S6-5
Current Status of ITER Full Tungsten divertor technology Development
ITER用タングステンダイバータ開発の現状
Koichiro Ezato, Yohji Seki, and Satoshi Suzuki, Satoshi Kakudate
江里幸一郎, 関 洋治，鈴木 哲, 角館 聡
Naka Fusion Institute, Japan Atomic Energy Agency
801-1, Mukoyama, Naka-shi, Ibaraki, 311-0193, Japan(独)日本原子力研究所 那珂核融合研究所 〒311-0193 茨城県那珂市向山801-1
Technology development for ITER full-tungsten (W) divertor outer vertical target (OVT) is in progress inJapan Atomic Energy Agency (JAEA), especially, tungsten monoblock technology that needs to withstandthe repetitive heat load as high as 20 MW/m2. To demonstrate the armor heat sink bonding technology andheat removal capability, 6 small-scale W monoblock mock-ups manufactured by different bonding technologies using different W materials in addition to 4 full- scale prototype plasma-facing Units. After
non-destructive test, the W components were tested under high heat flux (HHF) in ITER Divertor Test Facility (IDTF) at NIIEFA. Consequently, all of the W monoblocks endured the repetitive heat load at 20MW/m2 for 1,000 cycles (requirements 20 MW/m2 for 300 cycles) without any failure.

1. Introduction
After recommendation of the ITER council todevelop tungsten (W) monoblock technology forthe final decision of the target material of ITER
divertor in November 2011, ITER organization(IO) and Japan Atomic Energy Agency (JAEA) as
Japanese Domestic Agency (JADA) are actively
working on the development and demonstrationon the full-W divertor concept under the framework of the task agreement of ITER full tungsten
divertor qualification program instead of theCFC/W divertor concept development [1, 2].
JAEA is in charge of technology development
and demonstration for manufacturing ITER Divertor Outer Vertical Target (OVT, see Fig 1)
together with Japanese industries. In these activities, JAEA has manufactured small-scale
mock-ups to examine the durability of the W
monoblock itself and the joint of W monoblocks
to the Cu-Alloy (CuCrZr) cooling tube troughrepetitive high heat flux testing. This paper
presents the results of the Full-W Qualification
Program conducted by JAEA.

Fig 1. 3D view of the ITER W Divertor

2. Manufacturing Small-scale W-monoblock
mock-ups
The small-scale W-monoblock mock-ups thatwere fabricated in this program are shown in Fig. 2.
Prior to bonding the W monoblock to the CuCrZr
cooling tube with the outer and inner diameter of 15and 12mm, the pure copper (Cu) interlayer with thethickness about 1mm is bonded to the hole of the W
monoblock. In the present study, the W monoblocks are supplied from the three different manufacturers and they adopted their own bonding technologies for W/Cu interface such as HIPping, Casting, and unidirectional diffusion bonding.
The high temperature brazing for bonding of theW monoblocks with pure Cu interlayer to the CuCrZr cooling tube with Ag-free brazing filler. The
brazing filler is Ni-Cu-Mn alloy. The brazing heat
cycle is operated at around 980oC, which serves
also as solution annealing of CuCrZr, followed by
the gas quenching and by the aging heat cycle at
480oC. Before high heat flux testing, the joints for
two joint interfaces of W/Cu and Cu/CuCrZr wereinspected by Non-destructive examinations i.e. ultrasonic examination and mock-ups passed hydraulic pressure test and cold-He leak test.
3. High Heat Flux Testing on W monoblocksThe high heat flux testing on the small scale W
monoblock mock-ups fabricated with the technologies described in Sec. 2.1 were carried out by IO
and RFDA at an electron beam facility, ITER Divertor Test Facility (IDTF) at NIIEFA [3]. JADA
delivered 6 mock-ups and all of them were tested.
The test conditions are as follows; the cooling waterat 70oC and 4MPa, the heat load conditions under
10 MW/m2 for 5000 cycles and 20 MW/m2 for 300

cycles (IO requirements) and for the additional 700
cycles. The acceptance criteria for successful fatigue performance are defined as follows; (a) No
trace of substantial melting at the loaded W surfaces by visual examination, (b) No water leak fromthe loaded W monoblock/CuCrZr component, (c)No detachment of any W monoblock, (d) No appearance of any “hot spot” during fatigue cycling,and (e) No variation of the maximum surface temperature exceeding 20% between the initial and final thermal mapping. The mock-ups passed thecriteria mentioned above throughout the HHF testing, therefore, these tests demonstrate that the W
monoblock technologies of Japanese industries andJAEA satisfy the IO requirements regarding heatremoval capability and durability against the repetitive high heat loads.
The figure 3 shows the overview of the surfacesof the W monoblocks after 1000 cycles at 20
MW/m2. Although during the additional 700 cycles,
the heated surface of the W monoblocks show theprogress of the plastic deformation caused by highthermal stress, no macroscopic crack at the W surface after the test was observed.
Fig 4 (a) Full-scale PFU prototype as test assembly and (b) W surface after 5000 cycles at 10
MW/m2 and 1000 cycles at 20 MW/m2.
In parallel to the full-W qualification program,
JAEA has tested the full-length PFU prototype
based on the previous ITER divertor design with
CFC and W monoblocks as shown in Fig.1. Because these prototypes have a short W straight partwith the same dimensions as those of the current
reference W monoblock, this part was tested. The
four PFU prototypes were mounted on a test frame
dedicated to IDTF, called Test Assembly as shownin Fig 4 (a). In this activity, 5x4 W monoblocks
withstood against 5000 cycles at 10 MW/m2 and300 plus 700 cycles at 20 MW/m2 without any failure such as water leak from the cooling tube and thesubstantial W monoblock melting. The surface ofW monoblocks after the repetitive high heat loads
are shown in Fig. 4 (b). Although the crystal growthof W occurs, the no macroscopic crack at the surface is observed. Comparing the results from thesmall scale mock-ups case, the plastic deformationof the W surface is suppressed. This might be ascribed to the overheating occurred in thesmall-scale mock-up case because of the waterchemistry problem, that is, thermal barrier wasformed at the cooling tube by deposition of the impurity during the coolant boiling. This is discussed elsewhere [4]. From the both results of highheat flux testing mock-ups and prototypes, JADA
can draw the conclusion that that W monoblocktechnology including material production and manufacturing is available.
Disclaimer The views and opinions expressed herein do
not necessarily reflect those of the ITER Organization.
References[1]T. Hirai et al., Fus. Eng. & Des.88 (2013) 1798– 1801.
[2]T. Hirai et al., Phys. Scr. T159 (2014) 014006.
[3]K. Kuznetsov, et al., Fus. Eng. & Design 89 (2014) 955–959.
[4]G. Pintuk et al, Characterization of ITER tungsten and CFC
qualification mock-ups exposed to high cyclic thermalloads, (P2-088) in Symp. Fus Tech (SOFT) 2014.

(a) Test Assembly in IDTF

(b) W surface after HHF testing in IDTF

Fig. 3. W monoblock surface of the small-scale
mock-ups after 5000 cycles at 10 MW/m2 and 1000
cycles at 20 MW/m2 in IDTF. KMM1, KAL1 etc show
mockups’ IDs.

CFC side

W curved sideFig 4 (a)Full-scale PFU prototype as test assembly and(b) W surface after 5000 cycles at 10 MW/m2 and 1000
cycles at 20 MW/m2.