Physics Project

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

2. 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

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

4. Nuclear energy • One major form of energy • it is trappedinside 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.

5. Nuclear fission • It meansto 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.

6. 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).

8. 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.

9. Inside a nuclear plant Press For Animation

10. 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.

11. 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 slightlysupercritical so that the plant operators canraise and lower the temperature of the reactor. The controlrods give the operators a way to absorbfreeneutrons so that the reactor can be maintained at a criticallevel.

12. Military weapons • Uranium is used to makebombs 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-gradeUranium is highly-enriched >90% U-235.

13. What can go wrong?? • The reaction also createsradioactivematerial. This material could hurtpeople if released, so it is keptin a solidform. Spentreactorfuel is removed, stored, and then either reprocessed or disposed of underground. • Mining and purifyingUranium has not been a veryclean process

14. Improperlyfunctioningnuclearpowerplants can createbigproblems. The Chernobyl disaster is the best recent example. • Spentfuel from nuclear power plants istoxicforcenturies, and there is nosafepermanentstoragefacility for it. • Transportingnuclearfuel to and from plant posessomerisk.

15. 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 Advantages and disadvantages of nuclear energy

16. Solar energy • Energy derived ultimately from the sun. • It can be divided into direct and indirectcategories. • 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.

17. Solar thermal electric power plant • Solarthermalelectricpowerplantgeneratesheat by usinglenses and reflectors to concentrate the sun'senergy. • The heatcan be stored, so theycangeneratepowerwhen 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 electricitythan is currently being produced on the entire planet byfossilfuels.

18. SolarParabolicDishsystemsconsist of a parabolic-shapedconcentrator that reflectssolarradiationonto a receiver mounted atthefocalpointatthecenter. The collectedheatisutilizeddirectly by a heatengine mounted on the receiver and driving a turbineelectricgenerator which generateselectricity.

19. 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.

22. Advantages and disadvantages of solar energy Disadvantages: Doesn't work at night, and some days have littleor no sunlight Expensive to produce 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 smallfor watches, calculator etc Solar energy is free

23. Global Trend of Energy Reservation

24. Global Trend of Energy Consumption

25. 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

26. 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

27. THE END Thank you