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Chernobyl
A Timeline of The Worst Nuclear
Accident in History
By Marcia Wendorf
33 years ago, a series of missteps caused the
worst nuclear accident in history, and its effects are still being felt to this
day.
Located 65 miles north of Kiev, Ukraine, the
V.I. Lenin Nuclear Power Station at Chernobyl was a model of Soviet
engineering. Its four RBMK nuclear reactors produced enough electricity for 30
million homes and businesses.
The RBMK reactor is a class of
graphite-moderated nuclear power reactor that was designed and built by the
Soviet Union.
Certain aspects of the design contributed to the
Chernobyl disaster, and there were calls for the reactors to be decommissioned.
However, the reactors were redesigned, and as of
2019, ten are still in operation.
1,600 Radioactive U-235 Fuel Rods
In 1986, Chernobyl had four working reactors,
with two new ones under construction. The newest of the four, Reactor No. 4,
contained 1,600 radioactive uranium-235 fuel rods.
Because U-235 is unstable, its atoms
spontaneously release neutrons, which hit other U-235 nuclei, causing them to
release neutrons. This is what is called a chain reaction.
The byproduct of a chain reaction is the release
of enormous quantities of heat and energy, and this heat is what's used to turn
water into steam, which drives a turbine, that generates electricity.
To keep a chain reaction from running away with
itself and becoming a nuclear bomb, control rods containing a neutron absorbing
substance are inserted between the fuel rods.
Reactor No. 4 had 211 control rods made of the element
boron. If you raise the control rods, the chain reaction accelerates, if you
lower the control rods, the chain reaction slows.
Friday, April 26, 1986, 11:45 p.m.
176 workers were coming in for their shifts from
the neighboring town of Pripyat.
Built in 1970 as a company town for the power
station, Pripyat had a population of 50,000, and enjoyed many of the luxuries
denied to other Soviet citizens, such as well stocked supermarkets, good
schools, and plentiful sports facilities.
This night involved the continuation of a test
that was begun twelve hours earlier. It was a test of the plant's ability to
keep Reactor No. 4 cool in the event of a power failure.
Whether the plant’s still-spinning turbines
could produce enough electricity to keep the coolant pumps running during the
brief gap before the emergency generators would kick in.
To perform the test, they would have to shut the
reactor down, and by the time the night shift arrived, the reactor was
operating at 50% power.
"The odds of a meltdown are one in
10,000 years." -- Vitali Sklyarov, Minister of Power and
Electrification of Ukraine
Saturday, April 26, 1986 00:28 a.m.
The night shift foreman, Alexander Akimov, began
arguing with Chernobyl’s Deputy Chief Engineer, Anatoly Dyatlov, over how low
the amount of electrical power the reactor was generating should be taken.
Akimov cited a manual which stated that it
should not be less than 700 megawatts, while Dyatlov insisted that 200
megawatts was be safe. Since Dyatlov outranked him, Akimov had to agree.
1:19 a.m.
The Reactor Control Engineer, Leonid Toptunov,
blocked the automatic shutdown of the reactor due to a low water level, and
raised the reactor's power up to 7 percent by removing all but six of the
control rods. The reactor was now growing unstable.
1:23:40 a.m.
Readings showed the reactor's temperature had
climbed to 4,650 C, almost as hot as the surface of the sun.
An engineer who had been on a catwalk above the
reactor ran into the control room, shouting that the fuel rod caps were jumping
in and out of their sockets. These caps weigh 350kg (772 lb) each.
Alarmed, Akimov pressed a button to reinsert the
control rods, but instead of dropping their full seven meters, they stopped at
between two and 2.5 meters.
1:23:45 a.m.
The reactor reached 120 times its full power,
and its radioactive fuel disintegrated. There was a long, low, almost-human
sounding moan, then an explosion lifted the 1,000-ton concrete shield that was
above the reactor and wedged it at an angle.
This allowed air to reach the reactor, and the
oxygen in the air started a fire in the reactor's graphite. The air also caused
the metal in the fuel tubes to react with the water in the reactor to produce
hydrogen gas.
Hydrogen gas is highly flammable, and it
exploded, blasting debris into the air and onto the roof of the neighboring
Reactor No. 3.
In a study commissioned by the U.S. government
on the Chernobyl disaster, Richard Wilson of Harvard University described this second explosion as a small
nuclear explosion.
01:26:03 a.m.
"Call everybody, everybody" -- Chernobyl Dispatch
The first fire alarm came in to Paramilitary
Fire Station Number Two, based on the grounds of the power plant. The firemen
scrambled to Reactor No. 4 and climbed up onto its ruined roof.
Afraid to use water because of the exposed
electrical cables, the firemen threw sand and used their canvas hoses to beat
out the flames.
In Reactor No. 4's control room, two trainees,
Aleksandr Kudryavtsev and Viktor Proskuryakov, were sent to assess the damage.
They made it to the reactor hall where they
observed the 1,000-ton Upper Biological Shield jammed at an angle in the
reactor shaft, and blue and red flames raging in the reactor itself.
Both Kudryavtsev's and Proskuryakov's bodies
immediately darkened with what is known as "nuclear tan" as they
received a fatal dose of radiation.
2:50 a.m.
Workers inside the plant had accounted for all
the staff with the exception of Valery Khodemchuk. At the time of the accident,
Khodemchuk had been in the main circulating pump room, which was close to the
explosion. Unbeknown to his coworkers, he had been vaporized by the explosion.
Chernobyl's doctor, Valentyn Belokon, who had
been treating injured workers realized that the they were suffering from
radiation poisoning. He called the hospital in Pripyat and requested potassium
iodide tablets. Potassium iodide blocks radioactive iodine from being absorbed
by the thyroid gland.
7:30 a.m.
Akimov and Toptunov entered Reactor No. 4 in an
attempt to bring water into the ruined reactor. This would cost them their
lives. Akimov died on May 11th, having said that his conscience hurt more than
his injuries, and Toptunov died three days later.
8:00 p.m.
Inhabitants of Pripyat gathered on a railway
bridge that had a view of the nuclear power plant to view the beautiful flames
of all colors caused by the burning graphite.
A breeze from the power plant swept over them,
carrying a radiation dose of 500 Roentgens. No one standing on the bridge
survived, and it is called the "bridge of death".
Sunday, April 27, 1986 10:00 a.m.
The first of what will become almost 1,800
helicopter flights above the reactor began. The heliocopters dropped sand,
lead, clay, and neutron absorbing boron onto the burning reactor, but
practically none of the neutron absorbing materials reached the core.
Due to the radiation, the helicopter crews were
aware that theirs was most likely a suicide mission, but they went anyway.
2:00 p.m.
The authorities began an evacuation of the city
of Pripyat. Via loudspeaker, they told people to take enough food and clothing
for three days, and to leave their pets behind. In total, almost 350,000 people
were evacuated, and they would never return. The pets left behind were shot.
Monday, April 28, 1986
On his way out of the plant after a shift, a
worker at the Forsmark Nuclear Power Plant in Sweden went through a radiation
detector, and the detector went off.
It was quickly determined that a cloud of
radioactive gas had drifted across all of Scandinavia, Germany and
Czechoslovakia. Pharmacies in Denmark quickly sold out of potassium iodide
tablets.
Tuesday April 29, 1986
A U.S. reconnaissance satellite showed the roof
Reactor No. 4 blown off, and the glowing mass inside still smoking.
In an attempt to protect them from thyroid
cancer, Polish authorities began distributing potassium iodine tablets to
children living in the northeastern part of that country.
Friday May 2, 1986
There were two floors of pools containing water
directly beneath Reactor No. 4, plus the basement was flooded with water from
ruptured pipes and that used by the firefighters. The smoldering graphite,
nuclear fuel and other materials had formed a mass called corium,
which is a radioactive version of lava.
The mass was burning at a temperature of more
than 1,200 degrees C., and if it melted through the reactor hall floor and into
the pools of water, a steam explosion would hurl the mass into the air and would
eject even more radiactive material.
Three engineers volunteered to drain the water
from the pools - Alexei Ananenko, Valeri Bezpalov and, Boris Baranov. Their
mission was a success, but all three died from radiation sickness.
The China Syndrome
The molten mass still posed a threat if it
melted down to groundwater below the reactor building. This is the so-called
"China Syndrome".
At first, workers tried freezing the ground
beneath the reactor by injecting it with liquid nitrogen. Then, they filled the
reactor room with concrete.
In the "China Syndrome", the core
components of a nuclear reactor melt down, burning through the containment
vessel and the building housing the reactor, then they burn through the Earth's
crust and body until reaching the opposite side of the planet, which in the
U.S. is colloquially referred to as China.
In reality, a core couldn't penetrate the
several-kilometer thickness of the Earth's crust, and it certainly couldn't
travel back upwards against the pull of gravity. Also, China is not the
antipode of any landmass in North America.
May 6, 1986
Authorities closed the schools in the cities of
Gomel and Kiev, and they began relocating children. Kiev radio warned people
not to eat leafy vegetables, and to stay indoors as much as possible.
December 14, 1986
Work started on a concrete
"sarcophagus" that would completely encase Reactor No. 4, and protect
the environment from radiation for what was hoped to be at least 30 years.
300,000 tons of concrete and 6,000 tons of metal were used to build the
sarcophagus.
September 17, 2007
After realizing that the sarcophagus might not
be sufficient, work began on a new confinement structure designed by a French
consortium called Novark.
That structure was comprised of a 150 by
257-meter arch that would be slid into place. Construction costs were estimated
at €432 million euros, with a project time of five years.
The Aftermath
In the immediate aftermath of Chernobyl, a total
of 31 firemen and plant workers died. Some of their bodies were so radioactive,
they had to be buried in lead coffins.
A report by the World Health Organization estimated that 600,000 people within the
Soviet Union were exposed to high levels of radiation, and of those, 4,000 would die. Those who
lived near the Chernobyl site have reported increased instances of thyroid cancer, and they have an increased risk of
developing leukemia.
Anatoly Dyatlov and the director of the
Chernobyl plant, Viktor Bryukhanov, were sentenced to ten years each in prison
for their roles in the disaster.
The "Liquidators"
Scores of people stepped up to contain the
disaster, and they came to be called the "Liquidators". They include:
* Yuri Korneev, Boris Stolyarchuk and
Alexander Yuvchenko who are the last surviving members of the Reactor No. 4
night shift
* The firefighters who immediately
responded to the reactor accident
* The Civil Defense Troops of the Soviet
Armed Forces who removed contaminated materials and deactivated the reactor
itself
* Internal Troops and the police who
provided security, access control and population evacuation
* Military and civil medical and
sanitation personnel
* The Soviet Air Force and civil aviation
units who performed critical helicopter-assisted operations on the reactor
building, air transportation and aerial radiation monitoring
* A team of coal miners who built a
protective foundation to prevent radioactivity from entering the aquifer below
the reactor
* Construction professionals
* Media and performing artists who risked
their lives to document the disaster and to provide on-site entertainment for
the liquidators
* The photographers Igor Kostin and Volodymyr
Shevchenko who took photos in the immediate aftermath, including photos of
Liquidators conducting highly-hazardous manual tasks.
700 Million Years
The Chernobyl accident is one of only two
nuclear energy accidents that is classified as a "Level 7 Event," the
highest classification.
The other is 2011's Fukushima disaster in Japan.
At the lowest level of Reactor 4 lies the famous
"elephant's foot", a several-meter wide mass of corium that is still
giving off lethal amounts of radiation.
The half-life of radioactive elements is defined
as the amount of time it takes for the radioactivity to fall to half its
original value. The half-life of U-235 is 700 million years.
Marcia
Wendorf
Author
Marcia
is a former high school math teacher, technical writer, author, and programmer.
In much the same way as high school students in the U.S. are taught
"defensive driving", Marcia practices "defensive living":
staying on top of worldwide news about science, government policies, finance,
infrastructure, and medical issues. An outlier, Marcia is always "sniffing
the wind" for the latest trends and directions, and keeping her readers
abreast of these developments.
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Corium
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`` Containment structure
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The elephant's foot
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Exclusion zone
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Liquidator medals
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Pripyat
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Reactor No. 4 roof collapsed
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Reactor No. 4 burning core
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Reactor No. 4 schematic Source
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Reactor No. 4
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