Colossus reactors are reactors developed by the Terran Confederacy for use in their battlecruisers. Their output is greater than the standard battlecruiser reactors, and it was made specifically to compensate for the high energy consumption of the yamato cannon.[1] However, poor maintenance of these reactors would give them a tendency to leak.
In the aftermath of the Brood War, the power sources for Behemoth-class battlecruisers, colossus reactors included, were phased out in favor of fusion technology.[2]