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Araki, Shohei; Aizawa, Eiju; Murakami, Takahiko; Arakaki, Yu; Tada, Yuta; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Sumiya, Masato; Seki, Masakazu; et al.
Annals of Nuclear Energy, 217, p.111323_1 - 111323_8, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)JAEA has modified the STACY from a homogeneous system using solution fuel to a heterogeneous system using fuel rods in order to obtain criticality characteristics of fuel debris. The modification of the STACY was completed in December 2023. A series of performance inspections were conducted for the start of experimental operations. A new thermal power calibration is required for the performance inspections in order to operate at less than 200 W, which is the permitted thermal power. However, the thermal power measurement method and calibration data used in the former STACY is no longer available due to the modification of the modified STACY. We measured the thermal power of the STACY using the activation method that was improved to adapt to the measurement condition and calibrated the power meter system. Since the positions where activation foils could be installed were very limited, the thermal power was evaluated using numerical calculations supplemented by experimental data. Neutron flux data at the positions of the activation foil was measured by the activation method. Neutron distribution in the core was calculated by the Monte Carlo code MVP. A response function of the activation foil was calculated using the PHITS. The uncertainty of the thermal power measurement was conservatively estimated to be about 15%. Four operations were conducted for the thermal power measurement. The power meter was calibrated by using three operational data and tested with the one operational data. It was found that the indicated value of the meter adjusted by the STACY before the modification work would tend to overestimate the actual output by about 40%. In addition, the current calibration was able to calibrate the meter to within 3% accuracy.
Kamikawa, Yutaka; Suzuki, Makoto; Agake, Toshiki; Murakami, Takahiko; Morita, Yusuke; Shiina, Hidenori; Fukushima, Manabu; Hirane, Nobuhiko; Ouchi, Yasuhiro
JAEA-Technology 2023-030, 57 Pages, 2024/03
JAEA-Technology-2023-030.pdf:1.93MB
Owing to the publication of the latest data about aircraft crashes by Nuclear Regulation Authority (NRA), it was necessary to re-evaluate the probabilities of aircraft crashes for Nuclear Science Research Institute (NSRI). By using of the assessment method provided in "Regulatory Guide of the Assessment Standard for Probability of Airplane Crash on a Nuclear Power Reactor Facility", we re-evaluated the probabilities of aircraft crashes against the nuclear facilities in NSRI. As a result of the evaluations, the sum of the probabilities of aircraft crashes against Waste Treatment Facilities (maximum probability among all nuclear facilities in NSRI) is 5.68
10
(times/(reactor 
year)) which is lower than 10
(times/(reactor year)) that is the assessment criterion whether aircraft crashes is considered to be "anticipated external human induced events" in design basis or not.
Araki, Shohei; Murakami, Takahiko; Kamikawa, Yutaka; Arakaki, Yu; Tada, Yuta; Aizawa, Eiju; Ishii, Junichi; Seki, Masakazu; Izawa, Kazuhiko; Gunji, Satoshi
no journal, ,
We conducted thermal power measurements and thermal power calibration for a performance test in the modified STACY. The activation method was adopted in the thermal power measurements. The core for the measurements consisted of 253 fuel rods and a sample driver. The gold foils used for the activation foil method were installed in the sample driver. The operation was carried out twice, at 20-W and 50-W. The neutron flux in the core and the response of the gold foil were calculated using MVP and PHITS, respectively, with JENDL-5 as the nuclear data. In each measurement, the integrated power was 4.2-Wh and 8.9-Wh, respectively. The indicated power with default setting was found to be about 50% higher than the evaluated value.
Araki, Shohei; Arakaki, Yu; Maekawa, Tomoyuki; Murakami, Takahiko; Hasegawa, Kenta; Yoshikawa, Tomoki; Tada, Yuta; Kamikawa, Yutaka; Sumiya, Masato; Seki, Masakazu; et al.
no journal, ,
In the TEPCO's Fukushima Daiichi Nuclear Power Plant accident, fuel debris was formed by fuel melting and mixing with in-core structures. Although the detailed properties of the fuel debris are still unknown, it is thought to contain materials such as iron and concrete. Then, in order to understand the criticality characteristics of fuel debris, JAEA is conducting a comprehensive numerical analysis assuming the composition of fuel debris containing concrete and iron. However, integral experimental data including these materials are scarce, and the validation of the analytical results has not been fully investigated. Thus, JAEA modified the criticality facility STACY in order to obtain experimental data that will contribute to the validation. This report describes the outline and status of the modified-STACY, and the plan is also presented.
Araki, Shohei; Yoshikawa, Tomoki; Arakaki, Yu; Kamikawa, Yutaka; Hasegawa, Kenta; Tada, Yuta; Sumiya, Masato; Seki, Masakazu; Aizawa, Eiju; Ishii, Junichi; et al.
no journal, ,
In order to understand the criticality characteristics of the fuel debris generated by the accident at the Fukushima Daiichi Nuclear Power Plant, it is essential to obtain critical experiment data that includes reactor structural materials such as iron and concrete that are considered to be contained in the fuel debris. To gather such critical experiment data, JAEA had conducted a major modification of the critical assembly STACY, and the modified STACY achieved first criticality in March 2024. In this presentation, we will discuss the experiments conducted in the modified STACY, with a particular focus on iron, which is considered to have a significant impact on criticality safety due to its strong neutron absorption effect.
Kamikawa, Yutaka; Arakaki, Yu; Yoshikawa, Tomoki; Hasegawa, Kenta; Aizawa, Eiju; Seki, Masakazu; Ishii, Junichi; Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi
no journal, ,
JAEA resumed Static Experiment Critical Facility (STACY) operation in August 2024 after the renewal of the core to a light-water moderated heterogeneous critical assembly for the criticality experiments to clarify the criticality characteristics of the fuel debris. JAEA is currently proceeding the test operation along with pre-service inspections of the core loaded with debris structural material rods to study the nuclear characteristics of the fuel debris. In addition, for experiments simulating the properties of fuel debris, assuming the mixture of core internals and fuels, JAEA manufactures Stainless steel rods (debris structural material rods (iron)), Aluminum alloy rods which are filled with concrete pellets (debris structural material rods (concrete)), which are processed into the same shape as the fuel rods, Refillable fuel rods which have cylindrical shapes, made of zirconium alloy with a detachable end stopper, and Loading tubes which are made of aluminum alloy or zirconium alloy. In this presentation, we report on the fabrication of the experimental loadings such as debris structural material rods and the status of the pre-service inspections.
