Japan’s Fukushima nuclear crisis upgraded to level 7 on the INES

By Dorothy Davis  

Japan’s Nuclear and Industrial Safety Agency (NISA) has upgraded the Fukushima nuclear crisis to level 7, the highest point on the International Nuclear and Radiological Event Scale (INES).

The INES rating increase for the Fukushima nuclear complex from 5 (Accident with wider consequences) to 7 (Major accident), is not related to the recent high magnitude aftershocks that continue to batter Japan, but are the result of reassessments of the cumulative events that have occurred at the complex since March 11.

In a statement NISA said: "As a result of re-evaluation, total amount of discharged iodine-131 is estimated at 1.3x1017 becquerels, and caesium-137 is estimated at 6.1x1015 becquerels. Hence the Nuclear and Industrial Safety Agency has concluded that the rating of the accident would be equivalent of Level 7."

For comprehensive coverage of the Japanese nuclear power disaster and efforts under way to resolve it, visit PennEnergy’s Japan Earthquake and Nuclear Emergency 2011 special section. 

Before today, only the Chernobyl nuclear accident had been rated at the maximum level on the INES scale, however, it is important to understand that the INES scale is not designed to rate an ongoing nuclear crisis. Until an accident has been fully resolved, a rating is subject to change.

The INES scale was officially adopted by the International Atomic Energy Agency (IAEA) in 1990 to classify events at nuclear power plants, and then extended to enable it to be applied to all installations associated with the civil nuclear industry. By 2006, it had been adapted to meet the growing need for communication of the significance of all events associated with the transport, storage and use of radioactive material and radiation sources.

The IAEA explains that just like information on earthquakes or temperature would be difficult to understand without the Richter or Celsius scales, the INES Scale explains the significance of events from a range of activities and functions as a worldwide tool to communicate the safety significance of nuclear and radiological events after retrospective analysis.

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