In recent years the research on nuclear power generation focused on an innovative subcritical reactor concept, along with previous liquid-metal-cooled critical reactors. The accelerator-driven system reactor design matches higher and intrinsic safety requirements with the reduction of actinides and long-lived fission products, encumbrances on the nuclear waste final repository. The coupling of the accelerator technology with the reactor facility faces new challenges; the first is the design of the interface between accelerator and reactor. Currently two solutions are proposed and investigated: one with a solid beam-target window interface and the other one without a beam window. Our speculations focus on the windowless approach: No physical barrier is located in the interface region, so the ultrahigh vacuum environment of the accelerator is connected with the operative conditions of the reactor through an intermediate spallation target. In this work we describe our experimental activities and the numerical tool employed to give a basic characterization of the vacuum dynamics for a windowless interface, with particular regard given to proton beamline and target interface of the Ansaldo A80-XADS reference design.