Analytical study on stress behavior of core graphite components using simplified viscoelastic evaluation model

Saijo, Tomoaki; Shimazaki, Yosuke; Ishihara, Masahiro

JAEA-Technology 2025-010, 126 Pages, 2025/12

JAEA-Technology-2025-010.pdf:12.52MB

During the operation of the High Temperature Engineering Test Reactor (HTTR), thermal stress is generated in the graphite components. In addition, graphite exhibits dimensional shrinkage and creep deformation under neutron irradiation. As a result, residual stress remains in the graphite components during reactor shutdown. Therefore, in the design of the HTTR core graphite structures, stress analyses of the graphite components have previously been performed using the finite element analysis code VIENUS. In the HTTR, the graphite components are exposed to a wide range of temperature, from approximately 400C to 1200C, depending on their location. Consequently, irradiation-induced behaviors such as material property changes and irradiation shrinkage vary among the graphite components. On the other hand, since VIENUS code evaluates stress based on thermal fluid and heat conduction analysis results, it is not suitable for parametric studies. In this study, the influence of irradiation behavior on the stress behavior of graphite components in the wide temperature range (400C to 1200C) was analyzed using simplified viscoelastic evaluation model, consisting of two beam elements, to conduct efficient parametric studies. Operational stress exhibits two distinct patterns depending on whether the irradiation temperature is below or above 800C, due to irradiation shrinkage. Residual stress approaches the thermal stress, preventing excessive increase even when irradiation shrinkage is large. Moreover good agreement in stress behavior trends was observed between the stress analysis results by the simplified viscoelastic evaluation model and VIENUS code. These results indicate that the simplified viscoelastic evaluation model is beneficial in simulating stress behavior.

Proposal of simple model for investigating irradiation behavior of nuclear-grade graphite

Saijo, Tomoaki; Mizuta, Naoki; Hasegawa, Toshinari; Suganuma, Takuro; Shimazaki, Yosuke; Ishihara, Masahiro; Iigaki, Kazuhiko

JAEA-Technology 2024-002, 96 Pages, 2024/06

JAEA-Technology-2024-002.pdf:22.18MB

Nuclear-grade graphite is used for core components of High Temperature Engineering Test Reactor (HTTR) due to excellent heat resistant properties. The physical properties of this graphite change with temperature and neutron irradiation, as well as exhibit complex behavior such as irradiation deformation and creep deformation. Then, stress analysis code has been developed for the graphite. In previous study, the code has been used to evaluate the shutdown stress by residual strain that accumulates with neutron irradiation. However, the effects of change in physical properties such as Young's modulus and thermal expansion-coefficient on shutdown stress have not been fully understood. Therefore, an evaluation model based on a simplified beam model was developed to clarify the effects of changes in physical properties and complex deformations on stresses occurring during operation and reactor shutdown, and to contribute to the development of graphite structures with longer lifetimes. As an application example, the effects of changes on various physical properties on operational and shutdown stresses were clarified for graphite components in the temperature range from 600 to 800C.

Development of high-performance monitoring system under severe accident condition

Takeuchi, Tomoaki; Tsuchiya, Kunihiko; Komanome, Hirohisa*; Miura, Kuniaki*; Ishihara, Masahiro

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04

After the accident at the Fukushima Dai-ichi (1F) Nuclear Power Plant (NPP), the Japanese Government referred to "Enhancement of instrumentation to identify the status of the reactors and PCVs", in the report of Japanese government to the IAEA ministerial conference in June 2011. In response to these provisions, a research and development of a monitoring system for NPPs situations during severe accidents started in November 2012. The objectives of the R&D are composed of radiation-resistant monitoring camera, radiation-resistant in-water transmission system, and heat-resistant signal cable. For all the three objectives, the elemental technologies have been already developed and now trial system are being fabricated and tested under simulated conditions of severe accidents. The results will enable us to determine the basic specifications of the systems and to provide the information about application limits for users.

Radiation monitoring using manned helicopter around the Nuclear Power Station in the fiscal year 2015 (Contract research)

Sanada, Yukihisa; Munakata, Masahiro; Mori, Airi; Ishizaki, Azusa; Shimada, Kazumasa; Hirouchi, Jun; Nishizawa, Yukiyasu; Urabe, Yoshimi; Nakanishi, Chika*; Yamada, Tsutomu*; et al.

JAEA-Research 2016-016, 131 Pages, 2016/10

JAEA-Research-2016-016.pdf:20.59MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company (TEPCO), caused by the East Japan earthquake and the following tsunami occurred on March 11, 2011, a large amount of radioactive materials was released from the NPS. After the nuclear disaster, airborne radiation monitoring using manned helicopter was conducted around FDNPS. In addition, background dose rate monitoring was conducted around Sendai Nuclear Power Station. These results of the aerial radiation monitoring using the manned helicopter in the fiscal 2015 were summarized in the report.

Status of R&D of high-performance monitoring system under sever accident

Tsuchiya, Kunihiko; Takeuchi, Tomoaki; Komanome, Hirohisa*; Miura, Kuniaki*; Araki, Masanori; Ishihara, Masahiro

Nihon Hozen Gakkai Dai-13-Kai Gakujutsu Koenkai Yoshishu, p.375 - 378, 2016/07

no abstracts in English

Radiation monitoring using manned helicopter around the Fukushima Daiichi Nuclear Power Station in the fiscal year 2014 (Contract research)

Sanada, Yukihisa; Mori, Airi; Ishizaki, Azusa; Munakata, Masahiro; Nakayama, Shinichi; Nishizawa, Yukiyasu; Urabe, Yoshimi; Nakanishi, Chika; Yamada, Tsutomu; Ishida, Mutsushi; et al.

JAEA-Research 2015-006, 81 Pages, 2015/07

JAEA-Research-2015-006.pdf:22.96MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (NPS), Tokyo Electric Power Company (TEPCO), caused by the East Japan earthquake and the following tsunami occurred on March 11, 2011, a large amount of radioactive materials was released from the NPP. These results of the aerial radiation monitoring using the manned helicopter in the fiscal 2014 were summarized in the report.

Effect of experiments using Transmutation Physics Experimental Facility on the reduction of uncertainties in reactor physics parameters of an accelerator-driven system

Iwamoto, Hiroki; Nishihara, Kenji; Katano, Ryota*; Fukushima, Masahiro; Tsujimoto, Kazufumi

JAEA-Research 2014-033, 82 Pages, 2015/03

JAEA-Research-2014-033.pdf:6.53MB

The effect of experiments using Transmutation Physics Experimental Facility (TEF-P) is analysed from the viewpoint of the reduction of uncertainties in reactor physics parameters (criticality and coolant void reactivity) of an accelerator-driven system (ADS). The analysis is conducted by the nuclear-data adjustment method using JENDL-4.0 on the assumption that ve types of reactor physics experiments (a total of 44 experiments) are performed in TEF-P: (1) criticality experiment, (2) lead void reactivity experiment, (3) reaction rate ratio experiment, (4) sample reactivity experiment, and (5) fuel replacement reactivity experiment. As the result, 1.0% of uncertainty in criticality is found to be reduced to approximately 0.4%, and effective experiments for the reduction of uncertainty in criticality and coolant void reactivity are shown to be fuel replacement reactivity experiments and lead void reactivity experiments, respectively. Although these effects depend largely on the composition and amount of minor-actinide (MA) fuels, it is found that a combination of different types of experiments and database of existing experiments is effective in reducing the uncertainties.

2012 training using JMTR and related facilities as advanced research infrastructures

Kimura, Nobuaki; Takemoto, Noriyuki; Ooka, Makoto; Ishitsuka, Etsuo; Nakatsuka, Toru; Ito, Haruhiko; Ishihara, Masahiro

JAEA-Review 2012-055, 40 Pages, 2013/03

JAEA-Review-2012-055.pdf:93.64MB

Training courses using JMTR and related facilities as advanced research infrastructures have been newly organized for domestic students, young researchers and engineers since FY2010 from a viewpoint of nuclear human resource development in order to support global expansion of nuclear power industry. In FY 2012, two courses were carried for foreign as well as Japanese young researchers and engineers in order to carry out effective practical training. For the foreigner course, 16 young researchers and engineers were joined from July 23rd to August 10th. For the Japanese course, total 35 young researchers and engineers were joined two courses from August 20th to August 31st and from September 3rd to September 14th. Lectures of these training courses were consisted from basics of nuclear energy to its application, especially for irradiation tests in Motrin this paper, results of these foreigners and Japanese training courses are reported.

Development of Mo-Tc domestic production with high-density MoO pellets by (n,) reaction

Tsuchiya, Kunihiko; Tanase, Masakazu*; Takeuchi, Nobuhiro*; Kobayashi, Masaaki*; Hasegawa, Yoshio*; Yoshinaga, Hideo*; Kaminaga, Masanori; Ishihara, Masahiro; Kawamura, Hiroshi

Proceedings of 5th International Symposium on Material Testing Reactors (ISMTR-5) (Internet), 10 Pages, 2012/10

http://www.murr.missouri.edu/ismtr/papercall/Papers/JAEA/Tsuchiya_K=PAPER_Dev%20of%20Mo99-Tc99m%20Domestic%20Prod%20with%20HighDens%20MoO3%20Pellets.pdf

As one of effective uses of the JMTR, JAEA has a plan to produce Mo by (n, ) method, a parent nuclide of Tc. In case of Japan, the supplying of Mo depends only on imports from foreign countries. The R&D on production method of Mo -Tc has been performed with Japanese industrial users under the cooperation programs. The main R&D items for the production are (1) Fabrication of irradiation target such as the sintered MoO pellets, (2) Separation and concentration of Tc by the solvent extraction from Mo solution, (3) Examination of Tc solution for a medicine, and (4) Mo recycling from Mo generator and solution. In this paper, the status of the R&D is introduced for the production of Mo -Tc.

Proceedings of the Specialist Meeting on Mo-99 Production by (n,) Method; March 9-10, 2012, Yurakucho Asahi Hall, Tokyo, Japan

Ishitsuka, Etsuo; Ishihara, Masahiro; Suzuki, Masahide

JAEA-Review 2012-030, 247 Pages, 2012/07

JAEA-Review-2012-030.pdf:21.51MB

This report summarizes the documents presented in the Specialist Meeting on Mo Production by (n,) Method, which was held on March 9 to 10, 2012, at the Yurakucho Asahi Hall in Tokyo, hosted by Japan Atomic Energy Agency. The objective of the meeting is to exchange the information of current status, future plan for the Mo production, and to make a discussion of "How to cooperate" in each research and test reactors. There were 27 participants from Poland, Kazakhstan, Indonesia, Thailand, Malaysia, Netherlands, Korea and Japan. As a result of this meeting, it was recognized that to push forward the development of Mo production by (n,) method is necessary for the future steady supply of Mo. Moreover, an irradiation test using the high density MoO pellet developed by the Japan Atomic Energy Agency was proposed from a viewpoint of a merit for the common irradiation target in each research and test reactors.