The Nuke is similar to TNT, but has a much higher explosion radius, comparable to a Nuclear Reactor meltdown. Nukes can penetrate through all but the QuantumSuit, the only armor that will hold up to a nuclear explosion.
Walls composed of Reinforced Stone and Reinforced Glass will minimize the damage of the Nuke, but the walls should be at least 2.5 (effectively 3) layers thick to completely protect anything behind. A Nuke will even destroy Obsidian, as the blast resistance of Obsidian has been reduced to 60 in Industrial Craft 2 Therefore Tekkit/Tekkit lite. The only things that can survive a nuclear explosion are Bedrock, End Portal, Trade-O-Mat, force fields, and personal safes (on slower computers, Nukes may blast through and/or destroy Forcefields ). Although the Personal Safes don't take any damage from the explosion, they will allow the blast to pass through and damage items behind.
The blast radius of a Nuke is dependent on the blocks surrounding it. Underground, it will generally have a blast diameter of 20 blocks (10 block radius). Above ground in the open it will have a blast diameter of 76 blocks (38 block radius). The player, if standing directly on the nuke and completely protected, will be launched 191 blocks into the air.
The Nuke is usually turned off by default on Tekkit servers, to prevent a substantial amount of damage from being caused so easily. Older machines or clients with a small amount of memory are not recommended to detonate over 5 nukes at once, as the crater usually creates a large amount of memory usage (lag), while the client redraws the world. Some computers can't even handle 1 Nuke, which can result in not even being able to close the game and having to restart your computer.