An update of Tritium co-deposition in ITER using WallDYN3D

Abstract

The retention by co-deposition of fuel species in Be-layers, forming due to migration of Be eroded from the 3D-shaped main chamber wall in ITER, was modeled with WallDYN-3D. The goal was to investigate the influence of the 3D shaping on Be layer formation location, compared to previous 2D calculations for a perfectly toroidally symmetric main chamber Be wall. The calculation showed that the shaping results in a large number of partially plasma shadowed regions in the main chamber, where Be can deposit and form layers. Depending on the main chamber plasma solution, this results in a shift of the primary Be layer deposition location from the divertor in 2D to the main chamber in 3D calculations. The deposition location is important because the higher average hydrogen isotope (HI) particle energy in the main chamber affects HI content in the co-deposited layers. However, for the currently available HI/Be scaling laws the resulting increase in HI/Be is small. A comparison of the 3D-shaped Be-main chamber erosion calculated recently by ERO2.0 and by WallDYN-3D in this work, shows very similar erosion patterns. However, differences exist in the deposition locations because, in contrast to ERO2.0, WallDYN-3D takes re-erosion of deposited Be into account. To match the absolute amount of Be erosion the Be-sputter yields used by WallDYN-3D have to be increased by a factor of 1.5, due to a different erosion yield database used by ERO2.0 which results in higher yields at oblique impact angles. This uncertainty in the sputter yield, but also in the HI/Be scaling laws, make an uncertainty quantification necessary. Applying polynomial chaos expansion to the Be layer growth rate and HI-retention rate by co-deposition, yields an uncertainty of ≈ 100 % in both quantities, due to the uncertainties in the sputter yields and the fit parameters of the HI/Be scaling laws. • WallDYN-3D was applied to Be erosion/migration/layer deposition for the 3D shaped ITER main chamber wall. • 3D shaping leads shifts the location of Be layer deposition from the divertor to main chamber • A comparison with recent ERO2.0 calculations shows very similar erosion patterns. • WallDYN and ER02.0 use different Be erosion yield database which results in factor 1.5 increased erosion at oblique angles for ER02.0. • Uncertainty quantification results in a 100% uncertainty in both Be layer growth rate and D/T retention rate.