How come we have nuclear powered submarines and not large ships or cruiseliners?
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.