05pD05P
F82H鋼 におけるヘリウム照射効果による水素保持特性への影響評価
Effects of helium bombardment on hydrogen retention properties in F82H steel
芦川直子1,2, 廣岡慶彦1,2, 周海山2，山内有二3，吉田直亮4，信太祐二3，室賀健夫1,2，N. Ashikawa1,2, Y. Hirooka1,2, H.S. Zhou2, Y. Yamauchi3, N. Yoshida4, Y. Nobuta3, T. Muroga1,2
1

核融合研，2総研大，3北大，4九大

2NIFS, SOKENDAI, 3Hokkaido Univ., 4Kyushu Univ.,

Ferritic steel alloys are candidates as a lowactivation material in a fusion DEMO reactor suchas FFHR [1]. Helium ash produces in D-T fusion
reactions and hydrogen isotopes mix in the vacuum
vessel of DEMO reactors. To understand bulk
fueling retentions and tritium inventories of plasma
facing materials in DEMO reactors, analyzed dataof samples exposed to plasmas with hydrogen andhelium mixed gasses are important. But
investigations of bulk retention after plasma
exposures in F82H are not sufficient yet. In theprevious work, F82H samples exposed to hydrogenplasma and these amounts of retained hydrogen has
been measured [2]. In this study, samples exposedto hydrogen and helium plasmas and demonstrated
effects of helium bombardment by helium ash onhydrogen retention .
A low-activation ferritic steel alloy, F82H
(8Cr-2W), has been bombarded with steady-statehydrogen and helium plasmas under some of theconditions relevant to the first wall environment,using the VEHICLE-1 facility [3]. The plasma
density is the order of 1010 cm-3 and the electron
temperature is a few electron volts, resulting in theion fluencies of the order of 1016 - 1019 ions cm-2.
The ion bombarding energy is set at 100-200 eV byapplying a negative DC-bias onto the target
assembly. F82H samples are analyzed with X-ray
photoelectron spectroscopy (XPS), Transmission
electron microscope (TEM) and Thermal desorption
spectrometry (TDS).
Different types of discharges are operated tocompare with pure Hydrogen, pure helium, andhelium plasma pre-irradiation. Helium bubbles areobserved from TEM images of cross-section byfocus ion beam (FIB) milling process on F82H of(a) helium plasma pre-irradiation (200eV) and (b)helium plasma pre-irradiation (100eV) as shown inFigs.1. A depth distribution of helium bubbles by
200eV helium plasmas is approximately until 150
nm. These results suggest low energy helium
plasmas are also effective to produce helium
bubbles and it contributed as additional hydrogen
trapping sites in F82H.
Depth profiles of stopped helium ions with 200
eV were calculated about 50nm by TRIM code. In

Fig.1, cross-section images by TEM are shown
many helium bubble and typical diameters areabout 5nm. These bubbles are observed until 200
nm from the top surface. Two kinds of binding
energies of hydrogen in alpha iron are reported [4].
The case of intrinsic defects is 24-50 kJ/mol. andthe case of helium bubble is 67-86 kJ/mol. Then
temperature peaks in helium bubbles are higher
than in intrinsic defects by thermal desorption
spectrums in alpha iron. Higher thermal desorption
spectrums of hydrogen to helium irradiated target
are observed in F82H samples as shown in Fig.2.
Total amounts of retained hydrogen in F82H targets
exposed to pre-helium plasma are also higher than
exposed to pure hydrogen plasmas. This work is
supported by NIFS budget UFFF028.
1) A. Sagara et al., Fusion Engineering and Design
83 (2008) 1690-1695.
2) N. Ashikawa et al., 22nd International Tokiconference (2012).
3) Y. Hirooka et al., J. Nucl. Mater. 363-365 (2007)
775-780.
4) W.Y.Choo, et al., Met. Trans 14A (1983) 1299.

(b)

(a)
20nm

Figue.1
Partial Pressure (Pa)15 10-74 10-7

3 10-72 10
1 10Hydrogen
Pre-He plasma (200V)/H2 plasma-7Pre-He plasma (100V)/H2 plasma

H2 plasma-700100

200300400

Temperature (℃）

Figure.2500600