4.4.4 - Nuclear Fission and Fusion (Physics Only)

Atomic Structure

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 or 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 to 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 a nuclear reactor?

1. Fuel rods
2. Control rods
3. 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

What is nuclear fusion?

The joining of two light nuclei to produce a heavier nuclei and release energy

Name two isotopes of hydrogen which are commonly used in nuclear fusion.

Deuterium and Tritium

Which releases more energy, nuclear fission or nuclear fusion?

Nuclear fusion

Explain the difficulty of generating energy through nuclear fusion.

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them

Explain why nuclear fusion is currently not a viable way to produce energy on Earth.

With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss