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Journal Articles

Potential bacterial alteration of nuclear fuel debris; A Preliminary study using simulants in powder and pellet forms

Liu, J.; Dotsuta, Yuma; Sumita, Takehiro; Kitagaki, Toru; Onuki, Toshihiko; Kozai, Naofumi

Journal of Radioanalytical and Nuclear Chemistry, 331(6), p.2785 - 2794, 2022/06

 Times Cited Count:3 Percentile:71.05(Chemistry, Analytical)

Remnant nuclear fuel debris in the damaged nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP) has contacted the groundwater containing microorganisms for over ten years. Herein, we report the possibility of bacterial alteration of fuel debris. We investigated the physical and chemical changes of fuel debris simulants (FDS) in the powder and pellet forms via exposure to two ubiquitous bacteria, Pseudomonas fluorescens and Bacillus subtilis. In the experiments using FDS composed of the powders of Fe(0), solid solution of CeO$$_{2}$$ and ZrO$$_{2}$$, and SiO$$_{2}$$, Ce, Zr, and Si were hardly dissolved, while Fe was dissolved, a fraction of the dissolved Fe was present in the liquid phase as Fe(II) and Fe(III), and the rest was precipitated as the nano-sized particles of iron (hydr)oxides. In the experiment using P. fluorescens and FDS pellet pieces prepared by melting the Fe(0) particles and solid solution of CeO$$_{2}$$ and ZrO$$_{2}$$, the bacteria selectively gathered on the Fe(0) particle surface and made corrosion pits. These results suggest that bacteria in groundwater corrode the iron in fuel debris at FDNPP, change fuel debris into porous one, releasing the nano-sized iron (hydr)oxide particles into the water.

Journal Articles

Novel ${it Methanobacterium}$ strain induces severe corrosion by retrieving electrons from Fe$$^{0}$$ 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

 Times Cited Count:5 Percentile:86.59(Microbiology)

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$$_{2}$$/NaHCO$$_{3}$$ and Fe$$^{0}$$ as the sole carbon source and electron donor, respectively, in ground fresh water. Electrochemical analysis revealed that ${it Methanobacterium}$ 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$$^{0}$$ in anoxic freshwater environments and the necessity of understanding the corrosion mechanism to contribute to risk diagnosis.

Journal Articles

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.

Journal Articles

Removal of soluble strontium via incorporation into biogenic carbonate minerals by halophilic bacterium Bacillus sp. strain TK2d in a highly saline solution

Horiike, Takumi*; Dotsuta, Yuma*; Nakano, Yuriko*; Ochiai, Asumi*; Utsunomiya, Satoshi*; Onuki, Toshihiko; Yamashita, Mitsuo*

Applied and Environmental Microbiology, 83(20), p.e00855-17_1 - e00855-17_11, 2017/10

 Times Cited Count:14 Percentile:59.31(Biotechnology & Applied Microbiology)

Radioactive strontium ($$^{90}$$Sr) leaked into the ocean from the Fukushima Daiichi Nuclear Power Plant after the nuclear accident. Since the removal of Sr using general adsorbents is not efficient at high salinity, this study investigated removal of soluble Sr from a saline solution by biogenic carbonate minerals. An isolate, Bacillus sp. strain TK2d, from marine sediment removed more than 99 % of Sr in a saline solution. Sr adsorbed at the cell surface and then carbonate minerals containing Sr developed outside the cells.

Oral presentation

An Experimental study of microbial effect on simulant fuel debris

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

no journal, , 

Fuel debris was formed in severe accident in nuclear power plant. After the confirmation of microorganisms in water in damaged plant, it is necessary to consider the element migration of fuel debris. Here, some widespread bacteria were applied. By cultivation with simulant fuel debris, the migration mechanism was estimated.

Oral presentation

Study on the influence of microorganism on fuel debris degradation, 1; Disintegration of simulant fuel debris by widespread bacteria

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

no journal, , 

After severe accident, some microorganisms have been found coexisting with damaged fuel debris in nuclear power plant. It is accepted that the microbial reaction might affect fuel debris, such as deterioration and dissolution into water. By batch culture of widespread microorganism with simulant fuel debris, it was found that these bacteria would promote the disintegration of fuel debris in this study.

Oral presentation

Experimental study on the microbial degradation of the fuel debris

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

no journal, , 

In Fukushima Daiichi accident, molten core flowed down the structural materials and formed the fuel debris, which consists of uranium dioxide fuel, iron, zirconium, and concrete. Now the decommission of damaged nuclear plant and countermeasure of fuel debris are under discussion. It is essential to understand the current status of fuel debris and possible change during the defueling activities. Considering the appearance of microorganisms in TMI-2 and Chernobyl plant, the existence of microorganisms in Fukushima Daiichi Nuclear Power Plant was expected. Here, the microbial effect on fuel debris, specially the microbial degradation, was experimentally studied. It was found that oxidization and dissolution of iron and zirconium into the medium would mainly cause the degradation of fuel debris.

Oral presentation

Characteristic of environmental microorganisms around Fukushima Daiichi Nuclear Power Station

Dotsuta, Yuma

no journal, , 

There are a wide variety of microorganisms around us, such as the pedosphere and hydrosphere, as well as the human body surface and intestines. The radiation environment is no exception, and the presence of microorganisms has been reported after the severe accidents at the Three Mile Island Nuclear Power Plant and the Chernobyl Nuclear Power Plant. At the Fukushima Daiichi Nuclear Power Station (1F), injection of seawater immediately after the accident and inflow of groundwater, and it is thought microorganisms have invaded the building from the surrounding environment. It is important to understand the characteristics of microorganisms that have invaded the building in risk management since decommissioning takes a long time. In this study, we conducted gene analysis and culture tests of environmental samples (soil and groundwater) collected from around the 1F and examined the characteristics of the microbial community. As a result, it was clarified that in the sample used in this study, a microbial flora centered on the redox of iron and the metabolism of lower hydrocarbons and sulfur was constructed.

Oral presentation

Dissolution of fuel debris simulants by common bacteria

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

no journal, , 

For the decommissioning of the Fukushima Daiichi Nuclear Power Plant, it is necessary to understand the influence of microorganisms on the dissolution of fuel debris from the viewpoint of risk assessment of fuel debris. In this study, fuel debris simulant (UO$$_{2}$$/Fe(0)) was exposed to the bacteria that widely exist in nature to understand their changes over time. From the analysis results, it was confirmed that the dissolution of fuel debris was enhanced by the bacteria under the conditions of this experiment.

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