MAAP code analysis focusing on the fuel debris condition in the lower head of the pressure vessel in Fukushima-Daiichi Nuclear Power Station Unit 2

Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Cibula, M.*; Mizokami, Shinya*

Nuclear Engineering and Design, 404, p.112205_1 - 112205_21, 2023/04

https://doi.org/10.1016/j.nucengdes.2023.112205

Based on updated knowledge from plant-internal investigations, experiments and model simulations until now, the in-vessel phase of Fukushima-Daiichi Nuclear Power Station Unit 2 was analyzed using the MAAP code. In Unit 2, it is considered that the core material enthalpy was relatively low when it relocated to the lower plenum of the pressure vessel, then, cooled by the coolant and solidified there. Although the MAAP code tended to underestimate the degree of core-material oxidation during the relocation, this probable underestimation was compensated for by an existing study that was considered more reliable, so that more realistic debris conditions in the lower plenum could be obtained. Basic validity of the former prediction of the Unit 2 accident progression behavior was confirmed and detailed boundary condition for the later phase was provided. This boundary condition should be utilized for future studies addressing debris reheating process leading to lower head failure and debris relocation toward the pedestal.

The Experimental and simulation results of LIVE-J2 test; Investigation on heat transfer in a solid-liquid mixture pool

Madokoro, Hiroshi; Yamashita, Takuya; Gaus-Liu, X.*; Cron, T.*; Fluhrer, B.*; Sato, Ikken; Mizokami, Shinya*

Nuclear Technology, 209(2), p.144 - 168, 2023/02

https://doi.org/10.1080/00295450.2022.2121545

Formation of MPd (M = Gd, Np) by the reaction of MN with Pd and chlorination of MPd using cadmium chloride

Hayashi, Hirokazu; Shibata, Hiroki; Sato, Takumi; Otobe, Haruyoshi

Journal of Radioanalytical and Nuclear Chemistry, 8 Pages, 2023/00

https://doi.org/10.1007/s10967-023-08760-4

The formation of MPd (M = Gd, Np) by the reaction of MN with Pd at 1323 K in Ar gas flow was observed. Cubic AuCu-type GdPd ( = 0.4081 0.0001 nm) and NpPd ( = 0.4081 0.0001 nm) were identified, respectively. The product obtained from the reaction of NpN with Pd contained additional phases including the hexagonal TiNi-type NpPd. Chlorination of the MPd (M = Gd, Np) samples was accomplished by the solid-state reaction using cadmium chloride at 673 K in a dynamic vacuum. Pd-rich solid solution phase saturated with Cd and an intermetallic compound PdCd were obtained as by-products of MCl formation.

Non-Hookean large elastic deformation in bulk crystalline metals

Xu, S.*; Odaira, Takumi*; Sato, Shunsuke*; Xu, X.*; Omori, Toshihiro*; Harjo, S.; Kawasaki, Takuro; Seiner, H.*; Zoubkov, K.*; Murakami, Yasukazu*; et al.

Nature Communications (Internet), 13, p.5307_1 - 5307_8, 2022/09

https://doi.org/10.1038/s41467-022-32930-9

BWR lower head penetration failure test focusing on eutectic melting

Yamashita, Takuya; Sato, Takumi; Madokoro, Hiroshi; Nagae, Yuji

Annals of Nuclear Energy, 173, p.109129_1 - 109129_15, 2022/08

https://doi.org/10.1016/j.anucene.2022.109129

Development plan of failure mitigation technologies for improving resilience of nuclear structures

Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*

Transactions of 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 8 Pages, 2022/07

Utilizing fracture control, we are developing a technology to suppress the expansion of damage caused by an event that exceeds the design assumption. We made a plan to develop three issues; (1) Technology for mitigating failure consequence at extremely high temperatures, (2) Technology for mitigating failure consequence against excessive earthquakes, and (3) Methodology for improving reactor structure resilience.

Fully chelating NO-pentadentate planar ligands designed for the strongest and selective capture of uranium from seawater

Mizumachi, Takumi*; Sato, Minami*; Kaneko, Masashi; Takeyama, Tomoyuki*; Tsushima, Satoru*; Takao, Koichiro*

Inorganic Chemistry, 61(16), p.6175 - 6181, 2022/04

https://doi.org/10.1021/acs.inorgchem.2c00306

Based on unique 5-fold equatorial coordination of UO, water-compatible pentadentate planar ligands, Hsaldian and its derivatives, were designed as strong and selective capture of UO in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO/CO, pH 8), saldian shows the strongest complexation with UO to form UO(saldian) (log = 28.05 0.07), which is more than 10 order of magnitude greater than amidoxime-based or -inspired ligand systems most commonly employed for U capture from seawater. Good selectivity for UO from other metal ions coexisting in seawater was also demonstrated.

Breakdown of linear spin-wave theory and existence of spinon bound states in the frustrated kagome-lattice antiferromagnet

Mattan, K.*; Ono, Toshio*; Kawamura, Seiko; Nakajima, Kenji; Nambu, Yusuke*; Sato, Taku*

Physical Review B, 105(13), p.134403_1 - 134403_8, 2022/04

https://doi.org/10.1103/PhysRevB.105.134403

Spin dynamics of the spin-1/2 kagome-lattice antiferromagnet CsCuSnF was studied using high-resolution, time-of-flight inelastic neutron scattering. The flat mode, a characteristic of the frustrated kagome antiferromagnet, and the low-energy dispersive mode, which is dominated by magnons, can be well described by the linear spin-wave theory. However, the theory fails to describe three weakly dispersive modes between 9 and 14 meV. These modes could be attributed to two-spinon bound states, which decay into free spinons away from the zone center and at a high temperature, giving rise to continuum scattering.

Fundamental study for decorporation of plutonium by chelating agents; Coordination analyses of simulated plutonium with chelating agents by X-ray absorption spectroscopy

Uehara, Akihiro*; Shuhui, X.*; Sato, Ryotaro*; Matsumura, Daiju; Tsuji, Takuya; Yakumaru, Haruko*; Shiro, Ayumi*; Saito, Hiroyuki*; Tanaka, Izumi*; Ishihara, Hiroshi*; et al.

X-sen Bunseki No Shimpo, 53, p.223 - 229, 2022/03

no abstracts in English

Stabilization treatment of Pu-bearing organic materials

Morishita, Kazuki; Sato, Takumi; Onishi, Takashi; Seki, Takayuki*; Sekine, Shinichi*; Okitsu, Yuichi*

JAEA-Technology 2021-024, 27 Pages, 2021/10

JAEA-Technology-2021-024.pdf:2.41MB

In the case of Plutonium (Pu)-bearing organic materials, organic materials are decomposed by alpha rays emitted mainly from Pu to generate hydrogen gas and other substances. Therefore, to safely store Pu-bearing organic materials for an extended period of time, organic materials must be eliminated. In addition, carbide and nitride fuels must be converted into oxides for safe storage in order to prevent the exothermal reaction of these fuels with oxygen/moisture in air. A survey of the literature on the stabilization treatment of Pu-bearing organic materials confirmed that organic materials can be decomposed and removed by heating at 950 C (1223.15 K) or greater in air. Furthermore, based on the calculated thermodynamic parameters of oxidation reaction of carbide and nitride fuels in air, it was estimated that these fuels would be oxidized in air at 950 C because the equilibrium oxygen partial pressure in the oxidation reaction at 950 C was lower than 2.110 Pa (oxygen partial pressure in air). Therefore, it was decided to stabilize Pu-bearing organic materials by heating at 950 C in air to remove the organic materials and oxidize the carbide and nitride fuels. As a mock-up test to remove the organic materials, thin sheets of epoxy resin were heated in air. The changes in appearance and weight before and after heating in air showed that organic materials can be removed. After the mock-up test, Pu-bearing organic materials were also stabilized by heating in the similar condition.