Speaker
Dr
Yasuhisa Oya
(Shizuoka University)
Description
Elucidation of tritium dynamics is one of the key issues for sustainable D-T fusion. Tungsten will be exposed to high fluxes of tritium (T) accompanied with various energetic particles. Therefore, T retention and its trapping states will be dramatically changed by the accumulation of ion and neutron-induced damage and recovery by heating. These facts motivate us to perform extensive hydrogen isotope retention experiments in damaged W under the framework of Japan/US joint project, PHENIX. This paper presents recent results, including an analysis of D retention by various methods over a range of defect concentrations.
Disks of stress-relieved W were irradiated using 6 MeV Fe2+ at room temperature in TIARA, JAEA or 6.4 MeV Fe3+ at higher temperature in DuET, Kyoto University up to 1.0 dpa. These samples were then compared with neutron-damaged W (10-6 dpa for 14 MeV or 10-4 dpa for thermal neutrons). All the samples were exposed to 1 keV D2+ up to a fluence of 1.0 × 1022 D m-2 at room temperature. Thereafter, thermal desorption spectroscopy (TDS) was applied with the heating rate of 0.5 K s-1 up to 1173 K.
The D2 TDS spectra from Fe2+ damaged W showed that accumulation of damage shifted to higher desorption temperature, consistent with the formation of large voids. For W specimens damaged by 14 MeV fusion neutrons to 10-6 dpa, the D2 desorption at 700 K was found even at low defect concentrations, suggesting that the collision cascades result in the formation of vacancies. The simulations showed that D accumulated within 0.5 m of the exposed surface for W damaged by Fe2+ ions.
The results of D permeation experiment showed that D permeability for damaged W was reduced by damage introduction. Furthermore, by heating above 1100 K, D permeability were completely consistent with that for undamaged W. The nature of the defects is critical, and their stability will strongly influence D permeability.
In summary, the accumulation of defects resulted in the formation of stable trapping sites. The D trapping by defects reduces the number of available D diffusion pathways through the lattice, a mechanism that could lead to a reduction of D permeability. Finally, we note that dynamic recovery of damages is enhanced by high temperature irradiation.
| Country or International Organization | Japan |
|---|---|
| Paper Number | MPT/P5-31 |
Primary author
Dr
Yasuhisa Oya
(Shizuoka University)
Co-authors
Dr
Chase Taylor
(Idaho National Laboratory)
Dr
David Donovan
(University of Tennessee at Knoxville)
Dr
Dean Buchenauer
(Sandia National Laboratories)
Dr
Kazunari Katayama
(Kyushu University)
Mr
Makoto Oya
(Graduate school of Engineering, Osaka University)
Dr
Masashi Shimada
(Idaho National Laboratory)
Prof.
Naoaki Yoshida
(Kyushu University)
Dr
Otsuka Teppei
(Kyushu University)
Dr
Robert Kolasinski
(Sandia National Laboratories)
Dr
Sosuke Kondo
(Kyoto University)
Dr
Takeshi Toyama
(Tohoku University)
Dr
Takumi Chikada
(Shizuoka University)
Dr
Tatsuya Hinoki
(Kyoto University)
Prof.
Yoshio Ueda
(Osaka University)
Prof.
Yuji Hatano
(Hydrogen Isotope Research Center, University of Toyama)
Dr
Yuji Nobuta
(Hokkaido Univ.)
Dr
Yuji Yamauchi
(Hokkaido University)
Dr
Yukinori Hamaji
(National Institute for Fusion Science)
