All language subtitles for Fatal.Engineering.S01E06.1080p.WEB.h264-FREQUENCY_track3_[eng]

[narrator] In 1938,
in Berlin, Germany,

nuclear fission was born.

The nuclear age had arrived,
promising both

greatness and peril.

In 1957,
an uncontrollable fire

at Windscale, the UK's
largest nuclear power station.

We saw, to our horror,
four channels of fuel glowing

bright cherry red.

Nearly 30 years later,
Three Mile Island Nuclear

Power Plant.

Mechanical failures and human
errors trigger a partial

meltdown at
the practically new plant,

built for
700 million dollars.

The Three Mile Island accident

is marking a real turning

point in the perception and the
development of this technology.

But in 1986, the world is
stunned by the most terrifying

of all explosions,
the meltdown at the Chernobyl

power plant in what was
then the Soviet Union.

[Emmanuelle, in French]

Have these tragedies
taught us to approach

this powerful energy source
with greater caution?

Or will humanity's relentless
pursuit of nuclear supremacy

lead once again to a chilling
example of fatal engineering?

[theme song playing]

50,000 residents are enjoying
the beginning of their weekend

in Pripyat,

a city located in what was then
northern Soviet Ukraine.

With spacious apartments,
schools, hospitals,

cultural centers,
sports facilities,

and an amusement park,
it's considered a modern

and pleasant place to live.

[Rob] Life in Pripyat is pretty
good, until one night when

an accident at
the nearby power plant,

would prove to be fatal.

One that happened at a place

that everybody's
heard of -- Chernobyl.

Saturday, April 26th, 1986.

It's 1:23 a.m.

Two massive explosions
tear open reactor 4.

The first blast rips off
the reactor's roof,

a structure weighing
1,000 tons.

Two or three seconds later,
a second larger blast

sends huge lumps of toxic
debris flying in all directions

and a cloud
of radioactive material

high into the atmosphere.

[explosion roaring]

[Emmanuelle, in French]

[explosion roaring]

While the explosion itself
leaves two dead,

the firefighters
who immediately respond

to the site fall victim
to acute radiation syndrome.

caused by high dose
full body exposure.

[Shini] Vomiting, weakness and
fever would quickly take hold

as the radiation enters
the body, attacking the DNA,

turning healthy cells
into cancerous ones.

28 firefighters and plant
workers die of acute radiation

syndrome in the weeks
following the accident.

For some, it's a brutal,
fast-acting poison.

For others, a creeping,
silent killer.

A number of people
will develop cancer,

especially thyroid cancer.

Scientific organizations put
the death toll at 4,000.

Chernobyl's exclusion zone now
spans 4,760 square kilometers,

four times the size
of New York City.

It may take thousands of years
for it to be safely habitable.

[Emmanuelle, in French]

Was this a preventable
disaster?

Or was reactor 4 doomed to be
a case of fatal engineering?

to understand,
we must return to the day

before the explosion.

Constructed between 1970
and 1977, the Chernobyl nuclear

power plant was the largest
and most powerful in the USSR.

A symbol of Soviet nuclear
ambition, the plant's

four reactor cores converted
the thermal energy generated

from uranium fission
into electricity.

On the eve of the disaster,
all four reactors had been

running at full capacity for
years, supplying electricity

to roughly 5 million people,
which was 10%

of Ukraine's population.

At the heart of each reactor
sits a giant graphite core.

[Emmanuelle, in French]

Every hour, more than
45 million liters of water,

the equivalent of 18 Olympic
sized swimming pools,

were pumped
through the system to cool

the 1661 uranium
fuel rods.

These water pumps
were essential.

Without them, the reactor core
would overheat with potentially

devastating consequences.

It is precisely these pumps
that will play a critical role

in the unfolding catastrophe.

[Emmanuelle, in French]

1:00 p.m.

The shutdown process
for reactor four begins.

[Rob] To carry out the test,
the operators begin to drop

the control rods
into the reactor to slow down

the nuclear reaction.

Control rods.

These massive tubes are made
to absorb neutrons,

the particles that split
uranium atoms.

They release energy
and create electricity.

By manipulating the position
of the rods in the core,

operators could increase

or decrease the reactor's
power output.

Control rods are inserted into
the core to reduce its power

by half, down to
1,600 megawatts thermal.

All is going according to plan,
until one unexpected delay.

[Shini] Elsewhere in Ukraine,
another regional power plant

has unexplainably gone offline,
and Kiev's electrical grid

controller requests Chernobyl
postpone its power reduction

as power is needed to satisfy
the peak evening demand.

This continues throughout
the day until it becomes

nighttime, when the electricity
demand isn't as high.

It's now deemed a safe time to
continue the test of the backup

generators until a turning
point in history where

everything would change
for the families who live there.

Chernobyl Nuclear Power Plant

was the largest and most
powerful in the USSR.

On the eve of the disaster,
all four reactors

had been running at full
capacity for years

\{Emmanuelle in French]

It's now deemed a safe time
to continue the test

of the backup generators until
a turning point in history

where everything would change
for the families who live there.

A shift change.

While the day crew has
experience with these tests,

the night crew does not.

At around 12:00 a.m.,

the team receives permission
to continue the test

in reactor core four.

Then something goes wrong.

Without fully understanding
why, the operators see

the reactor's power
drop rapidly.

[in French]

To bring the power back up,

they begin pulling the control
rods out of the core.

They have no way of knowing it,
but this action further

destabilizes the reactor.

But this is not
the only problem.

[Rob] Too many control rods have
been removed, and now there's

a risk the chain reaction
becomes uncontrollable.

As the rods are withdrawn,
the power begins to rise again,

eventually stabilizing
after around 20 minutes.

Although this is far below
the 700 megawatts thermal

required for the test,
they decide to proceed anyway.

[Shini] Part of the pre-planned
test is to increase

the water flow rate
around the core,

and two additional pumps
are activated.

But this has a risk of
lowering the temperature

and the power again.

And with it already low,
the operators decide to remove

even more of the control rods.

1:23 a.m.

Despite the reactor's
low power, the operators

continued the test.

[in French]

As the water flow slows down,
it heats up more than usual.

Steam bubbles rapidly form
inside the core.

For the Chernobyl
reactor design,

this is a dangerous effect
due to them

being positive
void coefficients.

A positive void coefficient
means the reactor becomes

more reactive as water
turns to steam.

As the operators realize
that the heat is becoming

out of control, they decide
to drop the control rods back

into the core, shutting down
the chain reaction and bringing

the temperatures back
under their control.

40 seconds past 1:23 a.m.

Unlike the control rods in any
other reactor, the control rods

at Chernobyl have
graphite tips.

The rods themselves are made
of boron carbide, which absorbs

neutrons and slows
the reaction.

But their graphite tips
do the opposite.

They speed it up.

[in French]

When the control rods
travel the full height

of the seven-meter-tall
reactor core,

equivalent to a three-story
building, the graphite tips

come into contact with
the steam, and the core itself.

Had the control rods not been
fitted with those graphite

tips, it is likely that
the Chernobyl disaster would

never have occurred.

The accumulative effect causes
an unexpected and alarming

spike in reactivity.

Instead of a gradual controlled
decrease, the fission reaction

causes a surge in power.

Within seconds, power output
skyrockets, reaching 30,000

megawatts thermal, ten times
the reactor's normal capacity.

This is the last measurement
ever recorded.

44 seconds past 1:23 a.m.

Just four seconds after
the rods are inserted,

the core becomes an unstoppable
pressure cooker.

Superheated steam blows apart
the reactor,

sending the roof flying.

A second explosion follows,

scattering chunks of
radioactive graphite across

the site and igniting dozens
of fires, including a towering

blaze directly above
the gaping hole in the reactor.

[Emmanuelle, in French]

The reactor core begins
to melt, forming corium,

an extremely radioactive
lava-like substance.

It burns through 1.8 meters
of reinforced concrete,

inevitably moving
into the ground.

Anyone within several
kilometers is in mortal danger.

100,000 people are forced
to abandon their homes

and their lives.

Animals who have become highly
radioactive are killed

to prevent them from spreading
the radiation.

[Shini]
Back at the ruined reactor,
efforts are made to clear up

and contain the exposed
radioactive material

from leaking further.

During the operation,
a helicopter struck a crane

cable and crashed,
killing all four crew.

The moment, caught on camera,
became an iconic image

of the Chernobyl
disaster response.

In total, 5,000 tons of sand,
clay, boron, and lead are

dropped onto the reactor.

It will take 20 days
to extinguish the fire and stop

the corium from reaching
underground water sources.

[explosion blasts]

Two months after the disaster,
a concrete and steel structure

known as the Sarcophagus is
built to encase the reactor

and contain its lethal
radioactive particles.

Thirty years later, in 2016,

a new, more durable structure
replaces it.

It's a shield designed to
one day allow for the safe

dismantling of the reactor.

[Shini] Even with the remains
of Chernobyl reactor number

four gone, the legacy
of the world's worst example

of fatal engineering
will tragically remain

for thousands of years to come.

[Rob] This disaster remains one
of the darkest moments

in the history
of nuclear energy,

marking a real shift
in the perception

and the development
of this technology.

But just seven years earlier,
another incident,

a nuclear plant on the east
coast of the USA, where,

once again, nuclear fission
is in question, would become

the focus of
the world's attention.

Three Mile Island power plant.

It's March 28, 1979,

on the banks
of the Susquehanna River,

in the quiet borough
of Middletown, Pennsylvania.

Its 9,000 residents are
fast asleep.

A crisis has started
at the Three Mile Island

nuclear power plant.

It's 4:00 a.m.

A potentially deadly accident
has occurred overnight

in the reactor TMI 2,
and radioactive material has

been released into
the atmosphere above them.

[reporter] Three Mile Island
plant, an accident did occur.

It is my feeling that
the people within the radius

of a few miles,
especially pregnant women,

should be told that there is
a significantly increased risk

to their babies.

To understand what happened,
we have to go back 10 years

to a time when electricity
demand in the United States

was surging.

By the late 1960s,

domestic energy consumption
was booming.

Less polluting than coal
and capable of generating

massive amounts of electricity
at low cost, nuclear energy

seemed full of promise.

On May 18th, 1968,

construction began
on a next generation

nuclear power plant
built on an island

just five kilometers
or three miles

from Middletown,
Pennsylvania --

Three Mile Island.

[Emmanuelle, in French]

Together, its two reactors
produce 1,700 megawatts

of electricity,

enough energy to power a city
of 300,000 people.

Like all pressurized water
reactors, the reactors use

steam generated by the heat
produced in their core through

uranium nuclear fission
to spin a turbine

and generate electricity.

This takes place in the two
main circuits of each reactor,

the primary
and secondary circuits.

[Shini] The primary circuit
transports liquid water through

the reactor core, acting as
both a moderator and coolant.

It absorbs the heat
from fission and transfers it

to the steam generators.

The steam then powers
a turbine, which in turn

generates electricity.

In the event of a worst case
scenario, engineers have

designed three protective
shields to contain

the radioactive materials
inside each reactor core.

An ultra-resistant zircaloy
cladding that encases

the uranium fuel rods,

a fully sealed water based
primary cooling system,

and a reinforced concrete
containment structure built

to withstand extreme
pressure and temperature.

But for the system to function
safely, one critical condition

must be met.

The heat produced must be
effectively removed.

If the reactor becomes too
hot, the uranium inside can

cause overheating,
potentially causing a nuclear

meltdown and releasing lethal
radioactive materials capable

of endangering thousands.

A key component at the heart
of the disaster will prove

fatal for Three Mile Island --
the pressurizer.

Inside the reactor core,
water heats up to nearly

300 degrees Celsius,
a temperature at which water

naturally changes its state.

[Shini] At such high
temperatures, as we all know,

water would normally boil.

But in the design of a reactor
like TMI, it's crucial

that the water remains
in a liquid state.

The pressurizer keeps
the pressure in the primary

loop at 155 bars,
preventing it from boiling,

a proven system that is
used in around 60%

of nuclear reactors worldwide.

[in French]

A pressurizer valve opens to
lower the pressure by releasing

water into a relief tank
located inside the reactor's

containment structure.

Eight seconds later,
the reactor core shuts down

automatically,
while at the same time,

the emergency feed water system
for the steam generator

is activated along
with the turbine shutdown,

stabilizing the secondary side
of the plant.

Nuclear fission comes
to a stop.

[Emmanuelle, in French]

So far, for this type
of situation, everything is

proceeding as expected.

The operators follow protocol

and engage
the control to close the valve.

[Rob] The operators believe
that having pressed the button,

the valve has indeed closed.
But that's not the case.

But they've no way
of knowing that.

It's 4:01 a.m.

With the reactor shut down,
heat is no longer being

produced by fission reactions,
but residual heat is still

being generated
by the radioactivity

of the fission products.

Water from the primary circuit
escapes through an open valve,

and as a result,
the pressure begins to drop.

[Emmanuelle, in French]

At all costs, this heat must be
removed to prevent

the temperature from rising
inside the core.

4:02 a.m.

The water leak through the open
valve causes the pressure

in the primary circuit
to drop to 110 bars,

automatically triggering
the high pressure safety

injection system
to cool the core.

But because the have
an inaccurate view

of the system's condition,

they misinterpret what
they're seeing.

They're monitoring the water
level in the pressurizer,

rather than
in the reactor core.

[Shini] When they saw it rise,
they assumed they had injected

too much water and manually
closed the safety injection

after five minutes.

This was the point of no return.

4:05 a.m.

For over two hours, about 60%
of the water in the primary

circuit is discharged
into the relief tank inside

the containment building,
and the operators have no idea.

With the valve still open,
the second of three protective

shields designed to prevent
radiation from escaping

is not working.

[Emmanuelle, in French]

At 6:00 a.m.,
the day shift takes over.

One operator fully realizes
the seriousness

of the situation
and closes the valve.

The second containment barrier

is now able to function
properly again.

[Emmanuelle, in French]

6:14 a.m.

The radiation alarm goes off
in the reactor 2 building

at Three Mile Island.

As a result,
the temperature in the core

continues to rise,

and the dreaded scenario
is unfolding.

[Emmanuelle, in French]

A core meltdown inevitably
means the destruction

of a reactor worth several
hundred million US dollars.

Worse still, if the final
containment barrier fails,

radioactive materials will
spread through underground

structures and escape through
the exhaust stacks

of the Three Mile Island plant.

[in French]

Corium is highly radioactive.

If it isn't contained in time,
this man-made,

ruthless and destructive magma
can burn through even

the toughest structures.

[Shini]
Meanwhile, in the control
room, the operators are trying

to regain control
of the cooling

of the damaged core.

As the pressure continues
to rise, the operators decide

to reopen the valve,
where the entire issue began.

It's 6:54 a.m.

This opening allows
the now radioactive water

from the primary circuit...

to flow into the pressurizer
storage tank,

located within
the containment structure.

[in French]

[Shini] But the rupture disk
on this tank has already broken,

normally due to
the overflow of water.

As a result,
the now radioactive water is

spilling into the building.

This containment structure is
made of one-meter-thick

pre-stressed concrete.

That concrete is now the final
barrier and the last chance

to prevent a major disaster
from devastating

the town of Middletown

and possibly the whole state
of Pennsylvania.

[Emmanuelle, in French]

[Rob] At this point,
the alarm is raised

more generally,

alerting those in the area
what is happening.

It's 7:20 a.m.

Within hours, fear grips
the small town.

Schools close.

Many people take shelter
in their basements.

200,000 people take to
the roads, fleeing something

they can't see, but fear more
than anything else.

Panic spreads everywhere.

Meanwhile, plant operators
begin to regain control.

They restart the high-pressure
safety injection system,

which refills the reactor
vessel in just seven minutes.

The water enters the molten
corium and begins to cool it.

It's almost like when you see
lava flow from a volcano meet

the ocean, and it's
cooled quickly.

When water comes in contact
with corium, it produces

an extremely light chemical
element that can form

an explosive mixture
with air, hydrogen.

But at around 1:30 p.m.,
nearly nine and a half hours

after the start
of the accident,

the hydrogen that built up
inside the containment

triggers an explosion.

The final shield holds.

This is what saves the people
of Pennsylvania

from a catastrophic outcome.

In the days that follow,
cooling systems are

gradually stabilized,
the remaining hydrogen is

expelled, and the corium
begins to cool at the bottom

of the reactor vessel.

On March 28, 1979,
at 8:00 p.m.,

the immediate crisis is over.

[Rob] Nobody died as a direct
result of the situation

at Three Mile Island,
but it forced a new perspective

for the general population
on how it saw nuclear power,

slowing down progress with this
technology for years to come.

Reactor number 2
is a total loss --

700 million U.S. Dollars
gone just four months

after it started.

And yet, against all odds,
reactor 1 returns

to operation and continues
to produce electricity

for nearly 30 more years.

It is finally shut down in
2019, seemingly marking the end

of the nuclear era
at Three Mile Island.

Then, in 2023, a surprising
new chapter begins.

A giant tech company buys
the site to build a massive

data center, partially powered
by nuclear energy.

A new life for a site where
the current of history

never truly faded.

At Three Mile Island,
poor control room design led

to human error.

At Windscale, a basic lack
of understanding in fire

containment was evident.

In 1945, as the fires
of World War II

were finally
beginning to die down,

and the world entered a long
process of reconstruction

a new era was emerging...

...the nuclear era.

[Rob] The Americans have already
developed their own technology

and metre producing
atomic bombs.

And the British were involved
in that development.

But now the race is on
as the Russians are also

developing their technology.

Britain asked its ally,
the US, to share

their manufacturing secrets.

But President Eisenhower
and the US Congress

were reluctant to share
information about a weapon

that cost them
today's equivalence

of 28 billion US dollars.

A US law was passed making it
illegal to share

nuclear knowledge outside
the United States.

[Rob] Britain is undeterred
by this shirking

of the United States,
and so decided to develop

their own means,
their own technology,

their own facilities to produce
their own atomic weapons.

The British had to act quickly,
fearing that the Russians

would develop the bomb first.

[explosion blasts]

The British authorities decided
to build their nuclear facility

on the site of the former
Sellafield Munitions Factory.

And this site will become
known as Windscale, a name that

will go on to be associated
with the first nuclear accident

that would change the way
the world viewed

nuclear technology.

It was composed of two air
cooled reactors known as

Pile 1 and Pile 2.

Designed to transform uranium
rods into weapons-grade

plutonium, the core of each
reactor consists of thousands

of small channels drilled
into a massive

2,000-ton graphite block.

[Rob] Graphite is a really
important material used

at Windscale reactors.

It serves to moderate the speed
of neutrons as they're fired

out of the fission
reactions taking place.

[Shini]
And secondly is able to absorb
large amounts of excess heat

and energy created during
the nuclear reaction.

As the uranium rods move
through the channels,

a nuclear reaction takes place.

This is how plutonium
is created.

When each rod reaches the end
of its channel, it drops

into a water tank
where it is cooled.

The problem with the process
is the immense amounts of heat,

if not evacuated, can build
up and to cause a disaster.

To evacuate the heat,
massive fans are activated

to continuously blow cold air
over all the channels.

They expel the heat through
120-meter-high chimneys

on the other side
of the reactor core.

British Nobel prize-winning
physicist Sir John Cockroft

designed a protective shield
specifically for the plant

to be placed at the top
of these chimneys in the event

of radioactive leaks
outside the reactor.

A 50-ton filter composed
of successive layers

of gravel and sand.

It became known as
Cockroft's follies in the end

because many didn't feel
that they were needed.

Seven years after
the nuclear plant's opening,

these filters
would prove to be lifesaving.

Monday, October 7, 1957.
1:13 a.m.

The Windscale plant operators
must carry out

a delicate operation
to the core of Reactor Pile 1.

[Emmanuelle, in French]

This is what is
known as Wigner energy.

If not gradually released,
it can dangerously accumulate

and cause severe overheating
of the core.

[Shini]
To release the potentially
critical build up of

Wigner energy, engineers and on
site physicists

develop an empirical
method known as annealing.

[Emmanuelle, in French]

[Shini] Instead of triggering
a gradual release

of Wigner energy,
the increased power

causes a sudden and rapid spike
in temperature.

On Wednesday, October 9,
at 10 p.m., the graphite

reaches an abnormal temperature
of 405 degrees Celsius.

Scientists attempt a second
nuclear heating process

to release the energy,
but it does not have

the intended effect.

The graphite accumulates too
much energy and quickly reaches

critical levels.

The situation is unprecedented,
but the worst is yet to come.

[Rob] At this point,
the decision is made

to evacuate the site
with only the key workers left

to try and bring the situation
back under control.

Thursday, October 10, 4:00 p.m.

The reactor supervisor,
Tom Hughes, and another staff

member put on protective
clothing and visit the site

to assess
the graphite's condition.

As they approach the reactor
core, they are horrified

by the situation.

He inspects the core himself
and understands that one

of the cartridges
has split open.

The aluminum cladding
surrounding the uranium is

a crucial protective layer
that ensures a safe

nuclear reaction.

If it is ruptured, it means
the uranium is exposed

to open air.

This is where the Cockcroft
filters prove their worth.

Thanks to their design,
no radiation escapes

from the Windscale plant,
at least for now.

But the situation is
deteriorating fast.

At Windscale

a fire in the reactor core
threatens to trigger

the greatest nuclear disaster
the world has ever known,

with radioactive releases
potentially spreading across

the United Kingdom and Europe.

In an attempt to cool
the core, the fans are set

to their maximum speed.

Tom Tuohy, the deputy site
manager at Windscale,

takes over.

He begins trying to push
the burning cartridges out

of the core using
scaffolding poles.

However, at that moment,
the core is burning hot,

and the fuel cartridges cannot
be moved as the heat has

caused them to deform.

What started out as
an incident where one cartridge

is on fire develops into
an uncontrollable catastrophe

where multiple cartridges are
on fire and the temperature is

raising out of control.

This is not normal,

and it's never been
seen before.

On Friday, October 11,
at midnight, the fire reaches

temperatures up
to 1,300 degrees Celsius.

The men on site need to wait
to extinguish the blaze,

but all options carry risks.

[Emmanuelle, in French]

With time running out his team
have two options left.

The first option is
to smother the flames

with carbon dioxide.

They hope this will cut off
the oxygen supply

and suffocate the fire.

Again, it doesn't work.

The temperatures are now out
of control, and even the CO2 has

no effect.

Their last hope to extinguish
the fire turns out to be

the most
controversial -- water.

Water is well known for putting
out flames, but when used

on a heat source exceeding
400 degrees Celsius in such

a confined space,
it could trigger

an unprecedented explosion.

11 tons of uranium
have already burned.

Tom Tuohy and the fire chief
are the last men on site

to handle the situation.

Despite the risks involved,
they pump huge volumes of water

through the reactor core,
trying to bring

down the temperature.

8:55 a.m.

1,400 liters of water per
minute are injected

into two channels above
the top of the fire.

With no significant effect,
the flow is increased

to 3,600 liters per minute.

Outside, staff can now see
smoke rising from the chimney.

Tom Tuohy climbs into
the reactor again to check if

the water is having
the desired effect.

Once again, there's no effect.

The core is still radiating
with heat.

The situation seems hopeless.

Tom Tuohy makes
a final decision.

It's 10:10 a.m.

The decision's made to switch
off the fans because they're

not having an effect
on the core.

[water swooshing]

To their complete surprise,
the very fans installed to keep

the core safe from overheating
have been one of the main

reasons they've been unable
to get control of the situation.

The fans have been fueling
the fire all along.

like bellows on a wood fire.

By turning off the fans,
they've reduced the oxygen

that was supplied.

The fires went out,
and the temperatures eventually

became back under control.

By noon, two more hoses are
installed, and the water flow

is increased to 4,500 liters
per minute.

This flow continues
until 3:00 p.m.

the following day, and the pile
is finally cooled.

The site was decontaminated
over the following weeks

and months, but the reactor is
left with 1,700 damaged

cartridges within its core.

[Shini]
The reactor is sealed off
and remains to this day sealed

with approximately 15,000 tons
of uranium still inside it.

Pile 2 is also shut down
as a precaution.

And air cooled reactor have not
been built since.

Following this accident,
the British nuclear industry

underwent
significant reorganization,

with the creation of national
agencies to oversee operational

and safety measures.

[Rob] The accidents
at Windscale, Three Mile Island,

and Chernobyl is clear evidence
that there are risks involved

with nuclear energy.

[Shini]
Thankfully, every disaster has
contributed to global reform

within the sector and lessons
continue to shape

the nuclear industry.

Today, as awareness
of the devastating impact

of fossil fuels
continues to grow,

nuclear energy remains
a promising alternative,

but it's still dangerous if not
properly controlled.

we must remain constantly
vigilant if we don't want

our nuclear power plants
to turn into another case

of fatal engineering.