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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：0 Percentile：0.01(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 FeO 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 UO).
Ozu, Akira; Esaka, Fumitaka; Kawakita, Hiroshi*; Okamoto, Ryuta*; Imaki, Masaharu*; Kobayashi, Takao*
Reviewed and Revised Papers Presented at the 23rd International Laser Radar Conference (ILRC-23), p.107 - 108, 2006/07
We have demonstrated that asbestos particles in air can be visualized with laser-induced fluorescence emitted from asbestos. A ultra-violet (266 nm) laser pulse is used to excite asbestos particles suspended in a closed vessel. The fluorescence emitted from the asbestos in the region where the laser beam passes through is detected with a low-pass optical filter and an image intensified CCD camera with ultra-fast gate shutter. Many asbestos particles in the region are separately visualized on an image. It is possible to derive from the image the number and size of asbestos particles through image data processing. The method described in this study is expected to be useful in real-time monitoring of the concentration of asbestos particle.
Ozu, Akira; Okamoto, Ryuta*; Kawakita, Hiroshi*
Kurin Tekunoroji, 16(3), p.56 - 61, 2006/03
In recent years, particle counting devices capable of monitoring particles suspended in air on real-time basis are of considerable practical concern in the fields of semiconductor and large display panel industries. A remote particle counter, which had been developed for monitoring aerosols released in air from nuclear facilities, has been applied to a measurement system for clean rooms used in the fields. It can visualize the particles in narrow space at a distance of 6m and derive the number and size distribution of particles with diameter of above 0.5 microns. By improving the laser energy, sensitivity of the image intensifier camera, and magnification of the zoom lens used in the system, it is possible to detect the particles with diameters of below 0.5 microns. The method and the current performance of the measurement system are described.
Ozu, Akira; Kawakita, Hiroshi*; Okamoto, Ryuta*
Proceedings of 7th International Congress on Optical Particle Characterization (OPC 2004) (CD-ROM), 5 Pages, 2004/00
Optical particle counters (OPCs) using laser light-scattering methods are widely used for aerosol research because they can provide accurate in situ measurements on real time basis. However, in general, it takes a few minutes to count the number of particles suspended in the air. As a novel method, we have developed a remote particle counter (RPC) using an imaging lidar technique, capable of determining with a single laser shot the number and size distribution of particles in the air several meters apart from the observation station. An experimental study has been conducted to calibrate the RPC system. The results obtained in the laboratory test are described compared to those with a conventional OPC using laser light-scattering methods. As the result,the real time measurement of the number and the histogram based on the size distribution of particles in air has been successfully demonstrated with the RPC system.
Sakamoto, Atsushi; Sano, Yuichi; Kofuji, Hirohide; Watanabe, Masayuki; Koizumi, Kenji; Okamoto, Sanae*; Misumi, Ryuta*; Kaminoyama, Meguru*
no journal, ,
no abstracts in English
Okamoto, Masayuki*; Nakayama, Yuta*; Ogawa, Fumio*; Hashidate, Ryuta; Hiyoshi, Noritake*; Wakai, Takashi; Ito, Takamoto*
no journal, ,
no abstracts in English
Tonna, Ryutaro*; Sasaki, Takayuki*; Okamoto, Yoshihiro; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*
no journal, ,
Since fuel debris recovered from the Fukushima Daiichi Nuclear Power Plant may be directly disposed of in deep geological strata, knowledge of dissolution reactions of fuel debris in water and chemical states of dissolved nuclides is essential for safety assessment of disposals. The chemical composition and physical properties of fuel debris depend on the atmosphere and temperature, but the formation of FeUO
has been suggested at conditions under which air enters the reactor from outside. Uranium in FeUO is reported to be pentavalent, but no dissolution reaction in water has been investigated. In this study, FeUO was synthesized by heating at a predetermined temperature and oxygen pressure, immersed in nitric acid to remove unreacted uranium oxides, and then immersed in a solution of pH2-8. After the prescribed period, pH and Eh values were measured, and dissolved iron and uranium concentrations were measured by ICP-MS. X-ray absorption fine structure (XAFS) and powder X-ray diffraction (XRD) were used to evaluate the solid state before and after immersion. From these results, it was interpreted that the dissolution of FeUO was accompanied by a redox reaction between Fe(III)/Fe(II) and U(V)/U(VI) during dissolution.
