Project 1 Development on Neutron Imaging Application (R4P1)

概要

I-1.

PROJECT RESEARCHES
Project 1

-2-

PR1

Development on Neutron Imaging Application

Y. Saito

sure time is 0.5 ms. From experimental results, it was
found that The electrical field effect of the image intensifier due to the Joule heating and the pipe stretching due to
the high-temperature cause the image degradation, and
they should be clarified for highly accurate void fraction
measurement by high-speed neutron imaging.
ARS-2 applied to neutron imaging to water accumulation
in Polymer Electrolyte Fuel Cell (PEFC). A PEFC having
a single-serpentine gas channel with a cross-sectional
area of 1 × 1 mm2, an electrode area of 20 mm × 20 mm
was used. By varying the surface pressure, the water accumulation was measured in the gas diffusion layers
(GDLs). From the experimental results, it is considered
that the cell performance decreased due to the increase in
the diffusion resistance caused by the water accumulation
in the GDL.
ARS-3 investigated the effect of neutron scattering on the
accuracy of neutron imaging. By using a phantom and a
grid system, the influence of the luminescence in a dark
box was roughly estimated.
ARS-4 did not perform experiments due to the difficulties
for experimental setup.
ARS-5 applied neutron imaging to analysis of vapor
pressure in fire spalling of high-strength concrete. Measuring moisture transfer inside concrete quantitatively,
how vapor pressure inside concrete affect spalling was
considered.
ARS-6 proposed a mixer for the instantaneous heating of
the reactant solution and performed neutron radiography
measurements to confirm how supercritical water and
room-temperature water mixed in the proposed mixer.
From the experimental results, it was found that the proposed mixer was expected to produce metal oxide nanoparticles with smaller sizes and a narrower size distribution.
ARS-7 applied neutron imaging to visualization of plant
roots in soil containing organic materials. By using heavy
water instead of light water, the plant roots could be
clearly visualized by neutron imaging at the E2 port.
ARS-8 was trying to develop a method for quantitative
estimation of neutron imaging. For this, transmission
images of industrial materials such as screws were acquired at different measurement times. From the measurements, it was found that even short imaging time
and/or CT could meet the requirements for some purposes.
ARS-10 performed flow visualization of liquid infiltrating into a complex structures simulating an actual vehicle
stator coil. Experiments were performed at the B4 port,
by varying the flow rate and the heat applied to the
structure. From the experimental results, it was concluded
the initial liquid temperature is more crucial for effective
coolant spreading and cooling.

Institute for Integrated Radiation and Nuclear Science,
Kyoto University
1. Objectives and Allotted Research Subjects: Neutron imaging provides valuable information which cannot
be obtained from an optical or X-ray imaging. The purpose of this project is to develop the imaging method
itself and also the experimental environment for expanding the application area of the neutron imaging. The allotted research subjects are as follows:
ARS-1:

Measurements of Multiphase Dynamics by
Neutron Radiography (Y. Saito et al.)
ARS-2:
Effect of Water Accumulation in Polymer
Electrolyte Fuel Cell and the Cell Performances
due to the Difference in the Surface Pressure (H.
Asano et al.)
ARS-3:
Influence of Luminance Scatter in Darkbox
for Visualization by using Neutron Raidography
(H. Umekawa et al.)
ARS-4:
Frost Deposition Distribution Estimated by
Neutron Imaging and its mechanism (R. Matsumoto et al.)
ARS-5:
Effect of the moisture content of
high-strength concrete on the spalling phenomenon under fire (M. Kanematsu et al. )
ARS-6:
Effects of the mixer shape in a flow-type
supercritical hydrothermal reactor as evaluated by
neutron radiography (S. Takami et al.)
ARS-7:
Neutron Imaging of Plant Roots in Soil
Containing Organic Materials (U. Matsushima et
al.)
ARS-8:
Development of a method for quantitative
estimation of neutron imaging (M. Kitaguchi et
al.)
ARS-9:
In-situ Lithium diffusion behavior in NASICON-Type Structured Lithium Ion Conductive
Composite by Means of Neutron Radiography (S.
Takai et al.)
ARS-10:
Flow Visualization of Liquid Infiltrating
into Complex Structures (M. Kaneda et al.)
2. Main results and the contents of this report: To
develop neutron imaging, our imaging system was developed so that high-speed imaging could be performed
at thermal neutron flux of 107 n/cm2s. Such improved
system was shared with all of the project members and
valuable results were obtained as follows:
ARS-1 performed visualization of high temperature
boiling two-phase flow by high-speed imaging. Test section is a stainless-steel pipe with an inner diameter of
10mm, which was heated by Joule-heating. The neutron
experiments were performed at the B4 port. The imaging
system used in this study consists of an op-tical image
intensifier, a high-speed camera, and an 85 mm optical
lens (F1.2) [1]. The frame rate is 1000 fps, and the expo-

R4P1
-3-

PR1-1

Measurements of multiphase flow dynamics using neutron radiography

Y. Saito, D. Ito and N. Odaira
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: Neutron radiography (NRG) is
very useful for visualizing multiphase flow. The flow
structure and dynamics of boiling two-phase flow can be
measured. In this work, high-speed neutron imaging was
applied to observe the phase change behavior in a heated
pipe. The axial change of void fraction distribution at
different mass fluxes was evaluated.
VOID FRACTION DISTRIBUTIONS OF BOILING
TWO-PHASE FLOW: The boiling two-phase flow in
the stainless-steel pipe heated by Joule heating is visualized by high-speed neutron imaging. The schematic diagram of the test section is illustrated in Fig.1. The inner
diameter of the stainless steel pipe is 10 mm, and the
heated length is 300 mm. The heated length is larger than
the visualization area of the neutron imaging, so a manual
z-axis stage moves the test section axially. In this experiment, image sequences at five places are acquired and
arranged because the height of the image is about 75 mm.
The neutron imaging experiments are conducted at the
B-4 port in KUR. The imaging system used in this study
consists of an optical image intensifier, a high-speed
camera, and an 85 mm optical lens (F1.2) [1]. The frame
rate is 1000 fps, and the exposure time is 0.5 ms. The
empty, water-filled, and two-phase images can estimate
the void fraction distribution. The experiments are performed by varying mass flux, heat flux, and water subcooling.

Fig. 2.
Void fraction distributions of boiling
two-phase flow in a heated pipe; (a) G = 100 kg/m2s,
(b) G = 200 kg/m2s, (c) G = 300 kg/m2s, (d) G = 400
kg/m2s.
Fig. 2 shows temporally averaged void fraction distributions estimated from the neutron transmission images.
The axial change of the void fraction is investigated by
changing the mass flux at q= 290 kW/m2 and ΔTsub＝20K.
The boiling two-phase flow structure can be easily understood from these figures. The onset of nucleate boiling
moves downstream as the mass flux increases.
The electrical field effect of the image intensifier due to
the Joule heating and the pipe stretching due to the
high-temperature cause the image degradation, and they
should be clarified for highly accurate void fraction
measurement by high-speed neutron imaging.
REFERENCES:
[1] D. Ito and Y. Saito, Materials Research Proceedings,
15 (2020) 262-267.

Fig. 1. Schematics of the test section of
boiling two-phase flow experiments.

R4P1-1
-4-

PR1-2

Effect of Water Accumulation in Polymer Electrolyte Fuel Cell and the Cell
Performances due to the Difference in the Surface Pressure

H. Murakawa, T. Katanaya, K. Sugimoto, H. Asano,
D. Ito1 and Y. Saito1

to the accumulation in the GDL. For all conditions, the
water accumulation occurred significantly during 5
minutes from the power generation start. After that, the
change in the water thickness becomes moderate with the
operation time. As confirmed by Fig. 1, the change in the
water accumulation in the GDL becomes smaller when
the water starts to be discharged into the channel. The
amount of water accumulation varied depending on the
difference in P and the water accumulation was the lowest at P = 1.0 MPa. Table 1 shows the reaction and
ohmic resistances at 21 min. The resistances for P = 1.0
MPa take the lowest, indicating the cell performance was
the best. Compared with the results in Fig. 2, it can be
seen that the cell performance improved due to less water
accumulation in the GDL. At P＝0.5 and 2.0 MPa, it is
considered that the cell performance decreased due to the
increase in the diffusion resistance caused by the water
accumulation in the GDL.

Graduate School of Engineering, Kobe University
1
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
INTRODUCTION: A polymer electrolyte fuel cell
(PEFC) consists of a proton exchange membrane (PEM)
sandwiched between gas diffusion layers (GDLs) and gas
channels. Water transport in the PEFC is a key topic for
fuel cell performance. If water is accumulated in the
GDL, it may suppress the air supply to the cathode reaction site. It is well known that the water contents in the
PEM are related to the ionic conductivity resulting in a
change in the PEFC performances [1]. One of the important parameters for the PEFC setting is the surface
pressure, P, of the cell. If the pressure is much higher
than the appropriate pressure, the porosity of the GDL
may decrease resulting in the decrease of the gas diffusivity. On the other hand, low pressure may lead to an
increase in contact resistance. In this study, we focused
on the effect of water transport and the cell performances
due to the difference in the surface pressure. ...