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Journal Articles

Study on the relation between the crystal structure and thermal stability of FeUO$$_{4}$$ and CrUO$$_{4}$$

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

FeUO$$_{4}$$, CrUO$$_{4}$$, and Fe$$_{x}$$Cr$$_{1-x}$$UO$$_{4}$$ 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$$_{4}$$ and CrUO$$_{4}$$, their crystal structures were evaluated in detail. A Raman band was observed at 700 cm$$^{-1}$$ in all the samples. This Raman band was derived from the stretching vibration of the O-U-O axis band, indicating that Fe$$_{x}$$Cr$$_{1-x}$$UO$$_{4}$$ was composed of a uranyl-like structure in its lattice regardless of its "x"' value. M$"o$ssbauer measurements indicated that the Fe in FeUO$$_{4}$$ and Fe$$_{x}$$Cr$$_{1-x}$$UO$$_{4}$$ were trivalent. Furthermore, Fe$$_{x}$$Cr$$_{1-x}$$UO$$_{4}$$ lost its symmetry around Fe$$^{mathrm{III}}$$ with increasing electron densities around Fe$$^{mathrm{III}}$$, as the abundance of Cr increased. These results suggested no significant structural differences between FeUO$$_{4}$$ and CrUO$$_{4}$$. Thermogravimetric measurements for UO$$_{2}$$, FeUO$$_{4}$$, and CrUO$$_{4}$$ showed that the temperature at which FeUO$$_{4}$$ decomposed under an oxidizing condition (approximately 800 $$^{circ}$$C) was significantly lower than the temperature at which the decomposition of CrUO$$_{4}$$ started (approximately 1250 $$^{circ}$$C). Based on these results, we concluded that the decomposition of FeUO$$_{4}$$ was triggered by an ``in-crystal'' redox reaction, i.e., Fe$$^{mathrm{III}}$$ $${+}$$ U$$^{mathrm{V}}$$ $$rightarrow$$ Fe$$^{mathrm{II}}$$ $${+}$$ U$$^{mathrm{VI}}$$, which would not occur in the CrUO$$_{4}$$ lattice because Cr$$^{mathrm{III}}$$ could never be reduced under the investigated condition. Finally, the existence of Cr$$^{mathrm{III}}$$ in FexCr$$_{1-x}$$UO$$_{4}$$ effectively suppressed the decomposition of the Fe$$_{x}$$Cr$$_{1-x}$$UO$$_{4}$$ crystal, even at a very low Cr content.

Journal Articles

Investigation of high-temperature chemical interaction of calcium silicate insulation and cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*

Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09

 Times Cited Count:4 Percentile:57.22(Nuclear Science & Technology)

The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H$$_{2}$$ and Ar-4%H$$_{2}$$-20%H$$_{2}$$0 with maximum temperature of 1100$$^{circ}$$C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (Ca$$_{6}$$Si$$_{6}$$0$$_{17}$$(0H)$$_{2}$$), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730$$^{circ}$$C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0$$_{3}$$), the interaction occurred over temperature range 700-1100$$^{circ}$$C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H$$_{2}$$ and Ar-4%H$$_{2}$$-20%H$$_{2}$$0 atmosphere, cesium aluminum silicate, CsAlSi0$$_{4}$$ was formed with aluminum in the samples as an impurity or adduct.

Journal Articles

Measurements and analyses of the ratio of $$^{238}$$U captures to $$^{235}$$U fission in low-enriched UO$$_{2}$$ tight lattices

Nakajima, Ken; ; Yamamoto, Toshihiro; ; Suzaki, Takenori

Journal of Nuclear Science and Technology, 31(11), p.1160 - 1170, 1994/11

 Times Cited Count:7 Percentile:57.12(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Measurements of the modified conversion ratio by gamma-ray spectrometry of fuel rods for water-moderated UO$$_{2}$$ cores

Nakajima, Ken; ; Suzaki, Takenori

Nuclear Science and Engineering, 116, p.138 - 146, 1994/00

 Times Cited Count:16 Percentile:79.14(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Installation and execution of criticality and radiation shielding analysis codes on engineering work station

Masukawa, Fumihiro; ; Inoue, Osamu*; Hara, Toshiharu*

JAERI-M 93-024, 31 Pages, 1993/02

JAERI-M-93-024.pdf:0.84MB

no abstracts in English

JAEA Reports

JAEA Reports

Control rod effects on reaction rate distributions in tight pitched PuO$$_{2}$$-UO$$_{2}$$ fuel assembly

C-S.Gil*; Okumura, Keisuke;

JAERI-M 91-200, 61 Pages, 1991/11

JAERI-M-91-200.pdf:1.26MB

no abstracts in English

Journal Articles

Effect of fuel grain size on reactivity

Okuno, Hiroshi; Naito, Yoshitaka; Sakurai, Y.*

Journal of Nuclear Science and Technology, 28(10), p.958 - 960, 1991/10

no abstracts in English

JAEA Reports

JAERI contribution to the second NEACRP benchmark calculation on high conversion light water reactor lattices

Okumura, Keisuke; ; Tanaka, Kenichi*; C-J.Jeong*

JAERI-M 89-201, 150 Pages, 1989/12

JAERI-M-89-201.pdf:3.31MB

no abstracts in English

Journal Articles

Sensitivity analysis of cell neutronic parameters in high-conversion light-water reactors

*; *;

Journal of Nuclear Science and Technology, 24(8), p.610 - 620, 1987/08

 Times Cited Count:3 Percentile:38.59(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Vectorization of Continuos Energy Monte Carlo Code VIM

*; ;

JAERI-M 86-190, 52 Pages, 1987/01

JAERI-M-86-190.pdf:1.24MB

no abstracts in English

Journal Articles

Kinetics of the thermal decomposition of nickel iodide

Nakajima, Hayato; Shimizu, Saburo; ; Ikezoe, Yasumasa;

Nihon Kagakkai-Shi, 8, p.1257 - 1261, 1984/00

no abstracts in English

Journal Articles

Measurements of O/U ratio and oxygen potential for UO$$_{2}$$$$_{+}$$$$_{chi}$$(0≦x≦0.1)

Ugajin, Mitsuhiro

Journal of Nuclear Science and Technology, 20(3), p.228 - 236, 1983/00

 Times Cited Count:17 Percentile:84.4(Nuclear Science & Technology)

no abstracts in English

Journal Articles

The precipitation of thorium or plutonium(VI) oxalato complex ion with cobalt(III) or chromium(III) complex cation

;

Radiochem.Radioanal.Lett., 29(6), p.331 - 340, 1977/06

no abstracts in English

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