Tritium in plasma-facing components of JET with the ITER-Like-Wall

Abstract

The ITER-Like-Wall project has been carried out at the Joint European Torus (JET) to test plasma facing materials relevant to ITER. Materials being tested include both bulk metals (Be and W) and coatings. Tritium accumulation mechanisms and release properties depend both on the wall components, their location in the vacuum vessel, conditions of exposure to plasma and to the material itself. In this study, bulk beryllium limiter tiles, plasma-facing beryllium coated Inconel components from the main chamber, bulk tungsten and tungsten coated carbon fibre composite divertor tiles were analysed. A range of methods have been developed and applied in order to obtain a comprehensive overview on tritium retention and behaviour in different materials of plasma facing components (PFCs). Tritium content and chemical state were studied by the means of chemical or electrochemical dissolution methods and thermal desorption spectroscopy. Tritium distribution in the vacuum vessel and factors affecting its accumulation have been assessed and discussed.

Tritium distributions in castellated structures of Be limiter tiles from JET-ITER-like wall experiments

“…Pajuste et al examined T retention in Be tile PFSs by the dissolution method [11]. The T retention reported was smaller by a factor of 2-10 depending on the specimen location than the values evaluated in our previous papers [12,13] and those given in figure 10.…”

“…This difference can be ascribed, at least in part, to non-uniformity of T distributions in the tokamak and to differences in the measurement techniques. Nevertheless, it was reported in [11] that the highest T retention among the specimens examined was measured in the erosion zone (central part) of the OPL. This gives a strong indication that the results obtained by means of the IP technique and dissolution method show a similar tendency.…”

“…On the other hand, on the PFSs of Be limiters in the main chamber, there was no clear correlation between the deposition and T distributions. The T concentration was higher in the erosion-dominated areas than in the deposition zone on the outer poloidal limiter (OPL) [10][11][12][13] because deep implantation (micrometer range) of high-energy T was a dominant retention mechanism in PFSs of Be limiters [12]. As a consequence, the T retention in the erosion zone of those tiles was determined by the balance between the amount of T implanted at high energy and the amount removed by erosion and/or thermal desorption [12].…”

Fuel desorption from JET-ILW materials: assessment of analytical approach and identification of sources of uncertainty and discrepancy

“…This could be expected, since at present only trace amounts of T are present in JET-ILW tiles. This is due to the fact that between the installation of ILW and extraction of the tiles used for the measurements following the ILW3 campaign, only H and D were used in JET, and thus all the T present comes either from implantation of energetic T produced in the D-D reaction or neutron-induced transmutation of Be, in addition to residual inventory from the previous D-T campaign in 1997 (pre-ILW) [92]. On the other hand, T contents obtained in dissolution measurements do not result from QMS-based detection of molecular species but derive from the direct measurements of radioactivity of released T. This activity can be accurately measured even at very low T concentrations, and these measurements are not affected by the molecular state of T. Therefore, it can be concluded that at the current T levels in Be tiles of JET-ILWnamely, on the order of 10 12 atoms cm −2 -measurements of QMS-based TDS do not allow reliable quantification of T content and distribution.…”