Primary Coolant Tank
The Primary Coolant Tank is located in Main Engineering aboard a Sovereign Class Starship. The tank most likely performs the same function as the Main Stage Flux Chamber aboard the Constitution Class Starship.
It is safe to assume that since this particular component is named the Primary that there is also a Secondary Coolant Tank. This latter component has never been seen or mentioned on screen , although it is likely to exist. It may be that a secondary coolant tank may perform the same function as the Pre-Stage Flux Chiller aboard the Constitution class starship.
Background
The loss of Plasma Coolant causing adverse effects to the warp core does not seem to apply to the USS Enterprise-E. In Star Trek: First Contact, when Data breached the primary coolant tank in main engineering, it did not appear to have any adverse affect on the engines, even though the warp core was powered. It is possible that Starfleet engineered a solution to this problem. It can also be hypothesized that since the warp engines were not active during the "First Contact incident", the rupture of one of the two visible plasma coolant tanks was not sufficient to cause a thermal overload of the warp core reaction chamber.
