Wednesday, August 17, 2011

Nuclear Power Station : Part 1

       A generating station which converts the nuclear energy into an electrical energy is called nuclear power station.
       In such a power station, heavy radioactive elements like uranium (U235), Thorium (Th232), are subjected to the nuclear fission. The fission is breaking of nucleus of heavy atom into the parts by bombarding neutrons. This is carried out in a special nuclear reactor. During the nuclear fission, huge amount of energy is released.
       The heat energy that released is used in rising the steam at high pressure and temperature. The steam turbines are operated using the high temperature steam. The turbines converts the heat energy into a mechanical energy. The turbine drives the alternator which converts mechanical energy into an electrical energy.
       The energy conversion involved in the nuclear power station is shown in the Fig.1.
Fig. 1 Energy conversion

1.1 Conversion of Nuclear Energy
       According to Einstein's hypothesis, the relation between the energy released by the nuclear reaction of the mass given by,
                          E = mc2
where        E = Energy released in jouls
                 m = Actual mass converted into energy in kg
                 c = Velocity of light = 3 x 108 m/s
       There are three types of nuclear reaction, radioactive decay, fission and fusion. Out of this, only fission is used to produce the energy.
       The fission reaction is achieved by bombarding an electrically neutral neutron, on the positively charged nucleus of radioactive element. This results in the sustained reaction to release two or three neurons for eacj one absorbed in fission.
       The immediate products of fission reaction such as xenon (Xe140) and strontim (Sr94) are fission fragments and are the decay products. The complete fission of 1 gm of U235 nucleus produces 0.948 MW energy per day.
1.2 Factors selection of site
       The following factors are to be considered for the selection of site for the nuclear power station.
1. Availability of water : Water is a secondary working fluid and used as a coolant for the cooling purpose, in the nuclear power station. A huge amount of water is necessary for this purpose. Hence site must be near the river or canal so that abundant quantity of cooling water is availabe.
2. Disposal of waste : The immediate products of fission reaction are the waste products which are radioactive in nature. These can cause problems to the health of the people and hence must be disposal quickly. Such a waste is either burried in deep pits or disposal off in the sea. Hence the site should be selected so that their is sufficient arrangement for disposal of such radioactive waste products.
3. Distance from populated area : The radioactive elements are hazardous to the health of the people around. There is always danger of presence of radioactivity in the atmosphere near the plant. Hence as a safety measure the site itself must selected to far away from the populated area. Practically a dome is used in the plant, which restricts radioactivity to spread in the atmosphere.
4. Transportation facilities : For transporting the equipments and the machinery required, there must be adequate transportation facilities. The site must accessible by a rail or road so that it is easy for the movement of the workers, working in the plant.
5. Nearness to the load centres : Though the site should be away from the populated area near the river or sea, it should not be too large distance, due to which transmission cost may increase tremendously.
6. Cost and type of land : The land price must be reasonable and the bearing capacity of the land should be good enough to withstand the forces due to heavy equipments of the plant.
        All these factors affects the selection of site for the nuclear power station.
1.3 General Arrangement of Nuclear Power Plant
       The Fig. 2 shows the schematic arrangement of a nuclear power plant.
        The entire arrangement can be divided into following stages.
1.Nuclear reactor      2. Heat exchange (Steam generator)
3. Steam turbine         4. Alternator               5. Cooling water circuit.
Fig.2    Schematic arrangement of nuclear power station
See Nuclear Power Station : Part 2

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