I'm thinking that when the blast door is fully closed it also has some kind of energy field to redirect any explosion away from it.
Anyway, most of the power from the torpedoes detonation was going to be forced back out the opening toward the bow following the path of least resistance.
No, it was transparent neutronium.
They invented it a few centuries early because of some shenanigans involving an existential threat, time travel and life forms which unexpectedly proved to be intelligent.