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Journal Articles

Material data acquisition activities to develop the material strength standard for sodium-cooled fast reactors

Toyota, Kodai; Onizawa, Takashi; Wakai, Takashi; Hashidate, Ryuta; Kato, Shoichi

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 10 Pages, 2022/04

Journal Articles

Evaluation of the Japanese fatigue test data in Gr.91 for elevated temperature design

Ando, Masanori; Toyota, Kodai; Hashidate, Ryuta; Onizawa, Takashi

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 10 Pages, 2021/07

The ASME Boiler and Pressure Vessel Code (ASME BPVC) Section III, Division 5 had provided only one design fatigue curve for Grade 91 steel (Gr.91) at 540 $$^{circ}$$C until 2019 version. To overcome this disadvantage, The ASME Section III Working Group had taken an action to incorporate the temperature-dependent design fatigue curves for Gr. 91 developed by Japan Society of Mechanical Engineers into ASME BPVC Section III Division 5. As the results, the temperature dependent design fatigue curves are provided in the 2021 edition of the ASME BPVC. To clear the features of the best fit fatigue curve equation, 305 data stored in the database were analyzed and the statistic values and the values of 95% and 99% lower confidence bound calculated by failure probability assessment were clarified. Moreover, some additional available data of fatigue and creep-fatigue test obtained in Japan are also indicated for considering the creep-fatigue damage evaluation under elevated temperature condition.

Journal Articles

Proposal of maintenance rationalization for next-generation fast reactors based on the analysis of the prolonged maintenance of the prototype fast-breeder reactor in Japan, "Monju", 1; Analysis of plant schedule of "Monju" in cold shutdown

Hashidate, Ryuta; Toyota, Kodai; Takahashi, Keita; Yada, Hiroki; Takaya, Shigeru

Hozengaku, 19(4), p.115 - 122, 2021/01

In order to improve both safety and economic efficiency of a nuclear power plant, it is necessary to realize rational maintenance based on characteristics of the plant. The prototype fast-breeder reactor in Japan, Monju, spent most of the year for the maintenance. Thus, it is important to identify causes of the prolonged maintenance of Monju and to investigate countermeasures for implementation of rational maintenance of next-generation fast reactors. In this study, the authors investigated the causes of the prolonged maintenance of Monju during reactor cold shutdown based on the plant schedule of Monju. In addition, we proposed the maintenance optimization idea for next-generation fast reactors to solve the revealed issues.

Oral presentation

The Material property equations for 316FR steel at extremely high temperature

Okuda, Takahiro; Yamashita, Hayato; Toyota, Kodai; Shimomura, Kenta; Onizawa, Takashi; Kato, Shoichi

no journal, , 

This study describes the setting of the material property equations of 316FR steel at an extremely high temperature which can be applied to severe accident conditions of generation IV fast reactors. 316FR steel will be applied to structural materials, e.g. reactor vessel, in the generation IV fast reactors. After the severe accident in Fukushima Daiichi Nuclear Power Plants, the evaluation of structural integrity was found to be very important severe accident condition. The development of the generation IV fast reactors requires the material properties of 316FR steel at the extremely high temperature. However, such data has not been acquired. Therefore, tensile and creep tests were carried out in the temperature range over 700$$^{circ}$$C for 316FR steel. Based on the acquired data from the tests, the equations that can evaluate the material properties of 316FR steel at the extremely high temperature were set up. They are an elasto-plastic stress-strain equation, a creep rupture equation and a creep strain equation.

Oral presentation

Oral presentation

Analysis of issues related to maintenance period of the fast breeder prototype reactor Monju, 1; Analysis of plant operation for maintenance of cold shutdown Monju

Hashidate, Ryuta; Toyota, Kodai; Takahashi, Keita; Yada, Hiroki; Takaya, Shigeru

no journal, , 

In order to achieve both safety and economic efficiency of a nuclear power plant, it is necessary to realize rational maintenance based on characteristics of the plant. The fast breeder prototype reactor, Monju, spent most of the year for the maintenance. It is important to identify causes of the prolonged maintenance of Monju and to investigate countermeasures for implementation of rational maintenance of a next fast reactor. In this study, causes of the prolonged maintenance of Monju during reactor cold shutdown were investigated based on the plant operation of Monju. In addition, proposals for the maintenance optimization idea of a next generation fast reactor were presented to address the revealed issues.

Oral presentation

Analysis of issues related to maintenance period in the fast breeder prototype reactor Monju, 2; Analysis of plant maintenance plan

Toyota, Kodai; Hashidate, Ryuta; Takahashi, Keita; Yada, Hiroki; Takaya, Shigeru

no journal, , 

In order to achieve both safety and economic efficiency of a nuclear power plant, it is necessary to realize rational maintenance based on characteristics of the plant. The fast breeder prototype reactor, Monju, spent most of the year for the maintenance. It is important to identify causes of the prolonged maintenance of Monju and to investigate countermeasures for implementation of rational maintenance of a next fast reactor. In this study, causes of the prolonged maintenance of Monju during reactor cold shutdown were investigated based on the plant maintenance plan of Monju. In addition, proposals for the maintenance optimization idea of a next generation fast reactor were presented to address the revealed issues.

Oral presentation

Evaluation of defect number density in sodium equipment stainless steel welds

Toyota, Kodai; Hashidate, Ryuta; Yada, Hiroki; Takaya, Shigeru; Miyakoshi, Hiroyuki; Kato, Shoichi

no journal, , 

Probabilistic fracture mechanics (PFM) evaluation requires information on the probabilistic distributions of the number and size of initial defects, material properties such as crack growth rate due to fatigue and creep, and load to evaluate the failure probability of components. In this study, ultrasonic testing was conducted on the welds of the test equipment used in the research and development of fast reactors, and the number and size of defects were evaluated. The results could be used as conservative values of initial defects, and the values related to initial defects for PFM evaluation of FBR components were examined.

Oral presentation

Development of location identification method of reactor internal structures using ultrasonic phased array

Asahi, Manabu*; Tomita, Naoki*; Furuya, Masahiro*; Morita, Hidetoshi*; Toyota, Kodai

no journal, , 

To inspect reactor internal structures of Sodium-cooled Fast Reactors (SFRs) from the outer surface of vessel, the measurement method was proposed and developed to analyze noisy echo signals of an ultrasonic phased array flaw detector. The proposed method successfully reconstructs images of the stainless-steel structure by optimizing the measurement parameters.

Oral presentation

Evaluation of irradiation resistance of 316FR stainless steel under in-situ electron irradiation observation

Toyota, Kodai; Wakai, Eiichi; Onizawa, Takashi; Shibayama, Tamaki*; Nakagawa, Yuki*

no journal, , 

no abstracts in English

Oral presentation

Study of multi-simultaneous measurement system development under radiation environment and innovative materials

Wakai, Eiichi; Iwamoto, Yosuke; Shibayama, Tamaki*; Sato, Koichi*; Toyota, Kodai; Onizawa, Takashi; Wakui, Takashi; Ishida, Taku*; Makimura, Shunsuke*; Nakagawa, Yuki*; et al.

no journal, , 

In the fields of accelerator target systems, nuclear power, aerospace, etc., radiation degradation of structural materials and equipment occurs, and therefore, the development of materials with high durability and excellent functions is expected. In order to create innovative materials that can be used in radiation fields, we are developing a new non-destructive inspection technique that can accurately measure the internal defects of various materials in radiation fields. As an innovative material, high-entropy alloys (HEA) are known for their high strength and ductility, and are expected to be used in various applications. In this talk, we will report on the construction of a measurement principle that enables multi-simultaneous measurements even in radiation fields, the status of HEA prototypes, and the status and progress of irradiation analysis of metals and other materials.

Oral presentation

Machine learning of ultrasonic phased-array images for flaw detection

Tomita, Naoki*; Furuya, Masahiro*; Asahi, Manabu*; Hisamochi, Rikuya*; Toyota, Kodai; Yada, Hiroki

no journal, , 

Ultrasonic phased array is a phase composite imaging technology developed in the radar field and has recently been used for nondestructive inspection of power generation equipment. However, scattered waves in the inspection target make it difficult to distinguish a flaw from scattering from the edge surface. In this study, we developed a method to discriminate flaws with high accuracy by adjusting parameters such as output voltage and receiver sensitivity to make it easier to see the flaws and by deep learning of the optimized flaw images. First, actual measurements were made using an ultrasonic phased-array flaw detector on a stainless-steel specimen. Next, a model was created to discriminate the presence or absence of flaws using transition learning, one of the machine learning methods. As a result, we found that the highest accuracy was achieved when transition learning was performed using inceptionv3 and resnet101, a convolutional neural network architecture. These results show that the method developed in this study is effective for nondestructive inspection.

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