Vol.6 ,No.1, May 2019

Transactions on

GIGAKUSpecial issue of
The 7th International GIGAKU
Conference in Nagaoka(IGCN), 2018&
The 3rd STI-Gigaku, 2018

GIGAKU Press
Nagaoka University of Technology

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October 2018
Nobuhiko Azuma,President of Nagaoka University of Technology

1Editors (2018 to 2019):
Editor-in-chief:
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Co-Editors:
Dr. Kazunori Sato, Vice President, NUT (Professor, Department of Materials Science and Technology,
NUT)
Dr. Shigeru Nagasawa, Professor, Department of Mechanical Engineering, NUT
Dr. Masatoshi Takeda, Professor, Department of Mechanical Engineering, NUT
Dr. Yukio Miyashita Associate Professor, Department of Mechanical Engineering, NUT
Dr. Masahiro Iwahashi, Professor, Department of Electrical, Electronics and Information Engineering,
NUT
Dr. Tomoichiro Okamoto, Associate Professor, Department of Electrical, Electronics and Information
Engineering, NUT
Dr. Koichi Takimoto, Professor, Department of Bioengineering, NUT
Dr. Taichi Sugai, Assistant Professor, Department of Nuclear System Safety Engineering, NUT
Dr. Takaomi Kobayashi, Professor, Department of Science of Technology Innovation, NUT
Dr. Takashi Yamaguchi, Professor, Department of Science of Technology Innovation, NUT
Dr. Takashi Yukawa, Professor, Department of Science of Technology Innovation, NUT
Dr. Tadachika Nakayama, Professor, Department of Science of Technology Innovation, NUT
Dr. Yuichi Otsuka, Associate Professor, Department of System Safety, NUT
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Transactions on GIGAKU
Volume 6, No. 1, April 2019
The 7th International GIGAKU Conference in Nagaoka (IGCN)
and The 3rd STI-Gigaku(October 4-5, 2018, Nagaoka University of Technology, Nagaoka, Japan)
The IGCN is designed and organized to provide a cross-border, cross-sector, cross-disciplinary forum
for those researchers, educators, and industrial leaders who are creating and practicing GIGAKU invarious technology domains in various countries. Some papers presented in the IGCN are published inthis first volume of Transactions on GIGAKU.
The STI-Gigaku conference (hosted by NUT) is most importantly to focus on Sustainable Development
Goals (SDGs), which are the collection of 17 global goals set by the United Nations as 2030 Agenda,
aiming at its world-wide education network system to be proactively integrated onto the next steps
while connecting with parties involved in related fields, sectors, and nationalities to share research
progress and achievements.
Table of contents
1. Pages 06001/1-8
Enhancement of Evanescent-Light-Induced Wedge Waves
due to Water Confinement in a Point-Contact Configuration
Iwao Matsuya, Yuuki Hirai, Yasuhisa Oguro, Takumi Arai, Toshiki Machida,
Takayuki Ishibashi, Ikuo Ihara
2. Pages 06002/1-8
Development of Precision Measuring Robot of Crawler Type andFeasibility Study of Measuring Unit for Improvement of Measurement Accuracy
Ichiro Yoshida, Kazuhide Tanaka
3. Pages 06003/1-8
Effect of Ground Movement Direction on Ultimate Lateral Resistanceof Line Alignment Piles in Clay
Quang N. Pham, Satoru Ohtsuka, Koichi Isobe, Yutaka Fukumoto
4. Pages 06004/1-11
High Temperature Gas Cooled Reactor Regulation Development –Operation & Maintenance Perspective
I Wayan Ngarayana, Kenta Murakami
5. Pages 06005/1-11
Galet – Geant4 Based Application Templet for Primers
Tsukasa Aso, Wataru Takase, Takashi Sasaki
3

6. Pages 06006/1-8
Numerical Study on Core Degradation Behavior with TRAC andMCCI Behavior with MELCOR at Fukushima Dai-ichi Nuclear Reactor Accident
Kohei Ueta, Hiep Huy Nguyen, Kazuyuki Takase
7. Pages 06007/1-6
Basic property of the wind turbine with the circular cylinder blades
driven by longitudinal vortex
Yuya Kimura, Takumi Sankyo, Hayate Kimura, Syodai Sugimura, Takahiro Nomura,
Shigeru Ogawa, Yuji Yamada, Tsutomu Takahashi
8. Pages 06008/1-6
Observation of Three Dimensional Nanostructures Fabricated by TwoPhoton Polymerization Method
Son T. Nguyen1, M. A. Hariz B. Mohd Pauzi, Tadachika Nakayama, Tsuyoshi Takahashi,
Kenya Moriya, Yoshinori Tokoi, Hisayuki Suematsu, and Koichi Niihara
9. Pages 06009/1-8
Optimization of Mirror Magnetic Fields in a Permanent Magnet ECRIon Source for Generation of Multi-Charged Aluminum Ions
Tsubasa Nakamura, Shinji Yamada, Takumi Tomonari, Ayumu Inagaki, Hiroya Uyama,
Yuta Wada, Toyohisa Asaji, Kazumasa Takahashi, Toru Sasaki
10. Pages 06010/1-7
Purification and antigenicity evaluation of fish-disease bacterial outermembrane proteins for immersion vaccine development
Noriyo Mitome, Nagisa Hamada, Naoki Yamashita, Seng Eng Khuan

4

Transactions on GIGAKU 6(1)(2019)06001/1-8

Enhancement of Evanescent-Light-Induced Wedge Waves
due to Water Confinement in a Point-Contact Configuration
Iwao Matsuya1,*, Yuuki Hirai1, Yasuhisa Oguro1, Takumi Arai1, Toshiki Machida1,
Takayuki Ishibashi2, and Ikuo Ihara1
1)
Department of Mechanical Engineering, Nagaoka University of Technology,2)
Department of Materials Science and Technology, Nagaoka University of Technology,1603-1 Kamitomioka-machi, Nagaoka 940-2188, Japan*E-mail: matsuya@mech.nagaokaut.ac.jp

A new method for generating ultrasonic waves utilizing evanescent lightduring the total internal reflection at the surface of a half ball lens is presented.
A waveguide with a sharp wedge is employed as a specimen to launch a wedge
wave and the edge tip of the waveguide ridge is attached to the lens to create acontact point between them. A low-power pulsed Nd:YAG laser is irradiatedinto the lens to form the evanescent light. The effect of water confinement in apoint-contact configuration is investigated for the ability of generating wedge
waves by comparing in an open system. The amplitude of the first mode 1
wedge wave produced by the evanescent light is enhanced more than eighttimes due to the water confinement. The similar relationship between the direct
ablation and the confined ablation for the direct laser irradiation isdemonstrated.

1. Introduction
A laser ultrasonic technique is a powerful tool where an ultrasonic wave is excited by a pulsed
laser in a material and material properties are evaluated by detecting its elapsed time [1, 2]. In
association with the technique, a shock wave provided by the pulsed laser has been applied in medical
applications such as a drug delivery, killing tumors, and so on [3-8]. However, the applicable size has
still been limited to a relatively large-scale due to the diffraction limitation of the irradiated light, anda micro-nano scale application has not still been explored for the technique. Recently, in order toovercome the limitation, near-field optics, including evanescent light, has been offered as the method
in which the laser energy can be focused on a very small area [9, 10], and that has begun to combinewith laser ultrasonic technology [11-14]. If the evanescent light become available as a wave source,
especially in a liquid, the unprecedented usability for smaller objects in the application will be
developed broadly.
We have been attempting to generate bulk acoustic waves in an aluminum plate utilizing
evanescent light formed at a right-angle prism, and it has been successfully carried out [13]. However,
the amplitude of the obtained acoustic waves has been easily changed according to the contact statebecause the plane contact between the plate and the prism is imperfect due to the surface roughness ofeach plane. Besides, the excited wave signal has usually been nothing but a noise level. On the other
hand, there are two methods to generate ultrasonic waves utilizing a pulsed laser ablation. One is direct
ablation where the pulsed laser is directly irradiated onto a bulk sample and the ablation causes
ultrasonic wave, the other is confined ablation where the target sample is covered with a transparent
material such as a glass plate or a liquid and the enhanced ultrasound is generated in the closed system[15-17]. Although the confined ablation is a very important technology in terms of creating an intense
ultrasound, we could not have verified that as long as employing the plane-contact configuration.
A wedge wave is a kind of elastic guided wave propagating along a ridge of a sharp blade [18-21].
Wedge waves can propagate for a long distance with a low attenuation because its energy during thetravel concentrates in a small spot at the blade tip. The vibration of the wedge wave shows
asymmetrical movement across the ridge line and its amplitude is usually much bigger than the otherbulk elastic waves. The wedge wave is thus appropriate for being produced by the evanescent light1

Transactions on GIGAKU 6(1)(2019)06001/1-8

which only has a small energy. Moreover, the point contact between the waveguide and the prism
surface at which the evanescent light is formed can be easily achieved if the edge tip of the waveguideridge is attached to the prism. Therefore, the contact state is drastically improved compared with theplane contact, and most importantly, the confined ablation for the evanescent light can be realized byarranging a liquid around the contact point.
In the present work, we report a method for generating ultrasonic wave taking advantage of theevanescent light. The half ball lens is employed instead of the right-angle prism to avoid stray light at
the oblique side of the prism. A waveguide with a sharp wedge is used to create the intense signal of
the wedge wave and to make the point contact configuration. The generation of wedge waves is carriedout in both the open system and the closed system. The effect of the water confinement is investigated
for the ability of generating wedge waves.

Fig. 1 Scheme of evanescent light generation. (a) Evanescent light and total internalreflection of pulsed laser at medium 1-2 interface. (b) Electric field of evanescent light.

2. Evanescent Light
When the pulsed laser reflects at a boundary between two different mediums, if the incident angle
is more than the critical angle, the evanescent light is formed outside the boundary. Figure 1(a)illustrates the scheme of the evanescent light generation. During the total internal reflection of thepulsed laser irradiated from the medium 1 to 2, the evanescent light exhibits exponential decay with
distance from the interface. The electric field of the evanescent light at the interface is given by [22]
ଶగ ௡

ଶగ

௡

ଶ

‫ݔ(ܧ‬, ‫ܶ = )ݖ‬଴ ݁‫ ݌ݔ‬ቀ−݅߱‫ ݐ‬+ ݅ ఒ ௡భ ‫ ݔ‬sin ߠቁ ∙ ݁‫ ݌ݔ‬ቆ− ఒ ‫ݖ‬ටቀ௡భ ቁ sinଶ ߠ − 1ቇ
మ

మ

(1)

Here T0 is maximum amplitude of electric field, ω is angular frequency of the incident light, λ is wave
length of the light in the medium 2, and θ is angle of incident light, t represents time. The axis
perpendicular to the boundary is Z, the axis equivalent to the boundary is X. n1 and n2 are refractive
indexes of the medium 1 and 2, and the medium 1 is usually glass. Figure 1(b) shows the electric fieldof evanescent light along the Z-axis when the medium 2 is changed. The penetration depth ofevanescent light into the medium 2, which is the distance where the initial electric field decreases 1/e,
is expressed as follows [22],2Transactions on GIGAKU 6(1)(2019)06001/1-8

Λ=

ଵ

೙ మ
మഏ
ටቀ భ ቁ ୱ୧୬మ ఏିଵ
ഊ
೙మ

(2)

where Λ is penetration depth of evanescent light. The refractive indexes are 1.33 for water, 1.37 foraluminum, and 1.51 for glass [13]. In this work, the incident angle of the pulsed laser is determined to
be 69.0° which is larger than the critical angle of 62.1° derived from Snell’s law for the glass-waterinterface, and that of 65.1° for the glass-aluminum interface. Using Eq. (2), when the medium 2 ischanged, the penetration depths of evanescent light are 170 nm for air, 362 nm for water, 510 nm foraluminum. When the evanescent light illuminates a solid plate specimen which usually has more than
1 μm of surface roughness, it does not reach the medium 2 entirely due to the imperfect plane-contact.
In order to verify the ability of generating ultrasonic wave using the evanescent light, the point-contact
between medium 1 and 2 is essential.

Fig. 2 Schematic depiction of experimental setup. (a) Contact point configuration between
waveguide (around ridge) and half ball lens. (b) Picture of waveguide with 30° wedge.
3. Experiment
Figure 2 shows the experimental setup for launching wedge waves on the ridge of the waveguideby means of the evanescent light. A well-polished aluminum (A5052) waveguide with 10 mmthickness is used as a specimen. As shown in Fig. 2(b), the waveguide is 100 mm in length and has a
tip angle of 30°, the sharpness of which is measured at an average of 16.3 μm by a laser microscope.
The flat surface of the half ball lens with 10 mm diameter is positioned to be facing upward. The frontedge of the waveguide ridge is attached on the flat surface of the half ball lens to make a point contact
between them, the angle between the ridge line and the flat surface is fixed at 45°, and the surface Sof the waveguide and the flat surface are normal to each other, as shown in Fig. 2(a). The contact force
between the waveguide and the lens is carefully removed to be less than 50 g, which is confirmed not
to exceed the proof strength of aluminum by the 3-dimentional elastic analysis simulation. A pulsed
Nd:YAG laser (Tempest 30, New Wave Research, 1064 nm) is operated at a 8.2 mW single shot witha duration of 4 ns. When the evanescent light is irradiated on the front edge of the waveguide ridge,
the wedge waves are launched and propagated along the ridge of the waveguide. In order to detectwedge waves, a laser doppler vibrometer (OFV-505, Polytec) is used. The detection point in the middleof the waveguide is 50 mm away from the contact point, and the distance between the detection point
and the end edge of the waveguide is 50 mm.
Figure 3 shows the simulation result of the ray-trace for the optical system using the optical design
software, OpTaliX. A laser beam of 5 mm diameter is focused using a biconvex lens with a 200 mm
focal length. The beam is reflected at a mirror to enter the half ball lens at an incident angle of 69°.
The focal point is controlled to be placed at a point which is 2 mm away from the reflecting point in3

Transactions on GIGAKU 6(1)(2019)06001/1-8

the half ball lens, as shown in Fig. 2. If the pulsed laser is focused at the surface of the half ball lens,
it is easily broken due to an energy concentration. But employing this arrangement, the lens is able toendure the laser power up to approximately 22 mW for a single shot. The spot size on the flat surfaceof the half ball lens is derived at 0.33 mm and 0.18 mm in the major and the minor axis, respectively.
The generation of the wedge wave utilizing the evanescent light is carried out with and without wateron the flat surface of the half ball lens. For comparison, removing the half ball lens, the pulsed laser
is directly focused on the front edge of the waveguide ridge with and without a drop of water. The oval
focused-area on the surface S of the waveguide is 0.14 mm and 0.10 mm in the major and the minor
axis examined by the knife-edge technique [15].

Fig. 3 Ray-trace simulation for optical system. The inlet shows enlarged view of the half ball lens.
When the wedge waves are detected by the vibrometer, the voltage signals are captured using a
12-bit serial acquisition board at a sampling rate of 100 MHz. In order to evaluate the waveforms
purely, data processing such as a filter or an averaging is not conducted. To derive the velocities of thewedge waves from the waveform, the cross-correlation method is utilized to obtain the elapsed time
between the first and the reflected wedge waves from the end edge of the waveguide. The velocity V
for wedge wave in the air is reported as an empirical formula as shown below [18],ܸ = ܸோ sin(݉߶) (3)where VR is velocity of Rayleigh wave, m is order of wave mode, ϕ is wedge angle. Since VR for the
waveguide is experimentally obtained 2940 m/s, the velocities of the wedge wave are estimated to be1470 m/s for mode 1 and 2546 m/s for mode 2. Note that since Eq. (3) is an empirical formula, it isexpected that the velocity derived from Eq. (3) is different from the experimental value as the wave
mode increases [23].

4. Results and Discussion
Figures 4(a) and 4(b) show the waveforms of the wedge waves excited by the directly-irradiatedpulsed laser without water (direct ablation) and with water (confined ablation). In Fig. 4(a), the firstsmall wave is the surface acoustic wave (SAW). The wave packets A1 and A2 correspond to the mode
2 wedge wave, which is passed through the detecting point after the launch and is reflected from theend edge of the waveguide. The wave packets B1 and B2 correspond to the mode 1 wedge wave.
Because of the dispersiveness of wedge waves, the width of the wave packet B2 in time-domain is
widened compared to wave packet B1. The velocities of the mode 1 and 2 wedge wave are obtained to
be 1462 m/s and 2367 m/s for both cases, which agree well with Ref. 20 and 21 despite the differing
launch method. Considering the velocities of the wedge wave and the propagated distance, the wave
packets between A2 and B2 are the mode-converted wedge waves converted at the end edge of the
waveguide. The same tendency concerning the position of the wave packets can be observed in Fig.
4(b), except for the amplitude of the waves. Compared to Fig. 4(a), the peak-to-peak amplitude of the4Transactions on GIGAKU 6(1)(2019)06001/1-8

first mode 1 for the confined ablation is 7.12 times greater than the corresponding one for the direct
ablation, which is enhanced from 9.62 to 68.5 A.U.. In general, during laser heating, the producedpressure in confined ablation is 4-10 times greater than direct ablation [16], so this result is considered
to be appropriate.

Fig. 4 Waveforms of wedge waves obtained by (a) direct ablation and (b) confined ablation for directlaser irradiation. Those produced by evanescent light in (c) open system and (d) closed system
confined by water.
Figures 4(c) and 4(d) show the waveforms of the wedge wave generated by the evanescent lightwith and without water. Regarding the wave position, the first and the reflected mode 1 and 2 wedge
waves are observed as well as the above cases of the direct and the confined ablation. It has been
confirmed that the half ball lens vibrates by itself only if the lens breaks. In addition, any breakdown
inside the half ball lens was not observed following those experiments. Consequently, it is consideredthat those major waves in Figs. 4(c) and 4(d) are not brought by the vibration of the lens but excitedby the evanescent light. The velocities of the mode 1 and 2 wedge waves are 1446 m/s and 2329 m/s,
as shown in Fig. 3(c), and the corresponding ones in Fig. 4(d) are 1449 m/s and 2329 m/s. Those values
almost coincide with both cases of the direct and the confined ablation. The peak-to-peak amplitudeof the first mode 1 wedge wave in Fig. 4(c) is 1.58 A.U. and the corresponding one in Fig. 4(d) is 13.1
A.U. which is amplified 8.26 times. Although the amplitudes of the evanescent-light-induced wedge
wave are roughly one-sixth of those produced by the direct laser irradiation, the similar amplification
factor due to the water-confinement is indicated. When the front edge of the waveguide ridge isseparated less than 0.5 mm from the surface of the lens, which is far bigger than the penetration depthsof the evanescent light in the air and the water, no signal is observed regardless of the existence of thewater. Therefore, it is considered that the vibration of the water that absorbs the energy from the5

Transactions on GIGAKU 6(1)(2019)06001/1-8

evanescent light was not the excitation source for the wedge waves. Figure 5 shows the scanningelectron microscope (SEM) image of the apex of the front edge after the one shot of the evanescentlight confined by the water. A triangle-shaped damaged region is observed at the apex. It is consideredthat the temperature of the waveguide was rapidly increased by the evanescent light irradiation andthe apex was melted, vaporized and ionized in the water-confined geometry. Therefore, it is clearlyshown the wedge waves were excited by the ablation of the evanescent light on a small scale. We
considered the consumed energy for missing volume which is melted and evaporated by the evanescentlight. The missing volume is estimated to be 1.00×10-13 m3 at best by using the SEM image as shownin Fig. 6. Note that every corner of the 3D model in Fig. 6 is sharp, which is different from the actual
shape, the estimated burnout volume might be excessively large. The density of aluminum is 2.68×106
g/m3, therefore the mass of the missing part is derived to be 2.68×10-7 g. Using the mole number ofaluminum (26.98 g/mol), the missing volume is 9.93×10-6 mol. Consequently, the energy of theburnout of the apex can be calculated to be 3.0 J in the best case by taking advantage of that the heat
quantities for melting and vaporizing aluminum are 1.07×104 and 2.91×105 J/mol, respectively [24].
Compared to the total energy of the irradiated laser (2.1 MJ), the energy consumed by the burnout isconsidered to be extremely small due to the point contact.

Fig. 5 SEM image of apex of front edge after evanescent light irradiation confined by water.

Fig. 6 3D model of missing volume at the apex of front edge.

6Transactions on GIGAKU 6(1)(2019)06001/1-8

5. Conclusion
We have reported a novel method for generating ultrasonic waves utilizing evanescent light during
the total internal reflection at the flat surface of a half ball lens. The waveguide with a sharp wedge isused as a specimen to obtain clear signal of generated wedge waves which is much bigger than acoustic
bulk waves. The point-contact configuration between the tip of the waveguide and the half ball lens isemployed to achieve better contact state than the plane contact, and to examine the effect of confinedablation with water. The ray-trace simulation is applied to create the optimal optical system and to
avoid breakdown inside the half ball lens. The amplitude of the first mode 1 wedge wave generated
by the evanescent light is enhanced more than eight times due to water confinement, which shows asimilar relationship between the direct and the confined ablation for the direct laser irradiation.
Although the contact point configuration with the wedge was examined to produce wedge waves inthis work, it is also possible for the evanescent light to provide an ultrasonic wave or a shock wave forother applications, such as an extremely small material in a liquid medium.
Acknowledgments
This work was supported by JSPS KAKENHI grant numbers 15H03889, 16H04507, 17K18822,
and Nagaoka University of Technology (NUT) presidential research grant.
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[24] P. W. Atkins, “Atkins' Physical Chemistry,” Oxford University Press, England, 2014.
(Received: 11 October 2018, Accepted: 6 February 2019)8

Transactions on GIGAKU 6(1)(2019)06002/1-8

Development of Precision Measuring Robot of Crawler Type andFeasibility Study of Measuring Unit for Improvement of Measurement
Accuracy
Ichiro YOSHIDA1,*, Kazuhide TANAKA2
Department of Mechanical Engineering, Faculty of Science and Engineering, Hosei University,
2)
Major in Mechanical Engineering, Graduate School of Science and Engineering, Hosei University,
3-7-2 Kajinocho, Koganei-shi, Tokyo 184-8584, Japan*E-mail: yoshida.ichiro@hosei.ac.jp
1)

Precision geometrical quantity measurements are absolutely necessary inelectric power stations (steam power station, nuclear power station, and etc.)
for environmental load reduction, quality assurance, and safety. These
precision measurements are difficult manual operations. Specifically, thesemeasurements are often performed in high or narrow places, uncomfortableenvironments, and so on. As such, power station employees are subjected tostressful situations and painful postures, among other difficulties. Hence, we
studied and developed a precision geometrical measuring robot to relieve stressand improve the work environment. Herein, we propose the research on
precision measuring robot that is a precision measurement instrument withmobility. The robot proposed in this paper is a mobile, crawler-type precision
measuring robot that can perform surface roughness measurements. Handlingrobots that supply workpieces to surface roughness instruments have beendeveloped; however, we do not know of research on the robotization and selfpropulsion for roughness measurement instruments. Stiffness and stability ofmechanical structure is important for high-precision measurement; however,
the measurement accuracy of the measuring robot decreases because of thedecrease in stiffness and stability caused by the lightweight structure needed
for robotization. Therefore, we propose a measuring unit that uses
electromagnets. In this research, the mechanism and structure of the measuring
unit was designed and developed, and the effectiveness and capability of thedeveloped measuring unit were examined through experiments. From theresults of the measuring experiments, standard deviations of the roughness
parameter value, Ra, were improved from one third to half by using the
proposed measuring unit with electromagnets.

1. Introduction
Precision geometrical quantity measurements in electric power stations are absolutely necessaryfor environmental load reduction, quality assurance, and safety [1-3]. These precision measurements
are difficult manual operations. Specifically, these measurements are often performed in high, narrowplaces, uncomfortable environments, and so on. As such, power station employees are subjected tostressful situations and painful postures, among other difficulties. Hence, we study and develop a
precision geometrical measuring robot to relieve stress and to improve the working environment.
Examples of precision geometric quantity measurements in electric power stations include length
measurement, form measurement, geometrical tolerance measurement, surface roughness
measurement, surface texture measurement, and wear measurement, among others. In this work, we
propose and develop a precision crawler-type geometrical measuring robot that can measure surface
roughness, because surface texture influences the environmental loading and lifespan of power stations.
To the best knowledge of the authors, this research is the first that introduces a precision geometricalmeasuring robot with mobility for surface roughness measurement. Presently, handling robots that
supply workpieces for surface roughness instruments have been developed [4]; however, we do not1Transactions on GIGAKU 6(1)(2019)06002/1-8

know of research on robotization and self-propulsion for roughness measurement instruments.
Furthermore, in this research, we develop a measuring unit to improve the accuracy of the roughness
measurement. Weight reduction of the robot is essential to enable self-propulsion and smooth motion;
however, the measurement accuracy of the measuring robot deteriorates as its stiffness and stability
decrease as a result of the lightweight structures. Therefore, we propose a measuring unit using
electromagnets. In this research, we design and develops the mechanism and structure for themeasuring unit. The effectiveness and capability of the developed measuring unit are examinedthrough experiments. From the results of the measuring experiments, standard deviations of theroughness parameter value, Ra, were improved from one third to half by using the measuring unit withelectromagnets.
2. Precision Measuring Robot
In this research, we designed and developed a prototype of a precision measuring robot. In earlier
studies, we presented a basic concept and conceptual design for the precision measuring robot [5, 6].
Figure 1 shows the developed prototype precision measuring robot in this research. Figure 2 shows
the 3D CAD model of the prototype precision measuring robot as a schematic diagram. Specifically,
the precision measuring robot is a roughness measurement instrument that is capable of self-propulsion
by crawlers. The size of the robot is 400 mm long, 280 mm wide, and 220 mm high. Additionally, theprimary structure of the robot consists of aluminum plates and frames for weight reduction. As shownin Figs. 1 and 2, the crawlers for self-propulsion are arranged on both sides of the main body of therobot, and the surface roughness measuring unit is located at the center of the robot. The crawlers are
driven by two geared motors (TG-47G-SG-50-HA, TSUKASA Electric Co., Ltd.) and eight sprocket
wheels. The main components of the precision measuring unit are a contact-type surface roughness
measuring sensor, a drive unit for the roughness measuring sensor, electromagnets, and a verticallymoving unit for the roughness sensor, drive unit, and electromagnets. The details of the prototype
precision measuring unit are introduced in the following section.
Electronic circuits for controlling the crawlers and the roughness measuring unit are arranged on
top of the robot at the rear. A microcontroller in the electronic circuits uses Arduino, which is an opensource electronics platform based on hardware and software [6]. As shown in Fig. 3, the transmissionof control commands to the electronic circuits of the precision measuring robot and reception of
measured results by the precision measuring robot are performed wirelessly by a Bluetooth connection.
3. Precision Measuring Unit Using Electromagnets
In this research, we designed and developed a prototype precision measuring unit for improvementof measurement accuracy.
In general, precision measurement instruments are designed such that the stability and stiffnessof the instrument are high, because high measurement accuracy is a top priority. However, improving
the stiffness causes the instrument to be heavy. In contrast, a robot must be lightweight, because themotion of the robot becomes disabled if the weight of robot is designed as heavy as a precision
measurement instrument with high stiffness. However, the measurement accuracy of the precision
measuring robot deteriorates, because robotization of a precision measurement instrument involves a

Fig. 1 Prototype precision measuring robot for roughness measurement.
2

Transactions on GIGAKU 6(1)(2019)06002/1-8(a) Front view(b) Side view(c) Top viewFig. 2 Schematic diagram of prototype precision measuring robot.

Fig. 3 Radio communication via Bluetooth.
3

Transactions on GIGAKU 6(1)(2019)06002/1-8

decreased stability and stiffness associated with the weight reduction. Therefore, we devised an
application of electromagnets for the precision measuring unit to solve this problem and develop a
prototype of the precision measuring robot. Figure 4 shows the internal structure of the prototype
precision measuring unit. The measuring unit has three guide ball bushings and one ball screw coupled
to a geared motor. The measuring unit is vertically moved by the ball screw. The unit has fourelectromagnets (Uxcell Co., Ltd., 12 V, 0.24 A, 25 N of magnetic force, and 20 mm diameter), two of
which are located at the corner positions of the rectangular base plate of the measuring unit. The
electromagnet attracts the measuring machine and the measuring surface during measurement. We
consider that the electromagnet can suppress vibration of the measuring machine unit at the time of
measurement. The other two are located at nearby positions of both sides of the roughness sensor to
improve measuring accuracy. In the present study, the contact-type surface roughness measuring
sensor and the drive unit for the sensor were not developed; consequently, a portable surface roughness
tester SRT 6210 (Nihon Sonatest Advanced Inspection Technology Inc.) was utilized. When measuring
roughness, the stylus slides on the measuring surface. The stylus detects irregularities on the measure-(a) Perspective view(b) Side view(c) Top viewFig. 4 Internal structure of the precision measuring unit using electromagnets.
4Transactions on GIGAKU 6(1)(2019)06002/1-8(a) Side view(b) Bottom viewFig. 5 Stylus of the surface roughness tester SRT 6210
Table 1 Specification of the surface roughness measuring instrument [7, 8]
Parameters

Ra, Rz, Rq, Rt

Measuring Range

Ra, Rq: 0.005 - 16.00 μm
Rz, Rt: 0.020 - 160.0 μm

Accuracy≤ 10%

Fluctuation of display value≤ 6%

SensorTest Principle: Inductance typeRadius of Probe Pin

5 μm

Material of Probe Pin

Diamond

Dynamo-measurement of Probe

4 mN(0.4 gf)

Probe Angle

90 degrees

Vertical Radius of Guiding Head

48 mm

Maximum driving stroke

17.5 mm

Cutoff length (l)0.25 mm / 0.8 mm / 2.5 mm optional
sampling length = 0.25 mm, Vt = 0.135 mm/s

Driving speed

sampling length = 0.8 mm, Vt = 0.5 mm/s
sampling length = 2.5 mm, Vt = 1 mm/s

Profile digital filter

Filtered Profile: Gauss

Evaluation length

5 cut-offment surface. The roughness parameter is calculated by analyzing the unevenness of the measured
surface. The stylus is operated by the measuring unit. The position of the stylus is shown in Figure 5.
The measurement principle of the roughness sensor is a method of converting stylus deviations into
electrical signals with a piezoelectric element. Commands to, and results from, the measuring unit aretransmitted and received via Bluetooth wireless radio. Table 1 lists the specification of the surface
roughness measuring instrument.
4. ExperimentThis paper presents a basic experiment for the precision measuring robot. The robot elevates themeasuring unit after each roughness measurement, and thereafter, moves to a next position.
Subsequently, after movement to the next position, the robot measures the surface roughness at theposition by lowering the measuring unit. Table 2 lists the roughness measurement results obtainedusing the developed precision measuring robot. Experiments were performed on a cast iron precision
surface plate, and surface roughness parameters Ra, RzJIS, and Rq [9, 10] were measured. For
5

Transactions on GIGAKU 6(1)(2019)06002/1-8

inspection of the precision of the robot, the parameters were measured 10 times at each of two different
positions—A and B. To verify the validity of the measuring unit with electromagnets, measurements
were taken with the electromagnets turned on and off at each position. As listed in Table 2, themeasurement result is reasonable because it is within the accuracy of Table 1. When the electromagnets
are turned off, the average measurement results for position A are Ra is 0.287 mm, RzJIS is 0.812 mm,
Rq is 0.364 mm; and those for position B were Ra is 0.217 mm, RzJIS is 0.615 mm, and Rq is 0.264 mm.
When the electromagnets are turned on, the average results for position A are Ra is 0.284 mm, RzJIS is0.804 mm, Rq is 0.366 mm; those for position B are Ra is 0.213 mm, RzJIS is 0.603 mm, and Rq is 0.266
mm. To verify the validity of the measuring unit and electromagnets, the standard deviations and rangesof the measurement results are also shown in Table 2. When the electromagnets are turned from off toon, the standard deviations of Ra are improved from 5.6 nm to 2.4 nm at position A, and from 4.1 nm
to 1.0 nm at position B. Similarly, the standard deviations of RzJIS are improved from 15.8 nm to 6.9
nm at position A, and from 11.3 nm to 3.0 nm at position B. The standard deviations of Rq are
improved from 9.3 nm to 4.5 nm at position A, and from 3.0 nm to 1.8 nm at position B. Moreover,when the electromagnets are turned from off to on, the ranges of Ra are improved from 21.0 nm to 7.0
nm at position A, and from 14.0 nm to 3.0 nm at position B. Similarly, the ranges of RzJIS are improved
from 60.0 nm to 19.0 nm at position A, and from 38.0 nm to 9.0 nm at position B. The ranges of Rq
are improved from 33.0 nm to 13.0 nm at position A, and from 10.0 nm to 6.0 nm at position B. Fromthese experimental results, we consider that the use of the measuring unit with electromagnets results
in reduction of measurement variation. Table 3 lists the results of measuring similar measurement
points on a different surface roughness measuring machine SJ 210 (Mitutoyo Corporation) [11].
Comparing the measurement result by SRT 6210 when the electromagnets are turned off with themeasurement result by SJ 210, Ra and Rq are the same, and RzJIS is not the same. However, theTable 2 Measurement results of roughness parameters Ra, RzJIS, and Rq by the developed precision
measuring robot, and validity of the measuring unit and electromagnets.
Position A

Position B

Ra µm

RzJIS µm

Rq µm

Ra µm

RzJIS µm

Rq µm

Electromagnet

Electromagnet

Electromagnet

Electromagnet

Electromagnet

Electromagnet

Times

OFF

ON

OFF

ON

OFF

ON

OFF

ON

OFF

ON

OFF

ON

1st

0.276

0.289

0.782

0.817

0.342

0.371

0.207

0.211

0.587

0.597

0.257

0.262

2nd

0.283

0.282

0.801

0.798

0.355

0.364

0.214

0.213

0.606

0.603

0.262

0.265

3rd

0.289

0.282

0.817

0.798

0.366

0.366

0.217

0.214

0.616

0.606

0.264

0.267

4th

0.291

0.286

0.823

0.811

0.366

0.373

0.218

0.214

0.619

0.606

0.266

0.267

5th

0.297

0.286

0.842

0.811

0.375

0.371

0.217

0.214

0.616

0.606

0.264

0.267

6th

0.284

0.284

0.804

0.804

0.366

0.369

0.221

0.214

0.625

0.606

0.266

0.267

7th

0.286

0.282

0.811

0.798

0.369

0.362

0.217

0.213

0.616

0.603

0.265

0.266

8th

0.284

0.282

0.804

0.798

0.364

0.362

0.22

0.212

0.622

0.600

0.267

0.267

9th

0.289

0.283

0.817

0.801

0.369

0.364

0.218

0.213

0.619

0.603

0.266

0.268

10th

0.289

0.283

0.817

0.801

0.369

0.36

0.221

0.213

0.625

0.603

0.267

0.268

Average

0.287

0.284

0.812

0.804

0.364

0.366

0.217

0.213

0.615

0.603

0.264

0.266

5.6

2.4

15.8

6.9

9.3

4.5

4.1

1.0

11.3

3.0

3.0

1.8

21.0

7.0

60.0

19.0

33.0

13.0

14.0

3.0

38.0

9.0

10.0

6.0

Standard
deviation
nm
Range
nm

Table 3 Results of roughness parameters Ra, RzJIS, and Rq by SJ 210.
6

Transactions on GIGAKU 6(1)(2019)06002/1-8

Position A

Position B

Times

Ra µm

RzJIS µm

Rq µm

Ra µm

RzJIS µm

Rq µm

1st

0.284

1.098

1.756

0.195

0.819

0.253

2nd

0.286

1.149

1.836

0.192

0.777

0.25

3rd

0.285

1.178

1.841

0.195

0.796

0.253

4th

0.285

1.159

1.842

0.195

0.783

0.253

5th

0.285

1.174

1.851

0.196

0.800

0.255

6th

0.286

1.208

1.868

0.196

0.843

0.255

7th

0.287

1.202

1.897

0.197

0.804

0.256

8th

0.287

1.238

1.923

0.197

0.821

0.256

9th

0.287

1.229

1.914

0.197

0.813

0.257

10th

0.288

1.246

1.940

0.198

0.797

0.254

Average

0.286

1.188

1.867

0.196

0.805

0.254

Standard deviation nm

1.2

45.8

54.2

1.7

19.4

2.0

Range nm

4.0

148.0

184.0

6.0

66.0

7.0

standard deviation by SJ 210 is higher than SRT 6210. Therefore, the result of RzJIS cannot conclude
which surface roughness measuring machine is correct.
5. Conclusion
We designed and developed a precision measuring robot. Moreover, a measuring unit with using
electromagnets was proposed, and its effectiveness and capability was confirmed through experiments.
The main conclusions obtained in this study are as follows:
1) In this study, a precision roughness measuring robot was proposed as a new precision roughness
measurement instrument, and it was designed and developed. To the best knowledge of authors,
this research is the first that introduces a precision geometrical measuring robot that is a mobile
surface roughness instrument with mobility.
2) We proposed using electromagnets to mitigate the measurement accuracy deterioration of themeasuring robot due to the decrease in stiffness and stability. The prototype precision measuring
unit using electromagnets was designed and developed.
3) The proposed measuring unit with electromagnets can improve the standard deviations ofroughness parameters Ra, RzJIS, and Rq from one third to half, or greater. Because the effect ofutilizing electromagnets for measurement accuracy improvement was confirmed through a basic
experiment, the idea of this research is considered valid and efficacious.
Our plans for future work are as follows: 1) The authors will analyze the frequency characteristicsof the precision measuring robot and the measuring unit with electromagnets. The effect andmechanism of the electromagnets will be examined and clarified by both experimental and numericalanalysis. 2) The authors will design and develop an optimized measuring robot and unit by using thefrequency analysis results. 3) Demonstration experiments with the developed precision measuring
robot will be performed in industrial fields for commercialization.
Acknowledgment
A part of this work was supported by the JKA Foundation Research Project Number 2017M-102,
Japan. The authors would like to thank the JKA Foundation.
References7

Transactions on GIGAKU 6(1)(2019)06002/1-8[1] Ken Onishi, Yukifumi Kohata, Noriko Onishi and Kimihiro Shinoyama, “Development ofmanipulators for nuclear power plants’ maintenance and an hierarchical open system,” Journal of
the robotics society of japan, Vol. 34, No. 4, pp. 280-290, May. 2016.
[2] Seungho Kim and Chang-Hwan Choi, “The robotic technology applications on nuclear power
plants in Korea,” Journal of the robotics society of japan, Vol. 23, No. 5, pp. 548-551, July 2005.
[3] Lynne E. Parker and John V. Draper, "Robotics applications in maintenance and repair," Handbookof Industrial Robotics, 2nd Edition, edited by Shimon Nof, pp. 1-16, Mar. 1999.
[4] Kosaka Laboratory Ltd., “Non-contact surface roughness measuring instrument,” https://mectjapan.com/2017/visitor/information.php?ChargeNo=134, [accessed 18 August 2018].
[5] I. YOSHIDA, K. TANAKA, and H, KIM, “Precision measurement robot for assisting efficiency
improvement of energy plant,” The Hyper-Interdisciplinary Conference 2018, TEPIA Advanced
Technology Gallery, Tokyo, Japan, vol. 7, P-9, p. 84, 2nd- 3rd, Mar. 2018.
[6] I. YOSHIDA and K. TANAKA, “Development of Precision Measuring Robot of Crawler Typeand Feasibility Study of Measuring Unit for Improvement of Measurement Accuracy,” The 7thInternational GIGAKU Conference (IGCN2018), Nagaoka University of Technology, Niigata,Japan, RD-002, p. 15, 5th- 6th, Oct. 2018.
[7] Arduino homepage, https://www.arduino.cc/, [accessed 1 September 2018].
[8] AIT inc., “SRT-6210 manual Ver. 2402,” pp. 1-18, 2012.
[9] AIT inc., “SRT-6210 Home Page,” http://www.ait-ultrasonic.jp/details1122.html, [accessed 10
January 2019].
[10] ISO 4287:1997/ Amendment. 1: 2009, “Geometrical Product Specifications (GPS) – Surface
Texture: Profile Method – Terms, Definitions and Surface Texture Parameters,” Apr. 1997.
[11] JIS B 0601:2013, “Geometrical Product Specifications (GPS) – Surface Texture: Profile Method– Terms, Definitions and Surface Texture Parameters,” Mar. 2013.
[12] Mitutoyo Corporation, “Surface Roughness Measuring Machines Home Page,”https://www.mitutoyo.co.jp/products/hyomen/hyomen.html, [accessed 10 January 2019].
(Received: 17 October 2018, Accepted: 13 March 2019)8

Transactions on GIGAKU 6(1)(2019)06003/1-8

Effect of Ground Movement Direction on Ultimate Lateral Resistanceof Line Alignment Piles in Clay
Quang N. Pham1,*, Satoru Ohtsuka1, Koichi Isobe2 and Yutaka Fukumoto1
Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata, 940-2188, Japan
2
Hokkaido University, 13 Kita, 8 Nishi, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan*E-mail: s155066@stn.nagaoakaut.ac.jp

1

This study estimated the ultimate lateral resistance of pile group against
horizontal ground movement by using two-dimensional rigid plastic finite
element method (RPFEM). The effect of ground movement direction on theultimate lateral resistance was investigated through the case studies.
According to the results, it can be seen that changes in both the ultimate
lateral resistance and the failure mode of ground around piles were observed.
The impact of the pile spacing on load bearing ratios was studiously
investigated. Since each pile in the group affects other piles, it leads the load
bearing ratio significantly to depend on pile positions such as the front orback piles. Moreover, the load bearing ratio of each pile went up with anincrease in pile spacing, but it was different remarkably among piles. The
load bearing ratio varied with the directions of the ground movement.

1. Introduction
Pile foundation is designed not only to carry a vertical load of superstructures, but also to resist ahorizontal load and a bending moment. In earthquake engineering, the examination of lateral resistanceof pile group against horizontal movement of ground is an important task in the design of pilefoundation. These days, the design value for lateral resistance of pile has increased as an increase inmeasured ground response displacement of clayey soils during earthquakes. It makes the design ofpile foundation mainly severe on economical aspect. Therefore, it is crucial to assess the ultimate
lateral resistance of piles against large horizontal ground movement since it provides an extreme
condition of design on load applied to pile.
Several studies reported the ultimate lateral resistance of single pile such as Broms et al. (1964),
Randolph and Houlsby (1984). Broms (1964) studied the slip line method to calculate the ultimate
lateral resistance of single pile in the range of 8.28 cu-12.56 cu for various pile sections under smoothand rough conditions on the interface between pile and soils, in which cu is un-drained shear strengthof soil. Chen et al. (1994), Chen and Poulos et al. (1997), Georgiadis and Sloan et al. (2013) used thenumerical analysis to calculate the ultimate lateral resistance of pile groups. However, most of theprevious studies analyzed the limit load for the prescribed load applied to the piles. Hence, the pastwork focused on the ultimate lateral resistance of single piles because the load applying to each pilein a pile group was not known prior to an analysis. This study newly defines the boundary condition
for assessment of ultimate lateral resistance of pile groups against horizontal ground movement. The
author simulated the pile-soil system by employing a two-dimensional rigid plastic finite element
analysis based on the upper bound theorem. Rigid plastic finite element method (RPFEM) has been
applied to geotechnical engineering by Tamura et al. (1987) and developed for frictional material as
Tamura et al. (1991). In this method, the limit load is calculated without any assumption on potential
failure modes. The method is effective in computing the ultimate lateral resistance of pile group against
horizontal ground movement in clayey soil.
In this study, the pile-soil system is simulated for rough condition on the interface between pileand soils under two-dimensional condition. The ultimate lateral resistance of the pile group is affectedby many factors, such as pile spacing, number of piles, and directions of the ground movement.
However, only a few studies have considered the effect of loading direction on the ultimate lateral1Transactions on GIGAKU 6(1)(2019)06003/1-8

resistance such as Georgiadis et al. (2013), Zhao et al. (2017). They demonstrated the change in the
total ultimate lateral resistance and the failure mode of ground around the pile. The effect of thenumber of piles arranged in a row was not considered. This study investigated the effects of thedirections of ground movement on the ultimate lateral resistance by increasing the number of piles ina group. Load bearing ratios of piles in groups are calculated by adjusting the pile spacing.
2. Rigid plastic finite element method
Tamura (1991) developed the rigid plastic constitutive equation for frictional material. The
Drucker-Prager’s type yield function is expressed as follow.
f (σ ) = αI1 + J 2 - k = 0(1)

where I1 is the first invariant of stress σ ij and I 1 = tr(σ ij ) in which extension stress is defined positive.
J2 is the second invariant of shear stress s ij and J 2 =and k =

3c
9 + 12tan 2f

1
s ij s ij and the coefficients, α =2

tan f
9 + 12 tan 2 f

are the material constants in which ϕ is internal friction angle and c is cohesion

under the plane strain condition. The volumetric strain rate is expressed as follows:æ æös ö÷ ÷
æ ¶f (σ ) öçε v = tr(ε) = tr ç λ÷ = tr ç λç αI +÷=ç çè ¶σ ø
2 J 2 ÷ø ÷
è è
ø

3α

e

(2)

1
3α +
2
2

where λ is an indetermine multiplier and I is the unit stress tensor. The strain rate ε which is purely
plastic component should satisfy the volumetric constraint condition as follow:
3αh(ε) = ε v -e = εv - he = 0

1
3α +
2

(3)

2

in which εv and e indicate the volumetric strain rate and the norm of strain rate, respectively. The
parameter h is defined in Eq. (3). The rigid plastic constitutive equation is expressed by Lagrangian
method after Tamura (1991) as follows:
k

σ=

3α +
2

ε
ε ö
æ
+ βç I - h ÷

ø
e
e
è
1

(4)

2

where β represents a Lagrangian multiplier which indicates the equilibrating stress satisfying the yieldfunction expressed by Eq.(1). Moreover, the constraint condition on strain rate is introduced into theconstitutive equation directly with the use of penalty method (Hoshina et al. (2011), Quang et al.
(2018)). The stress-strain rate relation for the Drucker-Prager’s yield function is expressed as follow:
σ=

k
3α +
2

(

)

ε
ε ö
æ
+ κ εv - he ç I - h ÷
e ø
è
1 e
2

(5)

where κ is a penalty constant. FEM with this constitutive equation provides the equivalent equationof the upper bound theorem in plasticity so that this method is called as RPFEM in this study. It isnoted the property of this constitutive equation that the relationship between stress and strain rate is
specified. The norm of strain rate is substantially indeterminate since the limit state of structure isfocused. Stress is determined for normalized strain rate using its norm. Hoshina et al. (2011)
introduced the constraint condition on external work into the equilibrium equation by using the penalty
method. They reported that more rational results were obtained by the developed method than bymethods in previous works. The use of the penalty method is advantageous in that it can shorten thecomputation time and lead to stable computational results. Since this study focuses on cohesive soils,
as mentioned above, the constitutive equation is limited to the von Mises yield function where the2Transactions on GIGAKU 6(1)(2019)06003/1-8

ground is frictionless and deforms under a constant volume. The rigid plastic constitutive equation is
simple and effective for assessing the limit state of the ground due to the advantage of not using an
uncertain elastic modulus for the ground.

Model (a)Uniform distributed load

Model (b)Direction of ground movement

Typical finite element mesh and boundary condition

3. Ultimate lateral resistance of line alignment piles
3.1 Analysis boundary condition of model under plane-strain condition
Figure 1 shows two ways to simulate pile-soil system under different boundary conditions. The
typical finite element mesh and the boundary condition of single pile against horizontal groundmovement are shown in model (a). The soil and pile were assumed as rigid perfectly plastic material,with the following properties: the undrained shear strength of soil was cu=100 kPa and the internal
friction angle of soil was ϕ=0o, while the shear strength of pile material was cp=50000 kPa and theinternal friction angle of pile was ϕ=0o. Analyses were performed for a pile diameter of D=0.6m. In
particular, the outer boundary elements perpendicular to the direction of ground movement employ
rigid elements to simulate the homogeneous ground movement. A uniform distributed load wasapplied at all nodes of the rigid outer boundary elements to define the prescribed load and the load -Uniform distributed load

Failure modes of ground around pilese max0

pu=12.27 cu

pu=12.30 cu

Fig. 1 Boundary conditions and failure modes of single pile in two models

3

Transactions on GIGAKU 6(1)(2019)06003/1-8

coefficient. The ultimate lateral resistance was assessed by computing the limit value for this loadcoefficient, and be set up with the started load factor of 1. The center of the pile was set as a fixedvelocity boundary condition and the reaction of the piles was calculated to analyse the load bearing
ratio. Moreover, the distance from the center of the pile to four boundary surfaces was set at more than
10.0 D to avoid the effect of boundary conditions on the failure mode of the ground around pile. Model(b) shows the second boundary condition for directly applying the load on pile as the previous works.
The center of pile was set with the free condition but the four boundary surfaces were set by a fixed
condition. The analysis was performed by applying the uniform distributed load at all nodes of the pile
diameter.
The obtained results of strain rate distribution for two models are shown in Fig. 1. The norm of thestrain rate presented contour lines in the range of emax ~ emin (= 0) . The distribution of e shows thefailure mode of the ground reflecting pile-soil interaction effect. Figure 1 shows similarly to the failuremode of single pile in both boundary conditions. The failure mode of ground around pile is observedin the range of 1.5 D-2.0 D from the center of pile and same the slip-line of Broms (1964), Georgiadis
and Sloan (2013). The ultimate lateral resistance of single pile generally obtained a close value as
12.27 cu for the model (a), 12.30 cu for the model (b), in which the total resistance is normalized withthe length of the pile diameter. The difference in ultimate lateral resistance is about 0.24% andprobably due to the difference in finite element meshes. These values are almost similar 11.95 cu ofGeorgiadis and Sloan (2013). The difference may be caused by the fact that they employed different
models, namely, the soil and the pile were modeled as linear elastic-perfectly plastic and linear elastic
materials in their work.
In model (a), the obtained value of single pile was observed to coincide with model (b) and theprevious work. It proved that the method proposed for assessment of the ultimate lateral resistance ofpiles is rational and accurate. Hence, model (a) is effective to calculate not only total ultimate lateralresistance of piles, but also load bearing ratio of piles
3.2 Effect of direction of ground movement on ultimate lateral resistance.
As mentioned above, the purpose of this study is to investigate the effects of the direction of groundmovement on ultimate lateral resistance by considering the pile number. The ultimate lateral resistance
was systematically computed for changes in the pile spacing where the spacing s is the distance
between the centers of two piles. The horizontal direction angle is defined as the angle between the
direction of ground movement and the pile to pile axis, and varies from 0 to 90 degrees. This study
used the average ultimate lateral resistance of piles to discuss the effect of the direction of groundmovement. The average ultimate lateral resistance (q/cu) of piles is expressed as q/cu to indicate thenormalized value by the undrained shear strength of clay cu. The average ultimate lateral resistance q(kN/m2) is subsequently calculated by dividing the total ultimate lateral reaction force Q (kN/m) by
the pile diameter and the number of piles.
Figure 2 shows the relationship between the average ultimate lateral resistance and the pile spacing
for an increase in pile number. The ultimate lateral resistance of the pile is normalized by the lengthof the pile diameter. As a result, since the setting of shear strength and the pile diameter does not affectthe ultimate lateral resistance. In the case of two-pile, the average ultimate lateral resistance reduced
almost proportionally to the decrease in direction angle of ground movement in the range of 1.0 D-3.0
D and it coincided with that of single pile in the range of 4.0 D-6.0 D in pile spacing. While the average
ultimate lateral resistance increased non-linearly with an increase in pile spacing for all direction cases.
In the case of 90 degrees, the average ultimate lateral resistance was achieved slightly higher than thatof single pile in the range of nearly 1.0 D-1.75 D. It is because the intermediate ground between two
piles behaved as a rigid block as shown in Fig. 3(a). It seems appropriate that the average ultimate
lateral resistance was the greatest in case of 90 degrees, since the substantial distance of pile spacing
projected to the perpendicular plane against the ground movement was the largest even if the pile
spacing is the same. However, as the failure mode of the pile-soil system varied depending on the pile
spacing, the peak value in average ultimate lateral resistance was obtained at pile spacing of around1.25 D. The trend to locally form the peak value was observed for other inclination angles at aroundpile spacing of 1.25 D. In the case of three-pile and four-pile groups, the obtained results also show4Transactions on GIGAKU 6(1)(2019)06003/1-8

the similar trend with that of two-pile group in Figs. 2(b), (c). However, the difference in average
ultimate lateral resistance between the case of 90 and 0 degrees increased with an increasing numberof piles. In the case of 90 degrees, the average ultimate lateral resistance of pile obtained the same forpile spacing despite number of piles. However, in the case of 0 degrees, the average ultimate lateralresistance was shown to vary with the number of piles and to decrease with an increase in the numberof piles. The effect of the number of pile on the trend in ultimate lateral resistance against pile spacing(a)Average ultimate lateral resistance of pilein pile group (q/cu)

14.0
13.0
12.0
11.0
10.0
Direction of 90deg
Direction of 45deg
Direction of 30deg
Direction of 0deg
Single pile

9.0
8.0
7.0
1.0

3.0
4.0
Normalized pile spacing (s/D)

5.0

6.0

14.0
Average ultimate lateral resistance of pilein pile group (q/cu)

(b)

2.0

13.0
12.0
11.0
10.0
9.0

Direction of 90deg
Direction of 45deg
Direction of 30deg
Direction of 0deg
Single pile

8.0
7.0
6.0
1.0

2.0

3.0

4.0

5.0

6.0

Normalized pile spacing (s/D)
14.0
Average ultimate lateral resistance of pilein pile group (q/cu)

(c)

13.0
12.0
11.0
10.0
9.0
8.0

Direction of 90deg
Direction of 45deg
Direction of 30deg
Direction of 0deg
Single pile

7.0
6.0
5.0
1.0

2.0

3.0
4.0
5.0
Normalized pile spacing (s/D)

6.0

7.0

Fig. 2 Average ultimate lateral resistance of piles: (a) two-pile, (b) three-pile and (c) four-pile groups5Transactions on GIGAKU 6(1)(2019)06003/1-8changed with number of pile, where the range of pile spacing to vary the ultimate lateral resistancebecame wider. The other cases varying from 0 to 90 degrees were found to exist in between those of
0 and 90 degrees.
As discussed above, the effect of the direction of the ground movement was caused by the change
in the failure mode of the ground around the piles. The typical failure modes of two-pile, three-pileand four-pile groups were influenced by the direction of the ground movement at S=1.25 D spacing
shown in Fig. 3. In case of 0 and 90 degrees, the intermediate ground of piles did not yield any plastic
deformation, whereas it clearly yielded the plastic deformation in case of 45 degrees. It indicates theshearing of intermediate ground took place despite the same pile spacing with the case of 0 and 90
degrees. It is interesting that the failure mode changed due to direction of ground movement in spiteof smaller pile spacing, besides the ultimate lateral resistance varied continuously between the valuesof 0 and 90 degrees. From Figs. 3(a) to 3(c), it is apparent that the area of failed ground became wider
as the number of piles was greater. The failure zone of ground around pile was observed about 3.0 D3.5 D from the center of pile for two-pile group, 4.5 D-5.0 D for three-pile group and 5.5 D-6.0 D for
four-pile group.
e max0
Direction of ground movement

Direction of 0 degrees

Direction of 45 degrees

Direction of 90 degrees

(a)

(b)

(c)

Fig. 3 Failure modes of pile groups at S=1.25 D in cases of 0, 45 and 90 degrees, respectively(a) two-pile, (b) three-pile and (c) four-pile groups

4. Load bearing ratio of piles in the pile groups
In order to better understand the effect of the ground movement direction on the pile behaviour,the lateral resistance of each pile in a group is calculated. The ratio of the lateral resistance of eachpile to that of a single pile is defined as the load bearing ratio. The obtained results show significant

6Transactions on GIGAKU 6(1)(2019)06003/1-8

difference among piles in groups. The load bearing ratios were often less than 1.0 and showed thesame trend as to increase with a rising pile spacing. Table 1 and 2 express the summary of obtained
results on load bearing ratio of piles for two-pile and three-pile group in various direction of groundmovement. It can be observed that the load bearing ratio significantly depend on the pile spacing andthe direction of ground movement.
Table 1. Summary of load bearing ratios in case of 0 and 90 degrees

Direction of groundmovement

Group size

Load bearing ratio
2nd pile

Pile
spacing

1st pile

1.5D

0.76

0.67

2.0D

0.81

0.73

3.0D

0.93

0.86

4.0D
5.0D
1.5D

0.99
1.00
1.03

0.96
0.99
1.03

2.0D

0.97

0.97

3.0D

0.95

0.95

4.0D
5.0D
1.5D

0.98
1.00
0.72

0.98
1.00
0.52

0.57

2.0D

0.86

0.54

0.61

3.0D

0.94

0.75

0.76

4.0D
5.0D
1.5D

0.97
1.00
1.04

0.91
0.98
1.02

0.85
0.92
1.04

2.0D

0.98

0.90

0.98

3.0D

0.98

0.85

0.98

4.0D
5.0D

1.00
1.00

0.94
1.00

1.00
1.00

0deg.

90deg.

0deg.

90deg.

3rd pile

Table 2. Summary of load bearing ratios in case of 45 degrees

Direction of groundmovement

Group size

y

x

Pile
spacing

1st pile

Load bearing ratio
2nd pilexy

3rd pile
x
y

x

y

1.5D

0.04

0.93

0.05

0.87

2.0D

0.03

0.94

0.04

0.90

3.0D

0.03

0.97

0.03

0.95

4.0D

0.02

1.00

0.03

0.99

5.0D
1.5D

0
0.02

1.00
0.92

0
0.07

1.00
0.79

0.03

0.89

2.0D

0.02

0.93

0.06

0.80

0.03

0.91

3.0D

0.01

0.96

0.04

0.87

0.01

0.93

4.0D
5.0D

0
0

1.00
1.00

0.03
0

0.98
1.00

0
0

0.99
1.00

7

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In the case of 0 degrees, the two-pile and three-pile were investigated. The ratios of the front pile
were achieved greater than that of the back pile. The difference in the load bearing ratios of the piles
was significantly large. While the difference was greatly observed at a small pile spacing, and lessthan at large pile spacing. It is noted that the load bearing ratio of middle pile was the smallest as thepile spacing was small in the group of three-pile.
In the case of 90 degrees, the two-pile and three-pile were calculated. The load bearing ratioof each pile was obtained generally close to a single pile. The variance in the ratios wascomparatively small among the piles despite the pile spacing. In the computation results, the load
bearing ratio of the center pile was obtained smaller than that of the 3rd pile in case of 0deg, besides
less than that of the outer pile in case of 90deg. It is caused by overlapping degree in shear zones
for adjacent piles. These results agreed well with the model tests of Miao et al. (2008).
In the case of direction of 45 degrees, the same trend in load bearing ratios was obtained as in thecase of 90 degrees. However, it is interesting that two orthogonal components existed in the reaction
force, in which the x and y component indicate the perpendicular and the parallel components to thedirection of the ground movement, respectively. The x component of reaction was generally very smallin comparison to the y component of reaction. Hence, the load bearing ratio of the piles almost
coincided with the y component of reaction.
5. Conclusions.
The conclusions of this study are as follows:
1. The ultimate lateral resistance of isolated single pile was obtained about 12.27 cu for the perfectly
rough piles in clayey soils. The failure zone of the ground around the pile was found to be in range of
1.5D-2.0D from the center of the pile, and almost similar to the results of Broms (1964).
2. In the case of the piles in a row considering the pile number, the effect of the direction of the groundmovement on the ultimate lateral resistance was widely investigated. It can be seen that the ultimate
lateral resistance varied greatly depending on the direction of the ground movement and the numberof pile. For the piles in a row orthogonal to the ground movement, the ultimate lateral resistance ofeach pile was larger than that of a single pile at small pile spacing. On the contrary, for the piles in arow parallel to the direction of ground movement, the ultimate lateral resistance of each pile decreased
proportionally to the decrease in pile spacing. In addition, the failure zone of ground around the piles
became wider as the number of pile increased.
3. The load bearing ratio of each pile was computed in detail with the changes in the direction ofground movement. It varied among the piles by reflecting the directions of the ground movement.
References[1] Broms, B.B. Lateral Resistance of Piles in Cohesive Soils. Journal of the Soil Mechanics andFoundations Division. ASCE. 90 (2), 27-63 (1964).
[2] Chen, L.T. and Poulos, H.G. Piles Subjected to Lateral Soil Movements. J. Geotech. Geotech. Eng.
ASCE. 123 (9), 802-811 (1997).
[3] Georgiadis, K., Sloan S. W., Lyamin A.V. Effect of loading direction on the ultimate lateral soilpressure of two piles in clay. Géotechnique. 63 (13), 1170-1175 (2013).
[4] Hoshina, T., Ohtsuka, S. and Isobe, K. Ultimate bearing capacity of ground by rigid plastic finite
element method taking account of stress dependent non-linear strength property. Journal ofApplied Mechanics. 6, 191-200 (2011). (in Japanese)[5] Quang, N.P., Ohtsuka, S., Isobe K., Fukumoto Y. Group effect on ultimate lateral resistance ofpiles against uniform ground movement. Soils and Foundations. 58(6), 1-14 (2018).
[6] Tamura, T., Kobayashi, S. and Sumi, T. Rigid Plastic Finite Element Method for Frictional
Materials. Soils and Foundations. 27 (3), 1-12 (1987).
[7] Zhao, Z., Kouretzis, G., Sloan, S.W. and Gao, Y. Ultimate lateral resistance of tripod pilefoundation in clay. Computer and Geotechnics. 92, 220-228 (2017).
(Received: 9 October 2018, Accepted: 18 December 2018)8

Transactions on GIGAKU 6(1)(2019)06004/1-11

High Temperature Gas Cooled Reactor Regulation Development –Operation & Maintenance Perspective
I Wayan Ngarayana1,2*, Kenta Murakami1
Department of Nuclear System Safety Engineering, Nagaoka University of Technology,1603-1 Kamitomioka-machi, Nagaoka 940-2188, Japan
2)
National Nuclear Energy Agency of Indonesia
PUSPIPTEK Area, Serpong, South Tangerang, Indonesia*e-mail: ngarayana@batan.go.id

1)

Abstract. Demands for better safety, security, safeguard and economic aspects
have led to the emergence of innovative nuclear reactor designs. One of the
new designs is the High Temperature Gas Cooled Reactor (HTGR). HTGR andincluding all of the Generation IV nuclear reactors have a safety paradigm thatis completely different from current nuclear reactor technology. Since most of
the nowadays commercial Nuclear Power Plants (NPPs) operating in the world
are based on water coolant reactor technology, the development of HTGR
makes the current regulations will no longer suitable. Regulation is alreadyknown to have a strong correlation with operation & maintenance optimisationthat make the preparation of the new regulation become very important. As thepart of that purpose, this study is conducted in order to prepare the more
flexible regulatory framework for operation & maintenance activities but
without overriding the safety aspects. The safety functions of HTGR are
investigated by adopting the graded approach and examine the importance ofeach function. The regularly operating systems having high safety importanceare identified, and the reliability models of these systems are discussed.
Furthermore, a detailed reliability model of a regular system in an existing lightwater reactor is prepared to conduct a numerical demonstration on theapplication of risk information for operation & maintenance. This study
indicates that the current graded approach methodology is not suitable.
Therefore, new graded methodology should be proposed as the part of future
HTGR reliability-based regulation development.
Keywords: nuclear, power, plant, HTGR, Generation IV, operation,
maintenance, reliability, regulation

1. Introduction
Base on the Power Reactor Information System (PRIS) provided by International Atomic Energy
Agency (IAEA), in the end of 2018 there are 454 on operation commercial NPPs [1]. From all of those
NPPs, about 97% of them are water coolant based NPP. The rests are 3 Fast Breeder Reactors (FBR)
and 14 Gas Cooled Graphite Moderated Reactor (GCR). Those NPPs supplying about 298.65 GW
world energy demand [2]. Unfortunately, about 63% of them already more than 30 years old which
their operation must be extended soon by following ageing management requirements or be
decommissioned and replaced with the new one.
As a part of the old NPP replacement and the need of massive energy in some developing country
especially in China and India, there are about 56 under construction commercial NPPs around theworld that is dominated by water coolant based reactors [1]. The interesting thing is one of the underconstruction reactors are Generation IV nuclear reactor based on High Temperature Gas Cooled
Reactor (HTGR) technology that is located in China [3]. China able to become the first home of thecommercial demonstration Generation IV reactor not only because they need massif energy supply for
their strong economic development [4], but because of their regulation. China’s regulatory body1

Transactions on GIGAKU 6(1)(2019)06004/1-11

relatively easier to give license for the new type of nuclear reactor [5].
Regulation is the key points of nuclear safety. But on the other side, regulation is well-known asa factor which is very influential on the costs that must be incurred for the NPP starting from thelicense, construction, operation, to the decommissioning [6]. The structure of the regulation systemeffecting on the length of the process to get the license. Additional costs also arise due to the presenceof a number of non-nuclear permits that must be taken care. At the time of construction, nuclear
regulation and such other regulation such as labour and environment licenses are also very influential
on investment and overnight costs. On the operation stage, different regulations greatly affect the
freedom of the operator to utilize operational & maintenance optimisation [7].
Since most of the NPP technology adopted around the world is currently based on water coolant
reactor technology, causing almost all IAEA standards also based on that technology. In fact,
developed regulations based on water coolant reactors are not suitable to be used to regulate othertypes of the reactor including Generation IV NPPs. Therefore, studies and efforts to develop theregulatory framework to support the implementation of Generation IV NPP are needed.
In our previous study, we found that although many techniques, methods and strategies have beendeveloped in the effort to optimize NPP operation and maintenance, most of them could not be applied
due to constraints on regulatory issues [7]. As part of the commercialisation, the regulation also will
become the important thing of HTGR development. Therefore, the study in this article has been
conducted in order to harmonize the interests of operators in carrying out optimal operation &maintenance against the interests of regulators in providing safety assurance. For that purposes, on therest of this article, Section 2 will be started with the explanation of the basic concept of HTGR and its
safety function identification. Section 3 describing the methodology used in this study. Section 4
discussing the study result. And finally, on Section 5 this article will be closed by the conclusion.
2. Basic Concept of HTGRHTGR is an advanced development of the Gas Cooled Reactor (GCR) technology. GCR uses
carbon dioxide gas as its primary coolant. One disadvantage of carbon dioxide as a coolant is at a
relatively high operating temperature. Oxidation of carbon dioxide against moderator graphite can beruled out only at temperatures below 675°C [8]. At higher temperatures, carbon dioxide undergoes
radiolitic oxidation which produces carbon monoxide and attacks graphite so that it has the potential
to accelerate the degradation process. Therefore, to produce higher operating temperature around
900°C, HTGR adopts Helium as its cooler. As an inert gas, helium does not react to graphite and otherreactor components which make it one of the determinants in their inherent safety concept.
Base on the Generation IV International Forum (GIF) system arrangements and memoranda ofunderstanding as of January 2014, China, Europe Union, France, Japan, South Korea, Switzerland and
USA are the active countries doing research on HTGR as the part of Generation IV reactor
development [9]. GIF has also agreed on two types of HTGR designs, prismatic and pebble beds as
the standard basis of Generation IV HTGR technology. The major difference between them is only intheir core design. The prismatic core design is arranged exactly like GCR which consists of fuel pellets
which are inserted into the cladding and then put in such a way in a graphite block arrangement in apressure vessel reactor. In the other side, pebble bed type HTGR has a hollow core that is reinforcedby the structure of graphite and reactor pressure vessels on the outside. The fuel itself is shaped liketennis balls and are inserted into the hollow core. Unlike the prismatic type whose fuel is replaced
within a certain period of time and requires the shutdown condition, the pebble bed reactor has an
online fuelling capability where the pebble fuel experiences rotation in several rounds until it actually
becomes spend fuel. Both designs also have control of reactivity that can be inserted in a hole locatedin the side of the reflector. As a backup, several spherical reactivity controls are also prepared to force
shut down the reactor.
Although has different core design, both of prismatic and pebble bed HTGR using similar fuel,moderator and cooling concepts. Both HTGR types use Tristructural-isotropic (TRISO) spherical fuelparticle as the smallest part of its fuel component. Graphite is used as the neutron moderator, reflector
also has the function as the core structure. Helium gas is chosen as the cooling system because of its
inert characteristic that will able to minimize the degradation because of the chemical reaction between
core components with the cooler. The combination of TRISO fuel, graphite moderator and helium2Transactions on GIGAKU 6(1)(2019)06004/1-11

create an inherent safety design that is the main requirement of the Generation IV nuclear reactor. The
similarity and differences between those design furthermore can be seen in Fig. 1.

58 cm

Graphite Block

Fuel Rod
26 mm

39 mm

High density Pyrolytic
Carbon (PyC)UO2 kernel

Fuel CompactSilicon

Prismatic HTGR
0.9 mmCarbide (SiC)

Low density PyC

Tristructural-isotropic(TRISO)

6 cm

Spherical Fuel
Elements

Pebble Bed HTGR

Fig. 1 Pebble bed reactor design and prismatic reactor design
The main purpose of nuclear safety is to protect humans and the environment from the potentialof ionizing radiation risk [10]. To achieve this goal, there are three fundamental safety functions in the
nuclear reactor must be followed, including controlling reactivity, heat removal and radioactive
confinement [11]. Those fundamental safety functions are also followed by HTGR design.
As the part of inherent safety feature, TRISO fuel of HTGR consist of low enrichment uranium
or plutonium. The fission material is coated by three-layer, high-density Pyrolytic Carbon (PyC), lowdensity PyC, and Silicon Carbide (SiC) with the size only about 0.9 mm. Low density with highporosity PyC layer able to capture almost all the fission products. The next layers consist of highdensity PyC and SiC become the next deterrent against the release of fission products. The use of large
amounts of graphite material both in the TRISO fuel layer and as a moderator neutron, the reflector
and also the structure gives negative reactivity coefficient, low power density, and high thermal
conductivity characteristics. All of these characteristics cause the reactor temperature to never exceed
the predetermined threshold even without inserting control rod [12]. The characteristics of helium thatare not easy to react reduce the potential for core degradation due to corrosion and explosive gas
generation as can occur in a water-cooled reactor. Based on numerical and experimental studies, evenstation blackout or loss of cooling accident, decay heat removal process is capable to keep the fuelfrom exceeding its design temperature limit [13] [14].
Although control rod is not too important as the safety system because of its inherent safety3Transactions on GIGAKU 6(1)(2019)06004/1-11

capability, it is still needed to control the reactor power base on the demand. Both prismatic and pebble
bed HTGR use B4C material as their control rod that can be inserted on the hole beside the reflector.
In the case of loss of cooling accident, the core reactor power and temperature will become transient
below the safety limit [12]. As the backup, control rod is possibly needed to return the reactor back tonormal condition faster and avoid component degradation due to excessive temperatures exposure.
The backup reactivity control of prismatic HTGR is designed base on B4C pellets that can be inserted
into the channels bored in the control rod blocks. The pebble bed HTGR be equipped with B4C pebbles
that can be inserted as the reactivity control backup system.
Prismatic and Pebble Bed type HTGR has their own advantages and disadvantages, but tomaintain inherent safety design integrity, both usually designed no more than 600 MWth. In the otherside, although Pebble Bed HTGR has the capability to do online refuelling, some studies argue thatfriction on its fuel management system makes the limitation on the suitable design of Pebble Bed
HTGR become no more than 250 MWth for each reactor core. Friction between pebble during theoperation was reported has increased dust production which has the potential to shorten filter life on
the cooling systems [15]. To archive better performance, some new HTGR supported technologies arestill needed to be developed, such as fuel handling assembly, neutron start-up handling systems, heliumgas compressor improvement, reserve shutdown system, helium gas leakage detector, helium gas
handling, gas turbine technology, etc. [16]. Those developing technology should get special attention
in the reliability study and regulation development.
3. Methodology
The ultimate purpose of our study is to establish appropriate safety graded approach of HTGR to
support regulation development. For that purpose, we are doing some stage of study starting fromliterature study, applying current standards and guidance that usually used for LWR, developing new
methodology if needed, and finally establishing and proposing the appropriate graded approach forthe real graded approach examination.
This article is part of our preliminary study and because of that, the methods used are adopted
directly from current IAEA publications. IAEA has published some standards, guidance and technicalreport for graded approach purposes. One of that publication is IAEA TECDOC 1740 regarding gradedapproach for management system requirements for nuclear facilities and activities. That publication
discussing various types of graded approach techniques that can be followed according to their aims
and objectives, starting from the simplest ones using logic diagrams, Total Quality Ranking, Failure
Modes, Effects Analysis (FMEA), etc [17]. On this part of the study, we will only be applying two ofthem, simply applying the logic diagrams provided by that publication, and utilising FMEA techniquesupported by FMEA standard IEC 60812.
Logic diagram like can be seen on Fig. 2 will be used as the first method to classifying HTGR
Systems Structures and Components (SSCs) become four classes, safety class 1 as the highest
important SSCs, safety class 2 as the important SSCs, safety class 3 as the less important SSCs andthe last class 4 as the non-safety related SSCs.
Base on IEC 60812 standard, there are some stages should be done to do safety graded approachby using FMEA, but mainly can be classified become two, the analysis of FMEA itself by using anappropriate table, and doing critical analysis qualitatively by using Risk Priority Number (RPN) or
quantitatively by using Criticality Number [18]. Based on the standard, FMEA analysis should be
carried out in a group of experts. But due to limited resources and in its purpose in fulfilling theobjectives of the study, the analysis is only done in a limited study group with a small number of SSCs.
After completing the FMEA analysis we had chosen RPN instead of Criticality Number to calculate
the safety graded approach. This is because the calculation of RPN is much easier than the calculationof Criticality Number. On some perspective, Criticality Number is better than RPN but the detail of
failure rate, failure mode and operation time of each SSCs shall be known. As the new technology,
reliability data for HTGR is very limited and only available for some generic components that makeCriticality Number calculation become less suitable for this purpose. In the other side, qualitatively
graded approach by using RPN is very simple by multiplying between Occurrence (O), Severity (S)and Detectability (D).
ࡾࡼࡺ = ࡻ × ࡿ × ࡰ
4

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Before calculation, firstly, Occurrence, Severity and Detectability ranking shall be established on thesame grade, for example by using 10 scales like can be seen in Table 1, 2 and 3 that are adopted fromIEC 60812 [18] and US Army FMEA Guidance [19]. The other scale also can be used as long as
between Occurrence, Severity and Detectability has the same scale.

Fig. 2 NPP SSCs safety classification method [17]Table 1 Occurrence classification
Ranking
1
2
3
4
5
6

Probability≤ 1 × 10ିହComments
Remote probability of occurrence; unreasonable to expect failure to occur

1 × 10ିସ

Very low failure rate. Like past design that has, had low failure rates for given
volume/loads
Low failure rate based on similar design for given volume/loads
Occasional failure rate. Like past design, had similar failure rates for given volume/loads

2 × 10ିଷModerate failure rate. Like past design having moderate failure rates for given
volume/loads
Moderate failure rate. Like past design having moderate failure rates for given
volume/loads

5 × 10ିସ
1 × 10ିଷ
5 × 10ିଷ

5Transactions on GIGAKU 6(1)(2019)06004/1-11

7

1 × 10ିଶHigh failure rate. Like past design having frequent failures that caused problems

5 × 10ିଶ

Failure is almost inevitable

2 × 10ିଶHigh failure rate. Like past design having frequent failures that caused problems

10≥ 1 × 10ିଵ

Very high failure rate and almost certain to cause problems

Ranking
1
2
3
4
5
6
7
8
9

EffectNone
Very minor
Minor
Very low
Low
ModerateHigh
Very highHazardwithwarning
Hazard without
warning8
9

Table 2 Severity classification

10

Comments
No discernible effect
Effect of failure nearly negligible
Failure only cause minor problem on the part(s) of SSC
Local problem maybe occurs but do not affect the operation
Item operable but comfort item(s) operable at a reduced level of performance.
Item operable but comfort/convenience item(s) inoperable.
Item still operable but level of performance is decrees.
Loss of primary function of SSC
Very high severity ranking when a potential failure mode affects safe SSC operation
and/or involves non-compliance with government regulation with warning
Very high severity ranking when a potential failure mode affects safe SSC operation
and/or involves non-compliance with government regulation without warning.

Table 3 Detectability classification
Ranking

Detection probability

Comments

1

1/10+

Very easy to be detected and usually accurate

2

1/20

Easy to be detected and accurate

3

1/50

High to moderate detectability

4

1/100

Moderate detectability

5

1/200

Moderate to low detectability

6

1/500

Low detectability

7

1/1000Able to be detected with low accuracy

8

1/2000Hard to be detected and usually not accurate

91/5000

Very hard to be detected and usually not accurate

10

1/100000

Almost impossible to be detected

As the linguistic term, the ranking of Occurrence, Severity and Detectability can be judged by anexpert or group of experts easily. Regardless the issues of traditional FMEA which will be discussed
later, as the part of this study methodology, RPN FMEA graded approach is implemented as it is likewhat has been described on the IEC standard and US Army guidance.
4. Result and Discussion
The biggest problem on the HTGR SSC safety graded approach is caused by the availability of
the reliability data of each SSC. Based on several kinds of literature there are many reliable methods
that can be used for this purpose, such as Fault Tree Analysis (FTA), Reliability Block Diagram (RBD),
Bayesian Network, Petri Net, etc. Especially FTA is a mature technique and widely implemented forthe nuclear industry. Safety graded approach can be done easily base on FTA by deploying important
index concepts, such as by using Birnbaum, Fussell-Vesely, Risk Achievement Worth, and Risk
Reduction Value. But the main problem in applying this technique is in the availability of quantitative
data. All data reliability of the SSC must be known to calculate the important index. On the other hand,as already mentioned in the methodology above, the qualitative FMEA RPN and logic diagram are
one of the few techniques that can be used for safety graded approach and classification without
requiring the availability of quantitative data. That is one of the reasons why RPN FMEA is one of thebest techniques for technology that is being developed like HTGR.
Even though Prismatic and HTGR pebble beds have the same basic concepts, but because they6

Transactions on GIGAKU 6(1)(2019)06004/1-11

have different designs, of course, they also have several different SSCs. To avoid ambiguity and tosimplify the study, this graded approach is carried out especially based on High Temperature
Engineering Test Reactor (HTTR) design that has been established by the Japan Atomic Energy
Agency [20] [13]. HTTR is the prototype of prismatic type HTGR that expected will become the basic
technology of the future Japanese commercial HTGR. Simplification of study is also doing by limiting
the number of analysed SSCs only for 36 items. But for the real purposes and to get the more realistic
result, more detail study by breakdown each SSCs become sub-system, components and parts isneeded.
By using the classification methodology in Fig. 2, we found that only 5.6% of SSCs can be
categorized as class 1. Most of them, about 64.0% can be classified as class 2, 19.4% class 3 and11.0% class 4. Fuel and graphite moderator as part of the core structural components become safetyclass 1. Primary cooling systems, electricity facilities, control system, etc. that usually become safetyclass 1 on LWR become class 2 on HTGR. Each safety class has meaning as follows. Class 1 is all
SSCs that could lead directly to the increase in the radiological hazard risk and is likely to lead to aserious radiological risk. Class 2 is for the SSCs that their failure is likely to lead to major problems,
serious injury to persons, lead to significant cost penalty, or lead to a breach of the site license orenvironmental or statutory requirements but less serious radiological risk. Class 3 is for SSCs that the
failure is likely to reduce the integrity of plant items or systems and result in a less significant cost
penalty. And the class 4 SSCs is for all of the SSCs that are not quite important from the side view ofclass 1, 2 and 3.
FMEA analysis has been carried out using the Table 4 that is adopted directly from IEC 60812
standard. To shorten the article, detailed analysis of FMEA is not displayed on this article. After overall
SSCs used as study objects are analysed carefully, then criticality analysis has been carried out byadding additional columns on the right side of FMEA analysis sheet as a place to add values foroccurrence, severity and detectability for each SSC based on Table 1, 2 and 3. Finally, the RPN ofeach SSC can be calculated by multiplying those values. The RPN of each SSC and combined withthe result of logic diagram classification methodology can then be shown graphically in Fig. 3.
Table 4. FMEA Analysis Sheet
Item
ref.

Item description
and function

Failure mode

Failuremechanism

Possiblefailure causes

Local effectFinal effect

Detection
method1.0

Fuel as the main
sourceoffission energy
generation

Rupture of
TRISO
structure

Crack,
oxidation,
fracture, etc.

Lackofproduction or
qualitycontrol/quality
assurance

The releaseof FPs from
TRISO
structure tographite fuelcompact
structure

Increase thereleaseprobability of
FPs

Bach
qualitycontrol methodontheproduction andalmostimpossible to be
detected on theoperation

1.1

Graphite fuelcompact
degradation

Crack,
oxidation,
fracture, etc.

Thermal/seismic/
chemicalshock
anddegradation

Fuel compact
degradationmay
becausingswelling of
the fuel rod,
increasing
dust

Increase theprobability of
FPs releaseand dust on
the coolingsystemAlmostimpossible to be
detected on theoperation, but
able
to
be
detectedon
production and
after
the
operation

1.2

Swelling/
rupture/degradationof fuel rod

Ununiformchanging
of
micro
and
macrostructure

Thermal/seismic/
chemicalshock
anddegradation

Stuck of fuelroad on thegraphite
block

Fatal swellingmight cause
difficulty inrefuelling ormaintenanceactivities

Almostimpossible to be
detected on theoperation, but
able
to
be
detectedon
production and
after
the
operation

7

Compensating
provision against
failureCapturing FPs by
multiple barriers.
If TRISO failure,
will be captured
by fuel compact,
then by fuel rod,
graphite block,primary coolingsystem, etc.

If degradation offuel compact isfollowedbydegradation ofpreviousFPsbarrier, then fuelrod or graphite
block
and
another barrier
should capture
the FPs.
Graphite block isdesignedimpermanentthat make ifsomethinghappenswithfuel rod, entire
graphite block
moderator can be
moved out.

Remarks

Failure fraction
less than 10-4.
Major
failurebegins an about
2200∘ C and100% failure at
2400∘ C. The
main radiation
releasefromspent fuel only
gamma
and
neutron.
Small
fuel
compact
degradation will
give significant
impact on safety

Althoughproblemonswelling of fuel
rod
can
be
handledbymoving out thegraphite block, it
will take longer
refuelling timeandpossibleincrease the FPs
releaseandradiation
exposureTransactions on GIGAKU 6(1)(2019)06004/1-11

Fig. 3 HTGR SSCs Graded Approach & Classification
Base on RPN calculation, fuel and graphite moderator structure become the most importantcomponents considering these components are the key to inherent safety design and become the firstand most important fission products barrier. Fuel and graphite moderator then followed by graphite
core structure and reactor pressure vessel as the part of core structure become the top most importantsafety components that should get special attention. Although helium as the coolant also gives thecontribution to inherent safety but based on some experiment, the loss of cooling accident will nevercause reactor meltdown [12] [14] [21]. Loss of coolant will only effect on the increase of coretemperature and the release probability of the fission products. Because of that, cooling systems havenot become the topmost safety priority.
However, like can be seen in Fig. 3, the results between the safety classification based on the
logic diagram and the RPN FMEA looks not match. This is perhaps because of ambiguity between
serious with less serious radiological risk and the licence or statutory requirement on the logic diagram.
For example, is redundancy engineered safety systems that become mandatory for LWR. Theoretically,
HTGR safety is based on an inherent safety feature that does not have the potential to lead serious
radiological hazard if the quality and integrity of inherent safety feature related components are well­preserved. Thus, the main concern must be given to quality control and quality assurance of fuel andcore components integrity. As part of the defence in depth and multiple barriers, of course, some safetysystem function should be prepared. But on the other side that systems should not become
overprotective because could increase the overall cost. Based on the pre­feasibility analysis of HTTR,
the containment vessel requirement is one of the safety components that possibly can be reduced forthe future development because its construction was very costly, but the function looks not too
important. Deeper study regarding the possibility of eliminating some HTGR engineered safety
features that are currently subject of regulation is needed.
The inconsistency result of those methods is possibly also caused by the limitation of RPN FMEA
method itself. As mentioned in IEC 60812, traditional FMEA has several disadvantages, such as thesimilar weighting between occurrence, severity & detectability cannot provide adequate risk sense,
88% of RPN range is empty (only 120 from 1000 that used) and inadequate RPN scaling with very
sensitive with small changes [18]. As a qualitative graded approach, RPN that relies on expert
judgment also cannot be separated from two types of uncertainty, epistemic uncertainties and aleatory
uncertainties. Lack of knowledge uncertainties arising because our imperfect scientific understanding(epistemic) and uncertainties that for all practical purposes cannot be known in detail or cannot be
reduced (aleatory) and combined with the shortcomings of traditional RPN calculations will able toproduce graded approach result with very high uncertainty. In the other side, there are also several
problems on the expert judgment, such as its very difficult to find a universal expert for all aspect of
HTGR technology, every expert has their own subjectivity, and when multiple experts will be used,
special treatment should be conducted to catch the “true value”.
To overcome those problems, we are developing a new methodology that is expected able tosolve the used of expert judgment and traditional RPN issues. Some studies have been well conductedto solve traditional RPN issues such as by utilizing a database, using mathematical also psychological8Transactions on GIGAKU 6(1)(2019)06004/1-11

approach [22]. From those methods, we feel fuzzy logic theory is good enough to be used to solve
traditional FMEA deficiency. Fuzzy logic theory able to work as well as human thinking which is not
only based on right and wrong, black and white, or other opposite values. RPN is qualitative gradedapproach where the judgment is given in the form of linguistic terms. Linguistic terms often have themeaning in the "grey area" between two opposite values. The advantages of fuzzy logic are that it cantransform qualitative values into quantitative ones by reaching that grey area. To answer theuncertainty problems from the use of expert judgment, there is also a various method that has beendeveloped by researchers, including behaviour aggregation methods and mathematical aggregation
methods [23]. After reviewing each of these methods, we argue that there are several expert judgment
aggregation methods that should be used for HTGR graded approach. Behaviourally, the Delphi
method by allowing experts to communicate with each other but with some filters is the best.
Mathematically, if the “true value” of the evidence cannot be captured by consensus, then fuzzy
weighting method should be used. In case there is a “true value” but new robust evidence is available,
then Bayes belief theory should be applied.

Fig. 4 Proposed Methodology for HTGR Graded Approach
Currently, we are working to do exercise by implementing proposed methodology like can beseen in Fig. 4 for some HTGR SSCs. The major differences on this proposed methodology are locatedon how “true value” of occurrence, severity and detectability can be captured from multiple experts
based on the level of evidence and agreement, also on how to calculate RPN base on fuzzy logic theory.
Considering the scope and objective, in this article, we will not discuss this proposed methodology
deeply. We would like to discuss it on the other article after all the studies including verification andvalidation are complete.
5. Conclusion
There are some differences of HTGR safety paradigm impacted on the safe operation &9Transactions on GIGAKU 6(1)(2019)06004/1-11

maintenance activities and make some modification on the current standards & regulations is needed.
The main difference is caused by the inherent safety feature that makes it be the first and foremost
foundation in safe operation and maintenance activities. By using classification and graded approach
methodologies commonly used for LWR, trial graded approach for some HTGR SSCs have been
carried out. From that exercise, fuel, graphite structure and core components of HTGR have the highest
ranking. But by comparing between classification by using logic diagram and RPN FMEA
methodologies, there is some inconsistency that indicates some issues that should be solved. We argue
that both the logic diagram and the traditional RPN that we used in this study are too weak to be able
to be applied in the HTGR graded approach. Therefore, we are proposing a new method that thevalidation process and sensitivity analysis is being carried out.
Acknowledgements
The authors give many thanks to Dr Shoji Takada, Dr Etsuo Ishitsuka, and all member of High
Temperature Engineering Test Reactor (HTTR) department, Japan Atomic Energy Agency (JAEA)
Oarai that have given their support, help and opportunity to learn HTGR technology more deeply fromthe lessons learned from current High Thermal Test Reactor (HTTR). Some data and perspective weused on this article are based on the discussion that we got from them.
We also give special thanks to the anonymous reviewer for their valuable comment until thisarticle can be published.
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International Atomic Energy Agency, “Nuclear Power Reactors in the World,” Vienna, 2018.

[2]

International Energy Agency, “World Energy Outlook 2017,” Int. ENERGY AGENCY Together
Secure. Sustain., 2017.

[3]

G. Zhao et al., “Endurance test of full-scale mock-up helium circulator for HTR-PM,” Nucl. Eng.
Des., vol. 329, no. April 2017, pp. 20–24, 2018.

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China Nuclear Energy Association, “China’s Nuclear Energy Guide 2017,” Beijing, 2017.

[5]

Y. Zhou, C. Rengifo, P. Chen, and J. Hinze, “Is China ready for its nuclear expansion?,” Energy
Policy, vol. 39, no. 2, pp. 771–781, 2011.

[6]

World Nuclear Association, “Nuclear Power Economics and Project Structuring,” London, 2012.

[7]

I. W. Ngarayana, T. Do, K. Murakami, and M. Suzuki, “Nuclear Power Plant Maintenance
Optimisation : Models, Methods & Strategies,” Manuscript submitted for publication, 2018.

[8]

B. J. Marsden and G. N. Hall, Graphite in gas-cooled reactors, vol. 4, no. April 2015. 2012.

[9]

I. Pioro, Ed., Handbook of Generation IV Nuclear Reactors, Woodhead P. Duxford, UK: Elsevier,
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[10]

International Atomic Energy Agency, “Fundamental Safety Principles,” Safety Fundamentals, vol.
2, no. No.SF-1. p. 37, 2006.

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International Atomic Energy Agency (IAEA) - NS-R-1 and International Atomic Energy Agency,
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[12]

S. Nakagawa, K. Takamatsu, Y. Tachibana, N. Sakaba, and T. Iyoku, “Safety demonstration tests
using high temperature engineering test reactor,” Nucl. Eng. Des., vol. 233, no. 1–3, pp. 301–308,
2004.

[13]

T. Nishihara, X. Yan, Y. Tachibana, and T. Shibata, “Excellent Feature of Japanese HTGRTechnologies,” Tokai-mura, 2018.

[14]

K. Takamatsu et al., “Experiments and validation analyses of HTTR on loss of forced cooling under
30% reactor power,” J. Nucl. Sci. Technol., vol. 51, no. 11–12, pp. 1427–1443, Dec. 2014.

10

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P. W. Humrickhouse, “HTGR Dust Safety Issues and Needs for Research and Development,” Idaho,
2011.

[16]

Y. Shimazaki, F. Homma, H. Sawahata, T. Furusawa, and M. Kondo, “Development of themaintenance technologies for the future high-temperature gas cooled reactor (HTGR) using
operating experiences acquired in high-temperature engineering test reactor (HTTR),” J. Nucl. Sci.
Technol., vol. 51, no. 11--12, pp. 1413–1426, 2014.

[17]

International Atomic Energy Agency, “Use of a Graded Approach in the Application of theManagement System Requirements for Facilities and Activities.” IAEA, Vienna, 2014.

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Commission International Electrotechnical, “IEC 60812: Analysis Techniques for Reliability Procedure for FMEAs.” International Electrotechnical Commission, Geneva, 2006.

[19]

Department of the US Army, “Failure modes, effects and Criticality Analysis (FMECA) for
command, control, computer, intelligence, surveillance and reconnaissance (C4ISR) Facilities,” US
Army, no. September. US Army, Washington, p. 75, 2006.

[20]

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[21]

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Test With One Cooling Line Inactive in Vessel Cooling System of High-Temperature Engineering
Test Reactor,” J. Nucl. Eng. Radiat. Sci., vol. 3, no. 4, p. 041013, 2017.

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(Received: 3 October 2018, Accepted: 14 February 2019)11

Transactions on GIGAKU 6(1)(2019)06005/1-12

Galet – Geant4 Based Application Templet for Primers

1)

Tsukasa Aso1,*, Wataru Takase2, Takashi Sasaki2
Department of Electronics and Computer Engineering, National Institute of Technology, Toyama
College, 1-2 Nariya Ebie, Imizu 933-0293, Japan
2)
Computer Research Center, High Energy Accelerator Organization,
1-1Oho, Tsukuba 305-0801, Japan*E-mail: aso@nc-toyama.ac.jp
Geant4 is a Monte Carlo simulation toolkit to simulate interaction of particles
with matter. It has been designed and implemented on objected-oriented
technique and C++ programing language. Since Geant4 is distributed as atoolkit, users need to develop their Geant4 applications by themselves.
Therefore, the users are required enough expertise about software
engineering as well as particle physics. However, many of beginners ofGeant4 are not easy to satisfy these requirements. For the purpose ofminimizing users’ efforts in software developments, Geant4 based
application templet (Galet) has been proposed. Galet is a skeleton program tobe utilized as a primary code for integrating users’ applications. It provides
versatile and reusable concrete classes for various applications. In case of theminimum implementation, Galet requires to implement only three classes thatare relevant to construction of simulation geometry and scoring of simulated
results. Galet was applied to several applications in various field. The
efficiency and effectiveness of Galet were verified through those
applications.

1. Introduction
Geant4 [1-3] is a general-purpose Monte Carlo simulation toolkit to simulate the passage ofelementary particles through and interacting with matter. It provides complementary physics modelsof particle interactions such as electromagnetic physics, hadronic and nuclear physics, optical photon
physics. The energy scale covers ranging from a few eV to TeV. Therefore, it is widely used invarious science field such as high energy physics, nuclear physics, space engineering and medical
physics. Geant4 has been designed on the object-oriented technology (OOT) and implemented in C++
programing language. The source codes are distributed as a toolkit under the Geant4 software license. The
concept is openness that make the design and implementation of the physics open and transparent forusers. The toolkit consists of a series of class libraries, in which the classes are designed in a highly
reusable and a suitable granular level so that users can customize and replace parts of implementations
with their extended components according to the specification of their applications. Such design allows
users to incorporate the Geant4 within their own computational framework as well as to develop
stand-alone applications. The toolkit approach is one of unique features in Geant4 in comparison with theother Monte Carlo simulation projects [4,5] in which the simulation code is provided as an application
program.
The toolkit approach offers many advantages in application developments, however, it requires users
to develop their application program by themselves. The users are expected to be experts about softwaredevelopment in OOT and C++ programing. These requirements are regularly acceptable when we assume
a large project such as high energy physics experiments. In the project, software group usually consists ofexperts of Geant4 application developments. The software group designs and develops a specificapplication program as a simulation framework for the experiment. Many end-users in the project use it
for their physics and detector analysis. Eventually, the software group maintains and upgrades thesimulation framework by referring feedback from end-users. Same kinds of approach can be seen in
medical physics domain such as PTSIM[6] and TOPAS projects [7]. These projects developed the1

Transactions on GIGAKU 6(1)(2019)06005/1-12

simulation frameworks for radiation therapy on the collaboration of Geant4 experts and medical
physicists. These frameworks have been distributed to many radiation facilities for quality assurance ofbeam delivery system and dose calculations.
Due to the extendibility and reliability of Geant4, there is growing desire to use Geant4 in not only thelarge projects but also small projects such as laboratory scale experiments. The in-house simulation toolin small projects will usually have moderate complexity and have rather short lifetime, because the tool
will be frequently modified according to the stage of project for applying various analysis methods and/or
optimized experimental setups. Unlike to the large projects, developing an in-house simulation tool has tobe conducted by end-users without supports from Geant4 experts. In the situation, the end-users are
required to serve as Geant4 experts. However, such end-users are not easy to satisfy the requirement,
because they are usually beginners of Geant4.
For the purpose of assisting beginners to develop in-house Geant4 applications, the Geant4
application templet (Galet) has been proposed, which is a skeleton program of Geant4 application. In
this paper, firstly the brief concepts, design and implementation of Galet are described. Secondly
several example applications based on Galet are introduced as practical examples.

2. Methods
2.1 Concepts
The use-case of Galet was defined for an in-house Geant4 application development. We assumed
that the end-users develop in-house Geant4 applications by themselves, and they are beginners about
Geant4 and OOT software engineering.
Geant4 has many virtual classes to be mandatory implemented for the application. Developing atypical example application requires users to prepare concrete classes in C++ code for defining
materials, geometries of simulation space, primary particle conditions, physics processes to be
applied for interactions of particles with matter, and scoring functions. These user codes need to be
developed on the virtual classes of Geant4 and registered into the application as shown in Fig. 1.
%+ ''#!+!&%(,!)*) &*!%')&)$!)+,##***!%%++)!#!%!+!&% *) ++&) &%*+),+!&%&$+).!%!+!&%

#,!%)!$).')+!#!%!+!&% *))!$).%)+&) +!&% .*!*')&**!%!+!&% *) .*!*!*+ %*!+!- ++&)
 !+* !+* &##+!&%
 *) +!&%%!+!#!/+!&%
  +!&%%!+!#!/+!&%
 *),% +!&%
 *) -%+ +!&%&)!%,%+!&%*

Fig. 1 Schematic diagram about user codes and its virtual classes in Geant4 required for typicalGeant4 application development.
Among these virtual classes, only the minimum number of classes should be chosen to be
implemented by users, while the other virtual classes should be provided as general-purpose concreteclasses in Galet. On this concept, Galet offers users to focus on implementing the experimental
geometry setup and the scoring function according to their purpose of simulation, so that the results
can be easily achieved in a straightforward way.
For example, the scoring function needs to implement seven classes relating to many stages inthe simulation process. Figure 2 shows a schematic view of particle transport in Geant4. A particle is2

Transactions on GIGAKU 6(1)(2019)06005/1-12

tracked in the simulation space with steps. Here the step point is determined according togeometrical interfaces and physics interactions. The track information such as particle momentum
and position at step is obtained in class G4VSensitiveDetector from G4Track and G4Step instancesof Geant4. Since track information in these instances is overwritten in every step, some of theinformation has to be saved into an instance of class G4VHit. Then, the G4VHit instance needs to be
stored temporary into a collection class G4VHitsCollection for later use to calculate physics
quantities. Usually, class G4UserEventAction is used for calculating physics quantities such as
particle flux and total absorbed energy per one primary particle, in which the calculations need all
track information including secondary particles in the event. For the purpose of optimizing thesimulation efficiency, Geant4 is designed to be capable of calculating such physics quantities
directly in classes G4VSensitiveDetector and G4VHit. However, such optimized implementation
usually causes strong dependence on the other classes in the application. Therefore, Galet adopts toprovide general-purpose classes of them to store the original track information and postpone thephysics quantity calculations at the end of a history in class G4UserEventAction. Although, thisstrategy may have some disadvantages in terms of computational efficiency, however, it is very
advantageous at the point of easiness in application developments.

$

!#%#

!
!#!



!

!

"#% ##!



#

#
 # 

 #



 #" # #!& #%##%#

"! %##



 #



%#

$#"!$#
$# $#

Fig. 2 Overview of simulation stages and the scoring process in Geant4. The stages are categorized
to Run, Event and Tracking (left). The tracking stage consists of steps in particle transport. Scoringis processed with virtual classes in Geant4 (right). The scoring process is briefly described asfollows. Tracking stage: (1) getting track information from a step, (2) creating a hit instance, and (3)storing the hit instances into a hits collection. Event stage: (4) getting the hit instances from the hitscollection, (5) calculating physical quantities from the hit instances, and (6) compiling the physicalquantities for events. Run stage: Output the physics quantities to a file.
The users will use Galet as a primary code of Geant4 application developments, and some ofthem will become experts of Geant4 in future. In order to utilize Galet as a primer of Geant4, Galet
exactly follows the manner of Geant4 application development without veiling or replacing original
Geant4 functions. This policy also implies that all kinds of modules in Geant4 are acceptable forplug-in so that the product becomes a sophisticated Geant4 application.
2.2 Design and implementation
According to the defined concepts, Galet was developed as a skeleton program of Geant4
application. The virtual classes in Geant4 and the corresponding concrete classes in Galet are listed3

Transactions on GIGAKU 6(1)(2019)06005/1-12

in Table 1 for regular application development. In the table, the virtual classes are indicated withitalic characters, while the other classes are concrete classes. The three classes with bold characters
in Galet stand for skeleton classes that have to be partly implemented by users. The class
GaletDetectorConstruction is used for describing a simulation geometry. The classes
GaletRunAction and GaletEventAction are used for describing functions of scoring and recording
simulation results, in which the former and latter classes are used to define and fill histograms withcalculated physica quantities. The minimum application is usually realized by implementing thesethree classes. In consequence, users are able to efficiently develop their applications by focusing on
the simulation geometry and the physical quantities to be achieved.
Table 1 Class relationship between Geant4 and Galet
Geant4 virtual classes
Galet classes
main
Galet
G4VUserPrimaryGeneratorAction GaletPrimaryGeneratorAction
G4VUserActionInitialization
GaletActionInitialization
G4VUserPhysicsList
GaletPhysicsList
GaletPhysicsListMessenger
G4VUserDetectorConstruction
GaletDetectorConstruction
GaletDetectorConstructionMessenger
GaletMaterialFileConstruction
GaletMaterialFileMessenger
G4VUserActionInitialization
GaletActionInitialization
G4UserRunAction
GaletRunAction
G4UserEventAction
GaletEventAction
G4VSensitiveDetector
GaletSD
G4VHitGaletHit
G4VHitsCollection
GaletHitsCollection
In addition to these three classes, simulation conditions for a primary particle generator, physics
processes, geometries and materials have to be defined. Galet provides concrete classes for thispurpose. Those classes are designed to be versatile and reusable for various applications, andimplemented with messenger classes to provide user-interface (UI) commands. Therefore, theconfigurations can be changed by using UI commands without modifying the source code.
Galet uses G4GeneralParticleSource (GPS) of Geant4 for primary particle generator in class
GaletPrimaryGeneratorAction. The GPS provides variety of UI commands to specify primaryparticle parameters. For example, energy spectral, spatial and momentum distributions of primaryparticle can be flexibly assigned to configure primary source conditions.
The classes for physics-list registration and material definition are taken from PTSIM code. The
physics-list defines a set of physics processes with the interaction types and models. The classes
GaletPhysicsList and GaletPhysicsListMessenger configure the physics-list by registering physics
constructors by using UI commands. The physics constructors are referred from the Geant4
referenced physics-list, in which the physics constructors are categorized as electromagnetic physics,
hadron physics, radioactive decay physics, optical photon physics etc. In each physics category,several models are available. For example, the physics constructors of electromagnetic physics areavailable for standard, Livermore, Penelope and DNA models. The DNA model is an extension ofelectromagnetic physics that is applicable down to eV scale and water radiolysis. One of thesemodels is chosen by users according to the specification of simulation.
The material definition is managed in classes GaletMaterialFileConstruction andGaletMaterialFileMessenger. Materials in NIST material database are created by specifying thematerial name in UI command. User-defined materials are also created by specifying the name ofdata file in which the recipe of material is described in ASCII format.
The scoring is the most complicated part of application developments for beginners, because it
relates to geometry structure, physics processes and particle transports. The classes GaletSD and
GaletHit are designed to be versatile enough for various applications. The instance of GaletSD will4Transactions on GIGAKU 6(1)(2019)06005/1-12

be attached to the scoring volume in class GaletDetectorConstruction. When a particle track comes
into the scoring volume, it creates and stores an object of GaletHit as a temporal memory of track
information. Each instance of GaletHit memorizes track identification number, positions, time,
particle identification number, kinetic energy, deposited energy, deposited dose, volumeidentification number, created physics process type, created position, step length etc. Any kinds of
distributions and physics quantities needed for analysis can be derived from the information in
GaletHit instances.
Galet uses the class G4AnalaysisManager of Geant4 in classes GaletRunAction andGaletEventAction. The G4AnalysisManager is used for assembling simulation results into
histograms and/or database. The output format is chosen from CERN ROOT Analysis tool, XML
and CSV by compile option.
3. Results and Discussion
The usage of Galet has been tested on educational and research projects [8-12], in order to ensure
efficacy and expendability of Galet in various application developments. Four example applications
from those projects are introduced in following sections.
3.1 Galet-Edu
Galet-Edu stands for Galet for education in radiation simulation. Authors have been organizing
the KOSEN-KEK summer internship for computing in radiation researches since 2016 by the
support of Cooperative and Supporting Program for Researches and Educations in Universities in
KEK. By 2018, total 18 KOSEN students have participated the internship and experienced a Galetapplication development. The students were from various departments such as electricity, machinery,electronics and computing. Although most of students had not experienced about Geant4 and C++
programing until the internship, the students could engage on developing a simulation of NaI(Tl)detector on Galet in one day practice as shown in Fig. 3.
They created materials of NaI(Tl) by mixing atoms according to mass fractions in literature, andimplemented the simplified geometry of NaI(Tl) detector (Fig. 4) in class GaletDetectorConstruction.
The primary particle was set to be Cs-137 and placed at a certain distance along to the coaxial line ofthe detector by using GPS commands. Instead of simulating scintillating photons, deposited energy
in the NaI(Tl) crystal was simply accumulated to obtain the energy spectrum. In class
GaletEventAction, the energy fluctuation of detector response was emulated by using a random
generator of Gaussian distribution corresponding to the energy resolution of the detector, and taken
account to the accumulated energy deposit per decay. The students performed simulations withvarious experimental conditions. Then the students analyzed the number of counts in the full energy
peak in the spectrum by using CERN ROOT analysis tool. Figure 5 shows an example energy
spectrum in NaI(Tl) detector simulation with the fitting result by Gaussian and exponential
composite function.
Although these students were beginners of Geant4 and C++ programing language, they could
develop a Geant4 application on Galet within one day practice. It implies that Galet is an efficient
primary code to develop a simple Geant4 application for beginners.

5Transactions on GIGAKU 6(1)(2019)06005/1-12

$*/+,$"&$-%"&-%+-%%/ '%,*/Fig. 3 Snapshot of internship in 2018. Total of
8 students engaged on developing NaI(Tl)detector simulation based on Galet-Edu code.

Fig. 4 Simple NaI(Tl) detector geometry in
Galet-Edu including a NaI(Tl) crystal in
aluminum case and a dummy photomultipliertube (PMT).

Fig. 5 Example energy spectrum of Cs-137 in NaI(Tl) detector
calculated in Galet-Edu simulation. The red line shows a fitting
result of the full energy peak.
3.2 Galet-HPGe
Galet-HPGe is a Galet application of high purity germanium (HPGe) detector. It was developed
for verifying the conventional sum-peak method [13-15] and the modified sum-peak method [16,17]
in radioactivity determination. These methods are absolute measurement techniques which can beapplied to radionuclide emitting more than one gamma-rays in cascade.
Galet-HPGe simulation modeled a HPGe detector and a lead shielding box as shown in Fig. 6.
The geometries were implemented in class GaletDetectorConstruction. The geometric parameters
were taken from the datasheets of GMX-25190 Ortec. The HPGe is an open-ended coaxial photon
detector of n-type. The HPGe crystal was specified as a scoring volume. In class GaletEventAcction,
the energy spectrum was calculated by accumulating the deposited energy in the scoring volume,and the energy resolution was taken into account according to the energy dependent response
function obtained from measurements. Since the radioactive decay physics in Geant4 version 10.02
did not take into account the angular correlation between gamma-rays in Co-60 disintegration. We
developed a primary generator to produce two gamma-rays according to the angular correlation
function 𝑤 𝜃 of Co-60 and replaced GPS with it in class GaletPrimaryGeneratorAction.

6

Transactions on GIGAKU 6(1)(2019)06005/1-12,"#%#'!(0












''+"&+






 --(+

Fig. 6 Galet-HPGe geometry modeled a Fig. 7 Example energy spectrum of Co-60 gamma-rays
HPGe detector and a lead shielding box.
in HPGe simulation.
An example energy spectrum of Co-60 in the simulation is shown in Fig. 7. Here 𝑁! , 𝑁! and𝑁!" in the figure stand for the number of counts in each full energy peak for 1.17 MeV, 1.33 MeV
and sum peak, respectively. The simulation for a Co-60 point source was repeated by changing thesource-to-detector (S-D) distance. The simulated results were normalized by assuming the actual
number of decays to be 10,000. The modified sum-peak method is demonstrated in Fig. 8. The figure
shows the dependence of 𝑁!! = (𝑁! 𝑁! /𝑁!" )𝑤 0 on 𝑁! with 𝑤 0 =1.111. The simulated points
were fitted by a quadratic function and the number of decays was calculated as a value at theintersection of 𝑁! = 0. As shown in the figure, the calculated value is consistent with the actual
number of decays in the simulation. The detail implementation and discussion about the verificationof the modified sum-peak method are described in [8].

Fig. 8 Demonstration of the modified sum-peak method by using
the results of Galet-HPGe simulation. The series of data points
show the dependence of 𝑁!! on 𝑁! . The activity is calculated asa value of 𝑁!! at 𝑁! = 0.
3.2 Galet-LSC
Liquid scintillation counter (LSC) is used for a quantitative measurement of radioactivity, and it
is especially useful for low energy beta decay radionuclides such as tritium. In measurements,
radioactive sample is dissolved into a liquid scintillation cocktail in a vial. The radioactivity isquantified by counting the number of flushes of scintillation lights within a certain time period.
7

Transactions on GIGAKU 6(1)(2019)06005/1-12

However, counting efficiency varies with the quench level of the sample, which depends on
efficiency of energy transfer from the released beta ray in decay to the solute in liquid scintillator.
The quenching decreases the number of generated scintillation photons. Therefore, compensation ofcount rate loss is essential to determine the radioactivity. In order to study the dependence ofcounting efficiency on quench level, Galet-LSC was developed.
Galet-LSC modeled LSC system for measurements based on liquid scintillation counting. The
geometric parameters were taken from the LSC-5100 manufactured by Hitachi, Ltd. It consists of
two photomultipliers (PMTs) installed around an optical chamber as shown in Fig. 9. These
geometries were described in class GaletDetectorConstruction. Additionally, the optical properties
were assigned to materials and the surface of optical chamber, in order to simulate propagation of
optical photons that account for reflection and refraction at geometrical boundaries. C-14 or H-3 waschosen for a primary particle and randomly generated inside the scintillation cocktail volume by
GPS. The physics-list consists of radioactive decay, electromagnetic and optical photon physics. The
radionuclide emits a beta ray in radioactive decay physics. Then, optical photon physics generates
scintillation photons isotopically along to the beta ray trajectory and transports those photons inside
the optical chamber. The default yield of scintillating photons (Y) was set to 10 photons/keV for thematerial of liquid scintillator. An instance of GaletSD was attached to both PMT windows to bescoring volumes. In class GaletEventAction, scintillating photons at the PMT windows are randomly
sampled according to the quantum efficiency of PMT, and those are accumulated as a PMT signal in
one decay. The final pulse height in double coincidence method was calculated as the sum of two
PMT signals by requiring more than certain number of photons detected in both PMTs.
Example distributions of C-14 pulse height spectra in two scintillation photon yields aredemonstrated in Fig. 10. Here the unit of pulse height is given in the number of scintillating photonsof two PMTs in one decay. The counting efficiency is defined by a ratio of the number of double
coincidence events on the number of decays. The dependence of counting efficiency on scintillating
photon yields was studied in previous research as shown in Fig. 11. The detailed simulation andanalysis in comparison with C-14 and H-3 measurements are described in [9,10].

    






 

 

Fig. 9 Galet-LSC geometry modeled
LSC-5100 system manufactured by
Hitachi, Ltd. The system consists ofsample vial filled with liquid
scintillator, optical chamber and two
PMTs.

Fig. 10 Example pulse height spectra of C-14 in
Galet-LSC simulation. The scintillating photon yields
with Y = 10 photons/keV (red) and 4 photons/keV(blue) were chosen in the simulation for demonstrative
purpose.

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Fig. 11 Example results about dependence of counting efficiencies in
H-3 and C-14 on photon yields achieved with Galet-LSC simulation.

3.4 Galet-DNA
Geant4-DNA is an extension of Geant4. It has been developed by Geant4-DNA project [18-21]
for studying DNA damage caused by radiations. The interactions are newly taken into account for
low energy electromagnetic reactions of electrons and protons with water, water radiolysis,
diffusions and bimolecular reactions of radicals. The energy covers ranging from a few hundred
MeV down to eV. These interactions concern to DNA strand breaks through direct and indirectprocesses, which mean the direct energy transfer from charged particles and the bimolecularinteractions of radicals with the molecules in DNA. Many simple examples are supplemented inGeant4 source code to explain how to use the Geant4-DNA functions one by one.
Galet-DNA is our on-going project to develop a comprehensive application for studying DNA
damages by utilizing Geant4-DNA functions. Especially we focus on DNA damages caused by low
energy and low rate electrons. In such radiations, both direct and indirect processes contributecomparably. Therefore, the physics-list needs to include both physics constructors for the low energy
electromagnetic interactions and the chemical reactions, i.e. G4EmDNAPysics and
G4EmDNAChemistry packages in Geant4-DNA. In addition, the geometry of DNA and protein
molecular structure need to be imported into the simulation with a commonly used description
format.
We integrated Galet-DNA simulation by referring the parts of “chem3”, “chem4” and “pdb4dna”
example codes in extended medical example in Geant4-DNA. These example codes show how tovisualize trajectories of chemical species in chemistry processes, how to access the information offree radicals, and how to construct a geometry from the protein data bank (PDB) [22], respectively.
The classes in Galet-DNA are classified into Galet original layer, intermediary layer andGeant4-DNA layer. The schematic module structure and representative classes in Galet-DNA isshown in Fig. 12.

9

Transactions on GIGAKU 6(1)(2019)06005/1-12

 '
#'*%#( &+&&$%#&&%" +%"'%!%++% '+&&&'"' +% ! +&& ! !&'%+ ''#" "' ,'#"&( ,'#"!)# ('#"

 '( % "' ,'#" %" "'%')'+ '!'$$"'#"
#%"! $%#&& '!&'%+ "' ,'#" !&'%+"% ''"'#"

# ( #("'% ' '$$"'#" #!'%+ ' ''#%#"&'%('#"
#%"+&&$%#&& '

 ' #"&'%('#"  

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Fig. 12 Schematic module structure and the representative classes in Galet-DNA. The classes ingreen and yellow filled boxes are Galet-DNA classes, while the classes in white filled boxes are
Geant4-DNA classes. The classes in intermediary layer of Galet-DNA indicated in yellow filled
boxes were additionally introduced for importing a PDB geometry and analyzing reactions of free
radicals.
The modules for physics processes, geometries and scoring relevant to physics interactions weresuccessfully implemented on the original Galet framework, while we additionally introduced sixclasses in intermediary layer of Galet-DNA. The class names of these intermediary classes areshown in the figure with yellow filled boxes. The classes in the PDB geometry module,
GaletPDBConstuction and GaletPDBSteppingAction, are used for importing geometric parametersfrom PDB database and discriminating associate hits among molecules in the PDB geometry. The
other classes in intermediary layer are for accessing time and space information of free radical
species produced in chemical reactions of Geant4-DNA. The outcomes of particle transport are
stored in instances of GaletHit and G4MoleculeCounter relevant to physics and chemistry processes,
respectively. These instances are retrieved from the class GaletEventAction for further analysis andrecording.
Examples of a DNA geometry and radical trajectories in Galet-DNA are shown in Fig. 13 andFig. 14. Here the structure of a B-DNA dodecamer was imported from PDB data base, and theradicals were produced in water radiolysis by injecting a 1 keV primary electron. Because Galet
exactly follows the manner of Geant4 software development, integrating the Geant4-DNA functions
into Galet-DNA was simple and straightforward.

10

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Fig. 13 Geometry of DNA strand pairwith atomistic view imported from PDB
database in Galet-DNA. The spheres withgray, red, blue, yellow and orange standfor elements of C, O, N, S and P,
respectively.

Fig. 14 Example simulation of Galet-DNA. A 1 keVelectron was injected in water. The tracks in red, green
and blue lines stand for trajectories of radicals withnegative, neutral and positive charges such as OH ! ,H! O! and H! O! , respectively.

4. Conclusion
Galet minimize users’ effort in Geant4 application developments by providing the skeleton
program with versatile concrete classes. The extendibility and efficacy of Galet have been validated
though the developments of various example applications. Since Galet exactly follows manner ofGeant4 simulation toolkit, it can be utilized by beginners as a primer code of Geant4 application
developments, that has more important meaning in educating beginners to Geant4 application
developers. Furthermore, Galet is useful for developing an integrated simulation software withextensions such as Geant4-DNA, as well as mock simulation software for rapid prototyping.
Acknowledgments
This work was partly supported by JSPS KAKENHI Grant number 18K11650, 17H01084 and17K07006.
References[1] S. Agostinelli et al., “Geant4 – a simulation toolkit”, Nucl. Instrum. Meth., A506, pp. 250–303,
2003.
[2] J.Allison et al., “Geant4 developments and applications”, IEEE Trans. Nucl. Sci., 51, no. 1, pp.
270-278, 2006.
[3] J. Allison et al., “Recent developments in Geant4”, Nucl. Instrum. Meth., A835, pp. 186-225,
2016.
[4] T. Sato et al., “Features of Particle and Heavy Ion Transport Code System (PHITS) version 3.02”,
J. Nucl. Sci. Technol., 55, pp. 684-690, 2018.
[5] D.B. Pelowits Ed., “MCNPX Users Manual Version 2.7.0”, LA-CP-11-00438, 2011.
[6] T. Akagi et al., “Geant4 based particle therapy simulation framework for verification of dose
distributions in proton therapy facilities”, Prog. in Nucl. Sci. Technol. , 4, pp. 896-900, 2014.
[7] T. Akagi et al., “The PTSim and TOPAS projects, Bringing Geant4 to the Particle Therapy
Clinic”, Prog. in Nucl. Sci. Technol., 2, pp.912-917, 2011.
[8] T. Aso et al., “Geant4 based Monte Carlo simulation for verifying the modified sum-peakmethod”, Appl. Radiat. Isot., 134, pp.147-150, 2018.
11

Transactions on GIGAKU 6(1)(2019)06005/1-12[9] T. Aso et al., “Validation of Beta Ray Scintillation Spectra in Liquid Scintillation Counter using
Geant4 Simulation”, IEEE NSS/MIC Conf. Rec., N04-03, 2014.
[10] T. Aso et al., “Estimation of photon yield in liquid scintillation counter by using Geant4 Monte
Carlo simulation”, Prog. in Nucl. Sci. Technol., Accepted for publication, 2018.
[11] M. Hara et al., “Monte Carlo simulation of tritium beta-ray induced X-ray spectrum in various
gasses”, Fusion Engineering and Design 131, pp.125-129, 2018.
[12] M. Shoji et al., “Modification of LSC spectra of 125I by high atomic number elements”, Appli.
Radiat. Isot. 139, pp.131-136, 2018.
[13] G.A.Birnkman et al., “Absolute standardization with a NaI(Tl) crystal-I”, Int. J. Appl. Radiat.
Isot. 14, pp.153-157, 1963.
[14] G.A.Brinkman et al.,”Absolute standardization with a NaI(Tl) crystal-II”, Int. J. Appl. Radiat.
Isot. 14, pp.433-437, 1963.
[15] G.A.Brinkman et al.,”Absolute standardization with a NaI(Tl) crystal-III”, Int. J. Appl. Radiat.
Isot. 14, pp.503-510, 1963.
[16] Y. Ogata et al., “Development of a modified sum-peak method for activity determination ofsome gamma emitters”, Nucl. Instrum. Meth. Phys. Res., A775, pp.34-40, 2015.
[17] Y. Ogata et al., “Development of the modified some-peak method and its application”, A[[l/Radiat. Isot., 109, pp. 354-357, 2016.
[18] S. Incerti et al., “Geant4-DNA example applications for track structure simulations in liquidwater: a report from the Geant4-DNA Project”, Med. Phys. 45, e722-e737, 2018.
[19] M.A Bernal et al., “Track structure modeling in liquid water: A review of the Geant4-DNA very
low energy extension of the Geant4 Monte Carlo simulation toolkit, Phys. Med. 31, pp.861-874,
2015.
[20] S. Inceri et al., “Comparison of Geant4 very low energy cross section models with experimental
data in water”, Med. Phys. 37, [[.4692-4708, 2010.
[21] S. Incerti et al., “The Geant4-DNA project”, Int. J. Model. Simul. Sci. Comput. 1, pp.157-178,
2010.
[22] E. Delage et al., “PDB4DNA: implementation of DNA geometry from Protein Data Bank (pdb)
description for Geant4 DNA Monte-Carlo simulations”, Comput. Phys. Commun. 192,
pp.282-288, 2015.
(Received: 29 October 2018, Accepted: 7 February 2019)12

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Numerical Study on Core Degradation Behavior with TRAC andMCCI Behavior with MELCOR at Fukushima Dai-ichi Nuclear
Reactor Accident
Kohei Ueta, Hiep Huy Nguyen, Kazuyuki Takase*Department of Nuclear System Safety Engineering, Nagaoka University of Technology,1603-1 Kamitomioka-machi, Nagaoka 940-2188, Japan*E-mail: Takase@vos.nagaokaut.ac.jp

1)

As part of research for clarifying the cause of the Fukushima Dai-ichi
nuclear power plant (1F) accident, both phenomena on core degradation and
Molten Corium Concrete Interaction (MCCI) were analyzed numerically.
Thermal hydraulic behavior in a reactor core during the core degradation was
estimated with TRAC-BF1. On the other hand, MCCI behavior was evaluatedwith MELCOR. From the TRAC-BF1 estimation results, predicted
temperature and pressure distributions in the unit 1 of 1F under the different
start-up conditions of the reactor core Isolation cooling Condenser (IC) wereobtained. Moreover, predicted erosion characteristics on the pedestal of thecontainment vessel in Boiling Water Reactor (BWR) during MCCI were also
estimated by MELCOR (based on the severe accident condition such as 1F).

1. Introduction
At Fukushima Dai-ichi nuclear power plant (1F), scram of the unit 1 to unit 3 was carried out
because of the Pacific coast of Tohoku Earthquake happened on March 11th, 2011 2:46 pm. After that,the removal of residual heat was continued via Residual Heat Removal system (RHR) powered byEmergency Diesel Generator (EDG) as substitute for the lost external power source. However, EDG
was stopped due to the influence on seismic sea wave reached at 3:37 pm, making the station blackout.
At unit 1 to unit 3, the situation that was not capable of to inject water into the reactors had been
continued although the cooling was carried out with the actuation of core cooling function without
alternating power source. Therefore, the fuel rods were exposed and reactor core meltdowns were
happened at those units.
A reactor core Isolation cooling Condenser (IC) is a part of safety equipment for design basis
accident for Boiling Water Reactor(BWR)-3 and is able to cool down the steam of the Reactor Pressure
Vessel (RPV) using the water stored in its secondary side, and bring back the condensed water into
RPV via natural convection. IC has two independent systems of A and B, and external power source
is not needed to actuate IC except for opening and closing the valves. IC was actuated automaticallyand started the reactor core cooling after 300 s of the earthquake occurrence. In order to adjust thecooling rate, IC was stopped after 960 s of the earthquakes occurrence. The operators had controlled
the cooling rate (under 55°C/h) of Unit 1 by opening and closing an isolation valve on IC system A
until when station blackout occurred by seismic sea wave1-2). After the Direct Current (DC) power of
Unit 1 was lost, the operators tried to open the isolation valves, but it was found out that the valve
could not be driven due to the blackout. However, it was uncertain about how much the operation of
IC influenced the reactor core cooling. Thus, in the present analysis using TRAC-BF13) which is atransient reactor analysis code, thermal-hydraulics analysis targeted at the unit 1 of 1F was conducted,
and the core cooling situation in the reactor after the DC power of Unit 1 was lost was comprehended.
Inoperability of High Pressure Coolant Injection system (HPCI) was assumed, the possibility withregard to avoidance or delaying of core melt was considered using only IC.
On the other hand, Molten Corium-Concrete Interaction (MCCI) behavior was considerednumerically. As shown in Fig. 1, MCCI is one of the severe accident phenomena and occurs by core
meltdown. As a result, corium is relocated from the vessel into the reactor cavity where means the1

Transactions on GIGAKU 6(1)(2019)06006/1-8

pedestal of a Reactor Containment Vessel (RCV). The interaction involves melting and decompositionof concrete, chemical reactions between the concrete and corium materials, and heat transfer from thecorium to its surroundings. Uranium dioxide,zirconium dioxide, zirconium and stainless steel
comprise the core melt. The major constituents ofconcrete are SiO2, CaO, Al2O3, MgO, Fe2O3, K2O,
Na2O, free water, chemically bound water and CO2.
When the molten core material contacts the concreteand the temperature of the concrete reaches theablation temperature, the concrete begins to ablate anda layer of molten concrete or slag forms that separates
the solid concrete below from the overlying core melt.
Here, one of the most severe issues is the erosion of
concrete. Then, the amount of the erosion of concrete
at MCCI was predicted with MELCOR. MELCOR is
one of severe accident analysis codes and can predictphysical phenomena in the reactor related to the severe
accident. In the present analysis using MELCOR,
some assumptions were defined from severe accident
such as 1F. In order to comprehend the tendency oferosion, a prediction of the erosion characteristics on Fig. 1 Schematic diagram of BWR atsevere accident
the pedestal of RCV were conducted.

2. Numerical Analysis
2.1 TRAC-BF1 analysis
TRAC­BF1 is a transient reactor analysis code to provide advanced best­estimate predictions of
postulated accidents in BWR. Figure 2 shows a nodding diagram of TRAC­BF1 which simply
simulates major components of the unit 1 in 1F and consists of a pressure vessel (including fuelassembly, steam­water separator, downcomer, jet pump), water supply system, recirculation system,
main steam system, RCV and IC.
RPV was a cylindrical shape with an overall height of 19.6 m and shell inner diameter of 4.8 m.
The external wall was assumed to be an insulated wall without thickness, and the thermal conduction
from RPV to RCV and thermal capacity of RPV were neglected. The fuel assembly were high­burnup
8×8 and high­burnup 9×9, which was 68 bodies and 332 bodies, respectively. The axial direction
output distribution of fuel was configuring the output at several heights based on the output ratio
immediately before the earthquake which listed on the operating record. Besides, the output ratio
between fuel assemblies was assumed constant. The water supply system was connected to the top
position of downcomer, and the constant flow rate was injected with the water supply flow rate (689kg/s) and temperature (176.7°C) which are based on the application document for nuclear installation
license5). From the reactor scram until the station blackout, the injection flow rate was controlled
automatically in order to stabilize the water level on the upper side which was about 5 m from the topof reactor core.
RCV was simplified as a cylindrical that has an inner diameter of 17.7 m, and it also assumed thefollowing situations based on the application document for nuclear installation license5): spatial
volume of RCV was 6,030 m3, suppression pool water was 1,750 m3, initial suppression watertemperature was 30°C. As the lack of information had restricted the simulation of the flow path
resistance, the flow rate of a main steam piping system of IC was defined as 100.6 t/h. Here, it was
assumed that IC has the constant heat transfer coefficient of 3,000 W/m2K and the heat transfer
capacity of 36.2×105 kcal/h. The decay heat of fuel rod was obtained from the open information6).
In regard to the main parameter of steady operation before earthquake occurrence, Table 1 shows
the comparison with listed values in the application document for nuclear installation license5) andcalculated values. According to the analysis results, the reactor core coolant flow rate and steam quality
at core exit were estimated. As shown in Table 1, the flow rate at core inlet of the construction permit
2Transactions on GIGAKU 6(1)(2019)06006/1-8

condition was about 10% smaller than the calculation condition, and the value was vice versa for thecase of steam quality at core exit. This was attributed to the deficient adjusting pressure ratio of jet
pump. However, the effect of accelerated loss regarding jet pump decrease and the position pressure
loss must be dominative after the blackout. The influence on the analysis result after station blackout
was considered as small.

Fig. 2 Noding diagram of TRAC­BF1
Table 1 Comparisons between values in construction permit and calculation conditions
Construction permit Calculation
Parameterscondition
condition
Power [MW]

1380

1380

Pressure[MPa]

6.99

7.01

Flow rate at core inlet [kg/s]

6055

6570

Temperature at core inlet [K]

549.2

549.5

Steam quality at core exit [-]

0.116

0.101

Flow rate in recirculation[kg/s]

3028

3355

M ratio of jet pump[-]

1.00

0.95

As for each event and the occurrence time, the essential events were picked out from what waslisted in the government report1). The event time series put in the analysis is shown in Table 2. The all­control rod insertion time after the earthquake was zero. Figure 3 shows the comparisons with theoperation record4) as regards of the reactor pressure before and after the earthquake and the calculation
result. According to the operating record, the both IC (A) and IC (B) were started after 300 s ofearthquake occurrence, the reactor pressure was back to around 7.2 MPa by the manual shutdown of
IC after its pressure decreased from around 7.2 MPa to 4.5 MPa. Even in the calculation result, thesame change was shown and the change on reactor pressure was capable of predicting via IC actuation.
With reference to the increase in pressure before IC was turned on and after it was turned off, the3

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calculation result shows the increase rate about two times as compared with the operating record. The
reason was considered that thermal capacity of RPV was neglected in the analysis and the time change
on pressure was estimated sharply.

(a) Operation record(b) Calculation result
Fig. 3 Comparison of pressures between operation record and calculation
Table 2 Event time table

Time

Elapsed time [s]

Event

14:46

-100

Reactor scram

14:47

0

All control rods insertion
Main steam isolation valve (Closing)

14:52

300

Isolation Condenser (IC(A)(B)) on

15:03

960

(IC(A)(B)) off

15:17

1800

IC (A) on

15:19

1920

IC (A) off

15:24

2220

IC (A) on

15:26

2340

IC (A) off

15:32

2700

IC (A) on

15:34

2820

IC (A) off

15:37

3000

Station blackout

18:18

12660

IC (A) on

18:25

13080

IC (A) off

4

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The present analyses were carried out three different conditions in order to evaluate the influenceon the core cooling with IC. Case 1 is the event simulation described in the government report, whichis the condition that the IC was actuated for 7 minutes after 2.7 hours (12,660 s) of the station blackout.
On the other hand, Case 2 and Case 3 were just some assumption to the severe accident of 1F and not
the real phenomenon. Case 2 was the assumed analytical condition where IC was operable after 1.5
hours (8,400 s) of the station blackout, while Case 3 was the assumed analytical condition in which
the IC operated immediately after the earthquake.
2.2 MELCOR analysis
MELCOR is one of severe accident analysis
codes and can predict physical phenomena of core
meltdown, reactor vessel failure, hydrogengeneration, fission product release, etc. in addition
to MCCI. In this analysis using MELCOR, thetarget unit was not defined especially, however
some analytical conditions were assumed based on
severe accident such as 1F.
Figure 4 shows the present analytical modelfor the MELCOR analysis. Each component of
BWR is simply simulated. In the calculations, twoanalytical conditions were assumed; one is the dry
condition that the pedestal of RCV is no water;
another is the wet condition that the pedestal isoccupied with water with height of 5 m andtemperature of 300 K. In the present calculation,
analytical condition can be seen in Table 3 wasconsidered. The initial parameters at MCCI are
shown in Table 4. Here, the temperatures related
to both oxide layer and metal layer and the initialfuel debris compositions are decided based on Ref.
7­9).

Fig. 4 A calculation model of MELCOR
which simply simulates BWR structuralcomponents

Table 3 Analytical conditions

Event
Core has uncovered by waterCore supports plate breaks

Time (s)74.66
3452.35

Failure of lower head, beginning of debris ejection to pedestal
MCCI occurs

6043.746044.82

Table 4 Initial parameters at MCCI

Oxide layer
temp. [K]Metal layer
temp. [K]

3113

2098

Initial fuel debris compositions [kg]UO2

Zr

Stainless
steel

Total

96000

19200

15400

1306005Transactions on GIGAKU 6(1)(2019)06006/1-8

3. Results and Discussion
3.1 Predicted Core Behavior
Figure 5 shows the reactor pressure and thereactor water level, maximum temperature of fuelin Case 1. Here, reactor water level which is thequantity of water from the bottom of RPV was
obtained via integration. Case 1 simulated an actual
phenomenon, the reactor water level was gradually
decreased while changing since the steam
produced by decay heat was discharged from relief
safety valve to RCV. Hence, the reactor core was
fully exposed from the coolant due to sharp
decrease of the reactor water level after 3 hours(9,800 s).
The result of Case 2 is shown in Fig. 6. Thiscase simulates a situation in which the reactor
water level could be maintained via IC actuation
while the two­phase flow was forming. In Case 2,
for a faster IC operation, the pressure was stabilized(between 6 ~ 7 MPa) while condensing the steam,and the reactor water level was held as high as theheight of reactor core. Here, the void fraction ofreactor core was around 55%, the two­phase natural
circulation flow was formed and the entire fuel rods
were able to be cooled down, since the interface
between two­phase flow and steam single­phase wassituated around the upper steam­water separator.
Thus, the melting of the reactor core could possibly
be retarded for 8 hours (16 hours if B system is alsoused) if IC was actuated during forming the two­phase flow natural circulation flow. Besides, theresult of Case 2 demonstrates that there was a
possibility to avoid the reactor core melt if the water
injection was able to be carried out into RPV andsecondary side of IC in the interval.
Figure 7 shows the result of Case 3. When IC
operates normally, it is found that a meltdown would
be avoidable. However, there is a possibility in thisanalysis that the time change as regards to pressure
and temperature etc. was estimated sharply because
the thermal capacity of the structure was notconsidered. Furthermore, the steam dragged by thedowncomer was flowed with high void fraction to theunderneath plenum since the water injection of
coolant from the water supply system was lost.
Hence, it was considered necessary to verify theapplicability of correlation formula related to carry­
under phenomena in particular, since the formation oftwo­phase natural circulation flow has become an
important factor.

6

Fig. 5 Case 1: Actual results of unit 1 in 1F

Fig. 6 Case 2: Results when IC is early started

Fig. 7 Case 3: Results when IC is normally started

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3.2 Predicted Erosion Rates
The predicted erosion rates of the concrete in the pedestal of RCV by MCCI and their schematic
diagrams are presented in Table 5 and Fig. 8, respectively. In Table 5, the predicted erosion rates in
the radial direction are 0.307 m for the dry condition and 0.181 m for the wet condition, and similarly,
those in the radial direction are 0.213 m for the dry condition and 0.228 m for the wet condition. The
predicted erosion rate in the axial direction of the concrete was almost the same for both dry and wet
condition. In contrast, the predicted erosion rate in the radial direction of the concrete at the dry
condition was 1.7 times higher than that of the wet condition. Furthermore, the erosion as regards
radial direction are 0.307 m and 0.181 m, and the erosion as regards axial direction are 0.213 m and
0.228 m, as shown in the dry and wet condition. From this result, the following tendency was expected;
the corium spreads in radial direction under the dry condition after falling on the concrete. As thisreason, it is expected that since the erosion rate in the axial direction becomes almost the same underboth the dry and wet conditions, the dry condition that the temperature in an upper surface of thecorium becomes high compared with the wet condition will be remarkable to the erosion in the radial
direction.
Table 5 Predicted erosion rates

Dry condition

Wet condition

Radial direction [m]

0.307

0.181

Axial direction [m]

0.213

0.228

Fig. 8 Schematic diagram of erosion of concrete in pedestal of BWR

4. Conclusions
With regard to the unit 1 of Fukushima dai­ichi nuclear power plant, in order to comprehend thesituation of the core cooling in the reactor by the influence of both Pacific coast of Tohoku Earthquakeand seismic sea wave, thermal hydraulics analysis was operated with TRAC­BF1. As a result, it was
found that the reactor core was able to be cooled down during the formation of two­phase natural
circulation if the IC was able to use just after the reactor core started to be exposed. Moreover, MCCI
behavior after the core degradation was analyzed numerically with MELCOR. As for two kinds ofconditions that the pedestal of RCV is dry and wet, the predicted erosion rates in the axial and radial
directions in the concrete of RCV were compared and the difference on the erosion rates between bothconditions was clear. In the future, it is planned to improve the prediction accuracy of the present
analysis results based on the information which becomes clear with the process of thedecommissioning of 1F.
Acknowledgments
We would like to express our gratitude to Dr. Tamai and Dr. Akimoto for their kind cooperationand suitable advices regarding the numerical analysis.

7Transactions on GIGAKU 6(1)(2019)06006/1-8

References
1) Nuclear Emergency Response Headquarters, Report of the Japanese Government to the IAEA
Ministerial Conference on Nuclear Safety - The Accident at TEPCO’s Fukushima Nuclear Power
Stations ―, Nuclear Emergency Response Headquarters, Government of Japan, Jun. (2011).
2) Atomic Energy Society of Japan, Report of “Seminars to investigate the accident at the
Fukushima-Daiichi Nuclear Power Station” What were wrong? What should be done from now
on?, Atomic Energy Society of Japan, Mar. (2013).
3) J. A. Borkowski, N. L. Wade, TRAC-BF1/MOD1:An Advanced Best-Estimate Computer
Program for BWR Accident Analysis, NUREG /CR-4356 (EGG-2626)(1992).
4) Tokyo Electric Power Company, Touhoku Chiho Taiheiyouoki Jishin Hassei Touji no Fukushima
Daiichi Genshiryoku Hatsudensho Unten Kiroku oyobi Jiko Kiroku no Bunseki to Eikyo Hyouka
nitsuite, Tokyo Electric Power Company, 23 May (2011), [in Japanese].
5) Tokyo Electric Power Company, Fukushima Daiichi Genshiryoku Hatsudensho 1 Gouki no
6)
7)

Genshiro Secchi Kyoka Shinseisho, Tokyo Electric Power Company, May (1991), [in Japanese].
Tokyo Electric Power Company, Ronai Nenryou no Houkainetsu (Jisingo Yaku Hantoshikan no
Henka), News Release, Tokyo Electric Power Company, 26 May (2011), [in Japanese].
Nishimura, Satoshi, et al. "Severe accident analysis of a representative LWR plant with MAAP5.
01 and MELCOR2. 1. Comparison of station blackout analysis for a BWR-5/advanced Mark-II

containment type plant." Denryoku Chuo Kenkyusho Hokoku (2014): 1-4.
TEPCO. “Fukusima Dai-ichi Gensiryoku Hatudensyo 1 ~ 3 Gouki no Rosin Zyoutai ni tuite.”
http://www. tepco. co. jp/nu/fukushima-np/images/handouts_111130_09-j. pdf (2011), [inJapanese].
9) JNES. “Heisei 21 nendo Zishinzi Revel 2 PSA no Kaiseki (BWR).”
http://kagakucafe.org/jnes000017303.pdf (2010), [in Japanese].
(Received: 29 October 2018, Accepted: 14 February 2019)8)8

Transactions on GIGAKU 6(1)(2019)06007/1-6

Basic property of the wind turbine with the circular cylinder blades
driven by longitudinal vortex
Yuya Kimura1, Takumi Sankyo1, Hayate Kimura1, Syodai Sugimura1,
Takahiro Nomura1,*, Shigeru Ogawa1, Yuji Yamada1, Tsutomu Takahashi2
1)
Department of Mechanical Engineering, National Institute of Technology, Kure College,
2-2-11 Aga-minami, Kure 737-8506, Japan2)
Department of Mechanical Engineering, Nagaoka University of Technology,1603-1 Kamitomioka-machi, Nagaoka 940-2188, Japan*E-mail: nomura@kure-nct.ac.jp

Focusing on a wind turbine driven by a longitudinal vortex invented by
Takahashi et al. in 2016, a wind turbine with cylindrical blades driven bya longitudinal vortex was produced experimentally. Wind tunnel
experiment was conducted to clarify the basic characteristics of the
prototype. As a result, power coefficient curves related to rotational
speeds were experimentally obtained by changing the parameters of thenumber of the cylindrical blades and the thickness of the ring plate.

1. Introduction
Recently, energy shortage is urgent problems to be solved since energy demand are greatly
increasing across the world. Therefore it is keenly needed to construct electrical generating systems
using renewable energy such as wind and solar power. Among such renewable energy, wind power
generation is one of the renewable energies most introduced in the world. The wind turbine cangenerate electricity day and night and be installed in any electricity demanding areas if it is compact.
However, fundamental improvements of the wind turbine are required because Japan has no
sufficient installation places especially in the suburbs of metropolitan areas and is frequently
exposed to strong winds by typhoons every year. Faced with these circumstances, the authors havefocused on the wind turbine with the circular cylinder blades which can maintain sufficient strengthwith even a small size and conducted basic research to understand its characteristics [1,2]. This windturbine is a horizontal axis wind turbine driven by a longitudinal vortex, which was originallyinvented by Takahashi et al.[3] in 2016, and its basic mechanism and fundamental characteristics
were investigated by Sakamoto et al.[4,5] and Hemsuwan et al.[6-8]. However there still remain
many problems to be solved. For example, in Sakamoto et al.[4], the width of the ring plate is
optimal for w/d=1.0 and 1.5 from the viewpoint of wind turbine rotation speed, but the diameter andthickness of the ring plate are not shown. Also, by Koide et al.[9] and Kato et al.[10], it is assumed
that there is no influence of the thickness of the flat plate at the cross-crossing of the column-flat
plate system. They confirmed the range of the thickness of the flat plate from 5 to 22mm, however
not all the thicknesses were clarified. For this reason, the paper aims to verify the experimental
results of Takahashi et al. and studies the influence of both the number of the cylindrical blades andthe thickness of the ring plate behind the cylindrical blades on enhancement of power generation.

2. Methods of Experiment
2.1 Operating principle of wind turbine
The outlines of produced experiment equipment are shown in Fig.1. It’s a horizontal axis windturbine with circular cylinder blades, and a ring plate is arranged behind the circular cylinder blades.
Circular cylinder blades are fixed to a rotating shaft, and arranged so that the blades are orthogonal
to the wind like the propeller type of horizontal axis wind turbine. Mounting holes for circularcylinder blades were installed at intervals of 30, 36, 45 degrees on the rotating shaft, so that 2, 3, 4, 6,
8, 10, and 12 circular cylinder blades could be mounted according to experimental conditions.
1Transactions on GIGAKU 6(1)(2019)06007/1-6

N=2

N=10
(a) Appearance of experimental equipmentt [mm](b) Various parameters
Fig.1 Outline of experimental equipment

When the gap s between the ring plate and the circular cylinder blade is in a certain range, either
a trailing vortex or a necklace vortex[9] is generated in the vicinity of the intersection of the circularcylinder blade and the ring plate, as shown in Fig.2. When the necklace vortex is formed, thecylinder first swings and then starts to rotate. As a result, the circular cylinder blades steadily rotate
at a constant angular velocity, and the steady lift force due to the longitudinal vortex is generated.
The rotation direction has the same probability in both clockwise (CW) and counterclockwise(CCW) direction according to the initial rotation direction.

(a) Trailing vortex ( s/d ≤ 0.3 )(b) Necklace vortex (0.3 < s/d < 0.6)

Fig.2 Longitudinal vortices generated by flat plate2

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2.2 Wind tunnel device and Measurement system
The schematic diagram and specification of the wind tunnel experimental equipment used for theexperiment are shown in Fig.3. This wind tunnel has the open section. Airflows are accelerated in alaminar flow state through the inlet of the diffuser, passes through the experimental area uniformly,
and decelerated after passing through the diffuser of the exit side. Wind speeds setting in this windtunnel experiment were confirmed using a Pitot tube and a hot wire anemometer at the main placesin the experiment area without the wind turbine.

LengthDepthHeightExperiment area
Flow rate
Control method
Power supply

3700mm
1065mm
1900mmHeight 305mm × Depth 305mm × Length 600mm
0~36m/s (0~130km/h)
Motor drive control
3-phase AC200V, 26A, 50/60Hz

Fig.3 Outline of wind tunnel device
Experiments were carried out with the wind turbine setting in the experiment area of the windtunnel. The rotation number n [rpm], the torque T [Nm], and the power P [W] were measured by atorque meter (UTMⅡ-0.2Nm, UNIPULSE Co., Ltd.) and output to the PC through a torque monitor(TM201, UNIPULSE Co., Ltd.). Taking the average value of 1,500 pieces of data are acquired in 5
seconds with this torque monitor enables us to achieve high-accuracy power measurement and its
high repeatability. In addition, the rotation number, the torque, and the power were measured byconnecting the electromagnetic brake (HB0.5, OGURA CLUTCH Co., Ltd.) to the rotating shaft andcontrolling the voltage applied to the electromagnetic brake by the power supply unit (AD-8722D,
A&D Co., Ltd.). The outlines of the measurement system are shown in Fig.4. Furthermore, it is able
to confirm whether or not this wind turbine is driven by a longitudinal vortex by comparing eachrotation numbers measured in both CW and CCW rotational direction without load and with thesame rotation speed.

3Transactions on GIGAKU 6(1)(2019)06007/1-6

Fig.4 Outlines of the measurement system
2.3 Experimental conditions and Performance index
The experimental conditions are shown in Table 1. The ring-shaped flat plate was prepared with
two sizes of thickness t of t = 2.0mm and 5.5mm, and the number of circular cylinder blades N with
N=2, 3, 4, 6, 8, 10, and 12.
Table 1 Experimental conditions
Wind speed U [m/s]Blade diameter d [mm]Blade length l [mm]Gap s [mm]Gap ratio s/d [ - ]Ring diameter D [mm]Ring width W [mm]Ring thickness t [mm]Number of blades N [ - ]

10
20
60
7.0
0.35
155
20
2.0, 5.5
2, 3, 4, 6, 8, 10, 12

In order to create a λ-Cp curve as an index of the performance of the wind turbine from therotation speed and the power measured with each wind turbine shape, the tip speed ratio λ and thepower coefficient Cp are calculated. The indexes λ and Cp are defined by the equations (1) and (2).
Here, ω [rad/s] is the angular velocity, R (=(‫ ܦ‬+ ݈)/2) [m] the rotor radius, ρ [kg/m3] the fluid density,
and A (=ߨR2) [m2] the projected area of the wind turbine.
ఠோ

(1)

௉

(2)

ߣ= ௎

‫ܥ‬௣ = ଴.ହఘ௎ య ஺
3. Results and Discussion

3.1 λ-Cp curve
Fig.5 shows λ-Cp curves with blade number N = 2, 3, 4, 6, 8, 10 and 12 were employed asparameters. The main parameters of the wind turbine were used with gap ratio s/d = 0.35 and blade
length l = 60 mm at blade diameter d = 20 mm, which were obtained under the optimal conditions in
the previous experiments. The λ-Cp curves were evaluated with two types of the ring plate thickness t
to compare the fundamental characteristics. Both curves show that Cp has a peak value at a certain
speed ratio λ. Focusing on the vicinity of the peak value of Cp, it was found that Cp also increases
with blade number N = 2 to 8 in case of plate thickness t = 2.0 mm. Regarding the thickness t = 5.5mm Cp increases in proportion to blade numbers until N=10. This tendency seems due to increasing
longitudinal vortices, corresponding to the increase in blade numbers. However, this tendency is
restricted to the region where the longitudinal vortices generated from the circular cylinder blades do
not interfere with those from other circular cylinder blades with an increase in blade number N.
4

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0.02

0.02
N=2
N=3
N=4
N=6
N=8
N=10
N=12

Cp

0.015

N=2
N=3
N=4
N=6
N=8
N=10
N=12

t=5.5mm0.015

Cp

t=2.0mm

0.01

0.01

0.005

0.005

0

0
0

0.1

0.2

λ

0.3

0

0.4

0.1

0.2

λ

0.3

0.4

(b) the ring plate thickness t=5.5mm(a) the ring plate thickness t=2.0mm

Fig.5 λ-Cp curves for the number of blades N（s/d=0.35, ℓ=60mm）

3.2 N-Cp max curve

Fig.6. shows the N-Cp max curve obtained by extracting the maximum value Cp max of Cp at eachblade number N from the λ-Cp curves in Fig.5. There is a tendency that Cp max increase as blade
number N. Cp peaks in case of N = 10 at t = 5.5 mm and N = 8 at t = 2 mm. However, after reaching
the peaks Cp max tends to decrease sharply. In addition, compared with the same number of blades N,
Cp max is higher as the ring plate is thicker. This shows that the ring plate thickness t affects
generation of longitudinal vortex as the driving forces. Depending on the thickness of the ring plate,
it is assumed that it influences to develop the necklace-shaped vortex flow in the vicinity of the ringplate. Therefore, it is considered that there exists an optimum ring plate thickness to enhance thewind turbine performance. In the future it is necessary to further conduct experiments by changing
the ring plate thickness. In this experiment, the maximum Cp max value is about 0.016 at N = 10 and t= 5.5 mm, but it is lower than the Cp max value currently in practical use as wind power generation.
Therefore, it is necessary to examine basic characteristics in more detail and to find out the mostsuitable combination to increase the Cp max value.
0.02

0.016

Cp max

0.012

0.008
t=5.5mm

0.004

t=2mm
0
0

2

4

6

N

8

10

12

14

Fig.6 N-Cp max curves for the ring plate thickness t（s/d=0.35, ℓ=60mm）
5Transactions on GIGAKU 6(1)(2019)06007/1-6

4. Conclusion
We manufactured the wind turbine with the circular cylinder blades driven by longitudinal vortex
and conducted experiments with a wind tunnel. By examining the λ-Cp curve and the N-Cp max curve
obtained from the measurement values of the rotation speed and the power, with the basic shape of
the wind turbine as a parameter, the following basic characteristics were shown.
1) Regardless of the ring plate thickness t, Cp increases as the number of blades N increases.
However, the increasing tendency is that there is a limit number of blades N related to the ringplate thickness t, and when N exceeds the limit value, Cp does not increase.
2) Comparing Cp max to the same number of blades N, it was found that Cp max is larger as the
thickness t of the ring-shaped flat plate is larger. Since this is a comparison with two kinds ofplate thickness this time, it is necessary to further experiment by changing plate thickness
further.
Acknowledgments
This study has been supported from “NUT grant for collaborative research with Colleges ofTechnology”.
References[1] S. Ogawa et al., “Study on horizontal type turbine driven by longitudinal vortex system,” The
14th International Conference on Motion and Vibration Control, no. A-05, pp.249-250, Aug.
2018.
[2] S. Ogawa et al., “A new horizontal wind turbine with a circular cylinder driven by longitudinalvortex system,” Conference on Modelling Fluid Flow (CMFF’18) The 17th International
Conference on Fluid Flow Technologies, no. CMFF18-096, pp. 1-7, Sep. 2018.
[3] T. Takahashi et al., “A novel wind / water turbine with circular cylinder blades driven by steadylift force caused by longitudinal vortex,” JSME Fluids Engineering Conference, no. 0617, Nov.
2016.
[4] K. Sakamoto et al., “Performance test of a novel wind turbine propeller with circular blades
driven by longitudinal vortex,” JSME Fluids Engineering Conference, no. 0618, Nov. 2016.
[5] K. Sakamoto et al., “Enhancement of efficiency of a new horizontal type turbine driven bylongitudinal vortex,” 9th JSME-KSME Thermal and Fluids Engineering Conference,
TFEC9-1421, Oct. 2017.
[6] W. Hemsuwan et al., “Longitudinal vortex wind turbine: effect of the blade lengths,”
Fluid-Structure-Sound Interactions and Control, Springer, pp.117-123, May. 2018.
[7] W. Hemsuwan et al., “Lift force generation of a moving circular cylinder with a strip plate set
downstream in cruciform arrangement: floe field improving in tip-ends,” International Journal of
Aeronautical and Space Sciences, 19(3), pp.606-617, Aug. 2018.
[8] W. Hemsuwan et al., “A longitudenal vortex wind turbine: numerical study,” Journal of Wind
Engineering and Industrial Aerodynamics, 180, pp. 213-230, Sep. 2018.
[9] M. Koide et al., “Vibration control for a circular cylinder by a strip-plate set downstream in
cruciform arrangement (2nd report, generation and suppression of vortex excitation on elasticallysupported cylinder),” Transactions of the Japan Society of Mechanical Engineers. B., vol. 75-752,
no. 08-0591, pp. 123-131, Apr. 2009.
[10] N. Kato et al., “Vibration control for a circular cylinder by a strip-plate set downstream in
cruciform arrangement (1st report, influence of downstream strip-plate on the shedding of
longitudinal vortices from fixed system),” Transactions of the Japan Society of MechanicalEngineers. B., vol. 73-728, no. 06-0029, pp. 49-56, Apr. 2007.
(Received: 12 October 2018, Accepted: 7 February 2019)6

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Observation of Three Dimensional Nanostructures Fabricated by TwoPhoton Polymerization Method
Son T. Nguyen1,†,*, M. A. Hariz B. Mohd Pauzi1, †, Tadachika Nakayama2, Tsuyoshi Takahashi1,
Kenya Moriya2, Yoshinori Tokoi3, Hisayuki Suematsu2, and Koichi Niihara2
1)
Department of Creative Engineering, National Institute of Technology, Kushiro College, 2-32-1
Otanoshike-Nishi, Kushiro 084-0916, Japan
2)
Extreme Energy-Density Research Institute, Nagaoka University of Technology,1603-1 Kamitomioka-machi, Nagaoka 940-2188, Japan3)
Department of Electrical and Electronic System Engineering, National Institute of Technology,
Nagaoka College, Nishikatakai-machi 888, Nagaoka 940-8532, Japan†these authors contributed equally to this work
*E-mail: son@kushiro-ct.ac.jp

The development in three-dimensional (3D) printing technology has enabled
the ability to fabricate micromachines (MEMS) with feature size smaller than
100 nm. In this research project, a MEMS system with piston and filter forcracking bacterial cells and recovering useful precious chemical substances
inside was fabricated by two-photon polymerization method. The structure of
the created MEMS will be observed and analyzed with a high resolution
scanning electron microscope. Then, the MEMS will be put into an
experimental electric field to induce the movement of the piston. The piston
can destroy the bacterial cell and release precious matter. The useful matterswill pass through the filter of MEMS and will be collected at the other end of
the system for further research purposes.

1. Introduction
The recovery of precious nanoparticles like palladium (Pt), selenium (Se), silver (Ag) or gold (Au),etc., accumulated in bacterial cell has attracted many interest of scientists because of their potential in
nanofabrication, catalytic production, biomedical and environmental applications [1-4]. There areseveral methods which have been applied to extract those precious matter from bacterial cell. The
extraction is mostly conducted via biology and chemical routes, like wet heat sterilization process [5]or bioreduction method [4, 6]. However, there have been very limited attempt to extract the precious
particles via physically route though it would be low-cost and environmental friendly. The difficulty
in precisely controlling a physical impact on a small objects at bacteria cell level is the main reason
for this limitation.
In recent decades, nanofabrication has continuously developed and obtained remarkableachievements. One of these achievements is the application of two-photon absorption (TPA) methodin three-dimensional (3D) printing technology [7-8]. Different from the case of single photon
absorption, in TPA the illuminated polymer simultaneously absorbs two photons of near Infrared (IR)light. This method enables laser beams to be focused on a very small area called voxel as small as 65
nm. By using this technique, scientists and engineers can fabricate micro-level 3D structures whichfeatures smaller than 100 nm. This can give some clue to solve the above problem about physicallyextracting nanoparticles from cell.
In the present research, a micromachine (MEMS) containing a piston-and-filter system was 3Dprinted with TPA method. From scanning electron microscopy observations, it was concluded that ahoneycomb filter with a minimum hole diameter of 3.9 mm was successfully fabricated. The piston
then can be induced by electric field to move and breakdown a bacteria cell and extract its precious
matter through filtering holes (see Fig. 1). Our group has many experience in manipulating the motionof inorganic/organic microparticles in electric field [9-12]. Recently, we have been successful infabricating a microcar that can be well-controlled in electric field [13]. The current research objective
1

Transactions on GIGAKU 6(1)(2019)06008/1-6

is to find out whether the MEMS can be smoothly controlled by electric field inducement.

Fig. 1 Schematic illustration of 3D structure motion control by electric field to extract precious
matter from bacteria
2. Experiment
In this research, the 3D microstructure was designed by a solid modeling computer­aided design(CAD) software (SolidWorks 2012, Dassault Systemes, France). The MEMS have micrometer
dimensions, which are 150 mm (length) × 100 mm (width) × 80 mm (height) for the microfilter,and 96 mm (length) × 55 mm (diameter) for the piston. Filtering holes have hexagonal shape with
6.9 mm of maximal diameter and 4.0 mm of minimal diameter. The holes are arranged with honeycomb
pattern because this structure has high strength and firmness [3] and the thickness of vertical walls
between the holes is 0.7 mm. Figure 2 shows the design and dimensions of the microfilter and piston(see Fig. 2).
This design was used to fabricate the MEMS by using a micro 3D­printer (Photonic Professional
GT, Nanoscribe, Germany). IP­G780, a commercial photoresist from the same company, was used as
the material for printing the 3D microstructures. The printing process were conducted at Nagaoka
University of Technology, then the fabricated 3D structure were then sent back to National Institute ofTechnology, Kushiro College for further observation and analysis. The fabricated MEMS wasobserved by an optical microscope (BX51M, Olympus, Japan) and a field­emission Scanning Electron
Microscope (JSM­7001 FA, JEOL Ltd., Japan). Before scanning electron microscopy (SEM), sample
was cleaned with ethanol in a sonication bath and then sputtered with gold by a fine coater (JFC­1600,
JEOL Ltd., Japan) to avoid the charge­up effect on the sample surface.

2

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Fig. 2 Micromachine (MEMS) designed by Solidworks 2012: a) mircrofilter; b) piston
3. Results and Discussion
The optical micrographs of the filter and piston are shown in Fig. 3. The dimensions of the
microfilter and piston was also measured to compare with those of the original design. Dimensions of
the these structures were measured directly on the micrographs, showing that the microfilter is 151
mm (length) × 102 mm (width), and the piston is 151 mm (length) × 102 mm (width). These
measurements are in consistent with the dimension from the original CAD design, confirming the highprecision of the printing process.

Fig. 3 Optical micrograph of the 3D­printed microstructures: a) microfilter and b) piston
3

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The microstructure of the filter and the piston was investigated more carefully with the SEM
observation to verify if there are any artifact on the 3D­printed microstructure. As shown in Fig. 4,
several small artifacts appear on the surface of microfilter. Except a small artifact located at theentrance that may cause hindrance to the movement of the piston, other artifacts appear outside its
moving path thus can be considered negligible.

Fig. 4 SEM micrographs (top view) of the 3D­printed microstructures: a) microfilter and b) piston
These SEM micrographs in Fig. 4 confirms that the dimensions of microstructures are the samewith those measured by optical micrographs (Fig. 2). In Fig. 5, the same structures were observed
when the samples tilted 30 degree of angle to the horizontal plane, revealing the height of the
microfilter, which is estimated around 77 mm by geometry calculation. This is approximate to theheight of the original 3D design.

Fig. 5 SEM micrographs (tilt 30°) of the 3D­printed microstructures: a) microfilter and b) piston
Fig. 6 shows the microstructure of the filtering holes array. The sample was also tilted 30 degree
to reveal the hexagonal shape of the hole and the honey comb structure or the array. The holes are
confirmed well­shaped with hexagonal morphology, and their inner walls contain just a few artifacts
whose small size may not hinder the transmittance of precious particles through the holes in filtering
process. The average minimal diameter and maximal diameter estimated from the micrographs, are
3.9 mm and 7.2 mm, respectively. The inner wall between the holes, is thickest as 0.5 mm and thinnest
as 0.8 mm. These parameters are in acceptable range of the deviation from the original design (see Fig.
2). In addition, it is confirmed that there is no any cracks or flaws appear on the filtering holes arrayas well as on the whole structures.

4Transactions on GIGAKU 6(1)(2019)06008/1-6

Fig. 6 High resolution SEM micrograph (tilt 30°) of the filtering holes arrayThus, we can conclude that the 3D­printing process of the MEMS was quite precise, and thisMEMS is ready to be employed in filtering process.
4. Conclusion
In this paper, a MEMS designed for extracting precious matter on bacteria cell has beensuccessfully fabricated by 3D­printing using TPA method. The sizes of the microfilter and piston are
in consistent with the 3D design by SolidWorks, indicating that 3D­printing process was very precise.
In addition, SEM observation confirmed that the honeycomb morphology of filtering holes was well­printed. The present results enable us to utilize this piston­and­filter system for sterilization
applications. The next steps for this research are to apply an electric field onto the MEMS to control
the piston movement, then employ that to extract the precious particles from bacteria cell. Theseexperimental works are being conducted at Kushiro College and planned to be reported in future
articles.
Acknowledgments
The authors are grateful to Mr. T. Eguchi of National Institute of Technology, Kushiro College forhis assistance in SEM observation. This work was supported by Nagaoka University of Technology(NUT) Grant for collaborative research with National Institute of Technology (NIT).
References[1] Narendra Kulkarni and Uday Muddapur, “Biosynthesis of Metal Nanoparticles: A Review”, J.
Nanotechnology, vol. 2014, Article ID 510246, 2014.
[2] Matthew D. Yates et al., “Extracellular Palladium Nanoparticle Production using Geobacter
sulfurreducens”, ACS Sustain. Chem. Eng., vol. 1(9), pp. 1165-1171, 2013.
[3] Praveen Sonkusre et al., “Improved Extraction of Intracellular Biogenic Selenium Nanoparticles
and their Specificity for Cancer Chemoprevention”, J. Nanomed. Nanotechnol., vol. 5(2), Article
ID 1000194, 2014.
[4] Kevin Deplanche et al., “Involvement of hydrogenases in the formation of highly catalytic Pd(0)nanoparticles by bioreduction of Pd(II) using Escherichia coli mutant strains”, Microbiology, vol.
156, pp. 2630-2640, 2010.

5

Transactions on GIGAKU 6(1)(2019)06008/1-6[5] P. J. Fesharaki et al., “Biosynthesis of selenium nanoparticles using Klebsiella pneumoniae andtheir recovery by a simple sterilization process”, Brazilian Journal of Microbiology, vol. 41(2), pp.
461–466, 2010.
[6] M. Gericle and A. Pinches, “Biological synthesis of metal nanoparticles”, Hydrometallurgy, vol.
83, pp. 123-140, 2006.
[7] M. G. del R. Herrera Salazar et al., “Fabrication of Micro Three Dimensional Structures by Two
Photon Polymerization with SiO/Resin”, Advances in Science and Technology, vol. 100, pp. 93–
99, 2017.
[8] Linjie Li and John T. Fourkas, “Multiphoton polymerization”, Materials today, vol. 10, no. 6, pp.
30-37, 2007.
[9] H-B. Cho et al., “Self-assemblies of linearly aligned diamond fillers in polysiloxane/diamondcomposite films with enhanced thermal conductivity”, Compos. Sci. Tech., vol. 72(1), pp. 112118, 2011.
[10] S. T. Nguyen et al., “Linear assembly of oxidized surface treated nanodiamonds in polymerbased nanohybrids by electric field inducement”, Materials Science Forum, vol. 761, pp. 107111, 2013.
[11] Genki Onishi et al, “Demonstration of motion control of ZrO2 microparticles in uniform/nonuniform electric field”, Jpn. J. Appl. Phys., vol. 57, 02CB11, 2018.
[12] M.T.T. Huynh et al., “Electrical property enhancement by controlled percolation structure ofcarbon black in polymer-based nanocomposites via nanosecond pulsed electric field”, Compos.
Sci. Tech., vol. 154, pp. 165-174, 2018[13] M. G. del R. Herrera Salazar et al., “Development of Electrically Driven Microcar Using Two
Photon Microfabrication”, presented at Annual Meeting of the Ceramic Society of Japan, Tokyo,
Mar 2016.
(Received: 29 October 2018, Accepted: 20 December 2018)6

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Optimization of Mirror Magnetic Fields in a Permanent Magnet ECRIon Source for Generation of Multi-Charged Aluminum Ions
Tsubasa Nakamura1,*, Shinji Yamada2, Takumi Tomonari3, Ayumu Inagaki4, Hiroya Uyama5,
Yuta Wada6, Toyohisa Asaji7, Kazumasa Takahashi8, Toru Sasaki8
1)
Department of Electronic-Mechanical Engineering, National Institute of Technology, Oshima
College,2)
Department of Electronic and Information Technology System, National Institute of Technology,
Oshima College,3)
Department of Mechanical-Environmental System, National Institute of Technology, Oita College,
4)
Department of Mechanical Engineering, National Institute of Technology, Oita College,5)
Department of ECOdesign Engineering Course, National Institute of Technology, Toyama College,
6)
Department of Nuclear System Safety Engineering, Nagaoka University of Technology,
7)
Department of Mechanical Engineering, National Institute of Technology, Toyama College,
8)
Department of Electrical, Electronics and Information Engineering, Nagaoka University ofTechnology,1091-1 Komatsu Suo-Oshima-tyo, Yamaguchi, Japan 742-2193*E-mail: d814@oshima-k.ac.jp

We assumed the development of ion injection technology as a background in
the semiconductor manufacturing process. We carried out the study aiming at
optimization of Ar7+ and improvement of the generation efficiency. Bylowering the pressure in the chamber, the electric current of Ar7+ was about
130 nA. It improved to approximately 10 times in comparison with previous
results. When we changed the magnetic field by a solenoid coil, it improved toabout 3.6 times in comparison with that without any change. The improvementof the optimization and generation rate was able to be accomplished than theabove. In addition, following three parameters affect the generated ion beamelectric current: confinement time of the ion, ions charge state and electronic
density and plasma volume.

1. Introduction
In semiconductor manufacturing, ion injection to dope the substrate material has become an
indispensable technique in recent years. Among the semiconductor industries, in particular, the market
for power semiconductors is growing rapidly. Power semiconductor production and related techniques
have become indispensable for electricity conversion and control. Development of a technique for ion
injection of aluminum to SiC, which is the substrate material, has become the key for performance
improvement of these devices. In this study, we aimed at developing a technology for generation ofaluminum multi-charged ions, with improvement of the ion beam current and reduction of theacceleration voltage of the device. The main features of the study are as follows: 1) The ionizationenergies of Ar7+ and Al4+ are nearly same (Ar7+: about 124 eV, Al4+: about 120 eV). Therefore, we
detect Ar7+ ion, which is in gaseous state. 2) We improve the ion beam electric current of Ar7+.

1

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2. Electron Cyclotron Resonance Ion Source
An electron cyclotron resonance (ECR) ion source has been developed as a high intensity
multivalent ion beam supply device. Characteristics can be changed by using a semiconductor element
and irradiating ions, and material strength can be improved. Therefore, the ECR ion source device iscurrently used in a wide range of fields. Especially, the ECR ion source is an indispensable technology
for ion implantation in semiconductor manufacturing and has played a key role in activating the power
semiconductor market in recent years.
The ECR ion source confines the plasma in the chamber and uses a permanent magnet to introduce
microwaves into the chamber. Electrons in the plasma are then accelerated by electron cyclotron
resonance. This device constantly removes electrons from atoms and ions to generate multi-charged
ions.
Multi-charged ion refers to a state in which two or more electrons are removed from the atom. As
the number of electrons removed increases, it becomes easier to accelerate them. Plasma is formed by
the generated ions and electrons coexisting in the chamber; the ions and electrons are separated byapplying voltage to the chamber, and only the ions are extracted as a beam. Multi-charged ions are
more easily accelerated than normal ions, so if the multi-charged ions are increased in number andstabilized, the acceleration voltage applied during ion implantation can be lowered, which reduces thecost. Therefore, studies multi-charged ions are currently being undertaken.
In a typical ECR ion source, the magnetic field is formed by a set of solenoid coils (mirror magnetic
field) and 6 pole magnets and the plasma are confined. On the other hand, the Oshima-ECR ion source
used in our laboratory has a ring-shaped permanent magnet and an 8-pole permanent magnet. In
addition, three solenoid coils are used that can adjust the magnetic field in the chamber. Thus, theability to adjust the magnetic field in the chamber is one of the features of the Oshima-ECR ion source[1]. The Oshima - ECR ion source is used in our laboratory to generate multi-charged ions.

Fig. 1 Schematic view of the Oshima-ECR ion source2Transactions on GIGAKU 6(1)(2019)06009/1-8

3. Experimental Setup
The experimental procedure is explained with reference to the schematic of the Oshima-ECR ion
source shown in Fig. 1.
While keeping the Oshima-ECR ion source at vacuum (about 10-5 Pa), plasma is generated at thelower left ECR ion source. As a buffer gas for this purpose, argon gas is flowed at 0.01 sccm (standard
cc/min); this is because the ionization energy of Al+4 (about 120 eV) is close to that of Ar+7 (about 124eV) and therefore, the Oshima-ECR ion source can generate Al4+ theoretically, by observing Ar7+. Ar
gas is not necessary to vaporize it. Ar gas is not necessary to vaporize it to ionize. Thereafter, amicrowave (2.45 GHz) is applied to generate plasma in the chamber. Then, a high voltage is applied
into the chamber, and multi-charged ions generated in the chamber are extracted by electron cyclotron
resonance.
The extracted multi-charged ions consist of various components and are passed through an analysis
magnet. The emergent ion beam is measured in a Faraday cup to determine the ion beam electric
current.
The ion beam electric current can be optimized in the Oshima-ECR ion source through adjusting
the magnetic field in the chamber by using solenoid coils. Figure 2 shows the change of the magnetic
field in the chamber. In addition, the background of the Figure 2 is shown the figure of thechamber. The reason is to make it easy to understand the magnetic field distribution in
the chamber (positional relationship with Z axis.). This figure indicates that when the electric
current flowing in solenoid coil 1 increases, the magnetic field of the chamber (the microwave
applying side) becomes strong; as the electric current of solenoid coil 3 increases, the magnetic field(the drawer electrode side) becomes weak.
Coil 1 = 0 A, Coil 3 = 0 A
Coil 1 = 0 A, Coil 3 = -200 A
Coil 1 = 200 A, Coil 3 = 0 A

Magnetic Field Intensity [mT]300

Coil 1 = 0 A, Coil 3 = -100 A
Coil 1 = 100 A, Coil 3 = 0 A
Coil 1 = 100 A, Coil 3 = -200 A

250
200
150
ECR for
2.45GHz(87.5 mT)

100
50
0
0

Coil 3 Side

30

60

90

z-position [mm]

120

150
Coil 1 Side

Fig. 2 Magnetic field change in the chamber3Transactions on GIGAKU 6(1)(2019)06009/1-8

4. Experiment Parameters
On the upstream side of the Oshima-ECR ion source, we added a turbo molecular pump (Osaka
Vacuum Equipment Manufacturing TG 50 F), as shown in Fig. 3, to lower the vacuum pressure in thechamber and minimize the buffer gas flowing into the chamber.
As a result, it was possible to lower the pressure in the chamber for generating plasma from 7.71 ×
10-5 Pa (before expansion) to 2.73 × 10-5 Pa (after expansion).
Thereafter, argon was used as a buffer gas, and the ion beam current was measured. The
experimental parameters are shown in Table 1. For a comparison, the parameters before installing theturbo molecular pump are also listed.
Next, we changed the magnetic field in the chamber in the parameter that optimized in Ar7+
(parameter are solenoid coil 1 and 3) and estimated the corresponding change in the ion beam electric
current. The experimental parameters are shown in Table 2.
Table 1 Influence of pressure drop in the chamber
20171027-09

20171201-01(before expansion)(after expansion)-5

Ion source pressure

7.71×10 Pa

2.73×10-5 Pa

Beam line pressure

4.28×10-5 Pa

2.69×10-5 Pa

Microwave power (I/O)

80 W/6 W

80 W/7 W

Buffer gas/flow rate

Ar/0.01 sccm

Ar/0.01 sccm

Chamber voltage/current

5 kV/2.56 mA

5 kV/1.30 mA

Einzel lens voltage/current

3.8 kV/2.10 mA

3.8 kV/0.70 mA

Fig. 3 Setting point of the turbo molecular pump4

Transactions on GIGAKU 6(1)(2019)06009/1-8

Table 2 Change in the ion beam electric current when the magnetic field in the chamber is changed
1.03×10-5 Pa
Ion source pressure

5.1.

Beam line pressure

5.74×10-5 Pa

Microwave power (I/O)

100 W/6 W

Buffer gas/flow rate

Ar/0.01 sccm

Chamber voltage/current

5.05 kV/1.68 mA

Einzel lens voltage/current

3.52 kV/0.61 mA

Current of solenoid coil 1 and 30, 50, 100, 150, 200 A

5. Results and Discussion
Influence of pressure drop in the chamber

The results are shown in Fig. 4. The ion beam current of Ar7+ was about 20 nA before the installationof the turbomolecular pump, and reached about 130 nA after expansion, which is an increase of about
6.5 times. In addition, the generation amount of argon multi-charged ions could be substantially
improved.
The reason behind the increase in the amount of generated argon multi-charged ions is as follows.
Reducing the pressure in the vacuum chamber reduces the number of molecules in the chamber. Then,the collision frequency with electrons decreases, and the ion lifetime increases. As a result, the ion
beam current of multi-charged ions could be improved.

Fig. 4Comparison of the argon spectrum waveform.

5Transactions on GIGAKU 6(1)(2019)06009/1-8

5.2. Change in the ion beam electric current
We flew an electric current to solenoid coil 1 and 3 and changed the magnetic field in the chamber.
An example of the spectrum wave pattern is shown in Fig. 5. The blue line represents 100 A (solenoid
coil 1) and 0 A (solenoid coil 3). The red one indicates corresponding values of 100 A and -150 A.
The electric current of Ar+7 from this result is approximately 50 nA and 100 nA. Thus, a differenceof approximately 2 times occurred. This indicates that the ion beam electric current is changed bychanging the magnetic field in the chamber.
The change of the ion beam electric current of Ar+7 when we changed the magnetic field in thechamber is shown in Fig. 6.
When solenoid coil 1 current is constant, it becomes easy to draw the ion beam because the electric
current of solenoid coil 3 is large (the magnetic field in the extraction side of the chamber weakens.).
Therefore, we expected that the ion beam electric current will increase, but such correlation was notseen. From the result, when the electric current of solenoid coil 3 was -150 A, the ion beam electric
current of Ar+7 was about 100 nA (maximum).
Therefore, in this study, the maximum ion beam current can be obtained when the solenoid coil 1
and 3 are set to 100 A and -150 A, respectively.
The ion beam electric current considers a reason to change by adjusting the magnetic field in thechamber in this way.
The ion beam electric current of the multi-charged ions is calculated using the following equation
[2].

𝐼" ≅

$ &' "()*+
%

,'

(1)

#20180831-01, Coil 1 = 100 A, Coil 3 = 0 A

25,0001,500

Ion Beam Current [nA]

Ar+ :40 (m/z)

Ar4+ :10 (m/z)
Ar5+ :8

1,000

20,000#20180831-04, Coil 1 = 100 A, Coil 3 = -150 A

Ar6+ :6.67
500

15,000

0







Ar2+ :20 (m/z)
250
200
150
100
50
0

10,000Ar3+ :13.3
5,000

Ar7+ : 5.71

  







0











m/z

Fig. 5Spectrum wave pattern example when the magnetic field in the chamber is changed.
6

Transactions on GIGAKU 6(1)(2019)06009/1-8Here, nq is density of the ions of charge state q; τd the confinement time of these ions depending on
potential dip Δφ; Vol is the part of the hot-plasma volume that maps along the magnetic field lines into
the extraction area.
From this equation, if the confinement time of ion is short, the ion beam electric current will increase.
Otherwise, it is necessary to increase the density and the plasma volume of atomic value q. Therefore,
the magnetic field of the extraction electrode side weakens and the ion enclosure time thereby shortens;
thus, the ion beam electric current increases.
The reasons that cause a decrease in the ion beam electric current are stated below.
Assuming plasma charge neutrality𝑛( = ∑" 𝑛" 𝑞(2)

Using this equation and equation 1, we get equation 3.
)*+𝐼" ∝ 𝑛((3),2Thus, the production of high-intensity Iq, high-charge-state q ions results in a compromise between
the ionization conditions and the plasma confinement condition [2]. In addition, in plasma confined inan electromagnetic field, as for the ion, the possibility of recombination with electrons increases.
As a result, an electron is drawn in the opposite side of the extraction electrode. However, a part isleft in the plasma without being drawn under the influence of the magnetic field in the chamber.
Recombination with the ion occurs, which is thought to reduce the ion beam electric current.

Coil 1 = 0 A
Coil 1 = 100 A

Ion Beam Current [nA]120

Coil 1 = 50 A
Coil 1 = 200 A

100
80
60
40
20
0
0

-50

-100

-150

-200

Current of Coil 3 [A]Fig. 6

Change of the ion beam electric current by change in the magnetic field in the chamber.

7

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6. Conclusion
We assumed the development of ion injection technology as a background in semiconductor
manufacturing process. We carried out this study for the following purposes. 1) The ionization energies
of Ar7+ and Al4+ are nearly same (Ar7+: about 124 eV, Al4+: about 120 eV). Therefore, we detect an ionof Ar7+ which is gas. 2) We improve the ion beam electric current of Ar7+. It succeeded in the detectionof Ar7+ which we targeted by lowering the pressure in the chamber. The electric current was about 130
nA. Regarding the improvement of the generation of Ar7+, we were able to optimize it by adjusting
the magnetic field in the chamber. From the results of this study, a current of about 100 nA maximum
is produced when the currents of solenoid coil 1 and 3 are 100A and -150 A, respectively. In addition,
following three parameters influence the generated ion beam electric current: confinement time of theion, ions of charge state and electronic density and plasma volume.
Acknowledgments
This study was supported by the Nagaoka University of Technology（NUT）grant for collaborative
research with National Institute of Technology (NIT).
References[1] T. Nakamura, et al., Effect of axial magnetic field on a 2.45 GHz permanent magnet ECR ion
source, Review of Scientific Instruments, 87(02A737), 2015.12[2] R. Geller, Electron Cyclotron Resonance Ion Source and ECR Plasmas, Institute of Physics
Publishing, Bristol, p.370, 1996.
(Received: 15 October 2018, Accepted: 22 February 2019)8

Transactions on GIGAKU 6(1)(2019)06010/1-7

Purification and Antigenicity Evaluation of Fish-Disease Bacterial
Outer Membrane Proteins for Immersion Vaccine Development
Noriyo Mitome1*, Nagisa Hamada2, Naoki Yamashita 2, Seng Eng Khuan3
Department of Chemistry and Biochemistry, National Institute of Technology, Numazu College,
3600 Ooka, Numazu city, Shizuoka, 410-8501, Japan2)
Department of Chemical and Biological Engineering, National Institute of Technology, Ube
College, 2-14-1 Tokiwadai, Ube city, Yamaguchi, 755-8555, Japan3)
School of Chemical and Life Sciences, Nanyang Polytechnic, 180 Ang Mo Kio Avenue 8 Singapore,
569830, Rep. of Singapore*E-mail: mitome@numazu-ct.ac.jp
1)

The pathogenic marine bacterium, Edwardsiella tarda, causes the fatal disease,edwardsiellosis, in fish. Owing to the unavailability of a commercial vaccine
to prevent infection or the spread of the disease in fish stock, fish farms suffer
huge losses during edwardsiellosis outbreaks. Herein, we describe a platform
technology, i.e., a nanovaccine, to vaccinate fish and other animals.
Nanovaccines require specific antigens, such as the bacterial outer membraneproteins (OMPs) carried around and inside nanoparticles, to act as vaccines. In
this study, we developed a rapid and inexpensive method for the isolation andpurification of OMPs from marine bacteria and demonstrated the antigenicityof the purified OMPs using Koi carp (Cyprinus carpio). The purified OMPs
were then incorporated into the nanoparticles to generate a nanovaccine.
Nanovaccinated Koi carp produced antibodies against the OMPs of E. tarda.
We propose that the OMP purification method used in the present study isuseful for the production of nanovaccines and that such techniques are simple
to apply and effective to prevent disease outbreaks in fish farms.

1. Introduction
Owing to the rapid expansion of aquaculture, several farms now stock fish at a very high density.
The close proximity of fish and the occurrence of natural pathogens in the aquatic environment
increase the frequency of disease outbreaks, which may reduce fish stocks causing huge losses to fish
farms [1][2]. To overcome diseases, vaccines have been used as they can provide long-term protection.
In fact, the administration of fish vaccines has prevented the loss of fish in fish farms due to disease
outbreaks, enabling higher fish yield [3].
The current modes of vaccine administration include injection, oral administration, and immersion.
Injection vaccines are administered intramuscularly or intraperitoneally (in the abdominal cavity).
They provide long-term protection, i.e., for over a year, and allow multiple antigens to be combinedin a single vaccine and thus in a single administration. Despite these advantages, the administration of
vaccines via injection is an expensive method because of the heavy dependence on skilled manpower.
Moreover, it has a high risk of causing accidental injury to the fish and personnel. Furthermore,injection vaccines can only be administered when fish weigh > 10 g, and therefore, smaller fishes
cannot be vaccinated and thus remain unprotected from diseases.
Oral vaccines are either administered in the feed (mixed in or coated) or bio-encapsulated. Oralvaccines have more advantages as they can be easily administered, cause no stress to the fish, require
low labor investment, and can be applied at a large scale. However, oral vaccines have a very shortterm stability once mixed with the feed [4]. In addition, several oral vaccines have been found to beineffective due to the failure of fish to uptake a sufficient antigen dosage, and poor antigen delivery
and degradation in the digestive tract [4]. In most cases, only limited and short-term protection isoffered. Moreover, the injection of vaccine directly into an individual fish is preferred over oral
administration as a defined quantity of vaccine can be administered leading to longer protection.
1

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Immersion vaccination involves the functionality of mucosal surfaces. When fish are immersed inwater containing the diluted vaccine, the suspended antigens from the vaccine are adsorbed on to theskin and gills [5]. Specialized cells, such as antigen-presenting cells present in the skin and gillepithelium, are consequently activated and thus protect the fish when they are exposed to live pathogen
at a later stage. It is an effective method that results in relatively good protection. Although, immersion
vaccination is sometimes protective, not many effective immersion vaccines are currently available
for use.
The pathogenic marine bacterium Edwardsiella tarda causes parasitological diseases or
edwardsiellosis in cultured Japanese eel, flounder, red sea bream, and tilapia [6][7]. A vaccine against
E. tarda has been pursued for several years; however, a practical and commercially available vaccine
has not been developed. Only the attenuated vaccine for Edwardsiella ictaluri is commerciallyavailable in the USA. Moreover, a recent report has indicated that an outer membrane protein (OMP),
i.e., glyceraldehyde 3-phosphate dehydrogenase (GAPDH), from E. tarda is an effective vaccine
candidate against E. tarda [8]. In addition, the nanovaccine platform technology has been describedfor use in vaccinating fish and other animals [9]. Nanovaccines require a specific antigen, such as the
OMPs of bacteria carried around and inside the nanoparticles, to act as vaccines.
There are several methods to purify the OMPs. For example, porin, which is a typical OMP, hasbeen purified by selective solubilization because porin is tolerant to strong detergents such as sodium
dodecyl sulfate (SDS) [10]. Porin has also been purified by ion exchange and gel filtration with octylPOE [11]–[16] or by selective solubilization and gel filtration with LDAO and C8E4 [17]–[19]. Ferricenterobactin receptor (FepA) has been purified by selective solubilization with Triton X-100 in theabsence and presence of EDTA [20]. Most of the OMPs can be extracted with Triton X-100 and EDTA.
In this study, we developed a quick and low-cost method to isolate and purify the OMPs frommarine bacteria and demonstrated the antigenicity of the purified OMPs. The purified OMPs were thenincorporated into nanoparticles to develop a nanovaccine.

2. Experiments
Preparation of formalin-inactivated vaccine and evaluation of antigenicity
Edwardsiella tarda (NBRC 105688) cells were first cultured on a plate of NBRC medium No. 802(containing 1% hipolypepton, 0.2% yeast extract, 0.1% MgSO4ꞏ7H2O, and 1.5% agar) at 30 °C for 24
h. The cells were then cultured in 100 mL of NBRC medium No. 802 at 30 °C for 24 h. The cultured
E. tarda cells were diluted with sterilized physiological saline to obtain the OD660 of 8.0. The bacteria
cells were inactivated with formalin (1%) for 24 h at 4 °C. The inactivated cells were then stored insterilized physiological saline with 0.1% formalin. The bacterial cell suspension was used as a vaccine
in the subsequent experiments.
Koi carp (Cyprinus carpio) (n = 6), with an average body weight of 20 g, were housed in aquariums(30 L capacity) and were divided into three immune carp groups (tanks) and three control carp groups.
A mixture of vaccine and sunflower oil (1:2) was prepared, and then 100 mL of the mixture wasinjected into the abdomen of the carp. After 10 days, a booster dose (100 mL) was injected. In thecontrol group, the carp were similarly injected with a mixture of sterile physiological saline andsunflower oil (1:2).
On the 21st day after the first vaccination, blood samples (200 mL) were collected using thestandard venipuncture technique. The blood samples were incubated at 4 °C for 24 h and serum
samples were obtained by centrifuging the blood samples at 3000 × g for 10 min. Antigenicity wasconfirmed using the dot blot method.
Cultivation of E. tarda and preparation of membrane fraction
Edwardsiella tarda cells were first cultured on a plate of NBRC medium No. 802 at 30 °C for 24
h. Subsequently, the cells were precultured in 100 mL of NBRC medium No. 802 at 30 °C for 6 h, andthen 100 mL of preculture was added to 1 L of NBRC medium No. 802 and cultured at 30 °C for 16 h[6]. The bacterial cells were collected by centrifugation at 6500 × g for 5 min at 4 °C, washed in 200
mL of 10 mM Tris-HCl buffer pH 8.0, and collected again by centrifugation at 6500 × g for 5 min at
4 °C. We collected 20 g of bacterial cells from 1 L of culture, froze the cells using liquid nitrogen, andstored them at -80 °C. The bacterial cells were suspended in 10 mM Tris-HCl buffer of pH 8.0 using2

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4 mL of the buffer per gram of cells and disrupted by sonication. After removal of debris by
centrifugation at 6500 × g for 10 min at 4 °C, the membrane fraction was collected from thesupernatant by ultracentrifugation at 200,000 × g for 30 min at 4 °C. The membrane fraction was
suspended in 10 mM Tri-HCl buffer using the same volume as the weight of the starting cells, andstored at -80 °C.
Solubilization of membrane proteins
The membrane fraction was suspended in 10 mM Tris-HCl with 2% Triton X-100, incubated at
32 °C for 30 min, and ultra-centrifuged at 200,000 × g for 30 min at 32 °C [20]. The supernatant(Triton extraction) was stored at -80 °C to determine protein purity. The pellet (Triton insoluble
fraction) was suspended in 10 mM Tris-HCl with 2% Triton X-100 and 5 mM EDTA, incubated at
32 °C for 30 min, and ultra-centrifuged at 200,000 × g for 30 min at 32 °C. The supernatant(Triton/EDTA extraction) was frozen using liquid nitrogen and stored at -80 °C for use in the
preparation of nanovaccine. The pellet (Trion/EDTA insoluble) was suspended in 10 mM Tris-HCl
with 2% SDS, incubated at 32 °C for 30 min, and ultra-centrifuged at 200,000 × g for 30 min at 32 °C.
The supernatant (SDS soluble) and the pellet (SDS insoluble) were stored at -80 °C until further
analyses. The Triton/EDTA extract (2 mL of 1 mg/mL) was dialyzed twice with 2 L of phosphatebuffered saline (PBS) to dilute the detergent.
SDS-PAGE analysis of proteins
To confirm the purity of proteins, SDS polyacrylamide gel electrophoresis (SDS-PAGE) was
carried out by separating 15 μg of proteins on 12.5% gels. The proteins were confirmed by staining
with Coomassie brilliant blue.
Proteins quantification
Protein quantification was conducted by Bradford method using a standard solution of bovine
serum albumin (BSA) of known concentration.
Generation of nanoparticles containing bacterial OMPs
The mixture (20 mL) containing 50 mg/mL chitosan–clay and 100 mg/mL of the OMPs in
PBS was frozen using liquid nitrogen and dried using a freeze dryer (VirTis). The dry particles weresuspended in 20 mL of distilled water.
We analyzed the amount of proteins that could be absorbed by the chitosan–clay
nanoparticles. We mixed 100, 200, and 500 mg/mL of dialyzed OMPs with 50 mg/mL of nanoparticles
individually. These mixtures were then frozen using liquid nitrogen and dried using a freeze dryer.
After freeze drying, the chitosan–clay powder containing the OMPs was suspended in distilled water
to form the nanovaccines. To confirm the absorption of OMPs to the nanoparticles, we quantified theproteins in the supernatant after centrifugation at 6000 × g for 1 min.
Vaccination
Five milliliters of 50 mg/mL chitosan–clay suspension with or without 100 mg/mL OMPs
were added to 1 L of freshwater in which the fish were allowed to swim for 30 min. The vaccinatedand non-vaccinated fish were grown in separate aquariums. On the 21st day after the first vaccination,
200 mL of blood was collected from three carp in the control and treatment groups using the standard
venipuncture technique. The blood samples were incubated at 4 °C for 24 h and serum samples wereobtained by centrifuging the blood samples at 3000 × g for 10 min. The antigenicity of the nanovaccine
was confirmed by immunoblotting. The OMPs from E. tarda were separated by SDS-PAGE andtransferred on to immunoblot-designed polyvinylidene difluoride membranes. The membranes werethen blocked with PBS with 1% BSA at 4 °C overnight, followed by incubation with the serum, which
was obtained from vaccinated carp, diluted to 0.2% in PBS for 1 h at 4 °C. The membranes were thenwashed three times with PBS for 5 min each. The incubation with secondary antibodies was conducted
for 30 min with 1% secondary antibody conjugated with horseradish peroxidase (Anti-IgM, Carp/Koi
Carp (C. carpio), Mouse-Mono, HRP) in PBS at 4 °C. The bands were visualized using ECL Plus
Western Blotting Detection Reagents (GE Healthcare).
3. Results and Discussion
Formalin-inactivated E. tarda were injected into live carp. After three weeks, blood samples were3

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collected to obtain serum samples. The results of the dot blot analysis showed that E. tarda cells were
stained in the serum from carp that were vaccinated with formalin­inactivated E. tarda (Fig. 1). On
the contrary, Vibrio sp. was not stained in the serum from carp vaccinated with formalin­inactivatedE. tarda. Whereas, Vibrio sp. was stained in the serum from carp vaccinated with formalin­inactivatedVibrio sp. Contrarily, E. tarda cells were not stained in the serum from carp vaccinated with formalin­
inactivated Vibrio sp. These results suggested that the formalin­inactivated vaccine of E. tarda wasbound to E. tarda and that the formalin­inactivated vaccine of Vibrio sp. was bound to Vibrio sp.
The extraction procedure was primarily based on selective solubilization of inner MPs and OMPs
with Triton X­100 in the absence and presence of EDTA [16]. The inner membrane proteins weresolubilized with Triton X­100 (Fig. 2). The Triton­insoluble fractions mostly contained the OMPs.
Some of the OMPs were extracted by Triton and EDTA. The 97­, 43­, 40­, and 37­kDa proteins werevisible in this fraction (Fig. 2). The purified OMPs included several proteins, namely, 97, 43, 40, and37 kDa. These proteins were the same as those reported extracted using SDS in a previous study [21].
Especially, the 37­kDa protein, GAPDH, has been reported to be a candidate for vaccination [20]. In
the present study, we demonstrated that it is possible to purify GAPDH and other candidate OMPs
using this purification method for vaccine preparations. In the purification of OMPs, SDS is often used[21]. However, detergents, especially anionic detergents, such as SDS, which denature proteins areharmful to fish. Therefore, we used the non­ionic detergent, Triton with EDTA instead of SDS for the
purification of OMPs. Although dialysis resulted in the dilution of Triton, the direct vaccination of
OMPs at a concentration of 0.1% of the body weight resulted in the mortality of fish.
The purified OMPs were used to prepare the nanovaccine. Although several proteins were includedin the Triton and EDTA extract, we considered the use of a simple purification method to enable
practical application and to reduce cost.

Fig. 1 Dot blot analysis. Top circles: Spottedwith E. tarda. Bottom circles: Spotted with
Vibrio sp. Left: Spotted bacteria were probedwith the serum sample from Koi carp (Cyprinus
carpio) vaccinated with Vibrio sp. Right:
Spotted bacteria were probed with the serum
sample from carp vaccinated with Edwardsiellatarda.

Fig. 2 Coomassie brilliant blue­stained gel ofthe inner and outer membrane proteins. 1.
Membrane fraction. 2. Triton extract. 3. Triton
insoluble. 4. Triton/EDTA extract. 5.
Triton/EDTA insoluble.

Proportion of chitosan–clay and OMPs
We mixed the OMPs at various concentrations with chitosan–clay at a constant concentration of
50 mg/mL. Table 1 shows the estimated absorption of OMPs by chitosan–clay. When 100 mg/mL
OMPs was added, almost all proteins were absorbed by 50 mg/mL nanoparticles. When 400 mg/mL
OMPs was added, only 300 mg/mL OMPs was absorbed. These findings suggested that the additionof 100–300 mg/mL OMPs to 50 mg/mL chitosan–clay is suitable to manufacture a nanovaccine with
100–200 mg/mL OMPs.
4

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Table 1 Amount of absorbed outer membrane proteins by the nanoparticles.
100 mg/mL (a), 200 mg/mL (b), and 500 mg/mL (c) OMPs were mixed with 50 mg/mL
nanoparticles. After freeze­drying, the chitosan–clay powder that contained the OMPs was suspended
in distilled water and the proteins in the supernatant were quantified after centrifugation.

a

b

c

Concentration of chitosan–clay (mg/mL)

50

50

50

Concentration of outer membrane protein (mg/mL)

50

100

400

Protein concentration of supernatant (mg/mL)

0.0

0.0

95.6

Estimated concentration of absorbed protein in nanoparticle (mg/mL)

50

100

304.4

Three carp were treated with nanoparticles with (nanovaccine) or without (nanoparticle only) the
OMPs (Fig. 3). The administration of prepared nanovaccines, in which the detergents were diluted,

Fig. 3 Immersion vaccination for carp. Fivemilliliter suspensions of 50 mg/mL chitosan–
clay with or without 100 mg/mL outermembrane proteins were added to 1 L of
freshwater in which the study fish were allowed
to swim for 30 min.

Fig. 4 Evaluation of the production of antibodies
in the serum by immunoblotting. The outermembrane proteins from E. tarda were separated
by SDS­PAGE and transferred on to membranes.
The membranes were treated with the serum
obtained from the blood samples of vaccinatedcarp (left) and nonvaccinated carp (right) andsecondary antibody conjugated with horseradish
peroxidase. Bands appeared at 43, 40, and 37
kDa.
was demonstrated to be safe, i.e., none of the nanovaccinated carp died. After three weeks, blood wascollected from the carp and the production of antibodies was determined via immunoblotting. The
bacterial OMPs were stained in the blood serum. Bands appeared at 43, 40, and 37 kDa in the serumfrom nanovaccinated carp. This suggested that the carp produced antibodies against the OMPs in theserum.

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4. Conclusions
In this study, we developed a quick and low-cost method to isolate and purify the OMPs frommarine bacteria and demonstrated the antigenicity of the purified OMPs. The purified OMPs were thenincorporated into nanoparticles to develop a nanovaccine. We propose that our method of purificationof OMPs is useful for nanovaccine production and that the use of nanovaccine technology can prevent
disease outbreaks and the consequent production losses in fish farms.
Acknowledgments
We thank Dr. Saji George for the helpful discussions. We thank Ms. Anis Muthalib and Mr. Naoki
Yamashita for their technical assistance. This study was supported by the Japan Society for the
Promotion of Science (JSPS) KAKENHI (Grant Number 17K07922).
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(Received: 29 October 2018, Accepted: 21 January 2019)7