Development of numerical evaluation method for heat transportation with sodium mist in the cover gas region of sodium-cooled fast reactor

Hayakawa, Satoshi*; Hagiwara, Hiroyuki*; Imamura, Akira*; Onoda, Yuichi; Tanaka, Masaaki; Nakamura, Hironori*

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 8 Pages, 2024/11

In a sodium-cooled fast reactor, a cover gas region filled with argon gas is located above the sodium pool in the main vessel to prevent the hot sodium from contacting the structures. This region involves heat transportation by natural convection of the cover gas, radiation among liquid surface and structures, and sodium phase change between mist and vapor. In this study, the numerical evaluation method has been developed with a commercial CFD code, Fluent, incorporating the sodium mist transport and growth models, and the radiation scattering model. Simulations of a laboratory scale test with a cylindrical cover gas region was carried out for the validation of the method and showed that the temperature distribution and sodium mist concentration in the cover gas region are in good agreements with the test results. A simulation of a pool-type sodium cooled fast reactor has also conducted and the basic aspect of physical phenomena taking place in the cover gas region were evaluated.

Summary report in FY2022 of subsidy program for "the Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy, Thermal behavior Estimation, and Simplified Analysis of Fuel Debris)" started in FY2011

Koyama, Shinichi; Ikeuchi, Hirotomo; Mitsugi, Takeshi; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Tsai, T.-H.; Takano, Masahide; Fukaya, Hiroyuki; Nakamura, Satoshi; et al.

Hairo, Osensui, Shorisui Taisaku Jigyo Jimukyoku Homu Peji (Internet), 216 Pages, 2023/11

https://en.dccc-program.jp/wp-content/uploads/20231117_JAEA.pdf

In FY 2021 and 2022, JAEA perfomed the subsidy program for "the Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy, Thermal Bahavior Estimation, and Simplified Analysis of Fuel Debris)" started in FY 2021. This presentation material summarized the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning, Contaminated Water and Treated Water Management.

Thermal-hydraulic design calculations for JRR-3 cold neutron source with the new moderator cell

Tokunaga, Sho; Horiguchi, Hironori; Nakamura, Takemi

JAEA-Technology 2023-001, 37 Pages, 2023/05

JAEA-Technology-2023-001.pdf:1.39MB

The cold neutron source (CNS) of the research reactor JRR-3 converts thermal neutrons generated in the reactor into low-energy cold neutrons by moderating them with liquid hydrogen stored in the moderator cell. Cold neutrons generated by the CNS are transported to experimental instruments using neutron conduits, and are used for many studies of physical properties, mainly in life science, polymer science, environmental science, etc. Improvement of cold neutron intensity is essential to maintain competitiveness with the world's research reactors in neutron science, and we are developing a new CNS that incorporates new knowledge. The current moderator cell for the CNS of JRR-3 is a stainless-steel container which is a canteen bottle type, and the cold neutron intensity can be improved by changing the material and shape. Therefore, the basic specifications of the new moderator cell were changed to aluminum alloy which has a smaller neutron absorption cross section, and the shape was optimized using a Monte Carlo code MCNP. Since these changes in specifications will result in changes in heat generation and heat transfer conditions, the CNS of JRR-3 was re-evaluated in terms of self-regulating characteristic, heat transport limits, heat resistance and pressure resistance, etc., to confirm its feasibility in thermal-hydraulic design. This report summarizes the results of the thermal-hydraulic design evaluation of the new moderator cell.

Low-temperature magnetic fluctuations investigated by Te-NMR on the uranium-based superconductor UTe

Fujibayashi, Hiroki*; Kinjo, Katsuki*; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 92(5), p.053702_1 - 053702_5, 2023/05

https://doi.org/10.7566/JPSJ.92.053702

Application of CFD code with debris-bed coolability assessment model to pool Type SFR

Nakamura, Hironori*; Hayakawa, Satoshi*; Shibata, Akihiro*; Sasa, Kyohei*; Yamano, Hidemasa; Kubo, Shigenobu

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10

In order to evaluate long-term coolablity of the debris-bed with decay heat, a three-dimensional calculation method coupled with the debris bed module was developed in this study. The coupled code calculation results show that natural circulation of the coolant between the hot pool and the cold pool is established through the four intermediate heat exchangers after the activation of the dipped direct heat exchangers. The cold pool with the debris-bed is continually cooled not only by the natural circulation flow, but also by heat transfer to the hot pool through the plenum separation plate between the hot pool and the cold pool. The effect of the three-dimensional flow field around the core catcher on the temperature in the debris-bed is about 20K under the current calculation condition.

First observation of the de Haas-van Alphen effect and Fermi surfaces in the unconventional superconductor UTe

Aoki, Dai*; Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Ishizuka, Jun*; Yanase, Yoichi*; Harima, Hisatomo*; Nakamura, Ai*; Li, D.*; Homma, Yoshiya*; et al.

Journal of the Physical Society of Japan, 91(8), p.083704_1 - 083704_5, 2022/08

https://doi.org/10.7566/JPSJ.91.083704

Superconducting order parameter in UTe determined by knight shift measurement

Fujibayashi, Hiroki*; Nakamine, Genki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 91(4), p.043705_1 - 043705_4, 2022/03

https://doi.org/10.7566/JPSJ.91.043705

This study investigates the spin susceptibility in U-based superconductor UTe in the superconducting (SC) state by using Knight shift measurements for a magnetic field along the axis, which is the magnetic easy axis of UTe. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature , the -axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. This indicates that the spin susceptibility is nearly unchanged below . Considering the previous Knight shift results for and , the dominant SC state is determined to be in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. The present result shows that UTe is a spin-triplet superconductor with spin degrees of freedom.

Critical slowing-down and field-dependent paramagnetic fluctuations in the skyrmion host EuPtSi; SR and NMR studies

Higa, Nonoka*; Ito, Takashi; Yogi, Mamoru*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; Guguchia, Z.*; Higemoto, Wataru; Nakashima, Miho*; Homma, Yoshiya*; et al.

Physical Review B, 104(4), p.045145_1 - 045145_7, 2021/07

https://doi.org/10.1103/PhysRevB.104.045145

Anisotropic response of spin susceptibility in the superconducting state of UTe probed with Te-NMR measurement

Nakamine, Genki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; et al.

Physical Review B, 103(10), p.L100503_1 - L100503_5, 2021/03

https://doi.org/10.1103/PhysRevB.103.L100503

Te-NMR study on a single crystal of heavy fermion superconductor UTe

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

https://doi.org/10.7566/JPSJ.88.073701

We report Te-NMR studies on a newly discovered heavy fermion superconductor UTe. Using a single crystal, we have measured the Te-NMR Knight shift and spin-lattice relaxation rate for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static () and dynamical susceptibilities () in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate , when the field is applied along the easy axis of magnetization (= axis). This behavior suggests the development of longitudinal magnetic fluctuations along the axis at very low frequencies below 20 K.