Energy Production Flashcards
What is fuel enrichment for fissile material?
- 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
What are the most important energy end-use applications in the modern world?
- Residential use
- Commercial use
- Industrial use
- Transport use
What is non-renewable energy resources?
Sometimes called finite resources, this are energy sources that are consumed faster than they are replenished: nuclear power is non-renewable
What are renewable energy sources?
These are energy sources that remain undiminished or is replaced through natural processes in the environment in relevant human time-frames
what is primary energy?
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
What is secondary energy?
- 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
What factors are considered when choosing or searching for an energy source?
- Cost
- Transportability
- Availability
- Energy Source concentration
What is specific energy?
- E(s) = Energy / Mass
- This is the amount of energy in a fuel contained per unit mass of fuel consumed
What is energy density?
- E(d) = Energy/ Volume
- This is the energy of a fuel contained per unit volume of fuel consumed
What is a Sankey Diagram?
- They represent flows as directed lines that have widths proportional to flow quantity at at that location in the flow
What are the three stages evident in an energy flow diagram?
- Supply, such as a primary energy source, which becomes an input.
- Transformation; a conversion of energy to other forms, or to operate processes.
- 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.
Describe fossil fuels as sources of energy ?
- 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)
What are the advantages and disadvantages of fossil fuels?
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
Describe nuclear power as a source of energy.
- 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)
What is critical mass?
This is the minimum mass that must be present for a chain reaction to be sustained
What is a moderator and what is its role?
- 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
What are fuel rods?
These are the tubes containing uranium
What is a heat exchanger and what is its role?
- 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
What are control rods and what is their role in a nuclear reactor?
- 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
Provide the reaction equation of plutonium reaction, where Uranium is bombarded by neutrons
=> 1n+238 -U → 239 -U
=> 239-U → 239-Np+ e- + _ν
=> 239-Np → 239-Pu+ e- + _ν
What is the importance of the reaction leading to plutonium production?
=> Non-fissionable U-238 is converted to fissionable Pu -239
What are the advantages and disadvantages of nuclear power?
Advantages:
What is Stefan-Boltzmann law for a black body?
Power per unit area is proportional to the [absolute temperature (K) ] {^4}
Why is the average power absorbed per unit area at the Earth’s surface lower than the calculated solar power incident per unit area?
- Albedo of Earth means some radiation is reflected;
- Earth’s surface is not always normal to incident radiation;
- Some energy is lost as radiation travels to Earth
Explain, by reference to the greenhouse effect, why the average temperature of the
surface of the Earth is greater than the expected temperature?
- 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
Suggest why the burning of fossil fuels may lead to an increase in the temperature of the surface of the Earth.
- 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
