8.4+Non-fossil+fuel+power+production+Notes+2011

Back to IB PHYSICS > ENERGY, POWER AND CLIMATE CHANGE > PHYSICS CLASS 2011 COLLABORATIVE NOTES PROJECT You should write notes on the section which is allocated to you. Make sure your notes are easy to understand and include pictures, links and examples where appropriate. Explain the formulas from the data booklet where necessary. On each page, you will see the syllabus references. To write notes, click on EDIT. You can then write, insert files and pictures or links. You could link to useful web resources, java applets etc. You can obtain information from the text books or the Internet. You must login to be able to edit and you must be a member of the wiki. Deon || 8.2 World energy sources Notes 2011 Zac || 8.3 Fossil fuel power production Notes 2011 Bevis || 8.4 Non-fossil fuel power production Notes 2011 Reilly, Luke, Ryan || 8.5 Greenhouse effect Notes 2011 Luka, Antoine || 8.6 Global warming Notes 2011 Ivy, Matteo || =8.4 NON-FOSSIL FUEL POWER PRODUCTION (Reilly 1-11; Luke 12-17; Ryan 18-23)= 8.4.1 Describe how neutrons produced in a fission reaction may be used to initiate further fission reactions (chain reaction). Students should know that only low-energy neutrons (≈ 1 eV) favour nuclear fission. They should also know about critical mass. Splitting a nucleus of an atom such as 236U requires some energy in order to break the strong force binding the nucleus. This can be achieved by adding a neutron to this nucleus which, while increasing binding energy, will force it to split in two. This reaction leaves the nuclei with too many neutron, which are released and collide with other nuclei. These neutrons must be mving fairly slowly, having a low energy. This is because they cannot be moving quickly enough to simple pass by other nuclei. To combat this problem, moderator nuclei are added in order to slow these particles as they travel. Critical mass refers to the minimum mass for a fission reaction. If the mass is too small travelling neutrons will not have slowed enough by the time they exit the structure to create a reaction.
 * 8.1 Energy degradation and Power Generation Notes 2011
 * Aim 7: ** Computer simulations may be shown modelling nuclear power stations and nuclear processes in general.
 * Nuclear power **

8.4.2 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. Nuclear fission is based upon the release of neutrons during the reaction. If more than one neutron is released for every fission reaction it will accelerate, less than one it will decelerate. In an uncontrolled fission reaction (weaponry) the appropriate amount of 235U is simply mixed with a moderator, making the reaction go out of control. As the reaction is out of control, the exponential acceleration of the reactions creates massive amounts of energy. This can be kept from going off by keeping the moderator and the 235U separate, both below critical mass, until the desired time of explosion. In a controlled reaction there is a higher proportion of 238U to ease the reaction. However, this is difficult to control as the reaction becomes faster or slower. To counteract this, control rods, made of neutron absorbing materials (i.e. Boron) are added or removed between each fuel rod. Nuclear weaponry is bad. Many people die in incompressible numbers and the radiation leaves the site contaminated for years to come. However their existence holds back major wars to a point of non-conflict (Cold War).



8.4.3 Describe what is meant by fuel enrichment. Uranium is naturally made up of many isotopes, predominantly 238U which absorbs neutrons without splitting, therefore inhibiting fission despite emitting weak alpha particles. The useful isotope of Uranium is 235U which only makes up about 0.7% of the total mass. //Enrichment// is the act of increasing this percentage to approximately 3%. Another process to refine this is removing more of the 238U creating //depleted uranium//.

8.4.4 Describe the main energy transformations that take place in a nuclear power station.

8.4.5 Discuss the role of the moderator and the control rods in the production of controlled fission in a thermal fission reactor. 8.4.6 Discuss the role of the heat exchanger in a fission reactor. 8.4.7 Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu). 8.4.8 Describe the importance of plutonium-239 (239Pu) as a nuclear fuel.

8.4.9 Discuss safety issues and risks associated with the production of nuclear power. Such issues involve: • the possibility of thermal meltdown and how it might arise • problems associated with nuclear waste • problems associated with the mining of uranium • the possibility that a nuclear power programme may be used as a means to produce nuclear weapons. 8.4.10 Outline the problems associated with producing nuclear power using nuclear fusion. It is sufficient that students appreciate the problem of maintaining and confining a high‑temperature, high-density plasma. 8.4.11 Solve problems on the production of nuclear power. **Solar power** 8.4.12 Distinguish between a photovoltaic cell and a solar heating panel. Students should be able to describe the energy transfers involved and outline appropriate uses of these devices.

Solar heating panels are typically used for heating Swimming pools or household use. The method by which they function is by transferring the sun’s energy into heat energy to be carried by a substance(water). The sun’s light rays hit the glass and is absorbed below by a surface, in order to maxamise energy transfer, a black metal plate will be used. The metal will then be used to transfer the heat energy into the substance via conduction. The water will now be pumped to where it is needed. **Photovoltaic Cells:** Photovoltaic cells work by directly converting the sun’s light rays into electrical energy. When the photons (Light rays) hit the semiconductor surface, electrons are released, which will then flow out of the cell, in essence, making a photovoltaic cell a battery, but one that used photos rather than chemicals for power.
 * Solar Heating Panel:**

8.4.13 Outline reasons for seasonal and regional variations in the solar power incident per unit area of the Earth’s surface.

**Faults of Solar Power:** The amount of power generated from the sun is subject to the strength / prevalence of the sun’s rays. This means that if an object were to block or obscure the sun, generation of power would decrease or stop completely. As such, solar power is only viable in areas where the sunlight will be reliable. Another factor is geographical location, due to the fact that light rays from the sun will be weaker near the poles rather than on the equator, is may not be feasible to use and / or install solar power systems depending on the geographical location.

8.4.14 Solve problems involving specific applications of photovoltaic cells and solar heating panels. **Hydroelectric power** 8.4.15 Distinguish between different hydroelectric schemes. Students should know that the different schemes are based on: • water storage in lakes • tidal water storage • pump storage.

**Conventional:** Conventional hydroelectric power is generated from high-altitude lakes or dammed rivers. Using the PE of the stored water, electricity is generated by allowing water to flow downwards towards a turbine connected to an electrical generator. Power can then be generated using knowledge from emf. **Pumped Storage:** Same concept as Conventional hydroelectric power generation. Water is stored at an altitude above a power generator which is then released when there is a requirement for more power. The difference being that the method with which the water gets to a position above the generator. Water is literally pumped up into a tank or storage area for use when there is excess demand for electricity. **Run-of-the-river:** Based on the same principles as a conventional hydroelectric power station, just on a smaller scale. The natural flow and elevation drop of a river are used to generate electricity. However, run-of-the-river power stations have a much less substantial impact on the local environment and have a smaller footprint. This is coupled with much lower power production capabilities and it is considered an “unfirm” source of power. **Tidal Power:** Again, similar in terms of power generation. Water flow is used to turn a turbine which in turn, is used to generate electricity. How tidal power differs is in its methods of harnessing the water. The turbines are placed to sit in the water currents.



8.4.16 Describe the main energy transformations that take place in hydroelectric schemes. 8.4.17 Solve problems involving hydroelectric schemes. **Wind power** 8.4.18 Outline the basic features of a wind generator. Wind turbines, are mounted on a tower to capture the most energy. At around 30 meters or more above ground, they can take advantage of faster and less turbulent wind. Turbines catch the wind’s energy with their blades. Usually, two or three blades are mounted on a shaft to form a rotor. A blade acts much like an airplane’s wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin. The blades of the turbine are attached to a hub that is mounted on a turning shaft. The shaft goes through a gear transmission box where the turning speed is increased. The transmission is attached to a high-speed shaft that turns a generator that makes electricity

** Power = 0.5 x Swept Area x Air Density x Velocity3 ** http://www.alternative-energy-news.info/images/technical/wind-turbine.jpg A conventional horizontal-axis machine is sufficient. 8.4.19 Determine the power that may be delivered by a wind generator, assuming that the wind kinetic energy is completely converted into mechanical kinetic energy, and explain why this is impossible. 8.4.20 Solve problems involving wind power. **Wave power** 8.4.21 Describe the principle of operation of an oscillating water column (OWC) ocean-wave energy converter. Water columns are formed within large concrete structures built on the shore line or on rafts. The structure is open at both the top and the bottom. The lower end is submerged in the sea and an air turbine fills the aperture at the top. The rising and falling of the water column inside the structure moves the air column above it driving the air through the turbine generator. The turbine has movable vanes which rotate to maintain unidirectional rotation when the movement of the air column reverses. http://www.daedalus.gr/OWCsimulation2.html http://web.mit.edu/mitei/images/sidebar-ocean-waves-2-lg.gi Students should be aware that energy from a water wave can be extracted in a variety of different ways, but only a description of the OWC is required. 8.4.22 Determine the power per unit length of a wavefront, assuming a rectangular profile for the wave. The wave power per unit length of the wave front PL is given by (Twiddel & Weir. Renewable Energy Resources) as PL =ρga2λ/4T Where ρ is he density of the water (103 Kg/m3 ), a is the wave amplitude (half of the wave height), g is the gravitational constant (10 m/sec2), λ is the wave length of the oscillation and T the period of the wave.

8.4.23 Solve problems involving wave power