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Nakagawa, Akinori; Oyokawa, Atsushi; Murakami, Masashi; Yoshida, Yukihiko; Sasaki, Toshiki; Okada, Shota; Nakata, Hisakazu; Sugaya, Toshikatsu; Sakai, Akihiro; Sakamoto, Yoshiaki
JAEA-Technology 2021-006, 186 Pages, 2021/06
JAEA-Technology-2021-006.pdf:54.45MB
Radioactive wastes generated from R&D activities have been stored in Japan Atomic Energy Agency. In order to reduce the risk of taking long time to process legacy wastes, countermeasures for acceleration of waste processing and disposal were studied. Work analysis of waste processing showed bottleneck processes, such as evaluation of radioactivity concentration, segregation of hazardous and combustibles materials. Concerning evaluation of radioactivity concentration, a radiological characterization method using a scaling factor and a nondestructive gamma-ray measurement should be developed. The number of radionuclides that are to be selected for the safety assessment of the trench type disposal facility can decrease using artificial barriers. Hazardous materials, will be identified using records and nondestructive inspection. The waste identified as hazardous will be unpacked and segregated. Preliminary calculations of waste acceptance criteria of hazardous material concentrations were conducted based on environmental standards in groundwater. The total volume of the combustibles will be evaluated using nondestructive inspection. The waste that does not comply with the waste acceptance criteria should be mixed with low combustible material waste such as dismantling concrete waste in order to satisfy the waste acceptance criteria on a disposal facility average. It was estimated that segregation throughput of compressed waste should be increased about 5 times more than conventional method by applying the countermeasures. Further study and technology development will be conducted to realize the plan.
Ito, Hideaki; Noritsugi, Hiroaki; Suzuki, Toshiaki; Yamazaki, Manabu; Okawa, Toshikatsu
Saikuru Kiko Giho, (21), p.77 - 97, 2004/00
Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.
Yoshihara, Shizuya; Okawa, Toshikatsu; Inoue, Setsunari
no journal, ,
no abstracts in English
Karube, Koji; Aita, Tsuyoshi; Okawa, Toshikatsu
no journal, ,
no abstracts in English
Suzuki, Nobuhiro; Ito, Hiromichi; Sasaki, Jun; Okawa, Toshikatsu; Kawahara, Hirotaka; Kobayashi, Tetsuhiko; Sakao, Ryuta*; Murata, Chotaro*; Tanaka, Junya*; Matsusaka, Yasunori*; et al.
no journal, ,
no abstracts in English
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.
Ashida, Takashi; Takamatsu, Misao; Ito, Hideaki; Okawa, Toshikatsu; Yoshihara, Shizuya
no journal, ,
In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly (S/A) 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 incident necessitated the replacement of the UCS and the retrieval of the MARICO-2 sub-assembly for Joyo restoration. This paper describes the summary of Joyo restoration works. In-vessel repair techniques for sodium cooled fast reactors (SFRs) are important in confirming safety and integrity of SFRs. However, the demonstrated techniques under the actual reactor environment with high temperature, high radiation dose and remaining sodium are not enough to secure the reliability of these techniques. The experience and knowledge accumulated in the UCS replacement provides valuable insights into further improvements for in-vessel repair techniques in SFRs.
Aizawa, Kenji; Iseki, Atsushi; Okawa, Toshikatsu; Aita, Tsuyoshi; Kamata, Hidehisa
no journal, ,
no abstracts in English
