  The Beam Dump Facility (BDF) is a proposed general-purpose facility at CERN,
dedicated to fixed target and beam dump experiments, currently being developed
in the context of the Physics Beyond Colliders program. The design of the
facility will allow to host different types of experiments, of which SHiP is
planned to be the initial one. The core of the facility is a high-density
target/dump absorbing the full intensity of the SPS beam and generating a
cascade of particles that are detected downstream the target complex. The
target and its shielding blocks are positioned inside a vessel, which is
planned to be passivized with helium, in order to reduce the activation of the
gas surrounding the target and to extend the operational life of materials and
equipment. The passivation system that will be in charge of purifying and
circulating the helium is a critical component for the operation of the
facility. Fluid dynamics simulations have been performed to study the
circulation of the helium through the vessel. A detailed design of the helium
passivation system and its main components has been developed.
