P4 - Nuclear Power

Question 1

What are Nuclear power stations powered by?

Answer 1

Nuclear power stations are powered by nuclear reactors.

Question 2

How do nuclear reactors produce electricity?

Answer 2

• In a nuclear reactor, a controlled chain reaction takes place in which uranium or plutonium atoms split up and release energy in the form of heat, this is nuclear fission.
• This heat is then used to heat water to produce steam
• This steam turns a turbine which drives a generator that produces electricity.

Question 3

What is Uranium 235 used for?

Answer 3

Uranium 235 is used in some nuclear reactors and bombs.

Question 4

What is the process of the splitting up of uranium 235?

Answer 4

• Uranium 235 is quite stable on its own, so it needs to be made unstable before it will split.
• Materials can become radioactive when they absorb extra neutrons, so slow moving neutrons are fired at the uranium 235 atom.
• A neutron joins the nucleus to create U-236, which is unstable
• The U-236 splits into two smaller nuclei, releasing loads of energy and producing radioactive waste.
• Split nucleus also releases 2 or 3 fast moving neutrons which go onto produce a chain reaction.

Question 5

Why is the splitting of U-236 a chain reaction?

Answer 5

• To get a useful amount of energy, loads of U-235 atoms have to be split, so neutrons released from previous fissions are used to hit other U-235 atoms.
• Each split uranium nucleus releases more than one neutron
• These neutrons cause further nuclei to split, releasing more neutrons, which cause more nuclei to split and so on.

Question 6

What is an example of an out of control chain reaction?

Answer 6

Nuclear bombs are out of control chain reactions.

Question 7

How are chain reactions in nuclear reactors controlled?

Answer 7

They are controlled using control rods.

Question 8

How do control rods control nuclear reactoins?

Answer 8

• Free neutrons in the reactor “kick start” the fission process
• Neutrons collide with surrounding atoms, causing them to split and the temperature in the reactor to rise
• Control rods, often made of boron, limit the rate of fission by absorbing excess neutrons
• This stops the reaction going out of control, but allows enough neutrons to hang around to keep the process going.