Study on the relation between the crystal structure and thermal stability of FeUO and CrUO

Akiyama, Daisuke*; Kusaka, Ryoji; Kumagai, Yuta; Nakada, Masami; Watanabe, Masayuki; Okamoto, Yoshihiro; Nagai, Takayuki; Sato, Nobuaki*; Kirishima, Akira*

Journal of Nuclear Materials, 568, p.153847_1 - 153847_10, 2022/09

https://doi.org/10.1016/j.jnucmat.2022.153847

FeUO, CrUO, and FeCrUO are monouranates containing pentavalent U. Even though these compounds have similar crystal structures, their formation conditions and thermal stability are significantly different. To determine the factors causing the difference in thermal stability between FeUO and CrUO, their crystal structures were evaluated in detail. A Raman band was observed at 700 cm in all the samples. This Raman band was derived from the stretching vibration of the O-U-O axis band, indicating that FeCrUO was composed of a uranyl-like structure in its lattice regardless of its "x"' value. Mssbauer measurements indicated that the Fe in FeUO and FeCrUO were trivalent. Furthermore, FeCrUO lost its symmetry around Fe with increasing electron densities around Fe, as the abundance of Cr increased. These results suggested no significant structural differences between FeUO and CrUO. Thermogravimetric measurements for UO, FeUO, and CrUO showed that the temperature at which FeUO decomposed under an oxidizing condition (approximately 800 C) was significantly lower than the temperature at which the decomposition of CrUO started (approximately 1250 C). Based on these results, we concluded that the decomposition of FeUO was triggered by an "in-crystal" redox reaction, i.e., Fe U Fe U, which would not occur in the CrUO lattice because Cr could never be reduced under the investigated condition. Finally, the existence of Cr in FexCrUO effectively suppressed the decomposition of the FeCrUO crystal, even at a very low Cr content.

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.

Cabling technology of NbSn conductor for ITER central solenoid

Takahashi, Yoshikazu; Nabara, Yoshihiro; Ozeki, Hidemasa; Hemmi, Tsutomu; Nunoya, Yoshihiko; Isono, Takaaki; Matsui, Kunihiro; Kawano, Katsumi; Oshikiri, Masayuki; Uno, Yasuhiro; et al.

IEEE Transactions on Applied Superconductivity, 24(3), p.4802404_1 - 4802404_4, 2014/06

https://doi.org/10.1109/TASC.2013.2287311

Japan Atomic Energy Agency (JAEA) is procuring all amounts of NbSn conductors for Central Solenoid (CS) in the ITER project. Before start of mass-productions, the conductor should be tested to confirm superconducting performance in the SULTAN facility, Switzerland. The original design of cabling twist pitches is 45-85-145-250-450 mm, called normal twist pitch (NTP). The test results of the conductors with NTP was that current shearing temperature (Tcs) is decreasing due to electro-magnetic (EM) load cycles. On the other hand, the results of the conductors with short twist pitches (STP) of 25-45-80-150-450 mm show that the Tcs is stabilized during EM load cyclic tests. Because the conductors with STP have smaller void fraction, higher compaction ratio during cabling is required and possibility of damage on strands increases. The technology for the cables with STP was developed in Japanese cabling suppliers. The several key technologies will be described in this paper.

High-temperature X-ray imaging study of simulated high-level waste glass melt

Okamoto, Yoshihiro; Nakada, Masami; Akabori, Mitsuo; Komamine, Satoshi*; Fukui, Toshiki*; Ochi, Eiji*; Nitani, Hiroaki*; Nomura, Masaharu*

Proceedings of 4th Asian Conference on Molten Salt Chemistry and Technology & 44th Symposium on Molten Salt Chemistry, Japan, p.47 - 52, 2012/09

The molten state of the simulated high-level waste glass and the behavior of ruthenium element in the melt were investigated by using synchrotron radiation based X-ray imaging technique. Melting, generating and moving of bubbles, condensation and sedimentation of ruthenium element were observed dynamically in continuous 12-bit gray-scale images from the CCD camera. The existence of ruthenium in the X-ray CCD image was emphasized over the energy of Ru K-absorption edge. X-ray intensity was obtained easily by digitalizing gray-scale values in the image. Position sensitive imaging X-ray absorption fine structure (XAFS) measurement was performed to clarify the chemical state of ruthenium element in the melt.

Valence state of Am in (UAm)O

Nishi, Tsuyoshi; Nakada, Masami; Suzuki, Chikashi; Shibata, Hiroki; Okamoto, Yoshihiro; Akabori, Mitsuo; Hirata, Masaru

Journal of Nuclear Materials, 418(1-3), p.311 - 312, 2011/11

https://doi.org/10.1016/j.jnucmat.2011.07.016

The XAFS measurements at U-L and Am-L absorption edge of (UAm)O were performed in transmission mode. Moreover, to clarify the valence state of Am in (U,Am)O, the XANES spectrum of Am-L absorption edge of (UAm)O was verified using those of Am-L absorption edge of AmO and AmO. It was found that the XANES spectrum of the Am-L edge of (UAm)O is in good accordance with that of AmO. Thus, Am in (UAm)O is almost trivalent state.

Observation of Ru in high-temperature molten simulated glass by X-ray imaging

Okamoto, Yoshihiro; Nakada, Masami; Akabori, Mitsuo; Kawashima, Hidenori*; Komamine, Satoshi*; Ochi, Eiji*; Nitani, Hiroaki*; Nomura, Masaharu*

no journal, , 

The molten state of simulated high-level waste glass and the behavior of ruthenium element in the melt were investigated by using synchrotron radiation based X-ray imaging technique. Melting, generating and moving of bubbles, condensation and sedimentation of ruthenium element were observed dynamically in continuous 12-bit gray-scale images from the CCD camera. The imaging XAFS results of our experiment clearly show that the ruthenium in the high temperature glass melt exists as oxide.

Behavior of insoluble residue in the fused glass, 6; Chemical properties of simulated glasses by Fe-57 Moessbauer spectroscopy and synchrotron radiation imaging

Nakada, Masami; Nagayama, Sachiko*; Okamoto, Yoshihiro; Akabori, Mitsuo; Kawashima, Hidenori*; Komamine, Satoshi*; Ochi, Eiji*

no journal, , 

no abstracts in English

Analysis of redox and structural properties of Fe in clay minerals by Fe-57 Mssbauer spectroscopy

Morii, Shiori; Yomogida, Takumi; Nakada, Masami; Oka, Toshitaka; Kitatsuji, Yoshihiro; Takahashi, Yoshio*

no journal, , 

To understand the influence of redox properties of structural Fe in clay minerals on removal and immobilization of radionuclides in geological disposal environment, we are investigating redox and structural properties of Fe in clay minerals over a large range of redox potentials. Clay mineral sample was reduced by controlled-potential electrolysis. Redox state and structural properties of Fe in this prepared clay mineral sample was investigated by Fe-57 Mssbauer spectroscopy. From the Mssbauer spectra, we obtained information about the amount of structural Fe(II) which reduced from structural Fe(III) and structural properties of Fe(II).

Dependence of the redox state of structural Fe in nontronite on Eh and pH condition

Morii, Shiori; Yomogida, Takumi; Nakada, Masami; Oka, Toshitaka; Kitatsuji, Yoshihiro; Takahashi, Yoshio*

no journal, , 

The purpose of this research is to understand the redox reaction between structural Fe in clay minerals and concomitant elements in environments. Then, we are investigating redox properties of Fe in clay minerals over a large range of redox potentials (Eh) and pH. Redox state of the Fe-bearing clay mineral sample (nontronite) was controlled by potential electrolysis at various Eh-pH conditions. From this experiment, we obtained information about the dependence of the redox state of structural Fe in clay minerals on Eh and pH conditions.

Synchrotron radiation based imaging XAFS analysis of simulated high-level waste glass

Okamoto, Yoshihiro; Nakada, Masami; Akabori, Mitsuo; Komamine, Satoshi*; Fukui, Toshiki*; Ochi, Eiji*; Nitani, Hiroaki*; Nomura, Masaharu*

no journal, , 

Distribution and the chemical state of fission product elements like Zr, Mo and Ru in the simulated high-level waste glass were examined by using the synchrotron radiation based X-ray imaging technique. We used the high resolution imaging system and the high-speed CCD camera for imaging XAFS measurement of the glass sample at molten state. Position sensitive X-ray absorption spectra were obtained by analyzing gray scale in images of the CCD camera.