Influence of hydrogen trapping on WCLL breeding blanket performances

Abstract

Tritium transport simulations in water-cooled lithium lead (WCLL) breeding blankets have been performed with FESTIM. Fluid dynamics and heat transfer were coupled to evaluate how temperature and LiPb velocity fields affect tritium transport. The 2D WCLL model consisted of tungsten, EUROFER and liquid LiPb. Tritium inventories and permeation fluxes have been computed and the influence of trapping effects in solid domains was highlighted. It was evaluated that inclusion of trapping mechanisms increases inventory values by 15% and delays permeation to the cooling channels. A parametric study was conducted to investigate the impact of the uncertainty in the literature (2 orders of magnitude) regarding hydrogen solubility in LiPb on these quantities. Varying the lithium lead solubility over the range found in the literature was found to vary the EUROFER inventory by a factor of 25. Permeation fluxes to the coolant channels was found to vary over a factor of 3.

Influence of traps reversibility on hydrogen permeation and retention in Eurofer97

“…The assumptions that are required to validate the effective diffusivity model are not compatible with the irreversibility of the trapping sites in Eurofer97. Therefore, the estimation of tritium inventory and permeation at system level requires a model that takes into account all trapping site, using the McNabb & Foster equations such as FES-TIM [11] or a generalized Oriani approximation as developed in [47].…”

“…In particular for ITER, safety regulations set the maximum in-vessel retention to 700 g [2] and call for a careful prediction of the retention and of the amount of tritium permeating up to the coolant. These evaluations can be performed using diffusion-trapping codes [3][4][5][6][7][8][9][10][11] that rely on material properties such as diffusivity, solubility and trapping densities and energies.…”

Fuel retention in WEST and ITER divertors based on FESTIM monoblock simulations

“…Numerical modelling of H transport and retention in and outgassing from plasma facing components [4, 5,6,7] is therefore often required in order to tackle both issues. These simulations are supported by experimental work to determine key properties of fusion materials.…”

“…Hydrogen isotopes (H 7 ) transport in tokamaks is a crucial issue for several reasons. First, for safety reasons, the total inventory of radioactive material trapped in the reactor must be limited to a certain amount.…”

“…Numerical modelling of H transport and retention in plasma facing components [4][5][6][7] is therefore often required in order to tackle both issues. These simulations are supported IVT and OVT stand for inner and outer vertical target, respectively.…”