HEU, LEU fuelled or whatever, the design of the reactor, electrical power and propulsion units is not independent of the design of the rest of the boat. It is a fallacy to think that you can easily 'nuclearise' an existing design. If you want a nuclear powered boat buy one that was designed as a nuclear powered boat. It will be cheaper and quicker than designing a new boat that happens to have some bits that look like another conventional boat.
Systems integration is hard work.
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