Some doubts about the phase field method for calculating fissile gas bubbles

[shin-chan-cpu]

I have recently been studying the use of phase field method to simulate the generation of fission gas, and when I was researching the literature, I found that the content of the following literature was found to be calculated and reproduced, but I found that I could no longer calculate the growth of the bubble phase without setting the initial bubble, and it was also mentioned in the article that the initial bubble position needs to be set, but this cannot simulate the formation process of the bubble, please have a similar example for this kind of problem?
aagesen2018.pdf

[GiudGiud]

@laagesen