Nuclear+fission+-+Thomas

Physics 11.4 presentations Nuclear Fission  What is it? Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, sometimes (often) making free neutrons and lighter nuclei, sometimes even producing gamma rays. This is an exothermic reaction so as well as releasing heat energy it can also release electromagnetic radiation and kinetic energy. Nuclear fission produces energy for nuclear power which is what makes nuclear weapons explode. The heavy metal Uranium is a mixture of isotopes of which Uranium 235 is the most important. Some atoms of the isotope decay quite naturally, sending out high speed neutrons. If one of these hits the nucleus of a neighbouring uranium 235 atom, it may break into two nearly equal radioactive nuclei, often barium and krypton with two or three more neutrons. The neutrons which come out contain a lot of kinetic energy and might hit other nuclei of the Uranium 235, raising the atoms' average kinetic energy (temperature). This may create a chain reaction.

Example? An example of nuclear fission being used in the world would be a nuclear reactor. In a nuclear reactor, chain reactions occur at a steady rate which is controlled by instering or taking out rods which can absorb the neutrons along the uranium rods. The graphite core, or moderator, slows down the fission neutrons, therefore the fission of Uranium 235 occurs more readily with slow neutrons. CO2 gas is pumped through the core and carries off heat to the heat exchanger where steam is produced. Some gamma rays and neutrons might escape from the reaction, and the fission pieces have to be removed at a regular rate to achieve maximum nuclear fuel efficiency.

Energy Changes In a nuclear reactor, there would be many energy changes from the beginning to when the electrical is brought to a power grid. Firstly, nuclear energy is transformed into Thermal energy in the coolant, which is at the high pressure coolant loop. Next, the thermal energy stays the same but becomes water, at the low pressure coolant loop or steam generator. The energy then becomes both thermal and kinetic energy at the steam generator, which is then transferred into kinetic energy at the turbine. This energy is then transformed into electrical energy at the generator, which goes to the power grid.

Facts and Figures Speaking of this, the atomic bombs dropped in Hiroshima and Nagasaki in Japan were both nuclear fission bombs. In an atomic bomb there is an increasing uncontrolled chain reaction. The two bombs were extremely powerful, causing huge blast radii and many deaths. Even the first fission bombs ever were 1000 times more powerful than chemical bombs. Little Boy, one of the 2 big atomic bombs, weighed 4 tons, while its power was equivalent to 15 kilotons of TNT, which is 4.184 x 10^12 of Joules. The amount of free energy released in nuclear fuel is millions of times the amount of free energy released chemical fuels such as gasoline.

Environmental Impacts This makes nuclear energy a very tempting source of energy, however, the products of the process of nuclear fission are radioactive and remain like that for a very long time. This creates the problem of where to store nuclear waste. Waste heat from power plants is put into rivers and streams and might kill many fish there or disrupt the wildlife. Furthermore, the leaking of radioactive particles results in very serious health hazards. For example in Chernobyl, after the accident, many people there had birth defects and still do.

Advantages and Disadvantages

Advantages Relatively little fuel is needed and the fuel is relatively inexpensive and available in trace amounts around the world. Fission is also not believed to contribute to global warming or other pollution effects associated with fossil fuel combustion

Disadvantages There is the possibility of nuclear meltdown from uncontrolled reaction which leads to nuclear fallout with potentially harmful effects on civilians. Waste products can be used to manufacture weapons. There is also a high initial cost because plant requires containment safeguards.