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The thermal fracture resistance of plutonia Multihundred Watt (MHW) fuel spheres was analyzed assuming boundary conditions of (1) constant heating or cooling rate for the sphere surface, (2) heating or cooling with a constant surface heat transfer coefficient at the sphere surface, and (3) heating or cooling the sphere surface solely by radiation. Thermal damage resistance (mechanical weakening) of MHW spheres was analyzed in terms of the fracture energy and crack system present in the fuel. Using available property data for porous PuO/sub 2/ between 400 and 1200 deg C, and estimating other properties from available data for UO/sub 2/ and ThO/sub 2/ the thermal shock conditions that cause fracture of the fuel sphere were estimated. Experimental values for the tensile fracture strength and the elastic modulus of the fuel as functions of temperature are presently not available and estimates were made of these properties. (auth)