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Ikeuchi, Hirotomo; Sasaki, Shinji; Onishi, Takashi; Nakayoshi, Akira; Arai, Yoichi; Sato, Takumi; Ohgi, Hiroshi; Sekio, Yoshihiro; Yamaguchi, Yukako; Morishita, Kazuki; et al.
JAEA-Data/Code 2023-005, 418 Pages, 2023/12
JAEA-Data-Code-2023-005-01.pdf:24.59MBJAEA-Data-Code-2023-005-02.pdf:32.18MB
For safe and steady decommissioning of Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Station (1F), information concerning composition and physical/chemical properties of fuel debris generated in the reactors should be estimated and provided to other projects conducting the decommissioning work including the retrieval of fuel debris and the subsequent storage. For this purpose, in FY2021, samples of contaminants (the wiped smear samples and the deposits) obtained through the internal investigation of the 1F Unit 2 were analyzed to clarify the components and to characterize the micro-particles containing uranium originated from fuel (U-bearing particles) in detail. This report summarized the results of analyses performed in FY2021, including the microscopic analysis by SEM and TEM, radiation analysis, and elemental analysis by ICP-MS, as a database for evaluating the main features of each sample and the probable formation mechanism of the U-bearing particles.
Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.
Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07
This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.
-Orbital component in the Borromean nucleus 
BYang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.
Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02
Times Cited Count：45 Percentile：96.69(Physics, Multidisciplinary)A quasifree (
,
) experiment was performed to study the structure of the Borromean nucleus B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 
and 
orbitals, and a surprisingly small percentage of 9(2)% was determined for . Our finding of such a small component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B. The present work gives the smallest - or -orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of or orbitals is not a prerequisite for the occurrence of a neutron halo.
clusters in dilute neutron-rich matterTanaka, Junki*; Yang, Z.*; Typel, S.*; Adachi, Satoshi*; Bai, S.*; van Beek, P.*; Beaumel, D.*; Fujikawa, Yuki*; Han, J.*; Heil, S.*; et al.
Science, 371(6526), p.260 - 264, 2021/01
Times Cited Count：50 Percentile：99.36(Multidisciplinary Sciences)By employing quasi-free -cluster-knockout reactions, we obtained direct experimental evidence for the formation of clusters at the surface of neutron-rich tin isotopes. The observed monotonous decrease of the reaction cross sections with increasing mass number, in excellent agreement with the theoretical prediction, implies a tight interplay between -cluster formation and the neutron skin.
F from 
O
?Tang, T. L.*; Uesaka, Tomohiro*; Kawase, Shoichiro; Beaumel, D.*; Dozono, Masanori*; Fujii, Toshihiko*; Fukuda, Naoki*; Fukunaga, Taku*; Galindo-Uribarri, A.*; Hwang, S. H.*; et al.
Physical Review Letters, 124(21), p.212502_1 - 212502_6, 2020/05
Times Cited Count：14 Percentile：73.46(Physics, Multidisciplinary)The structure of a neutron-rich F nucleus is investigated by a quasifree (
) knockout reaction. The sum of spectroscopic factors of 
orbital is found to be 1.0 
0.3. The result shows that the O core of F nucleus significantly differs from a free O nucleus, and the core consists of 
35% O
, and 65% excited O. The result shows that the O core of F nucleus significantly differs from a free O nucleus. The result may infer that the addition of the proton considerably changes the neutron structure in F from that in O, which could be a possible mechanism responsible for the oxygen dripline anomaly.
Murakami, Masao*; Demizu, Yusuke*; Niwa, Yasue*; Nagayama, Shinichi*; Maeda, Takuya*; Baba, Masashi*; Miyawaki, Daisuke*; Terashima, Kazuki*; Arimura, Takeshi*; Mima, Masayuki*; et al.
no journal, ,
Morishita, Kazuki; Onishi, Takashi; Maeda, Koji; Mizokami, Masato*; Ito, Kenichi*; Mizokami, Shinya*
no journal, ,
no abstracts in English
Morishita, Kazuki; Onishi, Takashi; Maeda, Koji; Mizokami, Masato*; Ito, Kenichi*; Mizokami, Shinya*
no journal, ,
no abstracts in English
Sasaki, Shinji; Maeda, Koji; Morishita, Kazuki; Onishi, Takashi; Sato, Ikken; Mizokami, Masato*; Mizokami, Shinya*
no journal, ,
no abstracts in English
Morishita, Kazuki; Onishi, Takashi; Maeda, Koji; Mizokami, Masato*; Ito, Kenichi*; Mizokami, Shinya*
no journal, ,
Samples, collected from the operating floor of the reactor building of Fukushima Daiichi Unit 2, were immersed in deionized water and nitric acid. Immersed solutions were analyzed by gamma-ray spectrometry and ICP-MS. Analyses suggest small amount of Fe, Mn and Cu derived from structural materials of nuclear reactor, and Te, Cs and U derived from spent fuels.
Ouchi, Kazuki; Kitatsuji, Yoshihiro; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
Efficient Actinium-225 Separation from Ra-226 irradiated in fast reactor was studied. Ba and La were used as alternatives to Ra and Ac, respectively. By using DGA resin as an adsorbent, it can be expected that Ra and impurities generated by irradiation will be removed and Ac will be isolated.
Sano, Aaru; Sasaki, Yuto*; Sasaki, Shinji; Iwamoto, Nobuyuki; Ouchi, Kazuki; Kitatsuji, Yoshihiro; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
Ac-225 can be applied to cancer treatment of various sites, but world supply is scarce. In this study, in order to study the production of Ac-225 using fast neutrons, we evaluated the amount of Ac-225 produced by fast neutron irradiation of Joyo. Burn up calculations were performed with Ra-226 as the target using ORIGEN2.2 for the evaluation of the production amount. In addition, the uncertainty of Ac-225 production was evaluated from the nuclear reaction cross section of the target nuclide and the neutron flux of Joyo. This study showed that a large amount of Ac-225 can be produced by irradiating Ra-226 at Joyo. In the future, we will improve the accuracy of evaluation of the production amount through demonstration experiments.
Ouchi, Kazuki; Kitatsuji, Yoshihiro; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
In previous study, we have studied the purification process for efficient recovery of Ac-225 produced by neutron irradiation of Ra-226 in a fast reactor. In this presentation, the reuse process for re-irradiating Ra-226 after separation of Ac-225 was studied by using Ba and La as alternative elements. By using Ln resin as adsorbent and changing the nitric acid concentration, the conditions under which Ra can be isolated from impurities expected to be produced by irradiation were clarified. We propose a purification process for Ac using DGA resin and a recycling process for Ra using Ln resin.
Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
It has been reported that oxygen vacancies in cerium oxide (CeO
) affect catalytic activity. There is a need for highly sensitive in-situ measurements of the state and concentration of oxygen vacancies during catalytic reactions, and we are considering using the positron annihilation method. This time, we measured samples with different particle sizes to clarify the sites where positrons are trapped. From the lifetime spectrum of a particle size of 2 nm, which has a high intensity of the long-lived component, we first determined the lifetime value of the longest-lived component to be 390.81.6 ps. Next, in the lifetime spectrum of a particle size of 60 nm, where the longest lifetime component is the smallest, the longest lifetime component was fixed at 390.8 ps, and the lifetime value of the other positron trap site was determined to be 199.47.4 ps. These values are close to the lifetimes of positrons trapped in surface and neutral oxygen defects in first-principles calculations.
by using gamma-ray induced positron annihilation lifetime measurementDoshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
Gamma-ray-induced positron annihilation lifetime measurement (GiPALS), which utilizes the generation of positrons inside a sample by pair generation with gamma rays, has a significantly smaller background component than conventional measurement methods. It can perform measurements in harsh environments such as high temperature and high pressure because there is no positron source inside the sample. It has been reported that the positron annihilation lifetime spectrum of CeO can be fitted with two components. However, in reality, it is thought that there are at least three components: a component of annihilation in the bulk, a component of annihilation trapped in lattice defects, a component of annihilation trapped on the surface. Therefore, in this study, we tried to fit three components and assigned each by changing the particle size. In addition, we theoretically investigated the bulk, defect, and surface components in the positron annihilation lifetime of CeO using first-principles calculations.
