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Journal Articles

Verification of safety margin of reactor pressure vessel exposed to various thermal transients based on probabilistic approach

Suzuki, Masahide*; Murakami, Kenta*; Suzuki, Takashi*; Okayama, Ryuta*; Katsuyama, Jinya; Li, Y.

E-Journal of Advanced Maintenance (Internet), 11(4), p.172 - 178, 2020/02

no abstracts in English

Journal Articles

3D environment reconstruction based on images obtained by reconnaissance task in Fukushima Daiichi Nuclear Power Station

Hanari, Toshihide; Kawabata, Kuniaki

E-Journal of Advanced Maintenance (Internet), 11(2), p.99 - 105, 2019/09

This paper describes our trials on 3-dimensional environment reconstruction from plural images for recognizing the status in the reactor building of Fukushima Daiichi Nuclear Power Station. Structure from Motion is one of photogrammetry techniques to estimate 3-dimensional structure of the objects and the camera's trajectory. We try to apply a Structure from Motion method and a pre-processing to plural images obtained by the reconnaissance task inside Primary Containment Vessel of Unit 3 using remotely operated vehicle. For improving a visibility, Multi-View Stereo is conducted the data obtained by Structure from Motion. In this paper, we report the results of the partial 3D reconstruction using SfM (Structure from Motion) and the visibility improvement of the 3D reconstructed data using MVS.

Journal Articles

Operation and maintenance experience of sodium leak detector in Monju

Muto, Keitaro; Hamano, Daisuke; Kawabata, Mamoru; Tabakoya, Yasuhiro; Yanai, Chisato

E-Journal of Advanced Maintenance (Internet), 11(2), p.86 - 91, 2019/09

Gas sampling type sodium small leak detector, SID, Sodium Ionization Detector, a gas sampling detector installed to monitor small sodium leak in the Prototype Fast Breeder Reactor Monju, had been operated since it's system start up test through to the 40% reactors output test, It's use was terminated in April, 2018. SID showed some indication variations during its operation period, and necessary measures were implemented. As a result, the SID system maintained its functions without any critical malfunction until the end of its operation.

Journal Articles

Research on hydrogen safety technology utilizing the automotive catalyst

Ono, Hitomi*; Takenaka, Keisuke*; Kita, Tomoaki*; Taniguchi, Masashi*; Matsumura, Daiju; Nishihata, Yasuo; Hino, Ryutaro; Reinecke, E.-A.*; Takase, Kazuyuki*; Tanaka, Hirohisa*

E-Journal of Advanced Maintenance (Internet), 11(1), p.40 - 45, 2019/05

Journal Articles

Intergranular strains of plastically deformed austenitic stainless steel

Suzuki, Kenji*; Shobu, Takahisa

E-Journal of Advanced Maintenance (Internet), 10(4), p.9 - 17, 2019/02

In materials with an elastic anisotropy, a stress difference is generated between crystals when plastic deformation occurs, and it is known that this is deeply involved in material fracture. In this study, the residual stress for load direction in the plastically deformed material was investigated for each crystal orientation using the high-energy synchrotron radiation diffraction method. As a result, it was found that the residual stress is a tensile residual stress at an index with a high X-ray elastic constant (Young's modulus obtained for each diffraction surface) and a compressive residual stress at an index with a low X-ray elastic constant. We believe that this result will be useful for the technique of controlling the crystal orientation like the texture as improving the material strength.

Journal Articles

A Consideration on the use of shear waves to improve the sensitivity of an optical ultrasonic sensor for under-sodium viewers

Saruta, Koichi; Shirahama, Takuma*; Yamaguchi, Toshihiko; Ueda, Masashi

E-Journal of Advanced Maintenance (Internet), 10(2), p.1 - 8, 2018/08

Journal Articles

Prediction method of improved residual stress distribution by shot peening using large scale analysis method

Ikushima, Kazuki*; Shibahara, Masakazu*; Nishikawa, Satoru*; Furukawa, Takashi*; Akita, Koichi; Suzuki, Hiroshi; Morooka, Satoshi

E-Journal of Advanced Maintenance (Internet), 9(3), p.NT87_1 - NT87_5, 2017/11

Journal Articles

Thermal management of heat resistant FBG sensing for high temperature industrial plants

Nishimura, Akihiko; Takenaka, Yusuke*; Furusawa, Akinori; Torimoto, Kazuhiro; Ueda, Masashi; Fukuda, Naoaki*; Hirao, Kazuyuki*

E-Journal of Advanced Maintenance (Internet), 9(2), p.52 - 59, 2017/08

no abstracts in English

Journal Articles

R&D of multi-frequency ECT algorithms for FBR SG tubes

Mihalache, O.; Yamaguchi, Toshihiko; Shirahama, Takuma; Ueda, Masashi

E-Journal of Advanced Maintenance (Internet), 9(2), p.60 - 65, 2017/08

Journal Articles

Ultrasonic guided wave approach for inspecting concave surface of the laser butt-welded pipe

Furusawa, Akinori; Nishimura, Akihiko; Takebe, Toshihiko*; Nakamura, Masaki*; Takenaka, Yusuke*; Saijo, Shingo*; Nakamoto, Hiroyuki*

E-Journal of Advanced Maintenance (Internet), 9(2), p.44 - 51, 2017/08

The aim of this work is to investigate the applicability of ultrasonic guided wave for evaluation of laser beam butt-welding quality. Ten in total test pipes having welding seam is prepared. Two piece of pipe are jointed and continuous laser beam is irradiated on the edges, varying laser irradiation power, welding side and surface profile of the adjacent edges of the pipe. Ultrasonic guided wave testing experiment is performed on the pipes. Torsional mode guided wave is excited by EMAT. The experimental results are analyzed and issues are discussed. The reflection wave bullet from the poor interface of the welding seam is clearly observed, whereas no reflection from fine welded line. From the aspect of laser irradiation power, welding side and surface profile of the adjacent edges, the relation between the interface condition and detection wave bullet are analyzed. It is found that the ultrasonic guided wave technologies have the potential for evaluating laser beam butt-welding seam.

Journal Articles

Inventory estimation of $$^{137}$$Cs in radioactive wastes generated from contaminated water treatment system in Fukushima Daiichi Nuclear Power Station

Kato, Jun; Meguro, Yoshihiro

E-Journal of Advanced Maintenance (Internet), 7(2), p.138 - 144, 2015/08

Concentration of $$^{137}$$Cs in radioactive wastes such as used cesium adsorption vessels and sludge generated from the cesium adsorption device, the 2nd cesium adsorption device, and the decontamination device, which have operated or been suspended as a part of the contaminated water treatment system in Fukushima Daiichi Nuclear Power Stations, was calculated by using analysis data of the contaminated water. The total decontamination amount of $$^{137}$$Cs from Jun 6, 2011 to Aug 12, 2014 was estimated.

Journal Articles

Evaluation of wall thinning of the steel piping after long term operation at Fugen Power Station

Ando, Ryosuke; Abe, Teruyoshi; Nakamura, Takahisa

E-Journal of Advanced Maintenance (Internet), 6(4), p.153 - 164, 2015/02

Wall thinning of serviced carbon steel piping of the secondary cooling system after long term operation of Advanced Thermal prototype Reactor (ATR) Fugen power station has been investigated as a series of evaluation of validity and availability of utilization of serviced materials on research projects focused on aging management. Reliability of wall thinning rates of the steel piping has been examined referring the previous inspection data. Examinations also have been made on prediction of wall thinning rates, rationalization of management of pipe wall thinning and verification of countermeasures against wall thinning.

Journal Articles

Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

Abe, Teruyoshi; Nogiwa, Kimihiro*; Onitsuka, Takashi*; Nakamura, Takahisa; Sakakibara, Yasuhide

E-Journal of Advanced Maintenance (Internet), 6(4), p.146 - 152, 2015/02

Thermal embrittlement of cast austenitic stainless steel components from the decommissioned advanced thermal prototype reactor Fugen has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275$$^{circ}$$C. The "Fugen" material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considerations of the activation energy for embrittlement at low service temperatures.

Journal Articles

Study on the structural integrity of RPV using PFM analysis concerning inhomogeneity of the heat-affected zone

Masaki, Koichi; Katsuyama, Jinya; Onizawa, Kunio

E-Journal of Advanced Maintenance (Internet), 5(2), p.85 - 92, 2013/08

In order to obtain the technical basis to judge the needs of surveillance test specimens from HAZ materials, the features of inhomogeneity of HAZ in RPV steels were investigated. Concerning on the fracture toughness in HAZ, HAZ materials close to weld metal indicated higher toughness than that of base metal due to high-toughness phase, while HAZ materials close to base metal were equivalent or slightly lower toughness than that of base metal due to the same phase as base metal. A structural integrity assessment method concerning such inhomogeneous distribution of fracture toughness for HAZ materials was developed and incorporated into PFM analysis code PASCAL3. Case studies on postulated flaws distribution and chemical composition were performed by using PASCAL3. It was shown that in highly irradiated conditions, CPI and CPF in HAZ close to weld metal are lower than base metal, while those in HAZ close to base metal were almost equivalent to base metal.

Journal Articles

Fabrication of micro capsule containing fluorescent magnetic particles for advanced inspection of heat exchanger tubes

Ito, Fuyumi; Nishimura, Akihiko

E-Journal of Advanced Maintenance (Internet), 4(2), p.57 - 63, 2012/08

Stress corrosion cracking sometimes occurs in the heat exchanger tubes of aging nuclear power plants. At the present time, Eddy Current Testing (ECT) is used to inspect these heat exchanger tubes. When symptoms of corrosion or cracks are found on the inside wall of the tubes, they are usually repaired. As repaired tubes increase in number, the cost of repair work rises considerably. Therefore, discovering tiny cracks has the purpose of ensuring not only progress on safety but also economical benefit. Cracks are observed not only by ECT but also by Magnetic particle Testing (MT), which facilitates visual observation. In the case of MT, a dispersed liquid with magnetic particles is applied to a magnetized sample. However, this dispersed liquid could potentially enter inside the crack. To solve this problem, this paper proposes that magnetic particles be contained inside a micro capsule, this capsule calls Magnetic Particle Micro Capsule (MPMC).

Journal Articles

Future bearing inspection system using portable linac X-ray source

Yamamoto, Tomohiko; Uesaka, Mitsuru*

E-Journal of Advanced Maintenance (Internet), 2(4), p.200 - 206, 2011/02

We have developed an X-ray source using portable X-band (9.3-12 GHz) linear accelerator (linac) for bearing real-time inspection. This system can generate pulsed-X-ray, therefore if X-ray repetition rate synchronizes with bearing rotation rate, we can get still images without stopping rotation. We succeeded in static imaging of rotating equipment. We start to develop more advanced X-ray generators using portable linac and multi-beam klystron (MBK). The advanced systems use higher electron energy linac and MBK as more stable radio-frequency (RF) source. We used 950 keV linac and 250 kW magnetron for X-ray imaging. For the purpose of more stable operation and compactness of the system, we propose a multi-beam klystron (MBK) as its RF power source. In this paper, we show the basic parameters of the system which stability is tolerable for bearing condition based maintenance (CBM) in near future.

Journal Articles

Evaluation of weld residual stress near the cladding and J-weld in reactor pressure vessel head for the assessment of PWSCC behavior

Katsuyama, Jinya; Udagawa, Makoto; Nishikawa, Hiroyuki*; Nakamura, Mitsuyuki*; Onizawa, Kunio

E-Journal of Advanced Maintenance (Internet), 2(2), p.50 - 64, 2010/08

Weld residual stress is the most important factors to assess the structural integrity of RPV since it affects crack initiation and growth behaviors. Inner surface of the RPV is protected against corrosion by cladding. At the J-weld of the vessel head penetrations, Ni-based alloys are used for weld material. After the fabrication process, the residual stress remains in such dissimilar welds after PWHT. The residual stresses were measured using the DHD method. Thermal-elastic-plastic-creep analyses considering phase transformation were also performed. By comparing analytical results with measured ones, it was shown that there was a good agreement of residual stress distribution. It was suggested that taking phase transformation into account was important to improve the accuracy of analysis. Using the residual stress distributions, PWSCC behavior was calculated using PFM analysis code. Effects of the residual stress and scatter of PWSCC growth rate on the crack penetration were evaluated.

Journal Articles

Activities on public awareness of a prototype fast breeder reactor, Monju, and casebook of potential troubles

Yanagisawa, Tsutomu; Tabata, Hiroaki; Mori, Masaomi

E-Journal of Advanced Maintenance (Internet), 2(1), 7 Pages, 2010/05

Monju, the Japanese prototype of fast breeder reactor, has engaged in various activities to restore the public trust since the sodium leak accident occurred in 1995. Among the activities is the publication of a risk communication booklet "Response to the possible accident and trouble in Monju" which is compiled according to the operational progress of "Monju". This booklet is intended for promoting the public understanding toward the restart. The supplement of the booklet illustrates the outline and characteristics of "Monju", the recent troubles at not only "Monju", but also home and abroad, and the assumed troubles during the core confirmation test which is implemented when the system start-up test is commenced. These efforts for the restart are also explained.

Journal Articles

Examination of relation between IASCC susceptibility and magnetic property

Takaya, Shigeru; Nagae, Yuji; Yoshitake, Tsunemitsu; Nemoto, Yoshiyuki; Nakano, Junichi; Ueno, Fumiyoshi; Aoto, Kazumi; Tsukada, Takashi

E-Journal of Advanced Maintenance (Internet), 1(1), p.44 - 51, 2009/05

As the result of comparing the magnetic flux density and the IASCC susceptibility evaluated by SSRT test on neutron irradiated model alloys, it was shown that there is the relation without depending on dose level and chemical compositions as long as the contribution of neutron irradiation to SCC was seen. Furthermore, measuring the magnetic flux density of unirradiated simulated degraded materials indicates that not only change in chemical compositions but also some defects are needed for the magnetic flux density to increase. These results show the possibility of non-destructive estimation of susceptibility to IASCC by measuring magnetic flux density.

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.

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