Well geez, every one seems to be answering for the reactor that is used to propel the ship on its merry way. Were you asking about the fissile material in the armament (like 24 missiles w/8 warheads)?How much fissile material, in kilograms, would, say, an Ohio-class submarine carry?
If it's classified, what would be about a good estimate?
My specialty was Los Angeles class, but both are classified so a good estimate - enough to get the job done! Borek was close for one of the answers above with one of his estimates and being close counts in nuclear bombs!