7P54
Evaluation of tritium accumulation in castellated structure ofJET-ILW Be limiter tiles
LEE Suneui1, HATANO Yuji1, OYA Yasuhisa2, MASUZAKI Suguru3,
TOKITANI Masayuki3, MIYAMOTO Mitsutaka4, ASAKURA Nobuyuki5,
NAKAMURA Hirofumi5, IWAI Yasunori 5, HAYASHI Takumi5,
WIDDOWSON Anna6, RUBEL Marek7
1
U. Toyama, 2Shizuoka U., 3NIFS, 4Shimane U., 5QST, 6CCFE, 7KTH
An accurate tritium (T)retention
analysisinplasma-facing components(PFCs) is important forsafety assessment of fusion
reactors. JET ITER-likewall (ILW) project has
been carried out since 2011as a test-bed of ITER anddeuterium (D) plasma wasdischarged for the first
three campaigns in 201112(ILW1),
2013-14(ILW2)
and2015-16(ILW3). Main chamber
Fig. 1. Cross-section of
JET and positions oflimiter tiles were composed
IWGL and OPL.
of beryllium (Be) anddivertor tiles were made oftungsten (W). Tritium (T) is produced by DD fusion
reactions (2D + 2D -> 3T (1.01 MeV) + p (3.02 MeV))
and part of generated T was retained in PFCs of the JET
tokamak. Be limiter tiles were castellated to protect
tiles from thermo-mechanical and electromagnetic
loads of the plasma. T was accumulated not only on
plasma-facing surfaces (PFSs) but also in thecastellation grooves [1].
In this study, T inventory in the castellation groovesof inner wall guard limiter (IWGL) and outer poloidal
limiter (OPL) used in ILW1 or ILW3 was investigated.
The positions and photos of limiter tiles are given inFig. 1. Specimens for themeasurements were cut fromthe limiter tiles alongcastellationgrooves,asshown in Fig. 1. Imaging
plate (IP) technique wasapplied to analyze 2dimensional T distributions
on specimen surfaces. Plastic
reference samples labelledwith known amounts of T
were used for quantification.
Typical IP images of theFig. 2. IP images ofsurfaces
originally in thecastellation sides of
ILW1 samples.

castellation grooves (castellation sides) are shown inFig. 2, together with profiles of T concentration
evaluated from the signal intensity from IP. In the caseof OPL, the accurate evaluation of T profile near theentrance of the grooves was difficult due to theinterference by β-rays emitted from PFS and scatteredby air. Hence, the only T in the deeper region in thegroove (the distance from the entrance ≥ 0.5 mm) was
considered in the following evaluation. There were T
enriched regions near the groove entrances. The
analysis using X-ray photoelectron spectroscopy
showed that T enriched region was covered by BeO
layer whose thickness was ~50 nm. This observationsuggests that T was co-deposited with sputtered Be andO.
Fig. 3 shows T retention on castellation sides withthat on PFSs examined in our previous study [1].
Castellation sides showed smaller T retention thanPFSs by an order of magnitude or more. T retention oncastellation sides were comparable with each otherafter each campaign regardless to tile location.
Contrary, T accumulation on PFS was highly
dependent on limiter position; i.e., more T was retainedin OPL than IWGL [1]. This difference was due todifferent retention mechanisms; the implantation ofhigh energy triton for PFSs and co-deposition with Beand O for castellation sides. In conclusion, not thecastellation sides but the PFS of OPL was primary T
reservoir in the main chamber of JET.
References[1] S. E. Lee et al., Fusion Eng. Des. 160 (2020) 111959.

Fig. 3. T retention on castellation
sides and PFS of Be limiter tiles.