Nuclear powered cargo ships are generally not viable outside of a few niche roles. Trained operators are too expensive and in limited supply. Many nations won't allow such vessels into port due to concerns over security and accidents. There is an obvious risk of terrorist attacks to steal nuclear material or just cause a radiological incident. And several large merchant ships sink every year; no one wants a sunken reactor contaminating their coastal waters.

Even navies make very little use of nuclear power. It is mostly only for aircraft carriers and submarines. Experiments with nuclear powered surface combatants were mostly failures.

A more viable approach would be to locate the nuclear reactors on land where they can be operated more safely and economically. Then use the generated heat and power to manufacture carbon neutral synthetic fuels to power ships.