Solar Energy and Nuclear Energy Physics Project Solar Energy and Nuclear Energy Members: Yeung Shiu Wing Ng Hao Ming Luk Hon Yan Chu Kwok Ming Cheung Man King

Content Nuclear energy Nuclear fission Inside a nuclear plant Subcritical,critical and supercritical Other reactors Military weapons What can go wrong?? Advantages and disadvantages of nuclear energy

Solar energy Solar cell Advantages and disadvantages of solar energy Global trend of energy reservation Global trend of energy consumption Conservation of energy Reference

Nuclear energy One major form of energy it is trapped inside each atom it makes up about 17 percent of the world's electricity. Some country depend on nuclear energy more than other energy There are now more than 400 nuclear power plants around the world.

Nuclear fission It means to split an atom's nucleus apart and a large amount of energy is released. Uranium is used as a ‘fuel’ If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron. The U-235 will become unstable and split immediately. If expelled neutrons cause the nuclei of other U-235 atoms to split, releasing further neutrons, a fission 'chain reaction' can be achieved. When this happens over, a very large amount of heat is produced.

When the nucleus captures the neutron, it splits into two lighter atoms and throws off two or three new neutrons. The two new atoms then emit gamma radiation. There are two things about this induced fission process that make it interesting: The probability of a U-235 atom capturing a neutron as it passes by is fairly high. In a reactor working properly, one neutron ejected from each fission causes another fission to occur. The process of capturing the neutron and splitting is only picoseconds (1 x 10-12 seconds).

An huge amount of energy is released, in the form of heat and gamma radiation, when a single atom splits. The energy released by a single fission is 200 million electron volts (3.43 x 1016joules) is released by the decay of one U-235 atom. A pound of highly enriched Uranium as used to power a nuclear submarine or nuclear aircraft carrier is equal to something on the order of a million gallons of gasoline. A sample of Uranium must be enriched, so that it contains 2 - 3 % or more of Uranium-235. 3 % enrichment is sufficient for power generation. Weapons-grade Uranium is composed of 90 % or more U-235.

Inside a nuclear plant Press For Animation

Subcritical,critical,supercritical When a U-235 atom splits, it usually gives off two or three neutrons. If there are other U-235 atom nearby, then one of three things happens: If exactly 1 free neutrons from each fission hits another U-235 nucleus and causes it to split, then the mass of Uranium is said to be critical. The mass will exist at a stable temperature. A nuclear reactor must be maintained in a critical state.

If less than one of the free neutrons hits another U-235 atom, then the mass is subcritical. Eventually, induced fission will end in the mass. If more than one of the free neutrons hits another U-235 atom, then the mass is supercritical. It will heat up. In a nuclear reactor, the reactor core needs to be slightly supercritical so that the plant operators can raise and lower the temperature of the reactor. The control rods give the operators a way to absorb free neutrons so that the reactor can be maintained at a critical level.

Military weapons Uranium is used to make bombs before they became important for making electricity and radioisotopes. But the type of Uranium and Plutonium for bombs is different from that in a nuclear power plant. Bomb-grade Uranium is highly-enriched >90% U-235.

What can go wrong?? The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. Spent reactor fuel is removed, stored, and then either reprocessed or disposed of underground. Mining and purifying Uranium has not been a very clean process

Improperly functioning nuclear power plants can create big problems Improperly functioning nuclear power plants can create big problems. The Chernobyl disaster is the best recent example. Spent fuel from nuclear power plants is toxic for centuries, and there is no safe permanent storage facility for it. Transporting nuclear fuel to and from plant poses some risk.

Advantages and disadvantages of nuclear energy Advantages: -cause less pollution -it produce no greenhouse gases -small amount is needed for a large quantity of energy -it is reliable Disadvantages -it is dangerous if we use it improerly - its spent fuel is dangerous and safety storage facility for it

Solar energy Energy derived ultimately from the sun. It can be divided into direct and indirect categories. Most energy sources on Earth are forms of indirect solar energy, e.g. Coal, Oil, Natural Gas, Movement of the Wind and the Evaporation of Water Direct solar energy is what we usually mean when we speak of solar power – it is the use of sunlight for heating or generating electricity.

Solar thermal electric power plant Solar thermal electric power plant generates heat by using lenses and reflectors to concentrate the sun's energy. The heat can be stored, so they can generate power when it is needed, day or night, rain or shine. Utilizing only 1% of the earth's deserts to produce clean solar electric energy would provide more electricity than is currently being produced on the entire planet by fossil fuels.

Solar Parabolic Dish systems consist of a parabolic-shaped concentrator that reflects solar radiation onto a receiver mounted at the focal point at the center. The collected heat is utilized directly by a heat engine mounted on the receiver and driving a turbine electric generator which generates electricity.

Solar cell Photovoltaic (PV) cell (Also known as solar cells.) A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron and contains positively charged 'holes', which are missing electrons. The other type of silicon is doped with small amounts of phosphorus and it contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical en energy.

Advantages and disadvantages of solar energy Advantage: Solar power is renewable. It produces no greenhouse gases Excellent for remote areas that is not connected to the main electricity grid. Can be made very small for watches, calculator etc Solar energy is free Disadvantages: Doesn't work at night, and some days have little or no sunlight Expensive to produce

Global Trend of Energy Reservation

Global Trend of Energy Consumption

Conservation of energy Turn off the light when it is necessary switch off TV when you are not watching use fans instead of air-conditioner use solar energy if you can use electrical apparatus that is energy-efficient use Compact Fluorescent Bulbs in stead of common light bulbs

Reference http://www.howstuffworks.com/nuclear-power1.htm http://www.solarenergy.com/index.html http://www.ises.org/ises.nsf!Open http://www.solardev.com/SEIA-makingelec.php

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