In a future hydrogen-based economy, component reliability is a key prerequisite as hydrogen can contribute to a structure’s early failure (due, e.g., to hydrogen embrittlement). Hydrogen permeation, in conjunction with applied thermomechanical fields, has to be controlled to ensure the safety of in-service structures. In the specific case of nuclear fusion devices, hydrogen permeation and retention in components is also linked to safety issues. In ITER, the divertor plasma-facing components are actively cooled monoblocks. They consist of tungsten armor and CuZrCr cooling pipes in which pressurised water evacuates the heat deposited by the plasma power loads. A significant part of the plasma load is carried by energetic tritium ions that impact on the components, of which a fraction permeates in the monoblock to remain trapped or even enter the coolant flow. The related tritium retention and permeation must be understood. For a better understanding of this permeation process, a simulation of monoblock plasma exposure is conducted by means of the Abaqus finite element software. Hydrogen diffusion and trapping, assisted by thermomechanical fields, is modelled, using specific developments which permit the simultaneous resolution of transient heat transfer, mechanical stresses (including expansion) and diffusion and trapping problems. In the specific case of multimaterial components, chemical potential continuity is assumed to be linked only to the ratio of hydrogen concentration and solubility. Then, a parametric study is conducted to capture the influence of the boundary condition on the hydrogen retention and permeation in monoblocks.