ID 81
Title Construction of minor actinides reduction scenario in Japan utilizing fusion reactors
Author Yuki Furudatea, Hiroki Shishido, Noritaka Yusa, Hidetoshi Hashizume
Published in Progress in Nuclear Energy 103 (2018), 28-32.
Keywords high-level radioactive waste; partitioning and transmutation; fusion neutron; helical reactor; Monte Carlo simulation; burn-up simulation
Abstract This study demonstrates by numerical simulations how transmuting minor actinides in fusion reactors can contribute to nuclear fuel cycles in Japan. Minor actinides are installed into blankets of a helical-type fusion reactor to transmute them rather moderately so that neither large neutron wall loading nor removal of large heat are required. Neutron transport and burn-up simulations are conducted to optimize the position of minor actinides and the blanket's structure for transmutation. Whereas the ratio of transmuted minor actinides is not large, the total amount of transmuted minor actinides is revealed to be sufficient because of the system's large inventory. The simulations are followed by a plan that introduces fusion reactors intended for transmutation. Discussion based on Japan's present situation confirms that introduction of fusion reactors with a thermal fusion output of 1 GW by the year 2050 would mitigate many issues concerning disposal of high-level radioactive waste.

ID 82
Title Experimental Evaluation of Novel Hybrid Microwave/ Ultrasonic Technique to Locate and Characterize Pipe Wall Thinning
Author Wissam M. Alobaidi, Clifford E. Kintner, Entidhar A. Alkuam, Kota Sasaki, Noritaka Yusa, Hidetoshi Hashizume, Eric Sandgren
Published in Journal of Pressure Vessel Technology 140 (2018), 011501.
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ID 83
Title Development of long-range inspection using TE mode microwaves for detecting axial cracks
Author Takuya Katagiri, Kota Sasaki, Noritaka Yusa, Hidetoshi Hashizume
Published in Transactions of the JSME 84 (2018), 28-32.
Keywords Nondestructive testing, Microwave, TE modes, Axial cracks, Mode conversion, Pipeline
Abstract This study proposes nondestructive long-range inspection for axial cracks appearing at the inner surface of a metal pipe using microwave. Numerical simulations were conducted to design a mode converter that converts TEM into TE mode that is necessary to detect axial cracks. The simulations confirmed that situating coaxial cables circumferentially enables to propagate microwaves in TE mode inside a pipe. The results also revealed that the number and positions of coaxial cables affect the frequency range where microwaves propagate as TE01 mode dominantly. A mode converter with four coaxial cables was fabricated according to the results of the simulations aiming at the propagation of microwaves as TE01 mode. Experimental verification was conducted using a brass pipe with a total length of 11.6 m and an inner diameter of 19.0 mm, and having the mode converter at the center. The results showed significant difference between the signals with and without an artificial slit simulating a crack. This study also proposed a signal processing method to compensate for the dispersion of microwaves with an aid of a window function. The signal processing method gave the clearer signals corresponding to the slits to determine the predict position of the slit quantitatively using the time-of-flight of the signals.

ID 84
Title Questionnaire survey of the attitude of Laotian students aiming at the discussion on the factors affecting the public attitudes toward energy
Author Noritaka Yusa, Haicheng Song
Published in Maintenology 17 (2018), 93-99.
Keywords Education, Sociology, Questionnaire survey, Regional characteristics, Public acceptance, Student
Abstract This study reports the results of questionnaire survey to evaluate the attitudes of Laotian students towards energy. The survey was conducted at four high schools in three cities, including Vientiane capital, in Lao PDR in 2017, and also at the Faculty of Engineering, National University of Laos, in 2015-2017. The results of the survey were compared with earlier publications reporting the results of similar surveys targeting Japanese university students. The results revealed that Laotian students place higher importance on energy than the Japanese students do, evaluate 'renewable' energies, regard nuclear energy very negatively, and so on. It is very likely that Lao PDR will undergo drastic changes in education, economy, and also energy policy in a near future. Thus performing continued survey on the attitude of Laotian students and evaluating the results of the survey, including the discrepancy from the attitudes of Japanese students, on the basis of the environment surrounding them would contribute to discussing factors affecting the public attitudes towards energy.

ID 85
Title Experimental verification of long-range microwave pipe inspection of using straight pipes with lengths of 19-26.5 m
Author Kota Sasaki, Takuya Katagiri, Noritaka Yusa, Hidetoshi Hashizume
Published in NDT&E International 96 (2018), 47-57.
Keywords electromagnetic nondestructive testing, wall thinning, time of flight, signal processing
Abstract This study demonstrated the applicability of a nondestructive microwave testing method for the long-range inspection of pipe inner surfaces. Experimental verifications were conducted using pipes with lengths of 19-26.5 m, inner diameters of 11, 19, or 39 mm, and made of either brass or austenitic stainless steel. Microwaves were emitted from a probe attached to one of the pipe ends, and the reflections due to full circumferential wall thinning 50 mm in length and 1 mm in depth situated at various distances from the end were measured. The frequency range and the probe characteristics were decided so that microwaves propagating only in TM01 mode affect signals. After signal processing to compensate for microwave dispersion, the measured signals showed clear reflections caused by wall thinning situated 23.5 m from the pipe end at which microwaves were emitted. This study also discussed the attenuation of microwave reflection with the distance between a probe and wall thinning. The experimental results agreed well with a theoretical model describing the attenuation of microwave propagating inside a pipe, although the model does not consider the reflection of microwaves due to a flaw, the dependence of the reflection on the frequency of microwaves, or mode conversion of the microwave due to the reflection. The agreement revealed that not only frequency but also the inner diameter, electromagnetic property, and surface roughness of a pipe are needed to evaluate the length of the pipe that can be inspected by the method.

ID 86
Title Low Frequency Electromagnetic Testing for Evaluating Wall Thinning in Carbon Steel Pipe
Author Haicheng Song, Noritaka Yusa, Hidetoshi Hashizume
Published in Materials Transactions 59 (2018), 1348-1353.
Keywords nondestructive inspection, sizing, finite element simulation, erosion corrosion, wall thinning, inverse analysis, Gaussian process regression, profile likelihood
Abstract This study proposes an inverse algorithm to evaluate the depth of full circumferential wall thinning from low-frequency electromagnetic field signals. Finite element simulations were performed and revealed that normalizing the magnetic fields enabled the elimination of the effects of the length and the position of wall thinning and the dimensions of the pipe under test. Subsequently, this study attempted to evaluate the residual wall thickness on the basis of the maximum normalized magnetic field using Gaussian process regression. Forty-eight signals obtained by numerical simulations were used to develop a regression model. Eighteen further signals obtained by numerical simulations and nine signals obtained by experiments using a carbon steel pipe (diameter 101.6 mm and thickness 5.7 mm) were used for validation. The root mean squared error of the validation was 0.07 mm for the simulated signals and 0.23 mm for the signals obtained by the experiment. The 95% confidence intervals of the predictions, which would contribute to probabilistic risk analysis, were approximately 0.5 mm.

ID 87
Title Long-range inspection of a pipe with a bend using microwaves
Author Shoya Uoshita, Kota Sasaki, Takuya Katagiri, Noritaka Yusa, Hidetoshi Hashizume
Published in International Journal of Applied Electromagnetics and Mechanics 59 (2019), 1519-1526.
Keywords electromagnetic nondestructive evaluation, wall thinning, pipe degradation, time of flight, electromagnetic wave, finite element simulation
Abstract This study evaluated the effect of bends on the long-range nondestructive testing inspection of pipe surfaces based on microwaves propagating inside the pipe. Three-dimensional finite element simulations were conducted to reveal electromagnetic fields at bends with a diameter of 23 mm and various radii of curvature when microwaves were emitted into a pipe in the TM01 mode that had been mainly used in earlier studies. The simulations revealed that the effect of the bend on the microwaves is not significant when the ratio of curvature is larger than approximately 2, whereas in general a bend reflects a part of microwaves and causes non-TM01 modes. Subsequent experimental verifications, which used a pipe with a total length of approximately 4 m and a 90-degree or 180-degree bend, confirmed clear reflections due to artificial wall thinning in spite of the presence of the bend.

ID 88
Title Proposal of a TEM to TE01 mode convertor for a microwave nondestructive inspection of axial flaws appearing on the inner surface of a pipe with an arbitrary diameter
Author Takuya Katagiri, Kota Sasaki, Haicheng Song, Noritaka Yusa, Hidetoshi Hashizume
Published in International Journal of Applied Electromagnetics and Mechanics 59 (2019), 1527-1534.
Keywords nondestructive testing, axial cracks, TE modes, metal pipe, time of flight
Abstract This study discusses the characteristics of a mode converter to generate microwaves in the TE 01 mode for the long- range inspection of pipes. Numerical analysis was conducted to evaluate the effect of the pipe diameter and the number of coaxial cables inserted into the pipe on the efficiency of converting microwaves from the coaxial TEM mode to the circular TE 01 mode. The results reveal that the most efficient frequency range for TE 01 mode propagation strongly depends on the number of cables and pipe diameter. Subsequent experiments were performed using brass pipes with a length of 5 m and diameters of 39.0 and 74.0 mm. The results of these experiments are consistent with the results of the numerical analysis: the pipe with a diameter of 39.0 mm showed a clear signal from an axial slit 1.5 m away from the mode converter and the pipe with a diameter of 74.0 mm showed almost no difference between signals with or without the slit.

ID 89
Title Probability of detection analyses of eddy current data for the detection of corrosion
Author Noritaka Yusa, Takuma Tomizawa, Haicheng Song, Hidetoshi Hashizume
Published in Nondestructive Testing and Diagnostics 4 (2018), 3-7.
Keywords electromagnetic nondestructive evaluation, uncertainty, statistical analysis, ferromagnetic plate, artificial corrosion
Abstract This study evaluated the applicability of probability of detection (POD) analyses to eddy current tests for the detection of corrosions. Forty-three ferromagnetic plates with various corrosions were prepared, and eddy current inspections were performed to gather signals due to the corrosions using an absolute type pancake probe. The probe scanned the surface of the plates two-dimensionally with a constant lift-off to simulate nondestructive inspection of corrosion under insulating coatings. Subsequent POD analyses adopted two models: a conventional one wherein a flaw was characterized using a single parameter, and a multi-parameter model based on the combinational use of numerical simulations and measurements. The analyses demonstrated that the conventional model would overestimate the probability of detecting small corrosions. In contrast, the multi-parameter model characterized Pod more reasonably while its confidence interval was comparable to that of the conventional model.

ID 90
Title Detection of cracks with arbitrary orientations in a metal pipe using linearly-polarized circular TE11 mode microwaves
Author Guanren Chen, Takuya Katagiri, Haicheng Song, Noritaka Yusa, Hidetoshi Hashizume
Published in NDT&E International 107 (2019), 102125.
Keywords TE11 mode, microwaves, NDT, mode converter, crack detection
Abstract This study proposed a long-range non-destructive pipe inspection approach using linearly-polarized circular TE11 mode microwaves, enabling rapid detection of both axial and circumferential cracks on the inner surface of a metallic pipe. The applicability of the TE11 mode microwaves for crack detection was discussed in the light of the currents induced on the inner surface of a pipe due to the propagation of the TE11 mode microwaves. A dual-bend structured mode converter was designed to propagate linearly-polarized TE11 mode microwaves inside a pipe with a certain inner diameter, based on the theoretical and numerical analysis of mode conversion due to a bend. A 3.5 GHz working bandwidth of the mode converter was achieved with a conversion efficiency of the TE11 mode of over 90%. Experimental verification was conducted using stainless-steel pipes with an inner diameter of 23 mm and a total length of 7 m. An axial and a circumferential slit were introduced to simulate cracks. The experimental results confirmed reflections from both the axial and circumferential slits, indicating that the TE11 mode microwaves are applicable to crack detection. The results also confirmed the correlation between TE11 mode polarization and its detection sensitivity toward slits with different orientations along the circumferential direction. Furthermore, the axial and circumferential slits situated at different longitudinal and circumferential locations in the pipe were successfully detected by orthogonally deploying the mode converter to change the polarization of the TE11 mode by 90 degrees.

ID 91
Title Investigation of the correlation between the electrical contact resistance and the contact area of mechanical lap joint fabricated with high-temperature superconducting tapes using X-ray microtomography
Author Weixi Chen, Satoshi Ito, Noritaka Yusa, Hidetoshi Hashizume
Published in Fusion Engineering and Design 148 (2019), 111284.
Keywords High-temperature superconducting magnet, Joint-winding, Contact resistance, Non-destructive evaluation, X-ray Computer Tomography scan, Image segmentation
Abstract A mechanical lap joint fabricated with high-temperature superconducting (HTS) tapes is proposed for the application to joint-winding in HTS magnets for fusion reactors. The applicability of the joint has been validated, however, it could not be guaranteed because the joint resistance is unpredictable before the entire conductor is cooled and energized. Identifying the factors that affect the joint resistance is necessary to develop a method to predict this parameter at room temperature. In this report, we evaluated the correlation between the electrical resistance of contact interfaces (contact resistance) and the contact area observed using X-ray computer tomography scan (observed contact area), and discussed appropriate techniques for this prediction. A total of 40 mechanical lap joint samples were prepared. The observed contact areas were segmented from cross-sectional images of contact interfaces using a graph cut image segmentation, while the contact resistances were calculated from measured joint resistances. The correlation indicated that the prediction of contact resistance is more precise when base on the observed contact area compared to the conventional method using the nominal contact area. However, some of dispersive contact resistivity still remained due to inhomogeneous distribution of fine-structure on contact interface.

ID 92
Title Probabilistic analysis of electromagnetic acoustic resonance signals for the detection of pipe wall thinning
Author Noritaka Yusa, Haicheng Song, Daiki Iwata, Tetsuya Uchimoto, Toshiyuki Takagi, Makoto Moroi
Published in Nondestructive Testing and Evaluation 36 (2021), 1-16.
Keywords electromagnetic non-destructive testing, electromagnetic acoustic transducer, pipe inspection, probability of detection, false positive
Abstract This study proposes a probability of detection (POD) model for the probabilistic analysis of the detectability of electromagnetic acoustic resonance (EMAR) method for the detection and evaluation of pipe wall thinning. Forty-one carbon steel plate samples with an artificially corroded groove were prepared to simulate pipe wall thinning caused by flow-assisted corrosion. Experiments were performed to gather EMAR signals from the samples, and subsequently the depths of the grooves were evaluated based on the fundamental frequency of the measured signals. The results of the experiments showed that the error in evaluating the depth of a groove tended to increase with the depth. The results also confirmed that the surface roughness of the groove would contribute to the error, and the thickness of a plate without corrosion can be quite accurately evaluated. Analyzing the measured EMAR signals using the proposed POD model, which takes these characteristics into consideration, and a conventional one confirmed that the proposed model can more reasonably evaluate the probability of detection against small wall thinning, as well as the false positive rate.

ID 93
Title Investigation of the Effect of a Bend on Pipe Inspection Using Microwave NDT
Author Guanren Chen, Takuya Katagiri, Haicheng Song, Noritaka Yusa, Hidetoshi Hashizume,
Published in NDT&E International 110 (2020), 102208.
Keywords Microwaves, bend, pipe, mode conversion, NDT
Abstract This study investigated the effect of a bend on microwave NDT (non-destructive testing) applied for rapid pipe inspections. The factors affecting the mode conversion of microwaves due to a bend were deducted theoretically and verified through numerical simulation. Both theoretical and numerical results revealed that the mode conversion at a bend was actually determined by the frequency normalized by the cut-off frequency of an arbitrary mode (f/f ), the ratio of the curvature radius to the inner diameter of the pipe (r/D) and the bend angle (). Subsequent experimental evaluations were performed using four groups of pipes with different inner diameters and five different bends. The effect of a bend was quantitatively evaluated by comparing the reflection signals from pipe wall thinning in a straight pipe with those in a bent pipe. The results showed that the presence of a bend led to a decrease in the reflection signal behind the bend, and the extent of decrease also depended on r/D and of the bend. Furthermore, the length or the depth of the pipe wall thinning did not noticeably affect the decrease in reflection signal, when the bendfs dimensions were certain.

ID 94
Title Quantitative evaluation of the delamination length in mechanical lap joints of high temperature superconducting tapes using Lamb waves
Author Bo Feng, Weixi Chen, Satoshi Ito, Noritaka Yusa, Hidetoshi Hashizume, Artur L. Ribeiro, Helena G. Ramos
Published in Measurement 156 (2020), 107606.
Keywords guided wave, delamination, nondestructive testing, high temperature superconducting tapes
Abstract A mechanical lap joint is a critical part connecting rare-earth barium copper oxide (REBCO) tapes. Until now, the delamination in the joint region, which causes severe heating, has not been efficiently detected and evaluated at room temperature. This paper presents a nondestructive testing method using Lamb waves to evaluate delamination in the lap joint. The dispersion curves of Lamb waves in REBCO tapes and joints are calculated, and their characteristics indicate that the reflected wave produces consistent results for a broadband of frequencies, whereas the transmitted wave only produces good results in a specific range. Then, finite element simulations are performed and the results show that, for the same delamination, the change in arrival time of the reflected wave is larger than the transmitted wave. However, the reflected wave only responds to a delamination on the same side where the excitation is applied. Therefore, in the experimental tests, an ultrasonic probe is placed on both sides of the joints to make tests. The delamination lengths in three samples are determined from the arrival time of the reflected wave and the group velocity, and they are consistent with the results obtained by X-ray microtomography with a maximum difference of 2.0 mm.

ID 95
Title Investigation for contact interface of mechanical lap joint fabricated with high-temperature superconducting conductor using X-ray microtomography
Author Weixi Chen, Satoshi Ito, Noritaka Yusa, Hashizume Hidetoshi
Published in Plasma and Fusion Research 15 (2020), 2405014.
Keywords High-temperature superconducting magnet, Joint-winding, Mechanical lap joint, Contact resistivity, X-ray computer tomography scan
Abstract Joint winding of high-temperature superconducting (HTS) helical coil with conductor segments that are connected using bridge-type mechanical lap joints is considered as a promising method of fabricating magnet for a FFHR heliotron-type fusion reactor. Although methods for joining large-scale HTS conductor has been developed using the gsimple-stackh and gjoint-pieceh procedures, the difference between these procedures is unclear. In this study, the two-row-four-layer joint samples were fabricated via the two joining procedures and compared in terms of contact resistivity. Joint thickness and joint resistance were measured; the contact area at the contact interface was evaluated using an X-ray computer tomography scan, to obtain the precise contact resistivity of the joint. The contact resistivity of the sample fabricated via the "simple-stack procedure" ranged from 2.41-5.15 pm2, whereas that of the sample fabricated using the "joint-piece procedure" ranged from 1.98-6.07 pm2 . There was no significant difference between the procedures in terms of contact resistivity range. Considering the characteristics of joint thickness and location distribution of each lap joint, the inhomogeneous joining pressure was the primary factor affecting contact resistivity. As the similarity of electrical performances of the two procedures was clarified, future studies should focus on the manufacturability of large-scale joints.

ID 96
Title In-pipe crack detection for multiple diameters using TE11 mode microwaves,
Author Guanren Chen, Takuya Katagiri, Noritaka Yusa, Hidetoshi Hashizume,
Published in International Journal of Applied Electromagnetics and Mechanics 64 (2020), 39-46.
Keywords Microwaves, TE11, NDT, mode converter, crack
Abstract This study evaluated the effect of pipe diameter on the applicability of a technique using TE11 mode microwaves for in-pipe crack detection. Three TE11 mode converters of different inner diameters were designed based on theoretical calculations and veri?ed via numerical simulations. The working bandwidths of these mode converters were 7.0, 4.0, and 1.9?GHz. Experimental veri?cation was carried out using brass pipes with the corresponding three inner diameters, and with pipe lengths up to 21?25.5?m. An axial and a circumferential slit were introduced to simulate cracks and deployed at multiple positions along the pipes under test. The results showed that both axial and circumferential slits could be detected and located for an inner pipe diameter up to 39?mm and at a distance of 15?m?24?m.

ID 97
Title Probabilistic evaluation of detection capability of eddy current testing to inspect pitting on a stainless steel clad using multiple signal features
Author Takuma Tomizawa, Haicheng Song, Noritaka Yusa
Published in International Journal of Applied Electromagnetics and Mechanics 64 (2020), 47-55.
Keywords POD, multi-parameter, weld, corrosion, pressure vessel
Abstract This study proposes a probability of detection (POD) model to quantitatively evaluate the capability of eddy current testing to detect ?aws on the inner surface of pressure vessels cladded by stainless steel and in the presence of high noise level. Welded plate samples with drill holes were prepared to simulate corrosion that typically appears on the inner surface of large- scale pressure vessels. The signals generated by the drill holes and the noise caused by the weld were examined using eddy current testing. A hit/miss-based POD model with multiple ?aw parameters and multiple signal features was proposed to analyze the measured signals. It is shown that the proposed model is able to more reasonably characterize the detectability of eddy current signals compared to conventional models that consider a single signal feature.

ID 98
Title Probabilistic evaluation of the area of coverage of a probe used for eddy current non-destructive inspections
Author Noritaka Yusa, Takuma Tomizawa, Haicheng Song
Published in International Journal of Applied Electromagnetics and Mechanics 64 (2020), 11-18.
Keywords Electromagnetic nondestructive evaluation, probability of detection, surface breaking crack, fatigue crack, austenitic stainless steel, coverage path, Monte Carlo simulation, uncertainty
Abstract This study proposes a method to probabilistically evaluate the area of coverage of nondestructive inspections to detect defects on a surface of a structure. For the specific problem, this study considers the effect of the distance between two neighboring scanning lines on the detectability of eddy current testing against near-side cracks. Thirty-eight type 316L stainless steel plates having a fatigue crack were prepared, and eddy current examinations were performed with a sufficiently fine scanning pitch. The full width at half maximum of the spatial distribution of the amplitude of the signals was approximated using a Gaussian function. A probability of detection model considering the distance between two neighboring scanning lines is proposed because in actual inspections a scanning line does not always run directly above a crack. The results demonstrated that the proposed model enables a reasonable probabilistic evaluation of the effect of the distance between two neighboring scanning lines.

ID 99
Title Experimental verification of a TE01 mode converter to locate a crack in a metal pipe
Author Takuya Katagiri, Guanren Chen, Noritaka Yusa, Hidetoshi Hashizume
Published in International Journal of Applied Electromagnetics and Mechanics 64 (2020), 465-472.
Keywords nondestructive testing, metal pipe, surface crack, microwave, time-of-flight, TE01 mode, mode conversion
Abstract In this study, a TE01 mode converter was developed to locate an axial crack on the inner surface of a metal pipe. Three-dimensional finite element simulation was conducted to evaluate the effect of inserted coaxial cables on the transmission characteristic of the mode converter. The result showed that the energy of TE mode microwaves leaned to transmit to one side when the cables penetrated with inclination. To demonstrate the effectiveness of the mode converter, experimental verification was conducted. The mode converter was fabricated based on the simulation result. Microwaves were emitted through the pipe wall of the converter to propagate on both sides (eright sidef and eleft sidef) of a pipe with an artificial slit. Compared with the signals from each side, the reflection from the slit on the right side was more significant than that on the left side. This result is consistent with the numerical simulation result.

ID 100
Title Experimental verification of improved probability of detection model considering the effect of sensor's location on low frequency electromagnetic monitoring signals
Author Haicheng Song, Noritaka Yusa
Published in International Journal of Applied Electromagnetics and Mechanics 64 (2020), 191-199.
Keywords non-normal noise, probabilistic calibration, non-parametric probability density function, finite element simulation
Abstract Structural health monitoring (SHM) is a promising method for maintaining the integrity of structures. A reasonable approach is necessary to quantify its detection uncertainty by taking into account the effect of random sensor locations on inspection signals. Recent studies of the authors proposed a model that adopts Monte Carlo simulation to obtain the distribution of inspection signals numerically influenced by random sensor locations. This model can evaluate the effect not only of multiple defect dimensions but also of the placement of sensors on the detection uncertainty. However, its effectiveness has only been confirmed using pseudo-experimental signals generated by artificial pollution. This study aims to examine the effectiveness of the proposed model in quan-tifying the detection uncertainty of SHM methods using the experimental signals of low-frequency electromagnetic monitoring for inspecting wall thinning in pipes. The results confirm the capability of the proposed model to correctly characterize the distribu-tion of inspection signals affected by random sensor locations and to determine the reasonable probability of detection.