Removal of spent fuel sheared powder for decommissioning of Main Plant

Nishino, Saki; Okada, Jumpei; Watanabe, Kazuki; Furuuchi, Yuta; Yokota, Satoru; Yada, Yuji; Kusaka, Shota; Morokado, Shiori; Nakamura, Yoshinobu

JAEA-Technology 2023-011, 39 Pages, 2023/06

JAEA-Technology-2023-011.pdf:2.51MB

Tokai Reprocessing Plant (TRP) which shifted to decommissioning phase in 2014 had nuclear fuel materials such as the spent fuel sheared powder, the diluted plutonium solution and the uranium solution in a part of the reprocessing main equipment because TRP intended to resume reprocessing operations when it suspended the operations in 2007. Therefore, we have planned to remove these nuclear materials in sequence as Flush-out before beginning the decommissioning, and conducted removal of the spent fuel sheared powder as the first stage. The spent fuel sheared powder that had accumulated in the cell of the Main Plant (MP) as a result of the spent fuel shearing process was recovered from the cell floor, the shearing machine and the distributor between April 2016 and April 2017 as part of maintenance. Removing the recovered spent fuel sheared powder was conducted between June 2022 and September 2022. In this work, the recovered powder was dissolved in nitric acid at the dissolver in a small amount in order to remove it safely and early, and the dissolved solution was sent to the highly radioactive waste storage tanks without separating uranium and plutonium. Then, the dissolved solution transfer route was rinsed with nitric acid and water. Although about 15 years had passed since previous process operations, the removing work was successfully completed without any equipment failure because of the organization of a system that combines veterans experienced the operation with young workers, careful equipment inspections, and worker education and training. Removing this powder was conducted after revising the decommissioning project and obtaining approval from the Nuclear Regulation Authority owing to operating a part of process equipment.

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

https://doi.org/10.1126/science.aav7432

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Design of pencil beam formation system for high-accuracy carbon-ion microsurgery

Arakawa, Kazuo; Oikawa, Masakazu*; Shimada, Hirofumi*; Kamiya, Tomihiro; Nakano, Takashi*; Yusa, Ken*; Kato, Hiroyuki*; Sato, Takahiro; Agematsu, Takashi; Kashiwagi, Hirotsugu; et al.

Proceedings of 4th Annual Meeting of Particle Accelerator Society of Japan and 32nd Linear Accelerator Meeting in Japan (CD-ROM), p.279 - 281, 2007/00

no abstracts in English

Development of the washing device for dissolver, 2; Application of the high-pressure water washing device

Terunuma, Hirotaka; Shimoyamada, Tetsuya; Kogawa, Takayuki; Kikuchi, Hideki; Miyoshi, Ryuta; Yokota, Satoru; Nakamura, Yoshinobu; Hayashi, Shinichiro

no journal, , 

We have developed dissolver cleaning device which can clean up sludge inside dissolver with high pressure water spray. The device has been applied to TRP dissolvers and the sludge has been cleaned up successfully. This allowed smooth solution transfer and stable operation of the dissolvers.

Remote wall thickness measurement of the fuel basket of the dissolver

Yokota, Satoru; Hatanaka, Akira; Fujimori, Masahito; Shimoyamada, Tetsuya; Nakamura, Yoshinobu

no journal, , 

Three batch-type dissolvers in the Tokai Reprocessing Plant are a device for dissolving spent fuel. The dissolver is composed of one slab and two barrels (stainless steel 310s). Install a fuel basket (stainless steel 304L) in the barrel and accept the sheared spent fuel to dissolve it. The insoluble fuel cladding is taken out of the barrels with the basket. The dissolution time of operation for one batch is approximately 10 hours. During dissolution operation, nitric acid was added to the dissolver into the spent fuel in the basket with water. The solution was heated with steam. Corrosion failure has occurred in the past because the dissolver is exposed to a high corrosive environment (high temperature, high acid concentration). Therefore, we carry out the periodical wall thickness measurement of the barrel by the remote control. On the other hand, the wall thickness measurement of the fuel basket was carried out only once by destructive measurement at the time of renewal in 1999. The details of the corrosion tendency of the fuel basket are unknown, and it is urgent to establish a non-destructive measurement method by remote handling. Therefore, we examined the method of wall thickness measurement of the fuel basket and established the measuring technique.

Flush-out for Tokai Reprocessing Plant decommissioning, 2; Dissolution of the spent fuel sheared powder

Watanabe, Kazuki; Okada, Jumpei; Yokota, Satoru; Oyama, Daisuke; Yamada, Takashi; Yatabe, Hitoshi; Horie, Koji; Uchida, Naoki

no journal, , 

no abstracts in English