What is difference between REACTORS and vessels?
What is reactor define it briefly
In anatomical terms, "vessels" means a carrier of something. Veins are vessels... specifically, they are blood vessels. However, not all blood vessels are veins; some of them are, but some of them are capillaries, and some of them are arteries. It's rather like asking what's the difference between a horse and a Clydesdale. All Clydesdales are horses, but not all horses are Clydesdales.
The primary use of nuclear reactors is to produce electricity, which is the only way to use nuclear energy on a large scale. Small reactors are used for research, and are also used to produce radioisotopes for medical and industrial use. Reactors are also used to power some naval vessels and submarines. Reactors have also been used to produce plutonium and tritium needed to make nuclear weapons.