NO.1
Application of cavitation jet technique
to operating nuclear power plant
MITSUBISHI HEAVY INDUSTRIES, LTD.
Hironori Onitsuka
KORYO ENGINEERING CO.,LTD
Tadashi Shiraishi
NUCLEAR PLANT SERVICE
ENGINEERING CO.,LTD
Fumitoshi Nakao
September,12 2007
Mitsubishi Heavy Industries, LTD.
Kobe Shipyard & Machinery Works
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Application of the cavitation jet technique to
the operating plant（1/7）
NO.2
1. Introduction
Decontamination is implemented during periodical
inspection so that radiation exposure from
radioactive clad accumulated on systems is reduced
for workers engaged in operations, such as
inspection and maintenance.
For decontamination, to the extent possible costeffective method is required.
MHI promotes and implements cleanup and
decontamination by means of pressure impact
generated by the cavitation jet to meet these
requirements with agreement of customers.
This presentation introduces application of the
cavitation jet technique to the operating nuclear
power plant .
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Application of the cavitation jet technique to
the operating plant（2/7）
NO.3
2. Principle of cavitation jet generation
Cleanup and decontamination with cavitaion jet (CJ) are
technologies to generate cavitations by jetting high pressure
water through the dedicated nozzle into the water for the
purpose of striping off radioactive clad from the surface of
subject equipment .
Contraction
Bubble
Liquid
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Impact
wave
Application of the cavitation jet technique to
the operating plant（3/7）
3. Features
① Highly effective physical impact allows effective
removal of fouling such as clad, etc. comparing to
aerial high pressure water cleanup.
② Since the cleanup is implemented in the water, it
precludes propagation of possible contamination
such as dusts generated in the air. Water
shielding can limit radiation exposure during
decontamination activity.
③ Highly effective physical impact can be achieved
by compact facility.
④ No effect on the surface of the equipment may
occur due to short period of time required for
decontamination and cleanup.
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NO.4
Application of the cavitation jet technique to the
operating plant（4/7）
NO.5
4. Application examples
(1)Manual cleanup by operators
For parts replacement operation inside the SFP (facilities inside the
canal), removal of radioactive allows reduction of environmental
dose rate.
No decontamination → after decontamination：Approx.80 %
reduction of radiation dose for parts replacement operation
SFP
High pressure pump
Pure water for CJ
Ａ／Ｂ
Ｃ／Ｖ
Lifting frame and basket
Cleanup
device
Temporary
platform
Rail
Channel drain
Image of channel decontamination activity
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Fuel transfer
tube
Application of the cavitation jet technique to the
operating plant（5/7）
NO.6
4. Application examples
(2)Equipment decontamination in the dedicated cleanup tank
To accomplish reduction of radiation exposure during works for
periodical inspection, the dedicated cleanup system decontaminates
subject parts by means of cavitation jet. This achieves uniform
decontamination effect regardless of its irregularity of the surface
based on effective range of generated cavitation.
Full view of decontamination
tank
Before decontamination
After decontamination
Deposition of brownish-red
clad
Approx.DF8
（No significant clad stays）
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Application of the cavitation jet technique to the
operating plant（6/7）
NO.7
2.Application example
(3) High efficiency decontamination with abrasive particles
To reduce radiation exposure during maintenance of SG insert plate, surface dose rate is reduced by
adding abrasive particles to cavitation jet for removing highly adhesive radioactive clad.
○Maintenance activity without decontamination → Maintenance activity after decontamination :Approx. 60%
reduction (including radiation exposure during decontamination work)
High pressure pump for
CJ (the existing pump
utilized)
22MPa,15L/min
Nozzle transfer system
P
can
be
Before
decontamination
After decontamination
Several tens mSv/hr
< 1mSv/Hr
（over DF150）
F
Water recovery line
Control
panel
Decontamination
vessel
Strainer
Abrasive particles
suction nozzle
ＣＪ+Jet flow
Abrasive
particles
SG insert plate
Rotation table
Decontamination
unit
platform
(existing unit can
be utilized)
System schematic
Heat transfer tubes
(4) Application for other purpose than
radiation exposure reduction
(Sludge removal from SG tube sheet area)
Application of the cavitation jet technique
Approx.10mm
to remove accumulated sludge. This
achieves uniform decontamination of the
Jet direction of CJ
heat transfer tube surface and sheet
Verification test (Paint stripping test)
surface including shadow zones.
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Application of the cavitation jet technique to the
operating plant（7/7）
5. Summary
We MHI will further promote various
advanced techniques including
cavitation jet technique to flexibly meet
needs of operating plants based on the
principle of ALARA .
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NO.8