International Nuclear Event Scale

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.

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 (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, 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 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 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. The 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

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 epidemiological 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

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

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.
  • Davis-Besse Nuclear Power Station (United States), 2002; negligent inspections resulted in corrosion through 6 inches (15.24 cm) of the carbon steel reactor head leaving only 3⁄8 inch (9.5 mm) of stainless steel cladding holding back the high-pressure (~2500 psi, 17 MPa) reactor coolant.

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:

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:
  • Penly (Seine-Maritime, France) 5 April 2012; an abnormal leak on the primary circuit of the reactor n°2 was found in the evening of 5 April 2012 after a fire in reactor n°2 around noon was extinguished.[15]
  • 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.[16]
  • TNPC (Drôme, France), July 2008; leak of 18,000 litres (4,000 imp gal; 4,800 US gal) of water containing 75 kilograms (165 lb) of unenriched uranium into the environment.[17]

Level 0: Deviation

No safety significance.

Examples:

Out of scale

There are also events of no safety relevance, characterized as "out of scale".[21]

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.[22]
  • 29 September 1999: H.B. Robinson, United States: A tornado sighting within the protected area of the nuclear power plant.[23][24][25]
  • 5 March 1999: San Onofre, United States: Discovery of suspicious item, originally thought to be a bomb, in nuclear power plant.[26]

Criticism

Deficiencies in the existing INES have emerged through comparisons between the 1986 Chernobyl disaster and 2011 Fukushima nuclear disaster. Firstly, the scale is essentially a discrete qualitative ranking, not defined beyond event level 7. Secondly, it was designed as a public relations tool, not an objective scientific scale. Thirdly, its most serious shortcoming is that it conflates magnitude with intensity. David Smythe has proposed a new quantitative nuclear accident magnitude scale (NAMS).[27]

Nuclear experts say that the "INES emergency scale is very likely to be revisited" given the confusing way in which it was used in the 2011 Japanese nuclear accidents.[28]

See also

Notes and references

  1. ↑ "Event scale revised for further clarity". World-nuclear-news.org. 6 October 2008. Retrieved 13 September 2010.
  2. ↑ "Japan to raise Fukushima crisis level to worst". Retrieved 12 April 2011.
  3. ↑ "Japan raises nuclear crisis to same level as Chernobyl". Reuters. 12 April 2011.
  4. ↑ "Japan: Nuclear crisis raised to Chernobyl level". BBC News. 12 April 2011. Retrieved 12 April 2011.
  5. ↑ "Japan's government downgrades its outlook for growth". BBC News. 13 April 2011. Retrieved 13 April 2011. The death toll rose to over 15,000 with 8,206 missing and 5,363 injured the numbers are still rising.
  6. ↑ Krista Mahr (29 February 2012). "Fukushima Report: Japan Urged Calm While It Mulled Tokyo Evacuation". Time.
  7. ↑ 7.0 7.1 7.2 "The world's worst nuclear power disasters". Power Technology. 7 October 2013.
  8. ↑ Richard Black (18 March 2011). "Fukushima - disaster or distraction?". BBC. Retrieved 7 April 2011.
  9. ↑ Spiegelberg-Planer, Rejane. "A Matter of Degree". IAEA Bulletin. IAEA. Retrieved 16 March 2011.
  10. ↑ Canadian Nuclear Society (1989) The NRX Incident by Peter Jedicke
  11. ↑ The Canadian Nuclear FAQ What are the details of the accident at Chalk River's NRX reactor in 1952?
  12. ↑ FlohEinstein. "Versuchsatomkraftwerk Lucens". ENSI Bericht. ENSI. Retrieved 12 May 2014.
  13. ↑ G A M Webb et al. (March 2006). "Classification of events with an off-site radiological impact at the Sellafield site between 1950 and 2000, using the International Nuclear Event Scale". Journal of Radiological Protection 26 (1): 33–49. Bibcode:2006JRP....26...33W. doi:10.1088/0952-4746/26/1/002. PMID 16522943.
  14. ↑ Information on Japanese criticality accidents,
  15. ↑ (ASN) - 5 April 2012. "ASN:ASN has decided to lift its emergency crisis organisation and has temporarily classified the event at the level 1". ASN. Retrieved 6 April 2012.
  16. ↑ (AFP) – 10 août 2009. "AFP: Incident "significatif" à la centrale nucléaire de Gravelines, dans le Nord". Google.com. Retrieved 13 September 2010.
  17. ↑ River use banned after French uranium leak | Environment. The Guardian (2008-07-10). Retrieved on 2013-08-22.
  18. ↑ News | Slovenian Nuclear Safety Administration
  19. ↑ http://200.0.198.11/comunicados/18_12_2006.pdf (Spanish)
  20. ↑ http://www.jaea.go.jp/02/press2005/p06021301/index.html (Japanese)
  21. ↑ IAEA: "This event is rated as out of scale in accordance with Part I-1.3 of the 1998 Draft INES Users Manual, as it did not involve any possible radiological hazard and did not affect the safety layers."
  22. ↑
  23. ↑ "NRC: SECY-01-0071 – Expanded NRC Participation in the Use of the International Nuclear Event Scale" (PDF). US Nuclear Regulatory Commission. 25 April 2001. p. 8. Retrieved 13 March 2011.
  24. ↑ "SECY-01-0071-Attachment 5 - INES Reports, 1995-2000" (PDF). US Nuclear Regulatory Commission. 25 April 2001. p. 1. Retrieved 13 March 2011.
  25. ↑ Tornado sighting within protected area | Nuclear power in Europe. Climatesceptics.org. Retrieved on 2013-08-22.
  26. ↑ Discovery of suspicious item in plant | Nuclear power in Europe. Climatesceptics.org. Retrieved on 2013-08-22.
  27. ↑ David Smythe (12 December 2011). "An objective nuclear accident magnitude scale for quantification of severe and catastrophic events". Physics Today.
  28. ↑ Geoff Brumfiel (26 April 2011). "Nuclear agency faces reform calls". Nature.

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