P2 - Nuclear Power

Question 1

What is the factor that decides how much energy is released in nuclear fission?

Answer 1

How heavy the nucleus is

Question 2

What are the 2 most important fissile isotopes?

Answer 2

Uranium-235

Plutonium-239

Question 3

What are isotopes?

Answer 3

Variants of an element that have the same number of protons and electrons but a different number of neutrons

Question 4

What is nuclear potential energy?

Answer 4

Energy stored between the bonds holding the subatomic particles in the nucleus together

Question 4

What is nuclear fission?

Answer 4

The process of splitting nuclei in order to collect energy and start a chain reaction

Question 6

What is a fissile isotope?

Answer 6

An isotope that can maintain a nuclear chain reaction

Question 7

What is a thermal neutron?

Answer 7

A neutron that moves at the same speed as air particles at room temperature

Question 8

What are fission fragments?

Answer 8

The parts of a nucleus that have been split in nuclear fission
This is the radioactive waste

Question 9

Describe how nuclear fission works

Answer 9

A thermal neutron strikes a nucleus of the fissile isotope
The mass number of the isotope goes up by 1 because of the thermal neutron making the nucleus unstable
The instability causes the nucleus to split into 2 fission fragments
The fission fragments shoot off at high speed
A few neutrons also shoot off
One neutron hits another nucleus
This is why the chain reaction occurs

Question 10

What are the masses of fission fragments in comparison to the original nucleus?

Answer 10

One is a third of the mass and the other is 2 thirds of the mass

Question 11

In nuclear power stations, how are some of the neutrons stopped so that the chain reaction does not go out of control?

Answer 11

Control rods soak up the neutrons

Question 12

What are the 3 problems with nuclear fission as an energy source?

Answer 12

Disposal of waste is very hard and expensive to do

Cost of power plant and decommissioning is very high and it takes a long time

Risk of a major catastrophe like Chernobyl

Question 12

What are the 3 problems with nuclear fission as an energy source?

Answer 12

Disposal of waste is very hard and expensive to do

Cost of power plant and decommissioning is very high and it takes a long time

Risk of major catastrophe

Question 13

What is nuclear fusion?

Answer 13

The joining of 2 light nuclei to create a larger nucleus and release a large amount of energy

Question 14

What are the 3 advantages of nuclear fusion?

Answer 14

More energy than fission

Doesn’t leave behind a lot of waste

Lots of hydrogen to use as fuel

Question 15

What are the 2 disadvantages of nuclear fusion?

Answer 15

Can only happen at very high temperatures

You can’t hold the hydrogen at the high temperatures and pressures required for fusion in an ordinary container (very strong magnetic field is needed)

Question 16

Describe the first stage of the life cycle of a star

Answer 16

They initially form from clouds of dust and gas and the force of gravity makes the gas and dust spiral in together to form a protostar

Question 17

Describe the second stage of the life cycle of a star

Answer 17

Gravitational energy is transferred to heat and when the temperature gets high enough, hydrogen nuclei fuse together to form helium nuclei and give out massive amounts of heat and light

Question 18

Describe the third stage of the life cycle of a star

Answer 18

The star enters a long stable period where the heat created by the nuclear fusion provides outward pressure to balance the force of gravity pulling everything inwards

The star maintains its energy output for millions of years due to the massive amount of hydrogen

In this stable period, it is called a main sequence star

Question 19

Describe the fourth stage of the life cycle of a star

Answer 19

The hydrogen begins to run out and heavier elements such as iron are made by fusion of helium

The star swells into red giant if it is smaller and a red super giant if it is larger

It becomes red because the surface cools

Question 20

Describe what happens to red giants next

Answer 20

It then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula

This leaves behind a hot, dense solid core called a white dwarf that finally cools down to a black dwarf and eventually disappears

Question 21

Describe the next stage that occurs in red super giants

Answer 21

They start to glow more brightly again as they undergo more fusion and expand and contract several times forming elements as heavy as iron in various nuclear reactions

Eventually, they explode in a supernova forming elements heavier than iron and ejecting them into the universe to form new planets and stars

Question 22

Describe the final stage of red super giants

Answer 22

The supernova leaves an extremely dense core known as a neutron star

If this star is big enough, it will become a black hole