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Sudo, Ayako; M
sz
ros, B.*; Sato, Takumi; Nagae, Yuji
JAEA-Research 2023-007, 31 Pages, 2023/11
JAEA-Research-2023-007.pdf:3.61MB
For the criticality assessment of fuel debris generated by the accident in Fukushima Daiichi Nuclear Power Station, understanding of the elemental localization in fuel debris is important. Especially, the distribution of Fe and Gd, which may behave as potential neutron absorber materials in the fuel debris, is of particular important from the viewpoint of nuclear criticality safety. To investigate the localization tendency of Gd and Fe in molten core materials during solidification progress, liquefaction/solidification tests on core materials containing UO
, ZrO, FeO, GdO
, and simulated fission products (MoO, NdO, SrO, and RuO) and concrete (SiO, AlO, and CaO) were performed using cold crucible induction heating technique. During the test, the molten core materials gradually subsided and solidified from the bottom to the top of the melt. Elemental analysis showed that Fe content in the inner region increased approximately up to 3.4 times that in the bottom region. The concentration of Fe into the inner region was observed in all the samples regardless of the initial FeO composition, cooling rates, and phase separation. This suggests that FeO may be concentrated into the low temperature region, where the melt solidified later. In contrast, Gd content in the bottom region increased approximately up to 2.6 times that in the inner region. The concentration of Gd into the bottom region was observed when the initial GdO content was higher than 1 at.%. This suggests that GdO may be concentrated into the earlier solidified region. On the other hand, no significant localization was observed on the simulated fission products.
temperature measurement for lamp-based heating deviceSumita, Takehiro; Sudo, Ayako; Takano, Masahide; Ikeda, Atsushi
Science and Technology of Advanced Materials; Methods (Internet), 2(1), p.50 - 54, 2022/02
Sudo, Ayako; Sato, Takumi; Ogi, Hiroshi; Takano, Masahide
Journal of Nuclear Science and Technology, 58(4), p.473 - 481, 2021/04
Times Cited Count：6 Percentile：63.12(Nuclear Science & Technology)Dissolution behavior of Sr and Ba is crucial for evaluating secondary source terms via coolant water from ex-vessel debris accumulated at Fukushima Daiichi Nuclear Power Plant. To understand the mechanism, knowing the distribution of Sr and Ba in the ex-vessel debris is necessary. As a result of reaction tests between simulated corium and concrete materials, two layered structures were observed in the solidified sample, (A) a silicate glass-based ((Si-Al-Ca-Fe-Zr-Cr-U-Sr-Ba)-O) phase-rich layer in the upper surface region and (B) a (U,Zr)O particle-rich layer at the inner region. Measurable concentrations of Sr and Ba were observed in layer (A) (approximately 1.7 times that in the layer (B)). According to thermodynamic analysis, (U,Zr)O is predicted to solidify, in advance, in the concrete-based melt around 2177 
C. Then, the residual melt is solidified as a silicate glass, and Sr and Ba are preferentially dissolved into the silicate glass. During the tests, (U,Zr)O particles sank, in advance, in the melt because of its higher density, and the silicate glass phase relocated to the surface layer. On the other hand, silicate glass containing Sr and Ba is predicted to be hardly soluble in water and chemically stable.
Sudo, Ayako; Meszaros, B.*; Poznyak, I.*; Sato, Takumi; Nagae, Yuji; Kurata, Masaki
Journal of Nuclear Materials, 533, p.152093_1 - 152093_8, 2020/05
Times Cited Count：4 Percentile：39.72(Materials Science, Multidisciplinary)Sudo, Ayako; Mizusako, Fumiki*; Hoshino, Kuniyoshi*; Sato, Takumi; Nagae, Yuji; Kurata, Masaki
Nihon Genshiryoku Gakkai Wabun Rombunshi, 18(3), p.111 - 118, 2019/08
Cooling rate of molten core materials during solidification significantly affects the segregation of major constituents of fuel debris. To understand general tendency of the segregation, liquefaction/solidification tests of simulated corium (UO, ZrO, FeO, B
C and sim-FP oxides) were performed. Simulated corium was heated up to 2600C under Ar atmosphere and then cooled down with two different cooling processes; furnace cooling (average cooling rate is approximately 744C/min) and slow cooling (cooling rate in 2600C
2300C is 5C/min and in 2300C1120C is approximately 788C/min). Element analysis detected three oxide phases with different composition and one metal phase in both solidified samples. Solubility of FeO in these oxide phases was mostly fixed to be 12
5at% in both samples, which is in reasonable accordance with the value estimated from UO-ZrO-FeO phase diagrams. However, a significant grain-growth of one oxide phase, rich in Zr-oxide, was detected only in the slowly cooled sample. The composition of this particular oxide phase is comparable to the initial average composition. The condensation is considered to be caused by the connection of remaining liquid agglomerates during slow solidification.
Sudo, Ayako; Nishi, Tsuyoshi; Shirasu, Noriko; Takano, Masahide; Kurata, Masaki
Journal of Nuclear Science and Technology, 52(10), p.1308 - 1312, 2015/10
Times Cited Count：15 Percentile：75.79(Nuclear Science & Technology)For understanding the control blade degradation mechanism of BWR, the thermodynamic database for the fuel assembly materials is a useful tool. Although iron, boron, and carbon ternary system is a dominant phase diagram, phase relation data is not sufficient for the region in which the boron and carbon compositions are richer than the eutectic composition. The phase relations of three samples were analyzed by X-ray diffraction, scanning electron microscope and energy dispersed X-ray spectrometry. The results indicate that Fe(B,C) phase only exists in the intermediate region at 1273 K and that the solidus temperature widely maintains at about 1400 K for all three samples, which are different from the calculated data using previous thermodynamic database. The difference might be originated from the over-estimations of the interaction parameter between boron and carbon in Fe(B,C).
Sudo, Ayako; Onozawa, Atsushi; Takano, Masahide
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Sudo, Ayako
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In order to obtain the knowledge on the re-distribution of various elements under the solidification process of molten corium, the fundamental experiment on the U-Zr-Gd-O melt was performed. As the core-melt constituents, a powder mixture of wt.70%UO+30%ZrO with adding of wt.2%GdO was prepared with mass of 655.5g. These powders were melted in a cold crucible using induction heating technique in the air atmosphere with metallic zirconium (6g) as an initiator. For the corium microstructure study, sample pieces from solidified ingot were subjected to phase identification and elemental analysis by XRD and SEM/EDX. For the evaluation of the characteristics of corium debris under the various solidification processes, two heating tests with different cooling rates were performed. During quick-solidification test (J1) ingot of 4.8cm was obtained. The near-bottom region of J1 sample was crystallized and not melted. The structure of slow-solidification sample (J2) was similar to J1, however, it was formed big cavity under the upper crust of ingot. This cavity was formed during slow-solidification process due to volume shrinkage. Both of samples were found that Gd was concentrated in the inner region where the later crystallization of the melt was occurred.
Sudo, Ayako; Poznyak, I.*; Nagae, Yuji; Nakagiri, Toshio; Kurata, Masaki
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Sudo, Ayako; Poznyak, I.*; Nagae, Yuji; Nakagiri, Toshio; Kurata, Masaki
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Sudo, Ayako; Mizusako, Fumiki*; Hoshino, Kuniyoshi*; Sato, Takumi; Nagae, Yuji; Kurata, Masaki
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Nakagiri, Toshio; Sudo, Ayako; Yoshikawa, Shinji; Abe, Yuta; Sato, Ikken
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Temperature distribution and composition of atmosphere (H/HO ratio) in the accident of Fukushima Daiichi Nuclear Power Plant No.2 were evaluated using RELAP/SCDAPSIM code. Furthermore, distruption test of stainless steel specimen by metal melt assumeed to be generated in core melting phase in the accident was performed. From these results and the result of another plasma heating test using simulated fuel budle performed by JAEA, relocation behavior of melt in the accident was evaluated.
Sudo, Ayako; Nishi, Tsuyoshi; Shirasu, Noriko; Kurata, Masaki
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Sato, Takumi; Sudo, Ayako; Nagae, Yuji
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Takano, Masahide; Onozawa, Atsushi; Sudo, Ayako
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Sudo, Ayako
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Sudo, Ayako
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Sudo, Ayako
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simulated fuel debrisTakano, Masahide; Onozawa, Atsushi; Sudo, Ayako
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Sudo, Ayako; Nishi, Tsuyoshi; Shirasu, Noriko; Takano, Masahide; Kurata, Masaki
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Although Fe-B-C ternary system is a dominant phase diagram when considering the control blade degradation, phase relation data around eutectic composition were not sufficient. The phase relations of three Fe-B-C samples were analyzed by XRD and SEM/EDX and solidus were determined by DTA. The solidus detected in the present study was maintained at about 1400 K for all three samples, although preliminary calculation using conventional thermodynamic database estimated that solidus varies with roughly 50 K difference. The difference might be originated from the insufficient evaluation on the phase stability of Fe(B,C) in the database. The present results give useful information on improvement of iron-boron-carbon phase diagram.
