NUCLEAR ENERGY
A physical reaction which involves changes in the nucleus of an atom is called a nuclear reaction. The energy released during a nuclear reaction is called nuclear energy.
Nuclear energy can be obtained by two types of nuclear reactions:
(i) Nuclear fission reactions
(ii) Nuclear fusion reactions
The source of nuclear energy is the mass of nucleus. A small amount of mass of nucleus is destroyed -during a nuclear reaction which gets converted into a tremendous amount of energy.
The nuclear energy is released mainly in the form of heat (and some light). The nuclear energy is also known as atomic energy because it can be considered to be coming from the atoms.
NUCLEAR FISSION :
The word 'fission' means to 'split up' into two or more parts. The process in which the heavy nucleus of a radioactive atom splits up into smaller nuclei is called nuclear fission.
A tremendous amount of energy is produced in the nuclear fission process. The sum of masses of the smaller nuclei formed in a fission reaction is a little less than that of the mass of the original heavy nucleus. So, there is a small loss of mass in the nuclear fission process which appears as a tremendous amount of energy.
Working :
Nuclear fission is carried out by bombarding the heavy nuclei with low energy neutrons which are also called slow moving neutrons. The energy produced during nuclear fission reactions is used for making atom bomb and generating electricity at nuclear power plants .
When uranium-235 atoms are bombarded with slow moving neutrons, the heavy uranium nucleus breaks up to produce two medium-weight atoms, barium-139 and krypton-94, with the emission of 3 neutrons.
A tremendous amount of energy is produced during the fission of uranium. This fission reaction can be represented in the form of a nuclear equation as
Fission of 1 atom of uranium-235 produces 10 million times more energy than the energy produced by the burning of 1 atom of carbon from coal.
ATOM BOMB :
In nuclear fission reaction neutrons are used up as well as produced. The neutrons produced in a fission process cause further fission of the heavy nuclei leading to a self-sustaining chain reaction. For example, in the nuclear fission of uranium-235 , 1 neutron is consumed and 3 neutrons are produced in the fission of each nucleus.
When all the neutrons produced during fission of uranium-235 are allowed to cause further fission, then so much energy is produced in a very short time that it cannot be controlled and leads to an explosion called atom bomb.
How to control nuclear fission reaction :
We can control a nuclear fission reaction by using control rods made of boron. Boron has a property that it can absorb neutrons. So, when a nuclear fission reaction is carried out in the presence of boron rods, the excess neutrons produced during successive fissions of uranium-235 atoms are absorbed by boron rods and hence not available to cause further fission. Due to this a controlled fission reaction of uranium-235 takes place liberating heat energy at a slow, steady and manageable rate which can be used for generating electricity at a nuclear power plant.
Nuclear Power Plant
A power plant in which heat energy is obtained by nuclear reactions to make steam and turn turbines, is called a nuclear power plant.
The nuclear power plants use the nuclear fission reaction to generate electricity.
Most of the nuclear power plants use uranium- 235 as fuel to produce heat.
Construction:
In a nuclear power plant, the fission of nuclear fuel uranium-235 is carried out in a steel pressure vessel V of reactor R.
The enriched uranium-235 rods are inserted in a core made of graphite blocks inside the reactor. Graphite is called a moderator. It slows down the speed of neutrons to make them fit for causing fission.
between the uranium rods boron rods B are inserted. Boron rods are called control rods because they absorb excess neutrons and prevent the fission reaction from going out of control. Boron rods can be raised or lowered in the reactor from outside .
The reactor is enclosed in a concrete chamber M having thick walls to absorb the nuclear radiations (so as to protect the outside world from the dangerous nuclear radiations).
Liquid sodium (or carbon dioxide gas) is used as a 'coolant' to transfer the heat produced in the reactor by fission to heat exchanger (or boiler) for converting water into steam.
Working of a nuclear power plant :
The controlled fission of uranium-235 in the nuclear reactor produces a lot of heat energy. Liquid sodium (or carbon dioxide gas) is pumped continuously through the pipes embedded in reactor by a pump P.
Sodium absorbs the heat produced in the reactor. This extremely hot sodium is then passed into the coil of the heat exchanger H containing water. Water absorbs heat from hot sodium and boils to form steam. The hot steam at high pressure is introduced into a turbine chamber C having a turbine T.
The pressure of steam makes the turbine rotate. The shaft S of turbine is connected to a generator G. When the turbine rotates, its shaft also rotates and drives the generator. The generator produces electricity.
The spent steam coming out from the turbine chamber is passed through a condenser D. The condenser cools the spent steam to form water. This water is again sent to the heat exchanger for forming fresh steam.
A nuclear power plant can work day and night for two to three years with the same uranium fuel.
Nuclear Power Plants in India
There are a total of six nuclear power plants in India at present. These nuclear power plants are located at :
(i) Tarapur in Maharashtra,
(ii) Rana Pratap Sagar near Kota in Rajasthan,
(iii) Kalpakkam in Tamil Nadu,
(iv) Narora in Uttar Pradesh,
(v) Kaprapur in Gujarat, and
(vi) Kaiga in Karnataka.
At present only about 3% of the total electrical power produced in India is obtained from nuclear power plants while some of the industrialized countries like France, Germany and Japan, etc. produce more than 30% of their total electrical power.
NUCLEAR FUSION
The word 'fusion' means 'to join' or 'to combine'. The process in which two nuclei of light elemente combine to form a heavy nucleus is called nuclear fusion.
There is some loss of mass during the fusion process which appears as a tremendous amount of energy.
A fusion process is just the opposite of fission process. The energy produced in nuclear fusion reaction is much more than that produced in a nuclear fission reaction.
The energy produced during nuclear fusion can not controlled . So, nuclear fusion energy can not be used for generating electricity.
Condition for nuclear fusion :
When two nuclei are brought together, they repel each other due to their positive charges. Due to this a lot of initial heat energy and high pressure are required to force the lighter nuclei to fuse together to form a bigger nucleus. So, the conditions needed for carrying out nuclear fusion process are 'millions of degrees of temperature' and 'millions of pascals of pressure'.
In other words, nuclear fusion is carried out by heating the lighter atoms to extremely high temperatures under extremely high pressure.
HYDROGEN BOMB :
hydrogen bomb is much more powerful than an atom bomb.
The hydrogen bomb consists of heavy isotopes of hydrogen called deuterium (D) and tritium (T) along with an element lithium-6 (Li).
The detonation (or explosion) of hydrogen bomb is done by using an atom bomb (based on the fission of uranium-235 or plutonium-239).
When the atom bomb is exploded, then its fission reaction produces a lot of heat. This heat raises the temperature of deuterium and tritium to 107°C in a few microseconds. At this temperature, fusion reactions of deuterium and tritium take place producing a tremendous amount of energy. This explodes the hydrogen bomb releasing an enormous amount of energy in a very short time.
The function of lithium-6 used in hydrogen bomb is to produce more tritium needed for fusion.
This is because when lithium is hit by neutrous, it forms tritium and helium.
A hydrogen bomb is actually an uncontrolled nuclear fusion process. Thus, the source of energy of a hydrogen bomb is the same as that of the sun's energy, the only difference being that sun's energy supports life on earth, whereas the bomb destroys life on earth .
The Source of Sun's Energy
The sun is a huge mass of hydrogen gas and the temperature in it is extremely high. The sun may be considered a big thermonuclear furnace where hydrogen atoms are continuously being fused into helium atoms. Mass is being lost during these fusion reactions and energy is being produced. Thus, the sun which gives us heat and light, derives its energy from the fusion of hydrogen nuclei into helium nuclei, which is going on inside it, all the time.
Thus, nuclear fusion reactions of hydrogen are the source of sun's energy. Just like the sun, other stars also obtain their energy from the nuclear fusion reactions of hydrogen.
Advantages of Nuclear Energy
The advantages of nuclear energy are that:
(i) it produces a large amount of useful energy from a very small amount of a nuclear fuel (like uranium- 235).
(ii) once the nuclear fuel (like uranium-235) is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. There is no need for putting in nuclear fuel again and again.
(iii) it does not produce gases like carbon dioxide which contribute to greenhouse effect or sulphur dioxide which causes acid rain.
Disadvantages of Nuelear Energy :
The disadvantages of nuclear energy are that :
(i) the waste products of nuclear fission reactions (produced at nuclear power plants) are radioactive which keep on emitting harmful nuclear radiations for thousands of years. So, it is very difficult to store or dispose of nuclear wastes safely.
(ii) there is the risk of accidents in nuclear reactors. Such accidents- lead to the leakage of radioactive materials which can cause serious damage to the plants, animals (including human beings) and the environment.
(iii) the high cost of installation of nuclear power plants and the limited availability of uranium fuel make the large scale use of nuclear energy prohibitive.
No comments:
Post a Comment