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Journal Articles

Redox equilibrium of the UO$$_2^{2+}$$/UO$$_2^{+}$$ couple in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Sato, Nobuaki*; Kofuji, Hirohide; Myochin, Munetaka; Yamana, Hajimu*

Journal of Nuclear Materials, 454(1-3), p.159 - 163, 2014/11

 Times Cited Count:1 Percentile:8.95(Materials Science, Multidisciplinary)

The redox equilibrium of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was measured in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C by cyclic voltammetry and absorption spectrophotometry. The standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was approximately evaluated by cyclic voltammetry. Further, the absorption spectrum and equilibrium potential were measured, repeatedly adding UO$$_2^{2+}$$ source material into the melt containing UO$$_2^{+}$$. From the correlation between the equilibrium potential of the melt and the concentration ratio [UO$$_2^{2+}$$]/[UO$$_2^{+}$$] spectrophotometrically evaluated, the standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was determined to be -0.847$$pm$$0.010 V vs. O$$_{2}$$/O$$^{2-}$$.

Journal Articles

Optimization of chemical composition in the iron phosphate glass as the matrix of high level waste generated from pyroprocessing

Kofuji, Hirohide; Yano, Tetsuji*; Myochin, Munetaka; Matsuyama, Kanae*; Okita, Takeshi*; Miyamoto, Shinya*

Proceedings of 22nd International Conference on Nuclear Engineering (ICONE-22) (DVD-ROM), 6 Pages, 2014/07

For the research and development of the nuclear waste disposal concept suitable to the pyrochemical processing system and its performance evaluation, the iron-phosphate glass is examined as an alternative waste form for high level waste generated from electro-refining process. In order to enhance the waste element content in the glass matrix and improve the durability of the waste form, optimization experiments of the glass composition were carried out and the effect of additional other transition metal oxides was found out in this study.

Journal Articles

Synthesis and investigation of uranyl molybdate UO$$_{2}$$MoO$$_{4}$$

Nagai, Takayuki; Sato, Nobuaki*; Kitawaki, Shinichi; Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*; Myochin, Munetaka

Journal of Nuclear Materials, 433(1-3), p.397 - 403, 2013/02

 Times Cited Count:10 Percentile:61.35(Materials Science, Multidisciplinary)

In order to examine easily synthetic conditions of uranyl molybdate, UO$$_{2}$$MoO$$_{4}$$, used for the reprocessing process study of spent nuclear oxide fuels in alkaline molybdate melts, the uranium molybdate compounds were produced from U$$_{3}$$O$$_{8}$$ powder and anhydrous MoO$$_{3}$$ reagent. The results of having investigated them in solid state by using X-ray diffractometry and Raman spectrometry, it was confirmed that UO$$_{2}$$MoO$$_{4}$$ could be synthesized by heating mixed powder of U$$_{3}$$O$$_{8}$$ and MoO$$_{3}$$ with stoichiometric mole ratio at 770$$^{circ}$$C for 4 h under air atmosphere. Moreover, adding this UO$$_{2}$$MoO$$_{4}$$ into Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt, most of the dissolved uranium species in the melt were observed as hexa-valent uranyl ions by absorption spectrophotometry.

Journal Articles

Chemical durability of iron-phosphate glass as the high level waste from pyrochemical reprocessing

Kofuji, Hirohide; Yano, Tetsuji*; Myochin, Munetaka; Matsuyama, Kanae*; Okita, Takeshi*; Miyamoto, Shinya*

Procedia Chemistry, 7, p.764 - 771, 2012/00

 Times Cited Count:12 Percentile:95.16

As a part of the research and development for the nuclear waste disposal concept suitable to the advanced fuel cycle systems and its performance evaluation, the iron-phosphate glass is examined as an alternative waste form for high level waste generated from pyrochemical reprocessing. In order to enhance the waste element content in the glass matrix and improve the durability of the waste form, optimization experiments of glass composition were carried out and the effect of additional other transition metal oxides was found out in this study.

Journal Articles

Japanese programs in development of pyro-processing fuel cycle technology for sustainable energy supply with reduced burdens

Koyama, Tadafumi*; Ogata, Takanari*; Myochin, Munetaka; Arai, Yasuo

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 8 Pages, 2011/12

no abstracts in English

Journal Articles

Absorption spectra and cyclic voltammograms of uranium species in molten lithium molybdate-sodium molybdate eutectic at 550 $$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fukushima, Mineo; Myochin, Munetaka; Fujii, Toshiyuki*; Sato, Nobuaki*; Yamana, Hajimu*

Proceedings in Radiochemistry, 1(1), p.151 - 155, 2011/09

Absorption spectra of dissolved uranium species in molten Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic at 550 $$^{circ}$$C were measured by spectrophotometry, and their redox reactions were also investigated by cyclic voltammetry. Observed absorption spectra of uranium species were similar to those of UO$$_{2}$$$$^{+}$$ in molten chlorides. After purging oxygen into the melt, the absorption peaks of UO$$_{2}$$$$^{+}$$ decreased and UO$$_{2}$$$$^{+}$$ was thought to be oxidized to UO$$_{2}$$$$^{2+}$$. When the uranium species were not contained in the melt, we confirmed that alkali metals deposited at -0.7 V and a small reduction of this melt was observed at -0.3 V. When UO$$_{2}$$ was dissolved into the melt, the reduction of the uranium species was observed at -0.2 V. It was suggested that the dissolved uranium species are recovered as mixed uranium-molybdenum oxides by electrolysis.

Journal Articles

Precipitation behaviors of fission products by phosphate conversion in LiCl-KCl medium

Amamoto, Ippei; Kofuji, Hirohide; Myochin, Munetaka; Takasaki, Yasushi*; Yano, Tetsuji*; Terai, Takayuki*

Nuclear Technology, 171(3), p.316 - 324, 2010/09

 Times Cited Count:11 Percentile:59.27(Nuclear Science & Technology)

The separation technique by phosphate conversion of FP from NaCl-KCl or NaCl-2CsCl as the medium of the spent electrolyte of pyroprocessing is being developed at RIAR in Russia. To ascertain the technical feasibility of applying this RIAR's method for recycling of spent electrolyte which composed of FP such as AL, ALE, and REE and 3LiCl-2KCl as the medium, preliminary study was undertaken at JAEA. This study occupies an auxiliary role which is forwarded as a part of FaCT Project of Japan. As a first approach, the thermodynamic analysis to understand the behaviours of FP in the electrolyte was carried out after literature research and acquisition of required thermodynamic properties. Preliminary experiment was then undertaken to observe the conversion behaviours of chlorides to phosphate. In this paper, these results are shown and are evaluated to discern the feasibility of the phosphate conversion method.

Journal Articles

In-situ analyses of chemical state and ionic distribution in the extraction chromatography column

Watanabe, So; Sano, Yuichi; Myochin, Munetaka; Okamoto, Yoshihiro; Shiwaku, Hideaki; Ikeda, Atsushi; Suzuki, Shinichi; Yaita, Tsuyoshi

Nihon Ion Kokan Gakkai-Shi, 21(3), p.189 - 194, 2010/07

Journal Articles

Electro-deposition behavior of minor actinides with liquid cadmium cathodes

Kofuji, Hirohide; Fukushima, Mineo; Kitawaki, Shinichi; Myochin, Munetaka; Kormilitsyn, M. V.*; Terai, Takayuki*

IOP Conference Series; Materials Science and Engineering, 9, p.012010_1 - 012010_8, 2010/05

 Times Cited Count:0 Percentile:1.02

Journal Articles

Separation of lanthanoid phoshates from the spent electrolyte of pyroprocessing

Amamoto, Ippei; Kofuji, Hirohide; Myochin, Munetaka; Tsuzuki, Tatsuya*; Takasaki, Yasushi*; Yano, Tetsuji*; Terai, Takayuki*

Proceedings of 12th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM '09/DECOM '09) (CD-ROM), 9 Pages, 2009/10

This study is carried out to make the pyroprocessing hold a competitive advantage. As one of the measures is to reduce the volume of HLW, the phosphate conversion method is applied for removal of FP from the spent electrolyte in this paper. Though the removing target elements in the electrolyte are alkali metals, alkaline earth metals and lanthanoid elements, only lanthanoid elements and lithium form the insoluble phosphates by reaction with Li$$_{3}$$PO$$_{4}$$. Therefore, as the first step, the precipitation experiment was carried out to observe the behaviours of elements which form the insoluble precipitates. Then the filtration was experimented to remove precipitates in the spent electrolyte using Fe$$_{2}$$O$$_{3}$$-P$$_{2}$$O$$_{5}$$ glass system as a filtlation medium which is compatible material with the glassification. The result of separation of precipitates by filtration was effective and attained almost 100$$%$$.

Journal Articles

Current status on research and development of uranium crystallization system in advanced aqueous reprocessing of FaCT project

Shibata, Atsuhiro; Kaji, Naoya; Nakahara, Masaumi; Yano, Kimihiko; Tayama, Toshimitsu; Nakamura, Kazuhito; Washiya, Tadahiro; Myochin, Munetaka; Chikazawa, Takahiro*; Kikuchi, Toshiaki*

Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.151 - 157, 2009/09

As a part of FaCT project, Japan Atomic Energy Agency has been developing a U crystallization process for advanced aqueous reprocessing technology in collaboration with Mitsubishi Materials Corporation. We have carried out experimental studies and obtained fundamental data. Continuous operation tests were also carried out by an engineering-scale crystallizer to confirm productivity of the equipment and to investigate non-steady state conditions. The requirements for the U crystallization process in the FaCT project could be achieved except DF of Cs. More detail investigation is under way to settle the process condition without Pu-Cs double salt formation.

Journal Articles

Phosphate conversion behaviors of FP chlorides with spent electrolyte recycling

Kofuji, Hirohide; Amamoto, Ippei; Sasaki, Kazuya*; Yasumoto, Masaru*; Takasaki, Yasushi*; Myochin, Munetaka; Terai, Takayuki*

Denki Kagaku Oyobi Kogyo Butsuri Kagaku, 77(8), p.597 - 600, 2009/08

 Times Cited Count:0 Percentile:0.01(Electrochemistry)

The process flow of the phosphate conversion technique has been developed for the reduction of high-level radioactive waste (HLW) generated from the metal-electrorefining process. In this study, the results of thermodynamic calculations for the phosphate conversion reactions were examined by the basic experiments. The chlorides of rare earth elements (REE) turned out to be converted into phosphates easily. Furthermore, as the additive for the phosphate conversion reaction, high temperature behavior of lithium phosphate was evaluated to elucidate the thermodynamic property.

Journal Articles

Phosphates behaviours in conversion of FP chlorides

Amamoto, Ippei; Kofuji, Hirohide; Myochin, Munetaka; Takasaki, Yasushi*; Terai, Takayuki*

Journal of Nuclear Materials, 389(1), p.142 - 148, 2009/05

 Times Cited Count:15 Percentile:69.01(Materials Science, Multidisciplinary)

The spent electrolyte of the pyroprocessing by metal electrorefining method should be considered for recycling after removal of FP, such as AL (alkali metals), ALE (alkaline earth metals), and/or REE (rare-earth elements), to reduce the volume of HLW. Authors have been carrying out theoretical analysis and experiment showing the behaviours of phosphate precipitates so as to estimate the feasibility of the phosphate conversion method. From hitherto results, it was found that AL except Li, and ALE are unlikely formed phosphate precipitates. However, their conversion behaviours including REE were compatible with former presented theoretical analysis; in the case of lanthanum precipitate as one of REE, submicron-size particles could be observed while that of Li$$_{3}$$PO$$_{4}$$ was larger; under different conversion temperatures, the precipitates were apt to grow larger at higher temperature; etc..

Journal Articles

Evaluation of phosphate thermodynamic properties for spent electrolyte recycle

Kofuji, Hirohide; Amamoto, Ippei; Yasumoto, Masaru*; Sasaki, Kazuya*; Myochin, Munetaka; Terai, Takayuki*

Journal of Nuclear Materials, 389(1), p.173 - 178, 2009/05

 Times Cited Count:4 Percentile:30.6(Materials Science, Multidisciplinary)

Adaptation of the phosphate conversion technique was undertaken and evaluated for application to the recycle process of the spent electrolyte generated from metal electrorefining process which is a kind of pyrochemical reprocessing technologies. The conceptual flow sheet has been discussed based on the thermodynamic properties of constituent. However few data have been published relating to the phosphate, therefore, the thermodynamic data were attempted to be obtained by the calorimetry and vapor pressure measurements. The measurements have been started with pure substance such as lithium phosphate. Through the measurements of HTMS and TG-DTA, it was clarified that decomposition or phase transition of Li$$_{3}$$PO$$_{4}$$ occurred at specific temperatures below the melting point of Li$$_{3}$$PO$$_{4}$$. To avoid the influence of fragment substances which have high vapour pressures, improved method of the HTMS measurement was examined.

Journal Articles

Redox equilibria of Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in molten NaCl-CsCl eutectic as measured by absorption spectrophotometry

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Myochin, Munetaka; Yamana, Hajimu*

Radiochimica Acta, 97(4-5), p.209 - 212, 2009/05

 Times Cited Count:3 Percentile:24.54(Chemistry, Inorganic & Nuclear)

Redox behavior of uranium and plutonium in molten salts is the essential information for establishing an effective reprocessing process with spent MOX fuel. In an oxide electro-winning reprocessing process, the spent nuclear fuel is dissolved into the molten NaCl-CsCl eutectic, and the dissolved U(VI) and Pu(VI) species are reduced to be dioxides by electrolysis. In the present study, formal redox potentials of the Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in the molten NaCl-CsCl eutectic at 923 K were determined. The fractions of Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$ were determined by UV/Vis/NIR absorption spectrophotometry. PuO$$_{2}$$ was dissolved into the molten NaCl-CsCl eutectic by Cl$$_{2}$$$$_{2}$$ gas purging. Valences of plutonium (Pu$$^{0}$$, Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$) were controlled by changing the flow rates of Cl$$_{2}$$, O$$_{2}$$, and Ar gases.

Journal Articles

Oxide conversion of salt waste from dry reprocessing

Sato, Fuminori; Terunuma, Hitoshi*; Arai, Osamu*; Myochin, Munetaka

Nihon Genshiryoku Gakkai Wabun Rombunshi, 8(1), p.83 - 94, 2009/03

Oxide conversion using water vapor and boron oxide (B$$_{2}$$O$$_{3}$$) was studied to treat salt waste from dry reprocessing. Parameter tests to CsCl and NaCl-2CsCl salt were performed and fundamental data such as conversion rate, etc. were acquired. To understand the process behavior, a reaction analysis based on thermodynamic equilibrium calculation considering salt (NaCl, CsCl), oxide (Na$$_{2}$$O, Cs$$_{2}$$O, B$$_{2}$$O$$_{3}$$) and gas (H$$_{2}$$O, Ar, HCl, NaCl, CsCl) phase was performed. The validity of analysis was confirmed by comparison with the experiment. Using this result, process condition of the oxide conversion (ex. temperature, added amount of H$$_{2}$$O and B$$_{2}$$O$$_{3}$$, etc.) was discussed.

Journal Articles

Research and development of pyroprocessing technology in Japan

Inoue, Tadashi*; Koyama, Tadafumi*; Myochin, Munetaka; Arai, Yasuo

Proceedings of 2008 Joint Symposium on Molten Salts (USB Flash Drive), p.851 - 856, 2008/10

Recent progress of pyrochemical reprocessing technology based on metal electrorefining process and nitride electrorefining process is introduced. This technology can be applied to oxide fuel as well as metal fuel by adding the oxide reduction process. In addition to the development of process technology for electrorefining, thermodynamic database of actinides and lanthanides in molten salt or liquid metal has been prepared. The progress of pyrochemical reprocessing technology, which has the advantage of proliferation resistance and whole recovery of minor actinides, has been demonstrated.

Journal Articles

Effect of pulse electrolysis on morphology of co-deposited MOX granules

Kofuji, Hirohide; Okamura, Nobuo; Mizuguchi, Koji*; Myochin, Munetaka

Journal of Nuclear Science and Technology, 45(9), p.942 - 950, 2008/09

 Times Cited Count:1 Percentile:17.03(Nuclear Science & Technology)

In the oxide electrowinning method of nuclear fuel recycling, the applicability of the pulse electrolysis method to the MOX co-deposition process was evaluated. Several experiments were conducted involving uranium, plutonium, and elements simulating fission product (FP) or corrosion product (CP). Through study of the results of these experiments, the influences of the impurities and the effect of the waveform of electrolysis pulses on the electro-deposit were clarified. As a result, pulse electrolysis conditions which could restrain Pu enrichment of the deposited MOX were confirmed. Furthermore, it was found that the element distribution in the MOX granule obtained by the pulse electrolysis was homogenized, which is well suited for nuclear fuel fabrication. Finally, a qualitative model of the pulse electrolysis reaction near the field of cathode surface is proposed.

Journal Articles

Use of thermodynamic simulation for preliminary study on electrolyte recycle process by the phosphate conversion technique

Amamoto, Ippei; Kofuji, Hirohide; Myochin, Munetaka; Terai, Takayuki*

Shimyureshon, 27(3), p.189 - 197, 2008/09

Some specific FPs are apt to remain in the medium (electrolyte) used in pyroprocessing even after recovery of uranium and transuranic elements. It is desirable to have the spent electrolyte purified for recycling which in turn, could lead to the reduction of HLW. This study is carried out to evaluate the feasibility of the electrolyte recycle process by the phosphates conversion technique. The evaluation was undertaken mainly by thermodynamic simulation which was especially highlighted the conversion effect at the Spent Electrolyte Generation Step. The obtained computational value and a conceptual idea for recovery of precipitates by this simulation were then reflected to establish the preliminary conceptual flow diagram which would facilitate the next discussion and experiment for the realization of this process.

Journal Articles

Pyro-chemical reprocessing using molybdate melt chemical and electrochemical behaviors of uranium oxides in Na$$_{2}$$MoO$$_{4}$$ melt

Mizuguchi, Koji; Yasuike, Yoshiyuki*; Fukushima, Mineo; Myochin, Munetaka

Nihon Genshiryoku Gakkai Wabun Rombunshi, 6(4), p.484 - 490, 2007/12

We develop a new decladding process which integrates with dissolution using the molybdenum oxide melt. This melt possesses characteristics that can make actinide oxide dissolve at high speed without reacting with metal such as the cladding tube. To construct the new process, it is necessary to clarify the reaction mechanisms of uranium in dissolution, oxidation, and electrolysis in this melt. In this study, the gram-scale uranium examination was carried out, and the reaction mechanism of the uranium in the melt was clarified. In Na$$_{2}$$MoO$$_{4}$$ - Na$$_{2}$$Mo$$_{2}$$O$$_{7}$$ melts, uranium dioxide dissolves as Na$$_{4}$$U(MoO$$_{4}$$)$$_{4}$$ without changing its oxidation number. In the oxidation, uranium valence was oxidized from IV to VI with oxygen. In electrolysis process, it was clarified that the low current efficiency was caused by the re-dissolution of deposit. The granulated UO$$_{2}$$ was recovered on the cathode by adjusting the temperature of the melt to 700 degrees centigrade at which re-dissolution was reduced.

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