4.4 Nuclear fission and fusion (Triple)

Question 1

What is nuclear fission?

Answer 1

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

Question 2

Give an example of a fissionable isotope

Answer 2

● Uranium-235
● Plutonium-239

Question 3

What usually needs to happen to induce fission?

Answer 3

The unstable nuclei must absorb a neutron - spontaneous fission (where no neutron absorption occurs) is rare.

Question 4

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

Answer 4

2-3 neutrons
Gamma rays
Energy

Question 5

What form of energy do all fission products have?

Answer 5

Kinetic energy

Question 6

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

Answer 6

1. An unstable nuclei absorbs a neutron
2. The nucleus undergoes fission and releases 2-3 further neutrons
3. These induce more fission, which results in a chain reaction

Question 7

What is the consequence of an uncontrolled chain reaction?

Answer 7

The rate of fission events becomes too high and results in the production of too much energy. This can lead to a nuclear explosion.

Question 8

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

Answer 8

Fuel rods, control rods, moderator

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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 roads inserted, the slower the rate of fission.

Question 11

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

Answer 11

Fissile nuclei

Question 12

What is nuclear fusion?

Answer 12

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

Question 13

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

Answer 13

Deuterium and Tritium

Question 14

Which releases more energy, nuclear fission or nuclear fusion?

Answer 14

Nuclear fusion

Question 15

Explain the difficulty of generating energy through nuclear fusion

Answer 15

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

Question 16

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

Answer 16

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