Microbiome analysis of the restricted bacteria in radioactive element-containing water at the Fukushima Daiichi Nuclear Power Station

Warashina, Tomoro*; Sato, Asako*; Hinai, Hiroshi; Shaikhutdinov, N.*; Shagimardanova, E.*; Mori, Hiroshi*; Tamaki, Satoshi*; Saito, Motofumi*; Sanada, Yukihisa; Sasaki, Yoshito; et al.

Applied and Environmental Microbiology, 90(4), p.e02113-23_1 - e02113-23_23, 2024/04

https://doi.org/10.1128/aem.02113-23

Degradation of nuclear fuel debris analog by siderophore-releasing microorganisms

Onuki, Toshihiko*; Nakase, Masahiko*; Liu, J.; Dotsuta, Yuma; Satou, Yukihiko; Kitagaki, Toru; Kozai, Naofumi

Journal of Nuclear Science and Technology, 61(3), p.384 - 396, 2023/07

https://doi.org/10.1080/00223131.2023.2231951

An Experimental study on the degradation of UO/Fe(0) by bacteria

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Takano, Masahide; Onuki, Toshihiko; Kozai, Naofumi

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 2 Pages, 2022/10

Nuclear fuel debris, consisting primarily of nuclear fuel and structural material, was formed during the Fukushima Daiichi NPP accident and exists in the cooling water accumulated in the primary containment vessels. Microorganisms living in groundwater may come into contact with the fuel debris and react with it. To assess the degradation of fuel debris, it is necessary to evaluate the interactions between microorganisms and fuel debris. Here we performed an experimental study on bacterial degradation. A mixed powder of UO and Fe(0) was used as a fuel debris simulant. Bacillus subtilis, which is widespread bacteria in nature and thought to be present at the accident site, was used. The mixed powder was exposed to the Bacillus subtilis in a liquid medium for some days. It was found that the oxidative dissolution of the U(IV) and Fe(0) was accelerated by B. subtilis. A fraction of the dissolved U(VI) was precipitated together with iron precipitates which are probably amorphous Fe(III) hydroxides. The study indicates that microorganisms would cause the degradation of fuel debris.

Novel strain induces severe corrosion by retrieving electrons from Fe under a freshwater environment

Hirano, Shinichi*; Ihara, Sota*; Wakai, Satoshi*; Dotsuta, Yuma; Otani, Kyohei; Kitagaki, Toru; Ueno, Fumiyoshi; Okamoto, Akihiro*

Microorganisms (Internet), 10(2), p.270_1 - 270_12, 2022/02

https://doi.org/10.3390/microorganisms10020270

To understand the role of methanogens in corrosion under anoxic conditions in freshwater, we investigated the corrosion activities of methanogens in samples collected from groundwater and rivers. We enriched microorganisms that can grow with CO/NaHCO and Fe as the sole carbon source and electron donor, respectively, in ground fresh water. Electrochemical analysis revealed that strain can uptake electrons from the cathode at lower than -0.61 V vs SHE and has a redox-active component with electrochemical potential different from those of other previously reported methanogens with extracellular electron transfer ability. This study indicated the corrosion risk by methanogens capable of taking up electrons from Fe in anoxic freshwater environments and the necessity of understanding the corrosion mechanism to contribute to risk diagnosis.

Evaluation of the dissolution behavior of zircon using high-resolution phase-shift interferometry microscope

Kitagaki, Toru

Journal of Nuclear Materials, 557, p.153254_1 - 153254_8, 2021/12

AA2021-0312.pdf:1.55MB

https://doi.org/10.1016/j.jnucmat.2021.153254

Material characterization of the VULCANO corium concrete interaction test with concrete representative of Fukushima Daiichi Nuclear Plants

Brissonneau, L.*; Ikeuchi, Hirotomo; Piluso, P.*; Gousseau, J.*; David, C.*; Testud, V.*; Roger, J.*; Bouyer, V.*; Kitagaki, Toru; Nakayoshi, Akira; et al.

Journal of Nuclear Materials, 528, p.151860_1 - 151860_18, 2020/01

https://doi.org/10.1016/j.jnucmat.2019.151860

First-principles calculation of mechanical properties of simulated debris ZrUO

Itakura, Mitsuhiro; Nakamura, Hiroki; Kitagaki, Toru; Hoshino, Takanori; Machida, Masahiko

Journal of Nuclear Science and Technology, 56(9-10), p.915 - 921, 2019/09

https://doi.org/10.1080/00223131.2019.1604271

To elucidate the mechanical properties of fuel debris inside the Fukushima Daiichi Nuclear Power Plant, we use first-principles calculations to evaluate mechanical properties of cubic ZrUO, which is a main component of the fuel debris. We focus on the dependence of mechanical properties on the fraction x of zirconium, compare our results with recent experiment of simulated debris, in which dependences of elastic moduli and fracture toughness on the ZrO content showed deviation from a simple linear relation. We show that elastic moduli drop at around x=0.25 and increase again for larger values of x, as has been observed in experiments. The reason of the drop is a softening owing to disordered atomistic structures induced by the solute zirconium atoms. We also find that stress-strain curves for the x=0.125 case show marked hysteresis owing to the existence of many meta-stable states. We show that this hysteresis leads to slightly increased fracture toughness, but it is not enough to account for the significant increase of fracture toughness observed in experiments.

A Laboratory investigation of microbial degradation of simulant fuel debris by oxidizing microorganisms

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Yamaji, Keiko*; Onuki, Toshihiko

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 2 Pages, 2019/05

To decommission the Fukushima Daiichi Nuclear Power Plant (FDNPP), it is necessary to estimate the current status of fuel debris and predicate the possible change under various condition. Some microorganisms may enter the plant due to the seawater injection after accident and future defueling activity. In this study, microbial influence on fuel debris under aerobic condition was experimentally investigated. By culturing some bacteria in the presence of simulant fuel debris in liquid medium, the microbial degradation of fuel debris was observed.

R&D strategy on mid- and long-term behavior of fuel debris

Yano, Kimihiko; Kitagaki, Toru; Washiya, Tadahiro; Miyamoto, Yasuaki; Ogawa, Toru

Progress in Nuclear Science and Technology (Internet), 5, p.225 - 228, 2018/11

https://doi.org/10.15669/pnst.5.225

According to the roadmap for decommissioning of Fukushima Daiichi NPS, fuel debris retrieval will start from 2021, after a decade from fuel debris generation. Fuel debris will stay in the reactors until the end of defueling. In addition, it is not hard to anticipate that storage is necessary for fuel debris removed from reactors. In order to consider such a post-accident operation for fuel debris, it is indispensable to discuss the states and characteristics of fuel debris during several decades. Therefore, JAEA directed R&D strategy on mid- and long-term behavior of fuel debris tentatively and is making a start of fundamental studies on this issue in corporation with the domestic universities and other research institutes.

Mechanical properties of cubic (U,Zr)O

Kitagaki, Toru; Hoshino, Takanori; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji

Journal of Nuclear Engineering and Radiation Science, 4(3), p.031011_1 - 031011_7, 2018/07

https://doi.org/10.1115/1.4039847