So, in the last class we were talking about
nuclear power generation.
Well, if you toggle these two letters it becomes
unclear power generation and so, that should
not happen, right. It should be clear to you
what you are talking about. Now, here we have
a few types, distinct types of generators
that we have heard of. We have heard of the
boiling water reactor, we have heard of the
pressurized water reactor, we have heard of
the pressurized water reactor of two types
– one, where the water is normal water,
H 2 O and also the one where the pressurized
water is heavy water, deuterium. So, the two
types H 2 O and D 2 O; most of the Indian
reactors are of this type. Then, we have 
the gas-cooled reactors, where the moderator
is graphite. So, you have the situation where
the graphite is the moderator and you have
some gas, some inert gas working as the coolant
and we also have the liquid metal coolant
system or these are mostly used with the fast
breeder reactor, liquid metal fast breeder
reactor.
Why this word fast? What is the meaning of
that? The neutrons are fast. They are not
slowed down, so here you have the liquid metal
as the coolant, no moderator and the purpose
is both to generate electrical power as well
as to breed more fuel for future reactors
and for that you need fast neutrons. So, we
have the different types of reactors and in
another day, we will take up in detail the
prime consideration these days the safety
consideration and the environmental problems
that we will take up together, in a day when
we deal with the environmental problems both
of the coal, nuclear, as well as hydroelectric
power.
So, you have this few types of, possible types
of nuclear reactors. But, all these are fission
reactors, right where heavy nuclei are broken
up to form smaller, lighter nuclei and you
get some energy output and it is not difficult
to see that the reaction products, they are
all radioactive. The reaction itself is a
radioactive reaction and when you are talking
about the breeding of uranium 238 to plutonium
239 that is also a very, very radioactive
substance. So, there are inherent dangers
which have been, you know actually seen in
some specific hazardous cases, like there
was a Three Mile Island incident in US, there
was a Chernobyl incident in Russia, Ukraine
actually. So, you have these problems associated
with it, but the technology is well proven,
working.
One of the directions in which people are
working, trying to achieve another type of
reactor is the fusion reactor.
There is no fusion reactor as yet. This is
a futuristic research initiative, but as energy
engineers, you should be exposed to that possibility.
That is why today we will take up what are
the various directions in which people are
trying to achieve it. Fusion is essentially
the reaction that goes on inside the sun,
right. What goes on inside the sun? Hydrogen
fused to form helium, right. Let us consider
that process. Hydrogen nucleus means what?
A single proton. A helium nucleus means what?
Two protons.
Two protons and two …, so four nucleons;
four, four heavy things inside. So, can two
hydrogen nuclei fuse to form helium? No; that
is not possible. There has to be four of them
and it is not difficult to see that if you
put something in high pressure, then it is
possible that in spite of the electrical repulsion
between the nuclei, high pressure high temperature
means there will be a finite possibility they
will collide with each other. Two will collide
with each other, but what is the probability
that three collides with each other? Very
low; what is the probability that four will
collide with each other? Very low.
That is why four hydrogen nuclei coming together
at the same time and fusing into helium is
practically impossible. I should not say practically
impossible, because that does take place inside
some stars, some stars, not sun though.
That is not what happens inside the sun, because
inside the sun there is another reaction,
another process taking place whose end effect
is that; that it is consuming hydrogen and
producing helium, but the process is not that
hydrogen nuclei are simply colliding and forming
helium, no. There are other substances coming
in the process, including carbon. So, had
carbon not been there inside the sun, the
sun would not really have fusion. That requires,
simply hydrogen fusing into helium requires
far larger mass and pressure. So, obviously
when we try to do or enact this in Earth based
reaction, obviously we cannot view fusing
hydrogen into helium. Can we? We simply cannot.
We have to look at some possibility where
two nuclei, two not more than that, fuse and
produce something. Is that clear? So, it is
a common misconception that we are looking
at a fusion reaction in which hydrogen will
be fused into helium, no. Nobody is looking
into that; nobody is trying to fuse hydrogen
into the helium, because that is practically
impossible to enact on the surface of the
earth. So, what are we really looking at?
What we are really looking at is a reaction
where two isotopes of hydrogen, deuterium
and what is the third one?
Tritium.
Tritium, so that they merge together, they
fuse to produce helium.
So, what is the symbol of deuterium, is this,
to produce what? It will produce … Then,
you have one extra plus energy. So, it is
this reaction people look at, because that
can happen at a relatively lower temperature,
which that relatively lower temperature is
also very close to the temperature inside
the sun, but nevertheless it is not an impossibly
high temperature. So, it is this reaction
that people are looking at and obviously in
order for hydrogen and helium to fuse together,
they should be at very high temperature. Temperature
means nothing but the inherent speed of motion
of the molecules.
In that temperature, obviously they will not
be molecules they will be individual atoms,
but nevertheless not only individual atoms,
but also at that temperature the electrons
will be stripped off from them. So, electrons
and the nuclei will freely move together,
a state that is called plasma. So, we are
looking at a situation where these two things
are heated up to a temperature where it becomes
plasma. The temperature is so high that of
their own effort the deuterium and tritium
nuclei they can overcome their electrical
repulsion, because both are positively charged,
they can overcome the electrical repulsion
and they can fuse. The temperature is of the
order of a lakh of lakh of degrees, 10 to
the power of 6 degrees or so.
How can we produce that? Most importantly
if you really produce that temperature, obviously
you cannot really burn coal and they produce
that temperature; you cannot. So, there has
to be some way of generating that temperature
and then a greater problem is how to contain
it? Anything that will come in contact with
that will melt. So, these are the two major
problems that have to be overcome in order
to produce a fusion reactor. First, how to
produce that temperature and second, how to
contain that? Now, how to produce that temperature
is not all that big a problem; how to produce
that temperature is not all that big a problem.
For example if say, you generate high speed
neutrons which is possible now, nowadays and
put into the plasma. The energy that is there
in the neutrons will be, by means of their
internal collisions will be transferred into
the other substances inside and obviously
then that will increase their average speed
of motion which is nothing but temperature.
So, that is one way. You produce high speed
neutrons and bombard them; you put them into
that …... Suppose you have got a chamber
in which you have put deuterium and tritium
together and you will simply put in lot of
energy by that means. If you keep on putting
it and if you do not allow this energy to
escape by means of proper shielding, obviously
the temperature will go on increasing and
it is possible to reach that kind of a temperature.
There is also the possibility that you inject
radio waves which will ……, which frequency
will be tuned to the natural frequency of
oscillation of these things, so that they
will sort of oscillate in resonance and that
imparts the kind of the energy in the radio
waves into those nuclei. So, it is possible
to impart energy into that and if you keep
on doing that, it is possible to raise the
temperature to very high level. So, raising
the temperature to that high level is not
the big problem, but the big problem is really
the confinement. So, there are two issues.
One … and two, this is actually overcome
by injecting either an ion beam or a neutron
beam or whatever and the other is through
radio waves. The next problem is the bigger
problem that is plasma confinement. So, plasma,
do you understand what plasma is? It is where
the gas is raised to such a temperature that
the electrons are stripped off and you have
the electrons separate and the nucleus separate
moving inside the gas. That is, that state
is called plasma state. So, what we are talking
about is plasma confinement. How to confine
the plasma?
Now, there are essentially two methods of
plasma confinement that people are trying
off.
To understand the first one, try to picture,
visualize this. It is magnetic confinement,
magnetic confinement; try to picture like
this.
Suppose you have a magnetic field going into
the sheet of paper which means I will draw
it like this. Do you understand this notation?
This is going into the board and if I draw
it with a dot it comes out of board and suppose
here, there is one charged particle say an
electron say and say that this fellow has
a motion this way, so here is a I have, I
have drawn it here, but actually the magnetic
field is going everywhere and here is the
electron that is moving in the magnetic field
that direction. What will be the force felt
by the electron?
Yes, ….. in which direction?
Which law? Which law?
Yes, so do that and tell me which will be
direction of the force?
Downward, so because of that downward motion
what will be the resultant motion of the electron?
It will move; it will deviate from the straight
path, it will move towards this say it has
come here. When it has come here this is the
direction of the force, this is direction
of the velocity. What will be the direction
of the force? Again towards the center; so,
it will again be deflected, so it will be
moving in a circle, right. So what has happened
in effect is that the magnetic field is in
that direction and the electron is forced
to move around the magnetic field. Now, the
electron, there is no reason to believe that
the electron has only one direction of velocity.
Suppose it has also some component of velocity
along the magnetic field, what will happen?
That means it is moving in some arbitrary
direction which has a component this way,
another component along the magnetic field.
Will the component along that magnetic field
be affected?
No.
No, it will produce no force. So, if you have
a magnetic line of force going like this and
if you have an electron here, how will it
move? It will have two directions. As I told
you, one along the magnetic field another
perpendicular to the magnetic field and the
direction perpendicular to the magnetic field
will cause this rotational motion. As a result
what will happen? So, the electron in effect
has got locked into the magnetic field. It
cannot escape. That is exactly why in fact
you have the charged particles falling into
the Earth’s atmosphere through the north
pole where you see the Aurora Borealis, because
of this, because you have the magnetic field
going and the charged particles get locked
to that and go into the Earth’s atmosphere
through that point.
Similarly, if you have the proton with a different
charge, you will still have the locking effect;
only it will move in the opposite direction.
So, you have, if you have a magnetic field
produced, the charged particles get locked
to the magnetic field; charged particles get
locked to the magnetic field and they cannot
escape, right. Can we use that for producing
a confinement of the plasma?
Suppose you have got a magnetic field that
goes like this and these poor fellows will
get locked to that and will move like this,
fine; but, after that it will hit the wall,
after sometime. So, that wall will melt. So,
how can we, yes you are moving the hand like
this; yes, you are right, it has to then go
around which means the magnetic field has
to be circular. So, the magnetic field being
circular, how can you produce that magnetic
field? By winding a toroidal coil, right.
So, you will wind a toroidal coil that will
produce a magnetic field that goes in a circular
direction and the charged particles will be
locked to it, clear and since if you wind
a toroidal coil, the magnetic fields concentration
will move toward the center, less toward the
edge, so most of the material will be concentrated
at the center. It will move as concentrated
at the center and there will be very little
towards the edge. So, actually the plasma
will not touch the wall. Is that concept clear?
That concept was proposed quite long back
by Russian scientist. He is called Tokamak
and since then various groups around the world
including in our country our Saha Institute
of Nuclear Physics has a Tokamak reactor.
So, we have the Tokamak concept tried out
in various places, but the main problem as
yet is that the confinement that people have
been able to achieve is rather transient,
it does not last long. After that it tends
to escape, because the magnetic field and
plasma interact and there are instabilities.
The magnetic field does not really stay like
this; that sort of oscillates. So, the plasma
touches the wall.
One way people have tried to bring in some
stability is to have not only a toroidal coil;
a toroidal coil means something that goes
like this and comes back something like this
and you would wind like this, so that the
magnetic field is produced like, so that is
a toroidal coil. So, in effect, all these
windings are essentially around a circumference
of the torus. Some stability can be a brought
in if in addition to that you also have a
poloidal magnetic field, a poloidal winding
which goes more or less along that. So, as
a result, the magnetic field will be, you
know winding around; it should not be exactly
around the circle, but that produces some
amount of stability. So, in general the way
people try to overcome this problem is to
add, is to have a combination of both the
toroidal coil as well as the poloidal coil.
Now, the way the actual reactors are, I mean
people have tried and confinement have been
achieved for a period of a second or so, that
is considered to be a big break through, right.
When we are able to confine plasma and generate
energy out of such a thing for a second that
is also a big break through, because that
is how people proceed. Now, let me give you
a schematic diagram of the way people are
trying to do it.
You can see, so here in this case you see
these are the toroidal winding that goes around;
so, these are the toroidal windings that go
around. Here are the poloidal coils. Can you
see? Here are the poloidal coils that go like
so; not exactly like so, it also have a certain
amount of winding something like this.
If you, if you look at this picture here,
if you look at this picture here it will be
clearer, where these windings are the toroidal
windings and poloidal winding go like this.
These are the poloidal windings. Yes, it is
a bit twisted, right. Why do we need to have
them twisted? Because, if you have a high
amount of current flowing through, they will
try to fly off; so, unless you twist it there
is no structural stability. So, you have to
have a bit of twisting around it. So, there
are two windings really - the toroidal windings,
the poloidal windings. Inside you look at
the core. This is the section of the core.
At the center there would be the plasma that
is confined. Beyond that there would be a
first wall and then there would be some kind
of a blanket. Then, there will be cooling
system. So, there will be all sorts of, you
know, layers in that. You have to take the
heat out; there has to be a cooling system.
So, let us go back to this, this diagram and
let us see what it is. So, you have the internal
structure that you can see here. This is the
toroidal field produced and this is the poloidal
field produced. As a result, this will be
the direction, resultant direction of the
magnetic field. So, that will again wind around.
Teek hai? Now, there has to be some ports
through which you first inject the fuel, right;
so, there has to be similar ports for that.
There has to be also ports for the neutral
beam injection. As I told you, one way to
produce the heat is to accelerate something.
It is easier to accelerate by, easier to accelerate,
you know, charged particles, but ultimately
when you put it in, it has to be neutral.
So, you first accelerate and then neutralize
it and then put that in, so something goes
in with a high kinetic energy. These are done
through these neutral beam injector points,
right. So, if you put that in, can you see
that clearly? So, these are the neutral beam
injection points.
Here is another port that is for RF heater,
radio frequency heater. So, there are two
possible types of heating system, I told you.
Both are generally employed. So, this is the
RF heating, this is the neutral beam injection.
So these are the two ways of heating it up.
Now, after it is heated up, it is assumed
that that will circulate around, more or less
be concentrated towards the center, a line
and it will generate, what? Helium as well
as neutrons. Now, neutron, what do you do
with that neutron? What do you do with that
neutron? You cannot really collect the neutrons,
put in a bucket and keep it for your future
use; obviously you cannot do that and also
tritium is very expensive. So, one way people
try to overcome that problem is to make a
blanket, a blanket made of lithium. When that
is bombarded with neutrons that breeds tritium;
so, you need to produce tritium in that process.
That is the lithium is bombarded with neutrons
and that breeds tritium. So, you have the
tritium produced in the system and as the
product of the system is taken out, you get
helium inside the plasma and you get tritium
in the blanket. So, that can be used. So,
that is why there is a blanket.
Outside the blanket there is a cooling system.
Here you can see a cooling system through
which you can have the same way of water walls
that means water pipes go in to cool the system.
Then, there is a, just before the cooling
system there is a fast wall made of steel.
That means that really takes the heat and
stands there. So, there is a fast wall here
and inside you will have the plasma. You understand
the toroidal field, you understand the poloidal
field and these are the toroidal field coils,
there are the poloidal field coils. Initially
you can also have some ohmic heating. That
means you allow high current to flow through
wires that can also initially produce the
heat, but not much. Beyond that it has to
be either through ion beam injection or neutral
beam injection and the RF heating. So, is
that concept clear? Yes? So, this is the concept
of the Tokamak.
So, a Tokamak is nothing but a very large
system of producing magnetic field and this
magnetic field, in order to produce very high
magnetic field you have to have superconducting
magnets. So, all these things are generally
superconducting. Most of the Tokamaks which
we use are, use superconducting magnets. I
hope you are exposed to the idea of superconductivity.
At very low temperature certain materials
become superconducting, so that unless you
do that, at that high current it will also
produce a lot of heat. So, you cannot really
pass high current. The current will be limited.
As a result, the magnetic field will also
be limited. So, in order to produce a high
magnetic field you need superconducting magnet
and the superconducting magnetic technology
is more or less developed these days, you
can have.
Sir, …
With the cooling system, behind the first
wall you have the cooling system where there
are tubes, copper tubes. It is behind the
first wall, so it is not exposed to the neutron
beam. So, you have copper tubes through which
water passes. That water heats up and that
is carried to another channel. That coolant
could be anything really, that coolant could
even be liquid sodium, as you have seen earlier.
So, you can have water, you can have any substance,
but here the water should not boil. So, it
should be pressurized water, so that it effectively
takes out the heat, clear. Now, this is the
concept of magnetic confinement which people
are trying in various places to do it by the
Tokamak reactor.
The other concept is, the other concept is
called inertial confinement. In the inertial
confinement concept, we do not produce plasma
at all. Instead, we cool down the deuterium
and tritium to make them solids, so that you
can throw and solid means it is already confined.
So, that is how people try to do it. That
means the fuel is made into solid pellets,
but then they have to be heated to that temperature
in order to cause fusion. As you heat it to
that temperature, it will after all become
gaseous. So, how to, how to overcome this
problem? This is done by doing it in a fraction
of second. Very fast you fuse it, so that
it immediately produces the heat and that’s
it. So, the concept is something like this.
Can you see? So, imagine that this is the
reactor in which you have made those fuel
pellets. These are brought in here and injected
or sort of there is a gun here that you know
fires the bullets downwards. As it goes down
it is contained by means of its own inertia.
That means it is solid; solid thing is fired
which means that it moves with a certain velocity
and things does not escape and as it reaches
a certain point, very pointedly there are
port holes through which laser beams are injected
aimed at that moving pellet, so that the laser
beams from various directions converge onto
that pellet at a single moment and then, it
imparts a great amount of heat so that it
explodes and since you are heating it from
all the sides, it will implode really. There
will be heating from all the sides and they
will try to expand and the inner, inside part
will implode. That means inside part will
compress producing very high compression,
very high heat and as a result of that it
will fuse, clear.
So, that is the concept, where at this point
when it comes, it is bombarded from all directions
by laser beams and that is what makes it fuse.
Now, here also you will need to breed tritium
and for that the lithium is fed in as liquid
which sort of rains through absorbing the
emerging neutrons. As it falls here, it is
collected and it is taken out which has, which
contains the tritium, so that is the blanket.
It is a lithium shower that falls and breeds
a tritium. The whole thing is a pressure vessel
of very high, very thick steel construction.
So, what else is there? Is the concept understood
then? More or less I have said, so just, just
to repeat, you have a casing. You have got
a container, a thick steel container in which
there is a partition. Above the partition
you have the lithium, liquid lithium being
collected and through small holes here the
lithium rains through. There is a shower and
here you have the fuel pellet injection system
which is fired from the top. It goes down
and as it comes to this point, it is bombarded
from all the sides.
So, what happens is, essentially you have
the pellet which is bombarded from all the
sides, so it tries to explode. As a result,
the inside part is compressed and to such
an extent that in the inside part it produces
tritium.
So, you see, again after this is done, in
another second another will be injected, again
another will be injected, again there will
be explosion. Do you see what type is it?
It is like an internal combustion engine where
there are discrete NO x, discrete explosions.
Any internal combustion engine in a car, what
happens? You inject fuel, put a spark, it
explodes and then the rest of the cycle you
take the heat out. Again you put in fuel,
spark it, so the energy is not constantly
generated. It is generated in discrete times.
Here also it will be generated in discrete
times, as a matter similar to an internal
combustion engine. So, this is another direction
in which people are trying.
As yet it has not become clear which concept
will be a clear winner. Both concepts are
being tried out and by the time you become
engineers possibly you will see one concept
out of these two or a third concept, nobody
knows, emerging a clear winner. There have
been some reports, in the meantime, that there
has been cold fusion. That means there were
reports at some point of time that people
have been able to achieve fusion at room temperature,
but that has later been proved to be wrong.
So, if you hear of those things that it is
possible to have fusion at room temperature,
do not be carried. This is, this has been
proved to be a wrong report, so that is not
possible. You have to have that temperature
in order to produce fusion.
Notice the result of the fusion process, this
is nothing but helium. Helium is abundantly
available on this planet as well as in all
the other planets, as well as in the sun.
It is nonpolluting, it is inert, it is a nice
substance and so, fusion process if you really
are able to do it, will produce a nonpolluting
energy source, you know that.
So, that is exactly why not only the availability,
huge amount of availability, the fuel is also
abundantly available as we see. Deuterium
is abundantly available in the sea water,
tritium can be bred, lithium is available.
So, you have all the fuels quite abundantly
available on this planet and the product of
the fusion is also environmentally benign.
So, this is a very desirable process, but
we are yet quite a few miles for achieving
it. But, in India also there are attempts
to do this, so it is not, we are not trailing
behind the advanced countries in that, we
are in the game. So, you have the fusion reactor
concept more or less clear to you now.
There are other concepts also, but these are
somewhat off beat and these two are most vigorously
being pursued and that is why I talked about
that. You may hear about other concepts, but
you know there can be, people should always
try various concepts, but at some point of
time at the undergraduate level you should
know the ones that are hotly pursued. These
two are most hotly pursued. So, let us now
try to understand today rest of the class
and tomorrow’s class will be mainly considered
on the issue of environmental impacts of power
generation, environmental impacts.
We will have to, both, we have to consider
coal power generation, we have to consider
hydel and we have to consider nuclear. You
have understood all of them; I have talked
about all of them. So, you should now be able
tell what would be the possible impacts, environmental
impacts of coal power generation.
Air pollution.
Air pollution in form of what? So, air pollution
that to NO x, SO x, CO, CO 2, yes, suspended
particles and anymore?
S
S goes here. After the, after it burns, it
does not really go into the ash. Ash contains
a lot of things but that is a separate issue,
not air pollution. What else do you see? Water
pollution, solid pollution; I had given you
a brief idea about how to overcome this, but
let us just recapitulate that. Is suspended
particles a real problem in the modern power
plant? No, because you can have very good
electrostatic precipitators. You see black
soot coming out of the stacks only when the
electrostatic precipitator is not working
properly. So, this problem is more or less
known how to solve it. NO x, how to solve
it and what? No, no, that is for automobiles.
How to, how to bring down NO x? By bringing
down the temperature and you cannot bring
out the temperature in the pulverized coal
boilers.
So, you have to have the fluidized bed boilers
and bring the temperature down below the level
of NO x production. So, that is the way to
avoid NO x. SO x, one advantage Indian coal
does not have much of sulphur. It has, but
not as high a quantity as the European coal.
That is why acid rain is a bigger problem
is Europe than in India, but nevertheless
since it has sulphur, you should understand
how to overcome that. How can you overcome
that? Very difficult to do in pulverized coal
boilers, relatively easier in the fluidized
bed boilers, because with the fluidized coal
pellets, you know in fluidized bed you have
small chunks of coal that is fluidized. Along
with that if you mix a bit of lime, then that
absorbs the SO 2. So, that can be used as
a process.
CO, it is just a matter of proper stoichiometric
ratio. So, CO, CO production can be minimized.
Unless there is a, there is a bad mixing of
air, CO is not really produced. CO 2 is big
problem. CO 2 is not a big problem, could
not have been a big problem unless the amount
of coal power generation were so high. So,
now the total quantity of carbon dioxide in
the air is going on increasing as a result
of what? What happens? We have the global
warming problem. The global warming problem
is produced by certain gases, out of which
methane and carbon dioxide are considered
to be prime culprits and there is no way to
avoid production of carbon dioxide if you
use coal for power generation. So, that is
one of the major problems. That is why there
is an international treaty nowadays that if
you produce electricity by some other means,
then you gain, because you gain internationally;
also that has monitory benefits internationally.
So, those who produce electricity by producing
CO 2 have to pay those who do not. So, there
is a, there is a treaty regarding that and
as you can see, the more advanced countries
are producing huge amount of CO 2, because
they have to have a larger electricity production.
So, CO 2 is a problem, remember that and nevertheless
these ducts that carry the gas, that flue
gas does contain pollutants and where it touches
the ground there it directly affects the inhabitants
of the place, right. So, even though you install
a good amount of, a very good electrostatic
precipitator, there will be some particles
which on a long run, large space may not be
all that matter, but the fellow who is sitting
just there, who has a house there, for whom
it does matter a lot and you can see that
in the regions surrounding the Kolaghat thermal
power plant, there is a region where the plume
touches the ground and that is where there
is a huge amount of pollution and we will,
we will deal with this issue in the next class.
What is the water pollution source? No; there
are two things. One, the water is heated up.
The cooling water that is used from the river
or lake or whatever that is heated up and
released into the river, as a result of which
the flora and fauna that were adopted to that
particular temperature will now have to adopt
to a different temperature, which does not
happen. So, that is that is one source of
pollution. Again, you cannot do anything about
it. Remember, since the whole cycle works
on the basis of the Rankine cycle principle,
any cycle will have a source, a sink and the
limit is, there is a limit. Normally, you
have the thermal power plants efficiency less
than 40%, which means 60% of the heat must
be released into the atmosphere and most of
it is released into the atmosphere that is
40% in the water, 20% percent through the
chimney. Other than that, the solid material
that goes as the ash waste, that contains
various substances that mixes with the water
that seeps into the ground water. So, that
is another source of the water pollution problem.
So, you can see the coal as a source, is a
very polluting source. Remember that it is
not all that benign source; it is not all
that benign, clear. Today time is almost up,
nevertheless I will, do you have class after
this?
Yes, sir.
So, in that case, I cannot really continue,
I will then carry up in the next class. We
will consider the environmental effects of
hydel and nuclear and then we will make a
rational comparison between the three. So,
that is all for today.
