[Suicide Junkie]

If the warp reactor was just a tank, they wouldn't have to eject the damn thing if it became unstable and evacuate the crew.

Actually, if the reactor was just a tank of antimatter, they would really want to get a few hundred lightyears away from it before it exploded.

Although the reactor is not a fuel tank, it does have a significant amount of antimatter flowing through it in order to operate. (Fuel lines and gas in pistons)

Problem with antimatter, is that even a tiny amount can really make a mess.
A one-kilogram cloud of antimatter produces the same energy as a 40 megaton nuke when it annihilates with your reactor's wall.

EG:
The Yamato's destruction was due to leftover antimatter in the reactor core, even after most of it was flushed by the emergency systems (which were disabled by the computer infestation before they finished their job)