Fuel retention in JET ITER-Like Wall from post-mortem analysis

Abstract

Selected Ion Beam Analysis techniques applicable for detecting deuterium and heavier impurities have been used in the post-mortem analyses of tiles removed after JET ITER-Like Wall campaign. Over half of the retained fuel was measured from the divertor region. Highest figures for fuel retention were obtained from regions with thickest deposited layers, i.e. in the inner divertor on top of Tile 1 and on High Field Gap Closure tile, which resides deep in the plasma scrape-off layer. Least retention was found in the main chamber high erosion region, i.e. in the mid-plane of Inner Wall Guard Limiter. Fuel retention values were found typically to vary with deposition layer thicknesses. The reported retention values support the observed decrease in fuel retention obtained with previous gas balance experiments.

Experience of handling beryllium, tritium and activated components from JET ITER like wall

“…From section 3.1 the areal concentration of T is estimated at ~10 17 T atoms/cm 2 . By scaling TDS results for D concentrations for 2011-2012 [8] the distribution of T between the divertor and wall tiles is expected to be 10 18 -10 19 T atoms/cm 2 for divertor and 10 17 -10 18 T atoms/cm 2 for Be wall tiles for 1.91 × 10 26 T atoms injected during DTE2. This gives T inventories for divertor and wall tiles of 10 9 -10 10 Bq/cm 2 and 10 8 -10 9 Bq/cm 2 .…”

“…The T inventory can be estimated from the deuterium (D) retention measured on tiles exposed in JET from 2011 -2012, the first JET-ILW campaign. In this DD programme the total amount of D puffed into JET was 1.67 × 10 26 D atoms and the total amount retained in the vessel was 3.7 × 10 23 D giving a global long term retention of ~0.2 % [8]. Taking into account the operating time for 2011-2012 of 6.8 × 10 2 s the global retention rate is 5.5 × 10 18 D/s [8].…”

“…As a percentage of injected gas 6% (2 g) T was released on purging the vessel, 4% (1.5 g) T was held in deposits mainly on divertor tiles, 0.03% (0.3 g) T was trapped in tiles and 6% (2.2 g) T was attributed to flakes in remote areas, particularly in the inaccessible sub-divertor. For the JET-ILW the retention in deposits is 0.2% [8] with no additional contribution from flakes in the sub-divertor region as long range migration is almost totally absent and hence deposits are not spalling. Therefore the T retained after purging is expected to be 1.90 g in deposits, i.e., 0.2% of 950 g T injected.…”

“…Therefore the T retained after purging is expected to be 1.90 g in deposits, i.e., 0.2% of 950 g T injected. Whilst the error in the surface analysis of individual tiles is < 6% [8] the error in deriving the global retention value is dominated by the extrapolation from individual tiles to cover the whole vessel surface. Therefore the retention value could be 30% higher.…”

Determination of tungsten and molybdenum concentrations from an x-ray range spectrum in JET with the ITER-like wall configuration

“…Because the Mo concentration seems to be proportional to the W concentration, it is suggested that Mo sources are not special locations which plasmas attach occasionally but should be usual plasma wetted areas, similar to W sources. One of the possible sources is a Mo marker tile installed as an inner vertical divertor target [12]. It will be confirmed whether this tile can be a sufficient source for the determined Mo concentration.…”