Sub and ship reactors are effectively sealed units that are not intended to be refueled on a regular basis. They can be serviced and refueled eventually, but it

Sub and ship reactors are effectively sealed units that are not intended to be refueled on a regular basis. They can be serviced and refueled eventually, but it is a major overhaul to do so. https://en.wikipedia.org/wiki/Refueling_and_overhaul https://en.wikipedia.org/wiki/Refueling_and_overhaul