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Kobayashi, Taishi*; Sato, Yutaro*; Tonna, Ryutaro*; Matsumura, Daiju; Sasaki, Takayuki*; Ikeda, Atsushi
Dalton Transactions (Internet), 53(46), p.18616 - 18628, 2024/10
Times Cited Count:0 Percentile:0.00(Chemistry, Inorganic & Nuclear)Tonna, Ryutaro*; Sasaki, Takayuki*; Okamoto, Yoshihiro; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*
Journal of Nuclear Materials, 589, p.154862_1 - 154862_10, 2024/02
Times Cited Count:1 Percentile:34.39(Materials Science, Multidisciplinary)The dissolution behavior of FeUO compounds formed by a high-temperature reaction of UO
with iron, a stainless-steel component of reactor structural materials, was investigated under atmospheric conditions. The compounds were prepared in an electric furnace using U
O
and Fe
O
as starting materials, and their solid states were analyzed using X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, and X-ray absorption fine structure spectroscopy. The concentration of nuclides dissolved in water was examined by performing static leaching tests of FeUO
compounds for up to three months. A redox reaction was proposed to occur between trivalent Fe and pentavalent U ions in the early stage of FeUO
dissolution. It was thermodynamically deduced that the reduced divalent Fe ion was finally oxidized into a trivalent ion in the presence of dissolved oxygen, and iron hydroxide limited the solubility of Fe. Meanwhile, the concentration of hexavalent U (i.e., uranyl ion) was limited owing to the presence of secondary minerals such as metaschoepite and sodium uranate and subsequently decreased, possibly owing to sorption on Fe oxides, for example. The concentrations of multivalent ions of fission products, such as Ru and Ce, also decreased, likely for the reason above. By contrast, the concentration of soluble Cs ions did not decrease. The validity of this interpretation was supported by comparing the results with the dissolution behavior of a reference sample (Fe-free U
O
).
Tonna, Ryutaro*; Sasaki, Takayuki*; Kodama, Yuji*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki
Nuclear Engineering and Technology, 55(4), p.1300 - 1309, 2023/04
Times Cited Count:4 Percentile:82.11(Nuclear Science & Technology)Simulated debris was synthesized using UO, Zr, and stainless steel and a heat treatment method under inert or oxidizing conditions. The primary U solid phase of the debris synthesized at 1473 K under inert conditions was UO
, whereas a (U,Zr)O
solid solution formed at 1873 K. Under oxidizing conditions, a mixture of U
O
and (Fe,Cr)UO
phases formed at 1473 K whereas a (U,Zr)O
solid solution formed at 1873 K. The leaching behavior of the fission products from the simulated debris was evaluated using two methods: the irradiation method, for which fission products were produced via neutron irradiation, and the doping method, for which trace amounts of non-radioactive elements were doped into the debris. The dissolution behavior of U depended on the properties of the debris and aqueous medium the debris was immersed in. Cs, Sr, and Ba leached out regardless of the primary solid phases. The leaching of high-valence Eu and Ru ions was suppressed, possibly owing to their solid-solution reaction with or incorporation into the uranium compounds of the simulated debris.
Kobayashi, Taishi*; Fushimi, Tomokazu*; Mizukoshi, Hirofumi*; Motokawa, Ryuhei; Sasaki, Takayuki*
Langmuir, 38(48), p.14656 - 14665, 2022/12
Times Cited Count:2 Percentile:16.29(Chemistry, Multidisciplinary)no abstracts in English
Zhao, Q.*; Saito, Takeshi*; Miyakawa, Kazuya; Sasamoto, Hiroshi; Kobayashi, Taishi*; Sasaki, Takayuki*
Journal of Hazardous Materials, 428, p.128211_1 - 128211_10, 2022/04
Times Cited Count:6 Percentile:47.65(Engineering, Environmental)The influence of humic acid and its radiological degradation on the sorption of Cs and Eu
by sedimentary rock was investigated to understand the sorption process of metal ions and humic substances. Aldrich humic acid (HA) solution was irradiated with different doses of gamma irradiation using a Co-60 gamma-ray source prior to the contact between the metal ions and the solid sorbent. The HA molecule decomposed to smaller molecules with a lower complexation affinity. Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on the sorption of Cs
and Eu
ions. The addition of non-irradiated HA weakened the sorption of Eu because of the lower sorption of the neutral or negatively charged Eu-HA complexes compared with free Eu ions. The sorption of monovalent Cs ions was barely affected by the presence of HA and its gamma irradiation. The concentration ratio of HA complexed species and non-complexed species in the solid and liquid phases was evaluated by sequential filtration and chemical equilibrium calculations. The ratios supported the minimal contribution of HA to Cs sorption. However, the concentration ratio for Eu
in the liquid phase was high, indicating that the complexing ability of HA to Eu
was higher than that of HA to Cs
ions. Therefore, the sorption of free Eu
would predominate with the gamma irradiation dose applied to the HA solution under a radiation field near the HLW package.
Sato, Nobuaki*; Kirishima, Akira*; Watanabe, Masayuki; Sasaki, Takayuki*; Uehara, Akihiro*; Takeda, Shino*; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kobayashi, Taishi*
The Chemistry of Thorium, Plutonium and MA, 254 Pages, 2022/03
The chemistry of nuclear materials such as Thorium (Part 1) and Plutonium (Part 2) was described in relation from the fundamentals on solid chemistry and solution chemistry to the practicals on the experiment and evaluation method in detail. Minor actinides such as Neptunium, Americium, Curium and Protoactinium, was introduced the basics on the solid and solution chemistry.
Motokawa, Ryuhei; Kaneko, Koji; Oba, Yojiro; Nagai, Takayuki; Okamoto, Yoshihiro; Kobayashi, Taishi*; Kumada, Takayuki; Heller, W. T.*
Journal of Non-Crystalline Solids, 578, p.121352_1 - 121352_7, 2022/02
Times Cited Count:4 Percentile:22.03(Materials Science, Ceramics)Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso; Kobayashi, Taishi*; Iijima, Kazuki
Journal of Radioanalytical and Nuclear Chemistry, 326(1), p.303 - 314, 2020/10
Times Cited Count:7 Percentile:52.74(Chemistry, Analytical)Kobayashi, Taishi*; Sasaki, Takayuki*; Kitamura, Akira
Journal of Chemical Thermodynamics, 138, p.151 - 158, 2019/11
Times Cited Count:6 Percentile:20.98(Thermodynamics)The effect of -isosaccharinic acid (ISA) on the solubility and redox of tetravalent and hexavalent uranium (U(IV), U(VI)) was investigated in the hydrogen ion concentration (pH
) range of 6
13 and at total ISA concentration ([ISA]
) = 10
10
mol/dm
. The dependence of U(IV) solubility on pH
and [ISA]
suggested the existence of U(OH)
(ISA)
as a dominant species within the investigated pH
range of 6
12. For the U(VI)-ISA system, UO
(OH)
(ISA)
was suggested as a dominant species at pH
7
13. The formation constants of the U(IV)-ISA and U(VI)-ISA complexes were determined by least-squares fitting of the solubility data. The solubility of U(IV) and U(VI) in the presence of ISA and its effect on the redox behavior were thermodynamically interpreted based on the obtained constants.
Kobayashi, Taishi*; Nakajima, Shogo*; Motokawa, Ryuhei; Matsumura, Daiju; Saito, Takumi*; Sasaki, Takayuki*
Langmuir, 35(24), p.7995 - 8006, 2019/06
Times Cited Count:5 Percentile:19.14(Chemistry, Multidisciplinary)Rai, D.*; Kitamura, Akira; Altmaier, M.*; Rosso, K. M.*; Sasaki, Takayuki*; Kobayashi, Taishi*
Journal of Solution Chemistry, 47(5), p.855 - 891, 2018/05
Times Cited Count:11 Percentile:10.52(Chemistry, Physical)We have critically reviewed experimental data for Zr hydrolysis constant values for formation of several mononuclear and polynuclear species and a solubility product value for ZrO(am). We have determined new/revised values for the formation constants of Zr(OH)
, Zr(OH)
(aq), Zr(OH)
, Zr(OH)
and Ca
Zr(OH)
, and the solubility product for ZrO
(am) after the critical review.
Sasaki, Takayuki*; Kokami, Takayuki*; Kobayashi, Taishi*; Kirishima, Akira*; Murakami, Hiroaki; Amano, Yuki; Mizuno, Takashi; Iwatsuki, Teruki; Sasamoto, Hiroshi; Miyakawa, Kazuya
Journal of Nuclear Science and Technology, 54(3), p.373 - 381, 2017/03
Trace amounts of natural thorium and uranium in deep groundwater were investigated at two underground research laboratories situated at Horonobe and Mizunami, Japan. The groundwater was sampled from underground boreholes, and the colloid contribution was checked by in situ two size-fractionated ultrafiltration systems. A decrease in the concentration after in situ filtration suggested the presence of natural colloids and suspended matter that were carriers of a portion of the elements. The result of the Th and U concentrations in groundwater after 10 kDa filtration was analyzed thermodynamically using existing hydrogeological and geochemical data such as the mineral components in the groundwater at a given pH, ionic strength, concentration of co-existing ions, redox potential, and solid phase assumed. A crystalline solid phase made the solubility very low compared with that of the amorphous phase, and the solubility agreed well with the concentrations measured.
Kobayashi, Taishi*; Teshima, Takeshi*; Sasaki, Takayuki*; Kitamura, Akira
Journal of Nuclear Science and Technology, 54(2), p.233 - 241, 2017/02
Times Cited Count:8 Percentile:53.23(Nuclear Science & Technology)Zr solubility in the presence of gluconic acid (GLU) and isosaccharinic acid (ISA) was investigated as a function of hydrogen ion concentration (pH) and the total concentration of GLU or ISA. The dependence of the increase in Zr solubility on the pH
and GLU concentration suggested the existence of Zr(OH)
(GLU)
in the neutral pH region and Zr(OH)
(GLU)(GLU
)
in the alkaline pH region above pH
10 as the dominant species in the presence of 10
- 10
mol/dm
(M) GLU. In the presence of ISA, the dominant species Zr(OH)
(ISA)
and Zr(OH)
(ISA)(ISA
)
were proposed to occur in the neutral and alkaline pH regions, similar to those found in the presence of GLU. From X-ray diffraction analysis, the solubility-limiting solid phase in the presence of GLU and ISA was considered to be Zr(OH)
(am). The formation constants of the Zr gluconate and isosaccharinate complexes were determined by least squares fitting analysis of the solubility data, and the obtained values were discussed in comparison with those of tetravalent actinides.
Rai, D.*; Kitamura, Akira; Rosso, K. M.*; Sasaki, Takayuki*; Kobayashi, Taishi*
Radiochimica Acta, 104(8), p.583 - 592, 2016/08
Times Cited Count:6 Percentile:46.39(Chemistry, Inorganic & Nuclear)Solubility studies were conducted with HfO(cr) solid as a function of acid concentrations. These studies involved (1) using two different amounts of the solid phase, (2) acid washing the bulk solid phase, (3) preheating the solid phase to 1400
C, and (4) heating amorphous HfO
(am) suspensions to 90
C to ascertain whether the HfO
(am) converts to HfO
(cr) and to determine the solubility from the oversaturation direction. Based on the results of these treatments it is concluded that the HfO
(cr) contains a small fraction of less crystalline, but not amorphous, material [HfO
(lcr)] and this, rather than the HfO
(cr), is the solubility-controlling phase in the range of experimental variables investigated in this study. The solubility data are interpreted using both the Pitzer and SIT models. The log
of the solubility product of HfO
(cr) is estimated. The observation of a small fraction of less crystalline higher solubility material is consistent with the general picture that mineral surfaces are often structurally and/or imperfect leading to a higher solubility than the bulk crystalline solid. This study stresses the urgent need, during interpretation of solubility data, of taking precautions to make certain that the observed solubility behavior for sparingly-soluble solids is assigned to the proper solid phase.
Sasaki, Takayuki*; Ueda, Kenyo*; Saito, Takumi; Aoyagi, Noboru; Kobayashi, Taishi*; Takagi, Ikuji*; Kimura, Takaumi; Tachi, Yukio
Journal of Nuclear Science and Technology, 53(4), p.592 - 601, 2016/04
Times Cited Count:14 Percentile:76.34(Nuclear Science & Technology)The influences of pH and the concentrations of Eu and NaNO
on the sorption of Eu
to Na-montmorillonite were investigated through batch sorption measurements and time-resolved laser fluorescence spectroscopy (TRLFS). The pH had a little effect on the distribution coefficients (Kd) in 0.01 M NaNO
, whereas the Kd strongly depended on pH at 1 M NaNO
. A cation exchange model combined with a one-site non-electrostatic surface complexation model was successfully applied to the measured Kd. The TRLFS spectra of Eu
sorbed were processed by parallel factor analysis (PARAFAC), which corresponded to one outer-sphere (factor A) and two inner-sphere (factor B and C) complexes. It turned out that factors A and B correspond to Eu
sorbed by ion exchange sites and inner-sphere complexation with hydroxyl groups of the edge faces, respectively. Factor C became dominant at relatively high pH and ionic strength and likely correspond to the precipitation of Eu(OH)
on the surface.
Kobayashi, Taishi*; Sasaki, Takayuki*; Ueda, Kenyo*; Kitamura, Akira
Materials Research Society Symposium Proceedings, Vol.1518, p.231 - 236, 2013/10
For the nuclear waste management of TRU waste, it is necessary to assess the impact of nitrate salts contained in the waste. In the present study, the sorption behavior of Ni and Pd on the pumice tuff was investigated in the presence of NH(aq)/NH
. Under different NH
(aq)/NH
concentration, pH and ionic strength conditions, distribution coefficient (
) of Ni and Pd on the pumice tuff was determined by batch experiment. For Ni system, the
values showed no significant dependence on the initial NH
concentration in neutral pH region, agrees with the prediction from thermodynamic data. For Pd system, the
values decreased with an increase of [NH
]ini, suggesting the formation of stable ammine complex (Pd(NH
)
(
: 1 - 4)). The obtained
values for Ni and Pd were analyzed using the surface complexation model. By taking complexes predicted by thermodynamic data into account, the sorption behavior of Ni and Pd in the presence of NH
(aq)/NH
were well explained.
Tachi, Yukio; Kobayashi, Taishi*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 18(2), p.113 - 115, 2011/12
The 13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere (MIGRATION 2011) was held at Peking University, China on 18th-23rd, September, 2011. This report summaries overview of the conference and topics in each technical session, which indicate the state-of-the-art of international research activities on radionuclide migration for geological disposal.
Sasaki, Takayuki*; Kubo, Shintaro*; Kobayashi, Taishi*; Kirishima, Akira*; Kimura, Takaumi; Kubota, Takumi*; Takagi, Ikuji*; Moriyama, Hirotake*
Journal of Nuclear and Radiochemical Sciences, 6(1), p.51 - 54, 2005/07
no abstracts in English
Kumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Kirishima, Akira*; Akiyama, Daisuke*; Sato, Nobuaki*; Sasaki, Takayuki*; Kobayashi, Taishi*
no journal, ,
Fuel debris generated due to nuclear severe accidents is expected to contain a wide variety of uranium compounds. In this project, we have investigated chemical stability of simulated fuel debris containing elements from stainless steel (Fe, Cr, and Ni) against exposure to water. The simulated debris was prepared from the powders of UO and SUS304 by heating the mixed powder at 1200
C for 1 h under continuous gas flow of 2% O
in Ar. The produced powder was characterized by XRD, SEM-EDX, Raman micro-spectroscopy, and M
ssbauer spectroscopy. The series of characterization revealed that the simulated debris comprised U(Fe,Cr)O
, U
O
, and Fe(III) oxides. Then, the simulated debris was exposed to pure water for 30 days. The same leaching test of U
O
was performed for comparison. The chemical analysis of leached metals demonstrated that the U elution from the simulated debris was significantly lower than that from U
O
. In addition, Fe, Cr, and Ni were under quantitation limit as well. The Raman spectra showed that the exposure to water induced insignificant change in the spectra of the simulated debris, while the Raman band structure of U
O
seemed to become slightly unclear after 30 days immersion.
Sasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Watanabe, Masayuki; Kumagai, Yuta; Kusaka, Ryoji
no journal, ,
Fuel debris containing alloy phases is expected to be formed in the Fukushima Daiichi Nuclear Power Plant. In this study, two series of simulated debris samples comprising uranium-zirconium-stainless steel were synthesized. One series of the samples was prepared by the irradiation method, where the samples were irradiated by thermal neutron for fission generation. The other was prepared by the doping method, where stable isotopes of FPs were added during the synthesis. We performed leaching tests as an aging treatment, and then measured structural changes in the samples and the elution rates of U and FPs contained in the samples. Moreover, in order to evaluate the colloid formation of these elements, particle size distribution was analyzed by an ICP-MS method combined with filtration using different pore-size filters or size exclusion chromatography. Based on the results, the chemical stability of the simulated debris and the speciation of the eluted nuclides were discussed.