La construcción de un mundo más justo desde la amistad y el

Nuclear Energy:

Nuclear Fission:

 A process where a fissile isotope (usually Uranium-235) is bombarded by a neutron and then splits up into two smaller nuclei (and releases a large amount of energy.)

 This is called a nuclear reaction, and new elements are formed from the original.

 Neutrons are also released from these reactions and go on to bombard other nuclei, causing a chain reaction to occur (think of all that energy!)

 The Uranium -235 to start with is taken from Uranium ores. However, these ores contain 99.3% U238, and only 0.7% U235, so the ores must be refined for 3% U235.

 Uranium 238 can also be exploited by fast-breed reactors, decaying into Plutonium 239 to generate further energy.

 Uranium 235 nuclear reactions is the primary source of nucleur energy however, and occur in nuclear reactor power plants.

 In a nuclear reactor powerplant, the chain reaction occurs in a reaction vessel.

 Control rods and heavy water (deuterium oxide, 2H2O) moderate the rate of reaction in the vessel to a safe level. The reaction is shown:

 A small amount of the reactants nuclear energy in the bonds, are converted to kinetic energy in the products, and this then becomes thermal energy in the water.

 This then transfers to the boiler, creating steam which turns a turbine (mechanical energy) and this creates a current (electrical energy.)

 1kg Unranium produces the same amount of energy as 2500 tonnes of coal.

Now we look to the environmental impact involving nuclear reactors:

 Produces no gaseous emissions, but products are radioactive and pose waste problems that a long term.

 Uranium and Plutonium may be recycled for further use.

 Non renewable source of energy (Uranium is finite.)

 Nuclear waste is stored for 5 years so short lived isotopes/waste can decay and cool down. Long lived isotopes must be stored safely for thousands of years. This is done by burying in sealed tanks or deep mines in geologically stable regions,

stockpiling in air conditioned warehouses, dumping in ocean trenches or sealing in special types of glass.

 The other concern with nuclear power is the risk of release of radioactive substances (by accident or sabotage, terroist attack).

 Fears of Uranium being stolen for weapons (unlikely).

 Power Plants take a long time to build and have a reletively short working life.

 Advantages of Nuclear Energy: Relatively cheap, can be used as a baseload power source (power a whole population), high amount of energy per unit mass of fuel, no greenhouse gases released.

 Disadvantages of Nuclear Energy: Non renewable, waste is extremely tocix, potential terroist threats, nuclear meltdown potentially catastrophic.

Nuclear Energy: Energy Transformations Summary:

 Nuclear energy in the nuclear bonds of protons and neutrons  Fission & steam

 Thermal energy in the temperature of steam passes through turbine

 Mechanical energy in the motion of the turbine  Generates a current

 Electrical energy in the movement of electrons  Electricity used by public

Nucleaur Fusion:

 The opposite to fission, two or more nuclei are smashed together to form a larger one. This is the source of energy in the sun (when hydrogen fuses with helium).

 Fusion of one kilogram of fuel yields more than fission, may reach the same energy as 10000 tonnes of coal.

 However, great difficulty in sustaining a temperature in a reactor for fusion to occur. Temperature of 100,000,000 degrees needed as well as a place to contain.

Bioethanol, Biodiesel and Biogas:

 The fermentation of glucose (with a catalyst) from plant crops produces bioethanol, which can be blended with fuel to lower the demand and use of petroleum (less pollutants etc.)

 Biodiesel is derived from vegetable oils and animal fats, hydrolysed to fatty acids and esterified.

 Waste plant and animal material can be converted into syngas (carbon monoxide and hydrogen) or biogas (carbon dioxide and methane) which can generate heat/electricity.

Solar:

 Solar energy can be used directly.

 Solar efficient building designs reduce heating, cooling and lighting costs.

 Solar water heating systems provide hot water, for homes and for pools.

 However, solar cells are very expensive, and inability to be used efficiently when in the dark- either at night or in cloudy weather. There is also a need for large areas of land due to relatively poor energy conversion efficiency.

 Solar energy is renewable. Utilizes energy from the sun (which always provides energy.) Solar energy is stored for use as electricity.

Solar: Energy Transformations for STORING solar energy:

 Radiant energy in light waves from sun ^ Current made in solar panel.

 Electrical energy (movement of electrons) in solar panel ^ Recharges batteries

 Chemical energy of the reactants in the battery made.

The chemical energy is stored, now, more transformations occur for it’s use (below).

Solar: Energy Transformations for the USE of solar energy:

 Chemical energy of the reactants in batteries ^ Discharge of battery

 Electrical energy of movement of electrons^ Electricity for the home

 Advantages of solar: Renewable source of energy, no greenhouse gas emissions.

 Disadvantages of solar: Expensive, inefficient (only about 1% conversion), cant be used as a baseload power source (for an entire population.)

Hydroelectricity:

 Obtained by using falling water to turn turbines and generate electricity.

 Firstly, Solar energy evaporates this water transferring it to higher altitudes. The water thus obtains more Gravitational potential energy.

 Then, as the water falls, it is converted into mechanical energy as it spins a turbine, which generates a current for electrical energy.

 Hydroelectricity supplies about 25% of the world’s and 10% of Australia’s electricity.

 Developement of hydroelectric stations are restricted, due to the limited number of suitable sites and concern about it’s environmental impact. This is because storage dams are often requires to establish a good flow of the water at all seasons, but lead to further environmental concerns (loss of natural habitat.)

 Hydroelectricity is renewable.

Hydroelectricity: Energy Transformations Summary:

 Gravitational Potential energy in high altitude of water Water falls, turns turbine

 Mechanical energy of turbines movement ^ Generates a current

 Electrical Energy from movement of electrons (Current)  Electricity used by public

 Advantages of Hydroelectricity: No greenhouse gases, no toxic waste, renewable.

 Disadvantages of Hydroelectricity: Building dams results in destruction of natural habitat.

Wind Power:

 Can be used to generate electricity through wind turbines.

 Average wind speeds exceeding 5ms are suitable, but the turbines are only as reliable as the wind.

 The turbines are highly visible and loud, a number of them are needed to match the energy production of a coal-fired plant. (Wind turbines make less energy)

Tidal Power:

 Made in tidal power stations.

 Uses the movement of water caused by the moon to generate electicity.

 Sites are limited, as a large difference in water height between tides are required.

Geothermal Power:

 In volcanic regions, heat from underground rocks can reach underground water.

 This can cause steam to rise to the surface, which can be harnessed to spin turbines to create electricity.

 This is the principal of geothermal energy, however Geothermal power plants are again restricted to suitable sites- but are reliable.