I think there are a number major reasons this will never happen.
Weight....reactors are very heavy. You also have to include the weight of a steam turbine, multiple heat exchangers, reduction gears and condenser when you count the weight of the
power plant.
Safety and Politics...we all know the hazards of radiation. Most countries I imagine would ban any yachtie who wants to bring a nuclear reactor into their country.
Expense...I cant imagine a nuclear reactor ever being
cheap to operate.
Knowledge....these are not simple devices.
National
Security...just what the world needs is for enriched uranium to fall into the wrong hands. Can you imagine someone making a dirty bomb with one of these?
BTW, I am all for nuclear
power but I don't think that nuclear power for yachts is something we will ever see in our lifetimes.