Israel will not initiate a nuclear attack. It will use other means including a massive EMP attack followed by a conventional Bunker buster attack bit it will cause a major war within which Israel will show no more mercy as she has shown since 1973.
I can see the merits of an EMP strike on Iran, and Lebanon for that matter should Hezbollah attack Israel following Israel’s strike on Iran. Would the EMP need to take down Iran’s entire grid, or could it be limited to largely military facilities? also, I’m not sure that Israel’s 5000 lb bunker buster munitions can neutralize hardened Iranian nuclear facilities. I guess the Israelis could target the entrances and exits, for a temporary facility shutdown, but this would be suboptimal.
As the next middle eastern war thus nears, the wargaming becomes very interesting.