nuclear fission and fusion (topic 4)

Question 1

the smaller masses may be attracted by the star and become…

Answer 1

planets

Question 2

Answer 2

uranium-235

Question 3

describe what happens to the nucleus of an atom during nuclear fission (2)

Answer 3

• splits into two smaller parts
• and two/three neutrons

Question 4

Answer 4

• steam
• turbine
• generator

Question 5

Answer 5

protostar
red giant
black dwarf

Question 6

(protostar, red giant, black dwarf)

Answer 6

• Alpha Centauri A
• stars same size as Sun form black dwarfs

Question 7

describe the process of nuclear fission (3)

Answer 7

• uranium nucleus absorbs a neutron
• nucleus becomes unstable and splits into two two daughter nuclei and several neutrons
• releases energy in the process

Question 8

the diagram shows a nuclear fission reactor, label the following parts on the diagram:
- control rod
- moderator
- fuel rod
- shielding
- reactor

Answer 8

Question 9

explain the process of nuclear fusion (2)

Answer 9

• two light nuclei join together / combine
• to form a heavier nucleus, releasing energy in the process

Question 10

state the conditions necessary for nuclear fusion to occur (2)

Answer 10

• extremely high temperature
• high pressure

Question 11

explain why extremely high temperature and high pressure are needed for fusion to occur (2)

Answer 11

• nuclei are positively charged
• high temperature and pressure needed to overcome the electrostatic repulsion between nuclei

Question 12

explain why nuclear fusion is more desireable than nuclear fission (2)

Answer 12

• more energy released per kg of fuel
• the products of fission are radioactive and need careful disposal (or products of fusion are not radioactive)

Question 13

nuclear fusion naturally occurs in stars, describe what happens during nuclear fusion (3)

Answer 13

• small nuclei join
• to produce a larger nucleus
• releasing energy

Question 14

• water
• concrete
• proton
• neutron
• fuel rods
• neutrons
• chain
• control rods

Answer 14

Question 15

Answer 15

• mass number of 4 above He
• atomic number of 0 for the neutron

Question 16

explain why it is difficult to replicate the nuclear fusion of hydrogen on Earth (3)

Answer 16

• hydrogen nuclei are both positively charged
• need a high speed / high kinetic energy
• to overcome the electrostatic forces of repulsion

Question 17

compare the similarities and differences between nuclear fission and fusion (3)

Answer 17

• both fission and fusion release energy
• fission occurs when nuclei split whereas fusion occurs when nuclei join
• fission products are radioactive / fusion products are not radioactive

Question 18

Answer 18

Question 19

describe how the rate of fission can be reduced using a nuclear reactor (2)

Answer 19

• inserting the control rods will slow the rate of fission
• by absorbing more of the excess neutrons

Question 20

describe what is meant by a chain reaction (3)

Answer 20

• neutron absorbed by uranium nuclei
• causes it to split into two daughter nuclei and several neutrons
• neutrons released are absorbed by other uranium nuclei, causing further fission

Question 21

Answer 21

• total number of nucleons on left of arrow = 235 + 1 = 236
• number of neutrons released = 236 - 92 - 141 = 3 neutrons

Question 22

discuss how radioactive waste is disposed of and potential concerns (3)

Answer 22

• idea of strong containers
• idea of containers that can’t rust
• idea that rust-proof containers are difficult/expensive to manufacture
• reference to security of waste site
• reference to dilution in sea water
• reference to leakage into water table
• store underground (or away from people)

Question 23

Answer 23

• activity halves every half-life
• activity after 1 half life = 48 kBq
• activity after 2 half lives = 24 kBq
• activity after 3 half lives = 12 kBq
• activity after 4 half lives = 6 kBq
• activity after 5 half lives = 3 kBq
• 5 half lives = 5 x 15 million years = 75 million years

Question 24

Answer 24

Question 25

describe an advantages and a disadvantage of using nuclear fission power stations compared to coal-fired power stations (2)

Answer 25

**advantages:** - no greenhouse gases produced OR nuclear doesn't contribute to global warming - large amount of energy released from a small amount of fuel - low fuel cost compared to fossil fuel power plants **disadvantages:** - nuclear power stations are expensive to build - nuclear fission power stations produce radioactive waste - risk of nuclear accidents

Question 26

nuclear fission reactors are surrounded by thick concrete shielding, suggest why (2)

Answer 26

- radioactive products release gamma radiation which is harmful - shielding absorbs the gamma radiation - needs to be thick concrete as gamma is highly penetrating.

Question 27

a nuclear power station converts 35% of the energy from nuclear fission into energy which is transferred electrically through the National Grid, rission reactions release 1000 MJ per second, calculate the power of the energy distributed

Answer 27

Question 28

explain with reference to the parts of the nuclear reactor how the rate of fission could be increased to provide a higher output power (2)

Answer 28

- remove control rods - to reduce number of excess neutrons absorbed

Question 29

the required output is 700 MW, the nuclear fission power station converts 35% of the energy from fission into useful energy for transmission, calculate the energy released by fission reactions per second to meet this demand

Answer 29

Question 30

state two disadvantages of using nuclear fission power stations compared to solar farms (3)

Answer 30

- nuclear fission power stations produce radioactive waste - risk of nuclear accidents/meltdowns - nuclear power stations are expensive to build

Question 31

state two advantages of using a solar panel farm compared to a coal-fired power station (2)

Answer 31

- solar panels do not produce greenhouse gases - solar energy is a renewable resource

Question 32

Answer 32

Question 33

describe the purpose of the moderator in a nuclear fission power station (2)

Answer 33

- the moderator slows neutrons down - to make it more likely for them to absorbed by uranium nuclei