Answer (1 of 5): I do not know what you mean by an "on-demand" boiler. A US Naval reactor (submarine) uses the reactor as a source of heat to make steam. The steam is used to spin a turbine — either to produce electricity or to drive the sub. Even if …Learn More
Nuclear submarines have always used steam for propulsion; they create steam in a steam generator (very similar to a boiler). That steam then is piped to 1) gas turbine generators producing electricity, and 2) to turbines connected to reduction gears that are connected to the shaft and propellers, thus providing propulsion.Learn More