Argonne National Labs, which is 5th fastest I think, is used for weather models, material science, and more[1]
I checked the list of projects running on ALCF and I see some pretty obvious nuclear weapon stockpile stewardship and weapon design projects, such as "Validation Simulations of Macroscopic Burning-Plasma Dynamics"
(I know a guy that Los Alamos is trying to recruit to do some dark work for them, and he does nucleosynthesis in neutron star mergers.)
I think the folks simulating supernova and neutron stars have a lot of physics overlaps, but I don't think that data is used directly for stockpile stewardship.