The Mk48 torpedo is not configured for a nuclear warhead.
The long retired Mk45 ASTOR (Anti-Submarine Torpedo) was deployed from 1963 to 1975. It carried the W-34 nuclear warhead.
http://www.navweaps.com/Weapons/WTUS_PostWWII.htm
Other interesting anti-submarine weapons included the Mk7 Betty, Mk105 Hotpoint, Mk34 Lulu depth bomb, B57 depth bomb (which I worked), ASROC, and the B-90 (cancelled by Congress).
Yours, Mike