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Kai, Takeshi; Toigawa, Tomohiro; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yokoya, Akinari*
Journal of Chemical Physics, 158(16), p.164103_1 - 164103_8, 2023/04
New insight into water radiolysis and photolysis is indispensable in the dramatic progress of sciences and technologies in various research areas. In the radiation field, reactive hydrated electrons are considerably produced along radiation tracks. Although the formation results from a transient dynamic correlation between ejected electrons and water, the individual mechanisms of electron thermalization, delocalization, and polarization are unknown. Using a dynamic Monte Carlo code, we show herein that the ejected electrons are immediately delocalized by molecular excitations in parallel with phonon polarization and gradually thermalized by momentum transfer with an orientation polarization in a simultaneous manner. Our results show that these mechanisms heavily depend on the intermolecular vibration and rotation modes peculiar to water. We expect our approach to be a powerful technique for connecting physical and chemical processes in various solvents.
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 13(11), p.7076 - 7086, 2023/03
Times Cited Count：3 Percentile：81.33(Chemistry, Multidisciplinary)Scientific insights of water radiolysis are widely used in the life sciences and so on, however, the formation mechanism of radicals, a product of water radiolysis, is still not well understood. We are challenging to develop a simulation code to solve this formation mechanism from the viewpoint of radiation physics. Our first-principles calculations have revealed that the behavior of secondary electrons in water is governed not only by collisional effects but also by polarization effects. Furthermore, from the predicted ratio of ionization to electronic excitation, based on the spatial distribution of secondary electrons, we successfully reproduce the initial yield of hydrated electrons predicted in terms of radiation chemistry. The code provides us a reasonable spatiotemporal connection from radiation physics to radiation chemistry. Our findings are expected to provide newly scientific insights for understanding the earliest stages of water radiolysis.
O solutionKumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Sasaki, Takayuki*
Journal of Nuclear Science and Technology, 59(8), p.961 - 971, 2022/08
Times Cited Count：2 Percentile：53.91(Nuclear Science & Technology)We investigated potential degradation of fuel debris caused by HO, which is the oxidant of major impact from water radiolysis. We performed leaching experiments on different kinds of simulated debris comprising U, Fe, Cr, Ni, and Zr in an aqueous HO solution. Chemical analysis of the leaching solution showed that U dissolution was induced by HO. Raman analysis after the leaching revealed that uranyl peroxides were formed on the surface of the simulated debris. These results demonstrate that uranyl peroxides are possible alteration products of fuel debris from HO reaction. However, the sample in which the main uranium-containing phase was a U-Zr oxide solid solution showed much less uranium dissolution and no Raman signal of uranyl peroxides. Comparison of these results indicates that formation of an oxide solid solution of Zr with UO improves the stability of fuel debris against HO reaction.
Hata, Kuniki
Zairyo To Kankyo, 70(12), p.468 - 473, 2021/12
In order to estimate corrosive environment in the contaminated water at Fukushima Daiichi Nuclear Power Station, effects of oxidants, such as HO, which were generated from water radiolysis, should be taken into account due to the irradiation field in the reactor building. The process of water radiolysis and the amounts of these oxidants can change depending on the conditions of water and types of radiation. After the accident, a variety of factors, which can affect water radiolysis, such as seawater constituents, surface of oxides, and 
-radionuclides, had been discussed. In this paper, these effects on radiolysis are reviewed for the better understanding of the corrosive environment in the contaminated water.
induced by HO and 
-irradiationKumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*
Journal of Physical Chemistry C, 123(15), p.9919 - 9925, 2019/04
Times Cited Count：19 Percentile：62.54(Chemistry, Physical)Radiation-induced oxidative dissolution of uranium dioxide (UO) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO stoichiometry on the oxidative dissolution of UO induced by hydrogen peroxide (HO) and -ray irradiation. By comparing the reaction kinetics of HO between stoichiometric UO
and hyper-stoichiometric UO
, we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO reacted with HO much faster than the hyper-stoichiometric UO. The U dissolution from UO was initially much lower than that from UO, but gradually increased as the oxidation by HO proceeded. The -ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (0.2 mM) of HO. The exposure to higher HO concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by -ray irradiation.
Watanabe, Ritsuko*; Kai, Takeshi; Hattori, Yuya*
Radioisotopes, 66(11), p.525 - 530, 2017/11
To understand the mechanisms of radiation biological effects, modeling and simulation studies are important. In particular, simulation approach is powerful tool to evaluate modeling of mechanisms and the relationship among experimental results in different spatial scale of biological systems such as DNA molecular and cell. This article summarizes our approach to evaluate radiation action on DNA and cells by combination of knowledge in radiation physics, chemistry and biology. It contains newly theoretical approach to estimate physico-chemical process of DNA damage induction in addition to typical method of DNA damage prediction. Outline of the mathematical model for dynamics of DNA damage and cellular response is also presented.
Nagaishi, Ryuji
Radioisotopes, 66(11), p.601 - 610, 2017/11
no abstracts in English
Nagaishi, Ryuji; Morita, Keisuke; Yamagishi, Isao; Hino, Ryutaro; Ogawa, Toru
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
Two years after Three Mile Island Unit 2 (TMI-2) loss-of-coolant accident, radioactive contaminated water has been processed by Submerged Demineralizer System (SDS) with two types of zeolite adsorbents to remove radioactive nuclides. During and after the process, adsorption amount and distribution of nuclides on the zeolites, residual water content and thermal conductivity in the SDS vessels have been measured or estimated for verification of safety in the process, subsequent transportation and disposal. Hydrogen generation has been also evaluated mainly by direct monitoring in the large-scale of vessel after the process. In this work, the revaluation of hydrogen generation was demonstrated on the basis of the open information of vessel, and the latest experimental data obtained in adsorption and radiolysis occurring in small-scale of zeolite-water mixtures. As a result, the evaluated data was found to be comparable with the reported data obtained in the large-scale of real vessel.
Nagaishi, Ryuji; Inoue, Masao; Hino, Ryutaro; Ogawa, Toru
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
Since seawater has been used as a coolant for reactors and spent fuel pools in broken reactor buildings at Fukushima Daiichi NPS accident, radioactive contaminated water emitted following the accident has contained salt content of seawater at high concentrations, different from that at TMI-2 accident. Radiolysis of seawater leading to hydrogen generation and corrosion has been simulated and reported by several groups. However, the proposed radiolysis models cannot be always applied to water radiolysis at the wide range of salt concentrations present in the NPS, mainly because primary yields of radiolysis products of water and radiation-induced reactions are dependent on the salt concentration. In this study, the radiolytic behavior in diluted and concentrated systems of seawater was considered on the basis of results in steady state and pulse radiolysis experiments, in which the above salt effects were demonstrated from the obtained results.
Watanabe, Ritsuko; Saito, Kimiaki
Radiation Physics and Chemistry, 62(2-3), p.217 - 228, 2001/09
Times Cited Count：36 Percentile：90.76(Chemistry, Physical)no abstracts in English
Kobunshi, 10(111), p.526 - 530, 1961/00
no abstracts in English
rays irradiation, 3; Effects on depth of localized corrosionNakano, Junichi; Tsukada, Takashi; Ueno, Fumiyoshi; Yamagata, Ryohei
no journal, ,
In the Fukushima Daiichi Nuclear Power Station, it is considered that corrosion of primary containment vessel (PCV) and reactor pressure vessel (RPV) steels is accelerated by seawater injection and high radiation dose. In general, it is known that weight loss in steels increases near gas-liquid interface. Therefore, the lower half of the specimens was dipped in diluted seawater at 50
C under rays irradiation. Gas phase in flasks was air or N atmosphere. After the tests, oxide layer was removed and 3 dimension (3D) digital data were measured on the specimen surface using a 3D macro-scope. In air atmosphere, the maximum roughness height increased with time and dose rate. After rays irradiation for 500 h, the maximum roughness height in N atmosphere was lower than that in air atmosphere. Since O concentration in liquid was reduced by decrease of O partial pressure in gas phase, it was appeared that localized corrosion was suppressed.
Nakano, Junichi
no journal, ,
Seawater was injected into the reactor cores in the Fukushima Daiichi Nuclear Power Station (1F-NPP). Radiation dose is high in the primary containment vessels (PCVs) because of the fuel debris and the fission products. It is considered that corrosion of the reactor pressure vessels and the PCVs is accelerated by the products of water radiolysis. An amount of the injected seawater, temperature, radiation dose in the PCVs of the 1F-NPP and decommissioning plan are shown. Corrosion tests of low alloy steel and carbon steel under -rays irradiation conducted in the Japan Atomic Energy Agency are introduced. Uniform corrosion rates of the steels were hard to be accelerated remarkably in dose levels which were measured in the PCV of the 1F. Moreover, as a way of corrosion prevention, it was effective to have replaced the gaseous phase with N.
Kumagai, Yuta; Kimura, Atsushi; Taguchi, Mitsumasa
no journal, ,
Zeolite minerals are used for adsorption of radioactive cesium from water. After the water treatment, intense ionizing radiations would induce water radiolysis in the zeolite pores to produce hydrogen (H) and hydrogen peroxide (HO). Hence the radiation effects on zeolite-water mixtures were studied. Production of H from a mixture of natural mordenite and seawater was measured. The measurement suggests that H was produced due to the irradiation of mordenite additionally to H from the direct water radiolysis. Then, the effect of oxygen (O) on H production from a mixture of X-type zeolite and water was investigated. Decrease in H production was observed in the presence of O. The decrease indicates an effect of O to inhibit the additional H from the zeolite. Moreover, radiation-induced reactions of HO in a mixture with Y-type zeolite were studied. HO was effectively decomposed by irradiation. The decomposition can be explained by a radiation-induced reaction of HO adsorbed on the zeolite. The results show that the radiation-induced reactions of molecules adsorbed on zeolites have a key role in the radiation effects on the zeolite-water mixtures.
Furukawahara, Ryo*; Ogawa, Toru; Inoue, Masao; Nagaishi, Ryuji
no journal, ,
no abstracts in English
Nagaishi, Ryuji; Kondo, Takafumi*; Godo, Masao*; Yoshida, Yoichi*; Inoue, Masao
no journal, ,
no abstracts in English
Nishimura, Yuki; Shimada, Taro; Takeda, Seiji
no journal, ,
no abstracts in English
Kai, Takeshi; Ogawa, Tatsuhiko; Abe, Shinichiro; Sato, Tatsuhiko
no journal, ,
In study of radiation interaction induced in small spatial region of nanoscale, it is important to reveal electron behavior below 1 keV and its energy deposition. However, current radiation transport simulation code PHITS cannot simulate precisely the behavior in the materials. To clear the question, we have developed track structure code, also have an implementation plan of the code into PHITS. We calculated the microscopic behavior of the electron in water by using the developed code. As the results, we could predict theoretically that the electron thermalization progress contemporaneously with formation of prehydrated electron against previous prediction. In this presentation, we report our outcomes obtained from the developed track structure code, future plan for and implementation of the code into the PHITS as well as the functional extension.
Kai, Takeshi
no journal, ,
It is impossible to analyze radiation interaction in nano-scale by using particle transport codes such as PHITS because the code cannot simulate microscopic behavior of low energy electrons. We have developed a dynamic Monte Carlo code which can simulate the behavior. In this presentation, we explain the calculation methods of electron collision cross section included in the code as well as the electron behavior in water. We also show the calculated results for a primary electron transport and secondary electrons deceleration. From the results, we perform DNA damage prediction involved in the low energy electrons. We found novel complex DNA damage mechanism which induces radiation biological effect such as cell death or mutation. We also present an implementation of the code into PHITS and future plans for the functional extension of PHITS.
Kai, Takeshi
no journal, ,
Particle transport codes such as PHITS can calculate energy deposition in living system, however, it is impossible to analyze radiation interaction in nano-scale because the codes cannot simulate microscopic behavior of low energy electrons. We have developed a simulation code which can simulate the behavior. In this presentation, we explain the calculation methods of electron collision cross section as well as the electron behavior in water. We also show the results for a primary electron transport and secondary electrons deceleration. From the results, we perform DNA damage prediction involved in the low energy electrons. We found novel complex DNA damage mechanism which induces radiation biological effect such as cell death or mutation. We also present an implementation of the code into PHITS and future plans for the functional extension of PHITS.
