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.

Mesospheric ionization during substorm growth phase

Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Nishimura, Koji*; Hashimoto, Taishi*; Tanaka, Yoshimasa*; Kadokura, Akira*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Ogawa, Yasunobu*; et al.

Journal of Space Weather and Space Climate (Internet), 12, p.18_1 - 18_16, 2022/06

https://doi.org/10.1051/swsc/2022012

We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

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.

An Electron-capture efficiency in femtosecond filamentation

Nakashima, Nobuaki*; Yatsuhashi, Tomoyuki*; Sakota, Kenji*; Iwakura, Izumi*; Hashimoto, Sena*; Yokoyama, Keiichi; Matsuda, Shohei

Chemical Physics Letters, 752, p.137570_1 - 137570_5, 2020/08

https://doi.org/10.1016/j.cplett.2020.137570

Photo-redox reactions between Eu and Eu ions are induced by laser irradiation in alcoholic solution. Efficiency, wavelength dependence, and laser-power dependence are investigated with three different lasers. Nano second laser pulses at a wavelength of 308 nm is found to cause one-photon redox reactions with a quantum yield around 0.5. Nano second laser pulses at a wavelength of 394 nm induces two-photon reduction of Eu to form Eu. When the pulse energy is 5 mJ, the quantum yield is measured to be 0.015. Although the quantum yield is one order of magnitude lower than that of the one photon reduction, reduction phenomena can be easily observed under the moderate laser field strength. Because of the two-photon nature, there should be a room to improve the efficiency by increasing the laser field strength.

Study of container using hybrid technique for sulfuric acid decomposition of thermochemical water-splitting iodine-sulfur process

Ioka, Ikuo; Iwatsuki, Jin; Kuriki, Yoshiro*; Kawai, Daisuke*; Yokota, Hiroki*; Kubo, Shinji; Inagaki, Yoshiyuki; Sakaba, Nariaki

Mechanical Engineering Journal (Internet), 7(3), p.19-00377_1 - 19-00377_11, 2020/06

https://doi.org/10.1299/mej.19-00377

A thermochemical water-splitting iodine-sulfur processes (IS process) is one of candidates for the large-scale production of hydrogen with high cost performance. Severe corrosive environment which is thermal decomposition of sulfuric acid exists in the IS process. A hybrid material with the corrosion-resistance and the ductility was made by a plasma spraying and laser treatment. The specimen had excellent corrosion resistance in the condition of 95 mass% boiling sulfuric acid. This was attributed to the formation of SiO on the surface. To confirm the production characteristics of a container using the hybrid material, the container which has a welded part, a chamfer, a curved surface was experimentally made. There was no detachment in the plasma spraying and laser treated layer of the container after the laser treatment. It was confirmed that the construction of the container with high corrosion resistance in sulfuric acid was possible in the hybrid technique.

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.

Pretreatment works for disposal of radioactive wastes produced by research activities, 1

Ishihara, Keisuke; Yokota, Akira; Kanazawa, Shingo; Iketani, Shotaro; Sudo, Tomoyuki; Myodo, Masato; Irie, Hirobumi; Kato, Mitsugu; Iseda, Hirokatsu; Kishimoto, Katsumi; et al.

JAEA-Technology 2016-024, 108 Pages, 2016/12

JAEA-Technology-2016-024.pdf:29.74MB

Radioactive isotope, nuclear fuel material and radiation generators are utilized in research institutes, universities, hospitals, private enterprises, etc. As a result, various low-level radioactive wastes (hereinafter referred to as non-nuclear radioactive wastes) are produced. Disposal site for non-nuclear radioactive wastes have not been settled yet and those wastes are stored in storage facilities of each operator for a long period. The Advanced Volume Reduction Facilities (AVRF) are built to produce waste packages so that they satisfy requirements for shallow underground disposal. In the AVRF, low-level beta-gamma solid radioactive wastes produced in the Nuclear Science Research Institute are mainly treated. To produce waste packages meeting requirements for disposal safely and efficiently, it is necessary to cut large radioactive wastes into pieces of suitable size and segregate those depending on their types of material. This report summarizes activities of pretreatment to dispose of non-nuclear radioactive wastes in the AVRF.

Study on small-sized tailless beam formation using multipole magnetic field (Joint research)

Yokota, Wataru; Yuri, Yosuke; Watanabe, Shinichi*; Oshiro, Yukimitsu*; Kubono, Shigeru*

JAEA-Technology 2016-005, 21 Pages, 2016/03

JAEA-Technology-2016-005.pdf:2.24MB

The Center of Nuclear Science (CNS) of Tokyo University conducts the research on nuclear physics using CNS Radio-Isotope Beam Separator (CRIB) installed at the RIKEN AVF cyclotron. Takasaki Advanced Radiation Research Institute, JAEA has an AVF cyclotron of similar scale and is developing a technology to form a large-area uniform beam by an octupole magnetic field for the research on materials science. They carried out an R&D to increase the cyclotron beam intensity at a target under joint research. The nonlinear beam optics was designed to form a usual cyclotron beam having a large transverse tail into a small-sized tailless distribution so that the beam passes the gas target orifice (6 mm in diameter) of CRIB without a loss. As a result of particle tracking simulations based on the measured beam emittance, it has been found that an octupole magnetic field is effective in tail-folding and a 10-mm-diameter beam can be formed with two octupole magnets added in the present beam line. It has been also found that additional magnets need to be installed and the beam emittance should be reduced for the objective beam size of 6 mm. Moreover, the objective may be attained if the beam path length and configuration of the magnetic lens system are freely chosen.

Ionoluminescence analysis of glass scintillators and application to single-ion-hit real-time detection

Yokoyama, Akihito; Kada, Wataru*; Sato, Takahiro; Koka, Masashi; Shimada, Keisuke*; Yokota, Yuya*; Miura, Kenta*; Hanaizumi, Osamu*

Nuclear Instruments and Methods in Physics Research B, 371, p.340 - 343, 2016/03

https://doi.org/10.1016/j.nimb.2015.10.024

no abstracts in English

A Model of charmed baryon-nucleon potential and two- and three-body bound states with charmed baryon

Maeda, Saori*; Oka, Makoto; Yokota, Akira*; Hiyama, Emiko*; Liu, Y.-R.*

Progress of Theoretical and Experimental Physics (Internet), 2016(2), p.023D02_1 - 023D02_29, 2016/02

https://doi.org/10.1093/ptep/ptv194

A potential model for the interaction between a charmed baryon (, , and ) and the nucleon () is constructed. The model contains a long-range meson ( and ) exchange part and a short-distance quark exchange part. The quark cluster model is used to evaluate the short-range repulsion and a monopole type form factor is introduced to the long-range potential to reflect the extended structure of hadrons. We determine the cutoff parameters in the form factors by fitting the scattering data with the same approach and we obtain four sets of parameters (a)-(d). The most attractive potential (d) leads to bound c states with and once the channel couplings among and are taken into account. One can also investigate many-body problems with the model. Here, we construct an effective one-channel potential with the parameter set (d) and apply it to the 3-body system. The bound states with = 1/2 and 3/2 are predicted.