exploded sending a radioactive cloud across
Europe.]]
The International Nuclear and Radiological Event Scale (INES) was introduced in 1990 by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significance 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.
As INES ratings are not assigned by a central body, high-profile nuclear incidents are sometimes assigned INES ratings by the operator, by the formal body of the country, but also by scientific institutes, international authorities or other experts which may lead to confusion as to the actual severity.
Details
A number of criteria and indicators are defined to assure coherent reporting of
nuclear events by different official authorities. There are seven nonzero levels on the INES scale: three
incident-levels and four
accident-levels. There is also a level 0.
The level on the scale is determined by the highest of three scores: off-site effects, on-site effects, and defence in depth degradation.
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, 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 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 30 km exclusion zone was established.
:* Fukushima Daiichi nuclear disaster, a series of events beginning on 11 March 2011. Rated level 7 on 11 April 2011 by the Japanese government's nuclear safety agency. 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. An exclusion zone of 20 km was established around the plant as well as a 30 km voluntary evacuation zone. See also 2011 Japanese nuclear accidents.
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, Soviet Union, 29 September 1957. A failed cooling system at a military nuclear waste reprocessing facility caused a steam explosion that released 70–80 tons of highly radioactive material into the environment. Impact on local population is not fully known. This is the only accident to go over 5 on the scale besides Chernobyl and Fukushima.
Level 5: Accident with wider consequences
; 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:
:* Windscale fire (United Kingdom), 10 October 1957. 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. A combination of design and operator errors caused a gradual loss of coolant, leading to a partial meltdown. Radioactive gases were released into the atmosphere.
:* First Chalk River accident, 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.
:* 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
; 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:
:* Sellafield (United Kingdom) – five incidents 1955 to 1979
:* SL-1 Experimental Power Station (United States) – 1961, reactor reached prompt criticality, killing three operators.
:* Saint-Laurent Nuclear Power Plant (France) – 1969, partial core meltdown; 1980, graphite overheating.
:* Buenos Aires (Argentina) – 1983, criticality accident during fuel rod rearrangement killed one operator and injured 2 others.
:* Jaslovské Bohunice (Czechoslovakia) – 1977, contamination of reactor building.
:* Tokaimura nuclear accident (Japan) – 1999, three inexperienced operators at a reprocessing facility caused a criticality accident; two of them died.
Level 3: Serious incident
; 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:
:* THORP plant Sellafield (United Kingdom) – 2005.
:* Paks Nuclear Power Plant (Hungary), 2003; fuel rod damage in cleaning tank.
:* Vandellos Nuclear Power Plant (Spain), 1989; fire destroyed many control systems; the reactor was shut down.
Level 2: Incident
; Impact on people and environment: Exposure of a member of the public in excess of 10 mSv.
: Exposure of a worker in excess of the statutory annual limits.
; Impact on radiological barriers and control: Radiation levels in an operating area of more than 50 mSv/h.
: Significant contamination within the facility into an area not expected by design.
; Impact on defence-in-depth: Significant failures in safety provisions but with no actual consequences.
: Found highly radioactive sealed orphan source, device or transport package with safety provisions intact.
: Inadequate packaging of a highly radioactive sealed source.
:Examples:
:* Blayais Nuclear Power Plant flood (France) December 1999
:* Ascó Nuclear Power Plant (Spain) April 2008; radioactive contamination.
:* Forsmark Nuclear Power Plant (Sweden) July 2006; backup generator failure.
Level 1: Anomaly
; Impact on defence-in-depth: Overexposure of a member of the public in excess of statutory annual limits.
: Minor problems with safety components with significant defence-in-depth remaining.
: Low activity lost or stolen radioactive source, device or transport package.
(Arrangements for reporting minor events to the public differ from country to country. It is difficult to ensure precise consistency in rating events between INES Level-1 and Below scale/Level-0)
:Examples:
:* Gravelines (Nord, France), 8 August 2009; during the annual fuel bundle exchange in reactor #1, a fuel bundle snagged on to the internal structure. Operations were stopped, the reactor building was evacuated and isolated in accordance with operating procedures.
:* TNPC (Drôme, France), July 2008; leak of of water containing of uranium into the environment.
Level 0: Deviation
No safety significance.
:Examples:
:* 4 June 2008: Krško, Slovenia: Leakage from the primary cooling circuit.
:* 17 December 2006, Atucha, Argentina: Reactor shutdown due to tritium increase in reactor compartment.
:* 13 February 2006: Fire in Nuclear Waste Volume Reduction Facilities of the Japanese Atomic Energy Agency (JAEA) in Tokaimura.
Out of scale
There are also events of no safety relevance, characterized as "out of scale".
:Examples:
:* 17 November 2002, Natural Uranium Oxide Fuel Plant at the
Nuclear Fuel Complex in Hyderabad, India: A chemical explosion at a fuel fabrication facility.
:* 29 September 1999:
H.B. Robinson, United States: A tornado sighting within the protected area of the
nuclear power plant (NPP).
:* 5 March 1999:
San Onofre, United States: Discovery of suspicious item, originally thought to be a bomb, in nuclear power plant.
See also
Nuclear meltdown
*Core damage frequency
*Fuel element failure
*Loss-of-coolant accident
Nuclear power
Nuclear power debate
Radioactive contamination
Radioactive waste
Nuclear and radiation accidents
*Lists of nuclear disasters and radioactive incidents
*List of civilian nuclear accidents
*List of civilian radiation accidents
*List of military nuclear accidents
**United States military nuclear incident terminology
List of nuclear reactors
Nuclear safety
References
External links
Nuclear Events Web-based System (NEWS), IAEA
International Nuclear Event Scale factsheet, IAEA
International Nuclear Event Scale, User's manual, IAEA, 2008
Category:Nuclear accidents
Category:Civilian nuclear power accidents
Category:Nuclear safety
Category:Hazard scales
