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Nakamura, Takemi; Ogasawara, Reira; Ushijima, Hiroki; Okada, Yuji; Yamaguchi, Atsushi; Horiguchi, Hironori; Hirane, Nobuhiko
JAEA-Technology 2026-008, 39 Pages, 2026/07
JAEA-Technology-2026-008.pdf:2.55MB
Irradiation studies targeting thermal neutrons to fast neutrons are being conducted at the JRR-3 research reactor, and to accurately evaluate the irradiation effect, it is necessary to consider the influence of the neutron spectrum. Fuels and cadmium wires used as combustible absorbers are burned by reactions with neutrons because the JRR-3 is a high-power 20MW reactor, and the fuel shuffling and replacement are performed periodically to ensure uniform burnup and long-term operation. Since it is necessary to accurately reproduce the burnup history both temporally and spatially, it is difficult to evaluate the neutron spectrum with high accuracy through computational analysis. Hence, we investigated a method that can easily and accurately evaluate neutron spectra at irradiation facility in equilibrium core of JRR-3 silicide fuel and verified the validity of the evaluation results. This method uses data of initial guess spectrum and response functions for each irradiation field calculated using MCNP code, reaction rate measured from neutron fluence monitors such as Au-Al and Ni wire to perform unfolding using SAND-II. We conducted characteristic measurements from fiscal year 2023 to 2025 and performed unfolding using actual measured values from neutron fluence monitors for seven cycles. As a result, in all cases, the C/E ratio of the reaction rate was 1.000, indicating good convergence, and the difference from the unfolding and measured neutron flux was within 0.3% for hydraulic irradiation facility HR-1, within 0.8% for pneumatic irradiation facility PN-2, and 0% for vertical irradiation facility RG-2. This suggests that the results of the unfolded spectrum are valid. The application of this method can meet a wide range of user needs, and it is expected to greatly contribute to the advancement of irradiation research with improved reliability of the JRR-3 irradiation field.
Ha, Yoosung; Hata, Kuniki; Okada, Yuji; Ushijima, Hiroki; Mitsui, Kento; Fuyushima, Takumi; Ishijima, Yasuhiro; Nio, Daisuke; Watanabe, Masaya; Tagami, Susumu; et al.
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Hata, Kuniki; Okada, Yuji; Ha, Yoosung; Ushijima, Hiroki; Mitsui, Kento; Fuyushima, Takumi; Ishijima, Yasuhiro; Nio, Daisuke; Watanabe, Masaya; Katsuyama, Jinya
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Ushijima, Hiroki; Mitsui, Kento; Fuyushima, Takumi; Okada, Yuji; Endo, Yasuichi; Matsui, Yoshinori; Ha, Yoosung; Hata, Kuniki; Nakamura, Takemi
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Mitsui, Kento; Ushijima, Hiroki; Ogasawara, Reira; Okada, Yuji; Suzuki, Makoto; Kimura, Kazuya; Ouchi, Satoshi; Nio, Daisuke; Ishijima, Yasuhiro; Endo, Yasuichi; et al.
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Hata, Kuniki; Ha, Yoosung; Okada, Yuji; Ushijima, Hiroki; Mitsui, Kento; Fuyushima, Takumi; Watanabe, Masaya; Nakamura, Takemi; Toyama, Takeshi; Fukumoto, Kenichi*; et al.
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Okada, Yuji; Ushijima, Hiroki; Suzuki, Makoto; Endo, Yasuichi; Horiguchi, Hironori
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Ha, Yoosung; Hata, Kuniki; Watanabe, Masaya; Okada, Yuji; Ushijima, Hiroki; Mitsui, Kento; Fuyushima, Takumi
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Okada, Yuji; Mitsui, Kento; Ushijima, Hiroki; Fuyushima, Takumi; Nio, Daisuke; Ishijima, Yasuhiro; Kaji, Yoshiyuki; Endo, Yasuichi; Matsui, Yoshinori; Nakamura, Takemi; et al.
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Ushijima, Hiroki; Mitsui, Kento; Ogasawara, Reira; Okada, Yuji; Fuyushima, Takumi; Endo, Yasuichi; Ishijima, Yasuhiro; Nio, Daisuke; Kaji, Yoshiyuki; Watanabe, Masaya; et al.
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Ushijima, Hiroki; Mitsui, Kento; Ogasawara, Reira; Okada, Yuji; Endo, Yasuichi; Ishijima, Yasuhiro; Matsuda, Makoto
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Fuyushima, Takumi; Ushijima, Hiroki; Mitsui, Kento; Endo, Yasuichi; Matsui, Yoshinori; Okada, Yuji; Ha, Yoosung; Hata, Kuniki; Ishijima, Yasuhiro; Nio, Daisuke; et al.
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Takeda, Ryoma; Omori, Takazumi; Mitsui, Kento; Takeuchi, Tomoaki; Ushijima, Hiroki; Matsui, Yoshinori; Nio, Daisuke; Endo, Yasuichi; Okada, Yuji; Ide, Hiroshi
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Ushijima, Hiroki; Okada, Yuji; Mitsui, Kento; Nakamura, Takemi; Inoue, Shuichi
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We are renewing the aging equipment of JRR-3 to irradiate capsules with temperature control. The conventional equipment had to be manually adjusted whenever the capsule temperature fluctuates according to the position change of control rod. Hence, the goal of this renewal is to automate the capsule temperature control from before reactor startup to after shutdown. The new system uses vacuum control and heater control. We performed cold tests to check the performance of the equipment. It was found that the device performed satisfactorily by varying the mock capsule to several temperatures. In addition, reactor power values are captured by the new system. The target temperature in conventional equipment was maintained by feedback of changes in capsule temperature. On the other hand, the new equipment starts in conjunction with the reactor power before the capsule temperature changes, so that we expect improved accuracy in temperature maintenance.
Mitsui, Kento; Ushijima, Hiroki; Okada, Yuji; Ishijima, Yasuhiro; Kaji, Yoshiyuki; Nio, Daisuke; Endo, Yasuichi; Matsui, Yoshinori; Nakamura, Takemi
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