03pC13
タングステンモノブロックの表面損傷が熱負荷応答に与える影響
Effect of surface damage on thermal reaction of tungsten monoblock田中泰史1,上田良夫1,LEE Heun Tae1,永田正義 2,菊池祐介2,鈴木哲3,関洋治3
TANAKA Yasufumi1, UEDA Yoshio1, LEE Haun Tae1, NAGATA Masayoshi2, KIKUCHI Yusuke2,
SUZUKI Satoshi3, SEKI Yohji3
阪大院工, 2兵庫県立大学院工, 3日本原子力研究開発機構
Graduate School of Engineering, Osaka University, 1Graduate School of Engineering, University of Hyogo,
3
Japan Atomic Energy Agency
11

1. Introduction
Tungsten (W) monoblock will be used in thedivertor of ITER. In the divertor, transient heatloads such as Edge-Localized Mode (ELM) anddisruption will be applied in addition to steady-stateheat loads and slow transient. Recent investigations
have demonstrated that transient heat load gives thesurface damage such as melting or cracking on thetungsten surface [1]. In this study, we gave simulatedtransient heat loads to the W monoblock with thesurface damage (melting or cracking) by the electron
beam and pulsed plasma to investigate the change ofsurface structure and heat removal capability of the W
monoblocks. From this experiment, the effect of
surface damage on thermal response and heat removal
performance of W monoblocks were investigated.

2. Experimental
We prepared five W monoblocks and gave surface
damage to four monoblocks of them prior tosteady-state heat loading. ELM-like heat load (Energy
fluence of 0.7MJ/ ) using plasma gun of Universityof Hyogo [2] was applied to three tungsten
monoblocks with shot numbers of 20, 40, and 100 tomakecracks
onthesurface.
Moreover,disruption-like heat load (1GW/ , 5msec) using
JEBIS (electron beam of JAEA) [3] was given to themonoblock to cause melting on the surface. Finally,
repeated heat load using plasma gun (Energy Fluenceof 2.0MJ/ , 20 times) was given to the last one
monoblock to arise melting and cracking on thesurface. These five monoblocks were connected to acooling pipe. Heat load test simulating steady-stateheat load (10MW/ , 10sec, 300cycle) and slow
transient (20MW/, 10sec, 300cycle) were
performed by JEBIS. The changes of surface structure
after electron beam irradiation were observed using
laser beam microscopy.

3. Results
After electron beam irradiation, recrystallization(grain size ~50µm) and associated level difference
between grains (~10µm) occurred in the monoblock
without initial surface damage (Fig.1 E). In contrast,

progress of cracking and melting occurred in themonoblocks with the initial cracks (Fig.1 A~D).
Moreover, radial crack centered on the melting
position by the disruption-like heat load appeared(Fig.1 D). Furthermore, the longitudinal cracks overentire monoblocks appeared in all monoblocks. Thesecracking of the monoblocks with surface damage(Fig.1 A~D) occurred at 18 cycle or less of20MW/
heat loading but cracking of themonoblock without initial surface damage (Fig.1 E)
occurred at 101 cycle or later of 20MW/
heatloading. These cracks reached the cooling pipe. Level
difference around the longitudinal cracks wereobserved. In the monoblock melted by pulsed plasma,level difference was about 240µm (Fig.1 C). In
addition, around the longitudinal cracks, growth ofgrain was larger than other part of the monoblock,further, a lot of grain ejection occurred at themonoblock without initial surface damage (Fig.1 E)
and irradiated 100 times ELM-like heat load (Fig.1 A).
It is considered that there was no change of heatremoval performance because during heat load test,
the surface temperature was constant.

Fig.1 W monoblock after electron beam irradiation
References[1]M. Tokitani and Y. Ueda J. Plasma Fusion Res.
Vol.87, No.9 (2011)591-599[2]M. Nagata et al., IEEJ Trans. Electric. Electron.
Eng. 4 (2009) 518[3]K. Masaki, et al., Fusion Eng. Des. 61–62 (2002)
171.