materials used under the irradiation environment in nuclear reactors

Ueno, Fumiyoshi; Nagae, Yuji*; Nemoto, Yoshiyuki; Miwa, Yukio; Takaya, Shigeru*; Hoshiya, Taiji*; Tsukada, Takashi; Aoto, Kazumi*; Ishii, Toshimitsu; Omi, Masao; et al.

JAERI-Research 2005-023, 132 Pages, 2005/09

JAERI-Research-2005-023.pdf:33.03MB

JAERI and JNC have started a JAERI-JNC joint research program in fiscal year 2003, which has been aimed for efficient progress and synergistic effect on the research activities in both Institutes. This study has been chosen one of the joint research themes because it has been our common objective in the field of structural materials of FBR and LWR components. The purpose of the study is to clarify damage mechanism of structural materials used under irradiation, and then to develop the methods for damage evaluation and detection in earlier stage of progressing process of damage. In fiscal year 2004 and 2005, micro-corrosion measurement, electrochemical corrosion test and leakage magnetic flux density measurement apparatuses were developed and equipped in two hot facilities and irradiated and unirradiated crept specimens, irradiated high purity model austenitic stainless alloys were also prepared and applied to this study. These apparatuses and specimens were used for damage evaluation, and these feasibilities for nuclear power plant materials were studied.

Journal Articles

Development of SH Wave Electromagnetic Acoustic Transducer (EMAT)

Yang, X.; Tagawa, Akihiro; Ueda, Masashi; Yamashita, Takuya; Otsuka, Yusuke*; Osafune, Kazunori*; Nishikawa, Masahiro*

The Hellenic Society of N, 0 Pages, 2003/11

This paper describes a new structure of horizontally polarized shear(SH) wave electromagnetic acoustic transducer(EMAT). The EMAT with a Halbach magnet structure shows a stronger magnetic flux density as well as ultrasonic sound pressure than that of an EMAT with a general periodic permanent magnet(PPM) structure. The measured magnetic flux density and the ultrasound directivity distributions for both the Halbach and the PPM structure EMATs are in excellent agreement with those expected form a simulation calculation. The above EMATs were also used for inspection tests of many artificial slits; and it is found that the Halbach one performs a better detectability than the PPM one.

Journal Articles

A New structure of SH wave electromagnetic acoustic transducer (EMAT)

Yang, X.; Tagawa, Akihiro; Ueda, Masashi; Yamashita, Takuya

27th International Symposium on Acoustical Imaging, 0 Pages, 2003/04

In the present paper, the magnetic characterization of the halbach magnet arrangement and the ultrasonic directivity of SH wave (horizontally polarized shear wave) EMAT (electromagnetic acoustic transducer) with the above permanent magnet structure are numerically analyzed and compared with that for the general periodic permanent magnet (PPM) structure of SH wave EMAT. It is found that the ultrasonic intensity of SH wave EMAT with the halbach structure can be as large as 1.4 times of that with the PPM structure.

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