BRUpax, a problem with them doing that is that launching a nuke (or a number of them, Israel has ballistic missile defenses) at the Holy Land is in direct opposition to their Axis of Resistance posture.
Such a strike would render Israel (or as they see it, the rightful homeland of the Palestinian Muslims) - uninhabitable, at least for the near term.
The land would be poisoned, rather than restored to the Palestinians.
Having the weapon would be (1) a status symbol and (2) a possible deterrent to attacks on or invasion of Iran.
On the other hand, maybe they'd get to a point where they embrace the Götterdämmerung...but I never saw the Mullahs as suicidal.