International Nuclear Event Scale, 2011 Japan Nuclear Disaster

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International Nuclear Event Scale

  • Introduced in 1990 by IAEA

  • Enables prompt communication of safety significance in case of nuclear accidents

  • Logarithmic

  • There are 7 levels: 3 incident levels and 4 accident levels

  • Level 7 – Major accident: Chernobyl, 1986

  • Level 6 – Kyshtym disaster (Mayak, Soviet Union), 1957

  • Level 5 – Three Mile Island US, 1979; Wind scale Fire (UK), 1957

Image of International Nuclear Event Scale

Image of International Nuclear Event Scale

Chernobyl Disaster

Three Mile Island Disaster

2011 Japan Nuclear Disaster

  • At the three reactor units at the Fukushima Daiichi nuclear power station

  • Located in the town of Okuma in the Futaba District of Fukushima Prefecture, Japan. Combined capacity of 4.7 GW.

  • What caused it?

    • The earthquake caused a power failure

    • The subsequent tsunami knocked out the generators that produced the power

    • Lack of power in turn caused the cooling systems of the reactors to fail

    • This led to a partial meltdown in the three reactors

  • Background

    • Fukushima 1 reactor went critical in 1971

    • All the three are Boiling Water Reactors (BWR) and use demineralised water for cooling nuclear fuel

  • Methods that can be adopted to avoid a meltdown

    • Pump sea water to reduce the heat

    • Boric acid is an excellent neutron absorber. Using it would reduce the chances of nuclear reactions restarting even if the fuel is found loose inside the reactor core.

Nuclear Safety

  • The disaster has re-ignited the debate on the safety of nuclear power

  • AERB should be made an independent regulator


  • Ring of fire in the pacific ocean

  • Largest Earthquakes by Magnitude

    • Valdivia, Chile, 1960: 9.5

    • Prince Sound William, Alaska, 1964: 9.2

    • Sumatra, Indonesia, 2004: 9.1

    • Kamchatka, USSR, 1952: 9

    • Sendai, Japan, 2011: 9


  • Intensity measured by the Soloviev-Imamura tsunami intensity scale.

  • Major Tsunamis

    • 2011: Japan

    • 2004: Indian Ocean

    • 1908: Messina, Italy

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