P2.6 Nuclear Fission + Fusion

Question 1

Define nuclear fission?

Answer 1

The splitting up of a nucleus

Question 2

Explain the process of a nuclear fission chain reaction.

Answer 2

• Slow moving neutron is absorbed into uranium/plutonium nucleus
• The nucleus becomes unstable and splits
• This releases 2/3 neutrons which might hit another nucleus, keeping the reaction going
• This also splits into 2 smaller nuclei which are radioactive (wrong number of neutrons in them)

Question 3

What 2 types of fuel are usually used in nuclear fission?

Answer 3

• Plutonium-239

- Uranium-235

Question 4

Describe the process in a nuclear reactor.

Answer 4

• Atomic nuclei split and release heat energy
• This heats water to make stream
• This drives a steam turbine connected to a generator

Question 5

What is the advantage to nuclear fission?

Answer 5

Gives out a high amount of energy compared to a chemical reaction

Question 6

What is are 3 disadvantages to nuclear fission?

Answer 6

• Waste is very radioactive, hard to dispose of safely
• High cost of power plant and decommissioning
• Radiation leaks are dangerous

Question 7

What happens in nuclear fusion?

Answer 7

Two light nuclei (e.g hydrogen) join to create a larger one, releasing energy

Question 8

Where does nuclear fusion tend to happen?

Answer 8

In stars

Question 9

What are the two advantages of nuclear fusion?

Answer 9

• Gives out far more energy than fission

- No radioactive waste

Question 10

What are the two disadvantages of nuclear fusion?

Answer 10

• High temperatures and high pressures needed to hild hydrogen
• You need a strong magnetic field

Question 11

Name (don’t explain) the steps in the star cycle.

Answer 11

• Protostar
• Star birth
• Main sequence star

Bigger than sun:

• Super red giant
• Supernova
• Neutron star
• Black hole (if star big enough)

Same size/smaller than sun:

• Red giant
• Planetary nebula
• White dwarf
• Black dwarf

Question 12

What happens to make a protostar?

Answer 12

• Stars form from dust and gas clouds

- Gravity makes this spiral in together (protostar)

Question 13

How does the birth of a star occur?

Answer 13

• When the gravitational energy is converted to heat energy so the temperature rises
• When the temperature is high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
• This gives out massive amounts of heat and light

Question 14

How does a star stay stable during its main sequence period?

Answer 14

• Heat created by fusion creates outward pressure to balance gravity pulling everything inwards
• Massive amounts of hydrogen consumption maintains energy output for millions of years

Question 15

How long does a star stay as a main sequence star?

Answer 15

Several billion years

Question 16

Why do stars become red giants/red super giants?

Answer 16

• Eventually hydrogen begins to run out
• Heavier elements e.g iron are made from the nuclear fusion of helium
• Stars become red as the surface cools
• The star swells

Question 17

What happens during a supernova?

Answer 17

• Big stars glow brightly again
• They undergo fusion and expand and contract several more times
• This forms elements heavier than iron and ejects them into the universe - these form new planets and stars

Question 18

How do big stars become neutron stars?

Answer 18

The supernova throws out outer layers of dust and gas leaving behind a very dense core

Question 19

What happens during a planetary nebula?

Answer 19

• The star becomes unstable
• It ejects its outer layer of dust and gas
• This leaves behind a dense and heavy core (white dwarf) which cools to become a black dwarf