All language subtitles for Meltdown.Analyzing.the.Radiation.Leaks.2015.1080p.WEBRip.x265-RARBG2_English

- [Voiceover] More than
three years have passed

since the Fukushima Daiichi Power Plant

became the site of one of
the worst nuclear accidents

in history.

(beeping)

- [Voiceover] 8.6 microsieverts, 8.7.

It keeps going up.

- [Voiceover] Damaged
reactors released huge amounts

of radioactive materials,
forcing many people

to evacuate their homes.

Even now, no one fully understands
how the leaks occurred.

We found some important
information about five kilometers

from the plant.

Experts had assumed this
monitoring post had stopped working

after the earthquake in March 2011.

No one knew it, but detailed
data about radiation levels

right after the accident have
been stored in this device

since that time.

An analysis led to a new discovery.

Enormous amounts of radioactive substances

began leaking the day
after the earthquake.

The recently uncovered data

indicate that the substances began leaking

in high concentrations sooner
than previously thought.

(dramatic music)

The nuclear reactors had
multiple protective walls

but experts have
determined there was a flaw

in their construction.

- [Voiceover] A new
unexpected path has appeared.

- [Voiceover] The
emergency venting operation

must have caused the release
of radioactive materials.

(suspenseful music)

- [Voiceover] Experts are also
starting to figure out why

a critical structure for
containing radioactive substances

broke down.

The meltdown sent the temperature

of the nuclear fuel soaring.

Experts suspect that may have destroyed

the containment vessel, the final barrier

for keeping the substances
inside the reactor.

(foreign language)

- [Voiceover] We reenacted
what happened at the plant

during the crisis, based on accounts

from more than 400 people involved.

(rumbling noise)

(foreign language)

(chattering)

- [Voiceover] Throughout
this series, Meltdown,

NHK has been conducting
scientific investigations

into the causes of the nuclear disaster.

(beeping)
(man shouting)

(foreign language)

On this program, we'll
explore how huge amounts

of radioactive materials
escaped from the nuclear plant.

(suspenseful music)

(foreign language)

- [Voiceover] I'm now in
Kamihatori in Futaba town

Fukushima prefecture,

more than five kilometers
from the nuclear plant.

Access to this area is strictly limited

due to its proximity to
highly contaminated areas.

We have to wear protective
clothing like this.

We found something here that
has provided valuable clues

about why huge amounts of
radioactive materials leaked.

It's this monitoring post for
measuring radiation levels.

As it turns out, all the
information recorded here

three years ago has remained
intact all this time,

without anyone realizing it.

The data shows that before
the hydrogen explosion

of the Reactor 1 building,
there was a massive release

of radioactive substances.

This event coincided with
the venting operation

at the reactor.

The discovery of this
fact raises the alarm

about existing safety measures
for nuclear power plants.

- [Voiceover] The monitoring
post stored the data

for three years.

It shows radiation levels
captured at 20-second intervals

over three days from the
time the earthquake struck.

An analysis has revealed the seriousness

of the contamination for the first time.

About one full day after the earthquake

at 2:40 PM on March 12,
the rapid rise in radiation

reached a peak.

It measured about 4.6
millisieverts per hour.

If it had stayed there,
people would exceed

the annual limit for radiation exposure

in just 15 minutes.

When the radiation spiked,

what was happening at the
Fukushima Daiichi plant?

(ominous music)

At 2:01 PM, white steam was coming out

of an exhaust stack.

Workers were venting Reactor
1 in an attempt to reduce

pressure in the containment vessel.

Data from this time showed
that radiation levels

were rising on the plant's premises.

(foreign language)

- [Voiceover] I remember the
readings were abnormally high.

In some places, the
readings were off the scale.

We could guess how bad
conditions must have been

outside the reactor buildings.

- [Voiceover] An expert has
been studying how contamination

dispersed after the accident.

His name is Masamichi Chino.

He calculated how radioactive substances

released by the venting spread.

Here's the result of his simulation.

The substances drift northwest

and passed through kamihatori.

The estimated radiation level
at 2:40 PM matched the data

recorded at the monitoring post there.

(foreign language)

- [Voiceover] It appears
that particles were released

immediately after the
venting began at 2 PM.

Substances such as cesium leaked.

That's clear, although we
don't know in what ratio.

- [Voiceover] TEPCO officials had said

the amount of radioactive
materials released

wouldn't reach dangerous levels.

(foreign language)

- [Voiceover] There is
water below the reactor.

The steam will go through it
first, and then be vented.

That step will keep
radiation levels very low

even if the steam does contain
radioactive substances.

(instrumental music)

- [Voiceover] The donut-shaped
section toward the bottom

of the containment vessel
is equipped with a mechanism

to limit the release of
radioactive substances

during venting.

The suppression chamber is
designed to reduce pressure.

The water inside serves as a filter.

When the containment
vessel is depressurized,

the released steam goes through the water,

trapping most of the
radioactive materials.

This should limit the amount
of contaminants released

to just 1/10 of 1%.

(car engine noise)

So how did the venting procedure wind up

causing a massive radiation leak?

We went with the experts to
a huge experimental facility

in Italy.

First, we conducted an
experiment to understand

how the suppression chamber
can limit the release

of radioactive materials.

A three-meter high water tank represents

the suppression chamber.

Steam is injected through a pipe.

This type of investigation
could be very important

in order to enhance the safety

of the nuclear power plants.

(loud pops)

- [Voiceover] At first, the
temperature of the water

in the suppression chamber is low.

High-temperature steam
from the containment vessel

turns into bubbles that
immediately disappear.

This footage was taken
with a high-speed camera.

When steam is cooled, it
instantly changes to water.

The moment steam from
the containment vessel

turns into water, nuclear
materials inside are captured.

(dramatic music)

But experts suspect something
unusual was happening

in the suppression chamber at Reactor One.

(foreign language)

- [Voiceover] The water
closer to the surface

rises in temperature, but
water lower down doesn't,

resulting in thermal stratification.

The temperature of the
suppression pool was probably

quite high.

- [Voiceover] It's believed
that during the accident,

high temperature steam was already flowing

into the suppression
chamber from somewhere

other than the containment vessel.

As a result, a phenomenon
called thermal stratification

may have occurred.

Experts believe the upper
layer of water was boiling.

(suspenseful music)

Would stratification make
the suppression chamber

less effective at removing
radioactive materials?

The researchers boil the
water in the pool and inject

the same amount of steam as before.

Once they do this,

there is a dramatic change.

Now the steam turns into
bubbles that rise all the way

to the surface.

This means that radioactive
substances contained

in the steam don't get trapped
like they're supposed to.

Instead, they're released
into the atmosphere.

(suspenseful music)

This analysis indicates
that when the temperature

of the water is low,

the amount of radioactive
materials released

can be limited to 1/10 of 1%.

But when the water is boiling,

as much as half of the
materials could be released

into the air.

The Fukushima accident
highlighted the need

to re-examine the venting procedure.

(foreign language)

- [Voiceover] Three years
after the nuclear accident,

some 135,000 people from
Fukushima are still unable

to return to their hometowns.

Access to the area where
I'm standing right now

is permitted during the day,

but no one is allowed to live here.

Rebuilding efforts are virtually on hold

in places with significant amounts

of radioactive contamination.

It's as if time has stopped.

Many people had to abandon their homes

after the massive radiation leaks.

Authorities and experts
have conducted a variety

of investigations into the disaster.

But many issues remain unexplained.

More needs to be done.

Let's review the accident.

The day after the quake and tsunami,

Reactor 1 was the first
to lose its cooling system

and suffer a core meltdown.

Then hydrogen, that had
built up inside, exploded.

Two days later, the cooling
system in Reactor 3 stop working

and the day after that, the
one in Reactor 2 broke down.

The shutdowns triggered
additional meltdowns.

The graph shows the amount
of radioactive substances

that escaped.

There are brief spikes that coincide

with the hydrogen explosions
at Reactors 1 and 3.

There was no such explosion in Reactor 2,

but this is the reactor that
released the most radiation.

What exactly was going on
inside Reactor number 2?

The truth about the massive
leak of radioactive materials

is becoming clearer.

- [Voiceover] Meltdowns
occurred one after the next

in Reactors 1 and 3,
and hydrogen explosions

destroyed the buildings.

The building housing
Reactor 2 didn't explode,

but the situation inside
was actually more severe.

Reactor 2 released huge amounts
of radioactive materials.

They're believed to have leaked
from the containment vessel

through spaces around
piping joints and the lid.

This is a simulation based
on contamination data

from the time of the quake and tsunami.

Reactor 2 released large volumes
of radioactive substances

to the northwest of the
plant on March 14 and 15th.

The pollutants then spread further south

to the greater Tokyo area.

What caused the leaks in the first place?

In February 2014, our
cameras were allowed inside

the main control room
for Reactors 1 and 2.

At the time of the accident,
the tsunami had knocked out

all power supplies, leaving
this room in complete darkness.

Notes scribbled on a
wall suggest how workers

struggled to deal with
the unfolding emergency.

Experts suspect the failure
of an emergency procedure

called venting led to
the crisis in Reactor 2.

Venting is the last line
of defense for protecting

the containment vessel and
preventing a massive release

of radioactive materials.

Once a nuclear reactor's
core begins to melt down,

the resulting heat causes
pressure inside to surge.

This can destroy the outer
container in no time.

Venting the internal
steam lowers the pressure.

In this process, steam
first passes through water

to remove radioactive substances,

then it's released into the atmosphere.

But for some reason, the vent at Reactor 2

didn't work at all.

What was going on?

Our investigation has
uncovered some of the details.

We've reenacted the
situation based on accounts

provided by people who were there.

(foreign language)

This is the main control
room for Reactor 2.

The emergency cooling
system continued running

after the earthquake, but on March 14,

three days after the quake, it stopped.

(foreign language)

By 1:25 PM, the reactor
was rapidly losing water

needed to cool nuclear fuel.

A meltdown was looming.

At the time, workers in
the emergency headquarters

some 300 meteres away were
supervising the response.

The workers had been busy
addressing the hydrogen explosions

in Reactors 1 and 3.

Now they issued an order
for venting in Reactor 2,

to prevent a massive leak
of radioactive materials.

(foreign language)

An operator at that time
agreed to be interviewed.

He was involved in the crisis response.

(foreign language)

- [Voiceover] First and
foremost, we had to think about

protecting the containment vessel.

We needed to vent it to
maintain its integrity.

(chattering)

(foreign language)

(suspenseful music)

The main control room for
Reactor 2 had lost all power.

(foreign language)

Operators attempted to vent the reactor

using backup generators.

(foreign language)

But

the pressure in the
containment vessel didn't fall.

(foreign language)

(suspenseful music)

The workers suspected
their efforts to open

the air-operated valve were failing.

This is an essential step
in the venting process.

The valve opens when air is pumped in.

That releases pressure that is built up

in the containment vessel.

The workers figured
there wasn't enough air

to open the valve.

(beeping)

(multiple footsteps)

Some members of the team
raced to the reactor building

to check.

(foreign language)

The valve is inside the reactor building.

The power outage had knocked
out all the monitoring gauges

so team members had to go
inside and check the instruments

with their own eyes.

(beeping)

(multiple footsteps)

The entrance to the reactor
building has double doors

to keep radioactive materials inside.

(beeping)

(foreign language)

(cranking noise)

(beeping)

The team members had no
idea what they would find.

They proceeded slowly,
checking radiation levels

as they went.

(beeping)

(foreign language)

(cranking noise)

(suspenseful music)

(beeping)

(multiple footsteps)

They were now barely 10 meters
from the nuclear reactor,

which was on the verge of a core meltdown.

(suspenseful music)

They managed to locate
the tanks that supply air

to the valve.

(multiple scurrying footsteps)

(foreign language)

(beeping)

(scurrying noise)

(creaking noise)

(suspenseful music)

(multiple footsteps)

(foreign language)

(foreign language)

(foreign language)

(suspenseful music)

If the valve itself were
broken, there would be no way

to fix it right away.

(foreign language)

(suspenseful music)

The vent was not working.

Conditions in the reactor
continued to deteriorate.

(suspenseful music)

Heat generated by the
meltdown was starting to raise

pressure inside the containment vessel,

the structure that prevents
radioactive materials

from escaping.

(foreign language)

The team did have a last-ditch measure.

They could use a backup valve,

but it was also inside
the reactor building

protected by the double doors.

(beeping)

Team members went back
to the reactor building.

They found conditions there
had drastically changed.

(beeping)

(multiple footsteps)

(rapid beeping)

(man screaming)

(foreign language)

(rapid beeping)

The radiation reading was
so high, a person's exposure

would reach tens of millisieverts
in a matter of seconds.

The reactor building had
become filled with steam.

(suspenseful music)

At this point, it was impossible
to do any more work inside.

Masao Yoshida managed the plant

at the time of the accident.

Masatoshi Fukura was in
charge of crisis management

at the reactors.

Fukura had received reports
from workers at Reactor 2

about the vent failure.

(foreign language)

- [Voiceover] To vent the reactor,

we had to open a valve soon,
a big one or a small one.

We knew what we needed to do.

In fact, the other workers
on site were trying to do it.

But at that point, no one could
get near Reactor 2 anymore,

let alone reach the valve inside.

Right around the time
the team members found

they could no longer enter
the reactor building,

massive amounts of radioactive substances

were beginning to be released.

At this stage, pressure
inside the containment vessel

hadn't significantly
exceeded the design limit

so experts assumed it
wouldn't have been possible

for huge amounts of
radioactive materials to leak.

(mysterious music)

Then why did the team members detect

high levels of radiation?

Panels, including those
convened by Japan's

diadem government, have
conducted various investigations

but they didn't identify the cause.

We enlisted the help of
experts on reactor simulations

and nuclear power plant
facilities in a bid to find out.

(mysterious music)

Rather than focusing on the
containment vessel itself,

they zeroed in on something
that most people had overlooked,

a device outside the containment vessel.

(foreign language)

- [Voiceover] Unless the shaft is sealed,

steam from the reactor's pressure vessel

could leak through the turbine.

- [Voiceover] They suspected a problem

with an emergency cooling
system called the RCIC.

It uses steam to rotate a
turbine that circulates water

and cools the reactor's core.

It doesn't need electricity to function.

Steam from the reactor flows
directly into the turbine.

That's where the experts
suspect the leakage occurred.

But the shaft of the
turbine was tightly sealed,

with four layers of
disc-shaped packing material.

Could a leak occur around the shaft?

We decided to try an experiment.

(suspenseful music)

We obtained a detailed
diagram of the cooling system.

(foreign language)

- [Voiceover] The space here
is 140th of a millimeter.

- [Voiceover] We worked with an expert

in fluid engineering.

(tapping metal noise)

We used the diagram to create
a duplicate of the shaft

of the RCIC and the packing around it.

(mysterious music)

We injected steam into the device.

We applied the same amount
of pressure as existed before

the nuclear accident.

No steam leaks from around the shaft.

Then we gradually raise the pressure,

just as happened during the crisis.

(hissing noise)

Large volumes of steam
begin billowing out.

(foreign language)

- [Voiceover] It's much
more than I'd expected.

It's possible that huge amounts

of radioactive substances leaked.

- [Voiceover] How did this happen?

It turns out, there was a flaw

in the cooling system's construction.

It's designed to have a little space

between the packing disks.

If the pressure rises and
steam begins to escape,

there's a device to remove it.

But it needs electricity to function.

(suspenseful music)

When the device isn't
working, the cooling system

starts spewing steam.

(foreign language)

- [Voiceover] At this rate,
some 50 kilograms of steam

would flow out in an hour.

- [Voiceover] That much?

(suspenseful music)

The experts said that, judging
from the amount of steam,

it wasn't surprising that radiation levels

rose so sharply.

(foreign language)

- [Voiceover] When steam comes out,

the inside of the building
becomes completely white.

That's because steam takes up
much more volume than water.

It spreads really fast too.

- [Voiceover] The former
operator who took part

in the crisis management effort,

was surprised that the cooling system

could have been a source of the leak.

(foreign language)

- [Voiceover] It didn't occur to me

at the time of the accident.

But now that I think about it,

I realize the RCIC is one
of the possible sources

of the leak.

(suspenseful music)

- [Voiceover] A safety device designed

to help cool the reactor failed.

As a result, workers were
unable to vent the reactor

and contain the crisis.

(suspenseful music)

The workers couldn't do anything

inside the reactor building.

The situation was going from bad to worse.

The containment vessel would
not be able to withstand

the increasing pressure.

TEPCO officials kept a
record of discussions

at the plant's emergency
headquarters during the crisis.

It recounts in detail how
the core meltdown progressed

and tracks rising radiation levels

in the containment vessel.

The loss of the cooling
system triggered a crisis

in Reactor 2, about 11 hours later.

(foreign language)

The containment vessel was
on the verge of releasing

massive amounts of radioactive substances.

Then at 8:45 AM,

(foreign language)

(tense chattering)

- [Voiceover] this was the
highest radiation recorded

on the plant's premises.

(suspenseful music)

(foreign language)

This photograph captures white steam

rising from Reactor 2.

It was taken at the moment
that the containment vessel

broke and released huge amounts
of radioactive materials.

Attempts to vent the
containment vessel had failed.

As a result, the final barrier for keeping

radioactive substances
sealed in broke down.

(dramatic music)

(foreign language)

- [Voiceover] we Wewere trying
to do our best, of course,

but the situation just kept
getting worse and worse.

That's how it became
such a major accident.

There were so many things we wanted to do,

but we couldn't do any of them.

We felt powerless.

It's really regrettable.

High concentrations of
radioactive contamination

prevent people from
returning to their home towns

to this day.

The sequence of events inside Reactor 2,

illustrates how difficult it was to keep

radioactive substances inside
the containment vessel.

(foreign language)

- [Voiceover] The massive
release of radioactive materials

from Reactor 2 resulted
in severe contamination.

The emergency cooling device
has drawn little attention

in the past, but it may
turn out that it played

a pivotal role in triggering the leak

by obstructing the venting procedure.

The containment vessel was
considered the last means

of keeping radioactive
materials from getting out.

Research is underway to find
out where the vessel leaked,

but many questions remain
about what exactly happened

inside Reactor 2.

Investigations into what happened
in Reactor 1 offer a clue.

Venting did work there, but
it was the first reactor

to lose its cooling system,

and it quickly went into a meltdown.

The containment vessel also broke,

allowing radioactive materials to get out.

We had experts analyze the
results of the latest data.

They uncovered an unexpected weakness.

- [Voiceover] Where
did the breakdown occur

in the containment vessels?

Research is underway to find exactly where

the failures occurred.

The initial focus is on Reactor 1,

it was the first to
lose its cooling system

and go into a core meltdown.

Researchers are using a
remote-controlled boat

to avoid exposure to strong radiation.

There's a pool of radioactive water

surrounding the containment vessel.

Experts insert the boat there
and use an onboard camera

to look for cracks.

Here's what they found.

The camera captured images
of contaminated water

pouring out of piping around
the containment vessel.

That suggests there's a
crack in the back somewhere.

Experts say the amount
of radioactive water

indicates that the condition
of the containment vessel

is more critical than previously thought.

There's a hole somewhere.

If there's no leak on this
side, the hole is not here

but over here somewhere.

(dramatic music)

- [Voiceover] The location of the leak

indicates there's a crack in a lower part

of the containment vessel
that's surrounded by concrete.

Specialists had assumed
that cracks in this section

were unlikely.

(dramatic music)

We asked the experts to join us

in a more detailed analysis.

Right now, it's not possible
to get a firsthand look

at the area thought to be damaged.

Our analysis is based on a
diagram of the containment vessel

and a simulation of the meltdown.

(dramatic music)

Masanori Naitoh is an expert on accidents

at nuclear plants.

He's been using data to track

how the core meltdown progressed.

(dramatic music)

(foreign language)

- [Voiceover] There's actually
an opening in one place.

From there, the melted
nuclear fuel comes out.

Our calculations suggest the molten debris

didn't reach the wall.

- [Voiceover] We also consulted
with experts on structures

made of metal.

In this simulation, melted nuclear fuel

breaches the reactor and pours out

onto the underlying concrete.

The spilled fuel flows toward the wall

of the containment vessel,

but it stops about a meter away.

If the fuel didn't touch the wall,

could it still have broken the vessel?

(foreign language)

- [Voiceover] The nuclear
fuel is extremely hot,

with a temperature of more
than 2000 degrees Celsius.

So the radiant heat raises the temperature

of the drywell wall.

The question is, would the
structure of the drywell hold

in soaring temperatures?

(dramatic music)

- [Voiceover] The containment
vessel is made of steel

about 24 millimeters thick.

The experts use this
information and other data,

including the shape and material
of the surrounding layer

of concrete to explore
the effects of the heat

from the nuclear fuel.

They discovered an unexpected flaw

in the containment vessel.

The nuclear fuel, now at
a temperature exceeding

2000 degrees Celsius,

heats the wall of the containment vessel

to nearly 600 degrees.

The metal part of the
vessel, shown in red,

expands toward the outside.

A portion of the
surrounding concrete is made

of a different material.

This section appears to be
vulnerable to the extreme force

being applied.

The researchers' calculations
show that this section

would become unable to
bear the stress and break.

(foreign language)

- [Voiceover] Metals like
this kind of carbon steel

are not meant to withstand
such high temperatures.

They can't prevent thermal expansion.

(foreign language)

- [Voiceover] This was unexpected.

If molten debris from the nuclear fuel

comes close to the drywell
wall, as it does here,

the structure can't
maintain its integrity.

That's our conclusion.

- [Voiceover] In the past,
experts thought leaks

were more likely at the
joints connecting pipes

in the lid to the vessel.

But our research revealed a new weakness

in the containment vessel.

The heat from the nuclear
fuel could break it,

even if the fuel didn't
touch the vessel's wall.

What did the people in
charge of Fukushima Daiichi

think of this finding?

(foreign language)

- [Voiceover] If melted
nuclear fuel spreads out

to the containment vessel,
that could cause strain

in various places, leading
to radiation leakage.

I believe that's true.

At the very least, we'll take
measures at Fukushima Daiichi

where large-scale leaks occurred.

And we'll think about how
to prevent degradation

that could occur if
hot melted nuclear fuel

landed on the containment vessel.

We can also cover it with
materials that can withstand

extremely high temperatures.

There are still many things we
can do, and we will do them.

- [Voiceover] Are Japan's
power companies acting

on the lessons learned?

NHK surveyed six utilities
with nuclear reactors

of the same type as the
ones at Fukushima Daiichi.

TEPCO and two other utilities said

they will install new
venting devices with filters.

They said this would prevent leaks.

The other three firms also
said they plan to install

new equipment.

They said they are still
deciding what to use

or declined to comment.

But experts say rising temperatures

in the suppression chamber
may not completely explain

the high levels of radiation
indicated by the data.

- [Voiceover] I wonder if
enough thought had gone

into figuring out how
radioactive materials

would behave in water that's tainted

with all kinds of chemicals.

- [Voiceover] During a core meltdown,

a variety of chemicals are
generated inside a reactor.

Experts say the types and
quantities of these chemicals

may affect the amounts
of radioactive materials

that are released.

Have investigations into
the causes of the accident

been thorough enough?

We posed this question to the
Nuclear Regulation Authority,

which screens safety
measures at the nation's

nuclear power plants.

(foreign language)

- [Voiceover] When it comes to safety,

the thing we need to fear
most and guard against

is missing important points,

That's not always possible.

I believe we've made as
much effort as we can

to cover every possibility
concerning accidents,

but we shouldn't be satisfied with that.

We must constantly keep
striving to make improvements

and identify anything we've missed.

- [Voiceover] Various flaws
resulted in the release

of massive amounts of
radioactive substances.

Actual events surpassed
people's assumptions

and the measures that were in place.

The Fukushima accident has
shown just how difficult it is

to contain radioactive
materials and proven that

many things that happened
during an accident

can't be foreseen.

Many issues still haven't
been fully explained.

After the disaster, authorities drew up

new regulatory standards for
nuclear power facilities.

The Nuclear Regulation Authority

is conducting safety reviews
on 17 of Japan's 48 reactors.

Accidents like the one
at Fukushima Daiichi

must never happen again.

(dramatic music)

Investigations must continue,
leaving no stone unturned.

(dramatic music)

Have people truly learned
the lessons of the accident?

Are they applying them?

We need to keep asking questions

and remember that the full
truth about the catastrophe

has yet to be revealed.

(dramatic music)