“With the Atomic! perk, you are 25% faster and stronger whenever you're basking in the warm glow of radiation. Outside irradiated areas, your Action Points (AP) regenerate faster and faster the higher your level of radiation sickness becomes.”— in-game description
When eating foods that have a Rad effect longer than one second (such as Coyote meat), the perk will activate. Eating multiple coyote steaks will stack the Rads duration, giving the player a lengthy speed boost if many are consumed.
The AP regen bonus synergizes well with Rad Child.