A nuke behaves similarly to TNT; however, the explosion is a crater 5 times bigger than TNT.
Use the Nuke wisely...
Attempts at using the nuke in SMP using all different methods of triggering have shown it still doesn't work correctly and neither does ITNT.
Reinforced stone/glass is the most resistant material next to bedrock. Encasing a nuke in several layers should prevent most damage. Because of balance reasons, obsidian is nerfed down to a blast resistance of 60, removing its effectiveness.
It's not recommened to test over 15 nukes at once in a cluster on the same world you are building on, even if the testing place is very far away from your buildings. In the aftermath of all such big explosions, multiple water streams will emit from all affected nearby water blocks. Since the crater will be enormous if using over 15 nukes at once, there will also be a huge amount of water falling down in the hole, and also lava, from it's supply blocks, and a HUGE amount of loose items will be scattered around in the crater. Most computers can't handle it well, and aside from the explosion itself, the crater enviroment itself will mostly then cause a enormous lag. It will usually be better with time, and also getting a bit away from the crater may also get it better.
Unlike Industrial TNT, placed nuke blocks can be broken, just like ordinary TNT. Triggering nukes can be done in many ways, but many of them are fatal. A safer, but harder, way is to place a long redstone current to one or more nukes and detonate them from far away. The easiest way is to place Dynamite on a nearby block and detonate it with a Dynamite-o-mote from far away, but this can be very risky. You need to first right-click the dynamite after placing it, and if you do a small mistake, you might end up like...Coal Dust?
As of 1.106, nuke explosions, if they don't kill you, will add poisonous potion effects to your player. These effects will last a certain amount of time corresponding with your distance from the nuke when it explodes. The times below are approximations based on some tests that I ran.
|Distance (blocks from blast)||Duration|
And so on...
Recipe (IC² Experimental)