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.

Application of energy-resolving neutron imaging to major-component analyses of materials using four-channel superconducting detector

Vu, TheDang*; Shishido, Hiroaki*; Aizawa, Kazuya; Oku, Takayuki; Oikawa, Kenichi; Harada, Masahide; Kojima, Kenji M*; Miyajima, Shigeyuki*; Soyama, Kazuhiko; Koyama, Tomio*; et al.

IEEJ Transactions on Electrical and Electronic Engineering, 19(11), p.1888 - 1894, 2024/11

https://doi.org/10.1002/tee.24144

Investigating the influence of analysis parameters in three-dimensional elasto-plastic finite element analysis of a gate-type piping support structure

Takito, Kiyotaka; Okuda, Yukihiko; Nishida, Akemi; Li, Y.

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 9 Pages, 2024/07

In probabilistic risk assessment against earthquakes (seismic PRA), one of the important issues is the development of a realistic response analysis method for evaluating the fragility of equipment and piping systems subject to input ground motions exceeding design assumption. Particularly, piping systems have complex plant-specific three-dimensional geometries. The arrangement and rigidity of piping support structures have significant impact on the response characteristics of the entire piping system. Therefore, it is necessary to develop a seismic response analysis method for piping systems, including piping support structures. To this end, the authors have been working on the development of elasto-plastic analysis method for piping support structures in order to establish a realistic response analysis method for piping systems including piping support structures. In this study, parametric studies on important analytical parameters were conducted to understand the influence of the analytical parameters on the deformation in the elasto-plastic analysis of piping support structures. At first, a three-dimensional finite element analysis model was created for cyclic loading tests of a gate type piping support structure assuming large deformations. Using the model, parametric studies were conducted for analysis parameters such as yield stress, secondary stiffness and element size. As the result, the influences of the analysis parameters on the analysis results were quantitatively clarified, which provided insight into the methodology for setting appropriate analysis parameters on elasto-plastic analysis for piping support structures.

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure

Okuda, Yukihiko; Takito, Kiyotaka; Nishida, Akemi; Li, Y.

Mechanical Engineering Journal (Internet), 11(2), p.23-00405_1 - 23-00405_12, 2024/04

https://doi.org/10.1299/mej.23-00405

After the Great East Japan earthquake and the accident at the TEPCO's Fukushima Daiichi Nuclear Power Stations in March 2011, the regulation for nuclear power plants (NPPs) has been enhanced to take countermeasures against beyond-design-basis events. To improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion, the importance of seismic probabilistic risk assessment (PRA) has drawn much attention. It is essential to evaluate the realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA. In particular, since piping systems have plant-specific complex route geometries, it is known that the arrangement and stiffness of piping support structures have a significant impact on seismic response characteristics of the entire piping system. To construct a realistic seismic response analysis method for excessive input ground motion exceeding the elastic response, it is desired to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems including pipe support structures. In this study, the applicability of the method is confirmed by the simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. Moreover, based on the good correlation between the ductility factor and the damage status obtained from the test results and simulation analysis results, it is shown that the ductility factor is effective as a damage evaluation index for piping support structures.

Validation of numerical analyses on scabbing of reinforced concrete panels subjected to projectile impact

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

The outer walls of nuclear facility buildings consist of reinforced concrete (RC) panels. When a projectile collides with a nuclear facility building, local damages such as penetration, scabbing, and perforation can occur in the RC panels. Numerical simulation using finite element analysis (FEA) is generally employed to assess these damage conditions. However, the impact analysis by FEA modelled with continuum elements is difficult to address phenomena such as scattering fragments of concrete because the elements deletion method for large deformation is used to prevent interruption of numerical calculations. Recently, a numerical method known as Smooth Particles Hydrodynamics (SPH), one of the particle methods, has been employed to address discontinuous phenomena. In this paper, we focus on the scabbing damages to RC panels and report on the findings obtained through the validation of the numerical analysis using the SPH method.

Intrinsic factors responsible for brittle versus ductile nature of refractory high-entropy alloys

Tsuru, Tomohito; Han, S.*; Matsuura, Shutaro*; Chen, Z.*; Kishida, Kyosuke*; Lobzenko, I.; Rao, S.*; Woodward, C.*; George, E.*; Inui, Haruyuki*

Nature Communications (Internet), 15, p.1706_1 - 1706_10, 2024/02

https://doi.org/10.1038/s41467-024-45639-8

Refractory high-entropy alloys (RHEAs) have attracted attention because of their potential for use in ultrahigh-temperature applications. Unfortunately, their body-centered-cubic (BCC) crystal structures make them more brittle than the ductile and fracture-resistant face-centered-cubic (FCC) HEAs. RHEAs also display significantly lower creep strengths than a leading Ni-base superalloy and its FCC matrix. To overcome these drawbacks and develop RHEAs into viable structural materials, improved fundamental understanding is needed of factors that control strength and ductility. Here we investigate two model RHEAs, TiZrHfNbTa and VNbMoTaW, and show that the former is plastically compressible down to 77 K, whereas the latter is not below 298 K. We find that hexagonal close-packed (HCP) elements in TiZrHfNbTa lower its dislocation core energy, increase its lattice distortion, and lower its shear modulus relative to VNbMoTaW whose elements are all BCC, leading to the formers higher ductility and modulus-normalized yield strength. Consistent with our yield strength models, primarily screw dislocations are present in TiZrHfNbTa after deformation, but equal numbers of edge and screw segments in VNbTaMoW. Dislocation cores are compact in VNbTaMoW and extended in TiZrHfNbTa, and different macroscopic slip planes are activated in the two RHEAs, which we attribute to the concentration of HCP elements. Our findings demonstrate how electronic structure changes related to the ratio of HCP to BCC elements can be used to control strength, ductility, and slip behavior to develop the next generation of high-temperature materials for more efficient power plants and transportation.

Orientation mapping of YbSn single crystals based on Bragg-dip analysis using a delay-line superconducting sensor

Shishido, Hiroaki*; Vu, TheDang*; Aizawa, Kazuya; Kojima, Kenji M*; Koyama, Tomio*; Oikawa, Kenichi; Harada, Masahide; Oku, Takayuki; Soyama, Kazuhiko; Miyajima, Shigeyuki*; et al.

Journal of Applied Crystallography, 56(4), p.1108 - 1113, 2023/08

https://doi.org/10.1107/S1600576723005204

Development of seismic response analysis method of piping system; Proposal of the nonlinear spring model for piping support structures

Takito, Kiyotaka; Okuda, Yukihiko; Nishida, Akemi; Li, Y.

Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 10 Pages, 2023/07

In probabilistic risk assessment against earthquakes (seismic PRA) for nuclear power plants, the development of a realistic response analysis method for the fragility assessment of piping systems considering input seismic motions exceeding design assumptions is one of the important issues. Usually, piping systems exhibit complex three-dimensional shapes. The arrangement and stiffness of the piping support structures significantly affect the response characteristics of the entire piping system. Therefore, it is necessary to develop a realistic response analysis method of piping systems including piping support structures. In this study, a method for modeling the elasto-plastic hysteresis characteristics of piping support structures is developed to establish a seismic response analysis method of piping systems including piping support structures. First, we formulate an elatsto-plastic spring model that can express the elasto-plastic hysteresis characteristics of a piping support structure. Subsequently, we perform a simulation analysis for the loading test of a piping support structure using this model. As the analysis results and test results were in good agreement, we confirmed the effectiveness of the formulation of the model. The main contents, such as the formulation of the elasto-plastic spring model, the simulation analysis of the loading test, and the comparison between the analysis results and the test results, and the results of this study are reported in this paper.

Experimental study on scabbing limit of local damage to reinforced concrete panels subjected to oblique impact by projectile with semispherical nose

Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Mechanical Engineering Journal (Internet), 10(3), p.22-00370_1 - 22-00370_12, 2023/06

https://doi.org/10.1299/mej.22-00370

Many experimental studies have been reported on the impact resistance of reinforced concrete (RC) structures. However, most formulas were derived from impact tests based on normal impact to target structures using rigid projectiles that do not deform during impact. Therefore, this study develops a local damage evaluation method considering the rigidity of projectiles and oblique impacts that should be considered in realistic projectile impact phenomena. Specifically, we focused on scabbing, defined as the peeling off the back face of the target opposite the impact face, and conducted impact tests on RC panels to clarify the scabbing limit by changing the impact velocity in an oblique impact. The effects of the projectile rigidity and oblique impact on the scabbing limit were investigated based on the test results. This work presents the test conditions, equipment, results, and the scabbing limit on the local damage to RC panels subjected to oblique impacts.

Investigation on damage evaluation index with ductility factor based on simulation analysis for loading test of piping support structure

Okuda, Yukihiko; Takito, Kiyotaka; Nishida, Akemi; Li, Y.

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05

After the Great East Japan earthquake and the accident at the TEPCO's Fukushima Daiichi Nuclear Power Stations in March 2011, the regulation for nuclear power plants (NPPs) has been enhanced to take countermeasures against beyond-design-basis events. To improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion, the importance of seismic probabilistic risk assessment (PRA) has drawn much attention. It is essential to evaluate the realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA. In particular, since piping systems have plant-specific complex route geometries, it is known that the arrangement and stiffness of piping support structures have a significant impact on seismic response characteristics of the entire piping system. In contrast, the current seismic design procedure adopts an evaluation method assuming an elastic response. To construct a realistic seismic response analysis method for excessive input ground motion exceeding the elastic response, it is desired to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems including pipe support structures. In this study, the applicability of the method is confirmed by the simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. Moreover, based on the good correlation between the ductility factor and the damage status obtained from the test results and simulation analysis results, it is shown that the ductility factor is effective as a damage evaluation index for piping support structures.