WM2016 Conference, March 6-10, 2016, Phoenix, Arizona, USA. 1

WM2016 Conference, March 6-10, 2016, Phoenix, Arizona, USA.
Observation Technology for Remote Operation
in Contaminated Turbid Water – 16113
Manabu Kishimoto, Takashi Mitsui,
IHI Corporation, 1 Shin-Nakahara-cho, Isogo-ku, Yokohama, Kanagawa, Japan
ABSTRACT
Remote underwater work in contaminated tanks and pools is one of major
decontamination and decommissioning works under high-dose radiation
environment. Generally, in this kind of work, visual information obtained by a
camera (an optical camera) is limited due to turbid water caused by suspended
sludge particles in the water and it makes remote underwater work difficult to be
performed safely and efficiently. Therefore, some alternative observation methods
to optical cameras have been required.
In order to satisfy this requirement, the alternative observation technology which
can obtain visual information in contaminated turbid water has been developed
since 2014. It is a technology using an acoustic imaging system in a designated
airtight container. It provides the visual information in real time regardless of
turbidity without significant contamination of any parts of the system. Also, it is
able to provide the location information of underwater objects with contactless.
This paper will present development details of this innovative observation
technology and its effectiveness to various remote works in contaminated turbid
water.
INTRODUCTION
Remote work in contaminated water, such as sludge retrieval work in a waste tank,
maintenance work in a fuel or waste storage pool and dismantling work for reactor
internal structures, is one of major works for most of D&D facilities. To obtain
enough visual information is very important for such kind of works however there
are many cases that the visibility is limited due to suspended particles around
working area in the water.
In remote operation, the location of objects to be cut, grasped and removed is
usually recognized to touch the objects with the tip of remote equipment based on
the visual information provided by optical cameras. However, there is a risk of
damage to the remote equipment in case of limited visibility like an environment in
turbid water. For remote operations in such an environment, it is preferable to have
alternative method to know the location of objects with non-contacting.
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WM2016 Conference, March 6-10, 2016, Phoenix, Arizona, USA.
An acoustic camera, an infrared camera and a laser scanner seem to be major
technologies which can solve the problem shown above as alternatives to an optical
camera. Above all, an acoustic camera is a well-proven technology for underwater
use. It is also less subject to suspended particles and provides better resolution
even in turbid water.
Since 2014, IHI Corporation (IHI) has started to develop the alternative
observation system using an acoustic camera in order to provide more safe and
efficient remote works in radioactive contaminated turbid water in D&D facilities.
DEVELOPMENT OF OBSERVATION SYSTEM
Key factors to be considered to develop the observation system in contaminated
turbid water were the followings:
1. Obtain high resolution images as close as optical cameras
2. Minimize contamination of the equipment
3. Easy operation and maintenance
The unique point of this system is that the environment surrounding the system is
radioactive-contaminated water. An acoustic camera is usually used for
investigation activities in the sea, such as the seabed investigation and the survey
for the ecology of fishes. The camera wet by sea water and attaching suspended
particles in sea water is easily washed out to reuse itself. However, the camera
contaminated by radioactive substances is not easily cleaned out because person
has a limitation to approach to the camera, or touch it. Not to mention, it is very
difficult to remove the contamination if contaminated water enters into complicated
shape of parts of the camera.
For the reasons mentioned above, IHI particularly poured efforts into minimizing
contamination of the equipment for the development of the observation system.
Selection of Observation Equipment
At first the acoustic camera which seemed to be the most appropriate to this
observation system was selected. There are some types of acoustic cameras which
are usually called imaging sonar, and those are used in different ways for
underwater works in accordance to the use. In general, an acoustic camera has a
capability of taking image at wide range and long distance with low resolution, and
at narrow range and short distance with high resolution. For the application to
remote operations in contaminated turbid water, to obtain higher resolution was a
high priority function and thus, the acoustic camera which has the highest
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resolution in some options was selected. The selected acoustic camera can provide
real-time image in around 5m distance from the camera, 30 degree horizontal
viewing angle and 15 degree vertical viewing angle. Those features of the acoustic
camera provide an enough good image to perform any remote operations in turbid
water as well as optical cameras in clear water.
Development of Airtight Container
In order to minimize contamination of the acoustic camera, the designated airtight
container was developed. The acoustic camera is housed in the airtight container
which is made by stainless steel and used in contaminated environment. Because the
acoustic camera has to be filled with water when it is used, the container which
contains the acoustic camera is initially filled with clean water, and then it is
pressurized and sealed in order to prevent to enter the contaminated water in the
environment into the container. This container has a capability of over 0.3MPa of
pressure-resistance. It allows that the equipment to be applicable to the environment
of over 30m depth of water like the bottom area of light-water reactors. In addition,
the container may give a shielding effect against radiation exposure for the acoustic
camera to increase its thickness depending on radiation dose in the environment.
Figure1: Airtight container for the acoustic camera
Thin plate made by resin material which relatively has high radiation tolerance was
adopted as the interface (window) of the container to transmit and receive ultrasonic
waves of the acoustic camera. It gives a high resolution image even the camera is
housed in the container. Figure 2 shows that there are no differences of image taken
from the camera directly (no window) and the camera in the container (through the
window).
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Target: Bicycle Wheel
Image: A
Image: B
Figure 2: Images taken from the acoustic camera directly (Image: A)
and through the window (Image: B)
System Configuration
The observation system consists of the following major equipment:
 Observation Camera (Acoustic Camera in Airtight Container)
 Remote-Controlled Equipment
 Cable Management System
 Washing Equipment
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Figure 3 gives an example of the observation system. In this example, a single
manipulator arm is applied as the remote-controlled equipment for the observation
camera. However, it can be changed to the other remote equipment such as ROVs
and simple hoists according to the environment and purpose to use. The cable
management system which mainly consists of a remote-controlled cable reel allows
proper control of the cable length for power supply and transmitting image signals
following the motion of the remote-controlled equipment.
Figure 3: Example of observation system configuration
The washing equipment is installed on the entrance of the observation camera (e.g.
nozzle of tank). By using high pressure water and brushes, it decontaminates the
whole surface of the observation camera before the camera is fully retracted in order
to reduce operator’s radiation exposure as much as possible.
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Figure 4: Washing equipment for the observation camera
Demonstration Test
Through 2014 to 2015, several cold demonstration tests for the observation system
were performed in order to confirm the functions and performances of the system
in the simulated actual contaminated water. Figure 5 shows the example of the
simulated contaminated water used for the demonstration test. It was clouded by
magnesium hydroxide at first, and additionally a large amount of iron powder and
sand grain were put into the tank. The demonstration test was performed in enough
conservative condition using the simulated contaminated water which was much
worse turbidity than the actual condition.
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Figure5: Simulated contaminated water used for the demonstration test
Figure 6 is the image taken by the optical camera in the simulated contaminated
water. It shows how it is difficult to obtain a clear image by using the optical
camera in this condition.
Figure 6: Image taken by the optical camera in simulated contaminated water
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WM2016 Conference, March 6-10, 2016, Phoenix, Arizona, USA.
Several different kinds of targets were used for the demonstration tests in order to
know differences of performance for the observation camera according to the
targets. Figure 7 shows the major targets and their images taken by the
observation camera. Those targets were placed on the bottom of the tank, 2-3m
away from the camera. It is very easy to understand that the observation camera
could take much clearer image than the optical camera (Figure 6), even in such a
worse condition.
Distance measuring function which is another important function for the system
were also confirmed in the demonstration tests. Dimension measuring accuracy of
the target was 10 to 20mm, and distance measuring accuracy between the target
and the camera was 20 to 30mm. From those results, it was shown that the
observation system has an enough performance of distance measurement for
remote operations in turbid water.
Target: Cart
Image by the observation camera
Target: Concrete block
Image by the observation camera
Figure7: Images taken by the observation camera
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Target: Steel Plate
Image by the observation camera
Figure7: Images taken by the observation camera (Continued)
APPLICABILITY TO VARIOUS D&D WORKS
The observation system which has been developed as mentioned above is
applicable to various remote works in contaminated turbid water. The followings
show examples of expectable applications of the observation system:
Dismantling Works in Reactors and Tanks
A lot of dismantling works in reactors or tanks are planned in the world nuclear
decommissioning sites. Underwater cutting operations usually make surrounded
water turbid and difficult to obtain a good visibility using optical cameras. The
observation system provides the visual and location information in even such an
environment. Operator can recognize the proper location of the cutting tool to the
cut objects and observe the tool and the objects during cutting operation.
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WM2016 Conference, March 6-10, 2016, Phoenix, Arizona, USA.
Figure 8: Application example of the observation system to dismantling works
in reactor and tank
Inspection and Investigation Works using ROVs
There exist a lot of kinds of ROVs with optical cameras used for underwater inspection
and investigation works in various industries including nuclear D&D projects.
However, sometimes it is hard to use it in contaminated turbid water such as in old
tanks and pools which have stored spent fuels or wastes. The observation system is
applicable to those works using ROVs instead of optical cameras. The observation
camera is relatively small (200mm x 200mm x 300 mm) and it is capable of mounting
on some of ROVs mentioned above.
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Figure9: Application example of the observation system to inspection and
investigation works using ROVs
CONCLUSIONS
The observation technology is important to perform remote operations in radioactivecontaminated turbid water safely and efficiently. However, an optical camera is
basically limited to provide enough visual information in the turbid water and thus,
alternative observation technology to an optical camera has been required.
IHI has developed the alternative observation system applying acoustic camera which
gives much clearer image than optical cameras in the turbid water. It also provides
distance information which has enough accuracy for the remote operation.
Additionally, contamination of the equipment is minimized to reduce radiation
exposure to operators, and to give easy operation and maintenance works. This
observation system has a capability of providing safe and efficient remote operations
in the radioactive-contaminated turbid water in D&D facilities.
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