Deuterium

Deuterium is a fluid and an isotope of added by various mods.

Mekanism
Deuterium is the product of separating in an. It's used in a Fusion Reactor with Tritium, and optionally, some D-T Fuel, to produce large amounts of energy, and if water-cooled, very large amounts of steam.

NuclearCraft
Deuterium is the product of and can be synthesized in an.