Structural investigation of simulated waste glass surface drained in operation confirmation test of 3rd TVF glass melter

Nagai, Takayuki; Hasegawa, Takehiko*

JAEA-Research 2023-008, 41 Pages, 2023/12

JAEA-Research-2023-008.pdf:7.52MB

To reduce the risks posed by stored the high-level radioactive liquid waste (HAW), Tokai Vitrification Facility (TVF) is working to produce the HAW into vitrified bodies. With the aim of steady vitrification of HAW in TVF, the vitrification technology section has manufactured a new 3rd melter with an improved bottom structure and is working to verify the performance of this melter. In this study, solidified glass samples were taken from simulated vitrified bodies produced by flowing molten glass during the bottom drain-out test in the operation confirmation of the TVF 3rd melter. And the properties of the surface layer and fracture surface of the vitrified bodies were evaluated by using Raman spectroscopy, synchrotron radiation XAFS measurement, and laser ablation inductively coupled plasma atomic emission spectroscopy (LA ICP-AES) analysis. As a result of measuring the surface layer and fracture surface of the solidified samples produced on an actual scale, a slight difference was confirmed between the properties of the surface layer and those of the fracture surface. Since the chemical composition of these simulated vitrified bodies does not contain platinum group elements, it is expected that the glass structure of solidified glass samples is different from that of the actual vitrified body. However, this sample measuring was a valuable opportunity to evaluate samples produced by using the direct energized joule heating method. The properties of cullet used the operation confirmation of the TVF 3rd melter and the cullet of another production lot were measured and analyzed in the same manner under the measuring conditions of solidified glass samples. As a result, it was confirmed that cullet with different producing histories have different glass structures even with the same chemical composition, and that differences in glass structures remain in the glass samples after melting these cullet.

Structural evaluation of coagulated surface of simulated waste glass by using Raman spectroscopy

Nagai, Takayuki

JAEA-Research 2022-014, 84 Pages, 2023/02

JAEA-Research-2022-014.pdf:22.26MB

Most of the simulated waste glasses used for physical property evaluation are processed into a shape suitable for the measurement method from glass gob obtained by slowly cooling molten glass to room temperature. However, the actual vitrified waste glass material is obtained by cooling and being coagulated the glass drained from the bottom of glass melter into the canister. In this study, Raman spectroscopy was performed on the coagulated surface of molten simulated waste glass in the depth direction to evaluate the state of the Si-O bridging structure near the coagulated glass surface. The Raman spectra measured from the surface to the depth direction near the surface of the glasses produced by several melting and coagulation conditions of molten simulated waste glass cullet in the air atmosphere, and it was confirmed that there were changes in these spectra. On the other hand, the raw material glass cullet and the surface of the glass solidified in argon gas atmosphere showed little change in the spectrum in the depth direction, and the Si-O bridging structure near the glass surface was similar. It was also confirmed that the spectrum change in the depth direction measurement was small for the cut surface of the glass, and that the change in the spectrum for the broken glass fracture surface was also small. For glasses with a large change in Raman spectra in the depth direction near the coagulated surface, the molten glass was cooled from the molten state to room temperature in a muffle furnace with air atmosphere. That is, the magnitude of the spectral change with respect to the depth direction depends on the time from the molten state to coagulation. In order to confirm the reason why the number of bridging oxygen in the Si-O bridging structure is small on the coagulated surface of glass, the XANES spectra of Si-K edge and Ce-L3 edge were measured by XAFS on the coagulated surface and the cutting face. As a result, the Si-K edge peak on the coagulated surface is

Structural change by phosphorus addition to borosilicate glass containing simulated waste components

Okamoto, Yoshihiro; Shiwaku, Hideaki; Shimamura, Keisuke*; Kobayashi, Hidekazu; Nagai, Takayuki; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*

Journal of Nuclear Materials, 570, p.153962_1 - 153962_13, 2022/11

https://doi.org/10.1016/j.jnucmat.2022.153962

Simulated nuclear waste glass samples containing phosphorus, which increase the solubility of molybdenum, were prepared and analyzed using synchrotron X-ray Absorption Fine Structure (XAFS) analysis for some constituent elements and Raman spectroscopic analysis of their complex structure. Changes in local structure and chemical state due to different phosphorus additions and waste loading rates were systematically studied. Consequently, no crystalline phase due to the molybdate compound was observed even at a maximum waste content of 30 wt% (corresponding to 1.87 mol% MoO). Oxidation proceeded when the waste-loading rate was increased, whereas the reduction proceeded when phosphorus was added. In some cases, the effects of oxidation and reduction were offset. The local structure around specific elements can be classified as follows; Zn that is affected mainly by the waste-loading rate, Ce that is affected by both the waste-loading rate and phosphorus addition, and Zr element that is not affected by either of them. From the comparison between the analytical results of Mo and other elements, it was considered that the added phosphorus exists as a free PO structural unit and may deprive the alkali metal coordinated to the molybdate ion.

Nanoscopic structure of borosilicate glass with additives for nuclear waste vitrification

Motokawa, Ryuhei; Kaneko, Koji; Oba, Yojiro; Nagai, Takayuki; Okamoto, Yoshihiro; Kobayashi, Taishi*; Kumada, Takayuki; Heller, W. T.*

Journal of Non-Crystalline Solids, 578, p.121352_1 - 121352_7, 2022/02

https://doi.org/10.1016/j.jnoncrysol.2021.121352

Synchrotron analysis of simulated waste glasses different in boron isotope ingredient

Nagai, Takayuki; Okamoto, Yoshihiro; Baba, Yuji*; Akiyama, Daisuke*; Arima, Tatsumi*

Photon Factory Activity Report 2021 (Internet), 2 Pages, 2022/00

http://pfwww.kek.jp/acr/2021pdf/u_reports/pf21b0065.pdf

no abstracts in English

XAFS analysis of ruthenium in simulated iron phosphate radioactive waste glass

Okamoto, Yoshihiro; Kobayashi, Hidekazu; Shiwaku, Hideaki; Sasage, Kenichi; Hatakeyama, Kiyoshi*; Nagai, Takayuki

Journal of Non-Crystalline Solids, 551, p.120393_1 - 120393_8, 2021/01

https://doi.org/10.1016/j.jnoncrysol.2020.120393

The chemical state of ruthenium in simulated iron phosphate radioactive waste glass was investigated by conventional X-ray absorption fine structure (XAFS) and imaging XAFS analyses. The EXAFS analysis suggested that ruthenium was contained as glass phase when content of the waste components was less than 10wt.% in 30 mol%FeO-PO base glass. In other samples, crystalline RuO was predominant. According to the imaging XAFS analysis, RuO particles in all samples had length smaller than 50m. Aggregations of RuO, which are found in nuclear waste borosilicate glass, were not seen in any of the iron phosphate glass samples.

Structural investigation of simulated waste glass samples by using XAFS measurement in soft X-ray region (Joint research)

Nagai, Takayuki; Okamoto, Yoshihiro; Yamagishi, Hirona*; Ota, Toshiaki*; Kojima, Kazuo*; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*

JAEA-Research 2020-009, 48 Pages, 2020/09

JAEA-Research-2020-009.pdf:4.53MB

The local structure of glass-forming elements and waste elements in waste glass varies with its chemical composition. In this study, borosilicate glass frit and simulated waste glass samples were prepared and the local structure and chemical state regarding boron (B), oxygen (O), and waste elements of cerium (Ce), cesium (Cs) were estimated by using XAFS measurement in soft X-ray region. Following results were obtained by XAFS measurements of prepared glass frit and simulated waste glass samples: (1) The existence ratio of four coordinate sp structure (BO) tends to increase with increasing NaO content in glass samples. (2) The height of a pre-edge which appears by K-edge XANES spectrum of O is so high that the Fe content in glass samples. Following results were obtained by XAFS measurements of simulated waste glass samples after immersion test to investigate long chemical stability. (1) The existence ratio of four coordinate sp structure (BO) increases by immersion test. (2) Ce which exists in the surface layer is oxidized by immersion test, and much of Cs in surface layer is lost after leach testing. Even if the glass frit form (fiber cartridge or beads) and manufacturing method were changed and a glass sample of the similar chemical composition was prepared, these observed Raman spectra of samples were different.

XAFS measurement of simulated waste glass samples (Joint research)

Nagai, Takayuki; Sasage, Kenichi; Okamoto, Yoshihiro; Shiwaku, Hideaki; Yamagishi, Hirona*; Ota, Toshiaki*; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*; Takahashi, Tomoe*; et al.

JAEA-Research 2019-003, 94 Pages, 2019/09

JAEA-Research-2019-003.pdf:7.92MB

The local structures of glass-forming elements and waste elements would change by the chemical composition of waste glass including those elements. In this study, simulated waste glass samples were prepared from borosilicate glass frit including phosphorus (P) or vanadium (V), and we investigated local structures of boron, sodium, and waste elements in these P glass and V glass samples by using synchrotron XAFS measurements in soft and hard X ray region.

Synchrotron radiation based XAFS analysis of the simulated nuclear waste glass samples prepared by bottom drain test in the full-scale mock-up melter (KMOC) (Contract research)

Okamoto, Yoshihiro; Nagai, Takayuki; Shiwaku, Hideaki; Kano, Shigeru; Himeno, Haruyuki*; Kobayashi, Hiroshi*; Nakatani, Mikio*

JAEA-Research 2018-013, 18 Pages, 2019/03

JAEA-Research-2018-013.pdf:1.98MB

The chemical state and local structure of some elements in the simulated nuclear waste glass samples (20 batches) prepared by bottom drain test in the full scale mock-up tests using KMOC melter were investigated by synchrotron radiation based X-ray absorption fine structure (XAFS) analysis. As a result of the analysis of cerium element, it was confirmed that the oxidation proceeds gently as the batch advanced. For manganese, iron, and zinc, there was almost no difference between batches, which seemed to be stabilized by getting into the frame structure of the borosilicate glass. There were no elements that seemed to be clearly crystalline except for platinum group elements. Remarkable precipitation was hardly observed in zirconium and molybdenum with the imaging analysis.

Evaluation of uranium chemical state in borosilicate glasses by using XAFS measurement

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

Photon Factory Activity Report 2018 (Internet), 2 Pages, 2019/00

http://pfwww.kek.jp/acr/2018pdf/u_reports/pf18b0060.pdf

no abstracts in English