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Journal Articles

Effect of dissolved oxygen concentration on dynamic strain aging and stress corrosion cracking of SUS304 stainless steel under high temperature pressurized water

Hirota, Noriaki; Nakano, Hiroko; Fujita, Yoshitaka; Takeuchi, Tomoaki; Tsuchiya, Kunihiko; Demura, Masahiko*; Kobayashi, Yoshinao*

The IV International Scientific Forum "Nuclear Science and Technologies"; AIP Conference Proceedings 3020, p.030007_1 - 030007_6, 2024/01

Dynamic strain aging (DSA) and intergranular stress corrosion cracking (intragranular SCC) occur in high temperature pressurized water simulating a boiling water reactor environment due to changes in dissolved oxygen (DO) content, respectively. In order to clearly understand the difference between these phenomena, the mechanism of their occurrence was summarized. As a result, it was found that DSA due to intragranular cracking occurred in SUS304 stainless steel at low DO $$<$$ 1 ppb, while DSA was suppressed at DO 100 to 8500 ppb due to the formation of oxide films on the surface. On the other hand, when DO was increased to 20000 ppb, the film was peeled from the matrix, O element diffused to the grain boundary of the matrix, resulting in intergranular SCC. These results are indicated that the optimum DO concentration must be adjusted to suppress crack initiation due to DSA and intergranular SCC.

Journal Articles

Double diffusive dissolution model of UO$$_{2}$$ pellet in molten Zr cladding

Ito, Ayumi*; Yamashita, Susumu; Tasaki, Yudai; Kakiuchi, Kazuo; Kobayashi, Yoshinao*

Journal of Nuclear Science and Technology, 60(4), p.450 - 459, 2023/04

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Evaluation of the cryogenic tensile properties for aramid fiber rod

Saito, Toru; Okubo, Toshikazu*; Izumi, Keisuke*; Okawa, Yoshinao*; Kobayashi, Norihiro*; Yamazaki, Toru; Kawano, Katsumi; Isono, Takaaki

Teion Kogaku, 50(8), p.400 - 408, 2015/08

Aramid fiber-reinforced plastic (AFRP) has been developed as a structural material that has the advantages of light weight and high strength. In this study, tensile tests were carried out to measure the tensile properties of AFRP rod on the market for reinforcement of concrete at room temperature, 77 K and 4.2 K. Especially at cryogenic temperatures, it is difficult to perform a tensile test of the bar because the specimen slips through the jig grip. To prevent the rod from slipping, tensile tests were carried out with some filling conditions. The applicable and appropriate tensile test conditions were established by modifying the jig grip, treating the surface of the rod and using cryogenic epoxy infill to grip the rod. They were more than 1100 MPa. Additionally, the AFRP rod included a temperature dependence in which the Young's modulus increased as the test temperature decreased. It was confirmed that the Young's modulus increased because aramid fiber was more dominant than epoxy.

JAEA Reports

Development of the JNC Geological Disposal Technical Information Integration System Subjected for Repository Design and Safety Assessment -Document on Present State of Affairs-

Ishihara, Yoshinao*; Ito, Takashi*; Kobayashi, Shigeki*; Neyama, Atsushi*

JNC TJ8440 2004-005, 137 Pages, 2004/02

JNC-TJ8440-2004-005.pdf:2.42MB

On this work, system manufacture about disposal technology and safety assessment field was performed towards construction of the JNC Geological Disposal Technical Information Integration System which systematized three fields of technical information acquired in investigation (site characteristic investigation) of geology environmental conditions, disposal technology (design of deep repository), and performance/safety assessment.The technical information database managed focusing on the technical information concerning individual research of an examination, analysis, etc. and the parameter set database managed focusing on the set up data set used in case of comprehensive evaluation are examined.In order to support and promote share and use of the technical information registered and managed by the database, utility functions, such as a technical information registration function, technical information search / browse function, analysis support function, and visualization function, are considered, and the system realized in these functions is built.The built system is installed in the server of JNC, and the functional check examination is carried out.

JAEA Reports

The Computational Design of Geological Disposal Technology Integration Syatem(II)

Ishihara, Yoshinao*; Neyama, Atsushi*; Kobayashi, Shigeki*; Iwamoto, Hiroshi*

JNC TJ8440 2003-006, 250 Pages, 2003/02

JNC-TJ8440-2003-006.pdf:4.06MB

In order to develop "Geological Disposal Technology Integration System" that is intended to systematize as knowledge base for fundamental study of geologixal environment, repository design and safety assessment, the computational design of an indispensable database and main function of "Geolodical Disposal Technology Integrated System" was done. The prototype was made in order to verify the system function.

Journal Articles

Effect of seismic isolation on the tokamak in ITER

Tsunematsu, Toshihide; Namba, Haruyuki*; Akutsu, Yoichi; Okawa, Yoshinao; Yagenji, Akira; Takeda, Masatoshi*; Yajima, Kensaku*; Nitta, Yoshio*; Kobayashi, Kenichi*; Maeda, Ikuo*; et al.

Fusion Engineering and Design, 41(1-4), p.415 - 420, 1998/09

 Times Cited Count:3 Percentile:31.82(Nuclear Science & Technology)

no abstracts in English

Oral presentation

Effect of grain refinement on dynamic strain aging in SUS304L stainless steel under high temperature pressurized water

Hirota, Noriaki; Kondo, Keietsu; Nakano, Hiroko; Fujita, Yoshitaka; Takeuchi, Tomoaki; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*

no journal, , 

Dynamic strain aging (DSA) has been identified in shrouds of boiling water reactors and recirculation system piping of pressurized water reactors in the nuclear field. This phenomenon increases the work hardening rate of the material and causes a reduction in ductility. Rodriguez reported that using stainless steel, this work hardening increases with grain refinement, making DSA more likely to occur. The objective of this study is to evaluate the effect of grain refinement on DSA in a high temperature pressurized water (HTPW) simulating nuclear reactor environment utilizing ultrafine grained SUS304L (UFGS). UFGS was heat treated to adjust the grain size from 0.59 $$mu$$m to 68.6 $$mu$$m, and Hall-Petch relationship for 0.2 % yield stress was arranged. The k values obtained in this study were almost the same as the reference values previously obtained for SUS304L. Regarding the effect of grain size on fracture strain, a comparison of fracture strain between tensile test under air and slow strain rate test (SSRT) under 598 K / 15 MPa at dissolved oxygen $$<$$ 1 ppb showed that the fracture strain was lower than that under air as the grain size became coarser. The micrograph after fracture in a HTPW showed that ductile fracture surfaces were observed for materials with grain sizes less than 28.4 $$mu$$m. However, when the grain size coarsened to 68.6 $$mu$$m, more than half of all fracture surfaces were brittle fractured. For the material with a grain size of 0.59 $$mu$$m under HTPW, many correspondence grain boundaries of {111}/$$Sigma$$3 boundaries were observed in the fracture cross-section of the sample. But these distributions were rarely observed when the grain size was coarsened to 68.6 $$mu$$m. Therefore, the suppression of crack propagation by DSA to the fine grains in a HTPW can be attributed to the relaxation of dislocation accumulation by the {111}/$$Sigma$$3 boundaries.

Oral presentation

Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris, 1; Outline

Uno, Masayoshi*; Oishi, Yuji*; Kobayashi, Yoshinao*; Ueda, Shigeru*; Nagae, Yuji

no journal, , 

no abstracts in English

Oral presentation

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 9; Thermodynamics of evaporation of silicon compounds at high temperatures

Kobayashi, Yoshinao*; Ueda, Shigeru*; Sato, Isamu*; Osaka, Masahiko

no journal, , 

SiO and Si(OH)$$_{4}$$ can be Si source for Cs-bearing particle and other in-reactor compounds during Fukushima-Daiichi NPS accident. Dependencies of vapor pressure of those species on oxygen partial pressure and tenperature were evaluated thermodunamically. And experimental condition by chemical equilibrium method was determined in focusing Cs$$_{2}$$O-SiO$$_{2}$$ system.

Oral presentation

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 8; Behavior of Si in oxide layer on stainless steel

Zheng, L.*; Hosoi, Kazuya*; Ueda, Shigeru*; Gao, X.*; Kitamura, Shinya*; Kobayashi, Yoshinao*; Osaka, Masahiko

no journal, , 

Si source for Cs-bearing particle formed by Fukushima-Daiichi NPS accident has yet to be revealed. Stainless steel is possible Si source since it is used as structure material in the reactor and includes Si. In this study, Si vaporization behavior was evaluated by investigation of Si behavior in oxide layer formed in steam atmosphere at 1473 K.

Oral presentation

Cs Adsorption behavior evaluation on the surface of nuclear reactor structure materials under high temperature and high pressure steam

Sumita, Takehiro*; Yonekawa, Kazuo*; Sekio, Yoshihiro; Sato, Isamu*; Kobayashi, Yoshinao*; Osaka, Masahiko; Maeda, Koji; Akasaka, Naoaki

no journal, , 

During Fukushima Daiichi Nuclear Power Plant (1F) accident, high radionuclides such as $$^{137}$$Cs and $$^{133}$$I were mainly released as fission products (FPs) due to fuel melting in units 1 to 3, and it increased radiation dose in reactor buildings. With the aim of 1F decommissioning, it is necessary to establish methods to retrieve fuel and an adequate access route, which requires knowledge of Cs adsorption behavior on the surface of structural materials during Severe Accidents (SA). However, there are no Cs adsorption behavior evaluations under the simulated SA condition with high pressure in the previous studies. In this study, CsI adsorption behavior on SUS304L under the condition was evaluated using newly designed apparatus which can control temperature, pressure, moisture and gas atmosphere. The findings from microstructural observation and elemental analysis after the adsorption test suggested that the adsorption of CsI was influenced by especially pressure.

11 (Records 1-11 displayed on this page)
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