Some navy ship are nuclear powered. It's cost prohibitive for cruise ships, who wants to go that fast on the water anyway.

Cruise lines are notorious for hiring the cheapest labor possible. Nuclear techs do not fall under that category. Another reason is the security involved with a reactor nowadays, would be almost impossible on a cruise ship or commercial vessel. There were nuke freighters back in the 60s-70s. The "Savannah", "Otto Hahn",and the "Mutsu". The Russians have a nuke icebreaker, the name escapes me right now.

There are other reasons that are not touched on here. Part of the expense is due to personnel. The Navy pays their reactor operators the same as any other person of equivalent paygrade so they can ignore that cost. A civilian RTO would want so much money that the cruiseline would balk at hiring them. The fuel used in military reactors is "a little" purer than the stuff you see in a shore-based reactor, and that purification costs money. The purer you get, the more it costs. By the time you get to milspec purity, the cost would be so prohibitive that no civilian company would want to foot the bill. There is limited space onboard a nuclear vessel. Cruise ships NEED space for their ballrooms and pools and passenger accommodations. You can't stack paying passengers 3-4 high in a room with hundreds of other passengers like you can with an aircraft carrier, or hot-rack 'em like you do on a sub.

We may have these already, the public just may not be aware of it.

Not just submarines, we have nuclear powered aircraft carriers and cruisers.

The United States also has nuclear powered air craft carriers, and for a while, we had nuclear powered missile cruisers which were designed to be high speed escorts for the carriers. The nuclear cruisers were eventually decommissioned and no more were built. The U.S. built one nuclear powered merchant vessel in 1959, the N/S Savannah, but her high operating costs at the time resulted in her being decommissioned in 1975. She was built to be a cargo/passenger ship and was operated as such from 1965 to 1971, and was decommissioned in 1972. The N/S Savannah was really a concept ship, born out of the "Atoms for Peace" initiative. The reactor first achieved critical operations in 1962. After a period of testing and research, the ship was finally put into service in 1965. The ship operated wonderfully, by all accounts from those who operated her. But because she was designed as much to be a showboat as anything else, she was not optimally designed for economical cargo transport. She was built to demonstrate the technical feasability of nuclear power on a merchant ship, not as a profit venture. A lot of sacrifices were made in size and space because of this, so she did not turn enough of a profit to become a successful, profitable merchant vessel. Had she been designed from the start to be a large cargo vessel, she would have likely been in operation for many more years. Ironically 2 years after her decommissioning, the high costs of fossil fuel would have made her break even on operating costs, even with her cargo limitations. In her short term of service, she saved over 29 MILLION gallons of fuel oil. Only three other nuclear powered merchant ships were ever built: Germany: N/S Otto Hahn Japan: N/S Mutsu (Never carried any cargo) Russia: N/S Sevmorput (Cargo/ice breaker, still in service) http://www.nssavannah.net/?ID=31 http://www.globalsecurity.org/military/systems/ship/savannah11.htm http://en.wikipedia.org/wiki/NS_Savannah http://images.google.com/images?hl=en&rlz=1T4RNWN_enUS256US257&resnum=0&q=n/s+savannah&um=1&ie=UTF-8&ei=CjjXSozMF4bCNvz3kcsI&sa=X&oi=image_result_group&ct=title&resnum=4&ved=0CB0QsAQwAw http://en.wikipedia.org/wiki/List_of_civilian_nuclear_ships