What is difference between REACTORS and vessels?

The difference between avascular and vascular is that avascular is defined as having few or no blood vessels. Vascular is defined as relating to the blood vessels of the body.

Electricity, or propulsion in naval vessels.

Heavy water reactors uses heavy water (D2O) as moderator while Light water reactors uses Light water (H2O) as the moderator. Light water reactors are much more expensive than heavy water reactors because they require enriched uranium

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 difference is the heart is a organ and the blood is an substance

The cariovascular system includes the blood, the vessels and the heart.

In naval vessels, especially submarines and aircraft carriers

Bus reactors are the inductors that limit voltage transients between a couple sections of a bus or a couple separate buses. Line reactors are capacitor or user amperage stabilizers placed at points of usage or right before transformers.

A shunt is a passage between blood vessels which diverts blood. A stent is used to prop open an artery.

one is an organ the other a substance

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.

Red vessels are the vessels transporting oxygen-rich blood. They transport the oxygen from the heart to the body parts. (aorta) Blue vessels are the vessels transporting carbon dioxide-rich blood. They transport the carbon dioxide to the heart, to the lungs to be breathed out.

Animals and plants are different because animals have one system of vessels and plants have two systems of vessels that aren't connected.

The terms, afferent and efferent, refer to nerves. However, if applied to the circulatory system, the afferent vessels would be veins and the efferent vessels would be arteries.

Afferent vessels: Carry fluid/blood from body organ to heart. Efferent vessel : Carry fluid/blood from heart to body organ.