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NO.1

Application of cavitation jet technique tApplication of cavitation jet technique to operating nuclear power planto operating nuclear power plant

September,12 2007September,12 2007Mitsubishi Heavy Industries, LTD.Mitsubishi Heavy Industries, LTD.

Kobe Shipyard & Machinery WorksKobe Shipyard & Machinery Works

MITSUBISHI HEAVY INDUSTRIES, LTD.

　 Hironori Onitsuka

KORYO ENGINEERING CO.,LTD

　 Tadashi Shiraishi

NUCLEAR PLANT SERVICE ENGINEERI

NG CO.,LTD

Fumitoshi Nakao

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NO.2Application of the cavitation jet technique to the operating plant （ 1/7 ）

1. Introduction　 Decontamination is implemented during periodical i

nspection 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 cost- effective 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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NO.3Application of the cavitation jet technique to the operating plant （ 2/7 ）

　 2. Principle of cavitation jet generation　　 Cleanup and decontamination with cavitaion jet (CJ) are tech

nologies 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 .

Bubble

Liquid

ContractionImpact wave

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NO.4Application 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.5Application of the cavitation jet technique to theoperating plant （ 4/7 ）

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

High pressure pump

Ａ／Ｂ

Ｃ／Ｖ

Pure water for CJ

Lifting frame and basket Fuel

transfer tube

SFP

Channel drain

Temporary platform

Cleanup device

Image of channel decontamination activity

Rail

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NO.6Application of the cavitation jet technique to theoperating plant （ 5/7 ）

4. Application examples(2)Equipment decontamination in the dedicated cleanup tank　　 To accomplish reduction of radiation exposure during works for periodical insp

ection, 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.

Before decontamination

After decontamination

Deposition of brownish-red clad

Approx.DF8（ No significant clad

stays ）Full view of decontamination tank

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NO.7

Before decontamination

After decontamination

Several tens mSv/hr < 1mSv/Hr （ over DF150 ）

Application of the cavitation jet technique to theoperating plant （ 6/7 ）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)

(4) Application for other purpose than radiation exposure reduction

(Sludge removal from SG tube sheet area)　　 Application of the cavitation jet technique to re

move accumulated sludge. This achieves uniform decontamination of the heat transfer tube surface and sheet surface including shadow zones.

Heat transfer tubes

Approx.10mm

Verification test (Paint stripping test)

Jet direction of CJ

Control panel

Abrasive particles suction nozzle

Rotation tableDecontamination unit platform (existing unit can be utilized)

ＣＪ +Jet flow

Abrasive particles SG insert plate

Strainer

Water recovery line

High pressure pump for CJ (the existing pump can be utilized)22MPa,15L/min

Nozzle transfer system

Decontamination vessel

P

F

System schematic

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NO.8Application of the cavitation jet technique to theoperating 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 .