How does a nuclear reactor work?

Question

Please tell in brief.

Answer 1

Briefly:

- The fuel is Uranium - 238 nuclei, it absorbs a single neutron causing it to become unstable.
- The instability causes the atom to decay (split apart) releasing 3 more neutrons, a krypton and barium nucleus.
- These new neutrons go on to be absorbed by other uranium nuclei and a chain reaction is continued.
- This is called nuclear fission, energy is released becasue there is a difference in mass between the uranium and the products form. This 'loss' is mass is called the mass defect, and is converted to energy via the famous equation E = mc^2.
- In reactors this energy is trasferred as heat which heats water to make steam to drive turbines and generate electrcity.
- The nuclear reactions are kept from going out of control by lowering control rods, which absorb neutrons and prevents anymore fission.
- If this fails, a reactor can explode due to build up of energy, see Chernobyl nuclear disaster.

That is as brief as I can make it.

Answer 2

All our current functional nuclear reactors are fission reactors. Fission is the process of splitting the nucleus of an element into pieces. The nucleus is made of protons and neutrons. It is the number of protons that determines what kind of element the atom is. For example, if it has 1 proton, it's hydrogen. If it has 6 protons, it's carbon. If it has 92 protons, it's uranium.

A certain isotope of uranium (238) is unstable. It tends to break apart, releasing energy. If you gather a bunch of uranium 238 in one place, it breaks down even faster releasing more energy (in the form of heat). If you get enough of it really close together, it breaks down all at once, releasing so much energy that it explodes. This is how nuclear weapons work.

Inside a nuclear reactor, there are rods of uranium 238. In-between are rods made of carbon. The carbon rods interfere with the process by blocking the neutrons that fly out as the uranium atoms break apart. It is these neutrons that cause other uranium atoms to break apart. Basically, you get a bunch of uranium rods near enough to each other that they get very hot, but not so close that they explode. You now have a steady source of heat. This heat is used to boil water, and the steam rushes through turbines (big fans) which are connected to electric generators. Thus we get electricity from the nuclear reactor.

Answer 3

U-235 or Plutonium -239. U-238 is not used as fuel. It is the most common isotope.

Answer 4

There is a very good explanation at http://science.howstuffworks.com/fusion-reactor.htm that starts simple and gets deeper if you want to.