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The Chernobyl Disaster

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Title: Slide 1 Author: ITS Labs Last modified by: jobellanca Created Date: 5/2/2004 8:10:44 PM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

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Title: The Chernobyl Disaster


1
The Chernobyl Disaster
  • Katherine Culp
  • Erin Meyer

http//mt.sopris.net/mpc/military/v/reactor.cherno
byl.jpg
2
The Irony
  • This accident Three Mile Island could only
    happen in a capitalistic society where they put
    profits ahead of safety.
  • Professor Alexandrov, president of the Soviet
    Academy of Sciences
  • Good Evening Comrades. All of you know that
    there has been a incredible misfortune the
    accident at the Chernobyl nuclear plant. It has
    painfully affected the Soviet people and shocked
    the international community. For the first time,
    we confront the real force of nuclear energy, out
    of control.
  • Soviet President Mikhail Gorbachev

3
Background How a Nuclear Reactor Works
  • Uranium-235 can easily undergo induced nuclear
    fission free neutron U-235 ? fission
  • Plutonium-239 can also be used
  • Reactor operates at critical state one neutron
    ejected from each fission ? another fission
  • Enriched uranium pellets arranged in long rods
  • Bundle of rods submerged in coolant (water)
  • Bundle must be at supercritical state

4
Nuclear Reactors
  • Supercritical state if left alone, uranium
    bundles would overheat and melt
  • Control rods control rate of reaction
  • Made of neutron-absorbing material
  • Can be raised or lowered into bundle
  • Raising ? more heat generated
  • Lowering ? less heat
  • Completely lowering ? shut down reaction

5
Nuclear Reactors
  • Bundle heats water to form steam
  • Steam drives a steam turbine
  • Turbine spins a generator to produce power
  • Containment vessel prevents leakage of
    radioactive material

6
RBMK Reactor Reactor Bolshoy Moshchnosty Kanalny
http//classroom.psu.ac.th/users/ssmarn/pplant/Nuc
lear/NPP8_files/image002.gif
7
RBMK Reactors
  • Only in Russia
  • Produce power and plutonium for military use
  • Design Flaws
  • In order to remove the fuel rods for reprocessing
    and obtaining plutonium, a crane is needed.
    However, this makes the reactor too tall for a
    containment shell, which would keep radioactive
    material from spreading in case of an accident.
  • Carbon moderator used instead of water. Carbon
    moderators have a tendency to catch fire.
    Moderators are used to slow down rapid neutrons.

8
Positive Void Coefficient
  • Positive void coefficient if the water in the
    reactor boils, steam bubbles are produced. In
    other reactors, excess steam pockets reduce
    nuclear activity and slow down the nuclear
    reaction. But in RBMK reactors, the nuclear
    reaction speeds up.
  • With a positive coefficient, a reactor is
    unstable at low power and is susceptible to a
    rapid power surge that is uncontrollable.
  • In reactors with positive void coefficients, the
    moderator and coolant are in separate circuits or
    are different materials. However, RBMK reactors
    have no modifications to prevent the rapid,
    uncontrollable power surge that can be produced
    by a positive void coefficient.
  • There are 13 RBMK reactors in the world still
    operating today.

9
Construction Flaws
  • Gross deviations were present in the construction
    of the RBMK reactors at the Chernobyl plant.
  • The foundation was not poured properly, so there
    were gaps in the foundation which could allow for
    leakage.
  • Roof placement did not conform to design
    specifications.
  • There was also damage to the waterproofing, which
    could allow for radioactive contamination of
    groundwater. The damage was backfilled instead
    of repaired.

10
An Experiment
  • Reactor 4 was shut down for routine maintenance,
    and workers decided to run a test to determine
    if, during a shutdown, enough electrical power
    could operate the emergency equipment and core
    cooling pumps until the diesel supply returned.
  • Communication between group in charge of test and
    group operating the nuclear reactor broke down.
  • The emergency core cooling system was turned off
    reactor operated at ½ power.
  • The reactor stabilized at 1,000 MW, but operator
    error caused the power to drop to 30 MW, a power
    at which the positive void coefficient can be a
    problem.

11
April 26, 1986
  • Operators stabilized the system by withdrawing
    almost all the control rods. A minimum of 30
    control rods is required only 6-8 were left in
    place. If a power surge were to take place,
    operators would only have 20 seconds to lower the
    rods and to shut down the reactor
  • Reactor became extremely unstable operators had
    to make adjustments every few seconds in order to
    keep the power constant.
  • Operators decided to reduce the flow of water so
    that they could maintain the steam pressure.
    Turbine slowed ? pumps not providing as much
    cooling for the reactor.
  • More steam was created in the cooling channels ?
    power surge about 100 times the normal power.
  • Power surge ? steam explosion which blew off the
    top off of the reactor. A second explosion took
    place a few seconds later its origin is not
    understood.
  • Carbon moderator caught on fire burned for nine
    days.

12
Initial Release of Radiation
  • When Reactor 4 went supercritical and exploded
    there was a mechanical discharge of dispersed
    radioactive fuel, meaning that a plume of
    radioactive elements was released into the
    atmosphere. This release was made up of isotopes
    that closely corresponded to the fission
    products of spent fuel, including 89,90S, 131I,
    and 134,137Cs, which made up the largest part of
    the initial emissions.

13
The Days After the Accident
  • From April 26th to May 1st the rate of
    radioactive element release decreased because the
    core was covered with boron, lead, and sand in an
    attempt to extinguish the fire that had begun
    during the explosion.
  • This covering of the core, however, led to
    temperatures in the core increasing and to
    release of more radiation in the form of 131I.
    Estimates indicate that 50 of the cores 131I
    was released.

14
Soviet Disclosure
  • The Soviets did not initially inform other
    nations of the disaster. The first indication
    European nations had that a large-scale nuclear
    disaster had taken place was when nuclear plants
    in Scandinavia began to register unusually high
    levels of background radiation. The Soviets
    denied all knowledge about the accident for
    several days. Full disclosure was not made until
    August of 1986

15
Soviet Evacuation
  • The Soviet authorities did not evacuate the
    villages that surrounded Chernobyl until April
    27. At that time they also provided iodine
    supplements for the evacuated residents. These
    supplements are supposed to help prevent thyroid
    cancer by filling the thyroid with nonradioactive
    iodine so it doesnt take up the radioactive
    forms.

16
Soviet Response to Chernobyl
  • The Soviet authorities sent in cleanup crews to
    supplement the workers already in Chernobyl. Of
    those who were sent in to contain the fires and
    radiation damage, 29 died from intense ß burns.
    There were also reports of 237 cases of acute
    radiation sickness in the surrounding areas.
    Later research has questioned these numbers, and
    there is some evidence that the Soviets grossly
    underestimated the number of people made ill by
    the explosion and the subsequent release of
    radioactive isotopes.

17
Effects on the World
  • Chernobyl released radiation high into the
    atmosphere, where it eventually was carried
    across Europe. The amount of radioactive
    elements varied country by country, according to
    their proximity to the Ukraine and also
    meteorological patterns. Countries that received
    a lot of rainfall in the days after the explosion
    tended to have higher levels of radiation due to
    the elements being sent out in fine aerosol
    form that was best carried by a liquid medium.

18
Long-term effects
  • Using risk models, researchers have estimated
    that the risk of developing cancer is doubled in
    those who were within a thirty-mile radius of
    Chernobyl.
  • The modeled risks for those in Europe are
    considered statistically insignificant.

19
Health Effects
  • Researchers in 1996 indicated that, out of 235
    villagers in the area of Chernobyl at the time of
    the explosion, 35 had died of cancer. Many
    survivors suffer from possibly radiation-influence
    d conditions such as goiter and diabetes.
  • A Russian Health Ministry report from the same
    time indicates that half of the children in the
    areas irradiated by the fallout show signs of
    radiation sickness, including anemia, kidney
    failure, and lymph gland inflammation.
  • A Ukrainian biologists study indicates that 8500
    of those who went in to clean up the radiation
    hot spots had died by the mid 1990s.

20
The Chernobyl Legacy
  • After covering Reactor 4 with a cement
    sarcophagus that was intended to seal up the
    radioactive elements, the Soviets continued to
    operate the other reactors at Chernobyl.
  • By the mid-90s the sarcophagus was crumbling and
    international workers had to go into Chernobyl
    and reinforce it.
  • The last reactor was shut down in late 2000.
  • People are still not allowed to live in an
    eighteen mile radius from Chernobyl.

21
Sources
  • Anspaugh, Lynn R., et al. The Global Impact of
    the Chernobyl Reactor Accident. Science,
    242(Dec., 1988), 1513-1519.
  • ApSimon, Helen, et. al. Analysis of the
    Dispersal and Deposition of Radionuclides from
    Chernobyl Across Europe. Proceedings of the
    Royal Society of London. 425(Oct, 1989), 365-405
  • Brain, Marshall. How Nuclear Power Works.
    http//science.howstuffworks.com/nuclear-power.htm
  • Chernobyl Assessment of Radiological and Health
    Impact. Nuclear Energy Agency.
    http//www.nea.fr/html/rp/chernobyl/c01.html
  • Chernobyl Nuclear Disaster. http//www.chernobyl
    .co.uk
  • Dahlburg, John-Thor. Study Finds Chernobyl
    Radiation Worse than Originally Reported. Los
    Angeles Times. April 14, 1992, pg. 2
  • Fire near Chernobyl reported out. CNN.com,
    April 1996. http//www.cnn.com/WORLD/9604/23/chern
    obyl.htm
  • McCarthy, John. Chernobyl. http//www-formal.st
    anford.edu/imc/progress/chernobyl.html
  • The RMBK Reactor World Nuclear Association.
    http//www.world-nuclear.org/info/inf31.htm
  • Wilson, Richard. A Visit to Chernobyl.
    Science, 236(June, 1987), 1636-1640.
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