Development of a dissolution method for analyzing the elemental composition of fuel debris using sodium peroxide fusion technique

Nakamura, Satoshi; Ishii, Sho*; Kato, Hitoshi*; Ban, Yasutoshi; Hiruta, Kenta; Yoshida, Takuya; Uehara, Hiroyuki; Obata, Hiroki; Kimura, Yasuhiko; Takano, Masahide

Journal of Nuclear Science and Technology, 62(1), p.56 - 64, 2025/01

https://doi.org/10.1080/00223131.2024.2381553

A dissolution method for analyzing the elemental composition of fuel debris using the sodium peroxide (NaO) fusion technique has been developed. Herein, two different types of simulated debris materials (such as solid solution of (Zr,RE)O and molten core-concrete interaction products (MCCI)) were taken. At various temperatures, these debris materials were subsequently fused with NaO in crucibles, which are made of different materials, such as Ni, AlO, Fe, and Zr. Then, the fused samples are dissolved in nitric acid. Furthermore, the effects of the experimental conditions on the elemental composition analysis were evaluated using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), which suggested the use of a Ni crucible at 923 K as an optimum testing condition. The optimum testing condition was then applied to the demonstration tests with Three Mile Island unit-2 (TMI-2) debris in a shielded concrete cell, thereby achieving complete dissolution of the debris. The elemental composition of TMI-2 debris revealed by the proposed dissolution method has good reproducibility and has an insignificant contradiction in the mass balance of the sample. Therefore, this newly developed reproducible dissolution method can be effectively utilized in practical applications by dissolving fuel debris and estimating its elemental composition.

Combustion properties of glove-box panel resins under fire accidents

Tashiro, Shinsuke; Uchiyama, Gunzo; Ono, Takuya; Amano, Yuki; Yoshida, Ryoichiro; Watanabe, Koji*; Abe, Hitoshi; Yamane, Yuichi

Nuclear Technology, 10 Pages, 2024/00

https://doi.org/10.1080/00295450.2024.2329832

Contributing to the confinement safety evaluation of glove-box (GB) connected with high efficiency particle air (HEPA) filters for radioactive materials under fire accidents, combustion tests of a flammable polymer, Polymethyl methacrylate (PMMA), and a flame retardant polymer, Polycarbonate (PC), as typical GB panel resins have been conducted with an engineering-scale combustion apparatus. The combustion properties such as the mass loss rate (MLR) and the heat release rate (HRR) of PMMA and PC were investigated in the combustion tests. In the tests with the same shapes, it was found the followings; MLRs and HRRs of PMMA were larger than those of PC under the same supply flow rate into the combustion cell (Fv); MLRs and HRRs of PMMA and PC were constant under different Fv. Moreover, in the tests of PMMA with different cross section areas (S), MLRs and HRRs were found to be proportional to S. Using these results, the relationships of MLR and HRR to S of PMMA and PC were deduced.

Clogging properties of HEPA filter induced by loading of soot from burned glove-box panel materials

Tashiro, Shinsuke; Ono, Takuya; Amano, Yuki; Yoshida, Ryoichiro; Watanabe, Koji*; Abe, Hitoshi

Nuclear Technology, 208(10), p.1553 - 1561, 2022/10

https://doi.org/10.1080/00295450.2022.2045179

To contribute to the confinement safety evaluation of the radioactive materials in the Glove box (GB) fire accident, combustion tests with the Polymethyl methacrylate (PMMA) and the Polycarbonate (PC) as typical panel materials for the GB have been conducted with a relatively large scale apparatus. As the important data for evaluating confinement safety, the release ratio and the particle size distribution of the soot generated from the burned materials were obtained. Furthermore, the rise of the differential pressure (P) of the high efficiency particle air (HEPA) filter by the soot loading was also investigated. As results, the release ratio of the soot from the PC was about seven times as large as the PMMA. In addition, it was found that the behavior of the rise of the P with soot loading could be represented uniformly regardless of kinds of combustion materials by considering effect of the loading volume of the soot particle in the relatively low loading region.

Effect of nitrous acid on migration behavior of gaseous ruthenium tetroxide into liquid phase

Yoshida, Naoki; Ono, Takuya; Yoshida, Ryoichiro; Amano, Yuki; Abe, Hitoshi

JAEA-Research 2021-011, 12 Pages, 2022/01

JAEA-Research-2021-011.pdf:1.49MB

In boiling and drying accidents involving high-level liquid waste in fuel reprocessing plants, emphasis is placed on the behavior of ruthenium (Ru). Ru would form volatile species, such as ruthenium tetroxide (RuO), and could be released to the environment with coexisting gases, including nitric acid, water, or nitrogen oxides. In this study, to contribute toward safety evaluations of these types of accidents, the migration behavior of gaseous Ru into the liquid phase has been experimentally measured by simulating the condensate during an accident. The gas absorption of RuO was enhanced by increasing the nitrous acid (HNO) concentration in the liquid phase, indicating the occurrence of chemical absorption. In control experiments without HNO, the lower the temperature, the greater was the Ru recovery ratio in the liquid phase. Conversely, in experiments with HNO, the higher the temperature, the higher the recovery ratio, suggesting that the reaction involved in chemical absorption was activated at higher temperatures.

Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model; A Case for glovebox panel materials such as polymethyl methacrylate

Ono, Takuya; Tashiro, Shinsuke; Amano, Yuki; Yoshida, Naoki; Yoshida, Ryoichiro; Abe, Hitoshi

PLOS ONE (Internet), 16(1), p.e0245303_1 - e0245303_16, 2021/01

https://doi.org/10.1371/journal.pone.0245303

It is necessary to consider how a glove box's confinement function will be lost when evaluating the amount of radioactive material leaking from a nuclear facility during a fire. In this study, we build a model that consistently explains the weight loss of glove box materials because of heat input from a flame and accompanying generation of the pyrolysis gas. The weight loss suggests thinning of the glove box housing, and the generation of pyrolysis gas suggests the possibility of fire spreading. The target was polymethyl methacrylate (PMMA), used as the glove box panel. Thermal gravimetric tests on PMMA determined the parameters to be substituted in the Arrhenius equation for predicting the weight loss in pyrolysis. The pyrolysis process of PMMA was divided into 3 stages with activation energies of 62 kJ/mol, 250 kJ/mol, and 265 kJ/mol. Furthermore, quantifying the gas composition revealed that the composition of the pyrolysis gas released from PMMA can be approximated as 100 percent methyl methacrylate. This result suggests that the released amount of methyl methacrylate can be estimated by the Arrhenius equation. To investigate the validity of such estimation, a sealed vessel test was performed. In this test, we observed increase of the number of gas molecules during the pyrolysis as internal pressure change of the vessel. The number of gas molecules was similar to that estimated from the Arrhenius equation, and indicated the validity of our method. Moreover, we also performed the same tests on bisphenol-A-polycarbonate (PC) for comparison. In case of PC, the number of gas molecules obtained in the vessel test was higher than the estimated value.

Decomposition behavior of gaseous ruthenium tetroxide under atmospheric conditions assuming evaporation to dryness accident of high-level liquid waste

Yoshida, Naoki; Ono, Takuya; Yoshida, Ryoichiro; Amano, Yuki; Abe, Hitoshi

Journal of Nuclear Science and Technology, 57(11), p.1256 - 1264, 2020/11

https://doi.org/10.1080/00223131.2020.1780991

Emphasis has been placed on the behavior of ruthenium (Ru) in the evaporation to dryness accident due to the loss of cooling functions (EDLCF) of high-level liquid waste in fuel reprocessing plants. It is because Ru would form volatile compounds such as ruthenium tetroxide (RuO) and could be released into the environment with other coexisting gasses such as nitric acid (HNO), water (HO). To contribute to the safety evaluation of this accident, we experimentally evaluated the decomposition and chemical change behavior of the gaseous RuO (RuO(g)) under the various atmospheric conditions: temperature and composition of coexisting gasses. As a result, the behavior of the RuO(g) was diverse depending on the atmospheric conditions. In the experiments with the dry air or HO vapor, decomposition of RuO(g) was observed. In the experiment with the mixed gas which containing HNO, almost no decomposition of the RuO(g) was observed, and chemical form of the RuO(g) was retained.

High-rate performance of a time projection chamber for an H-dibaryon search experiment at J-PARC

Kim, S. H.*; Ichikawa, Yudai; Sako, Hiroyuki; Hasegawa, Shoichi; Hayakawa, Shuhei*; Nanamura, Takuya*; Sato, Susumu; Tanida, Kiyoshi; Yoshida, Junya; 11 of others*

Nuclear Instruments and Methods in Physics Research A, 940, p.359 - 370, 2019/10

https://doi.org/10.1016/j.nima.2019.06.050

New precise measurements of muonium hyperfine structure at J-PARC MUSE

Strasser, P.*; Abe, Mitsushi*; Aoki, Masaharu*; Choi, S.*; Fukao, Yoshinori*; Higashi, Yoshitaka*; Higuchi, Takashi*; Iinuma, Hiromi*; Ikedo, Yutaka*; Ishida, Katsuhiko*; et al.

EPJ Web of Conferences, 198, p.00003_1 - 00003_8, 2019/01

https://doi.org/10.1051/epjconf/201919800003

Migration behavior of gaseous ruthenium tetroxide under boiling and drying accident condition in reprocessing plant

Yoshida, Naoki; Ono, Takuya; Amano, Yuki; Abe, Hitoshi

Journal of Nuclear Science and Technology, 55(6), p.599 - 604, 2018/06

https://doi.org/10.1080/00223131.2018.1428121

In the boiling and drying accident of high-level liquid waste in the fuel reprocessing plant, behavior of ruthenium (Ru) has attracted much attention because Ru could form volatile compounds such as ruthenium tetroxide (RuO) and could be released into the environment. To contribute towards safety evaluation of this accident, the migration behavior and the leak path factor of the gaseous ruthenium compound has been experimentally measured in this study. The experiment was proceeded by using the Ruthenium Migration Evaluating Apparatus, which partially simulates the atmospheric condition (temperature, flow rate, and composition of water vapor and gaseous nitric acid mixture) of migration pathway in the accident. Experiments with dry air and water vapor were also performed as the control experiment to discuss the effect of nitric acid. As a result, the experiment with dry air and the experiment with water vapor demonstrated that the majority of the ruthenium deposited along the migration pathway. On the other hand, the experiment with the water vapor containing gaseous nitric acid demonstrated that almost all of the ruthenium passed through the migration pathway without deposition. These results suggested that the migration behavior of gaseous ruthenium will be affected by the gas-phase composition.

A Numerical simulation method for molten material behavior in nuclear reactors

Yamashita, Susumu; Ina, Takuya; Idomura, Yasuhiro; Yoshida, Hiroyuki

Nuclear Engineering and Design, 322, p.301 - 312, 2017/10

https://doi.org/10.1016/j.nucengdes.2017.06.032

In recent years, significant attention has been paid to the precise determination of relocation of molten materials in reactor pressure vessels of boiling water reactors (BWRs) during severe accidents. To address this problem, we have developed a computational fluid dynamics code JUPITER, based on thermal-hydraulic equations and multi-phase simulation models. Although the Poisson solver has previously been a performance bottleneck in the JUPITER code, this is resolved by a new hybrid parallel Poisson solver, whose strong scaling is extended up to 200k cores on the K-computer. As a result of the improved computational capability, the problem size and physical models are dramatically expanded. A series of verification and validation studies are enabled, which are in agreement with previous numerical simulations and experiments. These physical and computational capabilities of JUPITER enable us to investigate molten material behaviors in reactor relevant situations.