Visualizing cation vacancies in Ce:GdAlGaO scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.

Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08

https://doi.org/10.35848/1882-0786/aba0dd

To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAlO, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.

Ecological and genomic profiling of anaerobic methane-oxidizing archaea in a deep granitic environment

Ino, Kohei*; Hernsdorf, A. W.*; Konno, Yuta*; Kozuka, Mariko*; Yanagawa, Katsunori*; Kato, Shingo*; Sunamura, Michinari*; Hirota, Akinari*; Togo, Yoko*; Ito, Kazumasa*; et al.

ISME Journal, 12(1), p.31 - 47, 2018/01

https://doi.org/10.1038/ismej.2017.140

In this study, we found the dominance ofanaerobic methane-oxidizing archaea in groundwater enriched in sulfate and methane from a 300-m deep underground borehole in granitic rock.

The Catalog of solidification and volume reduction technologies for the treatment of radioactive waste generated by the decommissioning of Fukushima Daiichi Nuclear Power Station

Kato, Jun; Nakagawa, Akinori; Taniguchi, Takumi; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro

JAEA-Review 2017-015, 173 Pages, 2017/07

JAEA-Review-2017-015.pdf:6.67MB

Various radioactive wastes have been generated at the Fukushima Daiichi Nuclear Power Station (1F). To dispose of the wastes underground, it is necessary to make a suitable waste package by the volume reduction and solidification of the wastes. To plan the future decommissioning of 1F, it is also necessary to estimate feasibility of existing treatment technology for those wastes. Therefore the document survey has been performed about volume reduction and solidification technologies that have domestic or foreign experiences of practical treatment for radioactive wastes to assist selection of suitable treatment of the wastes. This report shows the arranged results. The 1F wastes are classified into two groups, homogeneous particulate and liquid wastes and heterogeneous solid wastes. The needful items for the feasibility study such as a technology name, a fundamental principle, treatment efficiency, and characteristic of solidified waste are summarized in each group.

The Hydrogen gas generation by electron-beam irradiation from ALPS adsorbents solidified by several inorganic materials

Sato, Junya; Suzuki, Shinji*; Kato, Jun; Sakakibara, Tetsuro; Meguro, Yoshihiro; Nakazawa, Osamu

QST-M-2; QST Takasaki Annual Report 2015, P. 87, 2017/03

https://repo.qst.go.jp/records/73804

no abstracts in English

Approaches of selection of adequate conditioning methods for various radioactive wastes in Fukushima Daiichi NPS

Meguro, Yoshihiro; Nakagawa, Akinori; Kato, Jun; Sato, Junya; Nakazawa, Osamu; Ashida, Takashi

Proceedings of International Conference on the Safety of Radioactive Waste Management (Internet), p.139_1 - 139_4, 2016/11

A variety of radioactive wastes have been generated in decommissioning of Fukushima Daiichi Nuclear Power Station. It is necessary to evaluate feasibility of conditioning methods to these wastes, because the majority of such wastes have not been solidified in Japan. The authors investigated an approach for screening of conditioning methods for the Fukushima wastes on the basis of the findings of the existing methods and results of fundamental solidification tests using synthetic Fukushima wastes. Here five solidification methods were selected, and also 13 wastes with different chemical composition are solidified, and characteristics of the solidified form are studied. A screening flow was proposed, and evaluation criteria on each step in the flow was set up. In this presentation a trial result was opened for a waste and improvements of the screening flow found in the trial evaluation was described.

Present status of J-PARC linac

Oguri, Hidetomo; Hasegawa, Kazuo; Ito, Takashi; Chishiro, Etsuji; Hirano, Koichiro; Morishita, Takatoshi; Shinozaki, Shinichi; Ao, Hiroyuki; Okoshi, Kiyonori; Kondo, Yasuhiro; et al.

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.389 - 393, 2014/10

http://www.pasj.jp/web_publish/pasj2014/proceedings/PDF/FSP0/FSP021.pdf

no abstracts in English

Occurrence and potential activity of denitrifiers and methanogens in groundwater at 140 m depth in Pliocene diatomaceous mudstone of northern Japan

Katsuyama, Chie*; Nashimoto, Hiroaki*; Nagaosa, Kazuyo*; Ishibashi, Tomotaka*; Furuta, Kazuki*; Kinoshita, Takeshi*; Yoshikawa, Hideki; Aoki, Kazuhiro; Asano, Takahiro*; Sasaki, Yoshito; et al.

FEMS Microbiology Ecology, 86(3), p.532 - 543, 2013/12

https://doi.org/10.1111/1574-6941.12179

Anaerobic microbial activity has a major influence on the subsurface environment, and should be considered in subsurface activities including the construction of radioactive waste repositories. We investigated denitrification and methanogenesis in anoxic groundwater from 140 m depth in two boreholes, where the redox potential fluctuated. The average maximum potential denitrification rates, measured under anaerobic conditions in the two boreholes using an N tracer. Methanogenesis candidates were detected by 16S rRNA gene analysis. Although the stable isotope signatures suggested that some of the dissolved methane was of biogenic origin, no potential for methane production was evident during the incubations. The groundwater at 140 m depth did not contain oxygen, had an Eh ranging from -144 to 6.8 mV, and was found to be a potential field for denitrification.

Foil scattering loss mitigation by the additional collimation system of J-PARC RCS

Yamamoto, Kazami; Yamazaki, Yoshio; Yoshimoto, Masahiro; Kamiya, Junichiro; Harada, Hiroyuki; Saha, P. K.; Hotchi, Hideaki; Kinsho, Michikazu; Kato, Shinichi*

Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.1605 - 1607, 2011/09

https://accelconf.web.cern.ch/IPAC2011/papers/tups033.pdf

In the J-PARC RCS, the significant losses were observed at the branch of H0 dump line and the Beam Position Monitor which was put at the downstream of the H0 dump branch duct. From the beam study, we were certain that these losses were caused by the scattering of the injection and circulating beam at the charge exchange injection foil. In order to mitigate these losses, we started to develop a new collimation system in the H0 branch duct. We present latest study results and overview of this new collimation system.

Optimization for the additional collimation system of J-PARC RCS

Kato, Shinichi*; Yamamoto, Kazami; Yamazaki, Yoshio; Yoshimoto, Masahiro; Kamiya, Junichiro; Harada, Hiroyuki; Kinsho, Michikazu

Proceedings of 8th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.296 - 300, 2011/08

https://www.pasj.jp/web_publish/pasj8/proceedings/poster/MOPS019.pdf

In the J-PARC RCS, the significant losses were observed at the branch of H0 dump line and the Beam Position Monitor which was put at the downstream of the H0 dump branch duct. These losses were caused by the large angle scattering of the injection and circulating beam at the charge exchange foil. To realize high power operation, we have to mitigate these losses. So, we started to develop a new collimation system in the H0 branch duct. In order to optimize this system efficiently, we primarily focused on the relative angle of collimator block from scattering particles. We simulated behavior of particles scattered by foil and produced by collimator block and researched most optimized position and angle of the collimator block. These simulation were performed by SAD and GEANT4. We present simulation results and anticipated performance of this new collimation system.

Development of advanced loop-type fast reactor in Japan, 5; Adoption of self-actuated shutdown system to JSFR

Nakanishi, Shigeyuki; Kubo, Shigenobu*; Takamatsu, Misao; Ikarimoto, Iwao*; Kato, Jungo*; Shimakawa, Yoshio*; Harada, Kiyoshi*

Proceedings of 2008 International Congress on Advances in Nuclear Power Plants (ICAPP '08) (CD-ROM), p.519 - 525, 2008/06

A self-actuated shutdown system (SASS) is a passive safety feature which inserts control rods by the gravity force, where the detachment of the rods would be achieved by the coolant temperature rise under anticipated transient without scram (ATWS) conditions. Various out-of-pile tests have already carried out to investigate the basic characteristics of SASS, and a demonstration test of holding stability under the reactor operation condition has been performed, where a function test of the driving system to re-connect and of pulling out the control rod have been done in the experimental reactor JOYO. The element irradiation tests have been also conducted to confirm that no impact will be foreseen by the irradiation. The effectiveness of SASS for a reference core design of JSFR has been evaluated through all types of ATWS. As a result, it is ensured that JSFR will have a reliable passive shutdown system.