In the reprocessing of spent solid fuels from nuclear reactors by direct volatilization, one of the major problems is the removal of heat from the highly exothermic gas-solid reactions. The use of fluidized beds of inert granular material as hent transfer media to control these exothermic reactions forms the basis of one approach to volatile reprocessing which is under development at BNL The engineering scale work carried out under this development program is discussed. (auth)