Bioterra: Nuclear power plant accidents: listed and ranked since 1952

Satellite image of Fukushima Daiichi nuclear plant

Nuclear power plant accidents: Number three reactor of the Fukushima nuclear plant is seen burning after a blast following an earthquake and tsunami Photograph: Ho/DigitalGlobe

How often do nuclear power plants go wrong? How many accidents and incidents are there?
The explosions and nuclear fuel rods melting at Japan's Fukushima nuclear power plant, following the Sendai earthquake and tsunami last week, have caused fears of what will happen next. Today Japan's nuclear safety agency has raised the nuclear alert level for Japan from four to five - making it two levels lower than the Chernobyl disaster in 1986.
So far, the Japanese authorities have maintained that there is "no cause to fear a major nuclear accident".
We have identified 33 serious incidents and accidents at nuclear power stations since the first recorded one in 1952 at Chalk River in Ontario, Canada.
The information is partially from the International Atomic Energy Authority - which, astonishingly, fails to keep a complete historical database - and partially from reports. Of those we have identified, six happened in the US and five in Japan. The UK and Russia have had three apiece.
Using Google Fusion tables, we've put these on a map, so you can see how they're spread around the globe:
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But how serious are they? The International Atomic Energy Authority ranks them using a special International Nuclear Events Scale (INES) - ranging from 'anomaly' to 'major accident', numbered from 1 to 7.
The events at Fukushima are level 5, so far and there has only been one 7 in history: Chernobyl in 1986. You can see the full ranking system below and on the attached spreadsheet
What can you do with the data?

Data summary

Nuclear power station accidents and incidents
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Year	Incident	INES level	Country	IAEA description
2011	Fukushima	5	Japan	Reactor shutdown after the 2011 Sendai earthquake and tsunami; failure of emergency cooling caused an explosion
2011	Onagawa		Japan	Reactor shutdown after the 2011 Sendai earthquake and tsunami caused a fire
2006	Fleurus	4	Belgium	Severe health effects for a worker at a commercial irradiation facility as a result of high doses of radiation
2006	Forsmark	2	Sweden	Degraded safety functions for common cause failure in the emergency power supply system at nuclear power plant
2006	Erwin		US	Thirty-five litres of a highly enriched uranium solution leaked during transfer
2005	Sellafield	3	UK	Release of large quantity of radioactive material, contained within the installation
2005	Atucha	2	Argentina	Overexposure of a worker at a power reactor exceeding the annual limit
2005	Braidwood		US	Nuclear material leak
2003	Paks	3	Hungary	Partially spent fuel rods undergoing cleaning in a tank of heavy water ruptured and spilled fuel pellets
1999	Tokaimura	4	Japan	Fatal overexposures of workers following a criticality event at a nuclear facility
1999	Yanangio	3	Peru	Incident with radiography source resulting in severe radiation burns
1999	Ikitelli	3	Turkey	Loss of a highly radioactive Co-60 source
1999	Ishikawa	2	Japan	Control rod malfunction
1993	Tomsk	4	Russia	Pressure buildup led to an explosive mechanical failure
1993	Cadarache	2	France	Spread of contamination to an area not expected by design
1989	Vandellos	3	Spain	Near accident caused by fire resulting in loss of safety systems at the nuclear power station
1989	Greifswald		Germany	Excessive heating which damaged ten fuel rods
1986	Chernobyl	7	Ukraine (USSR)	Widespread health and environmental effects. External release of a significant fraction of reactor core inventory
1986	Hamm-Uentrop		Germany	Spherical fuel pebble became lodged in the pipe used to deliver fuel elements to the reactor
1981	Tsuraga	2	Japan	More than 100 workers were exposed to doses of up to 155 millirem per day radiation
1980	Saint Laurent des Eaux	4	France	Melting of one channel of fuel in the reactor with no release outside the site
1979	Three Mile Island	5	US	Severe damage to the reactor core
1977	Jaslovské Bohunice	4	Czechoslovakia	Damaged fuel integrity, extensive corrosion damage of fuel cladding and release of radioactivity
1969	Lucens		Switzerland	Total loss of coolant led to a power excursion and explosion of experimental reactor
1967	Chapelcross		UK	Graphite debris partially blocked a fuel channel causing a fuel element to melt and catch fire
1966	Monroe		US	Sodium cooling system malfunction
1964	Charlestown		US	Error by a worker at a United Nuclear Corporation fuel facility led to an accidental criticality
1959	Santa Susana Field Laboratory		US	Partial core meltdown
1958	Chalk River		Canada	Due to inadequate cooling a damaged uranium fuel rod caught fire and was torn in two
1958	Vinča		Yugoslavia	During a subcritical counting experiment a power buildup went undetected - six scientists received high doses
1957	Kyshtym	6	Russia	Significant release of radioactive material to the environment from explosion of a high activity waste tank.
1957	Windscale Pile	5	UK	Release of radioactive material to the environment following a fire in a reactor core
1952	Chalk River	5	Canada	A reactor shutoff rod failure, combined with several operator errors, led to a major power excursion of more than double the reactor's rated output at AECL's NRX reactor

International Nuclear Events Scale (INES)
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Level	Definition	People and environment	Radiological barriers & control	Defence in depth	Example
SOURCE: IAEA
7	Major accident	Major release of radio active material with widespread health and environmental effects requiring implementation of planned and extended countermeasures			Chernobyl, Ukraine, 1986
6	Serious accident	Significant release of radioactive material likely to require implementation of planned countermeasures.			Kyshtym, Russia, 1957
5	Accident with wider consequences	Limited release of radioactive material likely to require implementation of	• Severe damage to reactor core.		Windscale, UK, 1957; Three Mile Island, 1979
		some planned countermeasures • Several deaths from radiation	• 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
4	Accident with local consequences	• Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than	• Fuel melt or damage to fuel resulting in more than 0.1% release of core inventory.		FUKUSHIMA 1, 2011
		local food controls.	• Release of significant quantities of radioactive
		• At least one death from radiation.	material within an installation with a high probability of significant
			public exposure.
3	Serious incident	• Exposure in excess of ten times the statutory annual limit for workers.	• Exposure rates of more than 1 Sv/h in an operating area.	• Near accident at a nuclear power plant	Sellafield, UK, 2005
		• Non-lethal deterministic health effect (e.g., burns) from radiation.	• Severe contamination in an area not expected by design, with a	with no safety provisions remaining.
			low probability	• Lost or stolen highly radioactive sealed source.
			of significant public exposure.	• Misdelivered highly radioactive sealed source without adequate procedures in place to handle it.
2	Incident	• Exposure of a member of the public	• Radiation levels in an operating area	• Significant failures in safety provisions	Atucha, Argentina, 2005
		in excess of 10 mSv.	of more than 50 mSv/h.	but with no actual consequences.
		• Exposure of a worker in excess of the	• Significant contamination within the	• Found highly radioactive sealed
		statutory annual limits	facility into an area not expected by	orphan source, device or transport
			design	package with safety provisions intact.
				• Inadequate packaging of a highly
				radioactive sealed source.
1	Anomaly			• 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