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Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Yamaguchi, Takashi; et al.
RIST News, (69), p.2 - 18, 2023/09
The contamination of radioactive materials leaked from the reactor has resulted in numerous hot spots in the Fukushima Daiichi Nuclear Power Station (1F) building, posing obstacles to its decommissioning. In order to solve this problem, JAEA has conducted research and development of the digital technique for inverse estimation of radiation source distribution and countermeasures against the estimated source in virtual space for two years from 2021 based on the subsidy program "Project of Decommissioning and Contaminated Water Management" performed by the funds from the Ministry of Economy, Trade and Industry. In this article, we introduce the results of the project and the plan of the renewal project started in April 2023. For the former project, we report the derivative method for LASSO method considering the complex structure inside the building and the character of the source and show the result of the inverse estimation using the method in the real reactor building. Moreover, we explain the platform software "3D-ADRES-Indoor" which integrates these achievements. Finally, we introduce the plan of the latter project.
Iwata, Keiko; Hata, Kuniki; Tobita, Toru; Hirota, Takatoshi*; Takamizawa, Hisashi; Chimi, Yasuhiro; Nishiyama, Yutaka
Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 7 Pages, 2021/07
Chimi, Yasuhiro; Iwata, Keiko; Tobita, Toru; Otsu, Takuyo; Takamizawa, Hisashi; Yoshimoto, Kentaro*; Murakami, Takeshi*; Hanawa, Satoshi; Nishiyama, Yutaka
JAEA-Research 2017-018, 122 Pages, 2018/03
JAEA-Research-2017-018.pdf:44.03MB
Warm pre-stress (WPS) effect is a phenomenon that after applying a load at a high temperature fracture does not occur in unloading during cooling, and then the fracture toughness in reloading at a lower temperature increases effectively. Engineering evaluation models to predict an apparent fracture toughness in reloading are established using experimental data with linear elasticity. However, there is a lack of data on the WPS effect for the effects of specimen size and surface crack in elastic-plastic regime. In this study, fracture toughness tests were performed after applying load-temperature histories which simulate pressurized thermal shock transients to confirm the WPS effect. The experimental results of an apparent fracture toughness tend to be lower than the predictive results using the engineering evaluation models in the case of a high degree of plastic deformation in preloading. Considering the plastic component of preloading can refine the engineering evaluation models.
Iwata, Keiko; Tobita, Toru; Takamizawa, Hisashi; Chimi, Yasuhiro; Yoshimoto, Kentaro*; Nishiyama, Yutaka
Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 6 Pages, 2016/07
The effect of warm pre-stressing (WPS) on fracture toughness was evaluated for a reactor pressure vessel steel. Various types of thermomechanical loadings were applied to 1T-CT specimens. The results were compared with predictions from several analytical WPS engineering models. The specimen size effect was subsequently investigated under the load-unload-cool-fracture transient condition using 1T-, 0.4T-, and 0.16T-CT specimens. Analyses of the plastic zone distribution and residual stress were conducted to identify the difference in the WPS effect among the specimens.
Tobita, Toru; Nakagawa, Sho*; Takeuchi, Tomoaki; Suzuki, Masahide; Ishikawa, Norito; Chimi, Yasuhiro; Saito, Yuichi; Soneda, Naoki*; Nishida, Kenji*; Ishino, Shiori*; et al.
Journal of Nuclear Materials, 452(1-3), p.241 - 247, 2014/09
Times Cited Count：17 Percentile：78.17(Materials Science, Multidisciplinary)Three kinds of Fe-based model alloys, Fe-0.018 atomic percent (at.%) Cu, Fe-0.53at.%Cu, and Fe-1.06at.%Cu were irradiated with 2 MeV electrons up to the dose of 2
10
dpa at 250
C. After the irradiation, the increase in Vickers hardness and the decrease in electrical resistivity were observed. The increase in hardness by electron irradiation is proportional to the product of the Cu contents and the square root of the electron dose. The decrease in electrical resistivity is proportional to the product of the square of Cu contents and the electron dose. Cu clustering in the materials with electron irradiation and thermal aging was observed by means of the three dimensional atom probes (3D-AP). The change in Vickers hardness and electrical resistivity is well correlated with the volume fraction of Cu clusters.
Tobita, Toru; Udagawa, Makoto; Chimi, Yasuhiro; Nishiyama, Yutaka; Onizawa, Kunio
Journal of Nuclear Materials, 452(1-3), p.61 - 68, 2014/09
Times Cited Count：10 Percentile：60.73(Materials Science, Multidisciplinary)To investigate the changes in the mechanical properties of cladding materials irradiated with high neutron fluence, two types of cladding materials were fabricated using the submerged-arc welding and electroslag welding methods. The tensile tests, Charpy impact tests and fracture toughness tests were conducted before and after neutron irradiation with a fluence of 10
n/cm
at 290 C. With neutron irradiation, the yield strength and ultimate strength increased, and the total elongation decreased. The Charpy upper-shelf energy was reduced and the ductile-to-brittle transition temperature was increased with neutron irradiation. There was no obvious decrease in the elastic-plastic fracture toughness (J
) of the cladding materials at high neutron fluence. The tearing modulus decreased with neutron irradiation, and considerable low J values were observed at high temperatures submerged-arc-welded cladding materials.
Ezure, Toshiki; Miyake, Yasuhiro*; Tobita, Akira; Kimura, Nobuyuki; Kamide, Hideki
JAEA-Research 2012-005, 56 Pages, 2012/05
JAEA-Research-2012-005.pdf:10.06MB
In the design of JSFR, a two-loop cooling system and a compact reactor vessel are employed to achieve the economical improvement. However, these innovative designs lead to the increase of coolant velocity. As the results, strong vortices at the H/L intake may cause the cavitation (vortex cavitation). Therefore, the evaluation of occurrence behavior of vortex cavitation is the important issue for the structural integrity of reactor. In the present study, fundamental water experiments were performed in the cylindrical tank geometry. The water temperature was varied from 10C to 80C to clarify the influence of kinematic viscosity, 
. The occurrences behaviors of vortex cavitation were evaluated quantitatively by visualization measurement and image analysis. As the results, it was clarified that there was little dependence on under the small conditions, while it was relatively obvious under the large conditions.
Kimura, Nobuyuki; Hayashi, Kenji; Tobita, Akira; Kamide, Hideki; Miyake, Yasuhiro*
JAEA-Research 2009-026, 160 Pages, 2009/10
JAEA-Research-2009-026.pdf:15.97MB
Thermal stratification after a scram is one of main thermal loads of a reactor vessel in sodium cooled fast reactor. Water experiments using an 1/10th scaled model were carried out for an advanced loop type sodium cooled reactor. The reactor vessel is highly compact and has an upper inner structure (UIS), which has a slit in radial direction for fuel handling. The jet from core outlet goes through the UIS slit and makes asymmetric and locally high velocity field in the reactor upper plenum. Steep temperature distribution across the stratification interface and temperature fluctuations were found near the UIS slit. It was revealed that they were resulted from the impingement of the jet through the slit at the interface. Parameter experiments showed the characteristics of thermal stratification interface.
Nakagawa, Sho*; Hori, Fuminobu*; Chimi, Yasuhiro; Ishikawa, Norito; Kitagawa, Michiharu*; Oshima, Ryuichiro*; Tobita, Toru; Taniguchi, Ryoichi*; Suzuki, Masahide; Iwase, Akihiro*
Nuclear Instruments and Methods in Physics Research B, 257(1-2), p.397 - 401, 2007/04
Times Cited Count：4 Percentile：35.7(Instruments & Instrumentation)Supersaturated Fe-1.2wt.%Cu alloys were irradiated with 200-MeV Xe and 200-MeV Au ions at elevated temperatures. To make an irradiated region and an unirradiated region in a specimen, a masking plate was put on the specimen during the irradiation. After the irradiation, the hardness was measured by using a conventional microhardness tester or a nano-indenter. We have found that the hardness only in irradiated region increases by the irradiation. The boundary of irradiated and unirradiated regions can be clearly identified by the difference in hardness. The present result implies that swift heavy ion irradiation can be used for the local modification of hardness in supersaturated alloys.
Iwase, Akihiro; Hasegawa, Tadayuki*; Chimi, Yasuhiro; Tobita, Toru; Ishikawa, Norito; Suzuki, Masahide; Kambara, Tadashi*; Ishino, Shiori*
Nuclear Instruments and Methods in Physics Research B, 195(3-4), p.309 - 314, 2002/10
Times Cited Count：12 Percentile：60.73(Instruments & Instrumentation)no abstracts in English
Morita, Kenji*; Ishino, Shiori*; Tobita, Toru; Chimi, Yasuhiro; Ishikawa, Norito; Iwase, Akihiro
Journal of Nuclear Materials, 304(2-3), p.153 - 160, 2002/08
Times Cited Count：13 Percentile：63.33(Materials Science, Multidisciplinary)To study the mechanism of irradiation embrittlement in pressure vessel alloys, we performed high energy ion irradiation experiments using FeCu model alloys. The dependences of Vickers hardness change by irradiation on ion fluence, irradiation temperature and Cu content were discussed.
Niwa, Hajime; Kawata, Norio; Ieda, Yoshiaki; Sato, Ikken; Ohno, Shuji; Uto, Nariaki; Miyahara, Shinya; Kondo, Satoru; Kamide, Hideki; Yamaguchi, Akira; et al.
PNC TN9410 94-154, 317 Pages, 1995/03
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Tobita, Toru; Chimi, Yasuhiro; Ishikawa, Norito; Suzuki, Masahide; Onizawa, Kunio; Iwase, Akihiro*
no journal, ,
no abstracts in English
Uezu, Yasuhiro; Tobita, Kazunori; Yamaguchi, Takenori; Momose, Takumaro; Murakami, Hiroyuki; Furuta, Sadaaki; Yamaguchi, Yasuhiro
no journal, ,
JAEA was established on October 1st, 2005 by integrating the Japan Atomic Energy Research Institute and the Japan Nuclear Cycle Development Institute. In these institutes, there were a several radiation control methods or original radiation control levels. After establishing JAEA, in order to make a harmonization of radiation control methods and levels, applications of these are investigated under actual situations.
Katsuyama, Jinya; Tobita, Toru; Chimi, Yasuhiro; Nishiyama, Yutaka; Onizawa, Kunio
no journal, ,
no abstracts in English
Ha, Yoosung; Takamizawa, Hisashi; Iwata, Keiko; Tobita, Toru; Chimi, Yasuhiro; Katsuyama, Jinya; Nishiyama, Yutaka
no journal, ,
The microstructure of heat affected zone (HAZ) in stainless over-ray clad is predicted by finite element method (FEM). From the results of FEM analysis, the coarse grain area and fine grain area could obtain from HAZ and base metal also obtained in 1/4 thickness part for the irradiation experiment. After ion irradiation, the irradiation hardening of HAZ has higher tendency than that of base metal. In addition, the change of hardening is observed in fine grain area.
Yamada, Susumu; Numata, Yoshiaki*; Sato, Tomoki*; Tobita, Yasuhiro*; Wei, S.*
no journal, ,
no abstracts in English
Miyamura, Hiroko; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Machida, Masahiko
no journal, ,
We develop interactive visualization engine on a mixed reality device to realize workers' safety and work efficiency during environmental improvement work under the high-dose radiation environment. After the inverse source estimation, the three-dimensional distribution maps of the air dose rate are obtained by simulation. It is necessary to present the maps to decommissioning workers by visualization techniques to help them understand their environment. The latest MR devices can be used to support the work of decommissioning workers by placing virtual visualization primitives in the real space. In this presentation, we report outline the results and future direction of the MR device visualization engine, including features such as immersive experience, interactive operation, and information sharing with remote specialists.
Machida, Masahiko; Shi, W.*; Yamada, Susumu; Miyamura, Hiroko; Numata, Yoshiaki*; Sato, Tomoki*; Tobita, Yasuhiro*; Yoshida, Toru*; Yanagi, Hideaki*; Furutachi, Naoya*; et al.
no journal, ,
no abstracts in English
Miyamura, Hiroko; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Iwata, Ayako*; Machida, Masahiko
no journal, ,
We propose a prototype of a decommissioning support system using an XR device, considering the system is effective for realizing the safety for the decommissioning workers the efficiency of the work. In this paper, we report the outline of the new function as we have added it with the use of Avatar in cyberspace for evaluating the exposure dose of the decommissioning workers. This function allows to create the work plan which is taken into account the worker's exposure dose rate.
