JOPSS - Search Results

Search Results: Records 1-20 displayed on this page of 41

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Journal Articles

Nature of the physicochemical process in water photolysis uncovered by a computer simulation

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

https://doi.org/10.1063/5.0149333

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.

Journal Articles

Initial yield of hydrated electron production from water radiolysis based on first-principles calculation

Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*

RSC Advances (Internet), 13(11), p.7076 - 7086, 2023/03

https://doi.org/10.1039/D2RA07274B

Times Cited Count：3 Percentile：73.63(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.

Journal Articles

Uranium dissolution and uranyl peroxide formation by immersion of simulated fuel debris in aqueous H $_{2}$ O $_{2}$ solution

Kumagai, 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

https://doi.org/10.1080/00223131.2021.2023055

Times Cited Count：2 Percentile：48.47(Nuclear Science & Technology)

We investigated potential degradation of fuel debris caused by H $_{2}$ O $_{2}$ , 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 H $_{2}$ O $_{2}$ solution. Chemical analysis of the leaching solution showed that U dissolution was induced by H $_{2}$ O $_{2}$ . 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 H $_{2}$ O $_{2}$ 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 $_{2}$ improves the stability of fuel debris against H $_{2}$ O $_{2}$ reaction.

Journal Articles

Radiolysis effects, which should be taken into account for safe decommissioning of Fukushima-Daiichi Nuclear Power Station

Hata, Kuniki

Zairyo To Kankyo, 70(12), p.468 - 473, 2021/12

https://doi.org/10.3323/jcorr.70.468

In order to estimate corrosive environment in the contaminated water at Fukushima Daiichi Nuclear Power Station, effects of oxidants, such as H $_{2}$ O $_{2}$ , 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.

Journal Articles

Impact of stoichiometry on the mechanism and kinetics of oxidative dissolution of UO $_{2}$ induced by H $_{2}$ O $_{2}$ and -irradiation

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

Journal of Physical Chemistry C, 123(15), p.9919 - 9925, 2019/04

https://doi.org/10.1021/acs.jpcc.9b00862

Times Cited Count：20 Percentile：64.95(Chemistry, Physical)

Radiation-induced oxidative dissolution of uranium dioxide (UO $_{2}$ ) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO $_{2}$ stoichiometry on the oxidative dissolution of UO $_{2}$ induced by hydrogen peroxide (H $_{2}$ O $_{2}$ ) and -ray irradiation. By comparing the reaction kinetics of H $_{2}$ O $_{2}$ between stoichiometric UO $_{2.0}$ and hyper-stoichiometric UO $_{2.3}$ , we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO $_{2.0}$ reacted with H $_{2}$ O $_{2}$ much faster than the hyper-stoichiometric UO $_{2.3}$ . The U dissolution from UO $_{2.0}$ was initially much lower than that from UO $_{2.3}$ , but gradually increased as the oxidation by H $_{2}$ O $_{2}$ 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 H $_{2}$ O $_{2}$ . The exposure to higher H $_{2}$ O $_{2}$ concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by -ray irradiation.

Journal Articles

Modern Radiation Chemistry (Applications), 26; Evolution of water radiolysis studies for measures against post-severe accidents

Nagaishi, Ryuji

Radioisotopes, 66(11), p.601 - 610, 2017/11

https://doi.org/10.3769/radioisotopes.66.601

no abstracts in English

Journal Articles

Modern radiation chemistry (Applications), 16; Computer simulation study of initial process of radiation biological effect

Watanabe, Ritsuko*; Kai, Takeshi; Hattori, Yuya*

Radioisotopes, 66(11), p.525 - 530, 2017/11

https://doi.org/10.3769/radioisotopes.66.525

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.

Journal Articles

Revaluation of hydrogen generation by water radiolysis in SDS vessels at TMI-2 accident

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

BB2014-1745.pdf:0.92MB

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.

Journal Articles

Consideration of radiolytic behavior in diluted and concentrated systems of seawater for computational simulation of hydrogen generation

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.

Journal Articles

Monte Carlo simulation of water radiolysis in oxygenated condition for monoenergetic electrons from 100eV to 1MeV

Watanabe, Ritsuko; Saito, Kimiaki

Radiation Physics and Chemistry, 62(2-3), p.217 - 228, 2001/09

https://doi.org/10.1016/S0969-806X(01)00195-5

Times Cited Count：36 Percentile：90.68(Chemistry, Physical)

no abstracts in English

Journal Articles

Radiation effect of polymers and the effect of water

Kobunshi, 10(111), p.526 - 530, 1961/00

http://ci.nii.ac.jp/naid/40017777729

no abstracts in English

Oral presentation

H $_{2}$ O $_{2}$ and -ray induced oxidative dissolution of stoichiometric UO $_{2.0}$

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

no journal, ,

We have investigated the effect of UO $_{2}$ -hyper-stoichiometry on the oxidative dissolution upon H $_{2}$ O $_{2}$ exposure and by water radiolysis. The oxidative dissolution of UO $_{2}$ is anticipated in the concept of geological disposal of spent nuclear fuel and also in the direct contact with coolant water after a severe accident. However, our understanding on the dissolution kinetics has so far not taken the hyper-stoichiometric nature of UO $_{2}$ into account. Thus, we have studied the oxidative dissolution of hyper-stoichiometric UO $_{2.3}$ and stoichiometric UO $_{2.0}$ and compared the results. The results show that the UO $_{2}$ stoichiometry largely affects the kinetics of oxidative dissolution. The oxidation of stoichiometric UO $_{2.0}$ in water proceeded fast accompanied with low initial U dissolution, but gradually the reaction became slower and U dissolution became more significant.

Oral presentation

Measurement of hydrogen generation in water radiolysis by low-penetrating radiations

Nagaishi, Ryuji; Kuwano, Ryo*; Matsumura, Taichi

no journal, ,

High-penetrating gamma-rays (Co-60) have been mainly used as an external radiation in irradiation experiments on water radiolysis for the 1F decommissioning, while the experiments using electron beams (EB) simulating beta-rays (Sr-90 and others) and X-rays simulating the bremsstrahlung of electrons have been also expected. However these are difficult because of the low-penetrating property of radiations. In this study, the experiments using EB and X-rays were conducted by using reaction vessels sealed with films having a good penetrating property for their radiations to measure H $_{2}$ and its geminate product of H $_{2}$ O $_{2}$ as radiolysis products of water.

Oral presentation

Water radiolysis in decommissioning environment at Fukushima Daiichi Nuclear Power Sation

Hata, Kuniki

no journal, ,

no abstracts in English

Oral presentation

Radiation-induced dissolution of uranium oxide materials in water

Kumagai, Yuta

no journal, ,

Uranium oxides in contact with water dissolves when exposed to ionizing radiation. The dissolution is induced by oxidation due to products of the water radiolysis such as hydrogen peroxide. This oxidative dissolution process has particular importance in deep geological disposal of spent nuclear fuels, because it dominates the release of radionuclides from the UO $_{2}$ fuel matrix to the underground environment. Similarly, the uranium oxidation is expected to have a key role in long-term degradation of fuel debris generated in severe accidents in nuclear power plants. Here, our recent studies of radiation-induced dissolution of UO $_{2}$ and also (U, Zr)O $_{2}$ , which is one of typical solid phase found in the fuel debris will be reported.

Oral presentation

Investigation on the temperature dependence of G value of H $_{2}$ in Reprocessing Solutions, 5; Experimental apparatus and its validation test for measuring radiolytic H $_{2}$ production from aqueous plutonium nitrate solution

Kumagai, Yuta; Oyama, Kanichi*; Sato, Tomonori; Ishijima, Yasuhiro; Taguchi, Mitsumasa*; Watanabe, Masayuki; Abe, Yuma; Nakano, Masanao*; Tamauchi, Yoshikazu*

no journal, ,

Radiolysis of water generates H $_{2}$ gas. The radiolytic H $_{2}$ production inevitably goes on when an aqueous solution contains radioactive nuclides such as plutonium nitrate solution in the nuclear fuel reprocessing. In order to obtain experimental data for the H $_{2}$ safety assessment, we carried our measurements of H $_{2}$ production from the aqueous plutonium nitrate solution at elevated temperatures. In this presentation, we will talk about experimental apparatus and results of a validation test of the apparatus using Co-60 gamma source.

Oral presentation

The Effects of hydrogen addition on the corrosive conditions of PWR primary coolant under irradiation, 9; Combind analysis of water radiolysis and ECP

Uchida, Shunsuke; Hata, Kuniki; Hanawa, Satoshi; Chimi, Yasuhiro; Sato, Tomonori

no journal, ,

A radiolysis and ECP combined code, WRAC-J, could obtain ECP calculation based on the empirical polarization curve. Newly developed WRAC-JAEA has consisted of (1) calculation of high temperature pH, (2) water radiolysis calculation, and (3) ECP calculation based on the anodic polarization curves of SS and Ni based alloys with involving oxide layer effects and the polarization curves of radilytic species, and then, it can calculate ECP based on plant operational conditions. By applying the WRAC-JAEA, radiolytic species concentrations are calculated based on plant operational conditions, radiation dose rate, pH, ECP is calculated based on the their concentrations direct effects of alkali metal ions, e.g., Li $^{+}$ , and then, the corrosive conditions in BWRs and PWRs are evaluated.

Oral presentation

The Effects of hydrogen addition on the corrosive conditions of PWR primary coolant under irradiation, 8; Evaluation of the effects of OH + H $_{2}$ = H + H $_{2}$ O reaction and its back reaction on water radiolysis

Hata, Kuniki; Uchida, Shunsuke; Hanawa, Satoshi; Chimi, Yasuhiro; Sato, Tomonori

no journal, ,

no abstracts in English

Oral presentation

Formation of a protective layer on (U, Zr)O $_{2}$ by the reaction of H $_{2}$ O $_{2}$

Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki

no journal, ,

A severe accident of a nuclear power plant generates fuel debris due to high-temperature reactions between nuclear fuel with surrounding materials. An oxide solid solution of U and Zr, i.e. (U, Zr)O $_{2}$ is a typical phase of the fuel debris. The decommission of a damaged reactor requires a long-term effort and therefore it is important to estimate possible degradation processes of the fuel debris for safe operation of the decommissioning. Hence, we have investigated reaction of (U, Zr)O $_{2}$ with H $_{2}$ O $_{2}$ because H $_{2}$ O $_{2}$ produced by water radiolysis may cause oxidative degradation of the fuel debris. H $_{2}$ O $_{2}$ reaction with (U, Zr)O $_{2}$ powder induced dissolution of U and Zr. The dissolution of U was more significant than that of Zr. The results indicate that a Zr-rich layer formed on the (U, Zr)O $_{2}$ surface. The repeated reactions with H $_{2}$ O $_{2}$ resulted in a remarkable decrease in the dissolution of U. Therefore, the formation of the Zr-rich layer is expected to inhibit the further U dissolution.

Oral presentation

H $_{2}$ O $_{2}$ -induced oxidative degradation of simulated fuel debris

Kumagai, Yuta

no journal, ,

We have been studying chemical durability of fuel debris generated during the accident at TEPCO's Fukushima Daiichi Nuclear Power Plants, in order to provide basic understanding of the fuel debris for safe retrieval and subsequent treatment and storage. The fuel debris remains in the reactors in contact with water and under the action of ionizing radiation. The radiolysis of water produces oxidants, such as hydrogen peroxide. Under such conditions, the degradation of the fuel debris matrix due to the oxidation by hydrogen peroxide is anticipated. Thus, we have carried out experiments on the oxidative degradation using simulated fuel debris samples, investigated dissolution of metal elements from the samples and formation of altered phases on the sample surface.