Chapter 8: Energy, power and climate change Flashcards
Outline and distinguish between renewable and non-renewable energy sources.
Renewable-most sources are directly or indirectly linked to the sun (solar, wind, wave, tidal energy).Non-renewable- are finite sources which are being depleted, and will run out. This includes fossil fuels and nuclear fuels. The energy stored is generally a form of potential energy which can be released by human action (oil, natural gas, coal, uranium).
energy density of a fuel
The energy that can be obtained from a unit mass of the fuel. Energy density is measured in J/kg
Discuss how choice of fuel is influenced by its energy density. (The values of energy density of different fuels will be provided.)
The greater the density the more energy can be gained.
Discuss the energy density of fossil fuels with respect to the demands of power stations.
- Energy density provides a useful comparison between the fuels
- It is defined as the energy liberated per unit mass of fuel consumed
- energy density=(energy released from fuel)/(mass of fuel consumed)
- Measured in J kg-1
- Fuel choice can be partially influenced by energy density when the fuel needs to be transported: the greater the mass of fuel that need to be transported, the greater the cost.
Describe how neutrons produced in a fission reaction may be used to initiate further fission reactions (chain reaction).
♠A nuclear reactor is a machine in which nuclear reactions take place, producing energy. The fuel is usually uranium-235. The neutrons produced will collide with other nuclei of uranium-235, producing more energy and more neutrons. This reaction is called a chain reaction.
♠The critical Mass is a certain minimum mass of uraninum-235 that must be present to cause more reactions. In the chain reactions, the neutrons are too fast for the uranium-235. To slow down the neutrons, fuel rods are used.
Distinguish between controlled nuclear fission (power production) and uncontrolled nuclear fission (nuclear weapons)
(Students should be aware of the moral and ethical issues associated with nuclear weapons.)
-The difference between controlled and uncontrolled nuclear fission is that the number of reactions is not kept at a low, constant level.
Describe what is meant by fuel enrichment
- Fuel enrichment is the process of enriching Uranium so that it is suitable for use in nuclear power-plants as well as for nuclear weapons.
- “Enriching uranium increases the amount of “middle-weight” and “light-weight” uranium atoms. Not all uranium atoms are the same. When uranium is mined, it consists of heavy-weight atoms (about 99.3% of the mass), middle-weight atoms (0.7%), and light-weight atoms (< 0.01%). These are the different isotopes of uranium, which means that while they all contain 92 protons in the atom’s center (which is what makes it uranium). The heavy-weight atoms contain 146 neutrons, the middle-weight contain 143 neutrons, and the light-weight have just 142 neutrons. To refer to these isotopes, scientists add the number of protons and neutrons and put the total after the name: uranium-234 or U-234, uranium-235 or U-235, and uranium-238 or U-238.”
Describe the main energy transformations that take place in a nuclear power station.
Nuclear reactions occur to produce energy. The energy produced is in the form of kinetic energy from the produced neutrons. The Kinetic Energy is then converted to thermal energy, which is then used to turn water into steam, which turns the turbines of the power station (thermal to mechanical energy) to finally produce electrical energy
Discuss the role of the moderator and the control rods in the production of controlled fission in a thermal fission reactor.
♠The moderator is a material surrounding the fuel rods that helps slow down the neutrons. The control rods are inserted in the moderator to control the energy released from the nuclear reactions.
♠A moderator reduces the velocity of fast neutrons by making them lose energy and creating instead thermal neutrons that are more likely to cause fission.
Discuss the role of the heat exchanger in a fission reactor.
The heat exchanger is pretty much just a device that allows the hot radioactive water loop to brush up against the non-radioactive water loop, allowing for heat to be transferred to the non-radioactive water, which will then power the turbines. This keeps the radioactive water isolated from the outside environment
Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu).
When an atom of uranium-238 is exposed to nuclear radiation, sometimes its nucleus will capture a neutron, turning the atom into uranium-239. After becoming uranium-239, the atom will discharge an electron and an anti-neutrino through the process of decay; this turns the atom into Neptunium-239. The Neptunium atom will then emit a second electron and anti-neutrino through the process of decay in order to become plutonium-239.
Describe the importance of plutonium-239 (239Pu) as a nuclear fuel
Plutonium-239 is the primary fuel used for the production of nuclear weapons along with uranium-235, and provides about one third of the energy in nuclear reactors. Plutonium-239 is produced when an atom of uranium-235 goes through the fission process, producing two or three neutrons, which are then absorbed by a uranium-238 atom.
Outline the problems associated with producing nuclear power using nuclear fusion.
- In order for a fusion reaction to take place, hydrogen (or other plentiful elements) atoms need to be heated to an extremely high temperature and kept there. It requires extreme amounts of energy to acquire such a high temperature, let alone maintain it indefinitely.
- It is also a problem to maintain the plasma in a state in which it is dense enough for fusion to take place.
Distinguish between a photovoltaic cell and a solar heating panel.
Solar heating panels use sunlight to heat water using various devices (pipes, reflective material). Photovoltaic cells convert energy from sunlight to D/C current with the use of semiconductors.
Outline reasons for seasonal and regional variations in the solar power incident per unit area of the Earth’s surface.
- Solar constant is the amount of solar energy that falls per second on an area of 1m2 above the Earth´s atmosphere that is at right angles to the Sun´s rays.
- This is not the same as the power that arrives on 1m2 of the Earth´s surface
- Different parts of the Earth´s surface (regions at different latitudes) will receive different amounts of solar radiation.
- The amount received will also wary from the with the season since this will affect how spread out the rays have become.
