Introduction to dismantling and decommissioning chemistry

Sato, Nobuaki*; Kameo, Yutaka; Sato, Soichi; Kumagai, Yuta; Sato, Tomonori; Yamamoto, Masahiro*; Watanabe, Yutaka*; Nagai, Takayuki; Niibori, Yuichi*; Watanabe, Masayuki; et al.

Introduction to Dismantling and Decommissioning Chemistry, 251 Pages, 2024/09

This book focuses on the dismantling and decommissioning of nuclear facilities and reactors that have suffered severe accidents. In Part 1, we introduce basic aspects ranging from fuel chemistry, analytical chemistry, radiation chemistry, corrosion, and decontamination chemistry to waste treatment and disposal. Then, Part 2 covers the chemistry involved in the decommissioning of various nuclear facilities, and discusses what chemical approaches are necessary and possible for the decommissioning of TEPCO's Fukushima Daiichi Nuclear Power Plants, how decommissioning should be carried out, and what kind of research and development and also human resource development are required for this.

Dissolution behavior and aging of iron-uranium oxide

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

https://doi.org/10.1016/j.jnucmat.2023.154862

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 UO 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).

Investigation of chemical state of uranium included in simulated waste glass

Nagai, Takayuki; Akiyama, Daisuke*; Kirishima, Akira*; Katsuoka, Nanako; Okamoto, Yoshihiro; Sato, Nobuaki*

2022-Nendo "Busshitsu, Debaisu Ryoiki Kyodo Kenkyu Kyoten" Kenkyu Seika, Katsudo Hokokusho (Internet), 1 Pages, 2023/09

https://five-star.sanken.osaka-u.ac.jp/report-file/2022/report_20221047.pdf

no abstracts in English

Phase analysis of simulated nuclear fuel debris synthesized using UO, Zr, and stainless steel and leaching behavior of the fission products and matrix elements

Tonna, 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

https://doi.org/10.1016/j.net.2022.12.017

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.

Structure, stability, and actinide leaching of simulated nuclear fuel debris synthesized from UO, Zr, and stainless-steel

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

Journal of Nuclear Materials, 567, p.153842_1 - 153842_15, 2022/08

https://doi.org/10.1016/j.jnucmat.2022.153842

To understand the chemical structure and stability of nuclear fuel debris consisting of UO, Zr, and Stainless Steel (SUS) generated by the Fukushima Daiichi Nuclear Power Plant accident in Japan in 2011, simulated debris of the UO-SUS-Zr system and other fundamental component systems were synthesized and characterized. The simulated debris were synthesized by heat treatment for 1 to 12 h at 1600C, in inert (Ar) or oxidative (Ar + 2% O) atmospheres. Np and Am tracers were doped for the leaching tests of these elements and U from the simulated debris. The characterization of the simulated debris was conducted by XRD, SEM-EDX, Raman spectroscopy, and Mssbauer spectroscopy, which provided the major uranium phase of the UO -SUS-Zr debris was the solid solution of UO (s.s.) with Zr(IV) and Fe(II) regardless of the treatment atmosphere. The long-term immersion test of the simulated debris in pure water and that in seawater revealed the macro scale crystal structure of the simulated debris was chemically very stable in the wet condition for a year or more. Furthermore, the leaching test results showed that the actinide leaching ratios of U, Np, Am from the UO-SUS-Zr debris were very limited and less than 0.08 % for all the experiments in this study.

A Study of HO-induced oxidative degradation of simulated fuel debris

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

Hoshasen Kagaku (Internet), (113), p.61 - 64, 2022/04

The severe accident at TEPCO's Fukushima Daiichi Nuclear Power Station resulted in generation of fuel debris. The fuel debris is in contact with water and the radiolysis of water can accelerate degradation of the debris. The analysis of particles sampled from inside or near the damaged reactors indicates the complicated compositions of the fuel debris. It is challenging to estimate the effect of water radiolysis on such a complicated material. Therefore, in this study, we investigated the potential degradation process by leaching experiments of simulated fuel debris in aqueous HO solution. The results show that the reaction of HO induced uranium dissolution from most of the samples and then formation of uranyl peroxides. In contrast, a sample that had U-Zr oxide solid solution as the major phase exhibited remarkable resistance to HO. These findings revealed that the degradation of the simulated debris reflects the reactivity and stability of the uranium phase in the matrices.

Speciation on the reaction of uranium and zirconium oxides treated under oxidizing and reducing atmospheres

Uehara, Akihiro*; Akiyama, Daisuke*; Ikeda, Atsushi; Numako, Chiya*; Terada, Yasuko*; Nitta, Kiyofumi*; Ina, Toshiaki*; Takeda-Homma, Shino*; Kirishima, Akira*; Sato, Nobuaki*

Journal of Nuclear Materials, 559, p.153422_1 - 153422_11, 2022/02

https://doi.org/10.1016/j.jnucmat.2021.153422

Distribution of studtite and metastudtite generated on the surface of UO; Application of Raman imaging technique to uranium compound

Kusaka, Ryoji; Kumagai, Yuta; Yomogida, Takumi; Takano, Masahide; Watanabe, Masayuki; Sasaki, Takayuki*; Akiyama, Daisuke*; Sato, Nobuaki*; Kirishima, Akira*

Journal of Nuclear Science and Technology, 58(6), p.629 - 634, 2021/06

https://doi.org/10.1080/00223131.2020.1854881

Investigation of chemical state of uranium included in simulated waste glass

Nagai, Takayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Okamoto, Yoshihiro

2019-Nendo "Busshitsu, Debaisu Ryoiki Kyodo Kenkyu Kyoten" Oyobi "Hito, Kankyo To Busshitsu O Tsunagu Inobeshion Soshutsu Dainamikku, Araiansu" Kenkyu Seika, Katsudo Hokokusho (CD-ROM), P. 20191107_1, 2020/11

no abstracts in English

Structural change of borosilicate glass by neutron irradiation

Nagai, Takayuki; Kobayashi, Hidekazu; Okamoto, Yoshihiro; Akiyama, Daisuke*; Sato, Nobuaki*; Uehara, Akihiro*; Fujii, Toshiyuki*; Sekimoto, Shun*

KURNS Progress Report 2018, P. 105, 2019/08

https://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep2018/KURNS_Progress_Report2018_web.pdf

To understand this structural change of a borosilicate glass by a neutron irradiation in detail, the irradiation test was carried out in KUR in 2017FY. The glass structure was estimated by using Raman spectrometry in 2018FY. Comparing with the Raman spectra of glass samples before and after irradiation, it could be observed the change of peak height of Si-O bridging structure by the irradiation.