A quick solution:
every time a capital/super/titan tries to undock from a citadel they have a 0.01%/0.03%/0.05% of chance of getting tangled on something and explode. Add a 0.01%/0.03%/0.05% chance that citadel explodes as well on when a cap/super/titan goes poof inside it.
Let the Happy Accidents happen! 