Mayak or Kyshtym nuclear complex (Soviet Union): 29
September 1957
A fault
in the cooling system at the nuclear complex, near Chelyabinsk, results in a
chemical explosion and the release of an estimated 70 to 80 tonnes of
radioactive materials into the air. Thousands of people are exposed to
radiation and thousands more are evacuated from their homes. It is categorised
as Level 6 on the seven-point International Nuclear Events Scale (INES).
Windscale nuclear reactor (UK): 7 October 1957
A fire in
the graphite-core reactor, in Cumbria, results in a limited release of
radioactivity (INES Level 5). The sale of milk from nearby farms is banned for
a month. The reactor cannot be salvaged and is buried in concrete. A second
reactor on the site is also shut down and the site decontaminated. Subsequently
part of the site is renamed Sellafield and new nuclear reactors are built.
Idaho National Engineering Laboratory (USA): 3
January 1961
A steam
explosion in reactor SL-1 during preparation for start-up destroys the small US
Army experimental reactor and kills three operators.
Three Mile Island power plant, Pennsylvania (US):
29 March 1979
A cooling
malfunction causes a partial meltdown in one reactor, resulting in a limited
release of radioactivity (INES Level 5).
The
site's first reactor (TMI One) on the Susquehanna river was closed for
refuelling. The second was at full capacity when two malfunctions occurred:
first there was a release of radioactive water, then radioactive gas was
detected on the perimeter. No deaths or injuries were reported.
It is
considered the United States' worst nuclear accident and led to major safety
changes in the industry.
Chernobyl power plant (Soviet Union): 26 April 1986
One of
four reactors explodes after an experiment at the power plant (INES Level 7).
The resulting fire burns for nine days and at least 100 times more radiation
than the atom bombs dropped on Nagasaki and Hiroshima is released into the air.
Radioactive deposits are found in nearly every country in the northern
hemisphere.
Two
people die in the explosion and another 28 from acute radiation sickness in the
immediate aftermath. Some experts predict thousands of extra cancer deaths as a
result of the disaster.
A huge
cover, known as the New Safe Confinement, is being built over the existing
sarcophagus. It is expected to cover the site by 2013.
Severesk, formerly Tomsk-7 (Russia): 6 April 1993
A tank at
a uranium and plutonium factory inside the plant explodes, resulting in
radioactivity being dispersed into the atmosphere contaminating an area of over
120 sq km (INES Level 4). A number of villages are evacuated and left
permanently uninhabitable.
Tokaimura nuclear fuel processing facility (Japan):
30 September 1999
Workers
break safety regulations by mixing dangerously large amounts of treated uranium
in metal buckets, setting off a nuclear reaction (INES Level 4).
Two of
the workers later die from their injuries, and more than 40 others are treated
for exposure to high levels of radiation.
Hundreds
of residents living nearby were evacuated from their homes while the nuclear
reaction continued, but were allowed home two days later.
Mihama power plant (Japan): 9 August 2004
Five
people die in an accident at the plant in the Fukui province (INES Level 1).
Seven people are also injured when hot water and steam leaks from a broken
pipe.
Officials
insist that no radiation leaked from the plant, and there is no danger to the
surrounding area.
Fukushima Daiichi power plant (Japan): 11 March
2011
A
powerful tsunami generated by a magnitude-9.0 earthquake out at sea slams into
the Fukushima Daiichi nuclear power plant, damaging four of six reactors at the
site.
A series
of fires are set off, after cooling systems fail. Venting hydrogen gas from the
reactors causes explosions, forcing engineers to use seawater in an effort to
cool overheating reactor cores.
Originally
classified as INES Level 5, the severity was raised to INES Level 7 on 12 April
2011 when a new estimate suggested higher levels of radiation than previously
thought had leaked from the plant.
Despite
the classification, the incident is said to be much less severe than Chernobyl,
and officials insist there is only a minimal risk to public health.
Macoule nuclear site (France), 12 September 2011
One
person is killed and four are injured - one with serious burns - after an
explosion in a furnace used to melt down nuclear waste and recycle it for
energy. No radiation leaks nor damage to the plant are detected.
