1.9.5 Boiling water reactor (BWR)
In this reactor, enriched uranium (enriched uranium contains morefissionable isotope U 235 than the naturally occurring percentage 0.7% asnuclear fuel and water is used as coolant. Water enters the reactor at thebottom. It takes up the heat generated due to the fission of fuel and gasconverted into steam. Steam leaves the reactor at the top and flows into theturbine. Water also serves as moderator. India’s first nuclear power plant at Tarapur has two reactors (each of 200 MW capacity) of boiling water reactortype.
Pressurised Water reactor (PWR
Fig. 1.11 Pressurised Water Reactor
pressurised water nuclear plant is shown in fig. It uses enricheduranium as fuel. Water is used as coolant and moderator. Water passesthrough the reactor core and takes up the heat liberated due to nuclearfission of the fuel. In order that water may not boil (due to its low boilingpoint 2120
F at atmospheric conditions) and remain in liquid state, it is keptunder a pressure of about 1200 p.s.i.g in the pressuriser. This enables waterto take up more heat from the reactor. From the pressuriser, water flows tothe steam generator where it passes on its heat to the feed water which inturn gets converted into steam.
1.9.7 Fast breeder reactor (FBR)
In this reactor the core containing U235 is surrounded by a blanket (alayer of fertile material placed outside the core) or fertile material U 238 . Inthis reactor no moderator is used. The fast moving neutrons liberated due tofission of U235 are absorbed by U 238 which gets converted into fissionablematerial Pu239 , Pu 239
is capable of sustaining chain reaction. Thus the reactoris important because it breeds fissionable material from fertile material U238
available in large quantities. This reactor uses two liquid metal coolantcircuits. Liquid sodium is used as primary coolant when circulated throughthe tubes of intermediate heat exchanger transfer its heat to secondarycoolant sodium potassium alloy. The secondary coolant while flowing throughthe tubes of steam generator, transfer its heat to feed water.Fast breeder reactors are better than conventional reactor both fromthe point of view of safety and thermal efficiency. For India which already isfast advancing towards self reliance in the field of nuclear power technologythe fast breeder reactor becomes inescapable in view of the massivereserves of thorium and the finite limits of its uranium resources.
1.9.8 Advantages of nuclear power plant
1.The fuel used in nuclear power plant is uranium; it does not releasechemical or solid pollutants into the air during use.2.Space required is less when compared with other power plants.3.Fuel consumption is very less.4.Fuel transportation cost is low and no large storage area for fuel isrequired.5.The plant is not affected by weather conditions. The plant can functionthroughout the year (Hydel power plants depends on monsoon)6.By using nuclear fuel we can conserve the fossil fuels like coal, oil, gasetc for other purposes. For example coal can be used to power steamengines, oil can be used for running vehicles, and gas be used forcooking.7.Number of workers required is less.8.Nuclear power plant is the only source which can meet the increasingdemand of electricity.9.A nuclear power plant uses much less fuel than a fossil fuel plant
1 metric ton of uranium fuel = 3 million metric tons of coal = 12 millionbarrels of oil
1.9.9 Disadvantages of nuclear power plant
1.Nuclear plants cost more to build than thermal or hydro electricpower plants of the same capacity.2.Radioactive wastes must be disposed carefully, otherwise it willadversely affect the health of workers and the environment as awhole.3.Maintenance cost of the plant is high.4.Not suitable for varying load conditions5.Well trained persons are required to operate the plant
1.9.10 Nuclear power stations in India
Tarapur Nuclear power station (Bombay) – Boiling water reactor –200 MW
Rana Pratap Sagar Nuclear power station (Kota in Rajasthan) – Two200 MW
Kalpakkam Nuclear power station – Two 235 MW – Pressurisedwater reactor
Narora Nuclear power station (Uttar Pradesh) – Two 235 MW –CANDU reactor
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