Nuclear fission and fusion

What is nuclear fission?

the splitting of a large and unstable nucleus (eg uranium or plutonium)

How can nuclear fission occur?

• spontaneously (rare)

• unstable nucleus must first absorb a neutron

Process of nuclear fission inside a nuclear reactor

• neutron absorbed by an unstable uranium nucleus

• nucleus splits into two parts (daughter nuclei)

• 2/3 neutrons are released

• gamma rays are emitted

• energy is released

What energy do all products of nuclear fission have?

kinetic energy

What can be done with the neutrons that are released in the fission reaction?

They can go on to start a chain reaction (another fission reaction)

Why does a chain reaction need to be controlled?

To control the energy released

what is an explosion caused by a nuclear weapon caused by?

An uncontrolled chain reaction

How is a nuclear fission reaction controlled?

• With control rods (made from elements such as boron)

• Control rods are lowered into the reactor

• neutrons are absorbed (by boron / control rods)

• there are fewer neutrons

• chain reaction slows down / stops

What is the energy released in nuclear fission used for?

to heat up water and turn it into steam, which can drive turbines which are connected to an electricity generator

Pros of nuclear fission

• uranium/plutonium fuel is relatively cheap

• Releases a large and steady amount of energy

• Does not produce greenhouse gases such as carbon dioxide

Cons of nuclear fission

• power plants are very expensive to build

• Nuclear waste produced is expensive to get rid of (has to be buried underground in special bunkers)

• Risk of major disaster if plant malfunctions (unlikely, but makes people suspicious of using nuclear energy)

what is nuclear fusion?

the joining of two light nuclei to form a heavier nucleus

Why is energy produced in nuclear fusion reactions?

In this process some of the mass from the original nuclei may be converted into the energy of radiation instead of being transferred to the new larger nucleus.

Why can’t nuclear fusion be carried out on Earth?

• Fusion only happens at very high temperatures (10,000,000 degrees) to overcome the repulsion of the positively charged nuclei

• Only occurs in stars (usually hydrogen nuclei fusing to become helium nuclei)

Advantages of nuclear fusion

• doesn’t produce any radioactive waste

• Can easily make the hydrogen that is needed as fuel

• Produces more energy than fission