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:

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 Click heading to sort table. Download this data 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) Click heading to sort table. Download this data Level Definition People and environment Radiological barriers & control Defence in depth Example 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

• DATA: download the full spreadsheet

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