Abstract: Carbon nanotubes (CNTs) reinforced UO2 fuel pellets were prepared by powder metallurgy, the flexural strength, compressive strength and hardness of composite fuels were studied, the effects of CNTs doping amount and length-diameter ratio (L/D) on the mechanical properties of composite fuels were analyzed, the strengthening mechanism of CNTs was discussed. The results show that with the increase of CNTs doping, the flexural strength, compressive strength and hardness of UO2-CNTs composite fuel increased, when the volume content of CNTs was 12%, the flexural strength, compressive strength and hardness of the composite fuel reached their peak values, which increased by 45.65%, 37.01% and 19.61%, respectively, when the volume content of CNTs exceeded 12%, the mechanical properties of the composite fuel increased in a downward trend. The effects of CNTs doped with different length-diameter ratio (L/D) on the mechanical properties of composite fuels were diffe-rent, when the length-diameter ratio (L/D) was 9×103, the flexural strength, compressive strength and hardness of the composite fuel increased by 57.61%, 54.32% and 34.87% respectively. SEM analysis showed that doping CNTs with suitable volume fraction and length-diameter ratio (L/D) are the key factor affecting the mechanical properties of composite fuel, otherwise CNTs will agglomerate in UO2 matrix, which is not conducive to the improvement of mechanical properties of fuel. The enhancement of mechanical properties of UO2 fuel by CNTs results from the transition of external load from UO2 matrix to CNTs, which is realized by means of fiber bridging, fiber pulling-out, absorbing fracture energy and changing crack behavior.
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