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Takamatsu, Misao; Kawahara, Hirotaka; Ito, Hiromichi; Ushiki, Hiroshi; Suzuki, Nobuhiro; Sasaki, Jun; Ota, Katsu; Okuda, Eiji; Kobayashi, Tetsuhiko; Nagai, Akinori; et al.
Nihon Genshiryoku Gakkai Wabun Rombunshi, 15(1), p.32 - 42, 2016/03
In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of "MARICO-2" (material testing rig with temperature control) had been broken and bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). This paper describes the results of the in-vessel repair techniques for UCS replacement, which are developed in Joyo. UCS replacement was successfully completed in 2014. In-vessel repair techniques for sodium cooled fast reactors (SFRs) are important in confirming its safety and integrity. In order to secure the reliability of these techniques, it was necessary to demonstrate the performance under the actual reactor environment with high temperature, high radiation dose and remained sodium. The experience and knowledge gained in UCS replacement provides valuable insights into further improvements for In-vessel repair techniques in SFRs.
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.
Ota, Katsu; Ushiki, Hiroshi*; Maeda, Shigetaka; Kawahara, Hirotaka; Takamatsu, Misao; Kobayashi, Tetsuhiko; Kikuchi, Yuki; Tobita, Shigeharu; Nagai, Akinori
JAEA-Technology 2015-026, 180 Pages, 2015/11
JAEA-Technology-2015-026.pdf:79.87MB
In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of "MARICO-2" (material testing rig with temperature control) had bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). The replacement of the UCS was conducted from May to December 2014. The design and manufacture of UCS was started from 2008, and the installation of UCS was completed successfully in November 21th 2014. The major results gained during the design and manufacture of UCS is as follows.
Ishiyama, Shintaro; Mamitani, Masataka*; Kondo, Mitsunori*; Hiki, Akinori*
Kagaku Kogaku Rombunshu, 39(6), p.545 - 552, 2013/11
Times Cited Count：3 Percentile：13.49(Engineering, Chemical)Chemical interface controlled dispersion and high speed shearing (CDS) washing verification test of high level radioactive contaminated soil over 570,000 Bq/kg was conducted using three kinds of radioactive contaminated soils of school ground, moor and road in Fukushima and the following results was obtained. (1) Washing rate of three kinds of contaminated soils reached up to 60-98% after 60 minutes CDS water washing. (2) Recovered amounts of reclamation soils of three type of soils(less than 8,000 Bq/kg) were 60-82 wt.%. Especially, 506 Bq/kg 
33wt.% was achieved in the case of contaminated soil of moor. (3) Volume reductions of 60-85wt.% were achieved in every case of contaminated soils. (4) Contain recoverable quantities of total radioactive sources contained in soils was over 90%. (5) Main FP trapping minerals contained in contaminated soil of school ground is lamellar silicate and that of moor and road is mordenite.
Ishiyama, Shintaro; Mamitani, Masataka*; Kondo, Mitsunori*; Hiki, Akinori*
Nihon Kikai Gakkai Rombunshu, A, 79(806), p.1504 - 1516, 2013/10
For the purpose of removal of 
Cs from highly densified contaminate soil produced after contaminated soil washing process, reclamation soil techniques of contaminated soil through use of structural instability of mordenite contained in contaminated soil under high temperature heating was testified and the following results were obtained; (1) Structural instability of Cs-typed typical native mordinite yielding in Tohoku area in Japan was observed and dissociation of Cs from this mordenite was found after heat annealing at 1173 K. (2) Remarkable dissociation rate in the early stages was observed and then was slowed down afterword. Dissociation rate of Cs reached up to 65% after 1173 K 1 hr annealing. (3) 100% recovery of Cs from vaporized Cs gas was achieved by technology combination of electric precipitation FP filter newly developed and cold trap.
Ishiyama, Shintaro; Mamitani, Masataka*; Kondo, Mitsunori*; Hiki, Akinori*
Kagaku Kogaku Rombunshu, 39(4), p.405 - 410, 2013/07
Times Cited Count：3 Percentile：13.49(Engineering, Chemical)Ion plating ceramic coating technique was applied for prevention of radioactive contamination and attrition of chemical interface controlled dispersion and high speed shearing washing machine during water washing with high level radioactive contaminated soil over 570,000 Bq/kg and the following results were obtained. (1) No contamination of Al
O
courted coupon with 5 
m thickness installed in plunger was found after 3 hours water washing process of slurry contained 50% contaminated soil and uniformed attrition of the coating surface was observed, whereas contamination of SUS coupon due to FP particle attack and implantation during washing was observed. This contamination source is attached to SUS surface and not removable. (2) Attrition rate of surface of coated coupon during washing was estimated as 0.14 m/hr in the case of installation on rotor of plunger and attrition of SUS exhibits 7 times higher than that of coated coupon in initial stage of washing process.
Ishiyama, Shintaro; Mamitani, Masataka*; Kondo, Mitsunori*; Hiki, Akinori*
no journal, ,
Contaminated soil washing test was implemented in Fukushima for the purpose of performance verification and set up of engineering database for construction of contaminated soil washing plant and the following results were obtained in this first field test. (1) Dispersion of the radioactive contaminated soil over 10,000 Bq/kg was enhanced in alkalized washing solution at base equilibrium point of pH=10.1
10.5. (2) Remarkable washing performance was achieved under the combination of dispersion and high speed shearing washing conditions. (3) Remarkable well ordered structural refinement and cumulation of the contaminated soil particle groups with strong FP confinement were observed at the particle size of 0.510 m after washing the contaminated soil particle grain size under 0.5 mm, and sieve classification technique can be applied for elective elimination of this soil particle groups.
Ushiki, Hiroshi; Ito, Hiromichi; Okuda, Eiji; Suzuki, Nobuhiro; Sasaki, Jun; Ota, Katsu; Kawahara, Hirotaka; Takamatsu, Misao; Nagai, Akinori; Okawa, Toshikatsu
no journal, ,
In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of MARICO-2 (material testing rig with temperature control) had bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS) in 2007. As a part of the restoration work, UCS replacement was begun at March 24, 2014 and was completed at December 17. In-vessel repair (including observation) for sodium-cooled fast reactors (SFRs) is distinct from that for light water reactors and necessitates independent development. Application of developed in-vessel repair techniques to operation and maintenance of SFRs enhanced their safety and integrity. There is little UCS replacement experience in the world and this experience and insights, which were accumulated in the replacement work of in-vessel large sturucture (UCS) used for more than 30 years, are expected to improve the in-vessel repair techniques in SFRs.
