ICMST-Tohoku 2018
Oct. 23 - 26, 2018
Sendai, Japan
ICMST-Shenzhen 2016
Nov 1 - 4, 2016
Shenzhen, China
ICMST-Kobe 2014
Nov 2(Sun) - 5(Wed), 2014
Kobe, Japan
Nuclear Regulation Authority Outline of the New Safety Standards for Light Water Reactors for Electric Power Generation
For Public Comment
Outline of New Safety Standard (Design Basis)
For Public Comment
New Safety Standards (SA) Outline (Draft)
For Public Comment
Outline of New Safety Standard(Earthquake and Tsunami)(DRAFT)

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OTjapan Measures for Tsunami Striking Nuclear Power Station in Japan
Special Article: The Great Tohoku Earthquake (1)
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Featured Articles
EJAM7-3NT72 A New Mechanical Condition-based Maintenance Technology Using Instrumented Indentation Technique
EJAM7-3NT73 Survey robots for Fukushima Daiichi Nuclear Power Plant

(in English)


Vol.11 No.4previousAA SP22 (AA165-166-167-168-169-170-171) NT96

Academic Articles
Vol. 11 No. 4 (2020) p.124 - p.178

Special Issue 22

The 4th International Conference on Maintenance Science and Technology (ICMST-Tohoku 2018)


ICMST-Tohoku 2018, the 4th International Conference on Maintenance Science and Technology was held at "Sakura Hall" on Tohoku University Katahira campus in Sendai, Miyagi, Japan between the 23rd and the 26th of October 2018. ICMST-Tohoku 2018 was the latest of a highly successful series which started in Tokyo (Japan, 2012) and continued in Kobe (Japan, 2014) and Shenzhen (China, 2016).

Maintenance is still an uncharted area for humankind, and we have to study energetically. After the Fukushima accident, the credibility of nuclear safety has been an important issue worldwide. The conference continues to be the key forum for scientists and engineers interested in maintenance science and technology for nuclear power plants.

ICMST-Tohoku 2018 featured 101 presentations given to 209 attendees from nine countries. Publication in these special issues was voluntary and after peer review. This could not have been achieved without the very significant efforts of both reviewers and authors. Without this work, these special issues could not exist, and I would like to thanks them on behalf of the Publication Committee. I hope that all those who attended would share my opinion that ICMST-Tohoku 2018 was a vibrant, exciting and productive conference and that these special issues give some sense of the success of ICMST-Tohoku 2018 to the reader.

Finally, I would like to thank the members of the ICMST International Steering Committee, the Organizing Committee, the Local Organizing Committee and the Secretariat without whose tireless work ICMST-Tohoku 2018 would not have succeeded.

Guest Editor,
Kenji Suzuki

Shigeru TAKAYA, Naoto SASAKI, Toshiki OKAMOTO and Hideo MACHIDA

This paper describes benchmark analysis of independently programmed structural reliability evaluation codes, REAL-P and GENPEP. An upper core structure of a prototype fast breeder reactor in Japan, MONJU, was chosen, and crack initiation time and crack propagation due to fatigue-creep interaction damage was evaluated in deterministic and probabilistic manners. Evaluation procedures follow the new guidelines on reliability evaluation of fast reactor components issued by JSME. The results obtained by two codes were compared, and the effects of differences in treatments of which details are not prescribed in the guidelines on results were discussed. As result, although slight difference was recognized in crack initiation evaluation especially due to difference in fairing treatment of fatigue life curves, the results estimated by two codes generally agreed very well for both deterministic and probabilistic evaluations. It was shown that the effects of differences in treatments of which details are not prescribed in the guidelines on results are small for structural reliability evaluation of fatigue-creep interaction damage, which is one of typical degradation mechanisms for fast reactor passive components.

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Kunio ITO and Nobuyuki TERAURA

RF tags have excellent characteristics in the management of moving items for traceability and identification, and are utilized in various fields including nuclear power plants. In this paper, we discuss the effective utilization of RF tags at nuclear power plants, especially for radioactive waste management during the decommissioning works. In its application to radiation field, it is necessary to prevent the corruption of the data stored in RF tag memory due to radiation damage. Especially, for the decommissioning work in high-level radiation environments at the Fukushima Daiichi reactors, the radiation resistant RF tag which has been developed by the authors is particularly effective.

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Hiroyuki NAKAMOTO, Philippe GUY and Toshiyuki TAKAGI

Corrosion and erosion lead to partial wear inside pipes. This wear induces some roughness of the inner pipe wall and decreases its thickness. This could cause a fatal accident in nuclear and thermal power plants. In general, nondestructive inspection by ultrasonic devices measures only the thickness, not the roughness. When reflected on a rough surface ultrasonic waves scatter and attenuate. Then this study aims to estimate the surface roughness of the pipe wall from ultrasonic attenuation estimation, based on the analysis of the acquired waveforms on several specimens that have been machined in order to simulated a corroded rough surface. The experimental data exhibit a clear relationship between the roughness and the ultrasonic attenuation, in good agreement with theoretical models available in the literature, for both bulk longitudinal and shear waves.

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Atsushi Iwasaki

In this paper, we propose a method for numerically evaluating the probability of failure from the diagnostic results of condition monitoring using the Bayesian theorem. When performing maintenance using real-time monitoring results, a diagnostic result without any inspection error is ideal. However, failure is not caused even if the monitoring method sufficiently overestimates any small damage that can cause failure. Moreover, failure is not caused even if the method slightly underestimates large damage. In other words, for reducing the probability of failure, improving the accuracy of estimating specific damage levels is necessary. In this study, a method for reducing the risk by improving the diagnostic accuracy of specific damage levels by means of controlling the sampling ratio of the training data employed for learning the use of a weight function is proposed. The consequences of overestimation and underestimation of damage differ. The risk caused by underestimation is called failure risk and that caused by overestimation is called economic risk. In this paper, the effect of weighted regression on risk reduction is discussed. The proposed method is validated by employing it to identify delamination in a CFRP beam via the electric potential change method.

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Mari ITO and Masaaki SUZUKI

To achieve the reasonable and effective maintenance of nuclear power plants, it is essential to optimize the aging management from the viewpoints of both safety and efficiency. We propose a maintenance-scheduling model that minimizes the cost of maintenance activities while ensuring the reliability of safety-critical functions. In this study, we formulate the maintenance-scheduling problem as a mathematical programming model and consider that the effective maintenance activity differs depending on the cause of the latent failure. Computing maintenance activity schedules for a single component and all the components of a safety-critical function, we verify that the proposed model provides the optimal schedule. The proposed model enables us to quantitatively evaluate the impact of the allowable unreliability value of a function of interest on the schedule and thereby the tradeoff between the reliability of safety-critical functions and the maintenance cost.

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Vu Nhut LUU, Kenta MURAKAMI, Thi Mai Dung DO, Masahide SUZUKI, Tomonori YAMADA, Takuya SHIBATA, Hiroyuki DAIDO

Previous studies on the effect of temperature on various types of concrete have been mainly focused on the case of fire in which the exposure duration is short. Limited data has been obtained regarding the effect of high temperature on concrete properties under severe accident condition in which the concrete structure may be exposed to heat radiation from melting nuclear fuels for a long time. The present study aimed to examine the applicability of the ultrasonic wave based method for concrete damaged extremely by heat simulating a severe accident. The conventional ultrasonic test was conducted in concrete cylindrical with the size of φ100 × 200 mm after exposure to high temperatures 105, 200, 400, 600, 700, 800 ℃. The results revealed that this method is sensitive to indicate thermal damage as results from water content loss and decomposition of portlandite. A strong correlation between dynamic and static elastic modulus was obtained for concrete exposed to temperature range of 25 to 400 ℃, corresponding to dynamic elastic modulus range from 20 - 40 GPa. The degradation within this range is due to water loss. At higher temperatures, the concrete integrity is not maintained due to the formation of cracks and the decomposition of cement paste phases, which cause a significant decay of the ultrasonic waves.

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Masahide SUZUKI, Kenta MURAKAMI, Takashi SUZUKI, Ryuta OKAYAMA, Jinya KATSUYAMA and Yinsheng LI

For the reactor pressure vessel (RPV) integrity assessment, deterministic fracture mechanics (DFM) is applied considering factors such as neutron irradiation embrittlement, postulated crack and thermals transients etc. On the other hand, probabilistic fracture mechanics (PFM) can evaluate the failure probability considering the uncertainties of several kinds of factors affecting the RPV integrity. The purpose of present study is to obtain insight concerning the further improvement of RPV structural integrity from the probabilistic approach consideration through careful comparisons with DFM approach. It was found that the transients which give rise to the re-pressurization have a possibility to deteriorate the deterministic – probabilistic correlation to some extent.

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