Comment by LgWoodenBadger

nuclear submarines are first and foremost built as a protective sarcophagus for the powerplant, and that's on top of submarines being designed to compartmentalize damage, anyway.

i.e. if it could totally destroy itself with a full payload that'd be a very bad design choice, not that there wasn't plenty of bad choices wrt the kursk.

They are designed for war. They have to assume that it will be hit at some point - you still want it to return as many of the highly trained people on board back home as possible. If you can repair it so much the better. They can't always meet this goal (the enemy goal is to make that impossible), but it is a design goal of any reasonable navy.