4.4.1 - Nuclear Fission

What is nuclear fission?

The splitting of large, unstable nuclei to form smaller, more stable nuclei (+ the emission of spare neutrons).

Give an example of a fissionable isotope.

Uranium - 235

What usually needs to happen to induce fission?

• The unstable nuclei must absorb a neutron.

• Spontaneous fission (where no neutron absorption occurs) is rare.

Alongside two smaller nuclei, what else is emitted in a fission reaction?

• Two or three neutrons.

• Gamma rays.

• Energy.

What form of energy do all fission products have?

kinetic energy

What takes place during a chain reaction in a nuclear reactor?

• An unstable nucleus absorbs a neutron.

• The nucleus undergoes fission and releases 2/3 further neutrons.

• These induce more fission, which results in a chain reaction.

What is the consequence of an uncontrolled chain reaction?

• The rate of fission events becomes too high and results in the production of too much energy.

• This can lead to a nuclear explosion.

What are the three main components of the core of a nuclear reactor?

• Fuel rods.

• Control rods.

• Moderator.

What is the role of the moderator in a nuclear reactor?

To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.

How is the chain reaction in a fission reactor kept under control?

• Control rods are positioned in between the fuel rods.

• The rate of fission is controlled by moving these rods up and down.

• The lower the rods are inserted, the slower the rate of fission.

What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?

fissile nuclei