Nuclear power is popular again, mainly because of the rising cost of oil and natural gas, and decades of problem free operation for hundreds of nuclear power plants (at least those not designed in the defunct Soviet Union.) Now there are serious proposals to install nuclear power plants in merchant ships. This was tried once before, in the 1950s. The NS (nuclear ship) Savannah cost $350 million (adjusted for inflation), with 60 percent of the cost being the nuclear power plant. Oil cost a lot less back then, and nuclear power plants a lot more. Thus the Savannah was only in service for ten years, being retired, and turned into a museum ship, in 1972.
Since then, oil has become a lot more expensive, and nuclear power plants a lot cheaper. There are a new generation of nuclear power plants that are smaller, cheaper and more reliable than anything available in the 1960s. So ship builders are looking at nuclear power again. The math is pretty straightforward. Nuclear fuel costs half a dollar per million BTU, while coal costs $3, and oil $12 (and rising). Deliver a simple and reliable nuclear power plant, and ship builders will install it.
Not only is nuclear cheaper, but it’s a lot cleanerr. Ships burn very dirty fuel, and the world's merchant fleet puts out as much pollution each year as 150 billion automobiles. That causes 60,000 early deaths a year from lung cancer and heart disease.
But the new generation of small, "appliance (as in ease of use) grade" nuclear power plants will get a hostile reception from a lot of people, and that might keep the steam ships going off oil for some time to come. Meanwhile, many countries, or port cities, have laws banning nuclear powered ships completely. While nuclear powered merchant ships are a growing possibility, they are not a sure thing either.