The Iron Dome is okay to destroy regular rockets sent by Hamas in Gaza or by Hezbollah in Lebanon or by Syria near the Golan Heights, but the Dome doesn't destroy all of them, some get through. A nuclear bomb is meant to explode in the air over the target, so intentionally blowing it up over land is the same as it exploding on its own. Israel has to destroy the nuclear facilities in Iran before a nuclear bomb can be sent.
The Dome is challenged by the very nearby origin of many of the missiles it would intercept.
It is a kinetic weapon i.e. blunt collision. Destroy the ability to detonate and you have some dirty atomic waste, but no nuclear explosion.