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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).
, Zr, and stainless steel and leaching behavior of the fission products and matrix elementsTonna, Ryutaro*; Sasaki, Takayuki*; Kodama, Yuji*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki
Nuclear Engineering and Technology, 55(4), p.1300 - 1309, 2023/04
Times Cited Count：2 Percentile：84.55(Nuclear Science & Technology)Simulated debris was synthesized using UO, Zr, and stainless steel and a heat treatment method under inert or oxidizing conditions. The primary U solid phase of the debris synthesized at 1473 K under inert conditions was UO, whereas a (U,Zr)O solid solution formed at 1873 K. Under oxidizing conditions, a mixture of UO and (Fe,Cr)UO phases formed at 1473 K whereas a (U,Zr)O
solid solution formed at 1873 K. The leaching behavior of the fission products from the simulated debris was evaluated using two methods: the irradiation method, for which fission products were produced via neutron irradiation, and the doping method, for which trace amounts of non-radioactive elements were doped into the debris. The dissolution behavior of U depended on the properties of the debris and aqueous medium the debris was immersed in. Cs, Sr, and Ba leached out regardless of the primary solid phases. The leaching of high-valence Eu and Ru ions was suppressed, possibly owing to their solid-solution reaction with or incorporation into the uranium compounds of the simulated debris.
-SUS system prepared by irradiation or tracer doping methodSasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki
no journal, ,
-SS systemSasaki, Takayuki*; Kodama, Yuji*; Tonna, Ryutaro*; Kobayashi, Taishi*; Kumagai, Yuta; Kusaka, Ryoji; Watanabe, Masayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; et al.
no journal, ,
no abstracts in English
-Zr-SS system; Irradiation or addition methodSasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Watanabe, Masayuki; Kumagai, Yuta; Kusaka, Ryoji
no journal, ,
We synthesized simulated fuel debris which containing stainless steel and zirconium. The fission of Uranium by the irradiation of thermal neutron or non-radioactive elements was fed in the simulated fuel debris as fission products (FP), and the sample was immersed in pure water or artificial sea water. In this presentation, we would report the behavior of the solubility of the FP and the interpretation of its results.
Sasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Watanabe, Masayuki; Kumagai, Yuta; Kusaka, Ryoji
no journal, ,
Fuel debris containing alloy phases is expected to be formed in the Fukushima Daiichi Nuclear Power Plant. In this study, two series of simulated debris samples comprising uranium-zirconium-stainless steel were synthesized. One series of the samples was prepared by the irradiation method, where the samples were irradiated by thermal neutron for fission generation. The other was prepared by the doping method, where stable isotopes of FPs were added during the synthesis. We performed leaching tests as an aging treatment, and then measured structural changes in the samples and the elution rates of U and FPs contained in the samples. Moreover, in order to evaluate the colloid formation of these elements, particle size distribution was analyzed by an ICP-MS method combined with filtration using different pore-size filters or size exclusion chromatography. Based on the results, the chemical stability of the simulated debris and the speciation of the eluted nuclides were discussed.
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.
