- Right now, underneath a
failed Russian nuclear reactor in a lowly basement room, there is two tons of radioactive lava. It's been more than 30 years
since it first formed there, and it's still hot. Let's get technical. (upbeat music) I've always been personally fascinated with nuclear physics and nuclear power. I guess you could say
I just think it's rad. But if you read up on these topics for any amount of time, you will inevitably hear about Chernobyl, a nuclear power plant in
the northern part of Ukraine that experienced the worst nuclear disaster in human history. The story of Chernobyl
is downright gripping, but perhaps because of this, it is sometimes difficult
to find less sensational and more informative
information on the topic. So for today's episode,
we are gonna go through how Chernobyl actually worked from an engineering perspective, how it melted down from
a physics perspective, and the lethality of what it left behind. So grab your gas mask
and a Geiger counter, we're going in. First, we need to know how
nuclear reactors make energy. The infamous Chernobyl nuclear reactor was a nuclear fission reactor. And nuclear fission is the
act of splitting larger, less stable atoms into
smaller, more stable ones. And this splitting requires
some initial particles like neutrons from the reactor, and what is produced
are those smaller atoms, some energy, and then more neutrons. The trick to creating fission power is building your device in such a way that you can guarantee that those neutrons you are creating from
this fission reaction will go on to hit other large
fuel atoms that you are using, like uranium-235. And that creates a
sustained fission reaction. Nuclear fission reactors
sustain these chain reactions specifically by putting
their radioactive fuel, usually in the form of some kind of rod, in a specific orientation
and geometry in the core, such that they are close enough together and in the right way, that
the neutrons that are produced from the fission reactions
happening inside of these rods go on to hit enough
atoms in the other rods, to make this chain reaction happen. The energy that is produced
is in the form of heat, and in Chernobyl's case,
that heat is then routed into a coolant that is water, and that water flashes into steam, that steam goes into turbines which turn and generate electricity. As you might expect, you would
not want a chain reaction to get out of control. So nuclear reactors have numerous controls on how quickly a reaction can proceed, and have ways to slow it
down to produce less heat and less electricity so
that nothing goes wrong. In Chernobyl's case, this is
what the reactor looked like in terms of producing power. You had fuel rods at the center flinging neutrons at each
other and getting really hot. And then you had coolant water
around those control rods, which would also absorb
neutrons and flash into steam, turn turbines, create electricity. But then you also had
control rods made out of some neutron absorbing
material that could, again, slow everything down when inserted. The grand promise of nuclear energy is that when all of this is done right, you can get literally millions of times more energy per kilogram
than we currently get from any fossil fuel,
terajoules per kilogram. And aside from the
dangerous nuclear waste, which admittedly we
haven't really figured out how to deal with yet,
nuclear energy is clean. Of course, this is when
everything goes right. When a nuclear reactor goes
wrong, it goes really wrong. Chernobyl's infamous
reactor was a so-called RBMK reactor, and if you
were to look inside of it, you would see something like this. The majority of the core
was made out of graphite, like you'd find in your pencil,
because it just so happens that graphite is a good neutron moderator. It slows down very fast neutrons because slow neutrons are
just better at sustaining nuclear reactions, that's
how the physics works out. Also inside, you had a
number of control rods made out of boron carbide,
which absorb neutrons, and then again, you had the
water, which absorbed neutrons and created that critical electricity. And keep in mind, we were
just zooming in there to look at the intricacies. If you zoom out, the entire core is huge. It's over 20 feet tall and 40 feet wide. The design of RBMK reactors in particular made energy production in
this Russian power plant a delicate balance of heating and cooling and reactivity and absorbing neutrons. And on April 26th, 1986,
a lack of that balance led to disaster. Thanks to a deadly combination of human error and design flaws, what happened next at Chernobyl
will be felt for centuries. On that April morning in 1986, the staff were running a risky test to see how Chernobyl's
reactor unit four would fare at low power with some of its
emergency systems shut off. And also during that test, they reduced the number of control rods
they would usually want from 30 to six. Adding to the danger, RBMK
reactors in Russia at the time had what is now considered
a serious design flaw, a positive void coefficient. Remember that running
throughout the zoomed in version of our reactor here, you
have water flowing around the uranium fuel rods acting
as both a neutron absorber and a coolant. These reactors are
supposed to create steam to generate electricity with all the heat coming
off of these fuel rods. However, if steam starts being
produced inside of the core next to these fuel rods because of, say, a surge in energy production, it can form voids, voids
in the form of steam where water should be, and
steam is not nearly as good as water at absorbing neutrons. So when the neutrons are coming off, they go through these voids
and hit the other fuel rods increasing the reactivity of the reactor, which creates more voids, more
steam, more heat, more voids. It creates a positive feedback loop that can spin everything out of control. And on 1:23 AM on that fateful day, that's exactly what happened. During reactor unit four's low power test, which involved a number
of procedural violations, a positive feedback loop of heat and steam started to take shape. Within an hour of starting the test, a domino effect of human
error and design flaws led to an increase in
reactor power of 12,000%. This intense flood of heat flashed all of the core's coolant
water to steam so rapidly, it created a steam
explosion that dislodged the top shield of the reactor. It weighed two million pounds. After another explosion, the rush of air coming into the failed reactor
set the graphite on fire, which is almost impossible to extinguish. Fire and explosion led
to an eventual release of eight tons of radioactive
material into the atmosphere. This was Chernobyl's
main release of radiation into the surrounding areas. With no check on the
uranium fuel's temperature, what happened next was meltdown. Inside of the ruined reactor, the fuel rods had no checks and balances on their temperature, so the uranium got hot enough
to literally melt down. And then they got to
about half the temperature of the surface of the
sun and started to glow incandescently with light. At the same time, firefighters
outside in helicopters were trying to douse the graphite fires with five million kilograms of sand, clay, and other materials. Many of the helicopter pilots died shortly thereafter from fatal
doses of radiation carried by these fires because it took nine days to put these fires out. The fires were extinguished,
but something was still burning at the bottom of reactor
unit four, radioactive lava. The core of unit four was
destroyed, but it wasn't all gone. Some of it was eating
its way into the Earth. If you wanted to know what
the most dangerous material humans ever created was,
corium would be a good answer. After the fuel rods in
reactor four melted down, they flowed like lava to the
bottom shield of the reactor. Eight days later, they had
eaten all the way through it, and then they ate through
two meters worth of concrete flowing into the basement
sections of Chernobyl through basement pipes
and steam corridors. Thousands of kilograms of uranium oxide, sand, silicate glass, molten metal was all flowing as streams of the composite
monstrosity known as corium and underneath unit four, it was forming unnatural and terrifying
stalactites and stalagmites. But the most famous of these formations was so uniquely dangerous that you may have already heard about it. Eight months after the
explosion that created a dead zone around Chernobyl, nuclear inspectors were in
the basement of unit four, looking for the remains of the core material and the fuel rods. They turned a corner and they saw this. There was a two ton mass of corium still eating its way into the Earth. It had taken on a grayish,
wrinkled appearance, and so, they dubbed it,
The Elephant's Foot. This photo in particular was taken in 1990 just four years after the incident, and it was given to a Dr. Zoller at the University of Washington. And I just wanted to read you
the caption on this image. Quote, "This is a slide I
attained from the Russians. "It shows what is called
The Elephant's Foot. "The Russians obtained this picture "by sending a man down
there with a camera. "He took one picture and
then he came back up. "I was told that he died from
the radiation he received. "So this picture cost a man his life." You're looking at possibly the most dangerous room in the world. When The Elephant's Foot was first found after sitting in a
basement for eight months, it was still extremely radioactive. If you were back in 1986 and you found yourself
standing next to it, as close as I am to it right now, you would be guaranteed a
lethal dose of radiation. You would die even with treatment after just 200 seconds. And over 30 years later, The Elephant's Foot is
still very dangerous. As the years have gone by, The Elephant's Foot has
changed rather substantially. It has cracked and cooled,
and it has become, yes, less radioactive, but in 2001,
those radioactivity levels were measured such that you
still would not be able to spend more than about 60 minutes in its presence or else you would get a
fatal dose of radiation. And if you extrapolated
that radioactivity to today, it's still radioactive enough
such that you wouldn't be able to spend more than a
few hours in its presence without receiving a fatal dose. And today, the radioactive lava
that is The Elephant's Foot is still eating into the
Earth below Chernobyl, and it is still hot. It's not as hot as it once was, like half the temperature
of the surface of the sun, but it's still hotter than the
surrounding air temperature thanks to the pulsing and burning radioactivity inside of it. The radiation released
around Chernobyl though is more immediately dangerous to humans. The explosion threw out enough fallout such that the surrounding
areas will remain unlivable for humans in the long-term for around three to six
centuries, if we're lucky. The vegetation and the wildlife
around Chernobyl though is doing surprisingly well, so maybe with a bit of luck,
humans will one day return. However, when dealing
with forces such as these, luck isn't always on our side. That's a picture of a real
elephant with its feet. That's, don't try to be funny, this is a serious, serious episode. There is so much more to this story, the politics, the people that decided to live in the exclusion zone, what happened to the
wildlife and is happening, how the entire place has
become a tourist attraction for Instagram influencers. It's all sobering and fascinating, and I recommend that you read into it more if you're interested at all. Chernobyl and the steel
sarcophagus that now contains it will still be there, and
if it's never cracked and cleaned up, so too
will The Elephant's Foot. It will just sit there for centuries alone in a dark basement, a
dangerous symbol and reminder of terrifying and amazing potential. Because Science. Obviously it's hard to
visualize what actually happened in the core of Chernobyl, and thankfully we have scientists that look into these kinds of things. So here at Argonne National Laboratories, they have scientists that are
actually working with corium. So this is what uranium
lava actually looks like. Yeah, scary. And this is what it looks like, here's a simulation of it
eating through concrete. I think it can eat
through a few feet per day or something like that, so
it is crazy hot and scary and we have people studying it. And you think corium is
scary when it's cooled down. Check it when it's hot. Thank you so much for
watching Katana Marshall. If you want more of me
and Because Science, you can follow us at these
social media handles here, and you can suggest ideas
for future episodes. Do it. And also, our first spinoff
show, Because Space, has a few of its episodes now live if you want to check it out. Let us know in the
comments what you think. That would be greatly appreciated. And hey, I appreciate you.
Nice video!