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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

A Significant role of non-thermal equilibrated electrons in the formation of deleterious complex DNA damage

Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Toigawa, Tomohiro; Watanabe, Ritsuko*

Physical Chemistry Chemical Physics, 20(4), p.2838 - 2844, 2018/01

 Times Cited Count:11 Percentile:69.76(Chemistry, Physical)

It is thought that complex DNA damage which induces in radiation biological effects is formed at radiation track end. Thus, the earliest stage of water radiolysis at the electron track end was studied to predict DNA damage. These results indicate that DNA damage sites comprising multiple nucleobase lesions with a single strand breaks can therefore be formed by multiple collisions of the electrons within three base pairs (3bp) of a DNA strand. This multiple damage site cannot be processed by base excision repair enzymes. However, pre-hydrated electrons can also be produced resulting in an additional base lesion more than 3bp away from the multi-damage site. This clustered damage site may be finally converted into a double strand break (DSB) when base excision enzymes process the additional base lesions. These DSBs include another base lesion(s) at their termini that escape from the base excision process and which may result in biological effects such as mutation in surviving cells.

Oral presentation

Earliest process of water radiolysis at the electron track end

Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yonetani, Yoshiteru*; Toigawa, Tomohiro; Sato, Tatsuhiko

no journal, , 

It is very important to study water radiolysis by electrons because the study are applied to fields involved in atomic industry and radiotherapy, the study is also useful to predict radiation damage to DNA in a living cell. In this study, we calculated deceleration process of secondary electrons produced by ionization at a primary electron track end, at which a primary and secondary electrons densely deposit those energies to water, to understand the earliest process of water radiolysis. From the results, the secondary electrons distributed 10 nm from parent cations at 300 fs, and the mean energy of the electrons reached 0.7 eV. At this timescale, we indicated that the energy distribution shows the non-equilibrium state strongly, and fraction of the electrons energy below 0.1 eV is more than 10$$%$$. The results may indicate a new insight of the formation of prehydrated electrons due to the extremely low energy electrons.

Oral presentation

Absorbed dose estimation for minor actinides separation process as a function of linear energy transfer

Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Kimura, Takahiro; Matsumura, Tatsuro

no journal, , 

To evaluate the feasibility of the solvent extraction process, absorbed dose of each quality of radiation for extraction solvents were estimated by using a Monte Carlo Particle and Heavy Ion Transport code System, PHITS. Our results suggest that low LET radiation will be dominant influence on absorbed dose. It was demonstrated the degradation yields of the extractants and the generation yields of the degradation products could be evaluated by reference to the experimentally obtained G-values.

Oral presentation

Current status of R&D of MA separation processes for P&T technology

Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Toigawa, Tomohiro; Tsutsui, Nao; Hotoku, Shinobu; Suzuki, Asuka

no journal, , 

no abstracts in English

Oral presentation

Study of radiolysis of HONTA extractant for MA/Ln separation

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho; Matsumura, Tatsuro

no journal, , 

Degradation of extractants and generation of radiolytic products are considered as problem for feasibility of the minor actinides separation process. In this study, degradation amount of hexaoctyl-nitrilotriacetamide (HONTA), which is a candidate extaractant for MA/Ln separation, and its products yields were obtained by using $$gamma$$-rays emitted from Co-60. Our results showed the cleavage sites in HONTA radiolysis and suggest that the mechanism for HONTA radiolysis is differ depending on the absorbed dose.

Oral presentation

Radiolysis of HONTA extractant for MA/RE separation

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro

no journal, , 

R&D on partitioning process of the minor actinides (MA) from high level liquid waste (HLLW) were carried out for reduction of the strain on the radioactive wastes disposal. In this study, degradation amount of hexaoctyl-nitrilotriacetamide (HONTA), which is a candidate extaractant for MA/RE separation, and its products yields were obtained by using $$gamma$$-rays emitted from Co-60. Our results showed the cleavage sites in HONTA radiolysis and suggest that the mechanism for HONTA radiolysis is differ depending on the absorbed dose.

Oral presentation

Continuous extraction and separation of Am$$^{3+}$$ and Cm$$^{3+}$$ using a high-performance ligand

Suzuki, Hideya; Tsubata, Yasuhiro; Toigawa, Tomohiro; Matsumura, Tatsuro

no journal, , 

The separation of minor actinide (MA) from HLLW is an important task in the partitioning and transmutation. After MA are separated from HLLW, the mutual separation of Am$$^{3+}$$ and Cm$$^{3+}$$ (Am/Cm separation) can be conducted. A highly practical reagent, called alkyl diamide amine (ADAAM), was developed. ADAAM gives the maximum separation factor up to 5.5. A continuous extraction test was conducted using a multistage countercurrent mixer-settler extractor with ADAAM in n-dodecane. Separation of Am and Cm was demonstrated in very high yield.

Oral presentation

Current status of R&D on reprocessing and minor actinide separation process with CHON ligands in JAEA

Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Hotoku, Shinobu; Tsutsui, Nao; Suzuki, Asuka; Toigawa, Tomohiro; Kurosawa, Tatsuya*; Shibata, Mitsunobu*; et al.

no journal, , 

PUREX process was established for industrial scale reprocessing plant. TRUEX and the 4 group separation were developed for partitioning of minor actinides from HLW, and demonstrated using genuine HLW. Although the extractants for the processes have excellent performance, the molecules contain phosphorus which could be cause for the secondary waste from the solvent extraction processes. To minimize the radioactive waste, we have conducted research and development of the new reprocessing and MA separation processes using innovative extractants in accord with CHON principle. The extractants for reprocessing process are monoamides as alternative extractants for TBP. For An(III)+RE recovery process, we developed TDdDGA. HONTA and ADAAM were developed for An(III)/RE separation process and Am/Cm separation process respectively. The separation performances of the flowsheets were evaluated by continuous extraction tests using simulated and genuine spent fuel and high level liquid waste.

Oral presentation

Dynamic behavior of electrons deposited energy in water

Kai, Takeshi; Toigawa, Tomohiro; Ukai, Masatoshi*; Fujii, Kentaro*; Watanabe, Ritsuko*; Yokoya, Akinari*

no journal, , 

Fundamental studies of water radiolysis by radiation and laser irradiation are applied to atomic industry, and provide useful fundamental insights to understanding of radiation DNA damage. We developed a code to simulate dynamic behavior of electrons produced in water by energy deposition at energies, also performed theoretical study for the behaviors. The spatial probability distributions of the electrons depend on the deposition energies, also show the exponential or Gaussian types. We also show calculated results of energy probability distributions of the electrons. We found that the distributions below 100 meV are gradually close to Maxwell distribution with the temporal evolution, while the distributions above 100 meV not depend on the temporal evolution due to effect of Coulombic field of the parent cation. The findings provide significant insights to a connection radiation physics and radiation chemistry.

Oral presentation

Simulation on energy transfer to extraction solvent during MA separation process

Toigawa, Tomohiro; Tsubata, Yasuhiro; Kai, Takeshi; Kimura, Takahiro; Ban, Yasutoshi; Suzuki, Hideya; Tsutsui, Nao; Hotoku, Shinobu; Matsumura, Tatsuro

no journal, , 

To evaluate the radiation Stability of the extraction agent applied to the solvent extraction process, energy transfer process to extraction solvent was estimated by using a Monte Carlo Particle and Heavy Ion Transport code System, PHITS. Our results suggest that low LET radiation will be dominant influence on absorbed dose. It was demonstrated the degradation yields of the extractant could be evaluated by reference to the experimentally obtained G-values.

Oral presentation

Influence of $$gamma$$-radiolysis of MA separation agent of HONTA on extraction performance

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro

no journal, , 

To evaluate the radiolytic stability of a novel tetradentate extractant of N, N, N', N', N", N"-hexaoctyl-nitrilotriacetamide (HONTA), batch extractions of lanthanide (Ln) elements were performed by using $$gamma$$-irradiated HONTA extraction solvents. The distribution ratios decreased exponentially with increasing the absorbed dose, and no difference between Ln could be observed. These indicate that the degradation products of HONTA did not act as Ln extractants, and the decay of Ln extraction were caused by degradation of HONTA.

Oral presentation

Influence of $$gamma$$-radiolysis of a minor actinide extractnt on lanthanides extraction

Toigawa, Tomohiro; Suzuki, Hideya; Ishii, Sho*; Tsutsui, Nao; Ban, Yasutoshi; Matsumura, Tatsuro

no journal, , 

To evaluate the radiolytic stability of an extractant agents for minor actinides such as N, N, N', N', N", N"-hexaoctyl-nitrilotriacetamide (HONTA), batch extractions of lanthanide (Ln) elements were performed by using $$gamma$$-irradiated extraction solvents. The distribution ratios decreased exponentially with increasing the absorbed dose, and no initial decrease could be observed.

Oral presentation

Solvent extraction process for reprocessing and minor actinides separation using CHON ligands

Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Hotoku, Shinobu; Tsutsui, Nao; Suzuki, Asuka; Toigawa, Tomohiro; Kurosawa, Tatsuya*; Shibata, Mitsunobu*; et al.

no journal, , 

PUREX process was established for industrial scale reprocessing plant. TRUEX and the 4 group separation were developed for partitioning of minor actinides from high level liquid waste from reprocessing process, and demonstrated by the continuous extraction test using genuine high level liquid waste. Although the extractants for reprocessing and MA separation processes, such as tri-n-butyl phosphate (TBP), n-octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and diisodecylphosphoric acid (DIDPA), have excellent performance for recovery of U, Pu or MA, the molecules contain phosphorus which could be cause for the secondary waste from the solvent extraction processes. To minimize the radioactive waste from nuclear fuel cycle, we have conducted research and development of the new reprocessing and MA separation processes using innovative extractants in accord with CHON principle.

Oral presentation

Research and development of the "SELECT process" for actinide separation, 1; Concept

Matsumura, Tatsuro; Ban, Yasutoshi; Hotoku, Shinobu; Suzuki, Hideya; Tsubata, Yasuhiro; Tsutsui, Nao; Morita, Keisuke; Toigawa, Tomohiro; Shibata, Mitsunobu*; Kurosawa, Tatsuya*; et al.

no journal, , 

no abstracts in English

Oral presentation

Study on radiolytic degradation of extractants for minor actinide separation

Toigawa, Tomohiro; Kumagai, Yuta; Yamashita, Shinichi*; Suzuki, Hideya; Matsumura, Tatsuro

no journal, , 

The radiolytic degradation of amidic extractants excepted to be used in the minor actinide sepation were observed by using the pulse radiolysis system in The University of Tokyo. It was found that a intermediate specie for degradation was generated not only by direct ionization of the extractant but also derived from the diluent ionization.

Oral presentation

Simulation of energy transfer to extraction solvent by radiation in minor actinides separation process

Toigawa, Tomohiro; Tsubata, Yasuhiro; Matsumura, Tatsuro

no journal, , 

Radiation energy transfer to extraction solvent in minor actinide separation process were simulated by using a Particle and Heavy Ion Transport code System (PHITS). PHITS enabled to calculate the absorbed dose to extraction solvent in situations of intricately shaped apparatus or oil-water mixed state because the code were based on Monte-Carlo algorithm. It was found that the absorbed dose value from $$gamma$$-ray depended on the size of the apparatus, while that from alpha-ray was depended on the droplet size in oil-water mixed state. It was demonstrated the degradation yields of the extractant could be evaluated by reference to the experimentally obtained G-values.

Oral presentation

Research and development of the "SELECT process" for Actinide separation

Matsumura, Tatsuro; Ban, Yasutoshi; Hotoku, Shinobu; Suzuki, Hideya; Tsubata, Yasuhiro; Tsutsui, Nao; Morita, Keisuke; Toigawa, Tomohiro; Shibata, Mitsunobu*; Kurosawa, Tatsuya*; et al.

no journal, , 

no abstracts in English

33 (Records 1-20 displayed on this page)