Nuclear Physics
Nuclear Reactors
A devise that is used to produce nuclear energy by controlled nuclear fission is called a nuclear reactor. The following picture shows the structure of a nuclear reactor and generator.
Diagram of a Nuclear Reactor
Parts of Reactor
1. Core: The fuel for fission is kept inside the core. The fuel is taken inside a sealed metal rod and stored in the core. These rods are called fuel rods.
2. Fuels: The fuels, commonly used are Uranium (U235, U233)and Polonium(PU239).
3. Moderator: Fast Neutrons are not capable for doing fission. Slow Neutrons are capable for doing fission. So to do effective fission the speed of Neutrons should be reduced. Moderator is used for that. Heavy water graphite are used as moderators.
4. Control Rods: As a result of fission in the nucleus an average of 2.5 neutrons are released. Among this only one neutron should do the next fission. The rest should be absorbed without doing fission. In this case Fission will take place in a limited rate. And if, the number of neutrons absorbed becomes less, The rate of fission will increase and cause explosion. So, substances which can absorb neutrons are used. Some rods like Boron, Cadmium etc are used for this and they are called control rods.
5. Coolants: As a result of fission reaction a lot of heat energy is generated. This heat is taken out of the core by some fuels like high pressure water, liquid metals and gases. They are called coolants.
6. Shield to protect radiation : To protect living beings from radiation some shields made of thick led and concrete are used around the core and the reactor.
Different Types of Reactors
Reactors can be differentiated according to the fuels used, moderators and manufacturing methods.
1. PWR(Pressurised Water-Cooled Reactor)
- Water under high pressure is used as Coolant
2. BWR(Boiling Water Reactor)
- Vapour is produced inside the reactor itself
3. AGR(Advanced Gas-Cooled Reactor)
- Carbondioxide or nitrogen under high pressure is used as coolant
4. HWR(Heavy Water Reactor)
- Heavy Water is used as coolant.
5. GWR(Graphite Water Reactor)
- Heavy Water is the coolant and graphite is the moderator.
Fast Breader Reactor
In the generally used rich uranium 97% is Uranium238 when fission reaction takes place in fuel rod, Uranium238 undergoes fission and at the same time one among average 2.5 neutrons produced, is used for new fission. Among the rest Uranium238 absorbs neutron at the rate of 0.6 and Pu239 is formed. While, about 100 fission of Uranium235 takes place, 50 -55 Pu239will be formed. If the lost 0.9 neutrons too can be utilised the rate of production of Pu239 will be increased. Pu239 is an isotope capable of nuclear fission. In this way, Fast Breeder Reaction is that which is capable of producing fuel also.
Reactor Becomes Critical
We say this, when a reactor starts its activity. Fuel rods are immersed after immersing control rodes completely into the core. Then control rods are gradually removed after filling with moderator and coolants. At that time the number of neutrons absorbed by them reduces and fission starts. Neutrons available in each fission comes near to one that in the preceding fission. At last it becomes exactly 1. At this stage the reactor is said to be critical.
Nuclear Power Station - Advantages and Disadvantages
Advantages
1. Suitable for places where electricity cannot be generated using water, fossil fuels, wind etc
2. If the chance of danger of radiation is kept inside, atmospheric pollution is less than thermal power station
3. Very low quantity of fuel is needed for nuclear power plants
4. Fuel can also can be produced along with energy production
5. Radio active isotopes used in industrial medical fields are formed as by products
Disadvantages
1. Because of the possibility of danger by reaction, so nuclear power station cannot be built in thick residential areas
2. Radioactive rays and substances produced in case of accidents, are harmful to living beings, agriculture and water sources
3. It is very expensive to establish a nuclear power plant, since many security arrangements are needed
4. Eradication of radio active wastes create many difficulties
5. In the guise of energy production, bomb can be manufactured using fuel and by products
Fast Breader Reactor
In the generally used rich uranium 97% is Uranium238 when fission reaction takes place in fuel rod, Uranium238 undergoes fission and at the same time one among average 2.5 neutrons produced, is used for new fission. Among the rest Uranium238 absorbs neutron at the rate of 0.6 and Pu239 is formed. While, about 100 fission of Uranium235 takes place, 50 -55 Pu239will be formed. If the lost 0.9 neutrons too can be utilised the rate of production of Pu239 will be increased. Pu239 is an isotope capable of nuclear fission. In this way, Fast Breeder Reaction is that which is capable of producing fuel also.
Reactor Becomes Critical
We say this, when a reactor starts its activity. Fuel rods are immersed after immersing control rodes completely into the core. Then control rods are gradually removed after filling with moderator and coolants. At that time the number of neutrons absorbed by them reduces and fission starts. Neutrons available in each fission comes near to one that in the preceding fission. At last it becomes exactly 1. At this stage the reactor is said to be critical.
Nuclear Power Station - Advantages and Disadvantages
Advantages
1. Suitable for places where electricity cannot be generated using water, fossil fuels, wind etc
2. If the chance of danger of radiation is kept inside, atmospheric pollution is less than thermal power station
3. Very low quantity of fuel is needed for nuclear power plants
4. Fuel can also can be produced along with energy production
5. Radio active isotopes used in industrial medical fields are formed as by products
Disadvantages
1. Because of the possibility of danger by reaction, so nuclear power station cannot be built in thick residential areas
2. Radioactive rays and substances produced in case of accidents, are harmful to living beings, agriculture and water sources
3. It is very expensive to establish a nuclear power plant, since many security arrangements are needed
4. Eradication of radio active wastes create many difficulties
5. In the guise of energy production, bomb can be manufactured using fuel and by products
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