The
International Nuclear and Radiological Event Scale (
INES) was introduced in 1990
[1] by the
International Atomic Energy Agency (IAEA) in order to enable prompt communication of
safety-significant information in case of
nuclear accidents.
The scale is intended to be
logarithmic, similar to the
moment magnitude scale that is used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident approximately ten times more severe than the previous level. Compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a
man-made disaster, such as a nuclear accident, is more subject to interpretation. Because of the difficulty of interpreting, the INES level of an incident is assigned well after the incident occurs. Therefore, the scale has a very limited ability to assist in disaster-aid deployment.
Level 7: Major accident
Impact on people and environment : Major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures
There have been two such events to date:
- Chernobyl disaster, Soviet Union,26 April 1986. A power surge during a test procedure resulted in a criticality accident, leading to a powerful steam explosion and fire that released a significant fraction of core material into the environment, resulting in a death toll of 56 as well as estimated 4,000 additional cancer fatalities (official WHO estimate) among people exposed to elevated doses of radiation. As a result, the city of Chernobyl (pop. 14,000) was largely abandoned, the larger city of Pripyat (pop. 49,400) was completely abandoned, and a permanent 30 kilometres (19 mi) exclusion zone around the reactor was established.
- Fukushima Daiichi nuclear disaster,Japan a series of events beginning on 11 March 2011. A month later the Japanese government's nuclear safety agency rated it level 7.[2][3]Major damage to the backup power and containment systems caused by the 2011 Tōhoku earthquake and tsunami resulted in overheating and leaking from some of the Fukushima I nuclear plant's reactors. Each reactor accident was rated separately; out of the six reactors, three were rated level 5, one was rated at a level 3, and the situation as a whole was rated level 7.[4] A temporary exclusion zone of 20 kilometres (12 mi) was established around the plant as well as a 30 kilometres (19 mi) voluntary evacuation zone;[5] In addition, the evacuation of Tokyo – Japan's capital and the world's most populous metropolitan area, 225 kilometres (140 mi) away – was at one point considered.[6] See also
Level 6: Serious accident
Impact on people and environment
Significant release of radioactive material likely to require implementation of planned countermeasures.
There has been only one such event to date:
- Kyshtym disaster at Mayak Chemical Combine (MCC.) Soviet Union, 29 September 1957. A failed cooling system at a military nuclear waste reprocessing facility caused a steam explosion with a force equivalent to 70-100 tons of TNT. About 70 to 80 metric tons of highly radioactive material were carried into the surrounding environment. Impact on local population is not fully known, but at least 22 villages were affected with deadly doses.[7]
Level 5: Accident with wider consequences[edit]
Impact on people and environment
Limited release of radioactive material likely to require implementation of some planned countermeasures.
Several deaths from radiation.
Impact on radiological barriers and control
Severe damage to reactor core.
Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.
Examples:
[7]
- Windscale fire (United Kingdom), 10 October 1957.[8] Annealing of graphite moderator at a military air-cooled reactor caused the graphite and the metallic uranium fuel to catch fire, releasing radioactive pile material as dust into the environment.
- Three Mile Island accident near Harrisburg, Pennsylvania (United States), 28 March 1979.[9] A combination of design and operator errors caused a gradual loss of coolant, leading to a partial meltdown. An unknown amount of radioactive gases were released into the atmosphere, so injuries and sicknesses that have been attributed to this accident can be deduced from epidemiolgical studies but can never be proven.
- First Chalk River accident,[10][11] Chalk River, Ontario (Canada), 12 December 1952. Reactor core damaged.
- Lucens partial core meltdown (Switzerland), 21 January 1969. A test reactor built in an underground cavern suffered a loss-of-coolant accident during a startup, leading to a partial core meltdown and massive radioactive contamination of the cavern, which was then sealed.[12]
- Goiânia accident (Brazil), 13 September 1987. An unsecured caesium chloride radiation source left in an abandoned hospital was recovered by scavenger thieves unaware of its nature and sold at a scrapyard. 249 people were contaminated and 4 died.
Level 4: Accident with local consequences[edit]
Impact on people and environment
Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls.
At least one death from radiation.
Impact on radiological barriers and control
Fuel melt or damage to fuel resulting in more than 0.1% release of core inventory.
Release of significant quantities of radioactive material within an installation with a high probability of significant public exposure.
Examples:
[7]
Level 3: Serious incident[edit]
Impact on people and environment
Exposure in excess of ten times the statutory annual limit for workers.
Non-lethal deterministic health effect (e.g., burns) from radiation.
Impact on radiological barriers and control
Exposure rates of more than 1
Sv/h in an operating area.
Severe contamination in an area not expected by design, with a low probability of significant public exposure.
Impact on
defence in depth
Near accident at a nuclear power plant with no safety provisions remaining.
Lost or stolen highly radioactive sealed source.
Misdelivered highly radioactive sealed source without adequate procedures in place to handle it.
Examples:
