[en] The conceptual design of a double walled titanium vaccum vessel is presented. The following details of this semi-monocoque construction are analyzed: vessel-plasma-coils electrodynamic interaction, tritium containment, structural requirements and thermal requirements. In the electrodynamic analysis, consideration is given to the characteristic magnetic diffusion time and vessel overpressure during a major disruption. In the structural analysis, membrane stresses and poloidal and toroidal static buckling are considered. In the thermal analysis both surface boiling and liquid turbulent heat transfer are found to be adequate. The coolant quantity and distribution is determined