4.4.4.1 - Nuclear fission

What is nuclear fission?

A type of nuclear reaction that is used to release energy from large and unstable atoms

What occurs during nuclear fission?

Nuclear fission refers to the splitting up of a large and unstable nucleus into smaller atoms

Name two nuclei that are often used for nuclear fission.

E.g. uranium or plutonium

What type of nuclear fission is rare?

Spontaneous nuclear fission is rare (naturally occurring)

Why is spontaneous nuclear fission rare?

As - usually - for fission to occur the unstable nucleus must first absorb a neutron

What dos the nucleus undergoing fission split into?

The nucleus undergoing fission spits into two smaller nuclei - roughly equal in size

What are all the products of nuclear fission?

• Two new lighter elements

• Gamma rays

• Two or three neutrons

What do all these products have?

All the products (so the two lighter elements and the neutrons) have kinetic energy

Why are gamma rays released?

The release of gamma rays is the release of all the energy that didn’t come kinetic energy

What can the energy released by the fission reaction be used for?

The energy released by the fission reaction can be used to heat water

How can one nuclear fission start a chain reaction?

If any of the neutrons (released by the previous nuclear reaction) are slow enough to be absorbed by another nucleus it can start a chain reaction

What can uncontrollable chain reaction cause?

Uncontrollable chain reaction can cause explosions - due to lots of energy being released

Such as in nuclear weapons

How is the amount of energy produced by fission in a nuclear reactor controlled?

The amount of energy produced by fission in a nuclear reactor is controlled by controlling (the speed of) the chain reaction

What is used to control chain reactions?

Control rods

How are control rods used to control chain reactions?

Control robs are lowered and raised inside a nuclear reactor

This therefore absorbs neutrons and so can slow down the chain reaction

And so the amount of energy released is controlled

By control rods absorbing neutrons, how do they slow down a reaction?

By absorbing neutrons, a control rod prevents the neutrons from causing further fissions.

Thus, when a control rod is inserted into a nuclear reactor it reduces the number of free neutrons available to cause the atoms to fission.

What is the energy produced in a nuclear reactor often used for?

The energy released from the fission reactions is used to boil water to drive turbines.