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TEACHING ASSISTANT (TA): So
if you guys don't remember me,
I'm one of your TAs.
I'm TA number three,
that's what I call myself.
I'm Ka-Yen.
And I'll be teaching your lesson
today because, well, Mike's
in Russia.
So, yeah.
Yeah, so I know you
guys had your first exam
a couple of days ago.
How did that go?
OK, sounds good.
All right, so we
won't talk about it.
But because you guys just
had a super intense exam,
we just want to give
you guys a break.
So today, I'll be teaching
you guys a little bit
about nuclear energy.
So this lesson won't
be super in-depth.
There won't be a lot
of crazy intense math.
Actually, there won't be
any crazy intense math
because we just want to
give you guys a break.
You guys are going
to be starting up
full cycle on Friday with
really cool topics like stopping
power.
So for now, we're
just kind of like--
it's a refresher.
A couple of fun facts.
A couple guys might already
know some of the concepts
that I'm mentioning, because
you guys are intelligent people.
But I walked into MIT not
knowing a single thing
about nuclear energy.
I was like, I wish someone
could have told me these things.
So that's what I want
to do for you today, OK?
So I'm going to be talking
about the functionality
and the benefits and the
problems associated nuclear.
But first let's start
with a very brief history
in a nutshell.
So between 1895 to
1945, that's really cool
people were developing
nuclear science.
So people like Madam Curie
or like Fermi, et cetera.
They were all designing
this nuclear science,
like they were developing
it, which is pretty cool.
Most of this development
happened between 1939 and 1945.
Does anyone want to
take a gander as to why?
What?
AUDIENCE: Manhattan Project?
TA: Yeah, exactly.
But what field of the
Manhattan Project?
AUDIENCE: Nuclear weapons.
TA: World War two.
Yeah.
So World War two was
happening during those times,
and they were trying to
develop the atom bomb, which
is why the majority
of nuclear science
was developed between these
like five or six years.
Then 1945 to 1960.
They've entered a phase of
like, well, the war is over.
Now what do we do
with ourselves?
So luckily we decided
to redirect this science
into using it for
energy and harnessing it
in a controlled fashion.
So mainly the focus was
actually for Naval submarines,
but they also realize that
we can use this for energy
as well, for
electricity as well.
So there's a lot of
really cool things
that happened in
between these years.
So in 1951, the first nuclear
reactor to produce electricity
was the experimental
breeder reactor,
the EDR1 was
developed and designed
and operated, and
actually kind of worked.
It was created by
Argonne National
Labs, which is in Idaho.
And they actually still exist.
So if you want to go work there
this summer, you totally can.
And then in 1953,
President Eisenhower,
he created something
called atoms for peace.
So this is just a
program that advocated
using nuclear for things
that were peaceful,
such as electricity instead
of nuclear weapons and stuff.
Also 1953 was the
creation of Mark 1.
So Mark 1 is the first prototype
Naval reactor that was created.
It was created in March.
And then finally in 1954,
the first nuclear powered
submarine, the USS
Nautilus was launched,
and is up and running.
So lots of cool things
happened between this time.
But the real heyday of
nuclear was actually
between 1960 to 1975.
So during the span
of 15 or so years,
this was the real
commercial energy boom.
People like Westinghouse were
creating nuclear reactors.
I think the first one
was called Yankee Rowe.
It's a 250 megawatt
electric nuclear power
plant, which is not
insignificant for a time
like the 70s.
So other different companies
and other different countries
were doing this as well.
basically, there was this
huge boom in nuclear energy.
So if you look at this
little chart over here,
this is nuclear
reaction construction
throughout the years.
So if you look in
this little chunk,
you can see what a
massive peak there was.
This was when everyone was
building nuclear reactors,
people thought it
was super jazzy,
and everyone tried
to jump on that.
Unfortunately, all good things
have to come to an end, though.
From 1975 to 2002, which is
about this chunk over here,
you can see a massive decline.
And you can see
that nothing really
happened between the 90s and
the 2000s, other than the fact
that we were all born.
But no new nuclear
reactors were being
commissioned during this time.
And then today, we're kind of--
I say we're back,
but basically we're
entering what
people like to call
a nuclear renaissance, which is
between this chunk over here.
You can see that there's
been a slight increase
in nuclear reactors
being produced.
But basically there's been a
whole new push for creating
more advanced reactors.
And currently, China,
India, and South Korea,
they are the main
players in this game.
So China itself has 32
operate reactors operating
at the moment, and have
20 more commissioned,
like literally right now,
which is kind of insane.
So yeah, do you guys have
any questions about this?
Great.
So what causes
nuclear resurgence?
This is the perfect time to talk
about why nuclear power's cool.
Again, you guys
probably know this.
But the main reason
is sustainability.
So right now we've
entered a phase in time
where people are
starting to realize
that we've done damage
to our environment,
we've got to fix this.
So global warming is a thing.
I promise you, it's
actually a thing.
And basically, we're
looking for a way
to produce electricity without
creating such a large carbon
footprint.
So if you look at
this chart over here,
you can see that
this is where nuclear
lies in the amount
of carbon that it
produces per-- what's the unit?
Per gigawatt hour
of electricity.
When you look at
that in comparison
to coal and natural gas, which
is our two primary sources
of energy at the moment, you
can see that this is definitely
more attractive.
So the statistic is
actually that nuclear
creates 75 times less carbon
emission than coal does,
and 35 times less
than natural gas does,
which is incredible and amazing.
So that's the main reason
why we're going for nuclear.
But there's other kinds
of really good reasons.
One is the amounts
of power output.
You guys actually calculated
this yourself in pset 1.
You know just how much
power or energy comes out
from one fission reaction.
So just so you guys
can double check
that you got that statistic
right in your pset,
it turns out that
It turns out that you get
3.5 million times more
energy than burning one
kilogram of coal does.
So you can see
that you definitely
need a lot less fuel
in a nuclear reactor
than you do in a normal
coal burning reactor.
And then finally the last
thing would be energy security.
So one of the good
things about nuclear
is that it can serve as a good
baseload source of energy.
So if you're working
in the energy sector
you probably see this
chart all the time
of like time versus like
energy that's being consumed.
And it's kind of like this
fluctuating little mass that
stays fairly constant, but
at certain times of the day
you need more energy than usual.
So this is just the energy
demand during the day.
That's what this chart
kind of crudely depicts.
So nuclear power is able to
provide a good baseload source.
That means it can provide
conserve energy at a really
high level all the time.
So this is why we kind
of want to replace
coal and natural
gas with nuclear,
because it can take this role.
Other alternative
forms of energy
might be better for the
environment, it might be safer,
and things like that, but it's
not really able to do this.
So for example, if you wanted
to replace all the coal burning
fire plants with solar panels,
if it's not sunny that day,
you're kind of out
of luck, right?
Like you can't produce energy
if it's not sunny outside.
Similar for wind.
If it's not windy
outside, you're
not getting any electricity.
Luckily for nuclear,
it doesn't have
to rely on any of these factors.
You can continuously
produce energy.
Right?
So do you guys
have any questions
about what I've mentioned?
Awesome.
So now we'll talk a little
bit about reactor types.
I'll just tell you guys
about some of the main ones
and how they work.
So how people like to
divide up the reactor
types is in generations.
So generation one,
which, is all the way
over there, that refers
to the trial reactors.
These are the ones
that didn't really
produce all that much
electricity at all.
They're more proof of
concept kind of things,
so that would be like
the Mark I that I
mentioned to you guys earlier.
Now we move on to
generation two.
So generation two is actually
what most of US reactors--
the category that most
US reactors fall into.
So these were developed between
the '70s and the '80s-ish, and
these are the ones that are
functioning mostly today.
And then we have generation
three, three plus, and four.
So these are the new
types of reactors
that people are
trying to build on
to create several improvements,
but we'll talk about them
a little bit more later.
OK?
So I want to start off
with light water reactors,
because these are
the reactors that
are most common in
the United States.
So light water
reactors, or LWRs,
are mostly broken up
into two subcategories:
boiling water reactors and
pressurized water reactors.
So how you guys can
think about reactors
is that honestly they're
just kind of glorified steam
turbines.
That's what they're doing.
So let's start with
boiling water reactors.
So boiling water reactors,
or BWRs, comprise about 21%
of the reactors that are located
and working in the United
States.
So it's a really,
really simple mechanism
and we can walk
through that right now.
So over here, this little
nubbin right over here,
this is the fuel core.
So this is what the
inside of a fuel core
looks like, that
picture over there.
So the fuel core is
basically just a bunch
of rods of uranium,
sometimes it's
clad in something
like zirconium,
and there's also control rods
to help slow down the process.
So uranium undergoes what?
AUDIENCE: Fission.
TA: Yes, fission.
So what gets released
during fission?
AUDIENCE: Heat.
TA: And?
AUDIENCE: Fission products.
TA: Cool.
And?
AUDIENCE: Neutrons.
TA: Neutrons, awesome.
So those three things
are all flying around
inside the reactor core at the
moment as the uranium undergoes
fission.
So the isotopes, we just
kind of let them be.
Like I don't--
I'm not completely sure
what we do with them.
We might filter them out, but
I think they just kind of hang
out there.
The heat obviously
goes to create power.
We'll talk about that
in just a second.
But the neutrons
come flying around.
So those other neutrons can
simulate other fissions,
and the control rods
are there to make sure
that there's not
too many fissions
happening in the fuel
core at a certain time.
Anyway, going back to the
heat, the heat that gets
created during these
nuclear fissions, that
goes and heats up the water.
So this is just one loop
of water, basically.
So the water flows through
the core and heats it up.
It creates steam so the steam
goes and spins a turbine.
The turbine creates electricity.
And it comes back
and gets recondensed.
That's literally it.
That's all that
happens during a BWR.
Yeah, that's actually just it.
So a cool thing about the BWR
is, because it's so simple,
it's also incredibly--
well, not incredibly,
but it is the cheapest
option out there
for creating nuclear power.
One of the downsides is
just that it might not
be as energy efficient as
it possibly could be, or not
be able to create as much
power as it possibly could
if it was a cooler technology.
But yeah.
Oh, and another downside
is that because we
have the nuclear material
interacting with the water
and-- so this is a coolant pump.
This is a coolant tube.
This is basically connected
to a lake or an ocean
or some other source
of cold water,
and that runs through
the primary loop
to cool down the water and
recondense it into steam.
If there ever is a
breach between these two,
the chances of leaking nuclear
material into the environment
exists.
Like it's not high
per se, but with BWRs
there is a higher chance of
leaking radioactive material
into the environment.
So that's one of the
downsides of BWRs.
Do you guys have any
questions about this?
Awesome.
So I just want to show you
guys this picture again,
because here's the
underside of a BWR.
I make it sound like
it's super simple
and like a walk in the
park, but this is actually
the amount of
technology that goes
into one of these reactors.
Like look at all those wires.
I don't even know
what they all do.
But it's kind of insane.
So the next kind of reactor
that falls under the light water
reactor category is the
pressurized water reactors.
So PWRs are actually more
important, if you will,
than BWRs.
So remember, BWRs
comprise about 21%
of the reactors in
the United States.
PWRs comprise about 60% of the
reactors the United States.
But they are functionally
essentially the same,
and it's just slightly
more complicated.
So over here we have
our fuel core again,
and again all it's doing
is heating up water
with its fission reactions.
But this time this
water is pressurized.
So does anyone
know why you would
want to pressurize the water?
Yeah?
AUDIENCE: So it doesn't boil?
TA: Yeah, exactly.
So when you increase
the pressure,
you're also increasing the
boiling point of the water,
and that allows you to function
at even higher temperatures
than if you're working
with a BWR, which gives you
more energy efficiency.
You guys will learn all about
that in 2005, by the way.
So yeah.
It heats up this
pressurized water
and this pressurized water
goes into a second loop which,
again, just heats up water.
That turns into
steam, that spins
a turbine that
creates electricity,
gets recondensed, et cetera.
And that's, again, all
that there really is.
So one of the upsides of using
a PWR is, like I mentioned,
the higher efficiency.
But also the chance of
leaking nuclear material
into the violent
becomes mitigated.
Because you have two separate
loops with the nuclear fuel
being more isolated
from the environment,
if there is a breach
between the condenser loop
and the secondary
loop, not a big deal.
Nothing really bad happens.
You'd have to have breaches
in both the loops, which
is very unlikely to happen.
Yeah.
So do you guys have any
questions about those two?
Yeah?
AUDIENCE: What's the standard
like operating temperature
of these kinds of reactors?
TA: I'm not completely
sure, but if you Google it
you should be able to
find it very easily.
OK.
So this next picture
is, again, just
to show you that like I
make it sound really simple
and like a walk in the
park, but it's really not.
There's a lot going on.
So this picture over here
is basically just showing
that there are a lot
of redundancy systems
inside these reactors.
Like we don't just have
one single primary loop
and if it fails, it fails.
We actually have four
at the same time,
and this is just called the n
minus two redundancy, something
like that.
OK?
So the next kind is
something much cooler.
It's got a heavy water reactor.
Actually it's just
a little bit cooler.
But the main heavy water reactor
that everyone can kind of
think of on their
minds is CANDU,
which is the one that's
located in Canada.
So the only difference
between heavy water reactors
and the light water reactors
as I mentioned before
is that it uses heavy water
instead of light water.
Does anyone know
what heavy water is?
AUDIENCE: Deuterium oxide.
TA: Yeah, exactly.
So it's just deuterium oxide.
So remember-- I'm sorry,
this might seem inane,
but this is water, right?
And this is heavy water,
where the D is just
a hydrogen with two
atomic particles instead.
So one proton and one neutron.
So the reason why they decide
to use heavy water instead
of light water is
because heavy water
has a much lower
absorption cross-section
than light water does.
So what this means is that
when neutrons are flying around
in the reactor there is a
chance of it hitting a fission
product and a piece of
fissionable material
and undergoing fission.
But there's also a chance that
the water that surrounds it
will absorb that neutron.
So if that neutron gets
pulled out of the system
you're not able to
create any more fissions.
This is actually
kind of a bad thing
because the whole point
of nuclear reactors
is to create heat and fission.
So we don't want those
neutrons to be absorbed.
You can see, if you look
at those statistics,
you can see that
the absorption cross
section of H2 or deuterium
is like 0.00052 barns,
in comparison to H1,
which is 0.332 barns.
So I'm bad at math, but I
think it's like 600 times less,
right?
Maybe?
Anyway, so you can see
why deuterium would
be a good option for this.
So because it's absorbing less--
because it has a chance of
absorbing less neutrons as it
undergoes its processes,
you're actually
able to use a lower enriched
uranium, which is really great
because that lowers fuel costs.
Yeah.
But the main downside of this
is that, even though you're
lowering your fuel costs,
deuterium is really expensive.
It's about 1,000 or so
dollars per kilogram,
which is kind of ridiculous
because a kilogram of water
is really not much
at all, you know?
So even though you're
counteracting the lower fuel
costs with higher water cost.
Also, because you're
using your reactor
with lower enriched
uranium, you actually
have to change out
your fuel more often.
That fuel gets
spent more quickly
and I'll describe
that in just a second,
and therefore you just
have to keep replacing it
more often than you would for
a normal light water reactor.
Cool?
Questions about this one?
Oh, I forgot to
mention, but aside
from that, everything else
with the heavy water reactors
and the PWRs, they're
the same mechanisms.
And finally we're going to
move on to breeder reactors.
So breeder reactors
are a really cool idea,
and they were most
popular between like
the '50s and the '60s-ish in
the very beginning of creating
nuclear reactors.
So what breeder
reactors are are,
again, they're
essentially the same thing
as light water reactors I
mentioned you guys before.
But instead, now there's
two little chunks
of extra material.
So do you guys know what the
difference is between fissile,
fertile, and
fissionable material is?
Cool.
All right, so all right, let's
start with fissile material.
So fissile material is
basically just the material
that is willing to undergo
fission with a thermal neutron.
OK.
So basically when
the thermal neutron
gets absorbed by this
fissionable material,
it's going to undergo a fission.
Makes a lot of sense, right?
So do you guys
happen to remember
what the energy of a
thermal neutron is?
You guys calculated
this in pset 1.
Huh?
AUDIENCE: 1 eV?
TA: Lower than that.
AUDIENCE: 0.025?
TA: Yeah, 0.025 eV.
Like super low energy.
And while we're at it,
how do you calculate this?
Bozeman constant times T. Cool?
Whew.
So main examples
of fissile material
would be U235 and plutonium 239.
There's four in
total, but those are
the two most important ones.
OK.
So this is the main fuel that
is inside a nuclear reactor,
but it's not all just U235.
Like you guys have heard of--
oh, shoot, what's it called?
Enrichment, right?
Enrichment is
basically the amount
of fissile material versus the
amount of other fissionable
material.
So moving onto
fissionable material.
So fissionable material
is just material
that is able to undergo fission
after the absorption of a more
energetic neutron.
So that's all it is.
So that's all it is.
So an example of
fissionable material
that's inside the other reactors
at the same time is U238.
So if a U238 absorbs
a thermal neutron,
it's not going to do much.
But if it absorbs a neutron
of about like, I would say,
like 2 meV, then it's more
willing to undergo fission.
Cool?
And finally we have
fertile material.
So fertile material is the
basis for breeder reactors.
But fertile material is just
material that absorbs a neutron
and then is able to become
a piece of fissile material.
So for our purposes,
the main types
of fertile material we use
are U238 and thorium 232.
So if you look at
these processes
you can see that U238
absorbs a neutron,
becomes U239, undergoes a
beta decay to come neptunium
and undergoes one more
beta decay to become
the beautiful plutonium 239.
If we start with
thorium 232 instead,
absorbs a neutron,
becomes thorium 233,
undergoes a beta decay
to become protactinium,
becomes uranium 233, which
is another fissile material
by the way, through a
series of beta decays.
Cool?
So that's what breeder
reactors are doing.
They're adding extra
chunks of uranium 238
and extra chunks of thorium
232 into the reactor.
If one of the
neutrons-- so imagine--
if you're looking at
the little fuel core,
there's a bunch of neutrons
that are flying around
and heat and other isotopes
and things like that.
So some of the neutrons will
go and create other fissions
with the material that's
hanging out in the red.
But other neutrons
might escape, and when
they escape, instead
of going into the water
dissipating and never to be
seen again or being reflected,
they instead create
more fissile material.
So you can understand
why this is
a kind of an attractive
idea, is that you're
creating your own fuel.
You're able to work at
a higher fuel efficiency
because you don't need to add
in as much fissile materials
as you would for a normal
light water reactor.
So people were really fascinated
with this idea, like I said,
in the 50s and 60s.
Because back in the
day they legitimately
thought that we would
run out of U235.
But luckily in the
60s we discovered
that we have a lot more uranium
ore than we thought we did.
We're probably not going
to run out anytime soon.
And after that discovery, people
were not nearly as interested
in breeder reactors.
The reason being is that,
one, because there's just
this extra material
that's hanging out,
this extra material could
be more fissile material
that creates more reactions.
It's not nearly as
power efficient.
And it's also slightly
more expensive
because you're not being
able to be power efficient.
And it also is better on paper
than it ever is in reality.
So on paper you're
like, oh, this is great,
because I can just create
more fissile materials.
I never need to add more.
This is never really
truly sustainable.
They always have to keep
adding more fissile materials,
because it's not as perfect
as they want it to be.
Any questions
about these things?
Great.
Cool beans.
And then finally
we're going to move on
to generation four reactors.
So generation four reactors are
all the new kind of reactors
that people want to build.
So the primary objective for
these new designs of reactors--
like, the ones I
just told you guys
about, they're
all good and well,
but we want to make
them better, right?
We want to make them cleaner and
safer and more cost effective.
Keep them robust
yet sustainable,
and also make them more
resistant to people
being able to divert materials
into creating nuclear weapons.
So yeah.
Here are the six
kinds of generation
four reactor types
that were deemed
to be the most promising.
So there's gas-cooled
fast reactors,
lead-cooled fast reactors,
molten salt reactors,
sodium-cooled fast reactors,
very high temperature gas
reactors, and supercritical
water-cooled reactors.
So I'm going to be
honest with you guys.
I don't know all
that much about these
and I don't want to like
spew out information that
might potentially be false.
So if you guys are
interested, one,
you can talk to
other lab members
or people in this department.
I know they're-- mostly
Mike's group, actually.
A lot of people in
Mike's group are
working on molten salt
reactors so you guys can go
ahead and ask them about that.
Or if you're interested you
can read more about them
with this hyperlink that
I included over here.
Hopefully he will
post the slides online
and you guys just
click it and there's
a awesome source all about these
different kinds of reactors.
OK?
All right.
Any questions?
Hi.
AUDIENCE: Do any of
these actually exist,
or is it all just theory?
TA: I'm pretty sure that
they were just kind of proof
of concept stage right now.
Like there aren't any that
are producing electricity
in the United States, at least.
Cool.
Good question.
All right.
So all the things that we've
mentioned before like how
great nuclear is and all
the cool applications of it
and how simple and
easy reactors are,
why aren't we using more of it?
So currently in the US there's
only 99 operating reactors
that are producing electricity,
which makes up about 19%
or about 20% of the
total electricity
output in the United States.
The main players
are still, you would
imagine, coal and natural gas.
So this is actually even worse
in the rest of the world.
In the rest of world, there's
only about 440 reactors
spread around 30 countries
and produces only 14%
of the global electricity.
So these proportions
are pretty low.
And you're wondering,
like, why aren't we
using more nuclear power?
What exactly is holding us back?
So it turns out that the main
things that are holding us back
is just social, economic,
and therefore like government
hesitance to start using
nuclear power more often.
So the main reason
why we're a little bit
hesitant to start using
more nuclear power
is because of safety issues.
So nuclear-- none of us can
argue that nuclear is like 100%
safe.
It actually does have
some dangers associated
with it, which is why it's
so important that we're
doing what we're doing.
But if you guys
look at this chart
that I showed you guys in like
the first or second slide,
you'll notice that there are
these events listed above.
What are these words?
Three Mile Island, Chernobyl,
Fukushima, what are they?
AUDIENCE: Nuclear accidents.
TA: Yeah, so they're some of
our biggest nuclear accidents
that we've experienced
in history.
And you can see that
after a nuclear accident
you can see a
pretty steep decline
in the amount of
nuclear reactors
that are being commissioned.
So this is especially noticeable
at Three Mile Island, which
is essentially the first nuclear
reactor accident that we all
had to go through.
You can see that, after
Three Mile Island,
you can see this
massive steep decline
in the amount of nuclear
reactors being commissioned.
This is probably causational.
We can pretty much assume that.
And then you can see
that Chernobyl-- once
Chernobyl happened, you
can see like this also
another massive decline.
And again Fukushima, once
again, with the amount
of reactors being commissioned
after the accident just
declines dramatically.
So I'm assuming
you guys probably
don't know exactly what happened
during each of these accidents.
Like you probably
know that they exist,
but like what
happened during them?
So if you do know, sorry,
but if you don't know,
you're about to know.
So Three Mile Island,
which is the first one,
it happened in 1979 on March 28.
So Three Mile Island reactor is
a PWR located in Pennsylvania.
So during this time it
underwent a core meltdown.
The cause of this
is just the fact
that there was some kind of
mechanical or electrical system
that prevented coolant
water from being
pumped into the primary system.
So because there
wasn't enough water
coming to cool up the core,
the core began to overheat.
So as the temperature
of the core rises,
the pressure also rises.
So they notice this and
they're like, oh, shoot,
we got to fix that.
So luckily there is like
a little emergency valve
that you can see in this
animation gets opened up
and pressure gets released.
So that's all good and
well, but unfortunately
after the pressure's
released, you
should close the valve again
and continue operation.
But it became stuck.
So this valve became
stuck and they
didn't realize that
it became stuck
because their equipment
and their instrumentation
wasn't able to detect that.
So they continued to operate
again but this valve was open,
so there was actually water
that was getting leaked out
of this primary loop.
So because the water
was getting leaked,
they noticed that, oh, shoot,
the pressure is dropping.
Well, what do you do when
the pressure's dropping?
Apparently you have to
make sure that there's not
too many vibrations that
could damage the reactor,
so they shut off
the coolant pumps.
Or they lower the operation
of the coolant pumps.
So now there's water leaking out
so the core is getting hotter,
but then they also
took out the water
that is usually used to
cool the reactor core,
so again it's also
getting hotter.
So this combination of events
led to a core meltdown.
So the core melted down.
That's never a good
thing, by the way.
Yeah.
And yeah, so the
core melted down,
the reactor wasn't able
to operate anymore.
But luckily at Three
Mile Island there
was containment that
prevented radioactive isotopes
from leaving the system.
So they actually
took a brief survey--
or not a brief survey.
That's probably a
long, long experience.
But they realized that
the two million people who
are around Three Mile
Island at the time,
within like a two mile radius
or like maybe a 30 mile radius
or something like that,
they realized that they
didn't get much dose at all.
They collected about a total
of 1 milligram more dose
than usual.
So to put that in perspective,
an x-ray is six milligrams.
So really nothing that
happened at Three Mile Island
other than they
had to shut it down
and they had to do
expensive repairs.
But people weren't hurt.
The environment wasn't damaged.
It wasn't that bad
of a situation.
I think the effect
was bigger in concept
than it was in actual damage.
Questions about Three
Mile Island accident?
All righty.
The next reactor accident, the
big kahuna I like to call it,
is Chernobyl.
So on April 25,
1986 an RMBK reactor
that was located in
Ukraine exploded.
So what they were
doing at Chernobyl
during the time
of this explosion
is that they're actually
running, ironically enough,
safety tests.
They were running the
reactor at low power
to see how it behaves.
So at low power, I don't think
they quite realized this,
but the coolant
pumps in the reactor
were also powered by the
nuclear reactor being generated.
So if they're running
this at low power,
their coolant pumps weren't
getting enough energy
to properly cool the fuel core.
So that was unfortunate,
and they realized
that this is a bad thing.
So the reactor starts
to go supercritical.
So when they realize that the
reactor was creating a lot more
fissions than it should
have been creating,
they decide to insert
the control rods.
So thank goodness we have these
high absorption control rods
to slow things down, right?
For some reason, I'm
not completely sure
why they did this, but
RBMKs, they have graphite
tipped control rods.
So as they lower
the control rods
into the water, this graphite
tip, which doesn't effectively
absorb neutrons, it displaced
a little bit too much water
than was necessary, and that
caused the first explosion.
So it went super duper critical
and caused the first explosion
at Chernobyl.
Then, for some reason like
a couple of minutes later,
there's a second explosion.
They're not completely sure why
the second explosion happened.
To this day we can't
really pinpoint why.
It could have been like
building up helium or just
a ton of other
fission reactions.
But there's a second
explosion that actually just
blew this entire core apart.
So that kind of stunk, but it
did stop the whole reaction.
Because a super critical
mass was all blown apart,
it was no longer super critical.
It was fine.
The whole debacle stopped.
But unfortunately,
there was a lot
of radioactive isotopes being
spread into the environment.
First of all, Chernobyl
didn't have the same kind
of containment that
Three Mile Island had,
so these isotopes were
just able to go everywhere.
And also the second
explosion had a lot of steam
with it that carried these
isotopes even further than they
probably should have gone.
So if you're looking at the
statistics of Chernobyl,
it turned out that
28 highly exposed
reactor staff and emergency
workers die from this radiation
or from thermal burns
during this time.
And officials also
believe that there
is about 7,000 cases of
thyroid cancer that occurred
because of Chernobyl.
They're pretty sure it was
Chernobyl because these
are all cases that
happened in people
who are less than 18 years old.
So you guys know that no one
really lives near Chernobyl
at the moment.
It's kind of been
deemed unlivable
because these radioactive
isotopes literally went
everywhere in this environment.
Like it was in the water,
it was in the plants.
It's not safe to live there.
It's a pretty
radioactive environment.
Luckily we see that there are
animals coming back now now.
If you look on
NationalGeographic.com
there's like little deer
roaming around Chernobyl.
But it's been about-- how long
has it been, like 30, 40 years?
People aren't advised
to live here still.
So Chernobyl was terrible.
Questions?
Yeah?
AUDIENCE: What does it mean for
a reactor to go supercritical?
TA: Oh, yeah, sorry.
So you guys will learn all about
criticality in a little bit,
but basically when
I say supercritical
it just means that there's
way too many fission
reactions happening.
Yeah?
AUDIENCE: You said it went
supercritical because it
wasn't being cooled enough or?
TA: I think I might
have skipped a detail.
It wasn't being cooled enough
so the water was evaporating
and then it became supercritical
because there was not
enough neutrons being
slowed down or absorbed.
My bad, I'm sorry.
Good?
All right.
So the next reactor accident
that we were alive for,
which is cool, was
Fukushima Daiichi.
So Fukushima Daiichi
happened in 2011 on March 11,
and Fukushima is in Japan.
So these reactors, I think these
are pressurized water reactors.
Yeah, I think so.
So following a major earthquake,
the generators that were--
pardon.
Yeah, so following
a major earthquake,
the things that were cooling
the core, they broke.
I think they're just like power
generators on the side that
did--
yeah.
They broke the cooling pumps.
So there wasn't
enough water being
able to go to the fuel core.
This is a very similar
problem, as you
can see that in all these
instances of the reactor
incidents, it's just kind
of like the fuel core was
misbehaving and we
weren't able to get
enough coolant water to it.
So following the earthquake,
these coolant pumps broke.
They're like, oh, that's OK.
What we can do is we
have backup generators
to continue running the pumps.
It'll be all OK.
Nothing will happen.
We're all good.
And then a tsunami hit.
So it was a foot
tsunami I think--
I think that--
15 meter tsunami, oh good gosh.
So a 15 meter tsunami
hit and it broke
the generators and then at that
point they're like, oh, no.
So they had no other
redundancy factors
to continue pumping cool
water into the fuel core.
So again, there
wasn't enough water
in the core, it
became supercritical,
it began to melt. So the
fuel rods began to melt,
but this is actually another
additional bad thing.
So the water was
evaporating, creating steam.
The fuel rods were
coated with zirconium.
So what you guys
might not know is
that when zirconium and steam
interact with each other,
that's not a good thing.
It starts to explode.
So as you can see, the
reactors at Fukushima Daiichi
began to explode.
There was radioactive
isotopes being spread out all
around the country.
You guys probably saw
the lovely flow charts
of the radioactivity
flowing out from Japan
and making it to California
and contaminating your fish
and stuff like that.
But luckily, no one was directly
hurt by burns or radioactive
exposure.
Cool?
All right.
Questions about Fukushima?
Solid.
So aside from these
safety issues,
these safety issues that happen,
they get elevated in the news
quite a lot.
So these are mainly the things
that people who don't really
have any background
in nuclear energy
hear about nuclear energy.
They're like, oh
shoot, well this thing
is going to explode
every 20 years.
Like, why do we keep using this?
Reactor accidents are
actually pretty rare.
If you think about it, it's
been about 60 or 70 years,
we have 440 reactors
operating around the country.
There's three main accidents
that have happened.
But because these are the
things that people get ingrained
into their mind-- thank
you, news stations--
people think that
nuclear reactors
are incredibly dangerous.
And that's why we have this
social hesitance, which
is why we aren't able to get
enough government funding
and which is why there's
all these bureaucracy
loopholes to jump through,
which is why nuclear power isn't
more of a thing.
Makes sense?
Yeah.
Another issue that's
associated with nuclear power
is nuclear waste.
So what in the world
do we do with it?
So first of all, the main thing
in nuclear waste is spent fuel.
So like I mentioned to
you guys, spent fuel rods
are made out of uranium oxide.
But after undergoing
a bunch of fissions,
these uranium particles get
transformed into other isotopes
that aren't fissionable or
fertile or even remotely
fissile, right?
So we eventually have to replace
them and add in new rods,
and this is a process that
happens every 12 or so years.
I'm not completely
sure on that statistic.
But the main issue's
like, what do we
do with all this material?
So this material that comes
out is pretty radioactive
and it's also
incredibly hot, so it
can be dangerous if someone
decides to come and eat it.
So that's why we've got to
figure out a way to expose it.
So the primary way of
disposing of the spent fuel
is putting it into
spent fuel pools.
So spent fuel pools are
just giant tanks of water
that exist at the reactor.
So these tanks of
water are mixed
with I believe it's boron,
which is a neutron absorber.
They basically just
put the spent fuel
rods all the way at
the bottom of the pool.
So this pool's about like
20 meters high, I think.
This is actually a
really good solution
because the water in the pool,
it cools down the reactor rods
and also prevents
a lot of neutrons
from escaping because water is a
really great neutron moderator.
You guys all know this.
It turns out it's
actually fairly safe.
Apparently you can go swimming
on the top of the reactor spent
fuel pool and
you'll be OK and not
be exposed to too much
radiation if you want.
So yeah.
So this is the main
solution that people
have been using
for years, but they
realize that this isn't
super sustainable,
because the amount of space
that we have in these spent
fuel pools is not infinite.
We have way too much
spent fuel to be
able to just continue to store
it in these spent fuel pools.
So like shoot, got to
find another solution.
So the next solution
was something
called dry cask storage.
So dry cask storage
is just a way
to keep this spent fuel
surrounded by an inert gas.
And it's held inside a cask,
a cask just being probably
like a steel drum
that's bolted and welded
shut, and then there's
additional pieces
of shielding around it like
cement and lead, et cetera.
So there's just
like gigantic tanks
basically that are
sitting outside.
So they put them
outside the reactor.
As you can see,
it looks like it's
sitting in a parking
lot outside the reactor.
And so this is an OK solution.
So basically what they do
is they take a spent fuel,
let it sit in the pool
for about a year or so,
maybe two or three years.
And then they're able to take
it out because at that point
it's significantly less
radioactive because, you know,
you guys know how to
calculate this, too.
You guys know like the half
life of different radioisotopes.
You see that the radioactivity
declines at a certain point.
It's also more cool now so
they put them in these tanks,
so they let these
tanks hang out outside.
And this is an OK solution,
except for the fact
that, again, we just have
way too much spent fuel
to be able to do this.
It turns out that if you were
to just keep all the spent fuel
that we create in
fuel casks, it'd
take about 300 acres of land,
which is absolutely insane.
And obviously no one
wants to take up that.
Brief little side note, when
I was googling like images
of dry cask storage
and I was looking
for the different types,
what I found particularly
disturbing was that there's
only two types listed:
vertical storage and
horizontal storage.
Like there's no
other solutions other
than these are giant tanks.
Anyway, so people
realize that we
need to figure out
yet another way
to dispose of the
spent fuel, hopefully
a way that doesn't get in the
way of people's backyards.
So the idea was something called
deep geological repositories.
So deep geologic
repositories literally just
means that they want to bury
the nuclear waste very deep
into the ground and never be
able to retrieve it again.
So the main push for this was--
well, first of all, it's a
permanent method of disposal.
They hope to put
it in the ground
and never have to
think about it again,
so therefore the
regions that they
choose to bury in
the ground have
to fulfill a lot of criteria.
So this criterion
includes not having
a lot of seismic activity.
Because we are keeping this
nuclear waste underground
in these casks for like
thousands of years,
if there is a huge
earthquake, those casks break,
radiation gets everywhere.
That's obviously
not a good thing
so we want to make sure
that doesn't happen.
We also have to make
sure that there's not
a lot of water
that leaks through,
because the water can
carry the radioisotopes
and carry them into the
environment, which is something
else that we don't want to do.
A lot of you guys chuckled
when you saw Yucca Mountain.
So Yucca Mountain is the primary
push by the United States
to find a deep geological
repository somewhere
in the United States so we
can deal with our spent fuel.
So in 2002 the main
push for this began.
They spent a lot of money.
They spent like
billions of dollars
finding the perfect location
to put our spent fuel.
They had like nine
different locations
and they finally narrowed
it down to Yucca Mountain.
They're like, yes,
this is the one,
and they started digging
down deep into Yucca Mountain
and making this happen.
But then things
weren't as peachy keen
as they hoped it would be.
So Yucca Mountain is
located in Nevada.
People in Nevada weren't
happy about this.
They're like, why are we
getting tossed on nuclear waste?
We don't even have nuclear
reactors in Nevada.
This is not fair.
There was a lot of opposition.
And because of the
social opposition
there was government
opposition and many loopholes
we had to jump through,
and so it was just
becoming a huge disaster.
They also realized that
it wasn't as geologically
sound as they had hoped.
There's a lot more groundwater
running through and seeping
through Yucca Mountain than
they thought there would be,
so it's actually not as
safe as they had hoped.
So there's a huge debacle.
Basically the costs are rising,
nothing much was happening,
there's a bunch of different
things preventing progression
from happening.
And then 2011, under the
Obama Administration,
he just called it quits.
There's no more government
funding to Yucca Mountain.
It's been abandoned, as you
can see from this lovely Google
picture.
It's permanently closed.
And you can also see that like
14 people went out of their way
to review Yucca Mountain.
But we're actually doing OK.
It's at like 3.6 stars,
just like a normal motel
or something like that, so
that has been abandoned.
This idea has currently been
abandoned in the United States.
We're kind of still looking
for other solutions,
but we really don't have it
figured out all that well.
There is one other kind of way
of dealing with nuclear waste,
which is repurposing.
I personally think
nuclear repurposing is
the coolest option out there.
And basically
repurposing just means
you take the spent
fuel and you chemically
separate out any material that
could be continued to be used--
any fissile material
that could be
continued to be used
in other reactors.
So basically you
take the spent fuel--
and it turns out that 96%
of a used fuel assembly
is recyclable.
So you take the spent
fuel, you take out
what it is useful, you throw
away what's not useful,
which is also still
radioactive waste that
has to be put in a fuel
pool or something like that.
But you have this
precious fuel that you
can put into another reactor.
So this is actually
something that France
and other places in Europe,
and Russia and Japan,
they use repurposing
quite a lot.
For some reason the United
States doesn't do it.
So the reason being is that
this is a really cool idea.
It's like recycling.
It's like very--
it's very clever.
I think I think it's personally
one of the cleverer solutions,
but the issue is that it's kind
of a really expensive process.
So repurposing fuel
takes a lot of money
and it turns out that the
act of repurposing fuel
actually costs more
than just buying
a new chunk of uranium 235,
which is why we don't do it.
It's not economically sound.
So yeah.
You guys have any
questions about anything
I've mentioned, about
deposition of nuclear waste?
Almost done.
OK.
So all these are issues.
Like, we have a lot of
nuclear waste to deal with.
It is kind of--
there is an inherent danger
with using nuclear power.
But the real thing
that holds us back
from just having
nuclear power everywhere
and creating about
90% of our electricity
as we would hope it
would is economics.
So in this world, money
really matters a lot.
The economics of nuclear
power is actually
a really complicated
topic and it changes
depending on who you talk to.
There's a lot of factors
that are involved,
so you can include
certain factors
into your calculations
like, oh, the cost
of building the reactor
in the first place
or like fuel costs
or operating costs
or maintenance costs or the
amount of money that comes out
of damaging the environment.
You can weigh all these
different factors in,
and everyone churns
out a different number.
But basically everyone you talk
to, if you look at this chart,
yellow is nuclear
power, the gray is coal,
and the blue is the natural gas.
But basically,
anyone you talk to,
you can see that
nuclear is not nearly as
economic of a source of
electricity generation
as any other of these
ones I mentioned.
Unless you talk to UK.
UK thinks it's OK.
But everyone else is saying that
it's not as money efficient.
So where are all these
costs coming from?
So the primary costs
actually lies with something
called capital costs.
So capital cost is
basically the sunk cost
of just building the reactor.
Building reactors takes
billions of dollars.
It also takes tons of time.
And because it
takes a lot of time,
interest rates also jack
up that price even further.
So basically it's just
this massive investment
they have to throw
in immediately,
and this is where most
of the issues lie.
Like it's really hard to go to
an investor and be like, hey,
can I have a billion dollars
to build this nuclear reactor?
It's going to take
five years and it's
going to take 20 more years for
you to get your profit back.
How does that sound?
No investor is going to be
like, yeah, that's a good idea.
That's the main
reason why we can't
get nuclear up and running.
We have a lot of plants
and we have the possibility
to create a lot of
plants, but we just
don't have the money to do so.
Because it's a huge chunk of
money, like I mentioned before,
it takes a while to
get your profit back.
And also, if for some
reason something happens,
you have to stop
building your reactor.
You just lost a billion dollars.
Like, there's no
turning back, right?
If you look at this
chart over here, which
is breaking up the
cost of nuclear energy
per kilowatt hour, I believe--
gigawatt hour?
Kilowatt hour.
Kilowatt hour.
You can see nuclear,
coal, and natural gas.
So this giant white chunk
over here refers to fuel.
So if you can look at nuclear
power, the majority of cost
actually doesn't come
from nuclear fuel at all.
It's just about $0.01
per kilowatt hour,
as compared to
natural gas, which
the majority of the
costs of electricity
actually come from the fuel.
If you look at operation
and maintenance,
again it's not that
large of a chunk.
It's about the same as
maintaining a coal power plant.
But then if you look at
the capital cost, which
is the dark gray color,
you can see how massive
that is in comparison to
building natural gas and coal
firing plants.
So yeah, I think
that's the main thing.
So because it is
more expensive, we
can't compete with other
forms of electricity.
People buy the electricity
that's cheapest,
not necessarily the
electricity that's
best for our grandchildren
or something like that.
Yeah, so that's why nuclear
power isn't more of a thing,
and that ends my pretty
lengthy slide show.
So do you guys have any
questions about anything
I mentioned?
If you guys are interested
about any of these topics,
like if any of these things
piqued your interest,
I recommend going to NRC.gov.
They have a lot of
really cool information.
Let me write that down,
because I talk quickly.
That's basically where I got
the majority of my information
for the slide show, and
it is a reliable source.
It might just be skewed
a little bit pro nuclear,
so just keep that in mind.
But there's a lot
of crazy sources
out there on the interwebs.
Take them with a grain of
salt. Take NRC.gov with less
grains of salt than usual.
Or if one of these things
really piqued your interest,
you guys can take
22.04, which is really
cool class that's offered
here I think this spring,
and if not this
spring, next spring.
But basically it's called
nuclear power society.
It's taught by a guy
named Scott Kemp.
He talks about all these
things and in a lot
of detail and slower.
So yeah, cool.
So thank you guys
so much for coming.
I know you guys could
have slept an extra hour,
but instead you heard
me ramble for an hour.
