Unit 5 - Nuclear Energy

Question 1

Define Binding energy of a nucleus.

Answer 1

The work done to seperate a nucleus into its consituent protons and neutrons

Question 2

Define mass defect.

Answer 2

The difference between the mass of the separated nucleons and the mass of the nucleus.

Question 3

Draw a graph of binding energy per nucleon against mass number.

Answer 3

Question 4

Why is energy released in a fission reaction?

Answer 4

• Fragments repel each other with enough force to overcome the strong nuclear
• The fragment nuclei and fission neutrons gain kinetic energy
• The fragments have a higher binding energy so the energy released is equal to the change in binding energy

Question 5

Outline the steps in a thermal nuclear reactor.

Answer 5

• The depth of control rods in the reactor control the number of fission neutrons which cause further fissions.
• The fuel rods are surrounded by a moderator which slows fission neutrons to thermal speeds so that fission may happen
• The masss of the fissile material must be greater than the critical mass.

Question 6

What safety features does a thermal nuclear reactor have?

Answer 6

• Thick steel vessel to withstand high pressure and temperature and absorb some radiation
• Housed in a building with very thick concrete walls
• Can insert control rods fully to stop the reaction in an emergency
• Sealed fuel rods are handled by robots

Question 7

What is high level radioactive waste?

Answer 7

Spent fuel rods, reaction vessel

Question 8

How can high level radioactive waste be disposed of?

Answer 8

Stored in cooling ponds for up to a year because they continue to release heat due to further fission.

Then stored in steel casks deep underground and can be vitrified by mixing with molten glass.