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Journal Articles

Functional test of the ISI system for pipes of MONJU primary heat transfer system

Maeda, Yukihiro; Yamaguchi, Toshihiko; Ueda, Masashi; Fujiki, Kazunari*

Nippon Hozen Gakkai Dai-10-Kai Gakujutsu Koenkai Yoshishu, p.599 - 601, 2013/07

An inspection system was developed for in-service inspection (ISI) of pipes in the primary heat transfer system of MONJU FBR. The system was updated and modified based on experience from the pre-service inspection and related tests. This paper describes the results of the functional tests of the new inspection system on a mockup and in MONJU, which confirmed it can satisfy the expected performance.

Journal Articles

Investigation of an on-line pipe wall defect monitoring sensor

Tagawa, Akihiro; Fujiki, Kazunari; Kojima, Fumio*

International Journal of Applied Electromagnetics and Mechanics, 33(1-2), p.639 - 647, 2010/12

This paper presents development of a defect monitoring sensor using electromagnetic acoustic transducer (EMAT). The present study investigates the possibility of the defect monitoring using a new EMAT structure. The current EMAT was unsuitable for monitoring because of the large sensor area, and also it was necessary to have a mechanical scanning. Therefore, it was developed a new EMAT, smaller in size which does not need a mechanical scanning. The new EMAT was manufactured for a trial purpose. Based on the result of the performance test, it was found out that the new EMAT is able to monitor a defect and also to monitor both a thin and thick piping wall.

Journal Articles

Investigation of an on-line pipe wall defect monitoring sensor

Tagawa, Akihiro; Fujiki, Kazunari; Kojima, Fumio*

Proceedings of 14th International Symposium on Applied Electromagnetics and Mechanics (ISEM 2009), p.207 - 208, 2009/09

In the paper it was also investigated the defect detection using the electromagnetic acoustic transducer (EMAT). However, EMAT needs a different processing of defect detection signal. Until now, it was studied a small one EMAT unit that has a non-couplant characteristic and uses additionally mechanical scanning to detect defects. In the present paper it is investigated one EMAT unit with two separate coils for transducer and receiver, that can monitor for defects without any mechanical scanning.

Journal Articles

The Durability test result in high temperature of EMAT for pipe wall thinning monitoring

Tagawa, Akihiro; Fujiki, Kazunari

Nippon Hozen Gakkai Dai-6-Kai Gakujutsu Koenkai Yoshishu, p.570 - 574, 2009/08

This study checks the high-temperature durability of the electromagnetic acoustic transducer (EMAT) for pipe wall thinning. We inserted EMAT into the oven and measured the 10 mm thickness specimen by EMAT about two years. Measurement was carried out by two kinds, a pulse echo method and a pulse echo resonance method. And high-temperature durability was checked by both of the measuring methods. Compared with the pulse echo method, the pulse echo resonance method of measurement accuracy was better. The filter processing of removing magnet signal is required high-temperature measurement. EMAT is a simple configuration of a coil and a magnetic combination. Therefore, a sensor does not break easily. Therefore, EMAT is applicable to the pipe wall thinning monitoring of a nuclear power plant.

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

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.

Oral presentation

Current status of non-destructive checking techniques on Fast Breeder Reactor and its improvement

Yamashita, Takuya; Nishimura, Akihiko; Tsuchida, Noboru; Yamaguchi, Toshihiko; Oka, Kiyoshi; Fujiki, Kazunari*; Shimada, Yukihiro

no journal, , 

The preservation techniques of safety research on "Monju" and the next generation Fast Breeder Reactors have been exhibited. The exhibition consists of (1) EMAT, (2) ECT, (3) Laser Processing Head. Both (1) and (2) are the checking techniques for the cracks on nuclear power plants, while (3) is the repairing technique for the heat exchanger. In 2009, these three techniques will have been integrated to be a new probing system. The hybrid optical fiber has been involved in (3), which the project "photo-Medical Valley in JAEA-KANSAI are now developing as a fiber surgery device.

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