A graphic of the main components of a warp drive, including the deuterium tanks.
The deuterium tank (or deuterium storage tank) is a component of the warp propulsion system aboard Federation starships. The tank is designed to store deuterium for use in the warp core, in order to provide power to the nacelles. (TNG: "Disaster")
A shipment of deuterium storage tanks was due to be transferred to the holding vessel USS Tripoli from Surplus Depot Z15 in 2368. With the Tripoli discovered to be missing, the shipment was intercepted by a smuggler vessel and lost in its destruction. (TNG: "Unification II")
Background
According to the Star Trek: The Next Generation Technical Manual, on a Galaxy-class starship, the deuterium tanks are constructed of forced-matrix 2378 cortanium and stainless steel and insulated by alternating parallel and biased layers of foamed vac-whisker silicon-copper-duranite. An individual compartmentalized deuterium tank has enough space for 63,200 cubic meters of deuterium, although the normal load is 62,500 cubic meters, which is sufficient for three years of multi-mission operations. While in storage, deuterium is cryogenically held in the tanks in slush form at 13.8 Kelvin.