Aerial monitoring around TEPCO's Fukushima Daiichi Nuclear Power Station and development of radiation monitoring technology for unmanned airplanes in fiscal year 2023 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nakama, Shigeo; Sasaki, Miyuki; Ochi, Kotaro; Nagakubo, Azusa; Sawahata, Yoshiro*; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; et al.

JAEA-Technology 2024-021, 232 Pages, 2025/03

JAEA-Technology-2024-021.pdf:25.79MB

The 2011 off the Pacific coast of Tohoku Earthquake on March 11, 2011, caused a tsunami that led to the TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS) accident, releasing a large amount of radioactive material into the surrounding environment. Since the accident, Aerial Radiation Monitoring (ARM) has been used to quickly and widely measure radiation distribution. As a commissioned project from the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) has continuously conducted ARM around FDNPS using manned and unmanned helicopters. This report summarizes the monitoring results for fiscal year 2023, evaluates changes in dose rate from past results, and discusses the factors contributing to these changes. Additionally, an analysis considering terrain undulation was conducted to improve accuracy for converting ARM data into dose rate. Furthermore, a method to discriminate airborne radon progeny was applied for ARM results to evaluate its impact. Moreover, to perform wide-area monitoring more efficiently, we advanced the development of unmanned airplane monitoring technology.

A Study on the fracture pattern change of high-burnup fuel cladding failed by pellet-cladding mechanical interaction failure under reactivity-initiated accident conditions

Li, F.; Mihara, Takeshi; Udagawa, Yutaka

Journal of Nuclear Science and Technology, 61(9), p.1265 - 1275, 2024/09

https://doi.org/10.1080/00223131.2024.2313553

Biaxial constraint effect on fracture toughness evaluation of reactor pressure vessel under pressurized thermal shock events

Shimodaira, Masaki; Yamaguchi, Yoshihito; Iwata, Keiko; Katsuyama, Jinya; Chimi, Yasuhiro

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 10 Pages, 2024/07

https://doi.org/10.1115/PVP2024-123136

no abstracts in English

Radiation monitoring via manned helicopter around the nuclear power station in the fiscal year 2022 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nagakubo, Azusa; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Arai, Yoshinori*; et al.

JAEA-Technology 2023-027, 146 Pages, 2024/03

JAEA-Technology-2023-027.pdf:18.12MB

By the accident at Tokyo Electric Power Company's (TEPCO's) Fukushima Daiichi Nuclear Power Station (FDNPS), caused by tsunami triggered by the 2011 off the Pacific coast of Tohoku Earthquake, a large amount of radioactive material was released into the surrounding environment. After the accident, Airborne Radiation Monitoring (ARM) via manned helicopter has been applied as a method to quickly and extensively measure the distribution of radiation. Japan Atomic Energy Agency (JAEA) has continuously conducted ARM via manned helicopter around FDNPS. In this report, we summarize the results of the ARM around FDNPS in the fiscal year 2022, evaluate the changes of ambient dose rates and other parameters based on the comparison to the past ARM results, and discuss the causes of such changes. In order to contribute to improve the accuracy of ambient dose rate conversion, we analyzed the ARM data taking into account undulating topography, and evaluated the effect of this method. Furthermore, the effect of radon progenies in the air on the ARM was evaluated by applying the discrimination method to the measurement results.

Fracture toughness evaluation of weld-HAZ in RPV steel using Mini-C(T) specimens

Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 7 Pages, 2024/03

Heat-affected zone (HAZ) produced by butt-welding in reactor pressure vessel (RPV) steel is one of the representative materials for surveillance program. The fracture toughness values of HAZ may show a large uncertainty due to inhomogeneous metallurgical structures. Also, the inhomogeneous microstructure in HAZ may influence on the degree of uncertainty in the fracture toughness and the sensitivity to irradiation embrittlement. We investigated the fracture toughness in HAZ of unirradiated material with respect to its distance from the fusion line of welds, where the amount of mixed microstructures change due to the thermal history during the welding. Mini-C(T) specimens of HAZ were harvested from the crack position at 0.5 mm, 1 mm and 2 mm from the fusion line of welds. The uncertainty of fracture toughness in HAZ, from the fusion line at 0.5 mm in particular, was larger than those of base metal at a quarter thickness. From the results of fracture toughness evaluation considering the standard deviation, there was the difference of reference temperature, in each position of HAZ. in all positions of HAZ was significantly lower than that of base metal, which means the fracture toughness in HAZ was greater than that of base metal at a quarter thickness.

Report on participation in the 6th Asian and Oceanic Congress on Radiation Protection

Yoshitomi, Hiroshi; Manabe, Kentaro; Ochi, Kotaro; Kono, Takahiko; Sasaki, Michiya*; Yoshida, Hiroko*

Hoken Butsuri (Internet), 58(2), p.105 - 111, 2023/08

https://doi.org/10.5453/jhps.58.105

This article gives the report on participation in the 6th Asian and Oceanic Congress on Radiation Protection (AOCRP6), which was held in Mumbai, India on between February 7th and 11th, 2023.

Behavior of high-burnup BWR UO fuel with additives under reactivity-initiated accident conditions

Mihara, Takeshi; Kakiuchi, Kazuo; Taniguchi, Yoshinori; Udagawa, Yutaka

Journal of Nuclear Science and Technology, 60(5), p.512 - 525, 2023/05

https://doi.org/10.1080/00223131.2022.2122616

Radiation monitoring via manned helicopter around the Nuclear Power Station in the fiscal year 2021 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nagakubo, Azusa; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Akutsu, Yuichiro*; Urabe, Yoshimi*; et al.

JAEA-Technology 2022-027, 148 Pages, 2023/02

JAEA-Technology-2022-027.pdf:19.64MB

By the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company (TEPCO), caused by the Great East Japan Earthquake and the following tsunami on March 11, 2011, a large amount of radioactive material was released from the FDNPS. After the nuclear disaster, airborne radiation monitoring via manned helicopter has been conducted around FDNPS. The results of the airborne radiation monitoring and the evaluation for temporal change of dose rate in the fiscal 2021 were summarized in this report. Analysis considering topographical effects was applied to the result of the airborne monitoring to improve the accuracy of the conventional method. In addition, technique for discriminating gamma rays from the ground and those from the airborne Rn-progenies was also utilized to evaluate their effect on airborne radiation monitoring.

Evaluation of anisotropic elastic and plastic parameters of Zircaloy-4 fuel cladding from biaxial stress test data and their application to a fracture mechanics analysis

Li, F.; Mihara, Takeshi; Udagawa, Yutaka

Journal of Nuclear Science and Technology, 59(12), p.1455 - 1464, 2022/12

https://doi.org/10.1080/00223131.2022.2062474

Improvement of load control unit in material irradiation test system (Contract research)

Okada, Yuji; Magome, Hirokatsu; Matsui, Yoshinori

JAEA-Technology 2022-014, 113 Pages, 2022/09

JAEA-Technology-2022-014.pdf:15.79MB

Material irradiation test system had been newly installed in JMTR (Japan Materials Testing Reactor) with taking 5 years which was from 2008 through 2013. The aim of material irradiation test system is to conduct IASCC (Irradiation Assisted Stress Corrosion Cracking) evaluation study. This system is mainly consist of water control unit, which can simulate elevated temperature and pressure of the light water reactor environment in the reactor, and load control unit, which can perform the crack propagation examination under irradiation. This load control unit gives a load to CT (Compact Tension) specimen, and perform the crack propagation examination. The principle of loading to CT specimen is using pressure difference between pressure generated by high temperature and high pressure water by water control unit in capsule and pressure generated by load gas pressure supplied by helium gas cylinder in bellows installed in load control unit. In 2013, the commissioning of material irradiation test system was carried out for adjustment. During this commissioning, the correlation between the differential pressure in load control unit and the load was confirmed by using the test container connected to load control unit with load cell. From the results of commissioning, the problem, which the load change speeds at loading and unloading were different due to different pressure change speeds by the piping resistance performance in the periodic loading test in which load from minimum to maximum repeatedly applied, was confirmed. This report summarizes the problem of load change speed due to the piping resistance performance, which was confirmed in 2013, the improvement and performance test of load control unit for solving the problem described above, which were carried out from 2014 to 2015, and operating procedure.