How does a nuclaer reactor work?

Answer 1

A nuclear reactor is composed of the following:

1. fissionable fuel
2. control rods
3. safety rods
4. moderator (omitted in a fast fission reactor)
5. cooling system

Most reactors are what are called thermal reactors, what this means is slow (aka thermal) neutrons are used in the chain reaction to cause fissions in the fuel. A moderator (e.g. water, graphite, heavy water) is required to slow the fast neutrons emitted by fissions to this slow speed before too many of them are captured by uranium-238, which removes them from the chain reaction.

Fast reactors do not need a moderator as they use highly enriched fuel with most of the uranium-238 removed.

The control rods can be inserted and removed as needed and are made of a material (e.g. cadmium) that easily captures neutrons, which removes them from the chain reaction.

The safety rods are only inserted in an emergency, in some reactor designs they cannot be removed once inserted. Like the control rods they are made of a material (e.g. boron, cadmium) that easily captures neutrons, which removes them from the chain reaction.

The cooling system removes heat from the reactor (and in power reactors carries it to the turbine room where it is used to generate electricity). Frequently there are redundant cooling systems, including an emergency one that floods the reactor core with water.

Starting a nuclear reactor is requires a special procedure to do it safely:

1. Insert all control rods as far as they go.
2. Attach a neutron source to the reactor.
3. Measure the neutron multiplication factor (neutron flux ÷ neutrons provided by the neutron source) of the reactor, it will be low and constant.
4. Slightly remove one control rod.
5. Measure the neutron multiplication factor of the reactor, it will be a bit higher than before and constant.
6. Repeat steps 4 and 5 until the neutron multiplication factor is no longer constant, but slowly rises on its own without further removal of control rods. The reactor is now very very slightly supercritical.
7. Remove the neutron source from the reactor.
8. The neutron flux in the reactor should settle to a constant value again and stay there. The reactor is now exactly critical.
9. The reactor is now fully started. To increase power level, slightly remove control rods. To decrease power level, slightly insert control rods.

Answer 2

Neutron radiation turns fertile material into fissionable material. Often reactors are designed to be both fission reactors and breeder reactors at the same time, though this is not a true breeder reactor.

Answer 3

Uranium-235 sometimes spontaneously undergoes fission. It does this naturally, making two much lighter new atoms, and three neutrons. When one of these neutrons hits another atom of U-235, it causes that atom to undergo fission, releasing three more neutrons. If there are a lot of U-235 atoms around, this reaction can go faster and faster. If it does this, it is said to have critical mass.

If the reaction is allowed to continue in an uncontrolled manner, there is an explosion. But if it is controlled, it can be used in a reactor. The nuclear fission reaction gives off a lot of heat because some of the mass in the atom is converted into energy. This reaction is millions of times more powerful than the oxidation of carbon.

The reactor is used as a heat source. For example it might be used to boil water into steam. This is then used to drive a turbine, which turns a generator, producing electricity.

Answer 4

A nuclear reactor work because of the fuel rods where radioactive elements are stored such as uranium. the fuel rods are put in water where the atoms split causing heat it then turns the water into steam which turns turbines.