I wouldn't say "many"; nuclear-powered vessels generally are ones that are going well beyond Earth's orbit. They also aren't "normal" nuclear reactors, since th

I wouldn't say "many"; nuclear-powered vessels generally are ones that are going well beyond Earth's orbit. They also aren't "normal" nuclear reactors, since they use the heat from radioactive decay to power thermocouples, as opposed to sustaining an active fission reaction like most nuclear power plants here do.