Why submarine reactors complicate surface ships

What makes submarine reactors difficult to use in surface ships?

Their cooling and emergency assumptions are designed around a submerged hull, so a surface installation needs additional pumping and safety provisions.

Submarine plants operate surrounded by readily available seawater and within a hull designed around underwater emergencies. That environment shapes both ordinary cooling and the assumptions behind emergency flooding or heat removal. A surface ship cannot rely on water entering under the same pressure and must provide additional pumping and safeguards. Directly reusing a submarine plant is therefore less simple than the shared label of nuclear propulsion suggests.