Dud

Welcome to Megaton. The bomb is perfectly safe. We promise. Duds are apparent antimatter bombs that failed to detonate before hitting the ground (hence the name), most likely as a result of some kind of war long ago. Presumably, it is an obsolete equivalent to the Balefire Bomb. If it successfully detonates, it will produce the Balefire explosion equivalent to a mini-nuke.

Where to find
The dud generates in every biome in the Overworld and is quite common.

Dangers
It may in fact explode. When it does it will spawn Balefire everywhere, an annoying type of fire that spreads, can be very laggy, and sets you on fire and gives you the contaminated potion effect level 10 for 5 seconds. (The dud is indestructible when trying to mine it, so the only way to get rid of it is either to use a high-tech bomb defusing device, or by detonating it.)

Loot and Uses
Using a magnetic extractor tool, you can attempt to extract the warhead components. Chances are determined by a randomly generated floating point number, if it is less than 0.01, it will explode, if it is less than or equal to 0.3, it will give you a gaseous Balefire cell, everything else will give you regular Antimatter. (Do note that doing this will increase your radiation level by a noticeable amount. It's best to do this while wearing a hazmat suit or any armor with high-enough rad-resistance.)

Can be used to create Euphemium, see Guide: Euphemium Creation.

Can be defused with a High-Tech Bomb Defusing Device. Doing so will remove the bomb and reward you with 10-24 Steel Plates, 2-6 Titanium Plates, and 1 Balefire Shard.

Detonating
It can be exploded be either getting the 1% chance with an empty cell or by directly using a detonator.

Refurbishing
You can build a small museum or shrine around it if you really want, other than that, the bomb cannot be repaired or upgraded. Use a Balefire Bomb, it is much more effective in that role. No one would be stupid enough to build a settlement around a dud.