High temperature gas-cooled reactors (HTGRs) employ fuel elements which are separated from the coolant stream by graphite. Pressure differentials induced by turbulent flow along the coolant channel length of the fuel assembly can cause transverse flow of the gas through the graphite sleeve. Such transverse flow could transfer fission products from broken fuel particles into the main coolant stream. Mathematical analysis shows that the thickness of the annular gap between the fuel element and the graphite sleeve is an important factor that controls fission product transport by this mechanism. The data obtained from experiments performed in a high temperature, pressurized helium loop correlate satisfactorily with this analysis, and an estimate of cesium release to the coolant via this mechanism has been made for the Fort St. Vrain reactor.