24P084-P
High heat loading properties on tungsten coated low activation material
タングステン被覆低放射化材料の高熱負荷特性
Tomohiro Hotta1, Kazuaki Tokunaga2, Kuniaki Araki2, Tadashi Fujiwara2, Yoshio Miyamoto2,Makoto Hasegawa2, Kazuo Nakamura2, Koichiro Ezato3, Satoshi Suzuki3, Mikio Enoeda3,Masato Akiba3, Ryuta Kasada4, Akihiko Kimura4
堀田智宏1, 徳永和俊2，荒木邦明2，藤原 正2，宮本好雄2，長谷川真2，中村一男2，
江里幸一郎3，鈴木 哲3，榎枝幹男3，秋場真人3，笠田竜太4，木村晃彦4
1

Interdisciplinary Graduate School of Engineering Sciences, Kyushu Univ, Kasuga, Fukuoka 816-8580, Japan
2
Research Institute for Applied Mechanics, Kyushu Univ, Kasuga, Fukuoka 816-8580, Japan
3Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan
4
Institute of Advanced Energy, Kyoto Univ, Uji, Kyoto 611-0011, Japan
1 九州大学総合理工学府 〒816-8580 福岡県春日市春日公園
2 九州大学応用力学研究所 〒816-8580 福岡県春日市春日公園
3 日本原子力研究開発機構 〒311-0193 茨城県那珂郡市向山
4 京都大学エネルギー理工学研究所 〒611-0011 京都府宇治市五ヶ庄

Heat loading experiments on tungsten coated reduced activation ferritic/martenstic (RAF/M) F82H (Fe-8Cr-2W) byproduced by Vacuum Plasma Spraying (VPS) have been carried out. In addition, quantitative analyses abouttemperature profile and thermal stresses have been carried out using the finite element analysis (FEA) to evaluate
thermal property. Distribution of thermal stress at a heat flux of 8 MW/m2 has been quantitatively calculated by thethermal analyses.

1. Introduction
Reduced-activation ferritic/martensitic steel(RAF/M) is a leading structural material candidateof the first wall/blanket and the cooling channels of
the divertor structural material for DEMO.
Furthermore, tungsten (W) coatings/jointing on
RAF/M is planning to be used because of low
erosion yield and good thermal properties oftungsten [1]. However, CTE of RAF/M is about 2times larger than that of W. As a result, thermal
stress would be applied between them bytemperature increase when the heat loading fromplasma is exposed to W surface.
In the present works, W coatings on RAF/M havebeen produced by Vacuum Plasma Spraying (VPS)
and heat flux experiments on them have been
carried out to evaluate their possibility as aplasma-facing armor in the fusion device. In
addition, quantitative analyses about temperature
profile and thermal stress have been carried out
using the finite element analysis (FEA) to evaluate
thermal property.
2. Experimental
W coatings with a thickness of 0.6 mm on
reduced-activation
ferritic/martensitic
steel(RAF/M) F82H (Fe-8Cr-2W) have been produced
by Vacuum Plasma Spraying (VPS). The W

coated F82H was machined to the dimensions of 10mm × 10 mm× 5.6 mmt (W: 0.6mmt, F82H: 5mmt)
followed by mechanical polishing.
Heat load experiments on the W-coated F82H
using an electron beam have been carried out by anelectron beam irradiation test simulator of theResearch Institute for Applied Mechanics, Kyushu
University. Schematic illustration of the electron
beam irradiation experiments is shown in Fig. 1
Samples are fixed on a water-cooled Cu blockusing a sample retainer with an aperture of 6mm.
Electron beam at 20 keV is irradiated on the centerof tungsten.
Heat flux is evaluated using a net electric
current, which is measured by applying a bias
voltage of 100 V to the samples to suppress
secondary electrons induced by the electron beamirradiation. Ejection of thermal electrons from theheated surface is also suppressed by the bias
voltage. Surface temperature of the W surface ismeasured with optical pyrometers. Temperatures ofF82H and the Cu block are also measured withthermocouples. The position for measurement pointof F82H is also indicated in Fig. 1. In addition, gasemission from the heated sample is measured using
QMS. Before and after the irradiation, the samplesurfaces are examined by SEM. Weight loss of thesample is also measured with an electronic balance.
3. Thermal and stress analyses
The thermal and elastic stress analyses have been
performed for the W/F82H using the finite element
code ANSYS to evaluate quantitative thermal
property. Fig.2 shows the model using in the presentanalyses. Only quarter of the geometry is
considered due to symmetry. Symmetric boundary
condition is defined at symmetry plane of the model.
For thermal conductivity, coefficient of thermal
expansion, elastic modulus and Poisson ratio of W
and F82H, temperature dependence data has beenused [2,3]. It is reported that thermal conductivityand elastic modulus of VPS-W decreases to 30%～50% and 20%～50% of pure W, respectively [4].
Therefore, in the present works, values of thermal
conductivity and elastic modulus of VPS-W areused as 40% and 35% of pure W, respectively. The
other physical values are used that of W.
Steady-state temperature profile and stress at heat
flux of 8 MW/m2 are calculated when base plane of
F82H is 20oC.
4. Result of thermal and stress analyses
Fig.3 shows Mises stress distribution nearboundary of W and F82H at a heat flux of 8MW/m2. In this case, it is found that stress of 620
MPa is applied near boundary between W andF82H. Fig. 4 shows stress profile of X and Ydirections. It is indicated that stress of F82H near W
is applied to direction of center of the sample, andstress of W near F82H to direction of outside
increases with the approaching to outside of thesample. In addition, stress is applied to direction
from F82H to W near boundary of W and F82H ofoutside.
5. Future plans
Temperature profile will be required to becoincident with the experimental data by varying
the physical parameter of W, and the contact
condition of F82H and the active cooling Cu.
Accurate evaluation of thermal property of thesample will be also required by comparison withstress calculated and observation of the sample after
the experiment.

Vol.87,No.3(2010)161-162[2] K.Shiba , A.Hishinuma , A.Tohyama , andK.Masamura:JAERI-Tech97-038(1997).34-39[3] JSME date book : heat transfer(4th edition )[4] http://www.nifs.ac.jp/kenkyo/kyodo-kenkyu/houko
kukai/h21/lhd_pdf/lhd_010.pdf

Fig.1：Schematic illustration of the electron beamirradiation experimentFig.2：1/4 model using FEM

Fig.3：Mises stress distribution at a heat flux of8MW/m2

References[1] A.Kimura : J.Plasma Fusion Res.
Fig.4：X and Y direction distribution of stress