Factual error: The marines' rifles are supposed to fire "standard armor-piercing rounds", which should have done way more damage than producing a few sparks on the frail sheet metal table in the med bay when Hudson shot the face-hugger threatening Newt. "Standard AP rounds" would have pulverized the table and created a huge hole in the wall behind it.
Factual error: If you damage a fusion reactor, it doesn't explode with a thermonuclear effect. It just shuts off.
Suggested correction: Actual fusion reactors don't exist, yet. Certainly not this size. You have no idea how this reactor works. It's not unlikely it uses fissile material to operate.