fukushima - chernobyl

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    FUKUSHIMA DAIICHI

    NUCLEAR PLANT

    DISASTER.

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    Accident cause

    11/03/2011, 2:46 p.m. local

    time near the Japanese

    island of Honshu was an

    earthquake of 9 on the

    Richter scale.The quake had an impact

    on section of north-east

    coast of Japan where they

    are located a series of

    nuclear power plants(NPP).

    Nuclear reactors have

    been shut down properly.

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    NPP DAIICHI before the earthquake

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    Timing of Reactor Events

    Earthquake Begins Fri. 2:46 PM JSTReactor shuts down Fri. 2:48 PM JST

    Off-grid, diesels provide power Seconds later

    Reactor cooled by emergency systems After diesels start

    Tsunami fails diesel generators Fri. ~3:45 PM JST

    Battery powers control of steam-driven Reactor CoreIsolation Cooling (RCIC) and automatic depressurization

    After diesels fail

    Battery power exhausted Sat. ~12:00 AM JST

    Report of suppression pool (wet well) becoming saturated Sat. ~2:00 AM JST

    Containment pressure 0.6 MPa (0.4 MPa normal) Sat. ~2:00 AM JST

    Steam vented from reactor to Refueling Bay Sat. 5:30 AM JST

    Water level drops to top of active fuel -

    Core oxidation occurs, releasing hydrogen -

    Hydrogen Explosion/Deflagration Sat. 3:36 PM JST

    Seawater injection begins Sun 8:20 PM JST

    Slide 4

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    INSIDE A REACTOR

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    CORE

    Suppression Systems 21

    The Defense

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    SAFETYLEVELS OF

    RADIATION

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    CHERNOBYL NUCLEARPOWER PLANT DISASTER.

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    Chernobyl

    Built in1978-

    1979

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    CHERNOBYL NPP

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    25-26 April 1986

    Engineers on the evening shift

    at Chernobyl's number four

    reactor began an experiment to

    see whether the cooling pump

    system could still function using

    power generated from the

    reactor under low power should

    the auxiliary electricity supply

    fail.

    However, too many rods were

    lowered and output dropped too

    quickly, resulting in an almost

    complete shutdown.

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    Safety systems disabled

    Concerned by possible instability,

    engineers began to raise therods to increase output. At 0030

    the decision was taken to carry

    on. By 0100 power was still only

    at about 7%, so more rods were

    raised.

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    The engineers continued to

    raise rods. By 0123, power had

    reached 12% and the testbegan. But seconds later, power

    levels suddenly surged to

    dangerous levels.

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    With power at roughly 100 times

    normal, fuel pellets in the core

    began to explode, rupturing thefuel channels. At about 0124,

    two explosions occurred,

    causing the reactor's dome-

    shaped roof to be blown off and

    the contents to erupt outwards

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    The Disaster

    01:23:48

    1st explosion

    01:23:55

    2nd explosion

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    April 26, 1986: Chernobyl nuclear

    power plant Operator errors cause areactor explosion

    Explosion releases 190

    tons of radioactive

    gasses into the

    atmosphere Fire starts that lasts 10

    days

    People: 7 million lived in

    contaminated areas; 3million were children

    Wind: Carries radiation far

    distances

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