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Journal Articles

Zeolite-assisted radiolysis of aromatic chlorides mitigating influence of coexisting ions in water matrix

Kumagai, Yuta; Kimura, Atsushi*; Taguchi, Mitsumasa*; Watanabe, Masayuki

Radiation Physics and Chemistry, 191, p.109831_1 - 109831_8, 2022/02

In this study, we investigated and compared the effects of a high-silica zeolite (HMOR) on the radiation-induced degradation of three aromatic chlorides, 2-chlorophenol (2-ClPh), 2-chloroaniline (2-ClAn), and 2-chlorobenzoic acid (2-ClBA), in order to examine its potential to reduce the influence of ions in water matrix in the irradiation treatment of water-soluble organic compounds. In the presence of ions reactive to radicals, the degradation of 2-ClPh in water was inhibited, but the combined use of HMOR much improved the degradation yield. This improvement was attributed to high performance of HMOR in adsorption of 2-ClPh. Similarly, HMOR was effective for adsorption of 2-ClAn and facilitated the 2-ClAn degradation by irradiation. In contrast, HMOR was poor at adsorption of 2-ClBA and consistently the degradation of 2-ClBA in the water-HMOR mixture was inhibited by the radical scavenger. These results demonstrate that HMOR can mitigate the influence of radical scavengers in water.

Journal Articles

The Kinetics and mechanism of H$$_{2}$$O$$_{2}$$ decomposition at the U$$_{3}$$O$$_{8}$$ surface in bicarbonate solution

McGrady, J.; Kumagai, Yuta; Watanabe, Masayuki; Kirishima, Akira*; Akiyama, Daisuke*; Kitamura, Akira; Kimuro, Shingo

RSC Advances (Internet), 11(46), p.28940 - 28948, 2021/08

 Times Cited Count:0

Journal Articles

Distribution of studtite and metastudtite generated on the surface of U$$_{3}$$O$$_{8}$$; Application of Raman imaging technique to uranium compound

Kusaka, Ryoji; Kumagai, Yuta; Yomogida, Takumi; Takano, Masahide; Watanabe, Masayuki; Sasaki, Takayuki*; Akiyama, Daisuke*; Sato, Nobuaki*; Kirishima, Akira*

Journal of Nuclear Science and Technology, 58(6), p.629 - 634, 2021/06

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Radiation-induced effects on the extraction properties of hexa-$$n$$-octylnitrilo-triacetamide (HONTA) complexes of americium and europium

Toigawa, Tomohiro; Peterman, D. R.*; Meeker, D. S.*; Grimes, T. S.*; Zalupski, P. R.*; Mezyk, S. P.*; Cook, A. R.*; Yamashita, Shinichi*; Kumagai, Yuta; Matsumura, Tatsuro; et al.

Physical Chemistry Chemical Physics, 23(2), p.1343 - 1351, 2021/01

 Times Cited Count:1 Percentile:70.6(Chemistry, Physical)

The candidate An(III)/Ln(III) separation ligand hexa-$$n$$-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions using a solvent test loop in conjunction with cobalt-60 gamma irradiation. We demonstrate that HONTA undergoes exponential decay with increasing gamma dose to produce a range of degradation products which have been identified and quantified by HPLC-ESI-MS/MS techniques. The combination of HONTA destruction and degradation product ingrowth, particularly dioctylamine, negatively impacts the extraction and back-extraction of both americium and europium ions. The loss of HONTA was attributed to its reaction with the solvent (${it n}$-dodecane) radical cation of ${it k}$(HONTA + R$$^{.+}$$) = (7.61 $$pm$$ 0.82) $$times$$ 10$$^{9}$$ M$$^{-1}$$ s$$^{-1}$$ obtained by pulse radiolysis techniques. However, when this ligand is bound to either americium or europium ions, the observed ${it n}$-dodecane radical cation kinetics increase by over an order of magnitude. This large reactivity increase to additional reaction pathways occurring upon metal-ion binding. Lastly nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived ($$<$$100 ns) HONTA radical cation as well as a longer-lived ($$mu$$s) HONTA triplet excited state. These HONTA species are important precursors to the suite of HONTA degradation products observed.

Journal Articles

Re-evaluation of radiation-energy transfer to an extraction solvent in a minor-actinide-separation process based on consideration of radiation permeability

Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Furuta, Takuya; Kumagai, Yuta; Matsumura, Tatsuro

Solvent Extraction and Ion Exchange, 39(1), p.74 - 89, 2021/00

 Times Cited Count:0 Percentile:0(Chemistry, Multidisciplinary)

Absorbed-dose estimation is essential for evaluation of the radiation feasibility of minor-actinide-separation processes. We propose a dose-evaluation method based on radiation permeability, with comparisons of heterogeneous structures seen in the solvent-extraction process, such as emulsions forming in the mixture of the organic and aqueous phases. A demonstration of radiation-energy-transfer simulation is performed with a focus on the minor-actinide-recovery process from high-level liquid waste with the aid of the Monte Carlo radiation-transport code PHITS. The simulation results indicate that the dose absorbed by the extraction solvent from alpha ray depends upon the emulsion structure, and that from beta and gamma ray depends upon the mixer-settler-apparatus size. Non-negligible contributions of well-permeable gamma rays were indicated in terms of the plant operation of the minor-actinide-separation process.

Journal Articles

Study on the mechanism of radiolytic degradation of an extractant for minor actinides separation

Toigawa, Tomohiro; Murayama, Rin*; Kumagai, Yuta; Yamashita, Shinichi*; Suzuki, Hideya; Ban, Yasutoshi; Matsumura, Tatsuro

UTNL-R-0501, p.24 - 25, 2020/12

This report summarizes the results obtained in FY2019 at Electron Linac Facility of University of Tokyo. The radiolysis process of a diglycolamide extractant, which is expected to be used in the separation process of minor actinides (MA), in dodecane and octanol solutions was investigated by pulse radiolysis. As a result, it was suggested that by adding alcohol, the decomposition process of the diglycolamide extractant was different from the decomposition processes in the single solvent of dodecane considered that the decomposition occurred via a radical cation species of the extractant.

Journal Articles

Spectroscopic studies of M$"o$ssbauer, infrared, and laser-induced luminescence for classifying rare-earth minerals enriched in iron-rich deposits

Aoyagi, Noboru; Nguyen, T. T.*; Kumagai, Yuta; Nguyen, T. V.*; Nakada, Masami; Segawa, Yukari; Nguyen, H. T.*; Le, B. T.*

ACS Omega (Internet), 5(13), p.7096 - 7105, 2020/04

 Times Cited Count:1 Percentile:21.55(Chemistry, Multidisciplinary)

Journal Articles

$$gamma$$-radiation and H$$_{2}$$O$$_{2}$$ induced oxidative dissolution of uranium(IV) oxide in aqueous solution containing phthalic acid

Kumagai, Yuta; Jonsson, M.*

Dalton Transactions (Internet), 49(6), p.1907 - 1914, 2020/02

 Times Cited Count:0 Percentile:0.01(Chemistry, Inorganic & Nuclear)

This study aims to reveal possible involvements of organic acids in the oxidative dissolution of UO$$_{2}$$. Using phthalic acid as a model compound, we have measured adsorption on UO$$_{2}$$ and investigated effects on the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$ and on oxidative dissolution induced by $$gamma$$-irradiation. Significant adsorption of phthalic acid was observed even at neutral pH. However, the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$ in phthalic acid solution induced oxidative dissolution of U(VI) similarly to aqueous bicarbonate solution. These results indicate that even though phthalic acid adsorbs on the UO$$_{2}$$ surface, it is not involved in the interfacial reaction by H$$_{2}$$O$$_{2}$$. In contrast, the dissolution of U by irradiation was inhibited in aqueous phthalic acid solution, whereas H$$_{2}$$O$$_{2}$$ generated by radiolysis was consumed by UO$$_{2}$$. The inhibition suggests that radical species derived from phthalic acid was involved in the redox reaction process of UO$$_{2}$$.

Journal Articles

Effect of H$$_{2}$$O$$_{2}$$ concentration on oxidative dissolution of U$$_{2}$$O

Kumagai, Yuta

Hoshasen Kagaku (Internet), (107), p.77 - 78, 2019/04

Reaction of hydrogen peroxide (H$$_{2}$$O$$_{2}$$) with uranium dioxide (UO$$_{2}$$) oxidizes U(IV) to water-soluble U(VI). In the concept of direct geological disposal of spent nuclear fuel, this reaction is expected to induce dissolution of UO$$_{2}$$ matrix of the spent fuel. This study investigate effect of H$$_{2}$$O$$_{2}$$ concentration on the kinetics and the yield of U(VI) dissolution of this reaction. A series of experiments of the reaction of H$$_{2}$$O$$_{2}$$ with UO$$_{2}$$ powder dispersed in water has been carried out. The experimental results reveal that increase in the H$$_{2}$$O$$_{2}$$ concentration slows down the reaction and decreases the yield of U(VI) dissolution. This observation suggests that a reaction intermediate is generated in the course of the H$$_{2}$$O$$_{2}$$ reaction on the surface of UO$$_{2}$$.

Journal Articles

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

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

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

 Times Cited Count:8 Percentile:50.98(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 $$gamma$$-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 $$gamma$$-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 $$gamma$$-ray irradiation.

Journal Articles

The Role of surface-bound hydroxyl radicals in the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$

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

Journal of Coordination Chemistry, 71(11-13), p.1799 - 1807, 2018/07

 Times Cited Count:18 Percentile:85.67(Chemistry, Inorganic & Nuclear)

In this work, we have studied the reaction between H$$_{2}$$O$$_{2}$$ and UO$$_{2}$$ with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of the reaction at different initial H$$_{2}$$O$$_{2}$$ concentrations. The results show that the consumption rates at a given H$$_{2}$$O$$_{2}$$ concentration are different depending on the initial H$$_{2}$$O$$_{2}$$ concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The U dissolution yield decreases with increasing initial H$$_{2}$$O$$_{2}$$ concentration. This is expected from the mechanism of catalytic decomposition of H$$_{2}$$O$$_{2}$$ on oxide surfaces. As the experiments were performed in solutions containing 10 mM and a strong concentration dependence was observed in the 0.2 - 2.0 mM H$$_{2}$$O$$_{2}$$ concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.

Journal Articles

Radiation-induced degradation of aqueous 2-chlorophenol assisted by zeolites

Kumagai, Yuta; Kimura, Atsushi*; Taguchi, Mitsumasa*; Watanabe, Masayuki

Journal of Radioanalytical and Nuclear Chemistry, 316(1), p.341 - 348, 2018/04

 Times Cited Count:1 Percentile:17.98(Chemistry, Analytical)

We studied effect of adsorption and condensation by zeolites on radiation-induced degradation of aqueous 2-chlorophenol (2-ClPh). This study aims to demonstrate that the solid-phase extraction using zeolites has potential advantage in treatments of aqueous organic pollutants. Among three zeolites examined in this study, a mordenite type zeolite (HMOR) that has a high Si to Al ratio (127 $$pm$$ 3) exhibited preferable performance as the matrix for the 2-ClPh degradation. HMOR adsorbed far more 2-ClPh than the other zeolites, which have lower Si/Al ratios. The irradiation of HMOR induced degradation of adsorbed 2-ClPh into Cl$$^{-}$$ and organic by-products. We found a significant increase in Cl$$^{-}$$ production by HMOR. The yield of Cl$$^{-}$$ production in the presence of HMOR was as high as the yield in aqueous solution of 2-ClPh at a concentration 10 times higher. The increased Cl$$^{-}$$ production indicates that the high concentration of adsorbed 2-ClPh led to effective use of the adsorbed energy of HMOR.

Journal Articles

Treatment of pharmaceuticals/antibiotics in wastewater by combination of zeolite adsorbent with ionizing radiation

Taguchi, Mitsumasa*; Kumagai, Yuta; Kimura, Atsushi*

IAEA-TECDOC-1855, p.106 - 116, 2018/00

The technology for the decomposition of trace amounts of halogenated pharmaceuticals/antibiotics was developed in wastewater by use of the combination method of zeolite adsorbent and ionizing radiation. HMOR, a hydrophobic high-silica mordenite-type zeolite, was employed to concentrate 2-chlorophenol (2-ClPh) as a simple model of halogenated pharmaceuticals/antibiotics. HMOR adsorbed above 99% of 2-ClPh from dilute aqueous solutions. The yield of Cl$$^{-}$$ production in HMOR mixture corresponded to the aqueous solution containing 10 fold higher concentration of dissolved 2-ClPh. Clofibrate and triclosan, one of chlorinated pharmaceuticals/antibiotics, in real wastewater were treated by use of the combination method of HMOR and ionizing radiation. Production yield of Cl$$^{-}$$ by use of the adsorbent was about twice higher than that in aqueous solution, and HMOR was contributed for effective reduction of chlorinated pharmaceuticals/antibiotics in real wastewater.

Journal Articles

Reaction of hydrogen peroxide with uranium zirconium oxide solid solution; Zirconium hinders oxidative uranium dissolution

Kumagai, Yuta; Takano, Masahide; Watanabe, Masayuki

Journal of Nuclear Materials, 497, p.54 - 59, 2017/12

 Times Cited Count:4 Percentile:40.62(Materials Science, Multidisciplinary)

We studied oxidative dissolution of uranium and zirconium oxide [(U,Zr)O$$_{2}$$] in aqueous H$$_{2}$$O$$_{2}$$ solution. The interfacial reaction is essential for anticipating how a (U,Zr)O$$_{2}$$-based molten fuel may chemically degrade after a severe accident under influence of ionizing radiation. We conducted our experiments with (U,Zr)O$$_{2}$$ powder and quantitated the H$$_{2}$$O$$_{2}$$ reaction via dissolved U and H$$_{2}$$O$$_{2}$$ concentrations. The dissolution yield relative to H$$_{2}$$O$$_{2}$$ consumption was far less for (U,Zr)O$$_{2}$$ compared to that of UO$$_{2}$$. The reaction kinetics indicates that most of the H$$_{2}$$O$$_{2}$$ catalytically decomposed to O$$_{2}$$ at the surface of (U,Zr)O$$_{2}$$. We confirmed the H$$_{2}$$O$$_{2}$$ catalytic decomposition via O$$_{2}$$ production (quantitative stoichiometric agreement). In addition, post-reaction Raman scattering spectra of the undissolved (U,Zr)O$$_{2}$$ showed no additional peaks (indicating a lack of secondary phase formation). The (U,Zr)O$$_{2}$$ matrix is much more stable than UO$$_{2}$$ against H$$_{2}$$O$$_{2}$$-induced oxidative dissolution.

Journal Articles

Modern radiation chemistry (Applications), 18; Radiation chemistry at solid/water interfaces

Kumagai, Yuta

Radioisotopes, 66(11), p.537 - 541, 2017/11

Radiation effects on the mixtures of inorganic oxides and water have been investigated for understanding radiation chemistry in solid-liquid systems. A number of studies revealed that energy deposition on solid phase stimulates reactions at the interface. This energy/charge transfer has been demonstrated by experiments to affect early stage of the radiation-induced reaction. However, the interfacial reactions subsequent to the energy/charge transfer require further studies. Here, we will see gaps between the basic understanding on the early stage and radiation effects in solid-liquid systems connected to applications, taking zeolite/water and uranium oxide/water interfaces for examples. Understanding of the interfacial reactions subsequent to the energy/charge transfer would bridge the gaps and enable to predict the radiation effects in applications.

Journal Articles

Hydrogen production by $$gamma$$-ray irradiation from different types of zeolites in aqueous solution

Kumagai, Yuta; Kimura, Atsushi*; Taguchi, Mitsumasa*; Watanabe, Masayuki

Journal of Physical Chemistry C, 121(34), p.18525 - 18533, 2017/08

 Times Cited Count:3 Percentile:17.05(Chemistry, Physical)

H$$_{2}$$ production by irradiation of zeolite-water mixtures was studied, to investigate effect of zeolites in the reaction process for H$$_{2}$$. Four different types of zeolites were examined comparatively under anoxic and under aerated conditions. High production yields of H$$_{2}$$ were observed for the zeolites of high Al contents at low water fraction and under anoxic condition, compared to zeolites having lower Al contents. A comparison of the H$$_{2}$$ yields in connection with chemical analysis of the zeolites suggests that extraframework Al species in the zeolites are involved in a reaction pathway for H$$_{2}$$. Meanwhile, under aerated condition and at high mixing ratio of water, the difference in H$$_{2}$$ yield among the zeolites was suppressed and the yields of H$$_{2}$$ were lower than those under anoxic condition probably due to H$$_{2}$$O$$_{2}$$ produced by water radiolysis. The comparable H$$_{2}$$ yields suggest another reaction pathway for H$$_{2}$$ which is less dependent on the structure and composition of the zeolites.

JAEA Reports

Preliminary missions for the decommissioning of the laboratory building No.1 for the plutonium research program

Segawa, Yukari; Horita, Takuma; Kitatsuji, Yoshihiro; Kumagai, Yuta; Aoyagi, Noboru; Nakada, Masami; Otobe, Haruyoshi; Tamura, Yukito*; Okamoto, Hisato; Otomo, Takashi; et al.

JAEA-Technology 2016-039, 64 Pages, 2017/03

JAEA-Technology-2016-039.pdf:5.24MB

The laboratory building No.1 for the plutonium research program (Bldg. Pu1) was chosen as one of the facilities to decommission by Japan Atomic Energy Agency Reform in September, 2013. The research groups, users of Bldg. Pu1, were driven by necessity to remove used equipment and transport nuclear fuel to other facilities from Bldg. Pu1. Research Group for Radiochemistry proactively established the Used Equipment Removal Team for the smooth operation of the removal in April, 2015. The team classified six types of work into the nature of the operation, removal of used equipment, disposal of chemicals, stabilization of mercury, stabilization of nuclear fuel, transportation of nuclear fuel and radioisotope, and survey of contamination status inside the glove boxes. These works were completed in December, 2015. This report circumstantially shows six works process, with the exception of the approval of the changes on the usage of nuclear fuel in Bldg. Pu1 to help prospective decommission.

Journal Articles

Degradation of 2-chlorophenol by $$gamma$$-ray irradiation in zeolite/water mixtures

Kumagai, Yuta

Hoshasen Kagaku (Internet), (99), p.53 - 56, 2015/04

Radiation-induced degradation of 2-chlorophenol (2-ClPh) in zeolite/water mixtures was studied in order to consider a possibility of adsorption on zeolites to improve efficiencies of irradiation treatments of water contaminated by organic compounds. The degradation of 2-ClPh by $$gamma$$-ray irradiation was investigated as a model compound. The degradation was evaluated by chloride ion (Cl$$^{-}$$) production. A high concentration of Cl$$^{-}$$ was observed after the irradiation of a mixture with a mordenite-type zeolite (NaMOR), whereas A-type and X-type zeolites showed no significant effect. Therefore, for the mixture with NaMOR, effects of pH of the solution and of the 2-ClPh concentration were examined. At pH 5.7, the excess production of Cl$$^{-}$$ was induced by the addition of NaMOR. Concurrently, adsorption of 2-ClPh on NaMOR was observed. When the mixture contained a higher concentration of 2-ClPh at pH 5.7, the Cl$$^{-}$$ production increased. The adsorption of 2-ClPh also increased with increasing concentration. The results suggest that organics adsorbed on zeolites are decomposed by irradiation effectively at high adsorption concentrations.

Journal Articles

Effect of oxygen on radiolytic hydrogen production from X-type zeolite-water mixtures

Kumagai, Yuta; Kimura, Atsushi; Taguchi, Mitsumasa

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

Journal Articles

Decomposition of hydrogen peroxide by $$gamma$$-ray irradiation in mixture of aqueous solution and Y-type zeolite

Kumagai, Yuta

Radiation Physics and Chemistry, 97, p.223 - 232, 2014/04

 Times Cited Count:2 Percentile:19.81(Chemistry, Physical)

156 (Records 1-20 displayed on this page)