By the mid-20th century, we’d already been
experimenting with radioactive materials for
numerous decades, leading to the development
of everything from nuclear bombs to indispensable
x-ray machines.
But it wasn’t until the ‘50s that atomic
energy for power became a reality, and the
first nuclear reactors were developed and
put into use.
In the following years, however, questions
about the safety, and long-term effects, of
nuclear reactors have only grown in importance.
This is Unveiled, and today we’re answering
the extraordinary question; what happens inside
an exploding nuclear reactor?
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There have been numerous nuclear accidents
over the years, from experiments gone wrong
to radioactive sources being stolen and causing
contaminations elsewhere.
But there have only been three large-scale
nuclear reactor meltdowns: Three Mile Island
in Pennsylvania in 1979 (a partial meltdown),
the Chernobyl Disaster in Ukraine in 1986,
and the Fukushima Daiichi meltdown in Japan
in 2011.
Of these, both Chernobyl and Fukushima are
considered number 7s on the International
Nuclear Event Scale, which is the highest
an accident can be.
Despite being the same ranking, however, the
Chernobyl disaster is still widely considered
the worst nuclear accident in human history
due to the number of direct deaths it caused,
and the volume of radioactive material dispersed
into the environment – which was significantly
larger than at Fukushima.
There are different kinds of nuclear reactors,
but the most common generate energy primarily
via fuel rods of an inherently unstable uranium
isotope, uranium-235.
This isotope, when its nucleus is purposely
split by a free neutron in the reactor core,
produces a reaction called nuclear fission,
which generates large amounts of energy.
This energy creates heat, which evaporates
water and produces steam, which in many nuclear
plants then turns a large turbine, and the
turbine generates electricity.
In other words, these plants make power the
same way, say, a coal plant does, with the
crucial difference of course being the raw
material.
Nuclear plants can generate much more power
with much less fuel, and are technically environmentally
“cleaner” — in terms of pollution, though
not radioactive waste — provided they work
as they’re supposed to.
Though the causes vary wildly, from preventable
design flaws to human error to an earthquake,
reactor meltdowns happen for just one reason:
the reactor ceases to function properly and
the radioactive fuel rods inside “melt down”
because nothing is cooling them.
This happens because nuclear fission is, unsurprisingly,
very very hot; a fully-functioning nuclear
reactor core is around 572 degrees Fahrenheit,
for instance.
Because of this, a coolant system — usually
water-based — is necessary to make sure
it doesn’t overheat.
The 2011 earthquake and resulting tsunami
that affected Fukushima was strong enough
to cut off power to the plant, meaning its
coolant system failed and three of the six
reactors went into meltdown.
At Chernobyl, a shift of workers carried out
a complex safety test they weren’t properly
prepared for that involved simulating how
well the reactor would manage in a power cut
— ultimately meaning again that a coolant
system failed.
When a meltdown happens, the nuclear reaction
goes completely out of control as the core
begins to rapidly decay, which can sometimes
result in an explosion.
Explosions at nuclear plants are very rare,
however.
At Fukushima, the meltdowns caused a different
reaction, which created hydrogen gas that
was eventually able to ignite and explode,
but this was still nothing compared to the
explosion at Chernobyl’s Reactor 4.
This enormous explosion that blew apart the
plant happened for multiple complex reasons
due to negligence and lack of attention to
safety protocols, leading to a massive buildup
of pressure, exacerbated by a design flaw
with the control rods.
Inside the reactor, these control rods, made
of boron, were inserted to shut down the reaction,
but their graphite tips briefly, yet consequentially
intensified the already precipitous release
of energy.
The resulting explosion was so huge, the roof
of the plant building was completely destroyed,
and large concrete structures had to built
to contain the area.
An exploding nuclear reactor is vastly different
from an exploding nuclear bomb.
Despite being designed to explode and cause
destruction, no atomic bomb can ever have
effects as long-lasting or far-reaching as
a nuclear plant accident if it were truly
out of control.
This is because of the volume of radioactive
fuel.
Little Boy, the bomb dropped on Hiroshima
in 1945, contained 141 pounds of enriched
uranium, while just one reactor at Chernobyl
contained over 30,000 pounds in its fuel rods.
At the same time, though there’s significantly
more nuclear material in a reactor, it’s
thankfully rare that it gets dispersed over
a large area; Chernobyl was an ostensibly
unique case, with many particular factors
contributing to the explosion and fire; the
Chernobyl Exclusion Zone is still 1000 square
miles in size to this day.
And a lot of care has also had to be taken
to try and prevent groundwater tables from
being contaminated by radioactive water in
Fukushima.
Nuclear reactor accidents simply have many
long-reaching consequences.
One thing nuclear events of all shapes and
sizes can produce is radiation sickness.
In order to develop Acute Radiation Syndrome,
which is radiation sickness caused by a high
dose over a short period of time, a human
needs to be exposed to 0.7 Grays of radiation
or higher.
It’s been estimated that Alexsandr Akimov,
the shift supervisor of Reactor 4 during the
Chernobyl accident, was subjected to a lethal
dose of 15 Grays during his work to try and
contain the disaster, which killed him within
two weeks.
If you were exposed to an exploding nuclear
reactor and didn’t die as a result of the
explosion, you’d almost certainly develop
ARS and be dead anyway in a matter of weeks
– and it’s not a pleasant death.
Some of the early symptoms of radiation poisoning
are diarrhea and vomiting, while later the
radiation burns get so severe that your skin
may slough off.
This is the proper term for what an animal
does when it sheds its skin, only humans aren’t,
of course, designed for this, so it is a horrible
way to die.
Radiation also makes you more susceptible
to secondary infections, made even worse by
the fact your skin is covered by open sores
and you’re plagued by internal bleeding.
The short-term death toll of the Chernobyl
disaster has stood at 54 since 2006, though
this is still a point of great contention
and it’s impossible to know the number of
long-term deaths due to exposure to radiation
and the toxic cloud that spread from the site
of the explosion, though it is often estimated
to be many thousands.
While at its best, atomic energy is powerful
and efficient, at its worst it can create
some of the most violent and deadly incidents
in human history.
And that’s what happens inside an exploding
nuclear reactor.
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Is there anything we missed?
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