Microstructural evolution in tungsten binary alloys under proton and self-ion irradiations at 800C

Miyazawa, Takeshi; Kikuchi, Yuta*; Ando, Masami*; Yu, J.-H.*; Yabuuchi, Kiyohiro*; Nozawa, Takashi*; Tanigawa, Hiroyasu*; Nogami, Shuhei*; Hasegawa, Akira*

Journal of Nuclear Materials, 575, p.154239_1 - 154239_11, 2023/03

https://doi.org/10.1016/j.jnucmat.2023.154239

Overview of accident-tolerant fuel R&D program in Japan

Yamashita, Shinichiro; Ioka, Ikuo; Nemoto, Yoshiyuki; Kawanishi, Tomohiro; Kurata, Masaki; Kaji, Yoshiyuki; Fukahori, Tokio; Nozawa, Takashi*; Sato, Daiki*; Murakami, Nozomu*; et al.

Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.206 - 216, 2019/09

After the nuclear accident at Fukushima Daiichi Power Plant, research and development (R&D) program for establishing technical basis of accident-tolerant fuel (ATF) started from 2015 in Japan. Since then, both experimental and analytical studies necessary for designing a new light water reactor (LWR) core with ATF candidate materials are being conducted within the Japanese ATF R&D Consortium for implementing ATF to the existing LWRs, accompanying with various technological developments required. Until now, we have accumulated experimental data of the candidate materials by out-of-pile tests, developed fuel evaluation codes to apply to the ATF candidate materials, and evaluated fuel behavior simulating operational and accidental conditions by the developed codes. In this paper, the R&D progresses of the ATF candidate materials considered in Japan are reviewed based on the information available such as proceedings of international conference and academic papers, providing an overview of ATF program in Japan.

Effect of helium on irradiation creep behavior of B-doped F82H irradiated in HFIR

Ando, Masami; Nozawa, Takashi; Hirose, Takanori; Tanigawa, Hiroyasu; Wakai, Eiichi; Stoller, R. E.*; Myers, J.*

Fusion Science and Technology, 68(3), p.648 - 651, 2015/10

https://doi.org/10.13182/FST14-963

Pressurized tubes of F82H and B-doped F82H irradiated at 573 and 673 K up to 6dpa have been measured by a laser profilometer. The irradiation creep strain in F82H irradiated at 573 and 673 K was almost linearly dependent on the effective stress level for stresses below 260 MPa and 170 MPa, respectively. The creep strain of BN-F82H was similar to that of F82H IEA at each effective stress level except 294 MPa at 573 K irradiation. For 673 K irradiation, the creep strain of some BN-F82H tubes was larger than that of F82H tubes. It is suggested that a swelling caused in each BN-F82H because small helium babbles might be produced by a reaction of B(n, ) Li.

Evaluation methods of the failure behavior of SiC/SiC composites with a scope of their application under severe environments

Nozawa, Takashi

Seramikkusu, 49(12), p.1034 - 1039, 2014/12

https://member.ceramic.or.jp/journal/vol_no/49/12/49_12.html

http://ci.nii.ac.jp/naid/40020508050

The small specimen test technique is a viable method for nuclear reactor materials irradiation because of reducing irradiation volume, radioactivity, and waste. It is important to develop the evaluation method to consider unique failure behavior of composites since composites generally show anisotropy due to discontinuity among various constituents with finite size. This paper reviewed recent progress of failure evaluation by various modes and summarized requirements and issues about the small specimen test techniques for composites. Finally, we discussed future perspectives of the small specimen test techniques toward standardization.

Stress envelope of silicon carbide composites at elevated temperatures

Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu

Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10

https://doi.org/10.1016/j.fusengdes.2013.12.032

A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.

4th Platform Meeting on DEMO Design

Sakamoto, Yoshiteru; Uto, Hiroyasu; Nozawa, Takashi

Purazuma, Kaku Yugo Gakkai-Shi, 90(5), P. 314, 2014/05

http://www.jspf.or.jp/Journal/PDF_JSPF/jspf2014_05/jspf2014_05-314.pdf

The 4th platform meeting was held with 35 participants from universities, industries and JAEA. The objective of the meeting is to discuss the technologies required for DEMO design by young scientists at the Rokkasho BA site. The participants have deeply discussed about design issues on fusion safety, standards, maintenance and requirements for electrical connection along the meeting theme of "Road to fusion electricity". The meeting was very meaningful and should be continued in the future.

Re-defining failure envelopes for silicon carbide composites based on damage process analysis by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10

https://doi.org/10.1016/j.fusengdes.2013.05.054

A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.

Characterization of failure behavior of silicon carbide composites by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11

https://doi.org/10.1002/9781118217535.ch7

This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.

Determining the shear fracture properties of HIP joints of reduced-activation ferritic/martensitic steel by a torsion test

Nozawa, Takashi; Noh, S.; Tanigawa, Hiroyasu

Journal of Nuclear Materials, 427(1-3), p.282 - 289, 2012/08

https://doi.org/10.1016/j.jnucmat.2012.05.019

A hot isostatic press (HIP) process is a key technology to fabricate a first wall with cooling channels of the fusion blanket system utilizing a reduced-activation ferritic/martensitic steel. This study aims to develop the torsion test method with a special emphasis to provide a reasonable and comprehensive method to determine interfacial shear properties of HIP joints during the torsional fracture process. Torsion test results identified that the torsion process shows yield of the base metal and following non-elastic deformation due to work hardening of the base metal. By considering this work hardening issue, we could propose a reasonable and realistic solution to determine the torsional yield shear stress and the ultimate torsional shear strength of the HIPped interface. Finally, representative torsion fracture process was identified.

Torsion test technique for interfacial shear evaluation of F82H RAFM HIP-joints

Nozawa, Takashi; Ogiwara, Hiroyuki*; Kannari, Jun*; Kishimoto, Hirotatsu*; Tanigawa, Hiroyasu

Fusion Engineering and Design, 86(9-11), p.2512 - 2516, 2011/10

https://doi.org/10.1016/j.fusengdes.2011.01.110

A hot isostatic press (HIP) process is a key technology to fabricate a first wall of the blanket system utilizing a reduced-activation ferritic/martensitic (RAFM) steel such as F82H. A primary objective of this study is to characterize interfacial properties of HIPed F82H joints by torsion to identify the feasibility of this test method. It is apparent that the absorption energies of the HIP joints varied by the processing conditions, although the maximum shear strength was not much different. According to the fracture surfaces, it is indicated that the reduction of the absorption energy was due to the oxide formed on the interface of the HIP joint and this was consistent with the results of charpy impact tests. In conclusion, the torsion test method enables to precisely evaluate the shear properties of the HIPed joint interface and becomes one of promising powerful techniques for inspection of the HIP joints.