Hi Sharif,
One thing that jumps out to me is the shape of the TRISO lattice. I’d try creating a TRISO lattice with a shape greater than (1, 1, 1). The lattice is used to accelerate the cell containment search when sourcing and tracking particles by limiting the search to TRISOs in the same lattice cell as the particle. With a shape of (1, 1, 1), all of the TRISOs are in the same lattice cell and in turn all of the TRISOs are in the search list, which is likely why it’s taking so long to source those particles.
As a starting point, I’ve used a shape that is something like the size of the TRISO region divided by 2 diameters of the TRISO particle in each dimension - meaning you’ll have ~8-10 TRISOs per lattice cell to search. For your model with a box width of 1 cm and an outer TRISO radius of 0.0613 cm this would result in a shape of (4, 4, 4). This is just a guideline though and something like (8, 8, 8) would be totally reasonable as well. The optimal shape for performance will vary model to model, so feel free to use your best judgement of course.
I hope this helps.
Best regards,