Fission & fusion

What is nuclear fission?

the splitting of a large atomic nucleus

What is a fissile material?

a material that easily undergoes fission

(e.g. uranium - 235)

Describe the chain reaction of nuclear fission

1. a slow moving neutron is absorbed by an unstable nucleus

2. this makes it even more unstable, causing it to split into 2 daughter nuclei

3. during this split, some more neutrons are released as well as energy (mainly kinetic energy but also gamma radiation)

4. the neutrons that were released repeat this process to make the chain reaction

What is a nuclear fission reactor?

a machine that contains and controls the chain reaction of nuclear fission while releasing heat at a controlled rate 

What is the purpose of the fuel rods in a nuclear fission reactor?

contains enriched uranium which fuels the fission chain reaction

What is the purpose of the removable control rods in a nuclear fission reactor?

to control the rate of fission by absorbing neutrons

(usually made of boron or cadium)

What is the purpose of the graphite core / moderator in a nuclear fission reactor?

to slow down neutrons by collisions so that their rate of absorption into a uranium - 235 nucleus increases

What is the purpose of the coolant in a nuclear fission reactor?

to prevent the system from overheating by transferring thermal energy from the fuel rods to the heat exchanger

What is the purpose of the heat exchanger in a nuclear fission reactor?

to convert water into high pressure steam using the thermal energy transferred from the coolant

What is the purpose of the concrete shield in a nuclear fission reactor?

to absorb any radiation that escapes the reactor core

What is a nuclear power plant?

a machine that uses the heat released from nuclear fission reactors to turn water into steam which is then used to drive wind turbines that generate electricity

What are the advantages & disadvantages of nuclear fission?

- does not release CO₂ which contributes to global warming

- only requires small amounts of uranium fuel so the supply will last a long time

- mining uranium is hazardous and expensive

- large amounts of radioactive waste is produced, some of which needs to be stored in secure & stable sites for a long time due to having a very long half-life

What is nuclear fusion?

the combining of 2 light atomic nuclei to form a heavier one

Why does fusion require high temperatures & high pressures?

because the nuclei of each isotope are both positively charged so they naturally repel each other

- high temperatures provide kinetic energy to overcome the electrostatic force of repulsion

- high pressures force the 2 positively charged nuclei of each isotope together

What are the advantages & disadvantages of nuclear fusion?

- releases a lot of energy

- uses materials that are easier & more available to collect (i.e. fusion uses deuterium as fuel which is found in sea water whereas fission uses uranium which needs to be mined)

- no radioactive waste is produced

- requires very high temperatures & pressures that are expensive and difficult to achieve