Development of prototype reactor maintenance, 3; Application to valves of sodium-cooled reactor prototype

Chikazawa, Yoshitaka; Takaya, Shigeru; Tagawa, Akihiro; Kubo, Shigenobu

Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 6 Pages, 2019/05

A maintenance management required to prototype nuclear power reactors has been developed. One of important mission of a prototype reactor is to develop maintenance program for commercial reactors step by step securing safety. Since operating experience at the early stage is limited, the maintenance program for the prototype reactor should be a progressive one. It has to be modified and improved frequently taking into account R&D insight and operation experiences. Additionally, the maintenance program has to consider features of the prototype reactor even at the early stage. To select maintenance grades on particular components/systems, risk informed and graded approaches are effective. And maintenance programs have to take into account degradation mechanism originally due to reactor features. In this paper, applications for maintenance program on sodium valves of prototype fast breeder reactor Monju are studied as an example of prototype sodium-cooled reactors (SFR).

Maintenance management of nuclear power reactors at the stage of research and development

Takaya, Shigeru; Chikazawa, Yoshitaka; Hayashida, Kiichi; Tagawa, Akihiro; Kubo, Shigenobu; Yamashita, Atsushi

JAEA-Research 2016-006, 66 Pages, 2016/07

JAEA-Research-2016-006.pdf:3.4MB

A maintenance management required to nuclear power reactors at the R&D stage was discussed. It is the most important to ensure safety of nuclear power plants by taking account of characteristics of nuclear power reactors at the R&D stage. In addition, it is needed to establish a system of maintenance management technologies suitable for reactor types. In this report, objectives of maintenance management of nuclear power reactors at the R&D stage was clarified. Next, requirements and consideration for maintenance management was discussed according to the objectives. "Codes for maintenance management of nuclear power plants" and "Guides for maintenance management of nuclear power plants" were refereed in the discussion. Then, a draft of codes for maintenance management of nuclear power plants at the R&D stage were newly proposed. Finally, an example that the draft codes were applied to components containing sodium, typical components of sodium-cooled fast reactor, was presented.

Radioactivity decontamination in and around school facilities in Fukushima

Saegusa, Jun; Tagawa, Akihiro; Kurikami, Hiroshi; Iijima, Kazuki; Yoshikawa, Hideki; Tokizawa, Takayuki; Nakayama, Shinichi; Ishida, Junichiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05

After the Fukushima nuclear accident, JAEA lead off demonstration tests to find out effective decontamination methods for various school facilities in Fukushima. It included (1) dose reduction measures at schoolyards, (2) purification of swimming pool water and (3) removal of surface contamination of playground equipments. Through these tests, they established practical methods suitable for each situation; (1) At school yards, dose rates were drastically reduced by removing topsoil which was then placed in trenches of 1 m deep; (2) For the purification of pool water, the flocculation-coagulation treatment was found to be effective for collecting radiocesium dissolved in the water; (3) Demonstration tests for playground equipments, such as horizontal bars and a sandbox wood frame, suggested that effectiveness of decontamination considerably varied depending on the material, paint or coating condition. This paper reviews these demonstrations.

Report for "Decontamination Pilot Projects for the environmental remediation of evacuation areas contaminated with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant accident; Decontamination Technology Demonstrations Projects" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro

JAEA-Review 2013-053, 84 Pages, 2014/03

JAEA-Review-2013-053.pdf:48.63MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2011 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 25 candidates. JAEA was commissioned by the Cabinet Office, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out a demonstration test and evaluation of 25 technologies (e.g., decontamination technology of soil classifiers, ultra-high pressure water jets and volume reduction of organic materials) to perform decontamination of the environment

Report for "FY 2011 Evaluation of Decontamination Technology Demonstrations Projects for the environmental remediation with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant accident" (Contract research)

Watanabe, Masahisa; Tagawa, Akihiro

JAEA-Review 2013-051, 244 Pages, 2014/03

JAEA-Review-2013-051.pdf:34.73MB

To discover technologies that can be utilized for decontamination work and verify their effects, economic feasibility, safety, and other factors, the Cabinet Office, Government of Japan launched the FY2011 Decontamination Technology Demonstrations Project to publicly solicit decontamination technologies that would be verified in demonstration tests and adopted 22 candidates. JAEA was commissioned by the Ministry of the Environment, Government of Japan to provide technical assistance related to these demonstrations. JAEA carried out technical advice of demonstration test and evaluation of 22 technologies (e.g., decontamination technology of Thermal decomposition, Bottom sediment of Pond and volume reduction of organic materials using biomass technologies) to perform decontamination of the environment.

Demonstration test on concrete with epoxy resin coating using ultra-high pressure water jet decontamination technology

Tagawa, Akihiro; Tezuka, Masashi; Terakura, Yoshihiro*; Naito, Masayuki*; Miyajima, Kenji*

Proceedings of 21st International Conference on Nuclear Engineering (ICONE-21) (DVD-ROM), 6 Pages, 2013/07

https://doi.org/10.1115/ICONE21-16721

It is one of the most urgent issues to remediate the nuclear power plants contaminated by radioactive materials discharged following the accident at the TEPCO's Fukushima Daiichi NPS. Concrete walls of nuclear power plants in Japan are coated an epoxy resin coating for easily performing decontamination. We experimented a cutting test in Fugen Decommissioning Engineering Center using maximum 280 MPa pressure and 30 L/min water quantity, ultra-high pressure water jet system and 40 m/min air quantity vacuum system. We are conducting a study of decontamination technology in environmental pollution using this decontamination system. This decontamination system has achieved a decontamination factor 10 to 100. Thus, we have confirmed the change in a cutting ability by changing parameters. Parameters are the water pressure, the water quantity and air quantity. The impact force for water jet is a function that contains the test parameters. We have considered it using this function. The results of the test showed that there is a correlation between the impact force for water jet and a cutting capability. This decontamination technology can decontaminate radioactive material of the surface adhesion contamination and reduce the amount of waste generated for a thin cutting. In addition, we have experimented that the water can be recycled by chemical precipitation. After we experimented flocculation test using aluminum sulfate and zeolite flocculant, we have confirmed that it can clean water up to the level of suspended solids 5 mg/L, in turbid water using zeolite flocculant. This suspended solids concentration can be passed to the water processing system in nuclear power plant. From the test results, we found that ultra-high pressure water jet decontamination technology has a possibility that it can be used for decontamination of Fukushima Daiichi Nuclear Power Plant.

Effects of ground surface decontamination on the air radiation dose rate; Results of a decontamination trial at a playground lot in a Fukushima residential area

Tagawa, Akihiro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 11(2), p.111 - 117, 2012/05

https://doi.org/10.3327/taesj.J11.041

The Japan Atomic Energy Agency decontaminated schools, playgrounds, swimming pools, and houses in non-evacuated, less-contaminated areas in Fukushima for the environmental restoration. A small, 150 m playground lot in the residential area was chosen for the decontamination demonstration, which used routinely available tools and commodities to carry out the work. The surfaces of playground lot equipment such as swings, slides, and horizontal iron bars were completely decontaminated by brushing with water and/or detergent. Side gutters around the playground lot were cleaned up by removing mud, then they were brushed and washed with a high-pressure water jet 7 MPa. The air dose rate at the playground lot was dominated by radiation from the ground surface and from adjacent surroundings such as apartments and rice fields. Two or three centimeters of the surface soil contaminated with cesium were removed manually with shovels, hoes and other gardening tools. This resulted in a significant decrease in the average air dose rate of the entire playground lot from 1.5 Sv/hr before decontamination to 0.6 Sv/hr. These results showed that ground surface decontamination can contribute measurably to a reduction in the air dose rate in relatively small areas in residential areas.

Development of an ISI robot for the fast breeder reactor MONJU primary heat transfer system piping

Tagawa, Akihiro; Ueda, Masashi; Yamashita, Takuya; Narisawa, Masataka*; Haga, Koichi*

Journal of Nuclear Science and Technology, 48(4), p.504 - 509, 2011/04

https://doi.org/10.3327/jnst.48.504

This paper describes the development of a new inspection robot for the in-service inspection of the heat transfer system of the fast breeder reactor MONJU. The inspection was carried out using a tire-type ultrasonic sensor for volumetric tests at high temperature (atmosphere, 55 C; piping surface, 80 C) and radiation exposure condition (dose rate, 10 mGy/h; piping surface dose rate, 15 mGy/h). An inspection robot using a new tire type for the ultrasonic testing sensor and a new control method was developed. A signal-to-noise ratio S/N over 2 was obtained during the functional test for a calibration defect with a depth of 50%t (from the tube wall thickness). In the automatic inspection test, an EDM slit with a depth of 9% from the pipe thickness was detectable and with an S/N ratio = 4.0 (12.0 dB).

Development of inspection and repair technology for the micro cracks on heat exchanger tubes

Nishimura, Akihiko; Shobu, Takahisa; Oka, Kiyoshi; Yamaguchi, Toshihiko; Shimada, Yukihiro; Mihalache, O.; Tagawa, Akihiro; Yamashita, Takuya

Reza Kako Gakkai-Shi, 17(4), p.207 - 212, 2010/10

A prototype probe system with a hybrid optical fiber scope was designed for inspecting and re-pairing the micro cracks on heat exchanger tubes in fast breeder reactors (FBRs). It comprised a laser processing head combined with an eddy current testing unit. Ultrashort laser pulse ablation was used to remove work-hardened layers. And spot laser welding was used to repair the micro cracks. This system has both safe and economical options for the maintenance of FBRs because it extends the lifetime of the heat exchangers.

Study on pipe health monitoring method by hybrid measurement using electromagnetic ultrasonic

Tagawa, Akihiro; Kojima, Fumio*

Hozengaku, 9(1), p.45 - 50, 2010/04

http://ci.nii.ac.jp/naid/40017096231

The purpose of this study is to develop a hybrid sensor to be able to measure two or more physical values with one sensor with an electromagnetic acoustic transducer. Each result of a measurement can improve the measurement precision by doing working that calibrate each other. The piping surface temperature was measured by converting the direct current resistance at the temperature by using the EMAT coil. As a result, it was confirmed that coefficients of determination reproduced by the accuracy of 0.99 or more and it was in the proportion the temperature and resistance. It was confirmed the amount of the pipe wall thinning is to be able to measure the board thickness of the piping of 10 mm at 200 C by using the pulse echo method and the pulse echo resonance method. Water temperature was calculated by using the distance between EMATs which carried out opposite arrangement and ultrasonic time of concentration.