May 2012



1. List and describe with one sentence on each the three main aspects that make an energy source sustainable? (6 marks)

Not substantially depleted by continued use for example solar energy is renewable as the no matter the extent the to which the energy reaching the Earth is exploited, this use will not decrease the solar output from the Sun.

No significant pollution emissions or other environmental problems for example wind energy will not produce any pollution once the turbines have been installed and begin generating electricity whereas combusting coal will produce greenhouse gases such as CO2, SOx, NOx, particulate matter and heavy metal vapours do is not sustainable.

Does not contribute to social injustice or other social issues e.g. health problems for example shale gas may not fit this definition as often local communities worry about the effect fracking will have on nearby water sources.

2. What does 'enriching' uranium mean? Why do we need to enrich uranium and how is this done? (12 marks)

Enriching uranium means to increase the proportion of U-235 within a raw uranium material as  the most common isotope found in uranium oxide (U3O8) tends to be U-238.  This is carried out by adding fluride to the uranium oxide and then either using a Zippe type centifuge or a gas diffusion membrane to seperate the two isotopes so that the U-235 can be isolated. Uranium material enriched with U-235 is required as the fuel stock for a  fission reaction in nuclear power stations where U-235 is bombared with a neutron. This neutron produces an unstable nucleus which then breaks down into Boron, Krypton, thee more neutrons and energy. The energy provided from this reaction provides many millions times more energy than a chemical reaction such as combusting coal.  There are some reactors such as advanced gas cooled reactors that can work with a lower quality fuel (less U-235) but the majority rely on an enriched uranium fuel for fission to occur efficiently. 

3. Describe the technologies that are used to mitigate pollution from coal fired power plants. (12 marks)

A 660MW / h coal fired power station produces 650 tonnes of C02, 1-20 tonnes of SOx, 1 tonne of NOx, 30g mercury and 20 tonnes of particulate matter. Many coal fired power stations especially in the UK need to remove the majority of these pollutants from their emissions to ensure compliance with standards such as the EU Industrial emissions directive and avoid the alternative fine. If SOx and NOx are not removed from emissions they can contribute to acid rain when they react with moisture in the atmosphere to form sulfuric and nitric acid. 90% SOx emissions can be removed throuogh flue gas desulpurisation, which involves the addition of Calcium carbonate to produce Calcium sulfate or Gypsum This  can then be sold on to the construction industry. NOx emissions can be removed with the addition of  ammonia to produce nitrogen gas and water. An alternative to this is to use low temperature…


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