hang on hang on.... I read David Weber.
He never says in the Honor Harrington series that the fusion cores cause a chain reaction etc... in most of his books its the magbottle FAILURE that's the issue, causing super dense, kept under pressure, million degree+ plasma to expand outwards.
now, correct me if I'm wrong, but that would vaporise pretty much everything around it, and could certainly cripple a vast portion of a ship it's in, if the ship is about six thousand meteres in length.
When a Mag bottle in a core in those books goes, the ships are often left as hulks, damaged by weapon fire, and huge gaping holes and twisted metal in the area of the core if the bottle goes/breaks the ships back (ie melting THROUGH it before the reaction stops).
Even if they eject the core, the expanding plasma cloud would melt INTO the hull, doing extreme damage.
Anyone else read Weber? I'm trying to think where he states a fusion core failure explodes and causes a chain reaction style explosion...