CHAPTER-10
NUCLEAR ENERGY
Text Book Question and Answers
I. Four alternatives are given to each of the following statement or question. Select the most appropriate alternative:
1. Which of the following source of energy is not considered as the transformation of solar energy?
(a)energy of food (b)energy of petroleum (c)energy of coal (d)energy of fission.
Answer: (d) energy of fission
2. Which of the following is a nuclear reaction?
(a)two hydrogen atoms combine to form hydrogen molecule.
(b)sodium atom gives up an electron to become sodium ion.
(c)water splits up into hydrogen and oxygen by electrolysis
(d)isotopes of hydrogen nuclei combine to form helium nuclei.
Answer: (d) isotopes of hydrogen nuclei combine to form helium nuclei
3. The equation E=mc2 was theoretical. It received experimental proof from.
(a)nuclear reactions carried out in the laboratory
(b)measurement of molecular mass of a compound formed by chemical combination.
(c)measurement of molecular mass of products of decomposition
(d)the phenomenon of radioactivity.
Answer: (d)the phenomenon of radioactivity.
4. Transmutation means.
(a)conversion of mass number of an atom
(b)conversion of charge number of an atom
(c)mass and energy are inter convertible
(d)creation of neutrons by fission.
Answer: (a) conversion of mass number of an atom
5. Nuclear power reactor is based on the principle of
(a)exothermic chemical reactions
(b)endothermic chemical reactions
(c)controlled nuclear fission
(d)thermonuclear fusion.
Answer: (c) (c)controlled nuclear fission
6. The nuclear fission chain reaction is initiated by the particle
(a)proton (b)neutron (c)electron (d)positron
Answer: (b) neutron
II. Fill in the blanks.
1. Fissionable isotope of uranium is 92U235
2. Increasing the percentage of fissionable isotope of uranium in the natural uranium is called Enriched uranium
3. The most dangerous radiation released by radioactive materials is gamma rays
4. The equation E=mc2 is derived by the scientist Albert Einstein
5. The nuclear reaction that cannot be controlled at present is Nuclear Fusion reaction
III. Match the following
1. 92U235 – Nuclear fuel
2. Graphite – Moderator
3. Control rod – Cadmium
4. Radiation shield – Lead and concrete
IV. Answer the following questions.
1. Draw a neat diagram of nuclear power reactor and label the parts.
2. Draw the schematic diagram of fission chain reaction of 92U235 isotope.
3. State any two places in india where the nuclear reactor are functioning.
a. Tarapur in Maharashra
b. Kalpakkam in Tamil Nadu
c. Kaiga in Karnataka
d. Kota in Rajasthan
4. State the precautions to be taken, while handling nuclear reaction materials.
Lead jackets are necessary for the workers in the nuclear laboratories
5. How should the spent fuel of a nuclear reator be disposed?
The radioactive matter is impregnated in glass slabs and disposed in the deep sea in strong steel containers, so that radiation cannot reach the level of Biosphere or diffusion of radioactive material cannot reach the level of Biosphere.
6. Explain nuclear fission with an example.
The process of splitting a heavy nucleus into two medium sized nuclei by bombarding the heavy nucleus along with release of neutrons is called nuclear fission.
92U235 + 0n1 -----> 56Ba142 + 36Kr91 + 3 0n1 + energy
Uranium + Neutron ® Barium + Krypton + 3 Neutron + energy
7. Explain nuclear fusion with an equation.
The process by which two or more nuclei of lighter atoms combine to form a heavy nucleus with the liberation of large amount of energy is called nuclear fusion.
1H2 + 1H2 ------> 2He4 + Energy
Deuterium + Deuterium ® Helium nucleus + Energy.
8. State any two differences between chemical reactions and nuclear reactions.
| Chemical reactions | Nuclear reactions |
| Valence electrons of the atoms participate in the reaction. | Electrons of an atom have no role to play in nuclear reactions. |
| Nucleus of an atom does not undergo any change | Nucleus of the atoms undergo a change |
| Products are predictable | Nuclear reaction is a chance reaction. Products depend upon conditions. |
| Mass is conserved | A small amount of mass is converted into energy |
| Inter conversion of compounds to elements or elements to compounds take place | Production of new elements and isotopes take place which is called transmutation. |
Additional Questions and Answers.
1. What are radioactive elements?
All elements which emit Becquerel rays are said to be radioactive and the elements are called radioactive elements.
2. What is radioactivity?
The property of spontaneous disintegration of certain unstable atomic nuclei with the emission of certain radiations is called radioactivity.
3. What are radioactive radiations?
The radiations emitted by radioactive elements are called radioactive radiations.
4. What is artificial radioactivity?
The phenomenon by which a non-radioactive nucleus is rendered radioactive by bombarding with energetic particles is known as artificial radioactivity.
5. Name the scientist who achieved the first nuclear transmutation.
The first ever nuclear transmutation was achieved by Ernest Rutherford. He could transform nitrogen atom into oxygen atom by bombarding the nitrogen atom with an alpha particle.
6. What are isotopes? Which are the isotopes of uranium?
Atoms of the same element having different mass numbers are called isotopes. The two common isotopes of uranium are U235 and U238
7. What are nuclear reactions? Name the two types of nuclear reactions.
Reactions involving changes in the nuclei of atoms are called nuclear reactions. The two types of nuclear reactions are nuclear fission and nuclear fusion.
8. What is nuclear energy?
Energy released during nuclear reactions as a result of conversion of mass into energy is called nuclear energy. It is also called atomic energy
9. Name the classification of radioactive radiations
Radiations can be classified into three types.
1. Alpha (a) rays: Alpha rays are nothing but helium nuclei.
2. Beta(b) rays: Beta rays are electrons
3. Gamma (g) rays: Gamma rays are high energy photons whose energy is higher than that X-rays.
10. Define 1 electron volt of energy. Express this in joule.
The work done on (or the energy gained by) an electron in accelerating it through a potential difference of one volt is called 1 electron volt (1 eV).
1 electron volt = 1.6 x 10-19joule
1 eV= 1.6 x 10-19J
11. What is transmutation?
The changing of one element into another is known as transmutation. Original atom is parent atom and the new atom produced is the daughter atom.
Example:
1. 7N14 + 2He4 ------> 8O17 + 1H1 (proton)
2. 88Ra226 - 2He4 ------>86Rn222
12. What is a chain reaction?
During the fission of U-235, 2 or 3 neutrons are released. These neutrons may cause further fission. The reactions continue further and further in the form of a chain with a multiplying effect. Such a self-sustained reaction is called a chain reaction
Or
Chain reaction is a continuous nuclear fission reaction.
Or
A chain reaction is that process in which number of neutrons keep on multiplying after each fission rapidly in geometric progression, till the whole of the fissionable material is disintegrated.
13. What is the composition of naturally occurring uranium?
Naturally occurring uranium is composed of two isotopes of uranium namely uranium-235 and uranium-238.
14. Why is uranium-238 not suitable to be used in a nuclear reactor?
The neutrons released during the fission of uranium-238 have very high kinetic energy. They escape out of the system and therefore maintaining the fission is not possible.
15. What is chain reaction? Explain with an example.
A chain reaction is defined as a reaction in which the particle that initiates the reaction is also produced during the reaction causing the process to continue on its own with multiplying effect.
To understand the chain reaction of nuclear fission, let us consider the fission of uranium-235 nucleus. The fission of each U-235 nucleus produces two or three neutrons. These neutrons in turn cause fission in three more nuclei which results in the production of nine more neutrons. These neutrons cause fission in nine other nuclei and so on. Thus the reaction proceeds in the form of a chain till all the U-235 available are subjected to fission. Such a self-sustaining reaction is called chain reaction of nuclear fission
16. What is meant by a controlled chain reaction?
In the chain reaction if the number of neutrons produced is kept constant then it is called controlled chain reaction.
Example: Nuclear reactor
17. What is meant by a uncontrolled chain reaction?
In the chain reaction enhances the number of neutrons and leads to explosion it is called uncontrolled chain reaction.
Example: Atomic bomb or nuclear bomb.
18. What is the principle of a nuclear reactor?
Controlled chain reaction is a principle of a nuclear reactor
19. What is the principle of a nuclear bomb?
Uncontrolled chain reaction is a principle of nuclear bomb.
20. What is Einstein's mass-energy relation? Explain.
According to Einstein, mass and energy are different forms of one and the same physical entity and are inter-convertible. During a nuclear reaction, mass-energy is conserved. The relationship between mass converted and the energy released is given by the equation ΔE=Δmc2. Here ΔE is the energy produced when mass Δm is fully converted and c is the speed of light in empty space.
21. Write Einstein rs mass-energy equation. Explain the meaning of the symbols used in the equation.
Einstein's mass-energy equation is E = mc2. Here, E is the energy obtained by converting mass m. c represents the speed of light in empty space.
22. What is the actual amount of energy produced by converting 1 unit (1 amu) of mass?
The actual amount of energy produced by converting one atomic mass unit is about 931 MeV
23. Where does the nuclear energy come from? Explain.
During a nuclear reaction, the sum of the masses of the products is slightly lower than the sum of the masses of the reactant particles. This means that a small amount of mass 'disappears’ during a nuclear reaction. This is called mass defect. Energy equivalent to this mass is changed into energy in accordance with Einstein’s mass-energy relation E = mc2. This is the source of nuclear energy.
24. What is nuclear reactor?
The device used to carry out the fission under controlled condition is called a nuclear reactor.
25. Name the three important types of nuclear reactor.
a. Breeder Reactor (To produce radio isotopes)
b. Power Reactor (To generate electricity)
c. Research Reactor (To carry out research programmes related to atomic energy)
26. Name the important component of a nuclear power reactor.
The important components are:-
a. Fissionable material
b. Moderator
c. Control rods
d. Pressure vessel(Shielding)
e. Cooling system with pump
f. Heat exchanger
27. Name any two fuels used in the nuclear reaction.
a. Uranium U-235
b. Polonium Pu-239
28. Write the unit of nuclear energy
Electro volt (E.V.) or Million electron volt (MeV)
29. What is nuclear power reactor.
A device which converts nuclear energy into electrical energy is called nuclear power reactor.
30. Explain the working of a nuclear power plant.
The nuclear fission is initiated inside the reactor by using stray neutrons. The fission rate is controlled by the automatic adjustment of the cadmium control rods. The moderator slows down the neutrons and makes them available for fission. The fission reaction is allowed to continue at a steady rate inside the reactor. The heat generated during fission is absorbed by the coolant material and carried to the heat exchanger. The heat contained in the coolant is used to heat water flowing through a coiled metallic tube placed inside the heat exchanger. The heat is sufficient to convert water into steam. The steam thus produced is used to run a turbine which in turn operates a generator which produces electricity.
31. What is the role of graphite in a nuclear reactor?
In a nuclear reactor, graphite is used as a moderator to slow down the speed of neutrons.
32. What are thermonuclear reactions? Where do they occur in nature?
Nuclear fusion reactions that are initiated and maintained at very high temperature are called thermonuclear reactions.
The energy of the stars including the sun is due to thermonuclear reactions taking place in them,
33. Write the functions of the following components used in a nuclear power reactor:
a. Moderator
b. Control rods
c. Coolant
d. reflector
e. shielding
a. Moderator: Moderator will slow down the fast neutrons released during fission reaction. Heavy water and graphite are commonly used as moderators
b. Control rods: Rods made of boron or cadmium which are neutron absorbers are used as control rods. The rods can be used to shut down the reactor
c. Coolant: coolant is circulated through the nuclear reactor to absorb the heat energy produced. Liquid sodium metal, high boiling point hydrocarbons, heavy water are some of the coolants.
d. Reflector: Reflector keeps the neutrons confined to the core as much as possible. A moderator can also be used as reflector.
e. Shielding: Reactor is enclosed in a concrete shielding with lead sheet because, to protect the workers and to prevent radioactive radiations being released into the environment.
34. Write the advantages of nuclear fusion over nuclear fission.
Nuclear fusion has no radiation hazards while nuclear fission poses radiation hazards. Energy produced per unit mass is higher in fusion than in fission. The nuclear fuel used in fusion is available in plenty whereas the fuel used for fission is scarce.
35. Why are nuclear weapons considered as weapons of mass destruction?
Nuclear weapons are the most dangerous weapons on earth. They can destroy a whole city, potentially kill millions instantaneously, injure many more and jeopardize the natural environment and lives of future generations through its long-term catastrophic effects. Hence, nuclear weapons are considered as weapons of mass destruction.
36. List some of the hazardous radiations and particles.
Radiations such as alpha rays, beta rays, gamma radiations, X-rays and ultraviolet radiations are dangerous to human health and to the other biotic environment. Even particles such as protons, neutrons and other subatomic particles are hazardous to the health of the fauna and the flora.
37. Write a note on hazards of nuclear radiation.
The particles and radiations emitted by radioactive substances are together called nuclear radiation. They mainly consist of alpha particles, beta particles and gamma radiation. These radiations cause pollution. The pollutants introduced by nuclear reaction are much more dangerous than the pollutants generated during chemical combustion of fuels. People get exposed^ to these radiations during mining and processing of nuclear fuels, while handling nuclear wastes and in events of nuclear explosions and accidents in nuclear reactors.
Exposure to radiations can have both immediate and long-term effects on human beings. The ionic particles in the radiation cause ionization of molecules in the body which may have serious consequences. Long-term effects include irreparable damage to the tissues, cancers of various types and changes in the genetic material. The radiations cause heavy damage not only to humans but to other components of our environment. Therefore, radiation risks should be avoided.
38. Name any one method of disposing off nuclear wastes.
Radioactive nuclear wastes are implanted in a glass slab and disposed in the deep sea. This is one of the ways of disposing of radioactive nuclear wastes.
39. Why radioactive materials are called an invisible enemy?
Radioactive materials emit dangerous and even lethal radiation which cannot be detected by our sense organs. This is why radioactive material is considered an invisible enemy.
40. Write the differences between nuclear fission and nuclear fusion.
| Nuclear Fission | Nuclear Fusion |
| A heavy nucleus is split into two lighter nuclei with the liberation of energy and neutrons | Two or more lighter nuclei fuse to form a heavy nucleus with the liberation of energy. |
| Nuclear fission reactions can be controlled | At present there is no mechanism to control fusion reactions. |
| The process of fission does not require high temperature. | The process of fusion requires extremely high temperature of the order 106 K. |
| Causes radiation pollution problems due to radioactive products | Does not cause radiation pollution since the products are not radioactive. |
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