Primary and secondary in todays devices arent as different as they once were in "spark plug" configs. These are boosted weapons. A hollow sphere of fission material is collapsed into a point. Hydrogen is inside to add fusion reactions, increasing the efficiency of the fission reaction without the need of a formal secondary.

https://en.m.wikipedia.org/wiki/Boosted_fission_weapon

There are also "hourglass" warheads with integrated secondarys that are much smaller than spark plug configs.