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Journal Articles

Oxygen potential measurement of (U,Pu,Am)O$$_{2 pm x}$$ and (U,Pu,Am,Np)O$$_{2 pm x}$$

Hirooka, Shun; Matsumoto, Taku; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Yamada, Tadahisa*

Journal of Nuclear Materials, 542, p.152424_1 - 152424_9, 2020/12

The measurement of oxygen potential was conducted at 1,673, 1,773, and 1,873 K for (U$$_{0.623}$$Pu$$_{0.350}$$Am$$_{0.027}$$)O$$_{2}$$ and at 1,873 and 1,923 K for (U$$_{0.553}$$Pu$$_{0.285}$$Am$$_{0.015}$$Np$$_{0.147}$$)O$$_{2}$$ by using a thermo-gravimeter and an oxygen sensor. Am inclusion in terms of substituting the U significantly increased the oxygen potential. Similarly, the inclusion of Np as a substitute for U increased the oxygen potential; however, the effect was not as large as that with the Pu or Am addition at the same rate. The results were analyzed via defect chemistry and certain defect formations were suggested in the reducing region and the near-stoichiometric region by plotting the relationship between PO$$_{2}$$ and the deviation from the stoichiometry. The equilibrium constants of the defect reactions were arranged to reproduce the experiment such that Am/Np contents were included in the entropy with coefficients fitting the experimental data.

Journal Articles

Measurements of thermal-neutron capture cross-section and resonance integral of neptunium-237

Nakamura, Shoji; Kitatani, Fumito; Kimura, Atsushi; Uehara, Akihiro*; Fujii, Toshiyuki*

Journal of Nuclear Science and Technology, 56(6), p.493 - 502, 2019/06

 Times Cited Count:2 Percentile:31.52(Nuclear Science & Technology)

The thermal-neutron capture cross-section($$sigma_{0}$$)and resonance integral(I$$_{0}$$) were measured for the $$^{237}$$Np(n,$$gamma$$)$$^{238}$$Np reaction by an activation method. A method with a Gadolinium filter, which is similar to the Cadmium difference method, was used to measure the $$sigma_{0}$$ with paying attention to the first resonance at 0.489 eV of $$^{237}$$Np, and a value of 0.133 eV was taken as a cut-off energy. Neptunium-237 samples were irradiated at the pneumatic tube of the Kyoto University Research Reactor in Institute for Integral Radiation and Nuclear Science, Kyoto University. Wires of Co/Al and Au/Al alloys were used as monitors to determine thermal-neutron fluxes and epi-thermal Westcott's indices at an irradiation position. A $$gamma$$-ray spectroscopy was used to measure activities of $$^{237}$$Np, $$^{238}$$Np and neutron monitors. On the basis of Westcott's convention, the $$sigma_{0}$$ and I$$_{0}$$ values were derived as 186.9$$pm$$6.2 barn, and 1009$$pm$$90 barn, respectively.

Journal Articles

Effect of re-oxidation rate of additive cations on corrosion rate of stainless steel in boiling nitric acid solution

Irisawa, Eriko; Yamamoto, Masahiro; Kato, Chiaki; Motooka, Takafumi; Ban, Yasutoshi

Journal of Nuclear Science and Technology, 56(4), p.337 - 344, 2019/04

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Journal Articles

Sorption behavior of Np(V) on microbe pure culture and consortia

Onuki, Toshihiko; Kozai, Naofumi; Sakamoto, Fuminori; Utsunomiya, Satoshi*; Kato, Kenji*

Chemistry Letters, 46(5), p.771 - 774, 2017/05

 Times Cited Count:0 Percentile:100(Chemistry, Multidisciplinary)

The sorption behavior of Np(V) by the microbe consortia and by a single pure culture of Fe reducing bacterium was studied at pH between 3 and 7 in resting cell conditions. The sorption of Np(V) by the Fe reducing bacterium obtained in the inert condition and by the consortia in aerated condition were higher than by the Fe reducing bacterium in aerobic condition at pH below 5, strongly suggesting presence of other mechanism than the adsorption on microbial cell surface, i.e. reduction to Np(IV).

Journal Articles

Development of metal corrosion testing method simulating equipment of reprocessing of spent nuclear fuels

Matsueda, Makoto; Irisawa, Eriko; Kato, Chiaki; Matsui, Hiroki

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 4 Pages, 2017/00

In the PUREX method, spent fuels are dissolved with nitric acid media. The reprocessing solution containing Fission Products derived from spent fuels is very corrosive to metal materials, the corrosion problem often appears on the surface stainless steel devices. The oxidizing metal ions such as Ruthenium (Ru) and Neptunium (Np) in the process solution is the key reason for severe corrosion of stainless steel. In order to obtain the corrosion rate of stainless steel, we installed the corrosion test apparatus inside an airtight concrete cell in a hot laboratory (the WAste Safety TEsting Facility (WASTEF) of the Japan Atomic Energy Agency), and performed the corrosion tests of stainless steel in the heated nitric acid solution containing Np. The corrosion tests were performed in the temperature range from room temperature to boiling point for 500 hours per batch. The results show that the presence of Np accelerate the stainless steel corrosion in the nitric acid solution.

Journal Articles

Activation measurements of neputunium-237 at KURRI-Linac

Nakamura, Shoji; Terada, Kazushi; Shibahara, Yuji*; Uehara, Akihiro*; Fujii, Toshiyuki*; Sano, Tadafumi*; Takahashi, Yoshiyuki*; Hori, Junichi*

KURRI Progress Report 2015, P. 67, 2016/08

The activation measurements of Np-237 were performed with neutron sources at KURRI-Linac. It was found that activation measurements supported the evaluated cross-section data of JENDL-4.0.

Journal Articles

Electrochemical and spectroelectrochemical behaviour of Np(VI) ions in nitric acid solutions

Kim, S.-Y.; Asakura, Toshihide; Morita, Yasuji

Radiochimica Acta, 93(12), p.767 - 770, 2005/12

 Times Cited Count:9 Percentile:43.05(Chemistry, Inorganic & Nuclear)

Electrochemical and spectroelectrochemical has been used to investigate the behaviour of Neptunium (VI) in concentration 1-8 M HNO$$_{3}$$ solutions. The electrochemical reactions of Np(VI) ions were found to occur quasi-reversibly. The formal redox potentials (E$$^{circ}$$) for Np(VI)/Np(V) couples were determined to be +0.906, +0.908, +0.909, +0.902, +0.896, +0.895, +0.888, and +0.884 V (vs. Ag/AgCl) for Np(VI) ions in 1, 2, 3, 4, 5, 6, 7, 8 M HNO$$_{3}$$ solutions, respectively. The reduction processes of Np(VI) ions were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from +1.10 to +0.60 V versus Ag/AgCl reference electrode redox couple for Np(VI) in HNO$$_{3}$$ solution have clear isosbestic points. These results indicate that the reduction product of Np(VI) is Np(V), which is considerably stable in HNO$$_{3}$$ solution.

Journal Articles

Separation of Np from U and Pu using a salt-free reductant for Np(VI) by continuous counter-current back-extraction

Ban, Yasutoshi; Asakura, Toshihide; Morita, Yasuji

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 5 Pages, 2005/10

An idea for controlling Np behavior in the Purex process is that Np(VI) extracted by TBP is selectively reduced to Np(V) by salt-free reagents and separated from U and Pu. Allylhydrazine is expected as a selective Np(VI) reductant from a view point of reduction rates for Np(VI) and Pu(IV). To confirm the applicability of allylhydrazine, a continuous counter-current back-extraction test of Np(VI) has been carried out using a miniature mixer-settler that consists of two steps: U-Pu recovery (3 stages) and Np separation (4 stages). Experimental results show that at least 90% of Np in feed are back-extracted and separated from U and Pu, therefore, it is confirmed that allylhydrazine is expected to be a selective salt-free reductant of Np(VI).

Journal Articles

Phase equilibria and thermal expansion of CaTiO$$_{3}$$ doped with neptunium

Sato, Tsuyoshi*; Yamashita, Toshiyuki; Matsui, Tsuneo*

Journal of Nuclear Materials, 344(1-3), p.67 - 72, 2005/09

 Times Cited Count:2 Percentile:80.62(Materials Science, Multidisciplinary)

Phase relationships between NpO$$_{2}$$ and CaTiO$$_{3}$$ or Ca(Ti, Al)O$$_{3}$$ were investigated by X-ray diffraction (XRD) analysis, using specimens prepared at 1773 K in Ar-8%H$$_{2}$$. Single phase solid solutions were formed 0-7.5 mol%Np and 1-10 mol%Np for CaTiO$$_{3}$$ and Ca(Ti, Al)O$$_{3}$$, respectively. By substituting Al for Ti in CaTiO$$_{3}$$, Np solubility in Ca(Ti, Al)O$$_{3}$$ increased. Solubility of Np was compared with those of U and Pu, and was discussed with oxidation states and ionic radii of dopants. Thermal expansions of (Ca,Np)TiO$$_{3}$$ were measured from room temperature to 1273 K in Ar-8%H$$_{2}$$ using high-temperature XRD technique. These specimens showed nearly the same value of volumetric thermal expansion coefficients, suggesting that the incorporation of tetravalent Np into CaTiO$$_{3}$$ had practically no effect on stabilization of the crystal lattice. This finding was in a marked contrast to that of Pu doped CaTiO$$_{3}$$, where pronounced stabilization in the crystal was observed by incorporating Pu into CaTiO$$_{3}$$.

Journal Articles

Interactions between anionic complex species of actinides and negatively charged mineral surfaces

Yamaguchi, Tetsuji; Nakayama, Shinichi; Yoshida, Takahiro

Radiochimica Acta, 92(9-11), p.677 - 682, 2004/12

 Times Cited Count:5 Percentile:61.78(Chemistry, Inorganic & Nuclear)

Adsorption of actinides onto negatively charged mineral surfaces was investigated under conditions that actinides were predominantly present as anionic complex species: Th(CO$$_{3}$$)$$_{5}$$$$^{6-}$$, Am(CO$$_{3}$$)$$_{3}$$$$^{3-}$$, Np(CO$$_{3}$$)$$_{2}$$(OH)$$_{2}$$$$^{2-}$$, UO$$_{2}$$(OH)$$_{4}$$$$^{2-}$$, NpO$$_{2}$$(OH)$$_{2}$$$$^{-}$$, Sn(OH)$$_{5}$$$$^{-}$$ and Pb(OH)$$_{3}$$$$^{-}$$. These solutions were left to stand for 2 days to confirm these elements stable in dissolved state, and then contacted with minerals, $$gamma$$-Al$$_{2}$$O$$_{3}$$ or SiO$$_{2}$$ (AEROSIL, specific surface area: 10$$^{5}$$ m$$^{2}$$ kg$$^{-1}$$). After desired contact time for 2 days or more, the solutions were ultra-filtered through 10$$^{4}$$-molecular-weight cutoff Millipore filters and the concentrations of the elements in the filtrates were determined. The sorption experiments were performed at room temperature (25$$^{circ}$$C) under Ar. Distribution coefficients decreased with the increasing pH and with increasing carbonate concentrations. The monotonous decrease in the distribution coefficients in the investigated pH range suggests that the electrostatic repulsion was a dominant interaction between anionic complex species of actinides and negatively charged mineral surfaces.

Journal Articles

Reduction kinetics of Np(VI) by $$n$$-butyraldehyde in tributyl phosphate diluted with $$n$$-dodecane

Ban, Yasutoshi; Asakura, Toshihide; Morita, Yasuji

Radiochimica Acta, 92(12), p.883 - 887, 2004/12

 Times Cited Count:7 Percentile:52.07(Chemistry, Inorganic & Nuclear)

The reduction kinetics of Np(VI) by $$n$$-butyraldehyde in 30%TBP solution diluted with $$n$$-dodecane were analyzed by spectrophotometry. Based on the results of both $$n$$-butyraldehyde and nitric acid concentration dependencies on the Np(VI) reduction reaction, the rate equation was obtained as -d$$t$$[Np(VI)]/d$$t$$ = $$k$$[$$n$$-C$$_{3}$$H$$_{7}$$CHO]$$^{0.8}$$[HNO$$_{3}$$]$$^{-2.0}$$[Np(VI)]$$_{t}$$ where $$k$$ = (1.0$$pm$$0.2) $$times$$ 10$$^{-3}$$ M$$^{1.2}$$min$$^{-1}$$ at 294 $$pm$$ 1 K. The activation energy of the reaction was 76 $$pm$$ 5 kJ/mol. Redox equilibrium between Np(V) and N(VI), and reaction mechanism were discussed.

Journal Articles

Electrochemical and spectroelectrochemical properties of neptunium(VI) ions in nitric acid solution

Kim, S.-Y.; Asakura, Toshihide; Morita, Yasuji; Uchiyama, Gunzo*; Ikeda, Yasuhisa*

Journal of Radioanalytical and Nuclear Chemistry, 262(2), p.311 - 315, 2004/11

 Times Cited Count:9 Percentile:43.92

no abstracts in English

Journal Articles

Electrode reaction of the Np$$^{3+}$$/Np couple at liquid Cd and Bi electrodes in LiCl-KCl eutectic melts

Shirai, Osamu; Uozumi, Koichi*; Iwai, Takashi; Arai, Yasuo

Journal of Applied Electrochemistry, 34(3), p.323 - 330, 2004/03

 Times Cited Count:24 Percentile:49.31

The electrode reactions of the Np$$^{3+}$$/Np couple at liquid Cd and Bi electrodes were investigated by cyclic voltammetry at 723, 773 and 823 K in LiCl-KCl eutectic melt. It was found that the diffusion of Np$$^{3+}$$ in the salt phase was a rate-determining step in the cathodic reaction when the concentration of NpCl$$_{3}$$ was less than about 1 wt.% and the liquid Cd or Bi phase was not saturated with Np. The redox potentials of the Np$$^{3+}$$/Np couple at liquid Cd electrode at 723, 773 and 823 K were observed more positively than those at Mo electrode by 0.158, 0.140 and 0.126 V, respectively. The potential shift would result from a lowering of activity of Np in Cd phase according to the alloy formation of NpCd$$_{11}$$ at 723 K and NpCd$$_{6}$$ at 773 and 823 K. The redox potentials of the Np$$^{3+}$$/Np couple at liquid Bi electrode at 723, 773 and 823 K were more positive than those at Mo electrode by 0.427, 0.419 and 0.410 V, respectively, which would be attributable to a lowering of activity of Np in Bi phase according to the formation of NpBi$$_{2}$$.

JAEA Reports

Synthetic methods of uranium and neptunium compounds from solutions

Saeki, Masakatsu

JAERI-Review 2003-030, 50 Pages, 2003/11

JAERI-Review-2003-030.pdf:3.41MB

In this review, synthetic methods of uranium and neptunium compounds mainly from solutions and their natures are summarized. For uranium, 3 compounds of trivalent, 4 compounds of tetravalent and 23 compounds of hexavalent are described in slight details. For neptunium, synthetic methods of stock solutions for pentavalent and hexavalent neptunium, 4 items (6 compounds) of trivalent, 8 items (19 compounds) of tetravalent, 28 items (29 compounds) of pentavalent, 10 items (14 compounds) of hexavalent and 5 items (9 compounds) of heptavalent are described in slight details. Furthermore, on compounds which can not be described in details, the names are listed with literatures. The materials used here have been collected during the research activities on Moessbauer spectroscopic studies of uranium and neptunium compounds, then, the reviews on Moessbauer spectroscopic studies of actinoid compounds are also listed.

Journal Articles

Migration mechanisms of $$^{237}$$Np and $$^{241}$$Am through loess media

Tanaka, Tadao; Mukai, Masayuki; Maeda, Toshikatsu; Matsumoto, Junko; Ogawa, Hiromichi; Li, Z.*; Wang, X.*; Fan, Z.*; Guo, L.*; Liu, C.*

Journal of Radioanalytical and Nuclear Chemistry, 256(2), p.205 - 211, 2003/05

 Times Cited Count:3 Percentile:72.7

Migration experiments of $$^{237}$$Np(V) and $$^{241}$$Am(III) have been performed using a column system, to investigate migration behavior of Np and Am through a column packed with loess, taken from Shanxi, China. Adsorption mechanisms of Np and Am on the loess were examined by a chemical extraction method. In the case of the Np, most of Np adsorbed on the influent edge of the column. The Np adsorbed on the loess was mainly controlled by surface complexation. However, the migration of Np in the loess media could be roughly evaluated by using the distribution coefficient. In the case of the Am, particulate Am species was formed in the influent solution and moved in the column. The Am adsorbed on the loess was controlled by irreversible reactions. The migration behavior of particulate Am in the loess media could be expressed by the filtration theory.

JAEA Reports

Cation-cation interaction in neptunyl(V) compounds

Krot, N. N.*; Saeki, Masakatsu

JAERI-Review 2003-005, 37 Pages, 2003/03

JAERI-Review-2003-005.pdf:2.12MB

The original manuscript was prepared by Professor N. N. Krot of Institute of Physical Chemistry, Russian Academy of sciences, in 1997. Saeki tried to translate that into Japanese and to add some new data since 1997. The contents include the whole picture of cation-cation interactions mainly on 5-valence neptunium compounds. Firstly, characteristic structures are summarized for the cation-cation bonding in compounds of neptunium. Secondly, it is introduced how the cation-cation bonding affects physical and chemical properties of the compounds. Then, detection-methods are shown for the cation-cation bonding in the compounds. Besides, the cation-cation interaction are shortly reviewed for compounds of other actinide-ions.

Journal Articles

Heat capacity of neptunium mononitride

Nakajima, Kunihisa; Arai, Yasuo

Journal of Nuclear Science and Technology, 39(Suppl.3), p.620 - 623, 2002/11

no abstracts in English

Journal Articles

Effect of neptunium ions on corrosion of stainless steel in nitric acid solution

Motooka, Takafumi; Kiuchi, Kiyoshi

Journal of Nuclear Science and Technology, 39(Suppl.3), p.367 - 370, 2002/11

A corrosion of a stainless steel in nitric acid solution containing Np has been studied. Using SUS304L stainless steel, corrosion tests in boiling neptunium nitrate solution were conducted under immersion and heat-transfer condition. By the weight loss measurement of stainless steel and the quantitative analysis of metallic ions dissolved in solution, the corrosion rates were obtained. The surface morphology was observed by scanning electron microscopy. The acceleration mechanism was investigated by electrochemistry and spectrophotometry. The corrosion rate was accelerated by addition of neptunium in nitric acid. Preferential intergranular corrosion was observed. The corrosion was enhanced under heat-transfer condition compared to immersion condition. In polarization measurements, the cathodic over-voltage was decreased; the cathodic current was increased by addition of Np. Spectrophotometric measurements showed that Np(V) oxidized to Np(VI) in boiling nitric acid. The corrosion acceleration mechanism in nitric acid solution containing Np suggested the re-oxidation of Np(V).

Journal Articles

Extraction behavior of TRU elements in the nuclear fuel reprocessing

Hotoku, Shinobu; Asakura, Toshihide; Mineo, Hideaki; Uchiyama, Gunzo

Journal of Nuclear Science and Technology, 39(Suppl.3), p.313 - 316, 2002/11

no abstracts in English

Journal Articles

Advanced technologies for long-lived nuclides separation in reprocessing

Uchiyama, Gunzo; Mineo, Hideaki; Asakura, Toshihide; Hotoku, Shinobu

Proceedings of International Conference on Back-End of the Fuel Cycle: From Research to Solutions (GLOBAL 2001) (CD-ROM), 8 Pages, 2001/09

no abstracts in English

61 (Records 1-20 displayed on this page)