|Fig. 1: NS Savannah, the only example of a U.S. built nuclear powered civilian merchant vessel (Source: Wikimedia Commons)|
Nuclear Marine Propulsion, the use of a nuclear power plant to power the motion of a marine vessel, has been present in the naval forces of some of the world's most prominent navies for decades. The same is not true for civilian projects (Fig. 1). Nuclear Marine Propulsion allows vessels to operate for years without needing to refuel, in sharp contrast to the ubiquitous reciprocating diesel engine, which is bound by the well-understood constraints of fossil fuels. Despite this advantage, nuclear powered vessels have unique and significant demands for infrastructure, expertise, and security, all of which impede their ability to disrupt and displace traditional fossil-fuel engines in their position as the power plant of choice for civilian commercial vessels.
All naval vessels require shore facilities to accommodate their maintenance, refueling, and miscellaneous logistical needs. Nuclear-powered vessels are no exception. Unfortunately for nuclear powered ships, specific infrastructure and personnel trained to maintain and service nuclear vessels are necessary. Nuclear naval shore facilities encumber civilian nuclear commercial fleets with an enormous up-front fixed cost - one that seems highly unattractive considering that existing shore facilities and fossil-fuel engines still accomplish their missions economically.
While certain militaries, in particular the U.S. military, have made significant investments into their naval fleets and their corresponding nuclear naval shore facilities, the economics remain problematic. By 1999, the U.S. military had commissioned more vessels with nuclear reactors than there were nuclear power facilities present on the U.S. mainland.  Despite this, the U.S. military still opts to equip the majority of its surface warfare fleet with fossil-fuel engines. The strategic value of not needing to refuel is outweighed by the hefty price tag and subsequent maintenance cost of a nuclear power plant. This is despite the U.S. Navy possessing the lions share of the world's nuclear naval shore facility infrastructure.
As with any ship, a trained crew is necessary in order for the ship to operate. Nuclear ships require nuclear engineers, who are distinct in their training from regular engineers. The greater complexity of a nuclear reactor relative to a traditional diesel power plant generally demands both a higher compensation for engineering staff and a greater number of engineering staff. Legal issues regarding this compensation and staffing need were a significant problem for the only U.S. example of a nuclear merchant vessel, the NS Savannah. 
Up until now there have been exceptionally few examples of nuclear powered civilian vessels. There are only four nuclear powered civilian merchant cargo ships in existence, with only one, Russia's Sevmorput still operational. These projects have enjoyed excellent publicity and financial backing and support from their host governments. But it has not been enough. If nuclear marine propulsion were to enter the mainstream, there would be an enormous question of securing both the vessels and their shore facilities against proliferators and other agents who may attempt to misuse their fuel elements for sinister purposes. While an accurate estimate is difficult to make, the cost of security infrastructure in other fields, such as aviation, has a historical precedent of being very high.
Civilian nuclear marine power remains a distant dream, with no real progress currently underway. The economic burden of switching to a nuclear infrastructure is too great for benefits that are too uncertain. The only instance where we see nuclear marine propulsion taking root is in the navies of highly developed nations. But this is largely due to valuing the strategic benefit of infrequent refueling over the cost. Until the economics are sensible for nuclear marine propulsion, its commercial application will be blocked by reciprocating diesel engines and other less costly concepts.
© Erik Holmvik. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 P. Tsvetkov, ed., Nuclear Power - Deployment, Operation and Sustainability (InTech, 2011).
 "First Nuclear-Powered Merchant Vessel," American Society of Mechanical Engineers, 15 Oct 83.