A naturally circulating air stream to remove decay heat from a nuclear reactor is a key feature of advanced liquid metal reactor concepts. General Electric and Rockwell International continue to develop innovative designs aimed at improving safety and enhancing plant licensability. Argonne National Laboratory provides technical support to both. Shutdown heat removal employs a passive system that rejects heat by radiation and natural convection to air to assure adequate cooling. Although calculations indicate viability of this system, uncertainties remain with respect to particular designs, changing environmental conditions and material properties. Needed data are gathered in a facility that simulates a full-scale segment of the reactor system.