So, in the previous lecture we talked about
the fate of neutrons in a nuclear reactor.
You remember the design, you have fuel core
which contains the fissile material and it
is surrounded by moderators, the fuel rods
are separated by the moderators in the reactor
core. And once you have some thermal neutrons
ready to fission; what happens to them that
we discussed last time, just to remind you
can look at the screen on which it is there.
So, you have these n thermal neutrons in the
fuel ready to cause fission. And of them some
are radiative captured they are absorbed and
they do not cause fission. Those which cause
fission create more fast neutrons back factor
we write as this eta. So, here it is so from
n it is n times eta fast neutrons. Then you
these some of these fast neutrons can also
cause fission because of uranium 238. And
that gives you this extra factor of epsilon.
So, eta times epsilon then of these neutrons
which go to the moderator some of them encounter
the uranium 238 fuel rod surface. And they
can get captured their through those resonance
reactions. And therefore which are finally
thermalized is here a factor p. And after
thermalization also they keep moving in the
moderator for quite some time and during that
time they can interact with the moderator
material itself. Some nuclear reactions can
go in the moderator, and another factor f
is converted is multiplied to get you slow
neutrons in the fuel rods once again.
So, this is 1 complete generation or 1 complete
cycle. So, in 1 generation; if you have these
n thermal neutrons the next generation here
you have these n eta epsilon p f thermal neutron.
So, from 1 generation to the next generation
the number of thermal neutrons in the fuel
rod is multiplied by eta times epsilon times
p times f which is known as reproduction factor.
But we have missed some points all this is
if you have infinitely big core in any real
nuclear reactor you will have finally a finite
volume. And the neutrons which are moving
with fast neutrons or slow neutrons; they
can just leak out of that volume that can
go out of the reactor core volume.
So, fast neutrons here they can these fast
neutrons which is produce some of them can
go out of the of the core volume. And that
is that factor is leak factor l f then only
1 minus l f that factor is going to the next
channels. And similarly once they are thermalized
slow neutrons slow neutrons also during their
random wondering; they can move out of the
core volume and that slow neutrons leak. If
you write that as l s then only that 1 minus
l s factor that will be surviving. So, this
should be multiplied by those factors 1 minus
l f and 1 minus l s. So, the fast neutrons
are leaking through the core volume and slow
neutrons leaking through the core volume that
should be taken care.
Then, it is the reproduction factor k. Without
these leak factor sometimes people say it
k infinity; assuming infinitely big core the
factor will be eta into epsilon into p into
f which is known as 4 factor formula because
there are 4 factors here. So, this is you
are going from 1 generation to the next generation;
this is the factor k by which the number of
thermal neutrons in the fuel rod ready to
cause fission gets multiplied. Let us see
something else.
So, that factor k is the factor by which the
thermal neutrons are getting multiplied from
1 generation to the next generation. But how
much time does it take from going from 1 generation
to the next generation the time scales? So, the  time scales if you look at the if the thermal
get absorbed in uranium 235 they will fission
almost instantaneous some 10 to the power
minus 14 seconds or so. But then the fast
neutrons which are created they will take
some time wandering here and there. And they
that lifetime of that neutron before it gets
absorbed or it causes fission or something;
that is something like 10 to the power minus
8 second.
So, fission itself may take very small time
but then the fast neutron lifetime in a typical
case maybe something like 10 to the power
minus 8 second. Then they go to the moderator
and their energy is reduced because of the
collisions in the moderator. And that thermalisation that will take  some time and not only that after thermalisation
also this slow neutrons keep moving in the
moderator volume; here and there scattering
from the moderator material. So, that time
before they really get into the fuel rod that
wondering time; if you add that also  wandering in moderator that is something like say
10 to the power minus 4 to 10 the power
minus 3 second milliseconds less than a millisecond.
So, that is the largest time in all these.
So, that finally decides the time scale going
from 1 generation to another generation; it
takes about a fraction of a millisecond.
So, in that fraction of a millisecond 10 to
the power minus 3, 10 to the power minus 4
seconds; those capital n thermal neutrons
in the fuel ready to cause fission have become
capital n into k; this k times. So, N becomes
N times k in this time frame 10 to the power
minus 3 seconds let us say. Therefore, it
is essential that the reproduction factor
this factor k is kept exactly at 1 almost
exactly at 1. Because if it is less than 1
then every millisecond; the number of neutrons
present in that thermal neutrons present is
going down.
And, whatever energy is created from this
nuclear reactions it is proportional to the
number of these neutrons in the core. And
every millisecond if it is going down very
soon it will reduced to almost 0 and the chain
reaction will stop. Similarly, if this k is
slightly more than 1; then every millisecond
the number of neutrons will keep on increasing
by this factor k which is more than 1. And
in every short time the rate of reactions
will be so high that it will be uncontrollable;
one can work out a formula for that. If you
write k as 1 plus epsilon; where epsilon is
a small quantity ideally we would like to
keep it at 1; so that the chain reaction sustains
just sustains. So, one neutron causes fission
and from that several neutrons are emitted.
And, only one neutron of that on the average
causes the next fission; that is the ideal
controlled nuclear reactor situation. But
if it is slightly more or slightly less you
can write it like this. In time t you have
t by tau generations going on; where tau I
am writing for this generation time scale
here 10 to the power minus 3 seconds or so.
So, these many generations have gone each
generation it is getting multiplied by k that
is 1 plus epsilon. Therefore, the rate of
reaction r at time t will be rate of reaction
time 0 and 1 plus epsilon that is the k t
by tau power t by tau.
So, the rate will depend on time, the rate
will increase with time if epsilon is positive
through this. You can write it in a more familiar
fashion you can take log of so ln (R) is equal
to l n R(0). And then this will be t by tau
and ln this is log on the base e; that is
1 plus epsilon here. And for a small epsilon
this log of 1 plus epsilon to the base e will
just be epsilon log of 1 plus x that series
if you remember f starts with x minus something
plus something. So, this is ln R(0) and then
t by tau and then this is epsilon. And therefore
if you write R that will be equal to R naught
e to the power epsilon times t by tau. The
rate changes exponential if the epsilon is
positive it grows epsilon is negative a it
goes down; but it goes exponentially and the
rate changes very fast.
A typical example we can take suppose k is
1.01; so that epsilon is 0.01. And in 1 second
what happens to the rate? So, 1 second if
t is 1 and if tau is 10 power minus 3 second;
t is 1 second. Then this will be r at t equal
to 1 second will be equal to r at 0. Then
e to the power epsilon which is 0.01 and that
is multiplied by t by tau that is 1 second;
and divided by tau is 10 power minus 3 here.
So, it is here. So, that will be 1000 and
this will be 10. So, it is r into e to the
power 10; e is remember it is around 2.73
or so. So, you can work out or your calculator
how much is this e to the power 10? And that
will turn out to be approximately 20000.
So, you rate is increased approximately by
this factor 20000 in 1 second. So, every second
the rate is increasing by more than 20000
factor. So, even a small increase in this
reproduction factor k can lead to a very high
energy output in very short time; and it can
be difficult to control and the things can
go up. And therefore it is it must be maintained
almost exactly at 1. How does one do that
for that one uses this control rods.
Control rods are some rods 
made of materials which absorb neutron; 
cadmium is the most popular choice cadmium absorbs
neutron. So, these rods are put in the core
and the fuel rods are separated and these
control rods can just go in between. So, when
you want to slow down the reaction; these
control rods are pushed inside. So, that they
start absorbing more neutrons and the rate
goes down and if the rate has to be increased;
if k has become less than 1. And you want
to make it k equal to 1 that is called critical;
the reactor is critical. When k is one reactor
is critical and if it is less than 1 it is
called subcritical and if it is more than
1 it become supercritical dangers.
So, if it is subcritical and you want to make
it critical; you want to increase the rate
of this fission reaction these cadmium rods
are lifted up. That means, up or whatever
so that less amount of less fraction of those
rods are inside the core. So, that is how
it is controlled but if it is controlled by
this mechanical moment of these rods. Then
these mechanical moments cannot be or it is
very difficult to control that at this millisecond
time scales 10 to the power minus 3, 10 to
the power minus 4 second time scales. In that
time scale it has to mechanically go in or
mechanically go out that will be very difficult.
So, how that is done?
That we are help with a phenomenon which is
known as delayed neutrons I talked about it
earlier. In a fission reaction some neutrons
are immediately emitted those are known as
prompt neutrons; and we had talked about prompt
neutrons in this 4 factor formula and all
that. But then some of these fission fragments
they emit beta rays to reduce their n by z
ratio; and the product nucleus of this beta
reaction that emits neutron. So, that is also
possible. For an example, if you have fission
fragment say 93 rubidium. So, this 93 rubidium
that beta decays with a half life of 6 seconds
and beta decays to 93 strontium. And this
93 strontium then emits a neutron and it becomes
92 strontium.
Now, this neutron that is here; it has come
on the average 6 second later than the main
fission event which has emitted which has
created this fission fragment. So, this neutron
has to wait because it will come from 93 strontium.
And 93 strontium will be created from 93 rubidium
through this beta decay process which has
a half life of 6 seconds. And therefore this
neutron will come with a delay of this order
of time. So, these are known as delayed neutrons.
We had talked about these delay neutrons earlier
they are about 2 percent of the prompt neutrons
but that 2 percent gives us the handle. The
whole design is made so that only on prompt
neutrons the reactor it is slightly subcritical.
And, then only when these delayed neutrons
are taken into account it becomes critical.
So, if that be the case only these delayed
neutrons are needed through make it critical
and these delayed neutrons are coming after
few seconds or 10 seconds or 6 seconds or
2 seconds or 5 seconds or 20 seconds. Then
we get enough time to control that mechanical
moment to follow the variation in k. So, that
is how it is controlled. Another aspect of
this chain reaction sustained chain reaction
is that this reproduction factor depends on
the temperature. Because reproduction factor
has all those absorption cross section and
different reaction cross sections and so on
and these depend on the temperature. So, finally,
this k also depends on the temperature.
So, if the temperature goes up k can increase,
k can decrease depending on the material,
depending on the geometry and depending on
the design. Now, if this k happens to be increasing
with increasing temperature then the situation
will be difficult to control. Because if the
rate of reaction by any chance goes up and
if the k is also increasing with temperature.
So, in that case so that means d k d t this
is greater than 0 and by the chance this temperature
increases in the core. Because of anything
less coolant flow will talk about the coolant
and all that due to factor if this temperature
goes up and k also increases. Then the rate
of reaction will further be increased. It
has increased because of some factors which
we were not able to control.
And, then the reaction rate also increases
because of the increase in temperature. And
as reaction rate increases the temperature
will rise further and as the temperature will
rise further the reaction will rate will again
increase. So, it is something like unstable
equilibrium in mechanics; where you are sitting
at the top of the of this potential function.
And if you slightly displace it further get
displace and displace and displaced. Similarly,
here if by any chance temperature increases
due to some factors reaction rate increases.
And reaction rate increases temperature increases
further; the temperature increases further
the reaction rate again goes up because of
this positive factor. So, this is dangerous
type of situation. So, for reactor stability
what we say reactors stability.
For reactor stability this d k d t this should
be negative. The choice of materials, the
choice of design all that should be such that
k as a function of temperature should give
you d k by d t negative. In that case if the
temperature goes up because of some factors
the k the value of k decrease. So, the neutron
multiplication is not that high and the rate
of reaction will decrease; and that will be
some kind of self correction. If the temperature
has increased the rate of reaction has decreased
and the temperature has also gone down. So,
this is for stability for reactor stability
this d k by d t that should be less than 0.
So, there are many things in reactor design
I am only telling some essential parts in it.
Now, what is the output of this reactor in
what form the output is? And in what form
we need that output? The output of nuclear
reactor is in the form of this thermal energy
generated. Even this fission takes place then
all this kinetic energy of the fission fragments
and the neutrons all that is absorbed. Finally,
in that core volume itself and that increases
its temperature. So, we say that heat is generated,
a thermal energy is generated. That is the
primary output in the core volume itself.
After that what use we have to make the most
common use is power generation electricity
generation. So, there are there the other
users can also be there to drive submarines
to get some kinds of neutron beams for research
and so on. But let me talk of the electricity
generation using this nuclear reactor. So,
the heat that is created in this reactor volume
that has to be taken out and then put in some
use.
So, for that a typical design  which most of Indian nuclear reactors have is what we call pressurized water reactor
PWR. And in place of water if you use heavy water then it is PHWR pressurized heavy water
reactors. Most of our 20 nuclear reactors
in India which are commercially producing
electricity 16 are of this type. So, what
is that? In this that reactor core; say this
the reactor core which contains all those
fuels and control rods. Let me schematically
say that these are the fuel rods and these
are those control rods. So, the control rods
can be inserted in can be taken out and in
this we put water or heavy water at very high
pressure. So, this is water H2O or D2O at
very high pressure and pressures are of the
order of say 100 atmosphere.
And, this is sent into this at high pressure
some pump is there, some tower in there; from
there this pressure is maintained. And this
water is pushed in and that this water goes
out of this through another outlet. So, it
goes out and at this higher pressure the boiling
point of water goes up and reaches something
like 300 degree Celsius or so. And therefore
it remains in liquid form although the temperature
increases to say to 250 degree or so much
above the normal boiling point. So, the heat
of this core is taken out of this core through
this coolant this is coolant; this water acts
as coolant one can have another types of coolant
depending on the design. But for this PWR
or PHWR it is cooled by this high pressure
water maintained at high pressure, water sent
at high pressure and then taken out. Not only
acts as the coolant to take the heat out.
It is also the moderator the same water is
also the moderator.
So, the fuel rods are surrounded by moderators
so that water is acting as moderator. And
the same water is taking away the heat is
getting heated because of this coolant cooled
water is coming from here. And then hot water
is going from here; it is a heat is taken
from here. Now, after that the heat is use
for steam generation to run a turbine; it
will go in some kind of heat exchanger. You
can have different designs of heat exchangers
one design would be to take tubes take this
water through tubes and so on. So, hot water
is coming like this at some 250 degrees or
so at very high pressure. It will finally
be recycle this will go here when it becomes
cold it will go here. And here one can send
say cold water at relatively low pressure.
So, that heat is given by this hot water in
the tubes to the cold water in this chamber;
and this water boils because it is not at
that high pressure. And therefore it boils
and makes steam. So, here it makes steam and
that steam can be taken to that turbine chamber.
So, that turbine chamber to run that turbine
and then that steam can go to another heat
exchanger. And from here that steam can you
can call it condenser. So, you sent this cold
thing here. So, this steams becomes water
condenses here and then it can that coldwater
can go to this. So, the coolant and the moderator
both functions are done by this water or heavy
water. What is the difference between water
and heavy water? Moderator has to be a low
z material.
If it is low z material it will reduce the
kinetic energy of the neutron very effectively.
And therefore water which contain hydrogen
the lightest nuclei would be ideal from that
kinematics. But then the neutron absorption
is also very important; this proton or hydrogen
nucleus proton that can capture a neutron
to make a stable isotope deuteron. So, there
is a reasonable cross section for that. So,
the neutrons get absorbed significantly if
you if one uses light water. In that case
to keep the reaction at reasonable rate one
has to use enriched uranium. So, uranium has
0.7 percent of uranium 235. And this uranium
235 is the main nuclear fuel in this type
of reactors. So, it has to be enriched some
3 percent, 4 percent and 5 percent then light
waters can be used as moderator.
But if heavy water is used in moderator then
that absorption cross section for neutron
is small. Although deuteron can also absorbed
neutron to make that triton 3 h and worse
it is radiative; deuteron is not radiative
this triton is radio actor. But then the cross
sections are small the probabilities of that
adoption is much smaller than the probability
of proton absorbing a neutron and making deuteron.
So, with heavy water as moderator coolant
one can use natural uranium without enrichment.
So, it is a trade off; heavy water is costly
one has to make heavy water from light water
that involves its own complications. But then
this enrichment of uranium that is that can
be saved a unnatural uranium can be used.
So, that that is the difference between PWR
and the PHWR. Now, another type of reactors
are called breeder reactors; in fact Indian
nuclear program is called 3 stage nuclear
program. So, let us first talk what is breeder reactor?
Breeder reactor is where you breed the nuclear
fuel. You know the fissile material 
uranium 235 and plutonium 239 and uranium
233 fissile which can be used in a nuclear
reactor where neutron goes into it and makes
the fission. Now, let us take this as a typical
example uranium plutonium 239. How this form?
It is formed by the absorption of neutron
in uranium 238 that gives 239 uranium and
then it beta decays. And after beta decay
it gives you neptunium and that gives you
finally plutonium 239. So, it can be produced
plutonium 239 can be produced if neutron is
bombarded on uranium 238. Now, in a normal
power reactor thermal reactor where we use
natural uranium has a fuel or even enriched
uranium as a fuel; there is a lot of uranium
238 available. For natural uranium you have
99.3 percent uranium 238.
And, even if you enriched the uranium to some
4, 5 percent of uranium 235 you have lots
of uranium 238 available. Even the spent fuel
rods where the uranium 235 is now over or
it is so small that it is it cannot be used
any more for power production it is uranium
238 in plenty. Now, of the fast neutrons which
are created in fission event 1 neutron can
go to this uranium 238 and make it plutonium
239. You will be producing new fissile material.
So, if a reactor is designed in such a way
that from fission you have say 2.5 neutrons
and 1 neutron is needed for sustaining the
chain reaction still you have 1.5 neutrons;
if it can be designed that out of that 1.5
one is directed towards uranium 238.
Then, you are producing one fissile nucleus
from when you consume one fissile nucleus
of uranium 235. So, this type of reactor although
with 2.5 neutrons it will be very difficult
to do this. But this type of reactors which
consume a fissile material to produce electricity
your power or whatever. And then from the
neutrons which are being lost radioactively
captured this that. If 1 neutron can be assured
to cause this conversion of uranium 238 to
plutonium 239; we are just producing the same
amount of fissile material. And if it can
be more than 1 on the average then we will
be producing more fissile material then what
we are consuming. Such reactors are called
breeder reactors. So, you have seen that these
neutrons which are produced in fission reaction.
If it is uranium 235 you get something like
on the average nu equal to 2.5. And if it
is mixture of uranium 235 and uranium 238
which will always be the case with lots of
uranium 238. The average number of fast neutrons
which come out from one fission reaction in
a natural uranium or enriched uranium will
be much less than 2.5. For natural uranium
it is 1.33 and for 3 percent enriched uranium
it is 1.84. Why? Because uranium 238 which
is plenty in that mixture in that fuel that
is not given the fission that is only absorbing
the neutrons. So, in that sense the factor
is not 2.5 the eta that we use in that 4 factor
formula is 1.33 or 1.84 and that cannot be
used for breeder reactions. For breeder reactor
you do need eta more than 2 because 1 neutron
is needed to sustain that chain reaction at
a constant rate. And at least 1 neutron is
needed to produce this new fissile material.
So, 2 are needed and all kinds of absorption
and leaking and all those things will be there.
So, this nu has to or eta has to be much more
than 2. So, breeder reactor is built with
plutonium 239 as the fuel.
So, breeder reactors 1 neutron to sustain
the chain reaction 
and more than 1 neutron if it is as to breed.
So, if it has to produce more nuclear fuel
then it is consuming; this should be in fact
more than one neutron for breeding. And therefore
that eta must be greater than 2 not only greater
than 2 is reasonably greater than 2. So, that
after all those radiative absorption and leaking
through the core. And all those things absorption
in the moderator still you have these 2 neutrons
or more than 2 neutrons available. One for
sustaining the reaction and one for breeding
the fissile material. And plutonium 239 is
reasonably or perhaps is the only good choice
because for this you can get eta around 3;
with uranium 235 plus uranium 238 the usual
fuel in the nuclear fission reactors that
will give you eta say 1.33 for natural uranium.
And 1.84 for 3 percent enriched uranium this
cannot be used.
Now, this thermalisation low kinetic energy
of neutrons moderation all these things where
for uranium reactor. Because the cross section
of fission for uranium 235 is very high 500,
600 barns at these thermal energies. So, to
utilize that all that moderator was needed
and other things. So, that neutron can be
taken out of that fuel rods, fast neutrons
they there kinetic energy is reduced and then
sends to the fuel rods again.
So, that large cross section of fission for
this uranium 235 can be utilized. Plutonium
239 does not need that; it can fission with
fast neutrons itself. And therefore no moderators
are needed in breeder reactors. In breeder
reactors is just then fast neutrons which
are produced from fission; they themselves
fission go for the next generation fission.
And so the moderators are not needed; coolant
has to go from outside the core. And normally
liquid sodium is used as coolant in this breeder
reactors. And they are known as fast breeder
reactors that is another classification of
reactors.
If the reactor is using thermal neutrons  if thermal neutrons are causing the fission;
 that kind is known as thermal fission reactor.
Another is intermediate energy moderation
is there but intermediate energy that is another
possibility; you can call it intermediate fission reactor. And  then the fast neutrons; if fast neutrons are
producing the next generation fission then
you call it fast reactor. So, breeder reactors
in the present designs are all fast reactors
because the fast neutrons which are produced
in fission of plutonium 239 they themselves
cause the next generation fission. So, they
are generally termed as fast breeder reactors
FBR. Another breeding reaction that is important
or possible is with thorium. Thorium 90; z
is 90 and A is 232. This thorium this is also
available in fact India has large reserves
of this thorium. This is not fissile material
as such but if a neutron is absorbed in it.
It can create 233 thorium and this can beta
decay to Protectium Pa and that can again
beta decay.
So, this will be 233 here and it can again
beta decay and this will become 92 that is
uranium and 233. So, this is a fissile material
the 233 uranium. So, a breeding reaction is
possible if you have 232 thorium which absorbs
neutron and then from there it can finally
give this. So, but this 232 thorium this itself
is to be placed properly there. So that the
neutrons from this fission reactions get absorbed
into it. So, what we have in India it is called
3 stage nuclear program of India. And what
are those 3 stages let us see.
So, 3 stages nuclear energy program  of India; the final vision is to use that large availability of thorium in India; the
uranium reserves are limited. But the thorium
reserves are in much more better conditions.
So, keeping that in mind the first stage is
to expand these fission reactors PHWR or PWR
using uranium fuel as usual. This is the usual
variety all fission reactors in the world
most of them are of this variety. So, expand
presently 20 such reactors are use; 16 use
this heavy water then to boiling water reactors.
Boiling water reactors means the coolant and
moderator; that water that is going that boils
there itself the pressure is not that high.
So, it boils in that core itself and the steam
is from there itself taken to the turbine;
that is boiling water reactor 2 of them. So,
expand this built more reactors not only that
we need electricity from that.
But the another output is that from this we
will get lot of plutonium 239 because in that
natural uranium; those uranium 238 is there
which are getting irradiated by the neutrons
in an natural way in the reactor. Plutonium
239 is being made there and from that it can
be separated chemical. So, by expanding this
nuclear reactor base we will be getting more
plutonium 239. So, that is plus electricity
of course; then the second stage. So, this
gives this us as an output plutonium 239.
Now, use this plutonium 239; second stage
fast breeder reactors FBR; fast breeder reactors
will need plutonium 239 as fuel. And if we
go for large amount of breeding number of
FBR then we will need corresponding amount
of plutonium 239 as fuel. And for that we
need the first phase reactors; normal uranium
reactors which will give us that plutonium
239 fuel.
So, this will be used here to construct to
run these FBR. And in these FBR this thorium
232 will be irradiated then that will give
us 233 uranium. So, once those fast breeder
reactors are in place with plutonium 239 as
fuel. In those fast breeder reactors we can
breed uranium 233. We can put our thorium
fuel their not fuel thorium material there
and irradiated with these neutrons breed that.
And then from using this reaction here we
can get this fissile material uranium 233.
And then the third stage is to build reactors
with this 233 uranium as the fuel. So, we
are at first stage at present but one FBR
in fact FBR fast breeder test reactor is running
for quite some time 1985 or so. So, we have
all that technology all those things ready
and one small reactor at kalpakkam is also
running at uranium233.
So, all technical aspects are all well tested.
And it is only a matter of doing it for first
stage, second stage and third stage. Now,
one more aspect must be talked when we are
talking of nuclear reactor and that is safety
aspect. Because when these fission reactors
reactions take place they create lot of radioactive
material. All these fission fragments are
radioactive, the beta decay they emit neutrons
and so on. Some of them have small lifetime,
some of them have large lifetime, thousands
of years or even more. So, we are producing
that much of radioactive material which has
long lifetime as well. So, to keep that radioactive
material isolated from water mass, from air
mass, from human population that is very important.
So, in any nuclear power plant lots of radioactive
materials are being produced; the spent fuel
rods there are all radioactive emitting radiations.
So, to keep them we are running the reactors;
we are piling up all these spent fuel rods.
So, to keep all that radioactive waste from
fission reactor is big challenge. And if something
goes wrong and if this radioactive material
goes into the human populations through whatever
means that will be disaster.
So, that is one thing containment of this
radioactive material and their final disposal.
Finally, what will happen? We can keep this
in our reactor complex in an isolated building
and so on but if it is piling up at the end
of it 100 years from now, 500 years from now,
1000 years from now. What will be its final
disposal? That is one issue. Another issue
is accidents; with all the good designs and
everything accidents do occur; in the history
of nuclear fission reaction we had 3 big accidents.
Let me give it on the screen those 3 famous
big accidents.
So, you can see that three serious nuclear
reactor accidents so far in the whole history.
What is known as this 3 mile high island in
USA that was in 1979? And in this there was
some malfunctioning of instruments, some wall
got stuck something happened and the operators
could not respond to that well; and so both
malfunctioning of instruments and human error
that cause explosions and melt down of the
of the these fuels and all that. So, that
was 1979 then the worst is Chernobyl former
USSR in 1986 there also it was essentially
some malfunctioning in some human error. And
this was the one in which some loss of life
was there. And also health hazards increase
in cancer cases and other things this the
worst. And very recently as everyone knows
in Japan Fukushima two thousand eleven no
human error here and no instrument failure
here. But it was a natural calamity when this
15 meters of tsunami waves entered the complex,
destructed the power supply, the cooling could
not be done. Although the reactor was shut
down automatically from the design itself
but even if it is shut down the radioactive
decay continues.
And, that creates heat and that could not
be cooled and everyone knows that this entire
complex is now unusable for any anything.
So, but this was a natural calamity. So, far
no loss of life has been reported or even
the radiation exposure is not very highly
alarming to the workers and people there.
But this chainable surely it is created lot
of problems and some 50, 56 or something is
reported casual it is human life, casual it
is and so on. So, this f t aspect has to be
kept in mind when we talk of reactors and
expansion of nuclear programs and all those
things. All these 3 accidents had have thought
us to deal with such situation, and we hope
that no more nucleus accidents in future.
