The effect of sink strength on helium bubble formation at elevated temperatures

In present study, the model Fe–9Cr alloy and two nanostructured ferritic alloys (NFAs) CNA1 and 9YWTV with high application potential in advanced nuclear power systems were selected to systematically investigate the effect of sink strength on helium bubble behavior at elevated temperatures. Helium bubble formation for a constant implanted He concentration of ∼7500 atomic parts per million (appm) was characterized using transmission electron microscopy (TEM) at 500 and 700 °C. A quantitative research and comparison of the influence for a specific sink strength on bubble formation was illustrated. Results showed that the introduction of nanoparticles into NFAs can effectively reduce bubble coarsening by sequestering the implanted helium into dispersed small bubbles due to the sufficient He entrapment by interfaces between the nanoprecipitates and the surrounding matrix. In addition, the NFAs with higher sink strength (9YWTV) revealed a higher suppression effects on bubble growth compared to general particle-free Fe–9Cr alloy and CNA1 with lower sink strength. This can be attributed to the comparable mean free path of He diffusion with the inter-particle distance for high particle density in 9YWTV. Meanwhile, the suppression effects of sinks on bubble growth decreased with increasing temperature from 500 to 700 °C. The sink strength of the order of 10¹⁵ m⁻² and 10¹⁶ m⁻² showed favorable suppression effect on bubble coarsening at 500 °C and 700 °C, respectively.