Dilithium chamber hatch

From Memory Alpha, the free Star Trek reference

The dilithium chamber hatch aboard Federation starships is a reinforced plate which fits over the exterior entrance to the matter-antimatter reaction assembly with the dilithium articulation frame immediately behind it.

In 2367, the dilithium chamber hatch aboard the USS Enterprise-D exploded; although sabotage was suspected, a subtle manufacturing flaw in the hatch (replaced at Earth Station McKinley earlier that year) was to blame. (TNG: "The Best of Both Worlds, Part II", "The Drumhead")