Hello, I welcome you all in this course on
Power Plant Engineering. Today, we will discuss
the nuclear power plants.
The topics to be covered in today's lecture
on first of all advantages of nuclear power
plants, then there are certain limitations
also for nuclear power plants, nuclear power
systems, nuclear reactors and their classification
because there are different type of nuclear
reactors so they are classified on different
criterias, essential component of nuclear
reactors.
So, first of all advantages of nuclear power
plant. The first advantages of the nuclear
power plant is it occupies less space; it
means the power density of the nuclear power
plant is quite high that is why you will find
very large capacity nuclear power plants in
a in a in a verycomparatively left less space.
Therefore, these, these power plants can meet
the large demand . So, nuclear power plants
they can cater the large power demand in a
country like India where there is a power
requirement is very large. So, these power
plants are more suitable if you compare with
the thermal power plants or the hydro power
plants.
As I said earlier in earlier lectures that
for though we may have a plenty of coal, but
we cannot go for a thermal power plants because
the concentration of carbon with increasing
in atmosphere, so in coming days the use those
thermal power plant will reduce. Hydro power
plants have some environmental related issue.
So, if you want to generate huge power, we
are left with the only option that is nuclear
power plants.
They have high load factor, load factor is
80 to 90 percent that is quite high for a
nuclear power plants. And and in nuclear power
plants the fuel transportation cost is less
if you compare with a thermal power plant,
we are vegans ofthe coal is transported by
the rails. However, in the case of nuclear
power plant, this transportation cost will
also be saved. And it produces fission material
which can be used for other purpose other
than the power generation .
So, end product is fission material which
can be used for the other purposes. And one
thing more this fission disposal of this fission
material is also an issue. So, around the
world the scientists are working on the issue
that this fission material can it this we
used used as a fuel in a nuclear power plant
ok. So, recycling of the fission material
is nowadays is a focus of nuclear research
is one of the focus of the nuclear research.
Operation reliability, operation reliability
is quite high in the nuclear power plants.
And you have heard some of the accidents there
were these accidents were caused when the
protocol was a disturbed or standard operating
procedure was disturbed, on that case only
these accidents are caused, because the reliability
is quite high in a nuclear power plant. If
the weather is a adverse, so nuclear power
plants are not affected, so they can operate
in the adverse weathers also. And expenditures
of pipes and material is less if you compared
with the thermal power plants. So, there are
certain advantages of nuclear power plants,
but there are certain limitations also. Nuclear
power plant nuclear power is costly.
So, high capital cost. And danger of radio
activity is always there though there may
not be any radio activities surrounding the
plants, but in our back of the mind or the
in the peoples back of the mind it is always
there, there is a danger of radioactivity.
So, this is also one of the limitations of
nuclear power plants. And another one is they
cannot operate on varying load. So, load has
to remain fixed in nuclear power plants that
is why their power factor is high, load factor
is high. Maintenance cost is also high for
nuclear power plants, because they work on
they they operate on a high temperature.
Disposal as I said disposal of fission material
is still is an issue burning issue for the
scientists. And it working conditions I mean
the those who are working in the power plant
they have alwaysapprehension that they are
under radiation though it may not be the case,
but it is always in the back of the mind.
This is also one of the disadvantages of nuclear
power plants.
Now, nuclear power systems, what are the systems
which are involved in the nuclear power plant,
so it has to have controlled fission heat
source 
fission heat source, because nuclear power
plant also works from the Rankine cycle. If
you look at the Rankine cycle on temperature-entropy
diagram right, so 1 2 is expansion in the
turbine, 2 3 condenser, and 2, this is 3,
3 to 1 4 1. So, process 3 to 4, 3 to 4, and
this is 5, and this is 1. So, 3 to 4 is pump
pumping, and 4 to 5 to 1 - this is heat addition
in a boiler. If you look at the Rankine cycle
typical thermal power plant, so this 4 to
5 to 1 takes place in a nuclear reactor in
a nuclear power plant, rest of the things
are same.
So, there is a controlled fission heat source
in a nuclear power plant. There is a heat
removal system here condenser, the power plant
has a turbine and it also has a pump . So,
this nuclear thermal nuclear power plant also
convert heat into the useful work. And for
this purpose the same Rankine cycle is used.
So, for the generation of heat there is a
term which is known as nuclear reactor where
chain reaction nuclear fission it is a controlled
nuclear fission. In controlled nuclear fission,
the heat is produced, and this heat is using
theRankine cycle, this heat is converted into
the useful work.
If you look at the classification, classification,
classification of a nuclear thermal power
plant, so number 1 it is a fast reactor, another
is intermediate reactor, and third one is
slow reactor. In slow reactor also the neutron
velocity is around 2100 meters per second
or it carries the energy equal to 1 upon 40
electron volt. So, slow reactor we have fission
reactor which are slow reactors.
Fast reactor the high the fission takes place
through high energy neutrons or intermediate
is between these two. So, we have slow reactors
where the using a moderator using a moderator
the the kinetic energy of or the velocity
of the neutron strike neutron which is a striking
the nuclei is reduced right and it is purposefully
done, so that a successful fission reaction
takes place right.
Now, the second type of classification is
fuel moderator assembly. One is called homogeneous
reactor, in homogeneous reactor fuel and moderator
are one right. If one means suppose dust particles
of uranium are mixed with the water right.
We have thermal power plants which havesolid
fuels. So, they are heterogeneous type. And
fuel and the moderators are separate, but
there arethere are nuclear power plants with
the fuel is mixed with the moderator right.
So, this is known as fuel moderator assembly.
So, there are two types of fuel moderator
assembly, one is homogeneous, another is heterogeneous.
And in homogeneous dust particles of the fuel
normally uranium is are mixed with the moderator,
and in heterogeneous the fuel and the moderator
are separate right.
Now, fuel is state, state of the fuel, fuel
state solid liquid and gas. Fuel can be in
the form of solid, it can be form of the liquid
or it can be in the form of the gases. Fuel
material right, natural uranium, uranium with
uranium 235, this is this is founded nature
only. When we enrich the when we increase
the quantity ofuranium 235 by some nuclear
reaction, andwhen it is more than 0.7, uranium
235, then it is known as enrich uranium. And
there certain manmade material also fuel that
is plutonium 239 and plutonium 241, they are
manmade uranium 233 is also manmade. So, there
are different type of fuels material which
are used as fuel innuclear power plants.
There are different moderators also. Moderator
the function of the moderator is to reduce
the kinetic energy of fast moving neutron.
So, in moderator normally it is it can be
water it can be D 2 O, it can be graphite,
it can be beryllium, and it can be beryllium
oxide . So, there are few options which are
available to be used as moderators.
Now, product this is alsowhat sort of a reactor
it is it can be a research reactor, then it
be power generating reactor, research reactor
where nuclear research is being carried out
right. There is a power reactor, which are
used for a power generation, and we are concerned
with this reactor only. Now, another one is
breeder reactor . In breeder reactor, fuel
is generated. The breeder reactor is such
a reactor which produces the fuel more than
the fuel which is being used to run the reactor,
suppose input is 1 kg, 1 kg of fuel, it will
produce and product is 1.5 or 1.3 or 5 kg
of fuel, and this is achieved through nuclear
reactions.
Every reactor has a coolant. The purpose of
the coolant is to to take away the heat from
from the reactor. So, coolant can be air,
it can be helium . So, these are the gases
which can be used or carbon dioxide, they
can be used as a coolant in a in a reactor
. If you want to go for the liquid then water,
or D 2 O, heavy water, this can be used as
a coolant. There are reactors which are liquid
metal coolants also metal liquid metal coolant
like sodium, sodium is used as a coolant also.
Now, we will go for the essential component
of a reactor essential components. Now, essential
component is one of is is reactor core where
this fission takes place and the heat generated.
Another is reflector. The purpose of the reflector
is to reflect the neutrons when the it is
in the containment wall they are put near
the containment wall, so if suppose this is
the containment and here is the reactor .
So, reflectors will be surrounding the the
core, this is core, not reactor, this is core.
So, reflector will be surrounding the core,
so that if any neutron which is a escaping
the reactor it is reflected back. Number 3
is control mechanism. Now, control mechanism
is to control the kinetic energy of the neutron
to control, the speed of the neutron. So,
for this purpose they are moderators ok water
can also be used as a moderator, there are
solid moderators also like like cadmium rods.
They are put in the reactor to slow down the
speed of the the neutrons in the in the in
the reactor, control mechanism.
Then moderator I have already discussed, now
moderator. Coolant, coolant is a real food
which take away the heat fission heat from
the reactor. And sometimes the working fluid
work as a coolant or there is a heat exchange
between coolant and the working fluid in the
turbine ok, there are different type of arrangements.Measuring
instruments, there are several measuring instruments
which are used in the nuclear power plants,
so that itworkseffectively. And the seventh
is shielding the entire reactors shielding
in a a concrete containment concrete and steel
containment, so the radiations do not go out.
I would like to further discuss here the control
mechanism, those rest of the things I have
already discussed. So, the control the function
of the control mechanism is it is used for
starting the reactor 
and to bring the reactor at a operation level.
This is the main function of the control mechanism
and maintaining that level because a reactor
cannot work on the different levels. So, it
has to and for shutting down the reactor.
These are the main function of the control
mechanism.
And there is an emergency conditions also
when there are emergency conditions, emergency
conditions means suppose there is a breakage
in the pipeline supposein a core there is
a breakage of the pipeline or there is a breakage
of the pipeline which is going to the core
. So, the coolant will come out. Now heat
will not be taken away from the core. So,
temperature of the core will start rising.
So, the reactor has to be immediately shut
down, this is known as loss of coolant accidental
- LOCA.
So, reactor has to be shut down immediately.
And for electric circuit is ok the moment
we put the switch off the light go goes off,
but thus this does not happen in the reactors.
In the reactors because though the fission
reaction is a stop, but is still heat will
continue to come, it is approximately 2 to
3 percent of the capacity of the reactor.
So, there is a emergency core cooling system
core cooling system emergency core cooling
system which immediately becomes operative
and and it cools down the core. So, these
are the control mechanisms which are there
in a nuclear power plant, and they have to
work very effectively for the proper operation
of the nuclear reactor.
Now, possible reactor cooling system, cooling
systems in the reactor. Now, possible cooling
system is one is indirect heating. Now, in
case of indirect heating as it implies from
the name itself suppose this is reactor core,
and so coolant is moving in reactor core,
sorry in this direction, the coolant is moving
in reactor core the fission heat is generated
here it takes heat from the reactor core,
it goes up and it circulated and sometimes
a pump is also used. It may be the natural
circulation or fore circulation right.
And then there is a heat exchanger here. Now,
heat exchanger through heat exchanger heat
is transmitted to the working fluid working
fluid is normally light water H 2 O, this
coolant can be H 2 O, or it can be D 2 O - heavy
water. So, this heat exchange and the pressure
is quite high here. So, when this exchange
of heat takes place, this heat goes to the
this water working fluid that is water. Water
is converted into the steam and this steam
goes to a turbine and the condenser and how
the power generation is completed right.
Now, another one is direct heating . Now,
in direct heating here we have a solid fuel
right. In direct heating, there is a mixture
of fuel and coolant. And the mixture of the
fuel and coolant comes to the heat exchanger,
and rest of the process is same, rest of the
process is same. Now, here there is a coolant
plus fuel mixture. So, the, so the the the
fuel the working fuel also is also circulated
in these pipes right. So, here there is only
coolant and here is the mixture ofcoolant
and fuel, and that is why this is known as
direct heating type of arrangement.
Some of thewater cooling like swimming pool
reactor, where the the the the fuel rod they
remain suspended in in a in a pool, it is
known as swimming pool type ofreactor. Pressurize
waterreactor, in a pressurize water reactor,
there is a core and this D 2 O, normally D
2 O, this is heavy water. It is circulated
it is works as a coolant. So, there is a closed
loop. So, it can be a natural circulation
or aforced circulation. If it is a forced
circulation, then the pump will also be there.
So, whatever fission heat is there it is taken
away by the D 2 O, and this heat is given
to again the working fluid H 2 O, this is
the heat exchanger I explained this earlier.
And this heat goes to a turbine sorry this
fluid this H 2 O, this steam, the steam goes
to the turbine and then there is a condenser
also, and here there is a pump right. So,
again it is pumped and it goes to the and
this is also a closed loop.
If you want to draw this on a temperature
entropy diagram, so it is entering from here
1, leaving here 2, 2 to 3, 3 to 4 increasing
the pressures through sorry 3 to 4 you are
right, and 4 to 5 and 5 to 6, 5 to 1. And
this takes place here 4 to 1 takes place here
in this heat exchanger right .
Now, if you go to the boiling water reactor,
boiling water reactor does not have this type
of arrangement. In boiling water reactor,
there is a there is a core, and the coolant
itself drives the turbine, the coolant itself
drives the turbine. There is no heat exchange
and coolant itself drives the turbine. This
is known as the arrangement in a boiling water
reactor . There are reactors which are liquid-metal
coolant, liquid-metal coolant normally sodium
is taken into account. So, in the liquid metal
type, arrangement is same like there is a
core, there is one loop ok, exchange takes
place with another loop, and then exchange
takes place with the third loop.
Now, here are the question is why there are
two heat exchangers? Why they are two, there
is one loop, second loop and third loop, why
there are three heat exchangers? Normally,
sodium is usedinliquid-metal type of coolant.
And when the sodium is there sodium reacts
I mean violently with water and air. If air
is moist in that case also because it in fact
it reacts violently with water.
So, there is a, so that is why in order to
avoid such a situation an intermediate provision
is made. So, sodium alloy, here sodium alloy
is a working fluid here, sodium is a working
fluid and here water is the working fluid
that is the only reason that is why we have
primary heat exchanger, and there is a secondary
heat exchanger.
Now, shielding there is a protective wall
around the nuclear reactor which prevents
the damageto the surroundings, this is known
as shielding. And it protects the operators
from the exposure also right.
So, if we now take the main component in the
nuclear power plant that is one is reactor
core ok, and coolant is entering from here.
There can be a pump or a pump house. And hot
coolant is coming from here, here there is
a steam generator we are known as headers
also, in headers the steam is generated right.
And here then this steam goes to a turbine
as I explained earlier turbine to condenser
and condensers back to the pump .
Normally the steam which is used in the steam
power plant it is a nuclear power plant, it
is a wet steam right. And thethe the beam
beam component which is different from the
typical thermal power plant is the reactor
core is the nuclear reactor reactor core,
where heat is generated using the nuclear
fission reaction right. So, this is the basic
of a a nuclear basic arrangements in a what
I explained is the basic arrangement in a
typical nuclear thermal power plant. In the
next lecture, we will take up different type
of nuclear power plants.
Thank you very much.
