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Mitsuguchi, Takehiro; Okabe, Nobuaki*; Kokubu, Yoko; Matsuzaki, Hiroyuki*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.96 - 110, 2024/12
Geological disposal of high-level radioactive waste requires not only selecting sites appropriate for the waste repository, where its isolation ability would not be damaged by natural phenomena for several tens of thousands of years, but also rationally constructing the disposal system depending on site-specific geological environments and their anticipated long-term variability. Recently, elemental/isotopic compositions of underground fluids (deep groundwaters, hot/cold spring waters, brines associated with oil and natural gas reservoirs, and so on) in Japan have been studied for evaluating the long-term stability of the geological environments of this country. Iodine and its radioactive isotope I (half-life = 15.7 million years) are included in the subjects of the study. The current review paper provides overviews of (i) the iodine content and iodine-129/127 ratio (
I/
I ratio) of various materials in Earth's surface layers, (ii) relevant sample pretreatments and measurements, and (iii)
I/
I data of the underground fluids in Japan, then gives (iv) some interpretations of the fluid
I/
I data, along with their problems and uncertainties, and (v) some implications towards evaluating the long-term stability of geological environments.
Niwa, Masakazu; Shimada, Akiomi; Asamori, Koichi; Sueoka, Shigeru; Komatsu, Tetsuya; Nakajima, Toru; Ogata, Manabu; Uchida, Mao; Nishiyama, Nariaki; Tanaka, Kiriha; et al.
JAEA-Review 2024-035, 29 Pages, 2024/09
This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2024. The objectives and contents of this research are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.
Mitsuguchi, Takehiro; Minakata, Keiji*; Sugihara, Kaoru*; Hiraoka, Masanori*; Yoshida, Masaaki*; Kokubu, Yoko
bioRxiv (Internet), 55 Pages, 2022/11
Mitsuguchi, Takehiro; Okabe, Nobuaki*; Yokoyama, Yusuke*; Yoneda, Minoru*; Shibata, Yasuyuki*; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko
Journal of Environmental Radioactivity, 235-236, p.106593_1 - 106593_10, 2021/09
Times Cited Count:5 Percentile:25.16(Environmental Sciences)For a contribution to developing the usage of iodine-129 (I) as a tracer of deep-seated fluid,
I/
I and
C were measured for annual bands (AD 1931-1991) of a modern coral collected from Northwestern Australia; the measurements were performed using the JAEA-AMS-TONO-5MV for
I/
I and an AMS facility of the University of Tokyo for
C. Results indicate that both
I/
I and
C distinctly increase from 1950s. The
C increase can be ascribed to atmospheric nuclear tests, while the
I/
I increase is due to nuclear-fuel reprocessing as well as atmospheric nuclear tests. These results are in good agreement with previous studies, indicating that the
I/
I measurement by JAEA-AMS-TONO-5MV has been further developed.
Kokubu, Yoko; Mitsuguchi, Takehiro*; Watanabe, Takahiro; Yamada, Tsutomu*; Asami, Ryuji*; Iryu, Yasufumi*
Radiocarbon, 61(5), p.1593 - 1601, 2019/10
Times Cited Count:1 Percentile:5.05(Geochemistry & Geophysics)We performed C measurements of two fossil and one modern corals using a combined system of an elemental analyzer and an automated graphitization equipment AGE3 (EA-AGE3 system) and JAEA-AMS-TONO. The
C concentrations (pMC values) of mid-Holocene Okinawa corals obtained by our EA-AGE3 system appear to be slightly higher than those obtained by the conventional graphitization method using phosphoric acid. The pMC increase in our EA-AGE3 system may result in significant underestimation of
C age especially for older samples (e.g., 10,000 BP); however, the pMC increase is negligible in
C measurements of modern or recent samples. We applied the EA-AGE3 method to the pre- and post-bomb annual-band samples from the modern Ogasawara coral for
C measurements. On the basis of the pre-bomb coral
C data, we estimated marine reservoir correction (
R) around Ogasawara Islands and its stability between
1900 and 1950 AD.
Yokoyama, Tatsunori; Kimura, Junichi*; Mitsuguchi, Takehiro; Danhara, Toru*; Hirata, Takafumi*; Sakata, Shuhei*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; Miyazaki, Takashi*; et al.
Geochemical Journal, 52(6), p.531 - 540, 2018/12
Times Cited Count:17 Percentile:60.82(Geochemistry & Geophysics)Yokoyama, Tatsunori; Mitsuguchi, Takehiro; Sueoka, Shigeru
no journal, ,
In recent years, it has become possible to carry out high-precision microscale age dating of geological samples using developed micro-analytical techniques such as SIMS, LA-ICP-MS, etc. Application of LA-ICP-MS-based microscale U-Pb dating is extending from U-rich heavy minerals such as zircon, apatite and monazite to U-depleted minerals such as calcite. This kind of method enables age determination of several types of mineral grains occurring within rock bodies, and thereby reveals chronological changes in chemical composition of source materials from which the minerals were crystallized, with some cases in which thermal history of the crystal formation system can be reconstructed. For research and development of geological disposal techniques for high-level radioactive wastes, we develop and facilitate geochronological dating techniques for evaluation of long-term stability in geological environments, at Tono Geoscience Center, Japan Atomic Energy Agency. In our presentation, we introduce the current status of our development for research on long-term stability of geological environments, U-Pb dating of calcite, U-Pb dating of young zircon and trace element analysis by using LA-ICP-MS.
Yokoyama, Tatsunori; Yuguchi, Takashi*; Sakata, Shuhei*; Ishibashi, Kozue*; Ogita, Yasuhiro*; Ito, Daichi*; Ono, Takeshi*; Kagami, Saya; Mitsuguchi, Takehiro; Sueoka, Shigeru
no journal, ,
Dating and trace elements analysis of zircons provide us the evidences of past thermal history about their growth events, such as timing and temperature of magmatism and crystallization. In granitic rocks, because the proposed closure temperature of zircon U-Pb (900
C) is often higher than crystallization temperature of the zircon, the zircon U-Pb age means the timing of crystallization. To clarify the growth history of granitic pluton, Yuguchi et al. (2016) performed the observation of internal structure of zircon (collected from the Toki granite, central Japan) using cathodoluminescence, deriving crystallization temperature and age using Ti-in-zircon thermometry and U-Pb dating. It is important to discuss the emplacement by such an approach to understand the history of upheaval and exhumation of igneous complex. In this study, for simultaneously estimating crystallization age and temperature of zircon, we performed U-Pb isotopic analysis and quantitative analysis of Titanium, in the same position of zircon, using LA-ICP-MS after the cathodoluminescence observation. As preliminary experiments, we analyzed zircons collected from Japan (e.g., Okue, Tono, Toki and Kurobegawa granites) to estimate their thermal history. We could estimate the crystallization ages and temperatures of zircons of Okue (556-946
C in 11.1-16.1 Ma), Tono (613-901
C in 110.2-127.4 Ma), Toki (575-734
C in 69.4-79.9 Ma) and Kurobegawa (636-779
C in 0.46-1.85 Ma), respectively.
Mitsuguchi, Takehiro; Okabe, Nobuaki*; Kokubu, Yoko; Matsuzaki, Hiroyuki*
no journal, ,
no abstracts in English
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Miyazaki, Takashi*; et al.
no journal, ,
Chronological and geochemical studies of calcium carbonates can provide precious information for changes in geochemical condition in deep geological environments. Because the carbonate can be found as common filling minerals in rocks, age zoning and spatial distribution of chemical composition in the carbonate could be a wide-use indicator to reconstruct the past environmental changes. Calcite and other carbonate materials have been dated by Isotope Dilution-Thermal Ionization Mass Spectrometry. On the other hand, a few of U-Pb dating studies in a micro scale area (less than 10 micrometer) such as using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) has been conducted on the carbonate. The U-Pb dating technique for the carbonates using LA-MC-ICPMS is still immature partly because of a lack of consensus international carbonate reference materials for the in-situ dating technique. In order to solve this problem, we performed a survey on the carbonate reference materials that may be suitable for high precision U-Pb dating using LA-MC-ICPMS. Additionally, we conducted experiments to make compositionally homogeneous carbonate (calcite) reference materials.
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro*; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; et al.
no journal, ,
no abstracts in English
Mitsuguchi, Takehiro; Okabe, Nobuaki*; Miyake, Masayasu*; Matsubara, Akihiro; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko
no journal, ,
A preliminary test for AMS I measurement of CaCO
samples was performed using a tandem Pelletron AMS system at Tono Geoscience Center, Japan Atomic Energy Agency (JAEA-AMS-TONO). An annually-banded coral collected from Vietnam was used for this test. The procedure of the test was as follows: (1) an annual-band sample of AD 1946-47 from the coral was treated with 1% HCl for removal of its surface portion; (2) the treated sample was dissolved in H
PO
solution; (3) an aliquot from the sample solution was used for
I measurement by ICP-MS; (4) the Woodward iodine standard was added as a carrier to the sample solution; (5) iodine was extracted from the solution by solvent extraction and back-extraction, resulting in an aqueous phase with extracted iodine; (6) AgNO
(aq) was added to the aqueous phase to obtain AgI precipitate; (7) the AgI precipitate was mixed with Nb and pressed into a copper cathode for
I measurement by JAEA-AMS-TONO. A blank test of this procedure was also made to evaluate the background
I effect in the sample preparation. Results we obtained were as follows: (1) the background
I/
I ratio was [4.3
0.1]
10
and (2) the background-corrected coral
I/
I ratio was [1.53
0.76]
10
. The coral
I/
I ratio is generally in agreement with previously-reported values of Chang et al. (2016), suggesting that AMS
I measurement of CaCO
samples has been generally established in JAEA-AMS-TONO.
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; et al.
no journal, ,
no abstracts in English
Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Watanabe, Takahiro; Mitsuguchi, Takehiro
no journal, ,
no abstracts in English