Energy Production

Question 1

What is fuel enrichment for fissile material?

Answer 1

• Uranium occurs naturally as two isotopes: 99.3% uranium-238 and 0.7% uranium-235. Only uranium-235 is fissile material, and its concentration must be brought up to about 3% for use in most reactors. This is done by processing uranium hexafluoride gas in a centrifuge system based on the same principle as sedimentation or blood centrifuges.
• The processed, enriched uranium is formed into a solid alloy that is then manufactured into long, cylindrical fuel rods

Question 2

What are the most important energy end-use applications in the modern world?

Answer 2

• Residential use
• Commercial use
• Industrial use
• Transport use

Question 3

What is non-renewable energy resources?

Answer 3

Sometimes called finite resources, this are energy sources that are consumed faster than they are replenished: nuclear power is non-renewable

Question 4

What are renewable energy sources?

Answer 4

These are energy sources that remain undiminished or is replaced through natural processes in the environment in relevant human time-frames

Question 5

what is primary energy?

Answer 5

This energy that is extracted and applied as found in nature and has not been changed through a transformation process. These include wood, uranium, wind, tides, lakes and rivers

Question 6

What is secondary energy?

Answer 6

• This is energy that has been transformed from a primary source into some other form,
• For example fossil fuel to heat water in a boiler, which creates superheated steam that is then used to turn a turbine and generate electricity in most electrical power stations

Question 7

What factors are considered when choosing or searching for an energy source?

Answer 7

• Cost
• Transportability
• Availability
• Energy Source concentration

Question 8

What is specific energy?

Answer 8

• E(s) = Energy / Mass
• This is the amount of energy in a fuel contained per unit mass of fuel consumed

Question 9

What is energy density?

Answer 9

• E(d) = Energy/ Volume
• This is the energy of a fuel contained per unit volume of fuel consumed

Question 10

What is a Sankey Diagram?

Answer 10

• They represent flows as directed lines that have widths proportional to flow quantity at at that location in the flow

Question 11

What are the three stages evident in an energy flow diagram?

Answer 11

1. Supply, such as a primary energy source, which becomes an input.
2. Transformation; a conversion of energy to other forms, or to operate processes.
3. Consumption; where flows are associated with the end-use of energy such as a sector of the economy, an energy service, or some sub-stage such as a boiler or motor.

Question 12

Describe fossil fuels as sources of energy ?

Answer 12

• Burning coal produces energy that turns water into steam in boilers. The turbine makes the coils of a generator rotate in a magnetic field, creating electricity by electromagnetic induction.
  -(cold water from nearby rivers condenses the steam into liquid water that can again be heated in the boilers)

Question 13

What are the advantages and disadvantages of fossil fuels?

Answer 13

Advantages:
- Relatively cheap
- High power output
- Variety of engines and devices use them directly and easily
- Extensive distribution network is in place
Disadvantages:
- Will run out
- Pollute the environment
- Contribute to greenhouse effect by releasing greenhouse gases into atmosphere

Question 14

Describe nuclear power as a source of energy.

Answer 14

• Energy is produced by nuclear fission reactions that take place in a nuclear fission reactor. The fuel for a nuclear reactor is typically Uranium-235
• Neutrons in the reactor are used to collide with other nuclei of Uranium-235, producing more fission, more energy and more neutrons. The reaction is thus self-sustaining (also known as a chain reaction)

Question 15

What is critical mass?

Answer 15

This is the minimum mass that must be present for a chain reaction to be sustained

Question 16

What is a moderator and what is its role?

Answer 16

• This is usually the material surrounding the fuel rods, and can be graphite or water
• It is used to slow down the neutrons to allow for further chain reactions. The neutrons interact with the atoms of the moderator in order to slow down

Question 17

What are fuel rods?

Answer 17

These are the tubes containing uranium

Question 18

What is a heat exchanger and what is its role?

Answer 18

• This is what is used to extract the heat from the moderator.
• After neutrons have interacted with the moderator atoms, they transfer energy to the moderator, increasing its temperature

Question 19

What are control rods and what is their role in a nuclear reactor?

Answer 19

• These are what are used to slow down the amount of neutrons in the moderator thus the rate of reaction in the reactor
• They absorb neutrons when too many, resulting in a decrease in the rate of reaction and are removed when the rate of reaction needs to be increased

Question 20

Provide the reaction equation of plutonium reaction, where Uranium is bombarded by neutrons

Answer 20

=> 1n+238 -U → 239 -U
=> 239-U → 239-Np+ e- + _ν
=> 239-Np → 239-Pu+ e- + _ν

Question 21

What is the importance of the reaction leading to plutonium production?

Answer 21

=> Non-fissionable U-238 is converted to fissionable Pu -239

Question 22

What are the advantages and disadvantages of nuclear power?

Answer 22

Advantages:

Question 23

What is Stefan-Boltzmann law for a black body?

Answer 23

Power per unit area is proportional to the [absolute temperature (K) ] {^4}

Question 24

Why is the average power absorbed per unit area at the Earth’s surface lower than the calculated solar power incident per unit area?

Answer 24

1. Albedo of Earth means some radiation is reflected;
2. Earth’s surface is not always normal to incident radiation;
3. Some energy is lost as radiation travels to Earth

Question 25

Explain, by reference to the greenhouse effect, why the average temperature of the
surface of the Earth is greater than the expected temperature?

Answer 25

• Radiation from the Sun is re-emitted at longer wavelengths
• (longer radiation) wavelengths are absorbed by greenhouse gases
• Some radiation is re-emitted back to Earth in all directions; This causes an increase in temperature

Question 26

Suggest why the burning of fossil fuels may lead to an increase in the temperature of the surface of the Earth.

Answer 26

• More CO2 is released into the atmosphere
• This results in an enhanced greenhouse effect
• This is due to more re-radiation of energy towards the surface of planet