Preparation of the highly dense ceramic-metal fuel particle with fine-grained tungsten layer by chemical vapor deposition for the application in nuclear thermal propulsion

The cermet fuel element was achieved by dispersing the UO_(2)particles with or without tungsten(W)coating layer uniformly in the W matrix.It is considered to be a robust and secure fuel for use in nuclear thermal propulsion in the near future.In this study,the effect of deposition temperature on the densification and grain refinement of the W coating layer was investigated.A high-density(19.24 g·cm^(-3))W layer with a uniform thickness(~10μm)and fine grains(~297 nm)was prepared by spouted-bed chemical vapor deposition.The prepared high-density,fine-grained W layer has the following advantages.It can prevent direct contact between fuel particles,resulting in a more uniform fuel distribution.In addition,it can decrease the reaction probability between the fuel kernel and H2,and prevent the release of fission products from the fuel kernel by extending the diffusion path at grain boundaries more efficiently.Moreover,the high-density,fine-grained W layer showed outstanding thermal and mechanical performance.Its average hardness and Young's modulus were approximately 7 and 200 GPa,respectively.The thermal conductivity of the W film was 101-124 W·m^(-1)·K^(-1)at 298-773 K.This work furthers our understanding of the potential application of the high-density,fine-grained W layer in nuclear thermal propulsion.

Mechanical property and thermal shock behavior of tungsten-yttria-stabilized zirconia cermet fabricated by spark plasma sintering

The cermet fuels have been considered as a potential key component for the nuclear thermal propulsion,and the homogeneity of the fuel particles in the metal matrix plays a crucial role in stabilizing the structure at extremely high temperatures.In this work,liquid paraffin was used as additive to improve the distribution of yttria-stabilized zirconia(YSZ,an appropriate surrogate for UO_(2) fuel)microspheres in the tungsten(W)matrix,and the W-YSZ cermet wafers(volume ratio 1:1)with a relative density of 97.6%were fabricated by spark plasma sintering with a specifically designed program.The effects of the paraffin dosage(0-5 wt.%)on the homogeneity,microstructure,mechanical properties,and the thermal conductivity of W-YSZ cermet were investigated.The W-YSZ sample with 2 wt.%paraffin shows the highest homogeneity and exhibits the best comprehensive properties,including the ultimate tensile strength of 132.2 MPa at 600℃,the bending strength of455 MPa and thermal conductivity of 50 W·m^(-1)·K^(-1)at room temperature.Moreover,the cermet could keep structurally sound after thermal shocked at a heat load of 20 MW·m^(-2).These results would be helpful for the design and optimization of the cermet fuels in the nuclear thermal propulsion.