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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
Times Cited Count：1 Percentile：68.64(Nuclear Science & Technology)A dissolution method for analyzing the elemental composition of fuel debris using the sodium peroxide (Na
O) 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.
Saito, Shigeru; Suzuki, Kazuhiro; Obata, Hiroki; Dai, Y.*
Nuclear Materials and Energy (Internet), 34, p.101338_1 - 101338_9, 2023/03
Times Cited Count：3 Percentile：45.58(Nuclear Science & Technology)In this study, a post-irradiation examination of pure tungsten (W) and tantalum (Ta) specimens irradiated at the Swiss Spallation-Neutron Source is conducted. W is used as a potential candidate for a solid spallation-target material owing to its favorable properties. However, W also suffers from several disadvantages such as poor corrosion resistance to water coolant and irradiation embrittlement. To improve these properties, cladding technologies using Ta for W alloys have been developed. In the present study, we investigated the irradiation effects on two tungsten materials, poly-crystal W (W-Poly) and single-crystal W (W-Sin), along with pure polycrystalline Ta. The tensile-test results revealed that W-Poly exhibited almost no ductility after irradiation of 10.2-35.0 dpa. W-Sin was irradiated up to 10.2 dpa and demonstrated 6% of total elongation (TE). With regard to Ta, TE decreased based on the increase in irradiation, reaching almost zero at doses of more than 10.3 dpa.
Matsui, Hiroki; Suzuki, Miho; Obata, Hiroki; Kanazawa, Hiroyuki
JAEA-Technology 2014-017, 57 Pages, 2014/06
JAEA-Technology-2014-017.pdf:20.43MB
The Reactor Fuel Examination Facility in JAEA has been used for Post Irradiation Examinations to verify the reliability and safety of the nuclear fuels irradiated in commercial reactors. EPMA (Electron Probe Micro Analyzer) has been utilized for the qualitative analysis of the fission product in the fuel pellet and the detailed observation of the oxide layers formed at the inner and outer surfaces of fuel cladding. Commercial EPMAs were remodeled so that the EPMAs can be applied for radioactive samples. Several shields was set in the EPMA to avoid the 
-rays which radiate from a radioactive sample to the proportional counter in the EPMA. It is important to calculate this shielding performance adequately to maintain the precision of analysis. This report describes the results of re-evaluation of the performance of the shields in the EPMAs in the RFEF by using the Particle and Heavy Ion Transport Code System and the examination results of -ray effect to the X-ray spectrum data by using a radioactive sample.
Honda, Junichi; Matsui, Hiroki; Harada, Akio; Obata, Hiroki; Tomita, Takeshi
JAEA-Technology 2012-022, 35 Pages, 2012/07
JAEA-Technology-2012-022.pdf:3.58MB
The advanced utilization of Light Water Reactor (LWR) fuel is progressed in Japan to save the power generating cost and the volume of nuclear wastes. The electric power companies have been continued the approach to extend the burnup and to rise up the thermal power of the commercial fuel. The government should be accumulating the detailed information of the newest technologies to make the regulations and guidelines for the safety of the advanced nuclear fuels. The remote controlled Electron Prove Micro Analyzer attached with crystal orientation analyzer (EPMA) has been developed in Japan Atomic Energy Agency (JAEA) to evaluate the fuel behavior effected by the cladding microstructure under the accident condition. The device was modified to the airtight and earthquake resistant structure for the examination of high radioactive elements. This paper describes the specification of EPMA and the test results of the cold mock-up to confirm their performances and reliabilities.
Honda, Junichi; Matsui, Hiroki; Harada, Akio; Obata, Hiroki; Tomita, Takeshi
JAEA-Technology 2012-021, 17 Pages, 2012/07
JAEA-Technology-2012-021.pdf:4.17MB
The advanced utilization of Light Water Reactor (LWR) fuel is progressed in Japan to save the power generating cost and the volume of nuclear wastes. The electric power companies have been continued the approach to extend the burnup and to rise up the thermal power of the commercial fuel. The government should be accumulating the detailed information of the newest technologies to make the regulations and guidelines for the safety of the advanced nuclear fuels. The ion milling for post irradiation examination has been developed in Japan Atomic Energy Agency (JAEA) to investigate cladding microstructure. This device has been modified to operate the high radioactive elements remotely and have the performance of earthquake resistant. This paper describes the specification of the device which were specialized for post irradiation examination and the test results of the cold mock-up to confirm their performances and reliabilities.
Obata, Hiroki; Toyokawa, Takuya; Tomita, Takeshi; Kimura, Yasuhiko
no journal, ,
Hydrogen absorption to the fuel cladding is increase on the high burn-up fuel. The concentration of absorbed hydrogen causes the cladding embrittlement which might become the origination of fractures of the cladding. Therefore, it's important to measure the hydrogen volume in the cladding to estimate the safety margin of the irradiated cladding. In the previous method of hot vacuum extraction, the hydrogen is released and measured as the melting condition of the cladding. It cannot be evaluated the hydrogen volume only in the cladding metal phase. The hydrogen absorption in the cladding metal phase is strongly-correlated the cladding embrittlement. The two-step heating method has the benefit to measure the hydrogen in metal phase and oxide layer separately. The measuring method including the extraction temperature condition using unirradiated cladding will be reported.
Motooka, Takafumi; Endo, Shinya; Sonoda, Takashi; Oki, Keiichi; Uehara, Hiroyuki; Obata, Hiroki; Tsukada, Takashi
no journal, ,
no abstracts in English
Takano, Masahide; Onozawa, Atsushi; Suzuki, Miho; Obata, Hiroki
no journal, ,
For the decommissioning of damaged cores of Fukushima Daiichi NPS, the retrieval operation of solidified core melt (corium) and its safe management are essential tasks. To understand characteristics of corium specific to the 1F cores, we have prepared and analyzed various types of simulated corium specimens in laboratory scale. To verify the effect of cooling condition found on the simulated corium, we revisit the actual corium specimens collected from the TMI-2 accident core, which have been stored at the Reactor Fuel Examination Facility (RFEF) in JAEA Tokai since 1991. Comparing the phases and microstructure, rapid-cooled specimens have dense microstructure and consist of single phase of cubic structure. On the other hand, the slow-cooled specimens consist of U-rich cubic and Zr-rich tetragonal phases distributed minutely. From these observations we have confirmed the similar dependence of microstructure and mechanical property on the cooling condition.
Saito, Shigeru; Kikuchi, Kenji*; Hamaguchi, Dai; Suzuki, Kazuhiro; Endo, Shinya; Obata, Hiroki; Kurishita, Hiroaki*; Watanabe, Ryuzo*; Kawai, Masayoshi*; Yong, D.*
no journal, ,
no abstracts in English
Uehara, Hiroyuki; Obata, Hiroki; Endo, Shinya; Kawamata, Yutaka; Motooka, Takafumi; Tsukada, Takashi
no journal, ,
no abstracts in English
Endo, Shinya; Motooka, Takafumi; Uehara, Hiroyuki; Obata, Hiroki; Kawamata, Yutaka; Ueno, Fumiyoshi
no journal, ,
no abstracts in English
Hashidate, Ryuta; Morioka, Tatsuya; Sawazaki, Hiromasa; Shiotani, Hiroki; Obata, Ikuhito; Uekura, Ryoichi
no journal, ,
We have been evaluating mainly the data acquired by the central computer so far, but we focused on evaluation using preservation data from this time. In this report, we report on the results of examination of the shaft sealing mechanism which constitutes the boundary of the cover gas including sodium vapor from the viewpoint of seal gas effect considered in the design stage for sodium vapor and sealability of the cover gas boundary by using the Monju plant data and conservation data for 20 years.
Kakiuchi, Kazuo; Narukawa, Takafumi; Obata, Hiroki; Amaya, Masaki
no journal, ,
JAEA has conducted studies on fuel behaviors during loss-of-coolant-accidents (LOCA) using high-burnup advanced fuel cladding tubes. We report the evaluation results on the effects of the burnup extension and the change in the alloy compositions on high temperature oxidation of high-burnup advanced fuel cladding.
Nakamura, Satoshi; Ban, Yasutoshi; Sugimoto, Mie; Tambo, Masaki; Fukaya, Hiroyuki; Hiruta, Kenta; Yoshida, Takuya; Uehara, Hiroyuki; Obata, Hiroki; Kimura, Yasuhiko; et al.
no journal, ,
In Nuclear Science Research Institute at JAEA, detailed studies with regard to the elemental and nuclide compositions of fuel debris have been proceeding. We have conducted dissolution of the samples by alkaline fusion with sodium peroxide and chemical analysis by ICP-AES, alpha and gamma spectrometer, and TIMS. After studying the dissolution methods with various types of simulated debris, a demonstration test with TMI-2 debris was conducted. The elemental composition in the dissolved solution of TMI-2 debris consistent with the results of SEM/WDX and XRD analyses, and the validity of the present method was confirmed. In this presentation, the details of each analysis and the issues raised through the analysis will be introduced.
Takano, Masahide; Onozawa, Atsushi; Suzuki, Miho; Obata, Hiroki
no journal, ,
no abstracts in English
Obata, Hiroki
no journal, ,
no abstracts in English
Obata, Hiroki; Toyokawa, Takuya; Tomita, Takeshi; Kimura, Yasuhiko
no journal, ,
The amount of hydrogen absorbed to the fuel cladding increases by extended burnup fuel. The absorbed hydrogen that exceed solid solubility limit precipitates as the hydride phase. The high concentration of hydride causes the fuel cladding embrittlement which might become the origination of fractures of the cladding. Therefore, it is important to measure the hydrogen content in the cladding to estimate the safety margin of the irradiated cladding. Hydrogen is absorbed not only in the cladding metal phase, but in the oxide layer. To evaluate the embrittlement of the cladding, it is necessary to measure the hydrogen content in the cladding metal phase and oxide layer separately. Therefore, the two-step heating method can measure the amount of hydrogen in the metal phase and the oxide layer separately. This paper shows the technical review of measuring method including the technique for the determination of extraction temperature.
Ida, Yuma; Obata, Hiroki; Kimura, Yasuhiko; Onozawa, Atsushi
no journal, ,
Saito, Ryota; Komuro, Kazuma; Obata, Hiroki; Onozawa, Atsushi
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