00:00The 1986 accident at the Chernobyl nuclear power
plant in today’s Ukraine was undoubtedly the worst
00:06nuclear disaster in history. To put things into
perspective, this incident released more than
00:10400 times as much radioactive material as the
atomic bomb that devastated Hiroshima in 1945.
00:18The Chernobyl disaster claimed 30 lives
directly and, according to many experts,
00:22thousands indirectly. The once-vibrant town of
Pripyat, located near the ill-fated power plant,
00:27was evacuated, transforming it into
a ghost town in less than 36 hours.
00:32How could a disaster of this
magnitude have even happened?
00:35On the surface, the Chernobyl disaster was the
product of “a remarkable range of human errors”
00:40and “specific reactor features which compounded
and amplified the effects of the errors,” as
00:45the 1986 Summary Report on the Post-Accident
Review Meeting on the Chernobyl Accident put
00:49it. In simpler terms, mistakes made by plant
operators and a flawed reactor design were to
00:55blame for this unprecedented disaster.
But is that all there is to it?
00:59Given the enormity of the Chernobyl disaster
and its far-reaching consequences, it’s easy to
01:04understand that the answer to this question is no.
Look at it this way – every war has its immediate
01:09and underlying causes. Take World War I as an
example; the assassination of Archduke Franz
01:15Ferdinand was the immediate cause of this
devastating war. But beneath the surface,
01:19an intricate web of alliances, nationalism,
and militarism fuelled the flame.
01:24Similar complexities underlie
the Chernobyl disaster.
01:27Sure, human error and poor reactor design caused
the infamous reactor number four to explode. But
01:32it was a systemic failure in the Soviet nuclear
program’s management that turned Chernobyl into
01:37a ticking time bomb. Essentially, it was a
culture of secrecy, a lack of transparency,
01:42and inadequate safety protocols that ultimately
ignited the catastrophic nuclear flame,
01:47not just technical shortcomings.
So, when exploring the causes behind
01:51the largest nuclear disaster in history, we’ll
look at every component of this lethal mix.
01:56Let’s start with the underlying causes.
Though many people—primarily Soviets—blamed
02:01the Chernobyl disaster on the operators’
recklessness and lack of competence,
02:05their actions on that fateful April night
were, above all, a direct reflection of the
02:09prevailing safety culture of the Soviet era.
Or, to be precise, a lack of safety culture.
02:15You see, despite being one of the
world leaders in nuclear technology,
02:18the USSR (the Union of Soviet Socialist
Republics) failed to implement and prioritize
02:23adequate safety practices for this technology.
At best, these practices can be described as
02:27“limited,” while calling the Soviet approach
to safety “lax” might even be a compliment.
02:32But let’s dig a little deeper. How did this lack
of safety culture enable the Chernobyl disaster?
02:38For starters, Soviet safety policies
never accounted for a catastrophe of
02:41such magnitude. When creating these policies,
Soviet decision-makers only factored in so-called
02:47“realistic” scenarios. This is on par with
designers behind the reactors used in the
02:52Chernobyl power plant, who didn’t consider
catastrophic scenarios when determining the
02:56most extreme malfunction these reactors should be
able to cope with, or the so-called Maximum Design
03:02Accident (MDA). They had no interest in those
only remotely possible scenarios, leaving the
03:08Soviet power plants ill-equipped to handle them.
For instance, a Soviet power plant could generally
03:13handle an isolated break in the largest
coolant-carrying pipe. But something like
03:17the reactor core melting was dismissed as
virtually impossible and thus not covered
03:22by any safety protocols. Also, the reactor’s
operating reactivity margin (ORM) was only seen
03:28as a way to control the reactor power and not as a
crucial safety parameter. And let’s not forget the
03:34complete lack of any safety features in the plant,
such as concrete containment and water moderators.
03:40Interestingly, the Soviets believed that this
approach increased the overall safety of their
03:44power plants. This might seem counterintuitive,
but here’s how they saw it – too many unnecessary
03:49backup systems can only lead to operational
complexities, thus decreasing the overall safety.
03:55While this explanation might seem somewhat
rational, the events that transpired during
04:00the Chernobyl disaster clearly exposed
the fatal flaw of this perspective.
04:04Now, you might wonder – is it possible
that no one in the USSR saw how tragically
04:08flawed this perspective was?
To answer this question,
04:11we must first examine how the Soviets approached
monitoring, reporting, and overall transparency,
04:16especially in the nuclear sector.
Recognizing the potential power of this sector,
04:21the USSR heavily invested in the development of
nuclear power facilities. The development of these
04:26facilities was followed by organizations
tasked with supervising their safety.
04:30So far, so good, isn’t it? Well, not quite.
You see, the primary organization tasked with
04:36this role was GosAtomEnergoNadzor (the State
Committee for the Supervision of Nuclear
04:42Power Safety). But this organization wasn’t
independent. Instead, it operated within the
04:46framework of established Soviet bureaucratic
entities in charge of power production. In
04:52other words, these so-called supervisors were
actually subordinates of their supervisees.
04:57With this in mind, it shouldn’t be surprising
that no red flags were raised surrounding the
05:01neglect of the existing nuclear equipment or
any potential mistakes in its management. The
05:06supervisors of the Chernobyl power plant—and every
other Soviet establishment—simply behaved as most
05:12Soviets at the time – they feared authority
and did their best to please their political
05:16superiors. This compliance-driven culture is
what prevented the operators concerned about
05:21the safety of the test that would lead to the
Chernobyl disaster from voicing their concerns
05:26and alerting their superiors.
Of course, such poor reporting
05:29was nothing new for the Soviets.
They boasted about not experiencing
05:33a single major failure with their reactors
in the late 1970s, but the evidence suggests
05:38otherwise. Though there are few details (no
surprise there!), it appears that the USSR
05:43had experienced at least five major reactor
incidents preceding the Chernobyl disaster.
05:48In 1974, a coolant loop ruptured in
a Leningrad nuclear power station,
05:53killing three individuals and spilling highly
radioactive water into the environment. Just
05:57three years later, half of the fuel assemblies
in the Beloyarsk Nuclear Power Plant melted,
06:02exposing the operators to severe radiation.
Another accident occurred in 1985 when human
06:08error caused a safety valve to explode in the
Balakovo Nuclear Power Plant, killing 14 people.
06:14Believe it or not, we’ve yet to cover the
worst Chernobyl disaster precursor incidents.
06:19The first of the two most alarming accidents
preceding the Chernobyl disaster happened in
06:231957 when a waste storage tank at
the Mayak Production Association,
06:28a nuclear weapons production site, exploded.
Though this disaster claimed no lives directly,
06:33it caused numerous radiation-related illnesses
and cancers in tens of thousands of people living
06:39nearby. The Mayak disaster is one of the worst
nuclear incidents in history, ranking second by
06:46radioactivity released. The only disaster that
released more radioactivity was the Chernobyl
06:51disaster itself. Yet, chances are this is the
first time you hear of the Mayak disaster. Why?
06:57The answer is simple – secrecy,
secrecy, and some more secrecy.
07:01Not even the residents of the affected areas
were initially informed about the incident.
07:06Instead, they were simply evacuated without any
explanation. It would take 18 years for the world
07:11to learn the true extent of this disaster. If this
weren’t the case, perhaps the Soviets would have
07:16adequately prepared for the Chernobyl disaster.
But there’s no point in playing this “would’ve,
07:20could’ve, should’ve” game with an accident
that happened some 1,500 miles away and
07:2429 years before the Chernobyl disaster of
1986. Especially given an incident taking
07:30place just four years prior at the same plant
wasn’t enough to break the chains of secrecy.
07:35That’s right. The 1986 disaster
wasn’t the first serious incident
07:39at the Chernobyl Nuclear Power Plant.
In 1982, during a trial run for a scheduled
07:44reactor shutdown, one of the pressure
channels broke and released radiation
07:48into the reactor compartment. Major General
Vakuylenko, who reported on the incident,
07:53stated that repairing the broken channel would
take five days and emphasized there was no
07:58high radioactive contamination at the premises.
However, a secret report would later show that
08:03contamination had actually reached an area of as
many as nine miles surrounding the power plant.
08:08Hiding these accidents from the Soviet
public and foreign observers was bad enough,
08:13but in most cases, they were also hidden
from other nuclear power personnel. This
08:17astonishing lack of transparency prevented
shared learning that could’ve led to an
08:22improvement in engineering and procedural flaws.
Now, you might think that once the Chernobyl
08:27disaster struck, this secrecy went out of the
window, and the Soviets did everything in their
08:32power to mitigate the consequences as quickly
as possible. Unfortunately, you’d be very wrong.
08:37The immediate aftermath of the Chernobyl
disaster revealed a continuation of the
08:41same old patterns: Downplay the severity
of the incident. Delegate any important
08:45decisions up the chain of command. Wait for
the bureaucratic processes to unfold. Repeat.
08:50Even though tests performed in Pripyat within
hours of the explosion showed alarmingly high
08:55levels of radioactivity—4.5 roentgen per day,
to be precise—no evacuation was ordered. This
09:01order would come more than 34 hours after the
incident when the levels of radiation reached
09:06600 milliroentgens per hour. To better understand
this figure, think of it this way: the Pripyat
09:12residents were subjected to a full-body
CT scan every hour. Compounding the issue,
09:17these poor residents were only given an hour and
a half to pack their belongings and evacuate.
09:21Had this decision been made sooner, the Pripyat
residents wouldn’t have been exposed to so
09:26much radiation, which eventually led to thyroid
cancer in many individuals, primarily children.
09:32Paradoxically, the Chernobyl disaster occurred
while the last leader of the Soviet Union,
09:36Mikhail Gorbachev, was attempting to reform the
country through two primary policies – Glasnost
09:42and Perestroika. You’ll immediately understand
what’s paradoxical about this once you learn that
09:47Glasnost focused on increasing transparency and
openness within the Soviet governmental system,
09:53promising better communication between
the authorities and the public.
09:56Surprising to no one, this communication
was nowhere to be seen in the aftermath
10:01of Chernobyl, demonstrating that nothing
truly changed within the Union. As always,
10:06the government cowered and remained silent at
first and took the “deny, deny, deny” route.
10:10When addressing the Chernobyl disaster
for the first time on TV on May 14, 1986,
10:16Gorbachev slammed international reports on this
incident as “malicious lies.” However, this time,
10:21the Soviet public didn’t fall for this, leading to
widespread distrust. Eventually, the policies that
10:26were meant to save the Soviet Union failed, taking
the entire Union with them. With this in mind, it
10:32becomes clear why Gorbachev cited Chernobyl as the
“real cause of the collapse of the Soviet Union.”
10:38But let’s not dive too deep into the aftermath
of the Chernobyl disaster just yet. Sure,
10:43we’ve covered all the primary underlying causes
of this catastrophic event so far. But we’re
10:47yet to explore the immediate causes of
the world’s largest nuclear disaster.
10:51As already mentioned, there were two of them –
poor reactor design and human error. Though these
10:57factors should never be discussed in isolation,
it’s important to recognize them as major elements
11:02in causing the Chernobyl disaster.
As far as the reactors go, one thing
11:06was abundantly clear to anyone who came in
contact with these Soviet creations – the
11:10RBMK (Reaktor Bolshoy Moshchnosty Kanalny)
reactors used at the Chernobyl Nuclear
11:13Power Plant were inherently unsafe.
There were several reasons for this.
11:18Firstly, as previously explained, these reactors
weren’t investigated by any independent safety
11:23bodies. If competent, independent experts
were allowed to inspect these reactors,
11:28they would likely raise two red flags – the
physical characteristics that prompted them
11:32to act unstable and the complete and total lack
of efficient safety systems. Both of these can
11:38be explained by the fact that the USSR started
their nuclear power program behind other developed
11:43nations and tried to catch up by any means
necessary. This also meant completely ignoring
11:48the human factor when designing the reactors.
As you can imagine, this led to nothing good.
11:53The RBMK reactors had a unique design that
combined graphite as a moderator instead of
11:58water and a water coolant. Graphite was
used because it is cost-effective yet
12:03allows for a significantly higher energy output.
However, graphite is also quite unpredictable.
12:09In water-moderated reactors, water will become
less effective in facilitating a reaction as
12:14it gets hotter. Graphite, on the other hand,
will keep promoting the reaction even if the
12:18temperature escalates. The only way to put
a stop to this reaction is to lower boron
12:23carbide control rods into the reactor.
The more control rods go in, the more
12:27effectively the reaction is controlled.
But as the Chernobyl disaster showed,
12:31this design characteristic was widely unsafe.
As you will soon learn, once the control rods
12:36were lowered during the Chernobyl disaster,
they jammed. But the trouble lay in their
12:40graphite tips, which not only prevented the
boron in the control rods from slowing the
12:45reaction but actually contributed to a
surge in reactivity. The water-cooling
12:49system further exacerbated the situation and
ultimately caused the explosion in the reactor.
12:54But it’s still not time to discuss the human
errors that led to this system activating. Not
12:59when there are more unsafe characteristics
of the RBMK reactors to break down.
13:04Another crucial feature of these reactors
that proved to be highly unsafe was the
13:08positive void coefficient. This coefficient is
what predominantly contributed to the overall
13:13power coefficient in the RBMK reactors.
What is the positive void coefficient?
13:18The positive void coefficient refers to
the reactor’s response to the formation
13:22of voids and steam bubbles in the coolant. In
“traditional” reactor designs used in the West,
13:28an increase in voids tends to reduce reactivity,
thus acting as a self-regulating mechanism.
13:34However, in the RBMK reactors, reactivity
increases as voids or steam bubbles form,
13:40which is precisely what happened during the
Chernobyl disaster. The rapid rise in reactivity
13:46exacerbated the uncontrollable chain reaction,
contributing to the severity of the catastrophe.
13:51However, the lack of a proper containment
structure made this event even more disastrous.
13:56In the West, this structure comes in the form
of a concrete and steel dome located over the
14:00reactor and designed to keep the radiation inside
the power plant in the event of an accident. The
14:06radiation shield used for the RBMK reactors wasn’t
enough to contain the release of radioactive
14:11materials after reactor number four exploded,
leading to elements like plutonium, strontium,
14:17and iodine being dispersed over a wide area.
But where do the power plant operators
14:21fit in this narrative?
To understand why the human
14:24error was the first identified culprit for the
Chernobyl disaster, let’s look at what precisely
14:28happened on April 26th, 1986, explaining
where the power plant operators went wrong.
14:34The trouble started on April 25th, when the
fourth reactor was to shut down for routine
14:38maintenance. The reactor crew at the Chernobyl
Nuclear Power Plant decided to take advantage of
14:43this shutdown to determine how the reactor
would behave following the loss of station
14:47power. Their goal was to establish whether the
slowing turbine would produce enough electrical
14:52power to sustain the reactor’s safety systems
until the emergency power supply kicked in.
14:57This test had already been attempted a year
prior, but the energy from the turbine was
15:01insufficient to keep the safety systems running.
That’s why the crew decided to repeat the test
15:06using newly developed voltage regulators.
Unfortunately, the team conducting this test
15:12didn’t consult the personnel in charge
of the safety of the nuclear reactor,
15:16which proved to be a fatal mistake.
Here’s how the operators put reactor number
15:20four in a dangerously unstable condition,
which essentially guaranteed an accident.
15:25The reactor shutdown commenced on April 25th at
1:06 a.m. by gradually lowering the power level.
15:31This process was halted at 3:47 a.m., as the
electrical load dispatcher insisted on maintaining
15:37a minimum power level for grid stability.
At 2 p.m., the operators shut off the reactor’s
15:42emergency core cooling system to prevent it from
interrupting the test. Though this move didn’t
15:47contribute to the accident, leaving this system
on could’ve at least slightly reduced its impact.
15:52Over 9 hours would pass before the grid
controller agreed to recommence the power
15:56reduction. This took place at 11:10 p.m.,
followed by a shift change at midnight.
16:02Here’s when the real trouble started.
Only half an hour after midnight,
16:05the power rapidly dropped to 30 megawatts
thermal. To understand just how bad this is,
16:10you should know that the operation of the
reactor below 700 megawatts thermal was strictly
16:15forbidden. This sudden drop was likely due to
operational error – either the operator failed
16:20to give the “hold power at required level” signal
or the system failed to respond to such signal.
16:26The operators tried to increase the power to
an acceptable level but were met with several
16:30challenges, including xenon poisoning and reduced
coolant void. To respond to these challenges,
16:35the operators withdrew numerous power rods, thus
violating the minimum operating reactivity margin
16:41(ORM) of 15 rods. However, this move
did result in stabilizing the reactor
16:48at about 200 megawatts thermal by 1 a.m., which
encouraged the operators to proceed with the test.
16:53The test commenced at approximately 1:23 a.m., but
only after the operators made a few more mistakes.
16:59For instance, they enabled additional cooling
pumps around 1:07 a.m., which caused them
17:04to remove more rods to prevent power levels
from falling. According to some calculations,
17:09only eight control rods were left in
the reactor. And if you remember – the
17:13minimum ORM required is at least 15.
Once the test started, it took about 40 seconds
17:19before things started going terribly wrong.
At 1:23:40 a.m., an operator pressed the
17:25emergency AZ-5 button, lowering all of the control
rods into the reactor’s core intended to shut down
17:32the reactor. Some believe that this move was
what caused the sudden power excursion. It took
17:37only three seconds for the power to reach 530
megawatts thermal, showing no signs of slowing
17:42down. This caused fuel elements to rupture,
increasing steam generation and further boosting
17:47power due to a large positive void coefficient.
And let’s remember – the Soviet reactors only
17:53accounted for an isolated element breaking down.
At this point, several fuel channels ruptured,
17:58increasing the pressure in the reactor. This
pressure was so great that the reactor’s
18:02radiation shield—a 1,000-ton support plate—
detached, causing the control rods to jam
18:08about halfway down into the reactor.
And then? Complete and utter chaos.
18:14The emergency cooling circuit ruptured,
feeding water into the core and causing
18:18intense steam generation. Here’s
when the first explosion took place.
18:22Another explosion ensued just two or three
seconds later, likely caused by the build-up
18:26of hydrogen from zirconium-steam reactions. The
second explosion threw out fuel and hot graphite,
18:33starting a number of fires. By the end
of these explosions, the reactor’s core
18:37was completely exposed to the atmosphere.
The core continued to burn for days after the
18:42accident, releasing radioactive particles into the
environment. In an effort to extinguish the blaze,
18:47helicopters dropped some 5,000 tons of sand, clay,
lead, boron, and dolomite onto the core for almost
18:54ten days straight. About 300 tons of water was
also injected per hour into the intact half of the
19:00reactor, but these efforts were soon stopped out
of fear of flooding reactors number one and two.
19:05Eventually, the remains of reactor number
four were encased in a hastily constructed
19:10concrete and steel structure known as the
“Sarcophagus.” Given how fast it was built,
19:15it shouldn’t be surprising that this structure
significantly deteriorated over the years,
19:19calling for several repairs. However, the ultimate
plan under the Shelter Implementation Plan project
19:24by the Chernobyl Shelter Fund was to build
a new, more secure, and permanent structure
19:29around the existing one. This structure,
called the New Safe Confinement (NSC),
19:34was completed in 2017, spanning over 850 feet.
But what happened to the people and the
19:40environment surrounding the Chernobyl Nuclear
Power Plant throughout all those years?
19:44Though this video primarily focuses on
the causes of the Chernobyl disaster,
19:48this catastrophe can’t possibly be discussed
without mentioning the terrible aftermath.
19:53As previously mentioned, this disaster claimed
30 lives directly. Two of them were power plant
19:57workers who died as a result of the initial
explosion in the reactor. The rest of the
20:02casualties were firefighters and emergency
clean-up workers who mostly died from acute
20:06radiation syndrome (ARS) in the first three
months after the accident. They were exposed
20:11to up to 20,000 milligrays of radiation in
the aftermath of the Chernobyl disaster. To
20:17understand just how high this is, you should know
that ARS occurs when an individual is exposed
20:22to more than 700 milligrays of radiation. This
makes such a high dose of radiation 100% fatal.
20:29But what about the residents of the affected
areas? How did the radiation affect them?
20:33Well, for starters, the entire town of Pripyat—a
little over 49,000 residents—was evacuated
20:3936 hours after the accident. The evacuations
continued in the subsequent weeks and months,
20:45resulting in around 200,000 people being
resettled into less contaminated areas.
20:50The Chernobyl disaster took a severe toll on
the physical and mental health of the affected
20:54residents. As far as physical health goes,
there were at least 1,800 documented cases
20:59of thyroid cancer in children following the
accident. In the mental health department,
21:04the worst consequence was the instances
of suicide among the affected population.
21:08Tragically, this population also includes Valery
Legasov, the Soviet chemist who played a key role
21:14in the initial response to the Chernobyl disaster.
Legasov hanged himself in his Moscow apartment the
21:20day after the second anniversary of the disaster
and a day before he was supposed to present the
21:25findings of his investigation into the causes
of the Chernobyl Nuclear Power Plant accident.
21:30Having learned the causes of this
terrible accident in this video,
21:33you can probably understand why the weight
of such knowledge, combined with the broader
21:38impact on public health and the environment, took
a heavy toll on individuals like Valery Legasov.
21:43But what do you think about the causes of the
Chernobyl disaster? Do you think there was any
21:47way to avoid such a catastrophic event? Share
your opinion in the comments section below then
21:52check out “What Happened Immediately After the
Chernobyl Disaster.” Or watch this video instead!
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