How to nucleate at grain boundaries instead of random locations

[Sabalei]

Hi moose community,
I am trying to simulate static recrystallization.
I am trying to follow the https://mooseframework.inl.gov/modules/phase_field/Nucleation/DiscreteNucleation.html instructions below:

"Direct order parameter modification
...

I want to know how to control nucleation at grain boundaries rather than random locations

[GiudGiud]

I think you'll want to modify DiscreteNucleation. You can create a new object called GrainBoundaryDiscreteNucleation.
The first step there will be to detect grain boundaries, which you can do by analyzing the order parameters