Development of inspection and repair techniques in reactor vessel of experimental fast reactor "Joyo"; Retrieval of the bent test subassembly

Ashida, Takashi; Ito, Hideaki; Miyamoto, Kazuyuki*; Nakamura, Toshiyuki; Koga, Kazuhiro*; Ohara, Norikazu*; Ino, Hiroichi*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 15(4), p.210 - 222, 2016/12

https://doi.org/10.3327/taesj.J15.032

In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of material testing rig named "MARICO-2" had been broken and bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). As the result, for Joyo restart, it was necessary to replace the damaged UCS and to retrieve the bent sub-assembly. This paper describes in-vessel repair techniques performed in the retrieval work of the obstacle inside of the reactor vessel. The devices which were prepared for this work demonstrated expected performance under the environmental conditions of an SFR such as high temperature and radiation dose, and the work was completed in 2014. The successful operation of this retrieval work of the damaged component inside of a reactor vessel will contribute to the development of in-service inspections and repair technics in an SFR.

Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Development of cover gas recycling system with precise pressure control

Ushiki, Hiroshi*; Okuda, Eiji; Suzuki, Nobuhiro; Takamatsu, Misao; Nagai, Akinori

JAEA-Technology 2015-042, 37 Pages, 2016/02

JAEA-Technology-2015-042.pdf:16.51MB

The reactor vessel of a sodium-cooled fast reactor (SFR) is filled with sodium coolant and cover gas (argon gas). In case of a cover gas boundary open (ie., in-vessel repair), installation of a temporary cover gas boundary and controlling the cover gas pressure slightly positive are required to prevent the cover gas release and the contamination of impurities, and during upper core structure (UCS) replacement in the experimental SFR Joyo from March to December 2014, a vinyl bag was installed as a part of the temporary cover gas boundary. However, because it has inferior thermal resistance, supply a cooling gas too much was required to maintain proper temperature for two months. On the basis of this requirement, a cover gas recycling system with precise pressure control was developed and adopted for UCS replacement. The system has a good pressure controllability and recyclability. The successful results of this system contributed to the certain promotion of UCS replacement. In addition, the insights and the experience gathered in this development are expected to improve the in-vessel repair techniques in sodium-cooled fast reactors.

Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Observation techniques development in a reactor vessel of the fast reactor, 2

Okuda, Eiji; Sasaki, Jun; Suzuki, Nobuhiro; Takamatsu, Misao; Nagai, Akinori

JAEA-Technology 2015-005, 36 Pages, 2015/03

JAEA-Technology-2015-005.pdf:44.42MB

In-Vessel Observations (IVO) techniques for Sodium cooled Fast Reactors (SFRs) are important in confirming its safety and integrity. In order to secure the reliability of IVO techniques, it was necessary to demonstrate the performance under the actual reactor environment with high temperature, high radiation dose and remained sodium. The IVO equipment for the Upper Core Structure (UCS) fitting area was specifically developed in the experimental fast reactor "Joyo". And the IVO was successfully completed as shown below. (1) Improvement of picture quality and resolution. The IVO of UCS fitting area with the gap of 5mm in minimum was achieved using the IVO equipment with video-scope under the actual reactor environment. The picture quality and resolution could be improved comparing with the radiation resistant fiberscope which was used in past IVO. (2) Prevention of video-scope hypofunction by high temperature / radiation dose. Since video-scope is inferior in thermal and radiation resistance, the IVO equipment was designed to be able to withdraw and insert video-scopes with cooling gas. This measure could achieve the observation in short radiation time with available temperature under the actual reactor environment. The IVO equipment for UCS fitting area provided useful information on UCS replacement. In addition, the experience provided valuable insights into further improvements for IVO techniques in SFRs.

Inspection and repair techniques in reactor vessel of sodium cooled fast reactor, 9-1; Program summary of Joyo restoration work

Ito, Hideaki; Maeda, Yukimoto; Yoshida, Akihiro; Takamatsu, Misao; Sekine, Takashi

no journal, , 

no abstracts in English

Measurement and analysis of in-vessel component activation and dose rate distribution in Joyo

Yamamoto, Takahiro; Maeda, Shigetaka; Ito, Chikara

no journal, , 

In the experimental fast reactor Joyo, the damaged upper core structure (UCS) was retrieved into the cask in May 2014 for its replacement as a part of the restoration work of the incident concerning with the irradiation test sub-assembly named MARICO-2. The dose rate on UCS surface was quite high due to the activation for over 30 years operation. In order to attain the optimum safety design, manufacture and operation of equipment for UCS replacement, the method to evaluate UCS surface dose rate was developed on the basis of C/E obtained by the in-vessel dose rate measurement in Joyo. In order to verify the evaluation method, the axial -ray distribution measurement on the surface of the cask, which contained UCS, was conducted using a plastic scintillating optical fiber (PSF) detector. As a result, the measured axial -ray distribution on the cask surface had a peak on proper location with considering the cask shielding structure and agree well with the calculated distribution and the C/E of axial -ray distribution on the cask surface was ranged from 1.1 to 1.7. It was confirmed that the calculation for UCS replacement equipment design had a margin of conservatively. Then, the results showed that the applied evaluation method for UCS replacement equipment design was sufficiently reliable. In the in-vessel repair work for sodium cooled fast reactors (SFRs), the design and work condition estimation are important. The accumulated experience provides valuable insights into further improvements for in-vessel repair techniques in SFRs.