Day Three (July 15, 2010)

[B-5] Maintenance Methods and Welding Technology (Part II)

B-5-1

About the seawater pipe linings deterioration diagnosis technique

Yuji KONDO, Tomokazu IWATA, Yasuharu SUDA and Tetsuji KAWAKAMI (Mitsubishi Heavy Industries, LTD.)

Abstract
In domestic plants, sea water is used for cooling the auxiliary coolers and rubbers, polyethylene, epoxy resins, and etc. are employed as anticorrosion materials (linings) inside of piping that include sea water. Due to the plant aging degradations, confirmed that, as for linings that have been continuously used since the construction, the deteriorations of those performances caused by degradations have been found and the maintenances of lining materials become the later issue for each power company.

MHI has adopted the NDE as a presumption method for deterioration evaluation and adhesion strength of lining materials and utilized it for the deterioration prediction. The MHI approaches that have been taken so far are introduced in this writing.

Keywords
deterioration diagnosis technique, linings, rubbers, polyethylene, blister, aging degradations, NDE, bondmaster method, alternating current impedance method

B-5-2

Maintenance program after Approval of Decommissioning Plan of Hamaoka Unit 1 & 2

Masahiro KOGUCHI, Masaaki NAKAMURA, Yoshiaki SHIMIZU and Chiaki YAMAMOTO (CHUBU Electric Power Co., lnc.)

Abstract
Hamaoka Nuclear Power Station got a regulatory approval for a decommissioning plan of Unit 1 & 2 on November 18, 2009. Currently, system decontamination and dismantlement of facilities outside radioactive control area are under process. At the same time, we still have our maintenance program for integrity of required system functions. This paper describes an outline of a revise of maintenance program associated with approval for the decommissioning plan.

Keywords
decommissioning, maintenance program under decommissioning plan

B-5-3

DEVELOPMENT OF STRESS REDUCTION METHOD IN THE SMALL-BORE PIPE

Yuka FUKUDA, Naohiko ORITANI and Shinobu OKIDO (Hitachi-GE Nuclear Energy, Ltd.)

Abstract
It is well understood that the reduction of the residual tensile stress in the welded zone is effective as inhibitor of occurrence and growth of SCC in low-carbon stainless steel. Therefore, some stress reduction methods for the pipe welded zone have already been developed. However, stress reduction method for small-bore, thin-wall pipes which nominal outside diameter are 60.5mm and below, have not been established. In this study, residual tensile stress reduction method that is applicable to small-bore pipe has been developed.

The stress reduction method of this study can reduce residual tensile stress by using thermal stress which is generated by transitive large temperature difference between inner and outer surface of the pipe wall by heating the pipe wall with an external heating device and rapidly quenching inner surface of the pipe with cooling water. And the effectiveness of this method is shown by mock-up tests.

Keywords
Stress Corrosion Cracking, Piping, Residual Stress, Heating, Cooling, Thermal Stress

B-5-4

Development of Underwater Remote Inspection Technique for Nuclear Reactor Core Internals

Satoru AOIKE (Hitachi, Ltd.), Koichi KUROSAWA, Shinya OHMORI and Masaaki TANAKA (Hitachi-GE Nuclear Energy, Ltd.)

Abstract
When a crack is detected in nuclear reactor core internals, it is important to survey details of a crack. In this study, to survey nuclear reactor core internals simply, new electrolytic etching method that applies "Gel Electrode" and underwater microscope were developed. To apply "Gel Electrode", we can see fusion boundary and grain boundary after electrolytic etching. To use underwater microscope, we can see surface figures of nuclear reactor core internals directly without taking boat samples or replicas that transcribe surface shape. By applying these methods, the investigation labor can be reduced greatly.

Keywords
Gel Electrode, Electrolytic Etching, Core Internals, Fusion Boundary, Grain Boundary

B-5-5

Seismic evaluation of BWR Spent Fuel Storage Racks using actual damping by vibration test in Water

Hiroto YAMASAKI (Hitachi-GE Nuclear Energy, Ltd.), Syuichi ORITA (The Tokyo Electric Power Company, Inc.), Shigeyoshi IWAKURA, Tetsuo IMAOKA, Kazue OKUMURA (Hitachi-GE Nuclear Energy, Ltd.) and Yoshio NAMITA (Hitachi, Ltd.)

Abstract
Damping value for BWR spent fuel storage racks has been used 1 percent damping, which is applied to welded steel structures in air as defined JEAG4601. However, it is considered that the actual damping is higher than that of the above mentioned, because of its underwater installation. This report shows the actual damping value of the Check Arrayed Rack by vibration test in water and Evaluation by the analysis of rack using actual damping.

Keywords
Spent Fuel, Storage Rack, Seismic Design, Damping, Fluid-structure Interaction, Virtual Mass

B-5-6

Development and its utilizing method of the equipment which search the position of sound source and display visually

Hiroyuki WADA (CHUBU Electric Power Co., lnc.), Masanao OWAKI (KUMAGAI GUMI CO.,LTD.), Yasuhiro YAMASHITA (Shinshu University)

Abstract
The symptom often appears as a sound change before equipment breaks down. Therefore, it is important to observe the state of the noise and the vibration caused while equipment is driving, and to detect abnormality of equipment at the early stage. However, even if abnormality of the sound can be perceived, it is difficult to specify abnormal parts. Then, we developed the equipment which search the position of sound source and display visually. In this paper, we explain the principle of the equipment.

Keywords
Sound source, Visualization, Frequency, Phase difference, Electro luminescence display

B-5-7

Tungsten balls charge method radiation shield system

Yukihide SHIMAZU, Hiroyuki MIZUMA (Nuclear Engineering,Ltd.) and Takeshi UEDA (Mitsubishi Heavy Industries, LTD.)

Abstract
In the outage at nuclear power plant, we try to reduce radiation exposure by installing shields in the work at places of high radiation dose rate.

Many of these shields consist of the sheets and plates of heavy metals, and it takes a longer time to install or remove them because heavy loads must be accompanied. At our company, therefore, we have developed a tungsten balls charge method radiation shield system, can reduce the exposure and workload of its installation/removal. We will further promote various advanced techniques including Tungsten balls shielding technique to flexibly meet needs of operating plants.

Keywords
Nuclear power plant, Radiation shield system, Tungsten balls, Metal jacket, Reduce radiation exposure

B-5-8

Development of Evaluation Tool of Radiation Dose Rate in Primary Containment Vessel for Reduction of Radiation Exposure

Hiromitsu INAGAKI (CHUBU Electric Power Co., lnc.) and Toshio KUZUYA (Techno Chubu Co., Ltd.)

Abstract
We are developing a radiation dose rate evaluation tool for work areas in the primary containment vessel (PCV) of the Hamaoka BWR plant in order to reduce radiation exposure to workers. The evaluation tool is composed of two calculation codes; a water chemistry code and a radiation dose rate code. The radiation dose rate calculates radiation maps of the work areas in the PCV of Hamaoka plant. We compared measured values with calculated values in order to improve the accuracy of the tool. In order to demonstrate the tool, we evaluated the effectiveness of the introduction of additional shields to Hamaoka-3.

Keywords
Dose reduction, Radiation management, Dose rate map, Calculation code, 3D display

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