Reactors are one-time use special weapons. Only one reactor can be carried. If you pick up another one, it will replace your current reactor. When you see a new reactor available, use your current reactor to avoid wasting it, then collect the new one. The color of a reactor determines its function.

Blue: Shoot a lighting ball that bounces between multiple targets.
Green: Shoot multiple pairs of homing missiles.
Orange: Shoot out a group of orange discs in all directions.
Purple: Shoot a concentrated laser beam directly in front.