chernobyl disaster :)

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  • 7/29/2019 Chernobyl Disaster :)


  • 7/29/2019 Chernobyl Disaster :)



    The Chernobyl disaster was a nuclear accident thatoccurred on 26 April 1986 at the Chernobyl NuclearPower Plant in Ukraine .

    An explosion and fire released large quantities ofradioactive contamination into the atmosphere, which

    spread over much of Western USSR and Europe.

    It is widely considered to have been the worst nuclearpower plant accident in history.

  • 7/29/2019 Chernobyl Disaster :)


    Where is Chernobyl?

    -In Northern Ukraine-10 miles awayfrom Belarus-80 miles North of


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    The Chernobyl Nuclear Power Plant Located 11 miles north of the city of Chernobyl Plant consisted of 4 reactors

    Produced 10% of Ukraines electricity

    Construction began in the 1970s

    Reactor #4 was completed in 1983

    At the time of

    the accident,

    reactors #5and #6 were

    in progress.

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    What happened?

    Saturday, April 26, 1986:

    -Reactor #4 was undergoing atest to test the backup powersupply in case of a power loss.

    -The power fell too low, allowingthe concentration of xenon-135to rise.

    -The workers continued the test,and in order to control the risinglevels of xenon-135, the controlrods were pulled out.

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    What happened? contd-The experiment involved shutting down the coolant

    pumps, which caused the coolant to rapidly heat up andboil.

    -Pockets of steam formed in the coolant lines. When thecoolant expanded in this particular design, the powerlevel went up.

    -All control rods were ordered to be inserted. As the rodswere inserted, they became deformed and stuck. Thereaction could not be stopped.

    -The rods melted and the steam pressure caused anexplosion, which blew a hole in the roof. A graphite firealso resulted from the explosion.

    -To save money, the reactor was constructed with onlypartial containment, which allowed the radiation toescape. 13%-30% of the material escaped.

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    Experiment.. The reactor that exploded in Chernobyl consisted of about 1,600 individual

    fuel channels, and each operational channel required a flow of 28 metrictons (28,000 liters ) of water per hour.

    There had been concerns that in the event of a power grid failure, externalpower would not have been immediately available to run the plant's cooling

    water pumps.

    Chernobyl's reactors had three backup diesel generators. Each generatorrequired 15 seconds to start up but took 6075 seconds to attain full speedand reach the capacity of 5.5 MW required to run one main cooling waterpump.

    This one-minute power gap was considered unacceptable, and it had been

    suggested that the rotational energy of the steam turbine and residualsteam pressure could be used to generate electricity to run the maincooling water pumps.

    while the emergency diesel generators were reaching the correct rotationalspeed (RPM) and voltage.

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    In theory, analyses indicated that this residual momentum and steampressure had the potential to provide power for 45 seconds whichwould bridge the power gap between the onset of the external powerfailure and the full availability of electric power from the emergencygenerators.

    This capability still needed to be confirmed experimentally, andprevious tests had ended unsuccessfully.

    An initial test carried out in 1982 showed that the excitation voltage ofthe turbine-generator was insufficient; it did not maintain the desiredmagnetic field after the turbine trip.

    The system was modified, and the test was repeated in 1984 but againproved unsuccessful.

    In 1985, the tests were attempted a third time but also yielded negativeresults. The test procedure was to be repeated again in 1986, and it wasscheduled to take place during the maintenance shutdown of Reactor


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    Test The test focused on the switching sequences of the

    electrical supplies for the reactor. The test procedurewas to begin with an automatic emergency shutdown.

    The Chernobyl power plant had been in operation fortwo years without the capability to ride through the

    first 6075 seconds of a total loss of electric power, andthus lacked an important safety feature.

    The station managers presumably wished to correctthis at the first opportunity, which may explain whythey continued the test even when serious problemsarose, and why the requisite approval for the test hadnot been sought from the Soviet nuclear oversightregulator

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    The experimental procedure was intended to run asfollows:

    1. The reactor was to be running at a low power level, between 700 MWand 800 MW.

    2. The steam-turbine generator was to be run up to full speed.

    3. When these conditions were achieved, the steam supply for theturbine generator was to be closed off.

    4. Turbine generator performance was to be recorded to determinewhether it could provide the bridging power for coolant pumps untilthe emergency diesel generators were sequenced to start and providepower to the cooling pumps automatically.

    5. After the emergency generators reached normal operating speed andvoltage, the turbine generator would be allowed to freewheel down.

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    Enggs .Alexander Akimovwas chief of the night shift

    Leonid Toptunov was the operator responsible for the

    reactor's operational regimen, including themovement of the control rods.

    Toptunov was a young engineer who had workedindependently as a senior engineer for approximately

    three months.

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    Test begins

    The conditions to run the test were established before the day shift of25 April 1986. The day shift workers had been instructed in advanceand were familiar with the established procedures.

    A special team ofelectrical engineers was present to test the newvoltage regulating system.

    As planned, a gradual reduction in the output of the power unit wasbegun at 01:06 on 25 April, and the power level had reached 50% of itsnominal 3200 MWthermal level by the beginning of the day shift.

    At this point, another regional power station unexpectedly wentoffline, and the Kievelectrical grid controller requested that the

    further reduction of Chernobyl's output be postponed, as power wasneeded to satisfy the peak evening demand.

    The Chernobyl plant director agreed, and postponed the test

    According to plan, the test should have been finished during the dayshift, and the night shift would only have had to maintain decay heat

    cooling systems in an otherwise shut down plant.

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    At 1:23:04 a.m. the experiment began. Four (of eight total) MainCirculating Pumps (MCP) were active.

    The steam to the turbines was shut off, and a run down of the turbinegenerator began. The diesel generator started and sequentially pickedup loads, which was complete by 01:23:43.

    During this period, the power for the four MCPs was supplied by theturbine generator as it coasted down.

    As the momentum of the turbine generator decreased, the water flowrate decreased, leading to increased formation of steam voids (bubbles)in the core.

    This caused yet more water to flash into steam, giving yet a furtherpower increase. However, during almost the entire period of the

    experiment the automatic control system successfully counteractedthis positive feedback, continuously inserting control rods into the

    reactor core to limit the power rise.

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    Explosion begins .At 1:23:40, as recorded by the SKALAcentralized

    control system, an emergency shutdown of the reactor,which inadvertently triggered the explosion, wasinitiated

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    Immediate Impact- 203 people were

    hospitalized immediately.31 of them eventuallydied. Most of thesepeople were workers inthe plant or local


    - NW winds from the BlackSea carried the radiationfor miles in the followingdays. Scandinavian

    detectors picked up onthe abundance ofradiation, but the Sovietgovernment deniedeverything.

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    Death s

    AUNSCEARreport places the total confirmed deathsfrom radiation at 64 as of 2008.

    TheWorld Health Organization (WHO) estimates

    that the death toll could reach 4,000 civilian deaths while the Union of Concerned Scientists estimate that

    for the broader population there will be 50,000 excesscancer cases resulting in 25,000 excess cancer deaths.

    Other reports from environmental groups have putthe predicted death toll at between 30,000 and200,000 deaths

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    These were firemen who helped put out the fires and helpedclean up the radiation

    Most did not realize the dangers of radiation. Many later died from radiation, because they didnt wear

    protection. An estimated 8,000-20,000 to date have died (20% from

    suicide) Robots

    United States supplied Specifically designed to enter reactor core and help build the


    Approximately 300,000 to 600,000 liquidators were involved in thecleanup of the 30 km evacuation zone around the plant in the yearsfollowing the meltdown.

    The Clean Up

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    Cement sarcophagus built in the monthsafter disaster

    5,000 tons of sand thrown on top ofreactor core


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    Effects of


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    Effects of Radiation Belarusian doctors identify the following effectsfrom the Chernobyl disaster on the health oftheir people:

    100% increase in the incidence of cancer and

    leukemia 250% increase in congenital birth deformities

    1,000% increase in suicide in the contaminatedzones

    Chernobyl AIDS--the term doctors are using todescribe illnesses associated with the damagedone to the immune system

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    Other problems Food & Water


    Farmers have towatch the radiation levelin milk.

    FishCannot be eaten,as water absorbsradiation and fatsconcentrate it

    Radioactive Floods everyspring

    Lives ruined

    Suicide and depression Even healthy people were


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    Living in the contaminatedzone in Belarus today

    People must change their clothes twice a day, and may notwalk in the woods for more than two hours a month.

    Radiation level charts are printed in the newspapers anddictate decisions such as whether children can be allowed outto play.

    People are told to wash food at least five times in clean water,but nobody is told where this clean water is to be found.

    Cattle are not supposed to graze in areas where the grass isless than 10cm high so their mouths will not touch the earth.

    Most people find it impossible to follow these nearlyimpossible instructions, so they simply give up trying.

    There are also housing shortages in Belarus and the rest ofthe ex-Soviet Union. This is a problem because people have ahard time moving out of the contaminated zone, since thereare no other places to live.

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    The Chernobyl nuclear power plant is located next to thePripyat River, which feeds into the Dnipro River reservoir

    system, one of the largest surface water systems in Europe. The radioactive contamination of aquatic systems

    therefore became a major problem in the immediateaftermath of the accident.

    In the most affected areas of Ukraine, levels ofradioactivity (particularly radioiodine: I-131, radiocaesium:Cs-137 and radiostrontium: Sr-90) in drinking water causedconcern during the weeks and months after the accident.

    After this initial period, however, radioactivity in rivers andreservoirs was generally below guideline limits for safedrinking water.[92]

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    Bio-accumulation of radioactivity in fish resulted in concentrations(both in western Europe and in the former Soviet Union) that in manycases were significantly above guideline maximum levels forconsumption.

    Guideline maximum levels for radiocaesium in fish vary from country

    to country but are approximately 1,000 Bq/kg in the European Union.

    In the Kiev Reservoir in Ukraine, concentrations in fish were severalthousand Bq/kg during the years after the accident.

    In small "closed" lakes in Belarus and the Bryansk region of Russia,concentrations in a number of fish species varied from 100 to 60,000Bq/kg during the period 199092.

    The contamination of fish caused short-term concern in parts of theUK and Germany and in the long term (years rather than months) inthe affected areas of Ukraine, Belarus, and Russia as well as in parts ofScandinavia.[92]

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