hi there is a particular topic I've been
interested in for a very long time there
are two major nuclear reactor accidents
that have happened so far in the world
in Chernobyl and Fukushima today I'll
dive in details on this and try to find
some similarities I'd like to apologize
in advance to the experts or those
related to the topic I'll try to put
complicated things the easiest way
possible I dunno the terms like a parade
of reactivity margin subcritical states
but I'll skip that science in my
explanation
on first side there is nothing common
between Fukushima and Chernobyl
accidents the trigger was the earthquake
at the horseshoes East Coast the
epicenter of the nine point earthquake
was on the Pacific ocean floor 120
kilometers away from the nuclear power
plant the plant systems were operating
normally upon the first earthquake
shocks all three generators were shut
down the shock destroyed the power line
communications and the plant's power was
off such conditions had been foreseen
South tenements diesel power generator
started known for his distractions came
the planned vulnerably survived the most
powerful earthquake in Japanese history
but it was just the beginning the shock
caused two massive tsunami waves the
first wave 4 meters high reached the
plant 40 minutes later a second 150
meters high flooded the plant and an
hour later the water went over the
protective wall and disabled all the
generators ironically the power plant
was left with no power its rooms went
black
so did all its indicators controls and
communications the staff lost control
over the scores from reactors cooling
with the help of pocket torches they
were trying to find the instructions but
there were none for a full planned
blackout in the possible emergencies
list the accident started to gradually
progress into a disaster the irony here
is that 25 years prior to that in
Chernobyl engineers had been testing a
system that would let a plan to work out
anonymously with no external power the
Chernobyl accident was completely
handmade though it is impossible to name
the guilty ones the development of
complex system is always a quest to find
the right balance between simplicity
reliability and usability the design
compromises had led to the situations
that made the reactor behavior
unpredictable the basic working
principle of a nuclear power plant is
similar to that of a steam machine
the difference is that rather than
turning water into steam by burning coal
it is heated by uranium fission the
reactive fuel is held in vertical
containers fuel assemblies inside them
water turns into overheated steam which
spins turbines thus producing
electricity controlling the steam
machine is simple adding more coal
increases the power output while
stopping to rebel decreases it reactors
are controlled in a different manner
with the help of board rods this
material consumes neutrons so the chain
reaction impossible without them stops
the rods moving reactors active zone if
the rods are fully lowered the reaction
is stopped
the reactor is inactive the more droids
are pulled from the reactor the more
aggressive the random fission and the
more heat is generated by the reactor
reactor operators task is to keep the
reaction stable so the random fission is
roughly constant the rods in Chernobyl
power plant had a peculiar feature the
so called and the fact it was that in
some conditions before the activating it
temporarily increased the power output
the official accident investigation
report even compared it to you speeding
up an automobile when a brake pedal is
pushed the engineers knew it well to
prevent accidents there were strict
instructions to follow and a few levels
of hardware scram and protection
circuits however on the 26th of April
1986 it just wasn't enough
by the way on the contrary to a common
misconception there were only one
circuit disabled during Chernobyl
accident the emergency core cooling
system ECC s the rest of them were
functioning normally as you can see from
the name ECC s is meant not for
controlling the reactor but for
abstracting the heat in case of
emergency C reactors have a huge thermal
lag even if the chain reaction is
stopped the reactor can't cool down
instantly the fuel assemblies still
generate a lot of hail for a long time
the test regulations received from the
top ordered that the system should be
turned off however it still wouldn't
help
why because experiment itself didn't go
as planned the experiment should have
started the day before on April 25th at
2:00 p.m. but a supervisor from given
era interfered he demanded that the
plant reactor power output decrease
would be postponed as an evening power
consumption peak was coming up this
person gave his permission for lowering
the power output only at 11 p.m.
contrary to the plan the reactor had
been active for additional nine hours in
transit mode due to that factor formed a
lot of xenon isotopes which made
controlling the reactor much harder
experts call such reactors poison
however it was decided that the
experiment would go on anyway exactly at
midnight on the 26th of April a new
reactor control shift started the
experiment went to its final phase by
1:00 a.m. the power output reached the
scheduled 700 megawatts but then it
started to drop quickly the shift
managed to stabilize the reactor only at
200 megawatts this time it was the shift
supervisor who decided to defy the
regulations the experiment was
deliberately set up on a lower power
level it is a common misconception that
there was a nuclear explosion in
Chernobyl but that is not true
the reactor blow up like an overheated
pressure cooker due to the failed
experiment the experiment was supposed
to check
if a caution turbo generator was enough
to supply the plant with the power for
normal operation three previous
experiments failed but the workflow
altered after that success promise
higher security for all the air pmk
reactors and pretty bonuses for all the
stuff at 1:23 a.m. the experiment
started the water level in the reactor
started to gradually decrease and the
power output started to increase
according to the plan the reactor was
supposed to be decelerated by the
controllers as normal
however system az5 was off because the
reactor had been working on lower energy
levels prior to that the deviation was
nowadays 36 seconds later the operator
puts the AC v button and control rods
went to the active zone remember that M
defect I talked about it led to a sudden
reactor power excursion the water in the
lower part of the active zone insolently
turned in the overheated steam and
rushed outwards at pressure of 70
atmospheres the upper part of the active
zone was covered with the biological
shield it is called the scheme e or
Elena that Elena waited 450 times it was
thrown up to the ceiling by the
explosion it broke a few loading crane
and fell back on the reactor crash
the first explosion was followed by a
second one it is still unclear whether
it was the overheated steam or perhaps
the hydrogen formed during the accident
it is not that big of a deal the main
reactor Hall roof partially collapsed
while in the active zone the graphite on
the inner sides of the reactor caught
fire in Fukushima the tragedy had been
unfolding much slower the first
explosion took place 24 hours after the
initial shock after the plant had been
floated all the time the plant staff had
been trying to restore cooling to the
shutdown reactors with all the means
necessary the engineers had to act
blindly they had been struggling to
restore power to the planet measuring
equipment and reactor cooling systems
were non-functional after the blackout
water circulation system valves closed
and sealed the tubes the reactor started
to overheat but nobody seemed to know it
yet the realization started to come on
let midnight there were no instructions
for such an accident so engineers had to
improvise the Lightning was partially
restored thanks to a portable power
generators provided by a local building
company the control panel of the surge
reactor was revived with 10 car
batteries from the employees cars and
the reactor cooling was being restored
by pumping water from three fire trucks
the sensors detect repression quiz
inside the reactor silt shells to
contend it seems like there had started
a reaction between zirconium and
overheated steam the reaction forms
hydrogen and creates a lot of heat the
engineers had a solution for them in
such case the containment would be
filled with nitrogen
it creates inert atmosphere and prevent
hydrogen from exploding but the pressure
in the sealed shell of the first reactor
was beyond critical a decision was made
to relieve the rejected gas from the
containment into the atmosphere at 2:00
p.m. the first reactor safety valve was
activated the pressure went back to the
appropriate level but an hour and a half
later a massive explosion occurred
the hydrogen haven't had come in contact
with normal atmosphere turned into a
powerful explosive the visibility of
such explosion outside of a protective
shell is never taken into concern
neither by nuclear plant constructors
nor by International Atomic Energy
Agency safety experts the explosion of
the first reactor destroyed the part of
the building and damaged the fire trucks
hoses so the engineers were facing the
reactor cooling problem once again the
radiation reached the level the second
explosion took place four days after the
earthquake on the 15th of March at 6:00
a.m. the fourth power generating unit
partially collapsed their accumulated
the hydrogen from the first reactors
containment
then a random spark made it explode and
started the fire there was no explosion
in the second reactor directive steam
blew off the containment nob dome hatch
and escape to the atmosphere only in
2011 nine months after the accident the
reactors were set to a cold shutdown
mode the Japanese companies will start
extracting the melted fuel from the
damaged generating units only in 2020s
it took Soviet experts ten days to
extinguish the fire unlike Fukushima it
was upstream above this caution reactor
the spread radioactive dust and heavy
isotopes during that time shocking 380
million Curie had irradiated the
atmosphere 15 million of Szell's per
down on adjacent regions of Ukraine
Russia Belarus turning them into
exclusion zones the reactor detonated
like a classic dirty bomb
it took experts six months to build the
protective cover over the kalapa
generating unit the building commonly
referred to as sarcophagus solved the
problem of reactive dust spread and
contaminating fallout almost 96% of the
fuel is still inside the destroyed plant
building the mouthfeel mixed with the
sealing concrete reactor remains and
flow to the lower levels of the plant
solidifying in
form of giant elephant legs this problem
is yet to be solved in the future
according to different reports the
children will cauldron witnessed
approximately from 600,000 to 1 million
people the official report states two
people died instantly upon the explosion
acute radiation syndrome claimed lives
of 31 people most of the firemen that
had worked on the side first 134 have
coped with the disease becoming heavily
handicapped about 115 to 200000 had to
leave their homes forever in Fukushima
tragedy three people died and 20 were
already aided gaining 170 millisieverts
approximate value of radioactive
material then in equals a quarter of
their insurable with the majority of the
material contaminating in the ocean
water nuclear disaster control and
rectification of the consequences is
still a controversial topic there are
many speculations from all sources what
the reactor extinguishing in Chernobyl
carried out in the right manner should
they have filled the active zone was
left and dust absorbent materials was
there an alternative to utilize inside
officers and soldiers and there are
plenty of questions on the accident in
Japan starting with the plant design and
on to the concealing the accident scale
there are many questions indeed but I
suggest we shouldn't judge experts had
to apply ly in unprecedented situations
finally I'd like to mention a quote I
heard from different people involved in
Chernobyl accident only in USSR there
could happen an accident like this and
only in USSR they could handle it like
they did as it turns out they were wrong
the history tends to repeat itself and
it's no joke
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