Three-dimensional electrical resistivity structure beneath a strain concentration area in the back-arc side of the northeastern Japan Arc

Usui, Yoshiya*; Uyeshima, Makoto*; Hase, Hideaki*; Ichihara, Hiroshi*; Aizawa, Koki*; Koyama, Takao*; Sakanaka, Shinya*; Ogawa, Tsutomu*; Yamaya, Yusuke*; Nishitani, Tadashi*; et al.

Journal of Geophysical Research; Solid Earth, 129(5), p.e2023JB028522_1 - e2023JB028522_22, 2024/05

https://doi.org/10.1029/2023JB028522

We elucidated the crustal heterogeneities beneath a strain concentration area on the back-arc side of the northeastern Japan Arc based on electrical resistivity. By deploying magnetotelluric surveys, we revealed the three-dimensional electrical resistivity structure in the crust, suggesting the coexistence of two types of strain-concentration mechanisms in the strain-concentration area. The shallow conductive layers and lower-crustal conductors appear to act as low-elastic-modulus and low-viscosity areas, respectively, and are responsible for the strain concentration. We found a spatial correlation between the edges of the lower-crustal conductors and the epicenters of large intraplate earthquakes. Weak shear zones in the conductive lower crust may cause stress loading on faults in the brittle upper crust, resulting in large earthquakes. We also identified vertical conductors ranging from the lower crust to Quaternary volcanoes, which may indicate fluid paths to these volcanoes.

Ion track etching of PVDF films irradiated with fast C cluster ions

Kitamura, Akane; Yamaki, Tetsuya*; Chiba, Atsuya*; Usui, Aya

QST-M-8; QST Takasaki Annual Report 2016, P. 37, 2018/03

https://repo.qst.go.jp/records/73811

We investigated the track-etched surface of PVDF films irradiated with C cluster ions, comparing the data with C monoatomic ions. PVDF films were irradiated with 6 MeV C cluster ions. The energy of the each carbon ion is 100 keV/atom; thus, for comparison, the PVDF films were also irradiated with 100 keV C ions. SEM and AFM observation showed that the surface irradiated with C cluster ions apparently possessed flat-bottomed pores with an average diameter and depth of approximately 400 and 250 nm, respectively. On the other hand, track-etched pores were also formed on the surface irradiated with C ions, but their morphology was irregular or obscure. In the irradiation with the C cluster ions, the surface diameter of track-etched pores increased with increasing the etching time. The tracks of the 100 keV C ions seemed to be hardly developed by the etching when the time. In conclusion, the C cluster ions irradiation caused a large size of etchable tracks on the PVDF surface. The result could represent the effect of local and simultaneous collision by the aggregated ions.

Development of novel technique of negative C ion production by electron attachment using cesium sputter ion source

Usui, Aya; Chiba, Atsuya; Yamada, Keisuke

JAEA-Technology 2016-034, 21 Pages, 2017/03

JAEA-Technology-2016-034.pdf:82.52MB

In the TIARA (Takasaki Ion Accelerators for Advanced Radiation Application), in order to propel the studies on the swift cluster ions, a novel technique was developed to increase the beam intensity of the fullerene ions which would have a considerably larger irradiation effect than any cluster ions. As a new method of negative ion production, the ionization mechanism by electron attachment was introduced as an alternative to the traditional method with the cesium sputtering to the existing cesium sputter type ion source (SNICS). In consequence, the intensity of the negative C ion beam produced using an existing ion source with a novel technique was increased thousand times as high as those using the previous one for 12 hour operation. In this report, we describe the problems in the traditional ionization method and explain the production technique of the negative C ions ionized via electron attachment process, which solves that only by the minor changes in SNICS.

Current status of electrostatic accelerator at TIARA

Usui, Aya; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Kitano, Toshihiko*; Takayama, Terumitsu*; Orimo, Takao*; Kanai, Shinji*; Aoki, Yuki*; Hashizume, Masashi*; et al.

Dai-28-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.117 - 119, 2015/12

no abstracts in English

SiC coating as hydrogen permeation reduction and oxidation resistance for nuclear fuel cladding

Usui, Takahiro*; Sawada, Akihiko; Amaya, Masaki; Suzuki, Akihiro*; Chikada, Takumi*; Terai, Takayuki*

Journal of Nuclear Science and Technology, 52(10), p.1318 - 1322, 2015/10

https://doi.org/10.1080/00223131.2015.1020901

SiC coating is one of countermeasures for the prevention of oxidation and hydrogen embrittlement of fuel claddings because SiC has high resistance of oxidation and hydrogen permeation. Hydrogen permeation and oxidation experiments for the cladding materials with SiC coatings were conducted in unirradiated conditions. The sputtering method was employed to make SiC coatings. In the hydrogen permeation experiment, SUS316 was used as a base material of the coating. SUS316 with SiC coatings showed hydrogen permeation reduction by one order of magnitude. In the oxidation experiments, Zry-4 and SUS316 were used as base materials of the coatings. The weight gain of the Zry-4 specimens with a SiC coating decreased by about one-fifth compared to the uncoated ones. This phenomenon was observed for SUS316 at 750 C as well. The peel-off of the coating was observed in some experiments, and it is considered that the peel-off was caused by the difference of the thermal expansions between coatings and base materials. Thicker coatings showed better oxidation resistance, but thinner coatings showed more tolerance of peel-off.

Novel technique for generating negative fullerene ions using a cesium sputter ion source

Chiba, Atsuya; Usui, Aya; Yamada, Keisuke

Dai-27-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.56 - 59, 2015/03

Utilization of the swift fullerene ion beam in TIARA using the tandem accelerator tends to increase year after year. However, only a few currents obtained by a generating method of negative ions with a cesium sputtering is hindrance to the progress of study. A generating method of the negative fullerene ions is developed on the basis of an electron attachment. As a result, the method permits us to obtain stable beam intensity more than a thousand-fold compared with that produced by the sputtering method.

Numerical simulation on the long-term variation of radioactive cesium concentration in the North Pacific due to the Fukushima disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*

Journal of Environmental Radioactivity, 136, p.64 - 75, 2014/10

https://doi.org/10.1016/j.jenvrad.2014.05.005

Numerical simulations on oceanic radioactive cesium dispersions in the North Pacific were conducted with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster. It was suggested that the Cs concentration had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.

Intercomparison of numerical simulations on oceanic dispersion of the radioactive cesium released because of the Fukushima disaster

Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*; Nishikawa, Shiro*; Ishikawa, Yoichi*

Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 7 Pages, 2014/08

Numerical simulations on oceanic dispersion of the radioactive cesium in the North Pacific from March 2011 to September 2013 were conducted to clarify the concentration of the radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant. We implemented the oceanic dispersion simulations with two independent ocean reanalysis dataset. It was suggested that the Cs concentration in the North Pacific was lower than the pre-Fukushima background level about two years after the Fukushima disaster. The intercomparison revealed that meso-scale eddies in the Kuroshio Extension region may have efficiently diluted the radioactive cesium concentration at the sea surface. In addition, it was suggested that the enhanced downward current accompanied by the meso-scale eddies played an important role in transporting the radioactive cesium into the intermediate layer.

Status report on technical developments of electrostatic accelerators

Yamada, Keisuke; Saito, Yuichi; Ishii, Yasuyuki; Matoba, Shiro; Chiba, Atsuya; Yokoyama, Akihito; Usui, Aya; Sato, Takahiro; Okubo, Takeru; Uno, Sadanori

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 159, 2014/03

https://jopss.jaea.go.jp/pdfdata/JAEA-Review-2013-059.pdf

no abstracts in English

JRTF decommissioning project; Evaluation of project management data concerning dismantling activities of glove boxes, 1

Muraguchi, Yoshinori; Kanayama, Fumihiko; Usui, Hideo; Izumo, Sari; Tachibana, Mitsuo

JAEA-Technology 2012-035, 69 Pages, 2012/12

JAEA-Technology-2012-035.pdf:4.96MB

Dismantling activities of equipment in JAEA's Reprocessing Test Facility (JRTF) used for wet reprocessing test started from 1996. Glove boxes and hoods installed in the main building were dismantled preferentially for securing temporary place of dismantled waste and dismantling tools by dismantling activities. Of these, 8 glove boxes (glove box group) were installed in room 232 of the main building. The glove box group was dismantled by setting up a large plastic enclosure (greenhouse) for work efficiency. In this report, dismantling procedure and actual data obtained from dismantling activity were arranged about dismantling activity of glove box group of room 232 in 1996. About dismantling activity of glove box group, manpower of the basic work items extracted by classifying into common work items and independent work items were analyzed. In addition, calculation equation was examined concerning dismantling of glove boxes.