Fission & Fusion

Question 1

What happens when you break apart really big nuclei or join together really small nuclei?

Answer 1

Lots of energy is released

Question 2

What is fission?

Answer 2

Splitting a nucleus to release energy

Question 3

What happens when Uranium-235 undergoes fission?

Answer 3

• nucleus splits & releases energy
• uranium-235 nucleus absorbs neutron, it alters number of protons & neutrons making it unstable
• unstable nucleus splits into 2 daughter nuclei
• these neutrons can be absorbed by another nucleus of uranium, which will eventually split into 2 nuclei & more neutrons in a chain reaction

Question 4

What are atomic bombs?

Answer 4

• energy released during nuclear fission chain reactions
• contain radioactive isotopes of uranium/plutonium

Question 5

How do nuclear reactors produce energy?

Answer 5

fission

Question 6

What do moderators do in nuclear reactors?

Answer 6

Reduces speed of neutrons, so they are more likely to be absorbed by a nucleus

Question 7

What do control rods in nuclear reactors do?

Answer 7

absorb some of the extra neutrons so only a single neutron is released per fission event

Question 8

In a nuclear reactor, what does the concrete shield do?

Answer 8

• covers the reactor
• so no radiation can penetrate out

Question 9

What are moderators in nuclear reactors usually made out of?

Answer 9

graphite

Question 10

What are control rods in nuclear reactors usually made out of?

Answer 10

boron

Question 11

What does the nuclear reactor do with the energy produced by fission?

Answer 11

• Kinetic energy of neutrons is captured and is used to heat water
• Water then evaporates into steam
• Steam drives a turbine & drives a generator, producing electricity

Question 12

What are the advantages of producing energy by nuclear fission?

Answer 12

• doesn’t produce polluting gases e.g. CO2, so doesn’t contribute to global warming
• low fuel costs
• only small amounts of fuel are needed, so it reduces effects of mining & transportation on environment
• power stations have a long life time

Question 13

What are the disadvantages of producing energy by nuclear fission?

Answer 13

• radioactive waste so needs to be carefully disposed of
• accidents can be catastrophic e.g. Chernobyl
• lots of hot water is produced so can harm marine life when disposed of
• can’t respond quickly to changes in electricity demand

Question 14

What is fusion?

Answer 14

• 2 small, light nuclei collide at high speed & join together to make 1 heavy nucleus
• occurs in stars where 2 hydrogen nuclei fuse to form helium nucleus
• during this, some mass in converted to energy, which radiates from star

Question 15

Why does fusion require extreme conditions?

Answer 15

It’s the joining together of 2 positive nuclei which would repel in normal conditions