Self-learning Monte Carlo method with Behler-Parrinello neural networks

Nagai, Yuki; Okumura, Masahiko; Tanaka, Akinori*

Physical Review B, 101(11), p.115111_1 - 115111_12, 2020/03

https://doi.org/10.1103/PhysRevB.101.115111

no abstracts in English

Effect of humidity and temperature on the radiation response of SiC MOSFETs

Takeyama, Akinori; Matsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Onoda, Shinobu; Tanaka, Yuki*; Kandori, Mikio*; Yoshie, Toru*; et al.

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.134 - 137, 2015/11

Replacement of upper core structure in experimental fast reactor Joyo, 1; Existing damaged upper core structure jack-up test

Ito, Hiromichi; Suzuki, Nobuhiro; Kobayashi, Tetsuhiko; Kawahara, Hirotaka; Nagai, Akinori; Sakao, Ryuta*; Murata, Chotaro*; Tanaka, Junya*; Matsusaka, Yasunori*; Tatsuno, Takahiro*

Proceedings of 2015 International Congress on Advances in Nuclear Power Plants (ICAPP 2015) (CD-ROM), p.1058 - 1067, 2015/05

In the experimental fast reactor Joyo (Sodium-cooled Fast Reactor (SFR)), it was confirmed that the top of the irradiation test sub-assembly had bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). There is a risk of deformation of the UCS and guide sleeve (GS) caused by interference between them unless inclination is controlled precisely. To mitigate the risk, special jack-up equipment for applying three-point suspension was developed. The existing damaged UCS (ed-UCS) jack-up test using the jack-up equipment was conducted on May 7, 2014. As a result of this test, it was confirmed that the ed-UCS could be successfully jacked-up to 1000 mm without consequent overload. The experience and knowledge gained in the ed-UCS jack-up test provides valuable insights and prospects not only for UCS replacement but also for further improving and verifying repair techniques in SFRs.

Development of grouting technologies for geological disposal of high level waste in Japan, 3; Numerical simulation for grout injection using equivalent continuum model

Koyama, Tomofumi*; Katayama, Tatsuo*; Hasui, Akinori*; Tanaka, Tatsuya*; Kishi, Hirokazu; Onishi, Yuzo*

Dai-41-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.83 - 88, 2012/01

In this study, to simulate the grout injection process, the 3-D numerical model based on equivalent continuum approach was developed. The viscosity measurements for silica sol was performed to measure the time-dependent viscosity. The developed numerical model was applied to the planned in-situ grout injection tests at Grimsel test site (GTS), Switzerland. The rock type is fractured granite and the equivalent porous media was created from the DFN (Discrete Fracture Network) based on the frature data obtained from the observation boreholes. The preliminary simulation was carried out to determine the suitable grout injection pressure and investigate the arrival distance of grout from injection boreholes.

Structure-based analysis of cooperativity in protein-DNA recognition

Tanaka, Akihiro*; Fujii, Satoshi*; Kono, Hidetoshi; Sarai, Akinori*

no journal, , 

Optimum structures for -ray radiation resistant SiC-MOSFETs

Takeyama, Akinori; Mitomo, Satoshi*; Matsuda, Takuma*; Murata, Koichi*; Yokoseki, Takashi*; Makino, Takahiro; Onoda, Shinobu; Oshima, Takeshi; Okubo, Shuichi*; Tanaka, Yuki*; et al.

no journal, , 

Oxide thickness dependence of -ray irradiation response on Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) was investigated. As a result of irradiation, the threshold voltage V for both SiC MOSFETs with gate oxide of 30 nm or 60 nm thick shifted to negative voltage-side gently. However, the V for 60 nm thick more immediately decreased over 400 kGy. It is found that SiCMOSFETs with smaller thickness has a higher radiation tolerance.

The Status and preliminary evaluation for the criticality safety design of Okuma Analysis and Research Center

Sato, Akinori; Tanaka, Kosuke; Kosaka, Ichiro

no journal, , 

According to "Mid-and-Long-Term Roadmap" established by the Inter-Ministerial Council for Contaminated Water and Decommissioning Issues, constructing new analysis facility to clarify the prospects of treatment and disposal methods and technologies regarding the safety of radioactive materials was requested. Based on the request, Japan Atomic Energy Agency (JAEA) has been constructing Radioactive Material Analysis and Research Facility. JAEA has established a cooperative relationship with Tokyo Electric Power Company Holdings for decommissioning of Fukushima Daiichi Nuclear Power Station (Fukushima Daiichi). Under this cooperation, JAEA will make analysis for the fuel debris removed from Fukushima Daiichi and the fuel debris will be handled in one of the facilities at Radioactive Material Analysis and Research Facility. Therefore the evaluation of the critical mass limit of the fuel debris is necessary as a preliminary study for the criticality safety of the facility. This presentation reported the status of Radioactive Material Analysis and Research Facility and the preliminary evaluation of criticality safety.

Self-learning Monte Carlo method with Behler-Parrinello neural networks

Nagai, Yuki; Okumura, Masahiko; Tanaka, Akinori*

no journal, , 

no abstracts in English

On the turn determination of crush zone activity; A Lesson from granitic basement rock holding the fast breeder reactor "Monju"

Shimada, Koji; Tateishi, Ryo*; Ishimaru, Tsuneari; Sasaki, Akimichi; Tanaka, Yukumo; Miyazaki, Masashi; Yasue, Kenichi; Niwa, Masakazu; Sueoka, Shigeru; Umeda, Koji; et al.

no journal, , 

Activity evaluation of crush zones encountered in basement rock is an issue of the seismic safety assessment of nuclear plant and geological isolation of radioactive wastes. The selection of crush zone of which has been evaluated should be defined as the latest one by means of turn determination of crush zone activity based on stratigraphic or structural geological method. A lesson from granitic basement rock (Kojaku granite) holding the fast breeder reactor "Monju" is presented. The Kojaku Granite form the oval Tsuruga peninsula (ca. 8km in width) on the southeastern coast of the Sea of Japan and the age is 68.5 plus/minus 0.7Ma (Zircon U-Pb age).1. Stratigraphy-oriented turn determination of crush zone activity. (1.1) Turn determination using cover sediments. (1.2) Turn determination using dyke, mineral and clay vein. 2. Structural-oriented turn determination of crush zone activity.

Electrical properties of SiC MOSFETs irradiated with -rays at elevated temperature

Matsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Takeyama, Akinori; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; Kandori, Mikio*; et al.

no journal, , 

Silicon carbide (SiC) is expected to be applied to Metal-Oxide-Semiconductor (MOS) FETs used in harsh radiation environments to decommission TEPCO Fukushima Daiichi nuclear reactors. To develop radiation resistant SiC MOS FETs, clarification of their radiation response under elevated temperature is required. We measured capacitance-voltage (C-V) characteristics of SiC MOSFETs irradiated with -rays at 423 K in nitrogen atmosphere. The samples were vertical power 4H-SiC MOSFETs with the blocking voltage of 1200 V and the rated current of 20 A with the gate oxide thickness of 45 nm. Typical C-V curve of a SiC MOSFET irradiated even up to 5 kGy was shifted to negative voltage side, suggesting that the positive charges generated in gate oxide by irradiation. While, no significant change in the slope of the curve was observed, indicating that interface traps between the gate oxide and SiC were merely generated. The radiation response of SiC MOS FETs under elevated temperature predominantly depends on the amount of positive charges generated in the gate oxide.