Japan’s Fukushima Daiichi Nuclear Power Plant, damaged by the March 11, 2011 earthquake and tsunami, represented another disaster in a listing of 9 major nuclear accidents rated on the IAEA’s International Nuclear and Radiological Event Scale (INES) as the worst the world has seen…so far.
10. Mihama Nuclear Power Plant, Japan, 2004 (INES 1)
Image via: Ayumu Kawazoe
The INES scale introduced in 1990 by the International Atomic Energy Agency (IAEA) is logarithmic, with each increasing level representing an accident approximately ten times more severe than the previous level - similar to the Richter scale used to judge the magnitude of earthquakes. Therefore our listing of the World’s Worst Nuclear Accidents begins with the August 9, 2004 steam explosion at Japan’s Mihama Nuclear Power Plant, given an INES rating of 1.
The Mihama Nuclear Power Plant is located in Japan’s Fukui prefecture about 320 km (about 200 miles) west of Tokyo. The plant, which was commissioned in 1976, was the site of several small nuclear-related accidents in 1991 and 2003. On August 9 of 2004, a water pipe in a turbine building adjoining the Mihama 3 reactor burst suddenly as workers prepared to conduct a routine safety inspection. Though no radiation was released, the steam explosion killed 5 plant workers and injured dozens of others. Mihama’s notoriety increased in 2006 when 2 plant workers were injured in an on-site fire.
9. Davis-Besse Reactor, USA, 2002 (INES 3)
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The Davis-Besse Nuclear Power Station, located about 10 miles (16km) north of Oak Harbour, Ohio, was commissioned in July of 1978 and is scheduled for final shutdown in April of 2017.
Image via: Ohio Citizen Action
The plant has racked up a number of safety problems over its lifetime, including being struck by an F2 tornado in 1998, but the worst of those occurred in March of 2002 when a serious corrosion issue forced the plant to close for roughly 2 years.
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During maintenance, plant workers discovered a 6-inch deep corrosion hole in the top of the carbon steel reactor vessel. Only 3/8” of steel cladding remained to prevent a catastrophic pressure explosion and subsequent loss of coolant. If nearby control rod mechanisms would have been damaged in the explosion, shutting down the reactor and avoiding a core meltdown would have been difficult to say the least.
8. National Reactor Testing Station, USA, 1961 (INES 4)
One of the earliest major nuclear power plant accidents occurred on January 3, 1961 when a steam explosion and meltdown killed 3 workers at Stationary Low-Power Reactor Number One (SL-1). The reactor, located at the National Reactor Testing Station roughly 40 miles (60km) west of Idaho Falls, Idaho, was of a now-discontinued design that featured a single large, central control rod.
A maintenance procedure that involved withdrawing the control rod about 4 inches (10cm) somehow went horribly wrong: the rod was lifted 26 inches (65cm) and the nuclear pile went critical. Three plant workers were killed in the resulting explosion and radiation release; one man was found impaled to the reactor building’s ceiling by one of the reactor’s shield plugs. About 1,100 Curies of nuclear fission products were released into the surrounding environment but any damage was mitigated by the station’s remote location in the Idaho desert. In the image above at top, you can see the damaged reactor core being lifted out of the containment building by a heavily shielded crane.
7. Jaslovské Bohunice, Czechoslovakia, 1977 (INES 4)
Image via: Kyberia
Talk about accidents waiting to happen. At the Bohunice Nuclear Power Plant in Jaslovské Bohunice, Czechoslovakia (now Slovakia), all the ingredients for a nuclear disaster were already in place by 1977 when A1, the plant’s oldest reactor, overheated and nearly caused a large-scale environmental disaster. Where to begin? Let’s see…the model KS-150 reactor was of a unique and unproven design from the Soviet Union which was built in Czechoslovakia. Not a good start, and then it gets worse.
Construction of A1 began in 1958 and took an amazing 16 years! The untested design of the KS-150 reactor soon revealed numerous flaws that led to over 30 unplanned shutdowns in the first few years of operation. Two workers were killed by a gas leak in early 1976. Just over a year later a botched fuel changing procedure compounded by human error - workers forgot to remove silica gel packs from the new fuel rods - resulted in a core cooling emergency. It’s expected that on-going efforts to decontaminate and fully decommission the A1 reactor won’t be completed until sometime in 2033.
6. Tomsk-7 Reprocessing Complex, USSR, 1993 (INES 4)
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The Siberian Group of Chemical Enterprises is a group of factories and nuclear power plants located in the Russian city of Seversk. Formerly a Soviet “secret city”, Seversk was until 1992 known as Tomsk-7, which is actually a post office box number. Though former Russian president Boris Yeltsin relaxed some of the restrictions on Seversk (including its name), to this day non-residents are not allowed to visit the city.
The Tomsk-7 Reprocessing Complex was one of the “enterprises” at Seversk, and on April 6, 1993, the facility achieved some very unwanted fame. Workers were cleaning out an underground tank at the Tomsk-7 Plutonium Reprocessing Plant using highly volatile Nitric Acid. The acid reacted with residual liquid inside the tank - liquid that contained traces of plutonium. An explosion then occurred which blew a reinforced concrete lid off the top of the tank, punched holes in the building’s roof, short-circuited the plant’s electrical systems and started a fire. Last and not least, the explosion released of a large cloud of radioactive gas into the surrounding environment.
5. Tokaimura Uranium Processing Facility, Japan, 1999 (INES 4)
Image via: LiveInternet
Human error compounded by rash business decisions led to the so-called Tokaimura Criticality Accident, which took place on September 30, 1999, at Japan’s Tokaimura Uranium Processing Facility in Japan’s Ibaraki prefecture north of Tokyo. The facility, formerly operated by JCO Ltd., processed and purified Uranium fuel used by Japan’s many nuclear power plants.
The accident was caused by poorly trained workers at the Tokaimura plant taking shortcuts in the refining procedure. Under pressure to complete their duties on time, the workers skipped several steps in the process. Uranium Oxide powder and Nitric Acid were mixed in 10-litre buckets instead of several dedicated tanks, and ended up dumping 7 times the recommended amount of Uranium/Acid mixture to a precipitation tank. The mixture reached critical mass and a chain reaction lasting 20 hours then ensued. Two of the plant workers died from radiation exposure and dozens of others were exposed to above-normal levels of radiation.
4. Three Mile Island, USA, 1979 (INES 5)
On March 28, 1979, coolant pumps in reactor TMI-2 at the Three Mile Island Nuclear Generating Station near Harrisburg, Pennsylvania, failed and a pressure-relief valve failed to close. Control room staff began to hear alarms and see warning lights. Unfortunately, faulty design of the sensors caused plant operators to miss and/or misread signs that the reactor core was first overheating, then actually melting.
Image via: Timemapped
By the time the situation was brought under control, half the reactor core had melted and approximately 20 tons of molten uranium was slowly solidifying at the bottom of the reactor’s containment vessel. Venting of steam and gas from inside the containment building allowed significant amounts of radioactive material to escape into the atmosphere and surrounding environment.
The Three Mile Island accident caused no deaths or injuries to plant workers or residents of nearby communities but it still is rated as the most serious accident in U.S. commercial nuclear power plant operating history. Extensive - some say sensationalistic - news coverage of the event, comparisons to the plot of the film The China Syndrome (released just 12 days before the accident), and a memorable sketch on Saturday Night Live all contributed to the incident’s prominent place in late 20th century pop culture. It’s no, er, accident that not a single new nuclear power plant has been built in the United States since.
3. Fukushima Daiichi Nuclear Power Plant, Japan, 2011 (INES 5+) [Now INES 7]
The Fukushima Daiichi Nuclear Power Plant, located 170 miles or 270 kilometres northeast of Tokyo, is one of the largest nuclear power plants in the world with 6 nuclear reactors supplying power to the Tokyo megalopolis and the Japanese electric power grid. In the immediate aftermath of the devastating 9.0 magnitude Sendai Earthquake on March 11, 2011, power outages caused the reactor coolant pumps to stop. Backup diesel generators had been stored in a low-lying area and were damaged by the quake-related tsunami.
By the time a working generator could be set up inside the building housing reactor No. 1, the core had begun to overheat and hydrogen gas built up to dangerous levels inside the containment building. A spark from the generator likely caused a hydrogen explosion that blew the roof off the containment building. The next day a similar, more powerful explosion occurred the next day in the building containing reactor No. 3, and on March 14 yet another explosion shattered the containment building of reactor No. 2.
[Update: Reactor No. 4 suffered enormous damage during the tsunami - a hydrogen explosion blew the roof off, leaving the highly radioactive fuel pool exposed to the open air - and its building remain crippled. The situation at Reactor No. 4 has raised new global worries and represent the greatest single threat to humanity.]
Here is a video of the first explosion: 福島第一原発 爆発の瞬間 Explosion at Fukushima nuclear plant, via Studiomu00
Image via: PopSci
Though the INES had given the on-going critical situation at the Fukushima Daiichi Nuclear Power Plant a provisory rating of 4, France’s ASN nuclear safety authority has suggested the rating should actually be much higher. “Level 4 is a serious level,” commented ASN President Andre-Claude Lacoste, speaking at a news conference on March 14, 2011, but “We feel that we are at least at level 5 or even at level 6.” On March 18, Japan’s nuclear oversight agency raised the INES rating of the disaster to 5. [Note: The rating was raised to 7 in April 2011 by the Japanese government and IAEA.]
2. Kyshtym Disaster, USSR, 1957 (INES 6)
In the Soviet Union’s frantic race to catch up with the USA in the post-war, Cold War nuclear arms race, corners were cut and mistakes were made. By far the largest of the latter occurred in September of 1957 at the Mayak nuclear fuel reprocessing plant in the closed city of Ozyorsk, formerly (before 1994) known as Chelyabinsk-40. A cluster of reactors at the site produced Plutonium for Soviet nuclear weapons and, as a by-product, nuclear waste. LOTS of nuclear waste. The waste was stored in underground steel cisterns set in concrete and cooled by an unreliable cooling system.
Image via: Bellona
In the fall of 1957, the cooling system around a vessel containing up to 80 tons of solid nuclear waste failed. Radioactivity quickly heated the waste to the point where the container exploded, blowing its 160-ton concrete lid into the air along with a massive cloud of very dirty radioactive fallout. Approximately 10,000 people were evacuated from the affected region and about 270,000 in total were exposed to dangerous levels of radiation. At least 200 deaths from cancer can be directly attributed to the accident and around 30 town names vanished from Soviet maps.
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Though the full extent of the Kyshtym Disaster was not revealed by the USSR until 1990, the CIA was aware of the incident yet decided not to reveal any information as it might reflect negatively on the American nuclear power industry. Meanwhile in Kyshtym, the vast East-Ural Nature Reserve (also known as the East-Ural Radioactive Trace) remains heavily contaminated by radioactive Caesium-137 and Strontium-90 over a roughly 300 square mile (800 sq km) area.
1. Chernobyl Disaster, USSR, 1986 (INES 7)
Image via: Stuck In Customs
As bad as the Kyshtym Disaster was, the Chernobyl Disaster was worse: 4 times worse, if dispersed radioactivity is the measuring stick. To date, the steam explosion and reactor meltdown of Reactor 4 at the Chernobyl Nuclear Power Plant is the only nuclear accident to rate a 7 on the International Nuclear Event Scale.
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The disaster began on April 26, 1986, when technicians at Reactor 4 were conducting an experimental power-down procedure. Human error led to a series of unexpected power surges that explosively burst the reactor’s containment vessel, starting a fire that impelled clouds of radioactive fission products and fallout into the open air. The cloud would eventually drift over large areas of eastern, western and northern Europe forcing over 335,000 people to be evacuated from a Zone of Alienation. Though only 53 deaths resulted directly from the accident, many thousands of other suffered (and still suffer) debilitating, chronic illness.
Image via: Funny Old Planet
These days the area around Chernobyl exhibits a strange dichotomy: the abandoned towns of Chernobyl and Pripyat slowly decay while wildlife in the surrounding woods and forests is booming now that the human presence has been removed. Reports of lynxes and even bears, which have not been seen in centuries, prove the eminent resilience of nature and life’s ability to adapt and adjust to even the most hostile of conditions.
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Chernobyl is the poster child for nuclear accidents, with atomic power protesters warning of “another Chernobyl” as often as anti-war advocates advising against “another Vietnam”. As for the apocalyptically named Zone of Alienation, Ukrainian authorities are finding it difficult to keep self-styled “stalkers” from conducting expeditions into the area aimed at fun and profit. Word to those contemplating such an adventure: what you can’t see, CAN hurt you!
Radiation In Your Nation?
Image via: Market Watch
Though the Chernobyl and Fukushima Daiichi Disasters are the only INES-rated Level 7 incidents on record, there’s no guarantee that another, even worse nuclear disaster will occur someday. Natural disasters, human errors and aging components are, unfortunately, facts of life (and death) for the nuclear industry. With nearly 500 nuclear power plants around the world in operation and under construction, the question isn’t IF another atomic accident will happen, but WHEN.
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