8P95

EVEDAリチウム試験ループで用いたターゲットアセンブ
リの二段絞りノズルの表面分析
Surface morphology evaluation of double contraction nozzle oftarget assembly used in IFMIF/EVEDA lithium test loop

小栁津誠、見城俊介、落合謙太郎、佐藤聡
M. Oyaidzu, S. Kenjo, K. Ochiai, S. Sato
量子科学技術研開発機構 六ヶ所研究所
National Institute for Quantum Science and Technology, Rokkasho Fusion InstituteWe plan to construct a fusion neutron source, AFNS, where liquid lithium will be used as self-coolingtarget. The limit of the erosion/corrosion (E/C)
thickness in the double contraction nozzle (DCN) havebeen tentatively defined to be 1 µm, since it is necessity
to keep the surface roughness of DCN less than 6.3 µm
to make a flat and stable target flow [1]. A flat liquid
lithium target flow with its velocity of 15m/s had beensuccessfully demonstrated by EVEDA lithium test loop(ELTL) under IFMIF/EVEDA project [2] over 1300
hours long until the end of ELTL operation [3].
Therefore, it is considered that the limit of the E/C
thickness of DCN in A-FNS could be alleviated to theE/C thickness observed in ELTL. In the present study,
the surface morphology of the inner surface of DCN
used in ELTL is evaluated to observe the surface
roughness and to estimate the E/C thickness to alleviate
the limit of the E/C thickness of DCN for A-FNS.
A preliminary model to estimate the E/C thickness
is considered. In this model, the corrosion is assumed
as dealloying with forming a quality changed layer(QCL). The erosion is assumed to depend on the wall
sheer stress (τw) and the average QCL thickness (X).
From these assumptions, X could be expressed as thefollowing equation.
𝑑𝑑𝑑𝑑 𝑘𝑘𝑐𝑐2=− 𝜏𝜏𝑤𝑤 𝛼𝛼𝑋𝑋𝛽𝛽
𝑑𝑑𝑑𝑑 2𝑋𝑋

microscope (AFM). To measure the thickness of QCL,
the cross section is also observed by SEM and anelectron dispersive X-ray spectroscope (EDX).
As the results of surface morphology observation
by SEM, it is indicated that hole-like structures ofapproximately 0.5 µm in diameter are observed in all
observation points. The populations of the holes
obviously increase with higher τw, indicating that theE/C would be more significant in higher τw. As theresults of surface roughness observations by AFM, thesurface roughness seems unchanged or slightly
decreases with increasing τw, indicating that the E/Cwould little affect the surface roughness. Based on thecross-sectional observations by SEM and EDX, theaverage QCL thickness (X) is measured at each of theobservation points and is plotted as a function of τw as
shown in Fig. 1. These plots are fitted by Eq. (1). The
eroded thickness (Y) at each τw is estimated using Eq.
(2) and superposed in Fig. 1. It is suggested from thisestimation that the limit of the E/C thickness of DCNfor A-FNS would be alleviated from 1 µm to 7 µm.

(1)where kc indicates the corrosion rate. α and β areconstants. From this equation, the eroded thickness, Y,
can be also estimated by integrating the second term ofright side by time as following equation.
𝑌𝑌 = � 𝜏𝜏𝑤𝑤 𝛼𝛼𝑋𝑋𝛽𝛽 𝑑𝑑𝑑𝑑

(2)

Based on the estimation of the wall sheer stress, whichlargely differ at the location of the nozzle [4], theobservation points of DCN in the present study weredetermined to be τw = 1.5, 6.9, 81 and 590 Pa.
The surface morphology is measured by a scanningelectron microscope (SEM) and an atomic force

Fig. 1 Average QCL thickness and eroded thickness asa function of wall sheer stress.
[1] M. Ida et al, J. Nucl. Mater. 307-311 (2002) 1686.
[2] J. Knaster et al, Nucl. Fusion 57 (2017) 102016.
[3] H. Kondo et al, Nucl. Fusion 57 (2017) 066008.
[4] H. Kondo et al, Fusion Eng. Des. 146 (2019) 285.