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The Japanese nuclear safety agency rated the damage at a nuclear power plant at Fukushima at a four on a scale of one to seven, which is not quite as bad as the Three Mile Island accident in the United States in 1979, which registered a five.But what does that mean? The International Atomic Energy Agency – an inter-governmental organization for scientific co-operation in the nuclear field – said it uses the scale to communicate to the public in a consistent way the safety significance of nuclear and radiological events.
The International Nuclear and Radiological Event Scale, or INES, ranges from one to seven with the most serious being a seven referred to as a “major accident,” while a one is an “anomaly.” The scale is designed so the severity of an event is about 10 times greater for each increase in level.
The following are some examples of accidents according to their INES level from the IAEA.
Level 7 - Major Accident:
A major release of radioactive material with widespread health and environmental effects, requiring implementation of planned and extended countermeasures.
Chernobyle, Soviet Union (now Ukraine), 1986
Level 6 - Serious accident:
A significant release of radioactive material likely to require implementation of planned countermeasures.
Kyshtymk , Soviet Union (now Russia), 1957 – Significant release of radioactive material to the environment from explosion of high activity waste tank
Level 5 - Accident with wider consequences:
A limited release of radioactive material likely to require implementation of some planned countermeasures and several deaths from radiation.
Three Mile Island, USA, 1979 - Severe damage to reactor core. This event galvanized opposition to a growing anti-nuclear power movement in the United States. After
this event, energy companies did not start the construction of any new reactors in the United States for over 30 years and stopped work on several reactors that were already under construction.
Windscale Pile, UK, 1957 - A release of radioactive material following a fire in a reactor core * Goiania, Brazil, 1987 - Four people died and six people received high doses of radiation.
Level 4 - Accident with local consequences:
A minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls and fuel melt or damage to fuel resulting in more than 0.1 per cent release of core inventory and the release of significant quantities of radioactive material within an installation with a high probability of significant public exposure.
Tokaimura, Japan, 1999 - Fatal overexposures of workers following a criticality event at a nuclear facility.
Saint Laurent Des Eaux, France, 1980 - Melting of one channel of fuel in the reactor with no release outside the site.
Eleurus, Belgium, 2006 - Severe health effects for worker at a commercial irradiation facility as a result of high doses of radiation.
