Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Replacement of upper core structure

Ito, Hiromichi*; Ota, Katsu; Kawahara, Hirotaka; Kobayashi, Tetsuhiko; Takamatsu, Misao; Nagai, Akinori

JAEA-Technology 2016-008, 87 Pages, 2016/05

JAEA-Technology-2016-008.pdf:18.11MB

In the experimental fast reactor Joyo, as a part of the restoration work of a partial dysfunction of fuel handling, the replacement of the upper core structure (UCS) was started from March 2014, and was completed in December 2014. In the jack-up test, the UCS was jacked-up to 1000 mm without significant sodium shearing resistance and interference. In the replacement of the UCS, a procedure was prepared with the use of wire-jack equipment assuming the interference. As a result, with the procedure and wire-jack were effectively functioned, the work was successfully completed.

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.

Replacement of upper core structure in experimental fast reactor Joyo, 1; Existing damaged upper core structure jack-up test

Ito, Hiromichi; Suzuki, Nobuhiro; Kobayashi, Tetsuhiko; Kawahara, Hirotaka; Nagai, Akinori; Sakao, Ryuta*; Murata, Chotaro*; Tanaka, Junya*; Matsusaka, Yasunori*; Tatsuno, Takahiro*

Proceedings of 2015 International Congress on Advances in Nuclear Power Plants (ICAPP 2015) (CD-ROM), p.1058 - 1067, 2015/05

In the experimental fast reactor Joyo (Sodium-cooled Fast Reactor (SFR)), it was confirmed that the top of the irradiation test sub-assembly had bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). There is a risk of deformation of the UCS and guide sleeve (GS) caused by interference between them unless inclination is controlled precisely. To mitigate the risk, special jack-up equipment for applying three-point suspension was developed. The existing damaged UCS (ed-UCS) jack-up test using the jack-up equipment was conducted on May 7, 2014. As a result of this test, it was confirmed that the ed-UCS could be successfully jacked-up to 1000 mm without consequent overload. The experience and knowledge gained in the ed-UCS jack-up test provides valuable insights and prospects not only for UCS replacement but also for further improving and verifying repair techniques in SFRs.

Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Development of repair techniques for UCS replacement of Joyo, 2

Ito, Hiromichi; Takamatsu, Misao; Kawahara, Hirotaka; Nagai, Akinori

JAEA-Technology 2014-024, 28 Pages, 2014/07

JAEA-Technology-2014-024.pdf:17.45MB

Because the gap between the UCS and rotation plug's guide sleeve is 5 mm in minimum, there is a risk of deformation of the UCS and guide sleeve with interference between UCS and guide sleeve in the UCS replacement work. In order to reduce the risk, R&D for below subjects is required.(1) UCS jack-up equipment with strict control of inclination, (2) Detection and escape method for interference between UCS and guide sleeve. In order to solve above (1), the jack-up equipment with applying three-point suspension is developed. Then, in the aspect of above (2), load-measuring devices are installed on three jacks of jack-up equipment. By means of detection eccentric load with interference, deformation of UCS and guide sleeve are prevented. And also, the location of interference can be investigated based on eccentric loads of three jacks. The performance is verified in the ex-vessel mock-up test using full-scale dummy of UCS.

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

Imaizumi, Kazuyuki; Saito, Takakazu; Tobita, Shigeharu; Nagai, Akinori; Kitamura, Ryoichi; Okazaki, Yoshihiro

JAEA-Technology 2012-027, 49 Pages, 2012/08

JAEA-Technology-2012-027.pdf:7.07MB

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. During the investigation of an incident occurred in Joyo, the following observation systems were specifically developed for Joyo. And the following two observations were conducted. (1) Simple overhead observation using a standard video camera for the top of the sub-assemblies and the in-vessel storage rack (2) Narrow space observation using remote handling device equipped with radiation-resistant fiberscope for the bottom face of the upper core structure. As a result, the observations under the actual reactor environment were successfully made even in the narrow space in the reactor vessel and the results provided useful information on incident investigations and planning of restoration work.

Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Development of a high radiation resistance fiberscope (Joint research)

Naito, Hiroyuki; Itagaki, Wataru; Okazaki, Yoshihiro; Imaizumi, Kazuyuki; Ito, Chikara; Nagai, Akinori; Kitamura, Ryoichi; Shamoto, Naoki*; Takeshima, Yoshiyuki*

JAEA-Technology 2012-009, 100 Pages, 2012/05

JAEA-Technology-2012-009.pdf:9.89MB

The radiation characteristics of image fiber and light guide fiber were evaluated to develop a high radiation resistant fiberscope for the fast reactor in-vessel observation. It is known that a pure silica core fiber has a high radiation resistance and radiation resistance is influenced with impurities in silica. Moreover it is necessary to change the clad material of the light guide fiber because that of the current light guide fiber is acrylate, which is weak against radiation. Hence the improved fibers consist of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad. As a result of a irradiation test, we confirm that OH inhibits the generation of the precursor by irradiation. About the clad material, we confirmed that the transmission loss of the fluorine-doped silica clad fiber is smaller than that of the acrylate clad fiber. About the mechanical strength of a fiber, we confirmed that there is no weakening the strength of the fiber and no exfoliation of the coating from the glass. In this study, we discovered the fiber which consists of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad has a high radiation resistance and it is possible to observe using this fiber under the 200 C after 510 Gy irradiation.

Development of observation techniques in reactor vessel of experimental fast reactor Joyo

Takamatsu, Misao; Imaizumi, Kazuyuki; Nagai, Akinori; Sekine, Takashi; Maeda, Yukimoto

Journal of Power and Energy Systems (Internet), 4(1), p.113 - 125, 2010/00

https://doi.org/10.1299/jpes.4.113

During the investigation of an incident that occurred with the experimental fast reactor Joyo, in-vessel observations using a standard Video Camera (VC) and a Radiation-Resistant Fiberscope (RRF) took place at (1) the top of the Sub-Assemblies (S/As) and the In-Vessel Storage rack (IVS), (2) the bottom face of the Upper Core Structure (UCS) under the condition with the level of sodium at -50 mm below the top of the S/As. A simple 6 m overhead view of each S/A, through the fuel handling or inspection holes etc, was photographed using a VC fixed to the rotating-plug with the acrylic panel for making observations of the top of S/As and IVS. About 650 photographs were required to create a composite photograph of the top of the entire S/As and IVS, and a resolution was estimated to be approximately 1 mm. In order to observe the bottom face of the UCS, a remote handling device equipped with RRFs (approximately 13 m long) was specifically developed for Joyo with a tip that could be bent into an L-shape and inserted into the 70 mm gap between the top of the S/As and the bottom of the UCS. A total of about 35,000 photographs were needed for the full investigation. Regarding the resolution, the sodium flow regulating grid of 0.8 mm in thickness could be discriminated, and the base of thermocouple sleeves 6 mm in diameter located 450 mm above the top of S/As were also clearly observed. In both types of observations, it was confirmed that lighting adjustments play a critical role. Particularly in narrow space observations, scattered lighting with automatic dimming controlled light source was available for achieving close observations of the in-vessel structures. In addition to the successful result of the incident investigation, these experiments provided valuable insights for use in further improving and verifying in-vessel observation techniques in sodium cooled fast reactors.

Inspection techniques in reactor vessel of sodium cooled fast reactor

Itagaki, Wataru; Saito, Takakazu; Imaizumi, Kazuyuki; Nagai, Akinori; Aoyama, Takafumi; Maeda, Yukimoto

Dai-14-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, p.435 - 438, 2009/06

no abstracts in English

None

; Nagai, Akinori; ; ;

PNC TN9440 97-014, 27 Pages, 1997/08

PNC-TN9440-97-014.pdf:1.43MB

None

The report on JOYO plant safety for sodium leak and fire protection

; ; Isozaki, Kazunori; ; ; Nagai, Akinori;

PNC TN9440 97-008, 410 Pages, 1997/05

PNC-TN9440-97-008.pdf:20.99MB

On the 8th in December 1995, the secondary sodium leak accident occurred at Prototype Fast Breeder Reactor MONJU. Experimental Fast Reactor JOYO was under the 11th periodical inspection then. Total review of the JOYO plant for check of the sodium leak related equipment, check of manuals, and a practice of disaster prevention for sodium leak, and so on were made to have assurance of plant safety, which was required based on official report of MONJU sodium leak accident. Moreover, we properly improved the equipment and reinvestigated the plant management. As the result of these checks, evaluations and improvements, plant safety for sodium leak and fire was secured, and JOYO was started reactor operation on the 3rd in March 1997 after the confirmation by Science and Technology Agency (STA) and Ibaraki prefecture, and on 24th, JOYO passed the 11th periodical inspection, and began to operate the JOYO plant duty cycle. This report describes about those JOYO plant safety for sodium leak and fire protection.