We are at Plant Vogtle in Eastern Georgia.
It's one of the newest nuclear power plants
in the United States,
where a process takes place that splits an atom in two,
called nuclear fission.
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To understand fission,
we need to look inside an atom,
where most of the action takes place.
Something really important to know.
With atoms, it's all about stability.
When things get unstable,
atoms will constantly try to stabilize.
Typically, an atom is stable when it has
the same amount of protons and neutrons in the nucleus,
and when there's not a lot of them.
That means, if you divide the number of neutrons
by the number of protons, with an equal number of each,
it's a one to one ratio.
So, if helium has two protons and two neutrons,
it's a stable nucleus.
Things get dicey when you have
an uneven number of protons and neutrons,
and if there are fewer neutrons,
things get downright unstable.
That's because a force inside the nucleus
called the strong nuclear force
just isn't strong enough
to keep a large number of protons
from repelling each other.
The strong nuclear force only works
at extremely short distances.
The width of an average sized atomic nucleus,
or ten to the negative 15th meters.
It is one of the four fundamental forces of nature,
along with a weak nuclear force,
the electromagnetic force, and the gravitational force.
When there are more protons,
the strong nuclear force is overcome
since a proton's natural tendency
is to repel each other.
That's why you need a higher ratio of neutrons
to generate enough strong force
to compensate for all those protons
and to keep the nucleus together.
If the nucleus gets big, more than 83 protons,
the net force causes the nucleus to fall apart.
The strong nuclear force is still present,
but it's just less effective
when all the protons and neutrons inside the nucleus
are spread out.
This is when the nucleus experiences radioactive decay.
In another segment,
you learned about the different ways atoms decay,
including emitting alpha and beta particles
and gamma radiation.
So, here's an example of how it works.
Let's take carbon-14.
The atomic number is 6,
which means 6 protons with a mass number of 14.
So, how many neutrons are there?
You subtract 6 from 14, and you get 8 neutrons.
Neutrons divided by protons, eight over six,
gives you a number greater than one.
That means the nucleus is unstable,
which means it regains stability
through radioactive beta decay,
converting a neutron into a proton,
which produces a different element, nitrogen-14.
When the nucleus is large, with 20 protons and above,
the ratio for a stable nucleus changes.
You need one and a half neutrons for every proton
to keep the nucleus stable.
Why do you think that is?
As we said, the strong nuclear force
keeps the protons and neutrons together,
but only at extremely short distances.
To keep all the protons from repelling each other
and leaving the nucleus with 20 protons or more,
you need a higher ratio of neutrons,
but there's only so much the neutrons can do.
Once you get more than 83 protons in the nucleus,
the repulsive force is just too great.
The nuclei will always be unstable
and undergo radioactive decay.
And when you take that instability and decay to the extreme,
you're looking at nuclear fission.
We can harness the energy released from nuclear fission
to create electrical power.
You'll see at this plant
how unstable atoms can pack a powerful punch.
It's inside a nuclear reactor
where nuclear fission happens,
in a very controlled environment.
Here we are with a nuclear reactor vessel
soon to be installed.
It's in there that all of this will take place.
Nuclear fission occurs when an unstable,
highly excited nucleus breaks apart into smaller,
more stable, but still radioactive nuclei.
Remember, the atom with a large nucleus,
with many protons and neutrons,
is already unstable,
and the strong nuclear force is having a difficult time
holding the nucleus together.
The final straw comes when that atom is struck
by a slow-moving neutron,
which was likely emitted from another nucleus
that broke apart.
Water inside the reactor is used as a coolant
to slow the neutrons.
Because they're moving slowly,
that neutron gets caught by the large nucleus,
and that causes it to become even more unstable.
And, in a sudden release of nuclear energy,
the nucleus breaks apart into two smaller,
more stable nuclei.
That's fission.
Here's a mystery for you.
When nuclear fission happens,
the total mass of the two smaller nuclei
is less than the mass of the original unstable nucleus.
Where's the missing mass?
In the early 1900's, physicist, Albert Einstein,
figured out the answer,
and it's tied into his best-known discovery.
He determined that mass is interchangeable with energy.
And that E, for energy, equals M, mass,
times the speed of light, C-squared.
Probably the most famous equation of our time.
E equals MC squared.
Considering the speed of light is 300 million meters per second,
we're talking about a lot of energy,
even for a small amount of mass.
During fission,
the binding energy that holds the nucleus together
is emitted when the nucleus splits apart,
and that amounts to the missing mass.
Thank you, Albert Einstein.
Here, at the nuclear power plant,
fission is what heats up the water into pressurized steam
that drives the turbine generators
to create an electric current.
Other plants burn fossil fuels, like coal, to heat up water.
At this nuclear power plant, instead of fossil fuels,
the fuel that heats the water is uranium-235.
An element that releases a lot of energy
when its nucleus splits apart during fission.
It takes much less nuclear fuel than fossil fuels
to do the same job.
You can get as much energy from a uranium pellet
the size of your pinky nail as burning one ton of coal.
So, you can understand why nuclear power plants
like this exist.
Nuclear fission is a powerful reaction,
and that's why people here take so much care
to harness this powerful force.
Nuclear reactors typically use enriched uranium.
Here's what that means.
In nature, there's less than 1% of the uranium-235 isotope
in uranium.
The rest is mostly uranium-238.
The main difference between the two is mass.
So, this allows us to separate
or enrich the percentage of U-235.
Most nuclear reactors require a concentration
of the uranium-235 isotope ranging between 3.5% and 4.5%.
By the way, uranium used for nuclear weapons
requires 90% concentration of U-235.
A big difference.
Nuclear fission occurs when chain reactions
are induced under very controlled reactors.
Here's how that chain reaction works.
When fission happens,
along with breaking up one big uranium-235 atom
into at least two smaller atoms,
neutrons are emitted, as well.
Each of these free flying neutrons can get caught
by other large unstable uranium-235 nuclei,
and when that capture happens,
it causes the big unstable nuclei to break apart.
So, once again, neutrons are emitted,
captured by other unstable atoms,
and you get the picture.
It's a self-perpetuating cycle, a chain reaction.
For the chain reaction to continue,
there must be enough heavy, unstable nuclei present,
but not too many.
The perfect range is called the critical mass.
If the mass of unstable nuclei is less than the critical mass,
the chain reaction slows to a halt.
If there's too many,
the reaction could get out of control.
To keep that from happening,
nuclear reactors use special rods
that maintain a safe reaction rate.
Control rods made of materials that will not fission
are inserted into the reaction chamber.
They act like sponges, soaking up neutrons
and slowing the reaction down.
So, to recap, nuclear energy is powerful stuff
with a wide range of applications.
Only certain unstable elements
can produce these powerful reactions,
and you now know that mass is energy,
and energy is mass.
Good to know as we move forward.
That's "Physics in Motion," and we'll see you next time.
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