NUCLEAR POWER PLANT

NUCLEAR POWER PLANT

If nuclear fission reaction is made to occur in a controlled manner, then the energy released can be used for constructive purposes like electricity generation. The arrangement or equipment used to carry out fission reaction under controlled conditions is called a nuclear reactor. The energy produced in a controlled manner can be used to produce steam which can run turbines and produce electricity. This arrangement is employed in a nuclear power plant to generate electricity.

BLOCK DIAGRAM: 

EXPLANATION:

Functioning of Nuclear power plant:

Nuclear power plants generate steam to drive electric turbines by circulating liquid through a nuclear reactor. The reactor produces heat through the controlled fission of atomic fuel. Normally the fuel for power reactors is slightly enriched uranium.

Detailed process of power generation in a thermal power plant:

(i)Nuclear Reactor:

It is an apparatus in which nuclear fuel (U235) is subjected to nuclear fission. It controls the chain reaction that starts once the fusion is done. If the chain reaction is not controlled, the result will be an explosion due to the fast increase in the energy released.

A nuclear reactor is a cylindrical stout pressure vessel and houses fuel rods of Uranium moderator and control rods. The fuel rods constitute the fission materials and release huge amount of energy when bombarded with slow moving neutrons. The moderator consists of graphite rods which enclose the fuel rods. The control rods are of Cadmium and are inserted in the reactor. Cadmium is strong neutron absorber and thus regulates the supply of neutrons for fission. When the control rods are pushed in deep enough, they absorb most of fission neutrons and hence few are available for chain reaction, which therefore stops. However, hence they are being withdrawn, more and more of these fission neutrons cause fission and hence the intensity of chain reaction is increased. Therefore by pulling out the control rods, power of nuclear reactor is increased, whereas by pushing them in, it is reduced. In actual practice, the lowering or raising of control rods is accomplished automatically according to the requirement t of load. The heat produced by the reactor is removed by the coolant, generally a sodium metal. The coolant carries heat to the heat exchanger.

Types of reactor:

 After the enzyme and the carrier system have been chosen, decision needs to be taken on reactor design, which can be any one of the following four types:

(a) Batch reactor: It is the simplest type of reactor. The immobilized enzyme is placed in a container with the reactants, and the reaction is allowed to proceed until the desired level of conversion is reached. Some stirring or agitation of reaction mixture is also required. Many modifications of these reactors have been designed to simplify recovery and reuse of the enzyme composite.

(b) Continuously stirred reactors: These types of reactors employ a stirred tank, to which reactants are continuously added and products continuously withdrawn.

(c)Fluidized-bed reactor:            In these reactors, enzyme system is fluidized by the upward flowing of substrate solution. This helps in eliminating any plugging of enzyme system, although small duration of contact may be insufficient for the desired conversion. This can be overcome by decreasing velocity of solution by different methods.

Glucose isomers and lactase have been shown to double their efficiency due to fluidization when compared with fixed beds.

(d)Fixed bed reactors: These are most widely used for large scale commercial operations. Different companies use these reactors for enzymes like

(I) Aminocylase

(II) Glucose isomers and

(III) Lactase.

These reactors will keep on dominating the large scale commercial application due to their.

(I) High efficiency and

(II) Ease and simplicity of operation.

There are many types of fixed bed reactors including those with packed bed of particular material to which enzyme is coupled.

(ii)Heat Exchanger:

The coolant gives up the heat to the heat exchanger which is utilised in raising the steam. After giving up heat, the coolant is again fed to the reactor.

(iii)Steam Turbine:

The steam produced in the heat exchanger is led to the steam turbine through a valve. After doing a useful work in the turbine, the steam is exhausted to the condenser. The condensers condense the steam which is fed to the heat exchanger through feed water pump.

(iv)Alternator:

The steam turbine drives the alternator which converts mechanical energy into electrical energy. The output from the alternator is delivered to the bus bars through transformers, circuit brakers and isolators.

THE NUCLEAR FUEL CYCLE:

The nuclear fuel cycle is the series of industrial processes which involve the production of electricity from uranium in nuclear power reactors.  Uranium is a relatively common element that is found throughout the world. It is mined in a number of countries and must be processed before it can be used as fuel for a nuclear reactor.

Fuel removed from a reactor, after it has reached the end of its useful life, can be reprocessed to produce new fuel.

The various activities associated with the production of electricity from nuclear reactions are referred to collectively as the nuclear fuel cycle. The nuclear fuel cycle starts with the mining of uranium and ends with the disposal of nuclear waste. With the reprocessing of used fuel as an option for nuclear energy, the stages form a true cycle.

ADVANTAGES:

1. They can be located very conveniently near the load centers.

2. Does not require shielding like required in nuclear power plants.

3. Unlike nuclear power plants whose power production method is difficult, for thermal             power plants it is easy if compared.
4. Transmission costs are reduced as they can be set up near the industry.
5. The portion of steam generated can be used as process steam in different industries.
6. Steam engines and turbines can work under 25% of overload capacity.
7. Able to respond changing loads without difficulty.

DISADVANTAGES:

1. Large amounts of water are required.
2. Great difficulties experienced in coal handling and disposal of ash.
3. Takes long time to be erected and put into action.
4. Maintenance and operating costs are high.
5. With increase in pressure and temperature, the cost of plant increases.
6. Troubles from smoke and heat from the plant.

SITE SELECTION PARAMETERS:

The following points should be kept in view while selecting the site for a nuclear power station.

(i)Availability of Water:

As sufficient of water is required for the cooling purposes, therefore the plant site should be located where ample quantity of water is available.

(ii) Disposal of Waste:

 The waste produced by fission in nuclear power station is generally radioactive which must be disposed off properly to avoid health hazards. The waste should either be buried in a deep trunch or disposed off in a sea quite away from the sea shore. Therefore the site selected for such a plant should have adequate arrangement for the disposal of radioactive waste.

(iii)Distance from populated areas:

 The site selected for a nuclear power station should be quite away from the populated areas as there is a danger of presence of radio activity in the atmosphere near the plant. However, as a precautionary measure, a dome is used in the plant which does not allow the radioactivity to spread by wind or underground waterways.

(iv)Transportation Facilities:

 The site selected for a nuclear power station should have adequate facilities in order to transport the heavy equipments during erection and to facilitate the movement of workers in the plant. From the above mentioned factors it become apparent that ideal choice for a nuclear power station would be near sea or river and away from thickly populated  areas.

STATUS OF NUCLEAR POWER PLANT:

Nuclear power stations
Power station	State	Total capacity (MW)
Kaiga	Karnataka	880
Kakrapar	Gujarat	440
Kalpakkam	Tamil Nadu	440
Narora	Uttar Pradesh	440
Rawatbhata	Rajasthan	1180
Tarapur	Maharashtra	1400
Kudankulam	tamilnadu	2400
jaitpur	maharashtra	3200
pati sonapur	orissa	6000
saurashtra	gujarat	2800

CONCLUSION:

            After study of the nuclear power plant we conclude that the nuclear power generation is more efficient than the other power plant so with help of small amount of the nuclear material like uranium and thorium we can generate a large amount of the electricity but more safety precautions are required than other power plant and the major problem is that the waste of nuclear material disposal is so difficult and it is also do effect on the ecology.

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