[en] The behaviour of hydrogen isotopes in ITER monoblocs was studied using the code FESTIM (Finite Element Simulation of Tritium In Materials) which is introduced in this publication. FESTIM has been validated by reproducing experimental data and the Method of Manufactured Solutions was used for analytical verification. Following relevant plasma scenarios, both transient heat transfer and hydrogen isotopes (HIs) diffusion have been simulated in order to assess HIs retention in monoblocs. Relevant materials properties have been used. Each plasma cycle is composed of a current ramp up, a current plateau, a current ramp down and a resting phase before the following shot. 100 cycles are simulated. The total HIs inventory in the tokamak during resting phases reaches 1.8 x 10^-3 mg whereas during the implantation phases it keeps increasing as a power law of time. Particle flux on the cooling channel of the monobloc is also computed. The breakthrough time is estimated to be t = 1 x 10⁵ s which corresponds to 24 cycles. Relevance of 2D modelling has been demonstrated by comparing the total HIs inventory obtained by 2D and 1D simulations. Using 1D simulations, a relative error is observed compared to 2D simulations which can reach -25% during the resting phase. The error during implantation phases keeps increasing. (authors)

[en] This study is focused on tritium retention and permeation through a 316L stainless steel diagnostic first wall during plasma operations in ITER. A set of data for migration properties is proposed by adjusting the values to fit a simulation using experimental results. A reactive–diffusion model coupled with a mechanical field, solved on 3DS Abaqus finite-element software, is applied to estimate tritium migration. Two-dimensional simulations are compared with one-dimensional simulations and the role of thermal expansion on plastic deformation and trap creation is discussed. (topical issue article)

[en] This work investigates the influence of hydrogen chemical potential continuity across solid material interfaces. The implementation of the mathematical model in FESTIM is verified using the method of exact solutions (MES) and the method of manufactured solutions (MMS) in 1D, 2D, with complex material properties and inhomogeneous temperature fields. A comparison test between FESTIM, TMAP7 and Abaqus codes is also performed and the codes show good agreement. The chemical potential continuity condition has an impact up to 40% on the outgassing particle flux on 4 mm composite slabs (W/Cu and Cu/EUROFER) compared to mobile concentration continuity. A method for rapid identification of materials properties from outgassing flux measurements is given. The influence of chemical potential conservation on monoblock inventory is then studied. It is shown that, for the 1D and 2D ITER divertor monobolocks cases, discrepancies only start to appear after approximately 5 × 10⁶ s of full power. (paper)

[en] Highlights: • An automated technique for materials properties identification is presented. • Thermo-desorption spectra are automatically reproduced. • Tungsten, EUROfer, Aluminium and Beryllium are analysed. A novel identification technique of hydrogen transport parameters using FESTIM (Finite Element Simulation of Tritium In Materials) has been demonstrated. FESTIM is a finite element code developed with FEniCS performing hydrogen transport simulations. The trapping parameters (detrapping energies and trap densities) are identified for various materials (Tungsten, Aluminium, EUROFER and Beryllium) by automatically reproducing thermo-desorption experiments. Several optimisation algorithms are tested and the Nelder–Mead algorithm shows the best efficiency. An optimisation test problem with five free parameters took only a few hours to solve whereas optimisation cases with two free parameters took a few minutes. Limitations of this technique are shown and discussed.