nuclear power (1)

8/6/2019 Nuclear Power (1)

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INTRODUCTION

� The ever increasing population of world has challenged

man-kind to find alternative sources of energy. One

breakthrough was to use the energy present in the

nucleus of an atom. All the stars in the sky, includingsun, radiates energy due to a series of nuclear reaction

occurring in them. We have also recognised and are

utilising the fact that nuclear energy can be used too

produce electricity.� It is the use of sustained nuclear fission to generate heat

and do useful work. Nuclear Electric Plants, Nuclear

Ships and Submarines use controlled nuclear energy to

heat water and produce steam.



� In space, nuclear energy decays naturally in a

radioisotope thermoelectric generator

� Nuclear power provides about 6% of the world's

energy and 13±14% of the world's electricity, with

the U.S., France, and Japan together accounting for

about 50% of nuclear generated electricity. Also,

more than 150 naval vessels using nuclear propulsion

have been built.



HISTORY

Nuclear energy was first discovered in 1934 by Enrico

Fermi. The first nuclear bombs were built in 1945 as a

result of the infamous Manhattan Project. The first plutonium bomb, code-named Trinity, was detonated on

July 16, 1945 in New Mexico. On August 6th 1945 the

first uranium bomb was detonated over Hiroshima.

Three days later a plutonium bomb was dropped on

Nagasaki. There is over 200,000 deaths associated with

these detonations. Electricity wasn¶t produced with

nuclear energy until 1951.



NUCLEAR REACTION

� When a nucleus interacts with another nucleus or a particle like neutron resulting in the formation of new

nuclei, the process is called a nuclear reaction.

Such reactions follow the following laws:

(i) The total charge (number of protons) before and

after the nuclear reaction remains the same.235

92 U + 10n 140

56Ba + 310 n + Energy

Total no. of protons before the reaction is

= 92 + 0 = 92

Total no. of protons after the reaction

= 56 + 36 + 3*0 = 92



(ii) The total number of nucleons before and

after the nuclear reaction remains the same.

In the above reaction, total number of nucleons before reaction = 235 + 1 = 236

Total number of nucleons after reaction

= 140 + 93 + 3*1 = 236

(iii) The total mass of the products is not equalto reactants. The diff erence in the mass is

converted into energy which can be

calculated by Einsteins mass energy relation

E = mc2 (where E = energy produced during

nuclear reaction; m = mass of reactants mass

of products; c = velocity of light)



NUCLEAR FORCE

� As the protons are packed very closely due to the small size of the nucleus, the repulsive electrostaticforces between the protons is large enough todisintegrate the nucleus. But this actually does not

happen. It can therefore be concluded that in case of a stable nucleus attractive forces exist between the nucleons which is stronger than the electrostaticforces of repulsion. These attractive forces are callednuclear forces.

� It has been found that the nuclear forces are independent of the charge on nucleons and existbetween proton-proton, proton-neutron, neutron-neutron.



� In small nuclei, nuclear forces are greater thanelectrostatic forde of repulsion and therefore, small

nuclei are stable. whereas., in big unstable nuclei,electrostatic forces of repulsion are greater than nuclear forces of attraction.

� Naturally occurring uranium consists of 2 isotopes.23892U is stable whereas 23592U has a delicate

balance between electrostatic forces of repulsion andnuclear forces of attraction. It has been found that if aslow moving neutron strikes U-235, the balance of theforces is disrupted and U-235 splits into 2 nuclei,

neutrons and releases energy. Such a nuclei which can be split thereby releasing energy is called fissile nuclei.

� Three such important nuclei are U235, Plutonium- 239and Thorium- 232.



NUCLEAR FISSION

� The process of splitting up of a fissile nucleus (like U235) by a slow moving neutron is called nuclear fission.

� When a slow moving neutron strikes the U-235 nucleus, it

may yield in any of the following products.

23592U + 1

0 n 23692U

Unstable

14056Ba + 93

36Kr + 310n + energy

14454Xe + 90

38Sr + 210n +energy

14455Cs + 90

37Pb + 210n + energy

13957La + 95

42Mo + 210n + 70

-1e + energy



� It has been observed U-235 splits into two groups of

nuclei.

a. A heavy group of nuclei with mass number 130 ± 140.

b. A light group of nuclei with mass number 85 ± 104.



NUCLEAR CHAIN REACTION� When a U-235 nucleus is bombarded by a neutron, it splits up

into 2 medium ± sized nuclei along with the emission of 2 or 3

neutron. These neutron may be absorbed by the surrounding U-

235 nuclei resulting in emission of more neutrons. Thus, one

fission reaction triggers another fission reaction. This is called

nuclear chain reaction.



CONTROLLED NUCLEAR REACTION

� A chain nuclear reaction can be controlled to release energy at

a rate which can be handled comfortably to produce

electricity.

� One U-235 nucleus fission releases 3.2 * 10-11 J of energy.

Theoretical calculations show that 1 kg of U-235 will release

8.18 * 1013 J of energy in less than 1 minutes time. This is a

very huge rate of release of energy with time. We do not have

devices to constructively use energy released at this rate.Therefore such a release of energy can only cause a big

explosion. This is the basis of atom bomb.

UNCONTROLLED NUCLEAR REACTION



NUCLEAR REACTOR

� A device in which electricity is produced by the processof controlled nuclear fission reaction is called nuclear

reactor.



Outside the core:

a. Heat Exchanger: The hot coolant, coming from the reactor

core, heats the water present in the heat exchanger into

pressurised steam.

b. Steam Turbine: The pressurised steam is passed on to the

steam turbine which rotates dynamo of generator producing

electricity.

Working:

� At the start, the fuel rods are placed in their positions and

control rods are inserted fully inside the core in between the

fuel rods. The space between the fuel rods and control rods isfilled with moderator. When the control rods are pulled out of

the reactor core, a stray neutron hits a U-235 atom and fission

reaction is initiated. This reaction releases more neutrons

thereby starting a chain reaction.



�� While a neutron moves from the surface of one fuel rod to theWhile a neutron moves from the surface of one fuel rod to theother, it strikes the atoms of the moderator. It transfers itsother, it strikes the atoms of the moderator. It transfers itsenergy to the moderator and slows down. This neutron isenergy to the moderator and slows down. This neutron is

called thermal neutron. When this thermal neutron strikescalled thermal neutron. When this thermal neutron strikesanother Uanother U--235 nucleus, a fission reaction takes and the235 nucleus, a fission reaction takes and the

process continues. process continues.

�� Excess neutrons are absorbed by control rods. When theExcess neutrons are absorbed by control rods. When thespeed of reaction increases, the control rods are inserted in thespeed of reaction increases, the control rods are inserted in the

core in order to absorb more neutrons. On the other hand, if core in order to absorb more neutrons. On the other hand, if the reaction speed decreases, control rods are pulled out.the reaction speed decreases, control rods are pulled out.

�� The heat generated in the core is absorbed by the coolant. AThe heat generated in the core is absorbed by the coolant. A pump moves the heated coolant at high pressure to the heat pump moves the heated coolant at high pressure to the heatexchanger. In the heat exchanger, heat is transferred from theexchanger. In the heat exchanger, heat is transferred from the

coolant to water. This water is converted into high pressurecoolant to water. This water is converted into high pressuresteam. This steam is guided to turn the blades of a turbinesteam. This steam is guided to turn the blades of a turbinewhich is connected to a generator which produces electricity.which is connected to a generator which produces electricity.The used steam is brought back to the heat exchanger throughThe used steam is brought back to the heat exchanger througha condenser in a closed loop.a condenser in a closed loop.



ALTERNATIVE FUEL FOR NUCLEAR

REACTION

�� PlutoniumPlutonium--239 is another fissile nucleus that is used as a239 is another fissile nucleus that is used as anuclear fuel. Punuclear fuel. Pu--239 does not occur in nature and is239 does not occur in nature and is

therefore, artificially prepared by the following set of therefore, artificially prepared by the following set of

reactions:reactions:

a.a. A high speed neutron is bombarded on UA high speed neutron is bombarded on U--238238238238

9292U +U + 1100nn 239239

9292UU

b. U b. U--239 being unstable emits a ß239 being unstable emits a ß -- particle particle239239

9292UU 2392399393 Np + Np + 00

--11ee

c. Npc. Np--239 (neptunium) again emits a ß239 (neptunium) again emits a ß ± ± particle particle239239

9393 Np Np 2392399494Pu +Pu + 00

--11ee

In the above process a non fissile UIn the above process a non fissile U--238 nuclei is converted238 nuclei is converted

into a fissile nuclei Puinto a fissile nuclei Pu--239. this is done in reactor called239. this is done in reactor called

breeder reactors. breeder reactors.



NUCLEAR ENERGY IN INDIANUCLEAR ENERGY IN INDIA

�� Developed countries depend heavily on nuclear reactor Developed countries depend heavily on nuclear reactor for their electricity generation requirements. Around 30%for their electricity generation requirements. Around 30%of the total electric power is generated from nuclear of the total electric power is generated from nuclear reactors.reactors.

�� In India, around 3% of the total electric power isIn India, around 3% of the total electric power isgenerated through nuclear reactors. The nuclear reactorsgenerated through nuclear reactors. The nuclear reactorsin operation are:in operation are: (a)(a) Tarapur Tarapur in Maharashtra, (b) Kota inin Maharashtra, (b) Kota inRajasthan, (c)Rajasthan, (c) KalpakkamKalpakkam in Tamil Nadu & (d)in Tamil Nadu & (d) Narora Narora

in Uttar Pradesh.in Uttar Pradesh. Some other nuclear power Some other nuclear power are in the pipeline which are expectedare in the pipeline which are expected

to become operational soon.to become operational soon.



�� India has major researchIndia has major research centrescentres for atomic energy:for atomic energy:

One of these isOne of these is BhabhaBhabha Atomic Research CentreAtomic Research Centre

(BARC) at Mumbai. Some others are located at(BARC) at Mumbai. Some others are located at

GulmargGulmarg in Srinagar and Kolkata in West Bengal.in Srinagar and Kolkata in West Bengal.



NUCLEAR FUSIONNUCLEAR FUSION

��

Nuclear Fusion is a process in which two or more lighter Nuclear Fusion is a process in which two or more lighter nuclei combine to form a heavy and stable nucleusnuclei combine to form a heavy and stable nucleus

resulting in the release of energy.resulting in the release of energy.

�� The mass of products of a nuclear fusion reaction is lessThe mass of products of a nuclear fusion reaction is less

than the mass of the reactants. This difference in mass isthan the mass of the reactants. This difference in mass isconverted into energy which can be calculated by theconverted into energy which can be calculated by the

formula E = mcformula E = mc22 , where,, where,

m = mass of reactantsm = mass of reactants ± ± mass of productmass of product

�� Some examples of nuclear fusion reactions are:Some examples of nuclear fusion reactions are:

2211H +H + 22

11HH 33

11H +H + 11

11H + Energy (4.0 MeV)H + Energy (4.0 MeV)

1111H +H + 11

11HH 22

11H +H + 00

+1+1e +e + 0000 + Energy (0.4 MeV)+ Energy (0.4 MeV)



Special Conditions for Nuclear Fusion

��

When 2 nuclei come near to each other, there will be aWhen 2 nuclei come near to each other, there will be astrong electrostatic force of repulsion between them.strong electrostatic force of repulsion between them.

This is because both the nuclei are positively chargedThis is because both the nuclei are positively charged

(due to presence of protons). To overcome the repulsive(due to presence of protons). To overcome the repulsive

force, so that the nuclei may collide, the nuclei shouldforce, so that the nuclei may collide, the nuclei should possess very high kinetic energy. The conditions in possess very high kinetic energy. The conditions in

which a nucleus can have such high amount of kineticwhich a nucleus can have such high amount of kinetic

energies are:energies are:

1.1. Temperature of the order of 10Temperature of the order of 1077--101088 K K 2.2. Using particle accelerators which are capable of Using particle accelerators which are capable of

generating high kinetic energy particles.generating high kinetic energy particles.



ADVANTAGE OF NUCLEAR FUSIONADVANTAGE OF NUCLEAR FUSION

OVER NUCLEAR FISSIONOVER NUCLEAR FISSION

�� The nuclear fusion reaction has a number of The nuclear fusion reaction has a number of

advantages over nuclear fission. These are:advantages over nuclear fission. These are:

1.1. The energy released per unit mass from nuclear fusionThe energy released per unit mass from nuclear fusion

reaction is more than nuclear fission reaction.reaction is more than nuclear fission reaction.2.2. Nuclear fusion reaction does not involve radioactive Nuclear fusion reaction does not involve radioactive

substances and therefore, is a better option thansubstances and therefore, is a better option than

nuclear fission reaction for generating electricity.nuclear fission reaction for generating electricity.



NUCLEAR HAZARDNUCLEAR HAZARD

� Nuclear fission process involves radioactive substanceswhich emit , particles, radiations. These are harmful

because of their high ionisation and penetrating power. If

these fall on us, the molecules (of which a cell is made up

of) are ionised which disturbs biochemical process. Theexact damage that these radiations can produce depends on

the dose of radiation, rate at which the dose is given.

Forms of Nuclear HazardsIn case of an atom bomb explosion a fallout cloud is

produced which emits harmful radiations killing lakhs of

people within a short span of time, also effecting a large

population who suffer from incurable diseases like cancer.



Hydrogen bomb which is based on fusion reaction, the

damage is more extensive.

Apart from radiation the tremendous amount of heat energy

and shock waves cause mass destruction. Hiroshima and Nagasaki are 2 examples of this in front of us.

Nuclear AccidentsIf something goes wrong in a nuclear reactor harmful

radiations may be released into the atmosphere. This can

effect a large population and environment around the

accident site. Sometimes the extent of damage can be upto hundreds of kilometres. Nuclear accidents like in 3

Mile Island reactor in the U.S, Chernobyle reactor in

former U.S.S.R and Fukoshima reactor in Japan are some

examples.



NUCLEAR WASTE STORAGEThe spent fuel rods are the most radioactive of all nuclear

wastes. These are temporarily stored in a storage pool nextto the reactor. The pool contains water and Boric Acid.

The Boric Acid helps in absorbing the radiations given out

by spent fuel rods. Later on deep mines, which are not in

use, or underground ocean floor are important places for their storage.

These radiation effect the human health in the following

ways:

1. Somatic Effect: This effect leads to diseases likecancer.

2. Genetic Effect: The radiation can cause a change in

the genes which are then passed on to the coming

generation.

nuclear power (1)

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