Topics – Nuclear Power, Nuclear Reactor, Fission , Fusion

1. Consider the following statements:
1. Plutonium-239 can be made artificially
2. Boron is used in a nuclear reactor to absorb unwanted neutrons
3. In nature, the availability of Uranium-238 is much more than that of Uranium-235
Which of these statements is/are correct?

a) 1 only
b) 1 and 2
c) 2 and 3
d) 1, 2 and 3

2. Which one among the following radioactive substances has maximum half- life period ?

a) Carbon-14
b) Plutonium-239
c) Radium-226
d) Uranium-238

3. Consider the following statements : In a nuclear reactor, self-sustained chain reaction is possible, because
I. more neutrons are released in each of the fission reactions.
II. the neutrons immediately take part in the fission process.
III. the fast neutrons are slowed down by Graphite.
IV. every neutron released in the fission reaction initiates further fission.

Which of these statements are correct ?
a) I, II and III
b) I and III
c) II and IV
d) II, III and IV

4. The Function of heavy water in a nuclear reactor is to

a) Slow down the speed of neutrons.
b) Increase the speed of neutrons.
c) Coll down the reactor
d) Stop the nucleus reaction.

5. Statement I : Heavy water is used as moderator in nuclear reactor.
Statement I : Thermal neutrons are used for fission reaction in a reactor.

a) Both the statements are individually true and statement II is the correct explanation of statement I
b) Both the statements are individually true but statement II is not the correct explanation of statement I
c) Statement I is true but statement II is false
d) Statement I is false but statement II is true

6. The main source of energy in Sun is :

a) Nuclear fusion
b) Nuclear fission
c) Chemical reaction
d) Mechanical energy

7. The difference between a nuclear reactor and an atomic bomb is that

a) no chain reaction takes place in nuclear reactor while in the atomic bomb there is a chain reaction
b) the chain reaction in nuclear reactor is controlled
c) the chain reaction in nuclear reactor is not controlled
d) no chain reaction takes place in atomic bomb while it takes place in nuclear reactor

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8. In an atomic explosion, release of large amount of energy is due to conversion of

a) chemical energy into nuclear energy
b) nuclear energy into heat
c) mass into energy
d) chemical energy into heat

9. What is the source of electrical energy in an artificial satellite ?

a) Thermopile
b) Solar cells
c) Dynamo
d) Small nuclear reactor

10. Consider the following statements:
1. The Nuclear Suppliers Group has 24 countries as its members.
2. India is a member of the Nuclear Suppliers Group.

Which of the statements given above is/are correct?
a) 1 only
b) 2 only
c) Both 1 and 2
d) Neither 1 nor 2

Answers 

1. D. Plutonium-239 can be made fairly easily in nuclear power reactors from uranium-238, an abundant but non fissionable isotope. It is a by-product, or “waste product,” of these reactors. It can be removed from the reactor, purified, and then re-used to make electrical power. Because of its ability to undergo fission with neutrons of all energies, plutonium-239 has considerable practical applications as an energy source in nuclear weapons and as fuel in nuclear power reactors.

Boron and Cadmium help to maintain the rate of nuclear fission by absorbing the excess neutrons, which if not removed may lead to an uncontrolled fission reaction. In short, they maintain the neutron flux in a nuclear reactor.

Uranium is present naturally in virtually all soil, rock and water. Uranium in soil and rocks is distributed throughout the environment by wind, rain and geologic processes. U-238 has abundance 99.2745%, and u-235 has o.7200%. The process used to increase the amount of uranium-235 relative to uranium-238 is known as uranium enrichment.

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2. D

Half-life (t1⁄2) is the amount of time required for a quantity to fall to half its value as measured at the beginning of the time period.After two half-lives, Half life of radioactive isotopethere will be one fourth the original sample, after three half-lives one eight the original sample, and so forth.

Isotope Half-life (yr)
Radium-226 1,600
Carbon-14 5,730
Plutonium-239 24,110
Uranium-238 4,468,000,000

3. A.

When a large, fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The nucleus splitsNuclear Fission Controlled chain reaction into two or more lighter nuclei, releasing kinetic energy, gamma radiation, and free neutrons. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction.

A possible nuclear fission chain reaction. 1. A uranium-235 atom absorbs a neutron, and fissions into two new atoms (fission fragments), releasing three new neutrons and a large amount of binding energy.2. One of those neutrons is absorbed by an atom of uranium-238, and does not continue the reaction. Another neutron leaves the system without being absorbed. However, one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and more binding energy.3. Both of those neutrons collide with uranium-235 atoms, each of which fissions and releases a few neutrons, which can then continue the reaction.

4.  A.

A neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction
involving uranium-235. Eg : Graphite, Heavy Water etc.

5. B

The hydorgen atoms in the water posses only one proton and one electron, and thus are almost exactly the same mass as the incoming neutrons. The problem with
Ordinary water is that the hydrogen atoms may absorb some of the neutrons, thus preventing them from getting through to the fissionable material and and the chain reaction can no longer continue. Heavy water, however, is deuterium oxide. Deuterium is an isotope of hydrogen with one proton and one neutron. Thus the hydrogen atom already has one extra neutron, and is much less likely to absorb another. This means that when heavy water is used as a moderator, enough neutrons get through.

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6. A .

The Nuclear Fusion Reaction is the basis on which sun releases light and heat. We receive a combination of this heat & light in the form of solar energy which we use for our benefit.

7. B.

A nuclear reactor is designed to allow a controlled chain reaction to take place. Moveable control rods are placed between the rods of nuclear fuel. These control rods absorb some of the neutrons, so fewer neutrons are available to split uranium nuclei.

8. C.

Atomic energy is based on the conversion of mass into energy. Albert Einstein put forward the following equation that provides the basis for calculating the amount of energy released when the nucleus of an atom is split. E = mc2 . The equation means that when the nucleus of an atom is split, the amount of energy released, E, in joules, is equal to the loss of its mass, m, in kilograms, times the speed of light squared, c2, in m/s2. Because c2 is a very large figure (300,000,000 X 300,000,000 = 90,000.000,000,000,000 ), a small amount of mass can be converted into an enormous amount of energy.

9. B.

Many artificial satellites and space stations use solar panels to provide electrical energy. For satellites around outer planets where the amount of solar radiation is much less, nuclear sources (usually the decay of plutonium) are used.

10. D.

India is seeking membership in the Nuclear Suppliers Group, a 48-nation body established  in May 1974 to ensure that civilian trade in nuclear materials is not diverted for military purposes.

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