Plasma and Fusion Research: Regular Articles

Volume 19, 1405020 (2024)

Irradiation Tests of the Sleeve for the Telescopic Arm of the ITER
Blanket Remote Handling System
Makiko SAITO, Yusuke KAWAI and Nobukazu TAKEDANaka Institute for Fusion Science and Technology, National Institutes for Quantum Science and Technology, Naka, Ibaraki
311-0193, Japan(Received 28 September 2023 / Accepted 3 April 2024)
The ITER blanket remote handling system (BRHS) must operate with high precision within the confines of
the ITER vacuum vessel, which will become a gamma-ray environment filled with radioactive dust. The main
structural component of the BRHS, a telescopic arm, will be covered with a sleeve that must prevent not only
the radioactive dust from infiltrating into the system but also lubricant from leaking out into the vacuum vessel.
Verifying the radiation resistance of this sleeve is crucial and will ultimately aﬀect the operation scenarios andtiming of preventive maintenance for the BRHS. Thermoplastic polyurethane was selected as a candidate material
for the sleeve. This paper presents the results of gamma-ray irradiation tests up to either 1 MGy or 2 MGy forpolyurethane sheets and the results of subsequent bending, tensile, and hardness tests. Based on the results ofthese tests, mock-ups of the sleeve were manufactured and were also irradiated up to either 1 MGy or 2 MGy,after which the mock-ups underwent expansion and contraction tests to simulate actual operations in ITER. We
have concluded from conservative estimates that, although these polyurethane sleeve mock-ups have over 1 MGyof radiation resistance, the sleeves of the BRHS should be replaced at 1 MGy.
c 2024 The Japan Society of Plasma Science and Nuclear Fusion Research⃝

Keywords: ITER, blanket remote handling system, remote maintenance, radiation resistance
DOI: 10.1585/pfr.19.1405020

1. Introduction
The ITER blanket remote handling system (BRHS),
shown in Fig. 1, will exchange the blanket modules (composed of first wall panels and shield blocks) in the vacuum
vessel after plasma shutdown [1]. These blanket modules
can weigh up to 4.5 tonne and must be handled stably andwith a high degree of positioning accuracy in a high radiation environment. The in-vessel components of ITER will
be activated by neutrons, resulting in gamma-ray radiation,
which in turn may cause the remote handling componentsof the BRHS to degrade. In this study, we focused on theradiation resistance of the BRHS components. The mostimportant operation for the BRHS is a two-year maintenance campaign in which all 440 first wall panels must be
replaced. This campaign is scheduled at the beginning of
D-T operation, during which the dose rate in the vacuum
vessel is estimated to be 250 - 500 Gy/h [2]. The radiation resistance of the BRHS components should be confirmed to assess the timing of preventive maintenance of
the BRHS in the two-years campaign. The telescopic armof the BRHS (Fig. 2) has a sleeve covering to prevent radioactive dust from entering the system and prevent lubricant from leaking out of the telescopic arm and into thevacuum vessel. This paper reports the results of irradiation
tests on polyurethane sheets and sleeve mock-ups.

Fig. 1 ITER blanket remote handling system.

Fig. 2 Telescopic arm and sleeve.

author’s e-mail: saito.makiko@qst.go.jp

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Science and Nuclear Fusion Research

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2. Experiments
The blanket modules will be regularly replaced by the
BRHS. A polyurethane sleeve having a bellows-like structure covers the telescopic arm of the BRHS to avoid being
contaminated by radioactive materials and also to avoid
contaminating the vacuum vessel with lubricant from the
BRHS. We examined the gamma-ray radiation resistanceof the polyurethane sleeve material. Subsequently, mockups of the sleeve were made. The mock-ups were subjected to irradiation tests using gamma-rays from a cobalt60 (Co60 ) source. After irradiation, the mock-ups underwent expansion tests to verify durability. Infrared spectra
were also used to investigate the degradation mechanism.

2.1 Irradiation tests of polyurethane as a
candidate material for the sleeve
Polyurethane sheets (210 mm × 297 mm, 0.3 mm inthickness, shown in Fig. 3) were irradiated at 3700 Gy/hto either 1 MGy or 2 MGy. Two types of sheets (with adhesion and without adhesion) were prepared to confirm
whether adhesion aﬀects strength. These sheets were irradiated at ambient air without humidity control at the Co60
gamma-ray irradiation facility of the Takasaki Institute forAdvanced Quantum Science [3]. Irradiation dose rates forthe sheets were estimated according to their distance fromthe radiation source.
After the sheets were irradiated, test pieces were cut
from the sheets according to the standard Japanese Industrial Standards (JIS) K 7161 (Fig. 4). Bending tests, ten-sile tests, and hardness tests were performed on these test
pieces. For the bending tests, each test piece (N = 3) was
secured to a testing machine (NABELL Corporation proprietary model, 40-mm strokes, test speed of 7 mm/min)and was bent for 10000 strokes. The test machine’s stroke
value of 40 mm is approximate to the distance between therings of the actual sleeve (45 mm). Changes in physical appearance of the test pieces were verified by visual inspection (Fig. 5). According to the manufacturer (NABELL
Corporation), wrinkles in the material could potentiallylead to failure so visual inspections were conducted tocheck for the presence of wrinkles on the test pieces. The
tensile tests were performed according to JIS K 7161,
Sec. 3.6.4. Each test piece (N = 3) was grasped from bothends by a testing machine and then pulled until they fractured. The maximum load and elongation percentage (displacement) were measured by dividing the displacement of
the head unit of the testing machine throughout elongationby the initial distance between the grips. The acceptancecriteria was to be within ±20% of the initial value after irradiation. The hardness tests were performed according to
JIS K 7311. An indenter struck each test piece (N = 3) ata pressurized load of 1 kgf and hardness values of the individual test pieces (0.3 mm thickness) were obtained basedon the depth of the indenter. The acceptance criteria was tobe ±2 of the pre-irradiation value (Shore A hardness scale).
All tests were performed 3 times with 3 diﬀerent test pieces
to examine reproducibility.

2.2

Fig. 3 Sheet sample with adhesion.

Manufacturing and irradiation tests ofsleeve mock-ups

Sleeve mock-ups were manufactured based on thepromising results of the tests using the polyurethane material. Table 1 shows the specifications of the sleeve mockups. These sleeve mock-ups have a square, bellows-type
structure that fits over the telescopic arm. Square shaped
sleeves, however, are prone to stress-induced creases because the folds of the bellows fold inwards and concentratestresses at the corners. The edges of the sleeve end platesalso tend to crack if they come into contact with the edgesof the sheets of the sleeve. These sleeve mock-ups were
designed with radiation- resistant materials, such as type
304 stainless steel (SUS304) for the rib rings and polyether

Fig. 4 Dumbbell-shaped test pieces (a) with adhesion and (b) without adhesion.

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Fig. 5 Bending test machine operation and test piece visual inspection point.

Table 1 Sleeve mock-up specifications.

Table 2 Design customizations for the BRHS sleeve mock-ups.

ether ketone (PEEK) for the intermediate supports [4]. Table 2 lists the customizations made to commercial-oﬀ-theshelf sleeves that were used for the BRHS sleeve mock-ups, such as corners and rings to maintain the shape andfunctionality of the sleeve even after they have been irradi-

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ated.
The sleeve mock-ups were irradiated at 150 2670 Gy/h, as determined by the distance from the Co60

source. The sleeve mock-ups themselves were quite large,
thus the dose rate diﬀered considerably between the side
nearest to the source and the side furthest from the source.
Accordingly, the dose rates were measured at six diﬀerent points around each sleeve mock-up (Fig. 6) and thesleeve mock-ups were physically moved so that all six
measurement points were irradiated uniformly up to either
1 MGy or 2 MGy. Sleeve mock-ups were fully contracted
for the irradiation tests, which were conducted at ambient air without humidity control, as the irradiation tests ofthe sheets. After irradiation the sleeve mock-ups were attached to a testing machine, a schematic drawing of whichis shown in Fig. 7.

2.3

Fig. 6 Six measuring points for the sleeve mock-ups (radiation
source is located at the upper side).

Expansion/contraction tests and surface
analysis by FT-IR

After irradiation, the sleeve mock-ups were attachedto the testing machine and expansion tests were performed
using the testing machine in Fig. 7 and the conditions
shown in Table 3. Overviews of the testing machine system and driving mechanism are shown in Figs. 9 and 10,

Fig. 7 Schematic drawing of the sleeve mock-up testing machine.

Table 3 Testing machine specifications and test conditions.

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Fig. 9 Testing machine system overview.

Fig. 8 Contracted length and expanded length of the sleevemock-up.

respectively. The sleeves were expanded and contracted
by a servomotor, which drives a rolled ball screw via aplanetary gear reducer. The rated speed of the motor was
278 mm/min. Thus, one full stroke (expanding and contracting the sleeve mock-ups, Fig. 8) takes approximately
5 minutes. The expansion and contraction of the sleevemock-ups were controlled by a program called LabVIEW(version 2015 made by National Instruments Co., Ltd),
which regulates and monitors servomotor speed by using analog voltage commands via a digital/analog conversion module and servomotor position by using counter signals via a counter module. The LabVIEW program provides only simple speed control and position monitoring,
not precise position control. The servo driver was configured to operate at a constant speed because it performs
proportional-integral control based on speed commands.
After a default number of strokes, the servo driver decelerates and returns to its original position. The sleeve mockups were also monitored for holes or tears by using a differential pressure gauge installed at the rear of the testingmachine and an analog measurement unit. A HEPA filter
was also installed at the rear of the testing machine because
the ITER BRHS sleeve will require ventilation to preventthe sleeve from rupturing and the support rings from dislodging as the internal pressure increases. This ventilationpassage must be covered with a filter to prevent dust fromentering [5].
The number of cracks on the sleeve mock-up irradiated up to 2 MGy was confirmed by submersion tests, thetest apparatus for which is shown in Fig. 11. One side of
the sleeve mock-up was sealed and secured vertically in awater basin (the sleeve mock-up endplates are airtight at

Fig. 10 Testing machine drive mechanism.

Fig. 11 Submersion test apparatus.

both sides). Water was filled to the halfway point of thesleeve mock-up and it remained submerged for 30 minutes
to check for cracks. After 30 minutes, the mock-up was
flipped over on its opposite side and the procedure was repeated.
Since the sleeves are made of ester-based
polyurethane and the humidity was not controlledduring the irradiation, hydrolysis was expected as a causeof degradation [6]. We performed Fourier transform
infrared spectroscopy (attenuated total reflectance, ATR-

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Table 4 FT-IR measurement conditions.

Fig. 12 Test pieces after bending tests (three test pieces were cut
out from each sheet and labelled a, b, and c).

FTIR) to analyze the cause of the polyurethane sheet
degradation [7, 8]. Nicolet iN10 MX and Nicolet 6700
measurement devices (Thermo Fisher Scientific Inc.) wereused, the measurement conditions of which are shown in
Table 4.

3. Results and Discussion
3.1 Radiation resistance of polyurethane as
the sleeve material
No cracks or fractures were observed in the dumbbellshaped test pieces irradiated up to 1 MGy or up to 2 MGyeven after 10000 bending strokes, as shown in Fig. 12. Figures 13 (a) and (b) show the changes in test piece elongation from before irradiation (0 MGy) to after irradiation(1 MGy and 2 MGy) for test pieces without or with adhesion, respectively. A decrease in elongation was observed in both cases. In particular, the elongation percentages were lower in the test pieces having adhesion. All
test pieces having adhesion broke at their adhesion zones,
which suggests that adhesion decreases tensile strength.
However, owing to the structure of the sleeves, tensile
forces were quite low. Figure 14 shows the hardness ofthe test pieces before irradiation (0 MGy) and after irradi-Fig. 13 Elongation percentage (measured by the method described in 2.1) of test pieces after irradiation (a) withoutadhesion and (b) with adhesion.

ation (1 MGy and 2 MGy). There was virtually no change
in hardness after irradiation. These results satisfy the acceptance criteria, and polyurethane can be used as the material for the BRHS sleeves. Sheet hardness did not affect adhesion, so the sheets were not diﬀerentiated based

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Fig. 15 Sleeve irradiated up to 1 MGy and after moving 450 strokes.

Fig. 14 Shore A Hardness (measured by the method describedin 2.1) of test pieces after irradiation.

on hardness. The sheet material itself is not being pulled,
rather, the material is folded in on itself, and then is extended and contracted. Although the elongation percentage of the sheets decreased, the polyurethane material canbe used in the sleeves up to 2 MGy because it is resistant
to bending.

3.2 Expansion/contraction tests and degradation mechanism of the sleeve
The sleeve mock-up irradiated up to 1 MGy and after moving 450 strokes is shown in Fig. 15. The corners
and adhesion zones of the sleeve were illuminated and observed every 10 strokes, but no cracks were observed. The
diﬀerential pressure outside the sleeve relative to inside thesleeve was also measured, as shown in Fig. 16. Based on
the data given in this figure (no change in pattern), we determined there were no cracks. Since a HEPA filter was
attached at the rear of the test machine, as shown in Fig. 6,
air flows through the filter as the sleeve expands and contracts. However, because the sleeve expands/contracts at aconstant speed, the change rates of volume and diﬀerential
pressure were constant, i.e., the diﬀerential pressure gauge

Fig. 16 Diﬀerential pressure gauge data (pressure outside thesleeve relative to pressure inside the sleeve) from the
1 MGy sleeve.

data has a rectangular block pulse waveform. Submersion
testing to check for cracks was not performed after irradiation up to 1 MGy. However, for the sleeve mock-up irradiated up to 2 MGy, after moving 420 strokes, cracks wereobserved on the corners, as shown in Fig. 17, even though
the diﬀerential pressure gauge data did not fluctuate abnormally. As a result of the submersion tests, nine cracks wereobserved at the corners of the sleeve mock-up irradiated up
to 2 MGy.
Figure 18 shows the FT-IR spectra before and after irradiation, with the horizontal axis showing the wavenumber (cm−1 ) and the vertical axis showing the absorbance.
Ester polyurethanes, as the name implies, have ester bonds(-COO-) and urethane bonds (-NHCOO-). The peakat 3335 cm−1 indicates urethane N-H bonds (measured
value is 3333 cm−1 in Fig. 18) and the peak at 1732 cm−1
indicates polyester polyol esters. Hydrolysis of ester
polyurethanes results in the formation of carboxylic acidand alcohol. This hydrolysis also cleaves the urethanebonds, which forms an amine. Therefore, as polyester moieties hydrolyze, the peak at 1732 cm−1 is expected to decrease, and the peak at 3335 cm−1 is expected to increase

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Fig. 17 Sleeve irradiated up to 2 MGy and after moving 420 strokes.

Fig. 18 FT-IR spectra (a) before irradiation, (b) after 1 MGy of irradiation, and (c) after 2 MGy of irradiation.

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Volume 19, 1405020 (2024)with additional peaks of NH2 , -COOH, and -OH. Comparing the spectra after 1 MGy and 2 MGy of irradiation(b and c, respectively) with the spectrum before irradiation (a), almost no change was observed in the polyester
moieties owing to hydrolysis. On the contrary, the peakfrom the urethane bonds decreased, indicating reduction inmolecular weight. After irradiation up to 2 MGy, degradation occurred only in the mock-up test and not in the sheet
test.

3.3 Applicability of the polyurethane sleeveThis anomaly as described in 3.2 (sheets irradiatedup to 2 MGy were maintained their structural integrity but
the mock-ups irradiated up to 2 MGy fractured) can be attributed to the low dose rates in the sleeve mock-up tests.
The mock-ups were irradiated at a dose rate of 4% at thelow end and 70% at the high end compared with the sheet
test. Therefore, the cracks observed after 2 MGy in the
mock-up irradiation tests are considered to be due to thelower irradiation rate. Urethane oxidizes about 0.2 mmfrom the surface when irradiated at low dose rates via
molecular chain scission [9]. In the sheet tests, no oxidative degradation occurred owing to the higher dose rate. In
the mock-up tests, however, oxidative degradation (molecular chain scission) occurred because of the lower dose
rate. Since the dose rate during the mock-up test is similar
to the actual conditions of ITER, the results of the mockup test are considered to show the radiation eﬀects on thesleeve in the ITER vacuum vessel. Furthermore, considering that the sleeve in ITER will perform 450 strokes
while being irradiated (not after being irradiated) up to 2 3 MGy, these sleeve mock-ups tests are conservative compared with the actual conditions of ITER because the 420
strokes were performed after being irradiated up to 2 MGy.

4. Conclusion
Thermoplastic polyurethane sheets and sleeve mockups were irradiated up to 2 MGy. We confirmed thatthe polyurethane sheets kept their typical characteristics(structural integrity) even after 2 MGy of irradiation. However, the mock-ups developed several cracks after 2 MGyof irradiation and after moving 420 strokes. We consider
that this disparity is due to the diﬀerence in the dose rate;
the sheets were irradiated at a high dose rate (3700 Gy/h)and the mock-ups were irradiated at a low dose rate (150
- 2670 Gy/h). Moreover, the cause of urethane degrada-tion was not hydrolysis. Rather, it was oxidation (molecular chain scission) according to the results of FT-IR spectroscopy. Since the dose rate used to irradiate the mockups is similar to the actual dose rate of ITER, we expectthat the sleeve will degrade at around 2 MGy of irradiationin the ITER vacuum vessel. Therefore, the sleeve should
be replaced with a new sleeve at 1 MGy of irradiation as apreventive maintenance measure for the ITER BRHS.

Acknowledgments
The authors would like to thank the Takasaki Institute for Advanced Quantum Science’s Irradiation Facilities Section for their advice on dosimetry and allowing us
to use their irradiation facilities and NABELL Corporation,
Clearize Co., Ltd., and Fujimoto Science Co., Ltd. for theirroles in the manufacturing and analysis of the mock-ups.

Disclaimer
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
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