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All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.1 Application of cavitation jet technique to operating nuclear power plant September,12 2007 Mitsubishi Heavy Industries, LTD. Kobe Shipyard & Machinery Works MITSUBISHI HEAVY INDUSTRIES, LTD. Hironori Onitsuka KORYO ENGINEERING CO.,LTD Tadashi Shiraishi NUCLEAR PLANT SERVICE ENGINEERING CO.,LTD Fumitoshi Nakao Slide 2 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.2 Application of the cavitation jet technique to the operating plant 1/7 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 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. Slide 3 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.3 Application 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 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. Bubble Liquid Contraction Impact wave Slide 4 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.4 Application of the cavitation jet technique to the operating plant 3/7 3. Features Highly effective physical impact allows effective removal of fouling such as clad, etc. comparing to aerial high pressure water cleanup. 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. Highly effective physical impact can be achieved by compact facility. No effect on the surface of the equipment may occur due to short period of time required for decontamination and cleanup. Slide 5 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.5 Application of the cavitation jet technique to the operating 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 Pure water for CJ Lifting frame and basket Fuel transfer tube SFP Channel drain Temporary platform Cleanup device Image of channel decontamination activity Rail Slide 6 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.6 Application of the cavitation jet technique to the operating plant 5/7 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. Before decontaminationAfter decontamination Deposition of brownish-red clad Approx.DF8 No significant clad stays Full view of decontamination tank Slide 7 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.7 Before decontamination After decontamination Several tens mSv/hr< 1mSv/Hr over DF150 Application of the cavitation jet technique to the operating 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 remove 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 table Decontamination unit platform (existing unit can be utilized) +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 Slide 8 All Rights Reserved, Copyright (C), MITSUBISHI HEAVY INDUSTRIES,LTD. NO.8 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.