Mechanical properties of 238PuO2

The mechanical properties of 238PuO2 have been examined in the Los Alamos Scientific Laboratory mechanical test facility built to handle α-radioactive materials. Compression tests were conducted as a function of temperature, strain rate, grain size, density, and storage time. At temperatures less than or equal to 14000C, test specimens of 238PuO2 exhibit pseudobrittle behavior due to internal cracks. Plastic deformation is ''localized'' at the crack tips. Generalized plastic deformation is observed at 15000C. Ultimate stress values decrease markedly with increasing temperature and decreasing strain rate, and decrease less with decreasing density, increasing storage time, and increasing grain size. Room temperature fracture is transgranular, whereas intergranular fracture predominates at elevated temperatures. Crack-free specimens of 239PuO2 exhibit extensive plastic deformation at 10000C and above. The relationship of these test results to the impact properties of 238PuO2 fuel in radioisotope thermoelectric generators is discussed